Contrasting Solid-State Fluorescence of Diynes with Small and Large

Subscriber access provided by CMU Libraries - http://library.cmich.edu

Article

Contrasting Solid State Fluorescence of Diynes with Small and Large Aryl Substituents: Crystal Packing Dependence and Stimuli Responsive Fluorescence Switching Avik Kumar Pati, Santosh J. Gharpure, and Ashok Kumar Mishra J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.5b08445 • Publication Date (Web): 28 Sep 2015 Downloaded from http://pubs.acs.org on October 3, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry A is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Contrasting Solid State Fluorescence of Diynes with Small and Large Aryl Substituents: Crystal Packing Dependence and Stimuli Responsive Fluorescence Switching Avik Kumar Pati,† Santosh J. Gharpure*‡ and Ashok K. Mishra*† †

Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036,

Tamil Nadu, India, ‡Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. ABSTRACT: There has been a significant current interest in solid state luminescence of organic molecules and their stimuli responsive fluorescence switching behaviour. Although small organic derivatives with olefinic, acetylenic, phenylenevinylenic, phenyleneethynylenic spacers are widely documented as solid state emitters in the literature, the solid state photophysics of organic derivatives with “butadiyne” spacer still remains unexplored. We provide detailed investigation on the solid state fluorescence properties of a series of butadiynyl fluorophores. Replacement of a phenyl ring, which is at periphery of the butadiyne bridge, with a large moiety such as pyrenyl group furnishes contrasting emissions in the solid state. While the butadiyne bridged phenyl derivatives show a blue shift of emission maxima in the solid powder with respect to monomer spectra in solution state, the butadiyne bridged pyrenyl derivatives exhibit a red shift in the solid state. The blue shift of the emission maxima of the butadiyne bridged phenyl derivatives in the solid powder is attributed to allowed excitonic transition in aggregates with nearly parallel transition dipoles. On the other hand, formation of pyrenyl excimer accounts for the red shift of the butadiyne bridged pyrenyl derivatives in the solid powder. In addition to that, the solid state fluorescence of the pyrenyl analogues is reversibly switched between two aggregate forms through external heating and rubbing stimuli.

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 36

KEY WORDS: Diacetylene, Solid state fluorescence, Aggregation, Fluorescence switching INRODUCTION Molecular engineering of organic derivatives exhibiting solid state fluorescence has found increased interest in recent years. Their wide applications in opto–electronic materials,1–8 solar cells,9–13 non-linear optics,14–17 and sensors18–22 as well as the challenge to understand the origin of emission have kept motivated the solid state photophysics community. The packing of aromatic organic chromophores strongly impacts their solid state fluorescence. Effort has been put forward to tune the molecular packing through structural modification and thereby influence the solid state fluorescence output.23–35 In this regard, small organic derivatives with olefin, acetylene,

phenylenevinylene

and

phenyleneethynylene

spacers

have

found

current

interest.19,24,36-40 Davis et al. reported the solid state fluorescence of alkoxy-cyano substituted diphenylbutadiene derivatives.24 Thomas et al. described the photophysical properties of alkoxy substituted phenyleneethynylenes in the solid state.40 The solid state fluorescence of some fluorinated diphenylpolyenes was reported by Sonoda et al.37 Lewis and Yang delineated the solid state fluorescence of some single olefin/acetylene spaced diphenyl derivatives with carboxamide substituents.41Although there has been a large amount of work on the solid state photophysics of olefinic, acetylenic, phenylenevinylenic and phenyleneethynylenic derivatives; structurally simple conjugated diynes as emitters in the solid powder are scarcely found in the literature. Here, we present a detailed understanding into periphery dependent contrasting solid state fluorescence of simple rod like butadiynyl derivatives. In addition, we report reversible fluorescence switching of some of the butadiynyl derivatives in the solid state by external heating and rubbing stimuli. Although there are reports on stimuli responsive fluorophores,42-57 reports pertaining to a single fluorophore are still limited. Further, the potential of conjugated


Page 3 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


diacetylenes as stimuli responsive fluorophores in the solid powder has not been looked at yet in the literature. EXPERIMENTAL METHODS Absorption and steady state fluorescence experiments. Solid state absorption spectra of all the derivatives were measured by necessary scattering correction, pasting small amount of solid powder on quartz plate using Shimadzu UV-2600 spectrometer. Fluorescence experiments were carried out with Horiba Jobin–Yvon FluoroMax-4 spectrofluorometer, with a 450 W xenon lamp as light source. The fluorescence spectra were measured in front face geometry to avoid selfabsorption. Single crystal XRD and scanning electron microscopy (SEM) experiments. Single crystal X-ray diffraction data were collected with a Bruker AXS Kappa Apex II CCD diffractometer. Scanning electron microscopy (SEM) experiments were carried out using FEI QUANTA-200 scanning electron microscope instrument. Hirshfeld surface plots. Hirshfeld surface and finger print plot calculations were carried out using CrysatlExplorer 3.1 software. Time resolved fluorescence measurements. Fluorescence lifetime experiment was done using a Horiba Jobin Yvon TCSPC lifetime instrument in a time-correlated, single-photon counting arrangement. 370 nm nano-LED was used as light source for all the experiments. The pulse repetition rate was set to 1 MHz and the instrumental full width at half maximum of the 370 nm LED, including the detector response was around 800 ps. The instrument response function was collected using a scatterer (Ludox AS40 colloidal silica). The decay data were analyzed using IBH software. A value of χ2, 0.99 ≤ χ2 ≤ 1.3 was considered as a good fit which was further verified by the symmetrical distribution of the residuals. RESULTS AND DISCUSSION 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 36

The butadiyne bridged phenyl-phenyl derivatives PBPOMe, POMeBPOMe, PBPNMe2 and pyrene-phenyl hybrids PyBP, PyBPCN, PyBPNMe2 (P, B, and Py imply ‘phenyl’, ‘butadiyne bridge’ and ‘pyrene’ respectively), which are under study here, are shown in Figure 1. The syntheses and solution phase photophysics of the derivatives were reported elsewhere.58-60 Steady state absorption in solid powder form. The absorption spectra of the derivatives in solid powder differ from their solution phase spectra (Figure 2). A red shifted absorption band is observed for the derivatives in the solid state with respect to their solution phase spectra. The red shifted absorption band in the solid powder suggests the formation of ground state aggregates of the butadiynyl derivatives. The vibrational fine structures as were observed in the solution state absorption spectra58 of PBPOMe and POMeBPOMe get significantly blurred in the solids (Figure 2a,b). The longest wavelength absorption (λmax

abs.)

band of PBPOMe and

POMeBPOMe in the solid powder is although not distinctively sharp; the onset of absorption is extended upto 500 nm; which is far beyond the solution phase λmax abs. of the derivatives at ca. 340 nm. Vibronic structure is observed in the solid sate absorption spectra of the phenyl-phenyl derivative PBPNMe2 and in the pyrene-phenyl derivatives, as was also observed in the solution phase absorption spectra (Figure 2c-f). A clear red shifted absorption band (the longest wavelength band) is noted for the pyrene-phenyl derivatives. The λmax abs. of PyBP, PyBPCN, and PyBPNMe2 in the solid powder is found to be ca. 18, 20, and 25 nm red shifted, respectively with regard to their solution state spectra. The full width at half maximum (FWHM) of the longest wavelength absorption band corresponding to S0→S1 transition in the solid state appears to be quite broad compared to the corresponding solution state spectra of the pyrene-phenyl derivatives. The broadening of FWHM in the solid state absorption spectra indicates strong intermolecular couplings61,62 in the aggregates of the pyrene-phenyl derivatives.


Page 5 of 36

Figure 1. Butadiyne bridged phenyl-phenyl and pyrene-phenyl hybrids (P, B, and Py indicate ‘phenyl’, ‘butadiyne bridge’ and ‘pyrene’ respectively).

(a)

0.12

(b) 0.09

(c)

0.08

0.06

0.04

0.03

0.03

0.00 0.06

0.00 0.03

0.00 0.06

0.04

0.02

0.04

0.02

0.01

0.02

0.09

Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.00 250

300

350

400

450

(d)

0.00 250

0.06

300

350

400

0.00 250

450

(e)

0.06

0.15

0.12

0.04

0.10

0.08

0.02

0.05

0.04

0.00 0.09

0.00 0.12

0.00

0.06

0.08

0.18

0.03

0.04

0.09

0.00 250

300

350

400

450

0.00 250

300

350

400

450

300

350

400

450

(f)

0.27

300

350

400

450

0.00 250

Wavelength (nm) Figure 2. Absorption spectra of the derivatives (a) PBPOMe, (b) POMeBPOMe, (c) PBPNMe2, (d) PyBP, (e) PyBPCN, and (f) PyBPNMe2 in solid powder form (black color) (‘absorbance’ in the absorption spectra in solid powder does not reflect to the concentration of the derivatives as the spectra are recorded by pasting solid powder on quartz plate), and a comparison with solution phase absorption spectra in dichloromethane (red color) (solution state absorption spectra are modified from ref: 58, 60). 5 ACS Paragon Plus Environment

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Normalized fluorescence intensity (a.u.)


1.2

λex = 335 nm

(a)

λex = 345 nm

1.0

Page 6 of 36

λex = 335 nm

(b)

λex = 330 nm C= 1 x 10-5 M

C= 1 x 10-5 M

0.8 0.6 0.4 0.2 0.0 1.2

(c)

λex = 380 nm

1.0

(d)

λex = 340 nm

λex = 340 nm

C= 1 x 10-5 M

λex = 380 nm

C= 1 x 10-5 M

0.8 0.6 0.4 0.2 0.0 1.2

(e)

1.0

λex = 360 nm,

C= 1 x 10-5 M

λex = 380 nm

(f)

λex = 390 nm

C= 1 x 10-5 M

λex = 380nm

0.8 0.6 0.4 0.2 0.0 350 400 450

500 550

600

650 350 400 450

500 550

600

650

Wavelength (nm) Figure 3. Emission spectra of the derivatives (a) PBPOMe, (b) POMeBPOMe, (c) PBPNMe2, (d) PyBP, (e) PyBPCN, and (f) PyBPNMe2 in solid powder (black color) (solid state emission spectra were recorded in front face geometry to avoid self-absorption) and a comparison with solution phase emission spectra in dichloromethane (red color) (solution state emission spectra are modified from ref: 58, 60). Steady state emission in solid powder form. Interestingly, all the derivatives show fluorescence in solid powder (Figure 3). The emission of the derivatives in the solid state was found to be different from their solution phase emission. While locally excited (LE) and intramolecular charge transfer (ICT) emissions were noted in solution,58,60 a new emission signature is observed in the solid state (Figure 3). This new emission band in the solid powder is attributed to aggregate emission. The red shifted absorption band (Figure 2) as well as longer lifetime components ca. 5-10 ns corresponds to the aggregate. Intriguingly, while the emission 6 ACS Paragon Plus Environment

Page 7 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


maxima of the phenyl-phenyl derivatives in the solid state are blue shifted with regard to their solution phase spectra; the emission maxima of the pyrene-phenyl derivatives are observed to be red shifted (Figure 3). The phenyl-phenyl derivatives PBPOMe and POMeBPOMe show the emission maxima centered at ca. 420 and 415 nm respectively in the solid powder form, which are ca. 39 and 75 nm blue shifted, respectively with regard to the solution phase emission spectra (Figure 3a,b). Thus, the emission maximum of POMeBPOMe with two -OMe shifts to the blue almost twice as much as the monosubstituted derivative. The emission maximum of PBPNMe2 having a strong donor NMe2 group, lies at ca. 465 nm, which is ca. 40 nm blue shifted than the corresponding solution state spectrum (Figure 3c). Vibronic structures are observed in the solid state emission spectra of the phenyl-phenyl derivatives. The pyrene-phenyl conjugates PyBP, PyBPCN, and PyBPNMe2, on the other hand, show two emission maxima in the solid powder— one of which is in the range ca. 450-500 nm and the other one is at ca. 550 nm (Figure 3d-f, see Figure S1, Supporting Information for Gaussian fit resolved emission spectra). The FWHM of the emission spectra of the pyrene-phenyl derivatives in the solid state is larger than the corresponding solution state spectra, suggesting strong intermolecular couplings in the derivatives.61,62 The emission maxima of PyBP, PyBPCN, and PyBPNMe2 at shorter wavelength in the solid state are ca. 80, 56, and 6 nm red shifted, respectively from the corresponding solution state spectra. The magnitude of red shift of the aggregate band of PyBPNMe2 in the solid state is less because the solution state emission band is highly red shifted for having the contribution of ICT emission.60 The contrasting shifts of the emission maxima of the phenylphenyl and pyrene-phenyl derivatives in the solids are expected to be because of different crystalline arrangements of the molecules and consequent intermolecular interactions in the solids. It is noted from Figure 3a-c that onsets of emission of the phenyl-phenyl derivatives are at ca. 350 nm, whereas the onsets of absorption for those fluorophores are close to 500 nm (Figure 7 ACS Paragon Plus Environment


2a-c). This could be because of allowed transition from excitonic state as was described by Kasha that excitonic delocalization leads to blue shifted allowed transition in aggregates with parallel transition dipoles.63 Excitation at longer wavelengths for the phenyl-phenyl derivatives does not show any new emission band (Figure 4a-c). Further, the two emission bands noted for the pyrene-phenyl derivatives (Figure S1, Supporting Information), suggesting two different

700

700 650

(a)

0 1.500E6 3.000E6

600

4.500E6 6.000E6

550

7.500E6

500

9.000E6

450 400 350 300 350 400 450 500 550 600 650 700

Excitation wavelength (nm)


aggregate sites, are not be observed separately through selective excitation (Figure 4d-f). 650

0 5.000E4 1.000E5 1.500E5 2.000E5 2.500E5 3.000E5 3.500E5 4.000E5 4.500E5 5.000E5

(c)

550 500 450 400 350 300 350 400 450 500 550 600 650 700



1.500E6 3.000E6 4.500E6 6.000E6

550

7.500E6

500

9.000E6

450 400 350 300 350 400 450 500 550 600 650 700

700

600

650

(d)

600 550 500

0 1.200E6 2.400E6 3.600E6 4.800E6 6.000E6 7.200E6 8.400E6 9.600E6

450 400 350 300 350 400 450 500 550 600 650 700

Emission wavelength (nm)

Emission wavelength (nm) 700 0 1.200E6 2.400E6 3.600E6 4.800E6 6.000E6 7.200E6 8.400E6 9.600E6

(e)

600 550 500 450 400 350 300 350 400 450 500 550 600 650 700



700 650

0

Emision wavelength (nm)

700 650

(b)

600



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 36

650

(f)

600 550 500

0 9.250E5 1.850E6 2.775E6 3.700E6 4.625E6 5.550E6 6.475E6 7.400E6

450 400 350 300 350 400 450 500 550 600 650 700


Figure 4. Excitation emission matrix fluorescence (EEMF) spectra of (a) PBPOMe, (b) POMeBPOMe, (c) PBPNMe2, (d) PyBP, (e) PyBPCN, and (f) PyBPNMe2 in solid powder (solid state emission spectra were recorded in front face geometry to avoid self-absorption). 8 ACS Paragon Plus Environment

Page 9 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Single crystal X-ray diffraction study. To better understand the solid state arrangement of the derivatives in depth, single crystal X-ray diffraction studies were carried out (Figure 5). Diffractable single crystals were obtained for the derivatives PBPOMe (see Figure S2 and Table S1, Supporting Information), POMeBPOMe (see Figure S3 and Table S2, Supporting Information), PBPNMe2 (see Figure S4 and Table S3, Supporting Information), and PyBPNMe2 (see Figure S5 and Table S4, Supporting Information). In the crystal structure of PBPOMe, it is observed that the molecule forms stacking through three types of intermolecular short contacts: i) O–H interaction between the oxygen of the OMe group and the H of the unsubstituted phenyl ring, ii) H–π interaction between the H of the OMe group and the π of the unsubstituted phenyl ring, iii) H–π interaction between the H of the substituted phenyl ring and the π of the butadiyne moiety (Figure 5a). The derivative POMeBPOMe also forms i) O–H interaction between the oxygen of the OMe group and the H of the phenyl ring, ii) H–π interaction between the H of the phenyl ring and the π of the butadiyne moiety, in addition to iii) an uncommon interaction64-66 (C– π) between the C of the OMe group and the π of the butadiyne moiety (Figure 5b). Although this type of C-π interaction is apparently surprising, such non-classical interaction is now being recognized in the literature, known as “carbon bonding”.65,66 In a recent work,66 Mani and Arunan pointed out that carbon of -CH3 moiety interacts with π electrons (non-covalent interaction), if the -CH3 moiety contains a group/atom which is of more electronegative character than carbon atom. Electron density topology calculations for a series of intermolecular systems have proved this.66 Here, the carbon of the methoxy group (-OCH3) is being attached to the electronegative oxygen atom, it serves (the carbon atom) as a Lewis acid while the π of the butadiyne moiety acts as a Lewis base. In other words, the π electrons of the butadiyne moiety functions as a carbon bond acceptor.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 36

For PBPNMe2, in addition to (i) a H–π interaction between the H of the NMe2 group and the π of the butadiyne moiety, and (ii) a C-H interaction between the C of the NMe2 group and the H of the unsubstituted phenyl ring; (iii) a π–π interaction between the unsubstituted phenyl ring and the NMe2 substituted phenyl moiety is observed (Figure 5c). However, the observed π–π interaction in PBPNMe2 is negligible as the overlap area of the phenyl rings between two neighbouring molecules is smaller. The interaction between the C of the NMe2 group (i.e the C is attached to an electronegative atom) and the phenyl H (i.e the H is a part of a π system) is not commonly found in the literature. Such unusual interactions have come to the fore only in recent time (during the last half-a-decade). Especially, post period of modification of IUPAC definition of ‘hydrogen bonding’67 has seen an increased search for many such uncommon interactions. Hydrogen bonding is now defined (IUPAC) as “an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation”.67 It is now well accepted that many factors such as electrostatics, polarizations, charge transfer, exchange-correlation, and dispersion forces etc. contribute to the hydrogen bonding. A comprehensive theoretical study on the intermolecular interactions in various D–X….A molecular systems is found in a current perspective by Shahi and Arunan.68 Here, D is the phenyl ring (X-bond donor), X is the H (attached to the phenyl ring), and A is the acceptor (Lewis acidic C in NMe2 because of the attachment of the electronegative N-atom). The non-classical interactions are not only supported by the theoretical calculations, but experimental evidences are also present in the literature.69 The methyl Hs of the NMe2 group are known to form hydrogen bonding to π electrons of diacetylenic moiety in the literature.70 Rodriguez et al observed that in the crystal structure of 1,4-bis[2-(N,N-dimethylamino)phenyl]buta-1,3-diyne.70


Page 11 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Thus it is found that these diacetylenes are a class of simple rod shaped molecules, where many such non-classical short contacts are prevalent. In the case of pyrene-phenyl derivative PyBPNMe2, (i) the pyrene rings of the adjacent molecules form a strong π- π interaction through a face to face overlap of the pyrene planes, (ii) the H of the phenyl ring forms H-π interaction with the π of the pyrene ring, and (iii) the H of the NMe2 group undergoes H-π interaction with the π of the diyne bridge (Figure 5d). Similar to PBPNMe2, the π–π interaction between the phenyl moieties is not significant in PyBPNMe2. The crystal structures of the phenyl–phenyl and pyrene–phenyl derivatives show twisted rotamers in the solid state (for dihedral angle of twisting, see Figure S6a, Supporting Information). The energy barrier of rotation around the butadiyne moiety between the planar and twisted states of the diphenyl butadiynyl derivatives is known to be low (order of 0.1 Kcal/mole) in the solution phase.59 Thus, isolation of the twisted/partially twisted rotamers of POMeBPOMe, PBPOMe, PBPNMe2, and PyBPNMe2 suggests a significant stabilization of the twisted/partially twisted form through non covalent interactions in the solid state over the planar conformers. Interestingly, not only the derivatives are found to be twisted; the diacetylenic moieties are noted to be bent (carbons in the diyne bridge deviate around 2-3o from usual sp linearity (180o), see Figure S6b, Supporting Information). Such bent nature of the diacetylene is not commonly found in ground state. The powder XRD pattern of a representative derivative POMeBPOMe matches well with the simulated one obtained from the single crystal XRD (see Figure S7, Supporting Information), thus suggesting similar arrangements in bulk and single crystal.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

Page 12 of 36

i)

i)

2.60 Ao

2.80 Ao

ii)

ii)

2.98 Ao

2.91 Ao

iii) iii) 3.43 Ao

2.94 Ao

(c)

(d) i)

2.95 Ao

3.54 Ao

i) 2.96 Ao

ii)

2.86 Ao

2.97 Ao

ii) iii) 3.42 Ao

3.44 Ao

2.86 Ao 2.96 Ao 2.96 Ao

Figure 5. Crystal packing diagrams of (a) PBPOMe, (b) POMeBPOMe, (c) PBPNMe2, and (d) PyBPNMe2 showing molecular geometries and different intermolecular interactions. Hirshfeld surface and finger print plot. In order to shed further light into the intermolecular interactions, Hirshfeld surface diagram71,72 and its corresponding finger print plot73 are described for the phenyl-phenyl derivative POMeBPOMe (Figure 6) and pyrene–phenyl hybrid PyBPNMe2 (see Figure S8, Supporting Information) as representative molecules. The Hirshfeld surface sheds light on the intermolecular interactions owing to the fact that this surface not only includes the molecule in a crystal but also the neighbours at the closest vicinity of the molecule.71 The red and blue colours on the Hirshfeld surface indicate hollow and bump 12 ACS Paragon Plus Environment

Page 13 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respectively on the surface, which participate in intermolecular interactions. Thus, the red spot on the butadiyne backbone shows its participation in the stacking in addition to the rest of the molecular entity. Figure 6a,b depict the Hirshfeld surface mapped with shape index at two different molecular views, showing possibilities of various intermolecular interactions at different sites. The finger print plots (Figure 6c,d) show two spikes exhibiting the H–π (Figure 5c) and O–H (Figure 5d) interactions in the derivative POMeBPOMe. The finger print plot suggests that the % of H–π interaction is higher in the phenyl–phenyl derivative POMeBPOMe (53.5%) than the pyrene–phenyl derivative PyBPNMe2 (46.8%).

x

(a)

y z

(b)

x

y (c)

de

(d)

H-π interactions

z de

O-H interactions

di

di

Figure 6. (a), (b) Hirshfeld surface mapped with shape index at two different directions and (c), (d) finger print plots of the derivative POMeBPOMe showing different interactions. de and di indicate the distance from a point on the Hirshfeld surface (i) to the closest nucleus outside the surface and (ii) the closest nucleus inside the surface respectively. 13 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 36

Aggregate morphology. The morphology of the aggregates in the solid state was examined by scanning electron microscopy (SEM) images (Figure 7). Our earlier studies on the solution phase steady state absorption and emission spectra of the pyrene–phenyl derivatives showed that the derivatives form aggregates on adding water into acetonitrile (CH3CN).60 Thus, here the SEM samples of the derivatives were prepared in mixed aqueous solvents. The derivative PyBPNMe2 formed crystalline microplates (Figure 7a) when the sample was prepared from slow evaporation in 40% water-CH3CN solvent mixture at open atmosphere. Interestingly, upon increasing the percentage of water (80%), the derivative PyBPNMe2 aggregated into microrods (Figure 7b). A large microrod was noted to be formed presumably through aggregation of several small microrods in a chain wise manner (see Figure S9, Supporting Information). Further increase of the water percentage (99% water-CH3CN) produced a bunch of microrods, which were stacking together (see Figure S10, Supporting Information). Similar aggregation behaviour was also observed for the derivatives PyBPCN (Figure 7c,d) and POMeBPOMe (Figure 7d,e). The derivative PyBPCN aggregated into microplates from solutions in 40% and 80% water-CH3CN solvent mixtures. Notably, the plates observed from the 80% water-CH3CN mixture were bigger in size (Figure 7d) compared to those obtained from 40% water-CH3CN mixture (Figure 7c). Addition of a higher amount of water, the poor solvent, into CH3CN led to higher aggregation (80% water-CH3CN), thus increasing the size of the microplates. The derivative POMeBPOMe formed microplates from 40% water-CH3CN (Figure 7e) and microrods from 80% water-CH3CN mixture (Figure 7f). The diacetylenic derivatives were also found to form microplates and microrods when the SEM images were collected directly from the solid powder (see Figure S11, Supporting Information).


Page 15 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

(b)

(c)

5 µm

2 µm

5 µm

(d)

(e)

5 µm

(f)

1 µm

5 µm

Figure 7. SEM images of PyBPNMe2 in (a) 40% and (b) 80% water-CH3CN (C = 1 X 10-6 M); PyBPCN in (c) 40% and (d) 80% water-CH3CN (C = 1 X 10-6 M); and POMeBPOMe in (e) 40% and (f) 80% water-CH3CN (C = 1 X 10-5 M). Insights into the contrasting shifts in the emissions of phenyl-phenyl and phenyl-pyrene derivatives. In order to understand the nature of the aggregates, especially if any specific aggregate such as H- or J-aggregate74-76 is formed, a detailed analysis of the results discussed above is carried out. Case I (phenyl-phenyl derivatives): The emission maxima of all the phenyl-phenyl derivatives in the solid state are blue shifted compared to those observed in the solution phase. This blue shifted solid state emission coupled with their distinct changes in the absorption profiles (in comparison with the solution phase absorption spectra) suggests allowed excitonic transitions because of parallel transition dipoles in aggregates, as was described by Kasha.63 Such aggregates with parallel transition polarization axis are now commonly termed as Haggregate in the literature. In the crystal structures of the phenyl-phenyl derivatives, it appears difficult to identify plane-to-plane stacking corresponding to H-aggregate geometry because of the twisting of the phenyl rings as well as the bending of the diacetylene backbone. However, 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 36

such assignment could be erroneous for these rod shaped butadiynyl derivatives as one of the possibilities of orientation of the transition dipole could be along the short molecular axis. To check this, we simulated the transition dipole of the phenyl-phenyl derivatives using density functional theory (CAM-B3LYP77/6-311+G(d,p)) in the Gaussian 09 computational suit78. For this purpose, we adopted the initial geometry from the crystal structures. It was found that the transition dipole is oriented along the short molecular axis for PBPOMe and POMeBPOMe and along the long molecular axis for PBPNMe2 (Figure 8a, for transition dipole moment values, see Table S5, Supporting Information). Thus, although the derivatives PBPOMe and POMeBPOMe are stacked along the long axis of the molecules, their transition dipoles are nearly parallel (considering a dimer as a simple case) to each other along the short molecular axis, which lead to excitonic splitting. The upper electronic state is being of in-phase dipole orientation possesses a positive transition dipole moment and a transition from this state is allowed, which essentially leads to a blue shifted emission (Figure 8b). It should be noted that although such excitonic splitting (nearly parallel transition dipole orientation) may lead to a blue shifted absorption; here for PBPOMe and POMeBPOMe, the absorption bands are blurred probably because of multiple aggregation sites. In the case of PBPNMe2, the transition dipoles are oriented as oblique (the crystal stacking shown in Figure 5c-i is not considered as it involves the intermolecular interaction which is not commonly observed) and thus the excitonic delocalization leads to a blue shifted emission as one of the possibilities, because transitions from both the upper and lower excitonic states are allowed. Substituted oligophenylenevinylenes,79,80 9,10-distyrylanthracene81 etc. exhibit a blue shifted emission in the solid state or in mixed aqueous solvents when compared with the monomer emission. Recently, in a theoretical calculation, Wu et al. attributed aggregation induced blue shifted emission in the solid state to smaller reorganization energy in the solid compared to the solution state.82 16 ACS Paragon Plus Environment

Page 17 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Case II (pyrene-phenyl derivatives): The pyrene-phenyl derivatives exhibit a red shifted absorption and emission in the solid state with respect to the solution phase. The possibility of Jaggregate formation is ruled out as the derivatives show large Stokes shift and unstructured emission spectra (J-aggregate generally shows small Stokes shift and structured emission spectrum). The observed large Stokes shift and the unstructured emission spectra hint at the possibility of the excimer emission.52,83 The crystal structure of PyBPNMe2 shows π-π stacking between two adjacent pyrenyl moieties in the molecules, which asserts to the fact that the photoexcited molecules eventually lead to an emission originated from the excimer state, which results to a red shift of the emission (Figure 8c). Such red shifted excimeric emission was observed in certain fluorinated distyrylbenzene derivative.53,84 The formation of a triplex can not be ruled out because of the involvement of the dimethylaminophenyl moiety as a donor to the pyrenyl excimer, as is observed from the crystal packing diagram depicted in Figure 5d-i. Thus, it is possible to tune the solid state optical properties of the butadiynyl fluorophores through suitable choices of peripheral moieties of the diyne bridge. While the small phenyl periphery leads to an excitonic coupling, large pyrene periphery facilitates the excimeric coupling despite the derivatives are being twisted/partially twisted along the diyne bridge as observed from the crystal structures (Figure 5). The π-π interaction observed in the twisted butadiynyl derivative (PyBPNMe2), leading to a red shifted absorption band, is in sharp contrast to many reported twisted molecules in the literature. Because of distortion of the molecular backbone, such molecules reported in the literature show blue shifted absorption bands.85 This indicates that the diyne spacer as well as the steric bulk at its periphery plays an important role in controlling the π-π interactions in the butadiynyl derivatives despite the peripheral groups are being twisted along the diyne bridge. This feature indeed gets reflected in the contrasting



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 36

emission behaviour of the phenyl-phenyl and pyrene-phenyl derivatives in the solid state (Figure 3). The solid state absorption spectra of the diynes (Figure 2) are extended to the red of the fluorescence spectra, suggesting inefficient excitation energy migration within the crystals. Otherwise, the low energy states observed in the absorption spectra would have served as excitation traps quenching the fluorescence. (a)

i)

ii)

iii)

(b)

(c) Phenyl-phenyl derivatives

Pyrene-phenyl derivatives

S1

S’1

S1

S1

S’’1 Blue shift

Red shift

S0

Solution state

S0

S0

Solid state (Excitonic delocalization)

Solution state

No π-π interaction

S0

Solid state (excimer emission)

Strong π-π interactions

Figure 8. (a) Transition dipole moment vectors of the phenyl-phenyl derivatives. (b) and (c) Schematic diagrams exhibiting the contrasting emissions from the phenyl-phenyl (PBPOMe and POMeBPOMe) and pyrene-phenyl derivatives respectively. 18 ACS Paragon Plus Environment

Page 19 of 36

(a)

(b)

Prompt λem = 425 nm

1000

Prompt λ em = 425 nm

1000

(τ1 = 0.8 ns, τ2 = 4.4 ns)

(τ1 = 1.1ns, τ2 = 5.1 ns) λ em = 450 nm

(τ1 = 0.7 ns, τ2 = 2.6 ns

100

(τ1 = 0.8 ns, τ2 = 1.9 ns

Count

Count

λem = 450 nm τ3 = 13.8 ns)

τ3 = 10.6 ns)

100

10

10 20

30

40

16

24

(c)

(d)

Prompt

40

Prompt λem = 490 nm

λem = 410 nm

1000

32

Time (ns)

Time (ns)

1000

(τ1 = 0.5 ns, τ2 = 2.5 ns)

(τ1 = 1.3 ns, τ2 = 6.7 ns) λem = 525 nm

Count

λem = 425 nm

Count

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(τ1 = 2.2 ns, τ2 = 4.7 ns)

100

10

(τ1 = 0.8 ns, τ2 = 2.9 ns)

100

10 15

20

25

30

20

Time (ns)

30

40

Time (ns)

Figure 9. Time resolved fluorescence decays of (a) PBPOMe, (b) POMeBPOMe, (c) PBPNMe2, and (d) PyBPCN (scattering corrected fluorescence decays) in solid powder form (λex = 370 nm). Instrument limited decay components in few cases are ignored. Time resolved fluorescence decay in solid powder form. Fluorescence lifetime data in solid powder are although expected to be not very good because of scattering, here it was recorded to understand the nature of excited state species of the fluorophores in the solids (Figure 9). All the derivatives show bi-exponential to tri-exponential fluorescence decays at different emission wavelengths in the solids. At shorter wavelength (λem 425 nm), the phenyl-phenyl derivatives PBPOMe (Figure 9a) and POMeBPOMe (Figure 9b) show bi-exponential behavior with lifetime ca. 1 and 5 ns. At higher wavelength (λem 450 nm), PBPOMe and POMeBPOMe exhibit tri-exponential decay with relatively longer lifetime components ca. 10-14 ns. The derivative PBPNMe2 shows the lifetime components 0.5 and 2.5 ns at λem 410 nm and 2.2 and 19 ACS Paragon Plus Environment


4.7 ns at λem 425 nm (Figure 9c). For PyBPCN, lifetime components 1.3 and 6.7 ns are observed at λem 490, whereas 0.8 and 2.9 ns components are noted at λem 525 nm (Figure 9d). In contrast to the solids (where both the shorter and longer lifetime components are observed), the derivatives show mainly shorter lifetime components (ca. 0.5-2.5 ns) in non-aqueous solvents corresponding to LE and ICT states. It is found that not only the lifetimes vary with changing wavelengths but also pre-exponential factor changes at different wavelengths (see Table S6, Supporting Information). This suggests the presence of multiple aggregates in the solids.

(b) Solid powder After heating After cooling followed by rubbing

1.0 0.8 0.6 0.4 0.2 450

500

550


(a) Normalized flu. intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 36

After heating

534

After cooling followed by rubbing

531 528 525 522 0

600

1

2

3

4

5

Number of cycles

Wavelength (nm)

(c) Heating Cooling followed by rubbing

Figure 10. (a) Solid state emission spectra of PyBPNMe2 after heating and cooling followed by rubbing (λex = 380 nm), (b) plot of emission wavelength vs. number of repeated cycles of heating and cooling followed by rubbing, and (c) fluorescence color images of solid powder of PyBPNMe2 pasted on a quartz plate on heating and subsequent cooling followed by rubbing. Stimuli responsive fluorescence switching. The presence of the π-π stackings in the pyrenephenyl derivatives inspired us to investigate their solid state fluorescence behaviour under thermal and mechanical stimuli. After heating of the solid powder of PyBPNMe2 to ~80 oC (for 20 ACS Paragon Plus Environment

Page 21 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3 min), the emission maximum gets 15 nm red shifted from 518 nm to 533 nm (Figure 10a). The red shift of the emission band (λem 533 nm) is retained even after cooling. Interestingly, subsequent rubbing of the sample with a spatula produces a blue shifted emission band at 521 nm, which is very close to the initial emission maxima (λem 518 nm) (Figure 10a). The emission spectra obtained after heating and subsequent cooling followed by rubbing were reproducible even after several cycles (Figure 10b), exhibiting reversible switching of the solid state fluorescence. The emission switching phenomenon was visually perceived from fluorescence color images of the solid powder of PyBPNMe2 depicted in Figure 10c. PyBPNMe2 which shows green color fluorescence in the powder form (as-prepared), turns into greenish-yellow on heating. It again switches to green upon cooling followed by rubbing (Figure 10c). Certain olefinic analogues such as alkoxy-cyano-substituted diphenylbutadienes reported by Davis et al. showed thermally reversible fluorescence switching between two polymorphs.24 The pyrenephenyl derivatives PyBP and PyBPCN showed broad emission spectra (slightly red shifted) upon heating (see Figure S12, Supporting Information). Similar to PyBPNMe2, the emission band (observed upon heating) remained unchanged after cooling. Subsequent rubbing again produced the blue shifted emission band (see Figure S12, Supporting Information). Such reversible fluorescence switching was not observed for the phenyl-phenyl analogues, probably because of the absence of π-π stacking between the phenyl moieties in the neighboring molecules. The cumulative contributions of the H-π interactions which are very large in numbers in the pyrene-phenyl derivative PyBPNMe2 appear to be more significant than the π-π stacking interactions between the pyrenyl moieties (Figure 5d). An increase in molar volume on heating probably leads to a better orientation of the molecules, assisting toward strong π-π interactions in large numbers between the pyrenyl rings as well as the phenyl moieties through planarization (at 21 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 36

least partially) of the molecules. Heating of the solid powder presumably provides the necessary activation energy between the stable fully twisted aggregate conformer and the less stable planar/partially twisted form. The aggregate structures which get trapped in the less stable form on heating do not come back to the stable one after cooling. Rubbing helps to get back the stable twisted aggregate conformer by releasing the free energy stored in the less stable form. Formation of slipped stacked structures upon heating the solid powder is ruled out because the slipped stacked geometry would result in a reduced π-π overlap, which can not account for the red shifted excimeric emission observed in Figure 10a. Fluorescence excitation and time resolved fluorescence decay studies to understand stimuli responsive fluorescence switching. To better understand the emission of PyBPNMe2 in the initial solid powder, after heating and cooling followed by rubbing; fluorescence excitation spectra were recorded (Figure 11a). The excitation spectrum in the solid powder (Figure 11ai) and that after heating (Figure 11aii) are observed to be not the same. The longest wavelength fluorescence maximum in the solid powder appears at ca. 440 nm, whereas it is red shifted to ca. 470 nm upon heating. This indicates that the heating changes the organization of the aggregate molecules in the solids. Again, cooling followed by rubbing brings back the longest wavelength fluorescence maximum close to ca. 440 nm. The shorter wavelength fluorescence maximum appearing at ca. 365 nm almost remains unchanged before and after heating, and cooling followed by rubbing. Time resolved fluorescence decay experiment of PyBPNMe2 shows triexponential decay behavior in the initial solid, after heating, and cooling followed by rubbing. Two lifetime components with ca. 2.5 and. 1 ns are observed in all the three forms of the solid (Figure 11bi-iii). However, the excited state population of the two species (with the lifetimes ca. 2.5 and. 1 ns) changes from the ‘initial solid’ to ‘after heating’, and ‘after cooling followed by rubbing’. In addition to that, a relatively longer lifetime component (16 ns) observed in the initial 22 ACS Paragon Plus Environment

Page 23 of 36

solid gets decreased to 11.6 ns upon heating, and then again increased to 14.7 ns upon cooling followed by rubbing. Thus, not only the abundance of the aggregate species varies on applications of external stimuli but also certain new aggregate sites are formed. This is reflected in the observed shift in the fluorescence spectra (Figure 10a) discussed in the earlier section.

(a) 2.5x10

7

i)

Solid powder

(b)

i)

Prompt Solid powder

7

2.0x10

1000

τ1 = 2.3 ns, α1 = 0.38 τ2 = 16 ns, α2 = 0.15

7

1.5x10

τ3 = 0.8 ns, α3 = 0.47

100 7

1.0x10

6

5.0x10

6

2.8x10

10

ii)

ii)

After heating

Prompt After heating

6

2.4x10

1000

Count

Fluorescence intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6

2.0x10

6

1.6x10

τ1 = 2.4 ns, α1 = 0.12 τ2 = 11.6 ns, α2 = 0.10 τ3 = 0.7 ns, α3 = 0.78

100

6

1.2x10

5

8.0x10

5

6x10

10 After cooling followed by rubbing

iii)

5

5x10

iii)

Prompt After cooling followed by rubbing

1000

5

4x10

τ1 = 2.7 ns, α1 = 0.29

5

3x10

τ2 = 14.7 ns, α2 = 0.13

100

τ3 = 0.8 ns, α3 = 0.58

5

2x10

5

1x10

10 0 300

350

400

450

500

20

Wavelength (nm)

40

60

80

Time (ns)

Figure 11. (a) Fluorescence excitation spectra of PyBPNMe2 at λem = 520 nm in i) solid powder, ii) after heating, and iii) cooling followed rubbing. (b) Time resolved fluorescence decay study of PyBPNMe2 in i) solid powder, ii) after heating, and iii) cooling followed rubbing (λem = 520 nm, λex = 370 nm; τ and α correspond to lifetime and relative excited state population, respectively).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 36

Conclusions In summary, we have investigated solid state fluorescence properties of a class fluorophores with “butadiyne” spacer in detail. Some key features include: (1) Substituted diphenylbutadiynes (phenyl-phenyl derivatives) and butadiynyl derivatives with pyrene and phenyl peripheries (pyrene-phenyl hybrids) exhibit contrasting fluorescence in solid powder form. The phenyl-phenyl and pyrene-phenyl derivatives show blue and red shifted emission spectra respectively in the solid state with regard to their corresponding monomer spectra in solution phase. (2) The solid state emission spectral behavior of the derivatives depends on their arrangement in the crystal structures. The observed π-π stacking in the pyrene-phenyl derivatives suggests formation of a static excimer, reflecting it in the red shifted absorption and emission spectra as well as the absence of rise time in time resolved fluorescence in the solid powder form. No π-π interactions are observed in the crystal structures of the phenyl-phenyl derivatives. The blue shift of the emission maxima of the phenyl-phenyl derivatives in the solid state is attributed to an allowed transition from excitonic state with nearly parallel transition dipoles. (3) The butadiynyl derivatives which are fully π conjugated, despite being expected to be planar are found to be twisted around the butadiyne backbone in the solid state. The butadiynyl carbons deviate around 2-3o from usual sp linearity (180o), exhibiting a bent character of the diynes. This bent “diyne” bridge in the molecules appears to be important as it participates in the molecular packing providing crystallinity in the solid, which in turn assists in the generation of fluorescence in the solid powder. The aggregates of the butadiynyl derivatives form well defined microstructures such as microplates and microrods. (4) The butadiyne bridged pyrenyl derivatives exhibit reversible fluorescence switching behavior in the solid state by external heating and rubbing stimuli. Such reversible switching of 24 ACS Paragon Plus Environment

Page 25 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


fluorescence is important because these derivatives could find potential applications in thermal and mechanical sensing. Supporting Information †Electronic supporting information (ESI) available: Gaussian fit resolved emission spectra of the pyrene-phenyl derivatives, crystal packing diagrams showing sheet like structures, dihedral angles of twisting, bending angles of diacetylene, PXRD data of POMeBPOMe, Hirshfeld surface and finger print plot of PyBPNMe2, SEM image of PyBPNMe2 in 80% and 99% waterCH3CN solvent mixture, SEM images in solid powder, emission spectra of PyBP and PyBPCN after heating and cooling followed by rubbing, crystal data, structure refinement parameters and CCDC numbers of PBPOMe, POMeBPOMe, PBPNMe2, and PyBPNMe2, transition dipole moment values, lifetime parameters of PBPOMe, POMeBPOMe, PBPNMe2, and PyBPCN in solid powder form. AUTHOR INFORMATION Corresponding Author *†

Tel.: +91-44-22574207; Fax: +91-44-22574202; E-mail address: [email protected]

(Ashok K. Mishra). *‡

Tel.: +91-22-2576 7171; Fax: +91-22-2576 7152; E-mail address: [email protected]

(Santosh J. Gharpure). ACKNOWLEDGMENTS Authors thank DST, New Delhi for financial support. Mr. V. Ramkumar and Dr. R. Jagan from IIT Madras are thanked for collecting single crystal X-rd data. AKP thanks CSIR, New Delhi for a research fellowship.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 36

REFERENCES 1. Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Light-Emitting Diodes Based on Conjugated Polymers. Nature 1990, 347, 539-541. 2. Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Electroluminescent Conjugated Polymers - Seeing Polymers in a New Light. Angew. Chem., Int. Ed., 1998, 37, 402-428. 3. Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.; Bre´das, J. L.; Lo¨gdlund, M.; and et al. Electroluminescence in Conjugated Polymers. Nature 1999, 397, 121-128. 4. Ho, P. K. H.; Thomas, D. S.; Friend, R. H.; Tessler, N. All-Polymer Optoelectronic Devices. Science 1999, 285, 233-236. 5. Bernius, M. T.; Inbasekaran, M.; O’Brien, J.; Wu, W. Progress with Light-Emitting Polymers. Adv. Mater. 2000, 12, 1737-1750. 6. Donat-Bouillud, A.; Levesque, I.; Tao, Y.; D'Iorio, M.; Beaupre, S.; Blondin, P.; Ranger, M.; Bouchard, J.; Leclerc, M. Light-Emitting Diodes from Fluorene-Based π-Conjugated Polymers. Chem. Mater. 2000, 12, 1931-1936. 7. Shih, H.-M.; Lin, C.-J.; Tseng, S.-R.; Lin, C.-H.; Hsu, C.-S. Synthesis of New Blue Anthracene-based Conjugated Polymers and Their Applications in Polymer Light-Emitting Diodes. Macromol. Chem. Phys. 2011, 212, 1100-1108. 8. Zhang, L.; Liu, Z.; Zhang, X.; Chen, J.; Cao, Y. Efficient Blue Light-Emitting Diodes Based on Conjugated Polymers with Fluorinated Silole Chemically Doped in Fluorene-Carbazole Main Chain. J. Inorg. Organomet. Polym. 2015, 25, 64-72.


Page 27 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9. Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J. Thermally Stable Efficient Polymer Solar Cells with Nanoscale Control of the Interpenetrating Network Morphology. Adv. Funct. Mater. 2005, 15, 1617-1622. 10. Maggioni, G.; Campagnaro, A.; Carturan, S.; Quaranta, A. Dye-Doped Parylene-Based Thin Film Materials: Application to Luminescent Solar Concentrators. Sol. Energ. Mat. Sol. C. 2013, 108, 27-37. 11. Slooff, L. H.; Kinderman, R.; Burgers, A. R.; Bakker, N. J.; van Roosmalen, J. A. M.; Buechtemann, A.; Danz, R.; Schleusener, M. Efficiency Enhancement of Solar Cells by Application of a Polymer Coating Containing a Luminescent Dye. J. Sol. Energy Eng. 2007, 129, 272-276. 12. Ishchenko, A. A. Photonics and Molecular Design of Dye-Doped Polymers for Modern Light-Sensitive Materials. Pure Appl. Chem. 2008, 80, 1525-1538. 13. Sharma, G. D.; Balraju, P.; Kumar, M.; Roy, M. S. Quasi Solid State Dye Sensitized Solar Cells Employing a Polymer Electrolyte and Xanthene Dyes. Mater. Sci. Eng. B Adv. 2009, 162, 32-39. 14. Mathy, A.; Ueberhofen, K.; Schenk, R.; Gregorius, H.; Garay, R.; Muellen, K.; Bubeck, C. Third-Harmonic-Generation Spectroscopy of Poly(p-phenylenevinylene): A Comparison with Oligomers and Scaling Laws for Conjugated Polymers. Phys. Rev. B 1996, 53, 4367-4376. 15. Eisler, S.; Slepkov, A. D.; Elliott, E.; Luu, T.; McDonald, R.; Hegmann, F. A.; Tykwinski, R. R. Polyynes as a Model for Carbyne: Synthesis, Physical Properties, and Nonlinear Optical Response. J. Am. Chem. Soc. 2005, 127, 2666–2676. 16. Slepkov, A. D.; Hegmann, F. A.; Eisler, S.; Elliott, E.; Tykwinski, R. R. The Surprising Nonlinear Optical Properties of Conjugated Polyyne Oligomers. J. Chem. Phys. 2004, 120, 68076810. 27 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 36

17. Meier, H.; Ickenroth, D.; Stalmach, U.; Koynov, K.; Bahtiar, A.; Bubeck, C. Preparation and Nonlinear Optics of Monodisperse Oligo(1,4-phenyleneethynylene)s. Eur. J. Org. Chem. 2001, 4431-4443. 18. Di Marco, G.; Lanza, M.; Pieruccini, M.; Campagna, S. A Luminescent Iridium(III) Cyclometallated Complex Immobilized in a Polymeric Matrix as a Solid-State Oxygen Sensor. Adv. Mater. 1996, 8, 576-580. 19. Costa, A. I.; Pinto, H. D.; Ferreira, L. F. V.; Prata, J. V. Solid-State Sensory Properties of Calix-Poly(phenylene ethynylene)s Toward Nitroaromatic Explosives. Sensor. Actuat. B Chem. 2012, 161, 702-713. 20. Yagai, S.; Okamura, S.; Nakano, Y.; Yamauchi, M.; Kishikawa, K.; Karatsu, T.; Kitamura, A.; Ueno, A.; Kuzuhara, D.; Yamada, H.; and et al. Design Amphiphilic Dipolar π-Systems for Stimuli-Responsive Luminescent Materials Using Metastable States. Nat. Commun. 2014, 5, 4013-4022. 21. Wang, L.; Yang, L.; Cao, D. Application of Aggregation-Induced Emission (AIE) Systems in Sensing and Bioimaging. Curr. Org. Chem. 2014, 18, 1028-1049. 22. Han, M.; Tian, Y.; Yuan Z.; Zhu L.; Ma B. A Phosphorescent Molecular "Butterfly" That Undergoes a Photoinduced Structural Change Allowing Temperature Sensing and White Emission. Angew. Chem., Int. Ed. 2014, 53, 10908-10912. 23. Chen, J.; Law, C. C. W.; Lam, J. W. Y.; Dong, Y.; Lo, S. M. F.; Williams, I. D.; Zhu, D.; Tang, B. Z. Synthesis, Light Emission, Nanoaggregation, and Restricted Intramolecular Rotation of 1,1-Substituted 2,3,4,5-Tetraphenylsiloles. Chem. Mater., 2003, 15, 1535–1546. 24. Davis, R.; Kumar, N. S. S.; Abraham, S.; Suresh, C. H.; Rath, N. P.; Tamaoki, N.; Das, S. Molecular

Packing

and

Solid-State

Fluorescence

of

Alkoxy-Cyano

Substituted


Page 29 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Diphenylbutadienes: Structure of the Luminescent Aggregates. J. Phys. Chem. C, 2008, 112, 2137–2146. 25. Liu, Y.; Tao, X.; Wang, F.; Shi, J.; Sun, J.; Yu, W.; Ren, Y.; Zou, D.; Jiang, M. Intermolecular Hydrogen Bonds Induce Highly Emissive Excimers: Enhancement of Solid-State Luminescence. J. Phys. Chem. C, 2007, 111, 6544–6549. 26. Lu, H.; Wang, Q.; Gai, L.; Li, Z.; Deng, Y.; Xiao, X.; Lai, G.; Shen, Z. Tuning the SolidState Luminescence of BODIPY Derivatives with Bulky Arylsilyl Groups: Synthesis and Spectroscopic Properties. Chem.-Eur. J. 2012, 18, 7852-7861. 27. Fan, Y.; Zhao, Y.; Ye, L.; Li, B.; Yang, G.; Wang, Y. Polymorphs and Pseudopolymorphs of N,N-Di(n-butyl)Quinacridone: Structures and Solid-State Luminescence Properties. Cryst. Growth Des. 2009, 9, 1421–1430. 28. Varughese, S. Non-Covalent Routes to Tune the Optical Properties of Molecular Materials. J. Mater. Chem. C, 2014, 2, 3499–3516. 29. Bandrowsky, T. L.; Carroll, J. B.; Braddock-Wilking, J. Synthesis, Characterization, and Crystal Structures of 1,1-Disubstituted-2,3,4,5-tetraphenylgermoles That Exhibit AggregationInduced Emission. Organometallics 2011, 30, 3559–3569. 30. Anthony, S. P.; Varughese, S.; Draper, S. M. Impact of Molecular Structure on Intermolecular Interactions and Organic Solid State Luminescence in Supramolecular Systems. J. Phys. Org. Chem. 2010, 23, 1074-1079. 31. Spies, C.; Huynh, A.-M.; Huch, V.; Jung, G. Correlation between Crystal Habit and Luminescence Properties of 4,4-Difluoro-1,3-dimethyl-4-bora-3a,4a-diaza-s-indacene, An Asymmetric BODIPY Dye. J. Phys. Chem. C, 2013, 117, 18163–18169.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 36

32. Mukherjee, S.; Thilagar, P. Fine-Tuning Solid-state Luminescence in NPIs (1,8naphthalimides): Impact of the Molecular Environment and Cumulative Interactions. Phys. Chem. Chem. Phys., 2014, 16, 20866–20877. 33. Moon, H.; Xuan, Q. P.; Kim, D.; Kim, Y.; Park, J. W.; Lee, C. H.; Kim, H.-J.; Kawamata, A.; Park, S. Y.; Ahn, K. H. Molecular-Shape-Dependent Luminescent Behavior of Dye Aggregates: Bent versus Linear Benzocoumarins. Cryst. Growth Des. 2014, 14, 6613–6619. 34. Li, Y.; Vamvounis, G.; Holdcroft, S. Tuning Optical Properties and Enhancing Solid-State Emission of Poly(thiophene)s by Molecular Control: A Postfunctionalization Approach. Macromolecules 2002, 35, 6900-6906. 35. Zhang, T.; Jiang, Y.; Niu, Y.; Wang, D.; Peng, Q.; Shuai, Z. Aggregation Effects on the Optical Emission of 1,1,2,3,4,5-Hexaphenylsilole (HPS): A QM/MM Study. J. Phys. Chem. A 2014, 118, 9094–9104. 36. Gierschner, J.; Park, S. Y. Luminescent Distyrylbenzenes: Tailoring Molecular Structure and Crystalline Morphology. J. Mater. Chem. C, 2013, 1, 5818–5832 and references cited therein. 37. Sonoda, Y.; Goto, M.; Tsuzuki, S.; Tamaoki, N. Fluorinated Diphenylpolyenes: Crystal Structures and Emission Properties. J. Phys. Chem. A 2007, 111, 13441-13451. 38. He, F.; Xu, H.; Yang, B.; Duan, Y.; Tian, L.; Huang, K.; Ma, Y.; Liu, S.; Feng, S.; Shen, J. Oligomeric Phenylenevinylene with Cross Dipole Arrangement and Amorphous Morphology: Enhanced Solid-State Luminescence Efficiency and Electroluminescence Performance. Adv. Mater. 2005, 17, 2710-2714. 39. Amrutha, S. R.; Jayakannan, M. Structure Control of π-Conjugated Polymers for Enhanced Solid-State Luminescence: Synthesis and Liquid Crystalline and Photophysical Properties of New Bulky Poly(p-phenylenevinylene)s and Oligo(phenylenevinylene)s Bearing Tricyclodecane Pendants. Macromolecules 2007, 40, 2380–2391. 30 ACS Paragon Plus Environment

Page 31 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40. Thomas, R.; Varghese, S.; Kulkarni, G. U. The Influence of Crystal Packing on the Solid State Fluorescence Behavior of Alkyloxy Substituted Phenyleneethynylenes. J. Mater. Chem., 2009, 19, 4401–4406. 41. Lewis, F. D.; Yang, J.-S. Solid-State Fluorescence of Aromatic Dicarboxamides. Dependence upon Crystal Packing. J. Phys. Chem. B 1997, 101, 1775-1781. 42. Sase, M.; Yamaguchi, S.; Sagara, Y.; Yoshikawa, I.; Mutai, T.; Araki, K. Piezochromic Luminescence of Amide and Ester Derivatives of Tetraphenylpyrene-role of Amide Hydrogen Bonds in Sensitive Piezochromic Response. J. Mater. Chem. 2011, 21, 8347-8354. 43. Anthony, S. P.; Varughese, S.; Draper, S. M. Switching and Tuning Organic Solid-State Luminescence via a Supramolecular Approach. Chem. Commun. 2009, 7500-7502. 44. Yamaguchi, S.; Yoshikawa, I.; Mutai, T.; Araki, K. Solid-state Luminescence of Tetraphenylpyrene Derivatives: Mechano/Vapochromic Luminescence of 1,3,6,8-tetra(4'carboxyphenyl)pyrene. J. Mater. Chem. 2012, 22, 20065-20070. 45. Yuan, M.-S.; Wang, D.-E.; Xue, P.; Wang, W.; Wang, J.-C.; Tu, Q.; Liu, Z.; Liu, Y.; Zhang, Y.; Wang, J. Fluorenone Organic Crystals: Two-Color Luminescence Switching and Reversible Phase Transformations Between π-π Stacking-Directed Packing and Hydrogen Bond-Directed Packing. Chem. Mater. 2014, 26, 2467-2477. 46. Rao M, R.; Liao, C.-W.; Su, W.-L.; Sun, S.-S. Quinoxaline Based D-A-D Molecules: High Contrast Reversible Solid-State Mechano- and Thermo-Responsive Fluorescent Materials. J. Mater. Chem. C 2013, 1, 5491–5501. 47. Yoon, S.-J.; Chung, J. W.; Gierschner, J.; Kim, K. S.; Choi, M.-G.; Kim, D.; Park, S. Y. Multistimuli Two-Color Luminescence Switching via Different Slip-Stacking of Highly Fluorescent Molecular Sheets. J. Am. Chem. Soc., 2010, 132, 13675–13683.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 36

48. Mutai, T.; Satou, H.; Araki, K. Reproducible On-Off Switching of Solid-State Luminescence by Controlling Molecular Packing Through Heat-Mode Interconversion. Nat. Mater. 2005, 4, 685-687. 49. Hariharan, P. S.; Venkataramanan, N. S.; Moon, D.; Anthony, S. P. Self-Reversible Mechanochromism and Thermochromism of a Triphenylamine-Based Molecule: Tunable Fluorescence and Nanofabrication Studies. J. Phys. Chem. C, 2015, 119, 9460–9469. 50. Dou, C.; Han, L.; Zhao, S.; Zhang, H.; Wang, Y. Multi-Stimuli-Responsive Fluorescence Switching of a Donor−Acceptor π-Conjugated Compound. J. Phys. Chem. Lett., 2011, 2, 666– 670. 51. Sagara, Y.; Yamane, S.; Mutai, T.; Araki, K.; Kato, T. A Stimuli-Responsive, Photoluminescent, Anthracene-Based Liquid Crystal: Emission Color Determined By Thermal and Mechanical Processes. Adv. Funct. Mater. 2009, 19, 1869–1875. 52. Oueslati, I.; Paixao, J. A.; Rodrigues, V. H.; Shkurenko, A.; Lesniewska, B.; Suwinska, K.; Eusebio, M. E. S.; Maria, T. M. R.; Seixas de Melo, J. S. Modulating the Self-Assembly of Calix[4]azacrowns to Design Materials with Improved Emission and Stimuli-Responsive Behavior. J. Phys. Chem. C, 2014, 118, 13118–13125. 53. Chen, S.; Liu, J.; Liu, Y.; Su, H.; Hong, Y.; Jim, C. K. W.; Kwok, R. T. K.; Zhao, N.; Qin, W.; Lam, J. W. Y.; and et al. An AIE-Active Hemicyanine Fluorogen with Stimuli-Responsive Red/Blue Emission: Extending the pH Sensing Range by "Switch + Knob" Effect. Chem. Sci., 2012, 3, 1804–1809. 54. Sagara, Y.; Kato, T. Mechanically Induced Luminescence Changes in Molecular Assemblies. Nat. Chem. 2009, 1, 605-610.


Page 33 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


55. Zhang, Y.; Sun, J.; Bian, G.; Chen, Y.; Ouyang, M.; Hu, B.; Zhang, C. Cyanostilbene-Based Derivatives: Mechanical Stimuli-Responsive Luminophors with Aggregation-Induced Emission Enhancement. Photochem. Photobiol. Sci., 2012, 11, 1414-1421. 56. Dong, Y.; Zhang, J.; Tan, X.; Wang, L.; Chen, J.; Li, B.; Ye, L.; Xu, B.; Zou, B.; Tian, W. Multi-Stimuli Responsive Fluorescence Switching: the Reversible Piezochromism and Protonation Effect of a Divinylanthracene Derivative. J. Mater. Chem. C, 2013, 1, 7554–7559. 57. Yuan, M.-S.; Wang, D.-E.; Xue, P.; Wang, W.; Wang, J.-C.; Tu, Q.; Liu, Z.; Liu, Y.; Zhang, Y.; Wang, J. Fluorenone Organic Crystals: Two-Color Luminescence Switching and Reversible Phase Transformations Between π-π Stacking-Directed Packing and Hydrogen Bond-Directed Packing. Chem. Mater., 2014, 26, 2467–2477. 58. Pati, A. K.; Mohapatra, M.; Ghosh, P.; Gharpure, S. J.; Mishra, A. K. Deciphering the Photophysical Role of Conjugated Diyne in Butadiynyl Fluorophores: Synthesis, Photophysical and Theoretical Study. J. Phys. Chem. A 2013, 117, 6548-6560. 59. Pati, A. K.; Gharpure, S. J.; Mishra, A. K. Substituted Diphenyl Butadiynes: a Computational Study of Geometries and Electronic Transitions Using DFT/TD-DFT. Phys. Chem. Chem. Phys. 2014, 16, 14015-14028. 60. Pati, A. K.; Gharpure, S. J.; Mishra, A. K. On the Photophysics of Butadiyne Bridged Pyrene-Phenyl Molecular Conjugates: Multiple Emissive Pathways Through Locally Excited, Intramolecular Charge Transfer and Excimer states. Faraday Discuss. 2015, 177, 213-235. 61. Nemkovich, N. A.; Rubinov, A. N.; Tomin, V. I. Inhomogeneous Broadening of Electronic Spectra of Dye Molecules in Solutions. Top. Fluoresc. Spectrosc. 2002, 2, 367–428. 62. Bushuk, B. A.; Rubinov, A. N; Stupak, A. P. Inhomogeneous Broadening of Spectra of Dye Solutions Due to Intermolecular Hydrogen Bonding. J. Appl. Spectrosc. 1987, 47, 1251–1254.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 36

63. Kasha, M.; Rawls, H. R.; El-Bayoumi, M. A. Exciton Model in Molecular Spectroscopy. Pure Appl. Chem. 1965, 11, 371-392. 64. Politzer, P.; Murray, J. S.; Clark, T. Halogen Bonding and Other σ-Hole Interactions: A Perspective. Phys. Chem. Chem. Phys. 2013, 15, 11178-11189. 65. Mani, D.; Arunan, E. The X–CY (X = O/F, Y = O/S/F/Cl/Br/N/P) ‘Carbon Bond’ and Hydrophobic Interactions. Phys. Chem. Chem. Phys., 2013, 15, 14377-14383. 66. Mani, D.; Arunan, E. The X−C···π (X = F, Cl, Br, CN) Carbon Bond. J. Phys. Chem. A 2014, 118, 10081−10089. 67. Arunan, E.; Desiraju, G. R.; Klein, R. A.; Sadlej, J.; Scheiner, S.; Alkorta, I.; Clary, D. C.; Crabtree, R. H.; Dannenberg, J. J.; Hobza, P. and et al. Definition of the Hydrogen Bond (IUPAC Recommendations 2011). Pure Appl. Chem., 2011, 83, 1637-1642. 68. Shahi, A.; Arunan, E. Hydrogen Bonding, Halogen Bonding and Lithium Bonding: An Atoms in Molecules and Natural Bond Orbital Perspective Towards Conservation of Total Bond Order, Inter- and Intra-Molecular Bonding. Phys. Chem. Chem. Phys., 2014, 16, 22935-22952. 69. Thomas, S. P.; Pavan, M. S.; Guru Row, T. N. Experimental Evidence for ‘Carbon Bonding’ in the Solid State from Charge Density Analysis. Chem. Commun., 2014, 50, 49-51. 70. Rodriguez, J. G.; Lafuente, A.; Martin-Villamil, R.; Martinez-Alcazar, M. P. Synthesis and Structural Analysis of 1,4-Bis[n-(N,N-dimethylamino)phenyl]buta-1,3-diynes and ChargeTransfer Complexes with TCNE. J. Phys. Org. Chem., 2001, 14, 859-868. 71. Spackman, M. A.; Jayatilaka. D. Hirshfeld Surface Analysis. CrystEngComm. 2009, 11, 1932. 72. McKinnon, J. J.; Jayatilaka, D.; Spackman, M. A. Towards Quantitative Analysis of Intermolecular Interactions with Hirshfeld Surfaces. Chem. Commun. 2007, 3814-3816.


Page 35 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


73. Spackman, M. A.; McKinnon, J. J. Fingerprinting Intermolecular Interactions in Molecular Crystals. CrystEngComm 2002, 4, 378-392. 74. Spano, F. C. The Spectral Signatures of Frenkel Polarons in H- and J-Aggregates. Acc. Chem. Res. 2010, 43, 429–439. 75. Würthner, F.; Kaiser, T. E.; Saha-Moeller, C. R. J-Aggregates: From Serendipitous Discovery to Supramolecular Engineering of Functional Dye Materials. Angew. Chem. Int. Ed. 2011, 50, 3376-3410. 76. Eisfeld, A.; Briggs, J. S. The J- and H-Bands of Organic Dye Aggregates. Chem. Phys. 2006, 324, 376-384. 77. Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange-Correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51-57. 78. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B., Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; and et al., Gaussian 09, Revision C.01, Gaussian, Inc., Wallingford CT, 2010. 79. Oelkrug, D.; Tompert, A.; Egelhaaf, H.-J.; Hanack, M.; Steinhuber, E.; Hohloch, M.; Meier, H.; Stalmach, U. Towards Highly Luminescent Phenylene Vinylene Films. Synth. Met., 1996, 83, 231–237. 80. Oelkrug, D.; Tompert, A.; Gierschner, J.; Egelhaaf, H.-J.; Hanack, M.; Hohloch, M.; Steinhuber, E. Tuning of Fluorescence in Films and Nanoparticles of Oligophenylenevinylenes. J. Phys. Chem. B, 1998, 102, 1902–1907. 81. Dong, Y. J.; Xu, B.; Zhang, J. B.; Lu, H. G.; Wen, S. P.; Chen, F. P.; He, J. T.; Li, B.; Ye L.; Tian, W. J. Supramolecular Interactions Induced Fluorescent Organic Nanowires with High Quantum Yield Based on 9,10-Distyrylanthracene. CrystEngComm. 2012, 14, 6593–6598.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 36

82. Wu, Q.; Zhang, T.; Peng, Q.; Wang, D.; Shuai, Z. Aggregation Induced Blue-Shifted Emission - the Molecular Picture from a QM/MM Study. Phys. Chem. Chem. Phys., 2014, 16, 5545-5552. 83. Catalan, J.; Zimanyi, L.; Saltiel, J. Medium-Controlled Aggregation of trans-Stilbene. J. Am. Chem. Soc. 2000, 122, 2377-2388. 84. Gierschner, J.; Ehni, M.; Egelhaaf, H.-J.; Milian Medina, B.; Beljonne, D.; Benmansour, H.; Bazan, G. C. Solid-State Optical Properties of Linear Polyconjugated Molecules: π-Stack Contra Herringbone. J. Chem. Phys. 2005, 123, 144914/1–144914/9. 85. Piacenza, M.; Della S., Fabio; F., Gianluca M.; Martinelli, C.; Gigli, G. Large Blue-Shift in the Optical Spectra of Fluorinated Polyphenylenevinylenes. A Combined Theoretical and Experimental Study. J. Phys. Chem. B 2008, 112, 2996–3004.

TOC Graphic:


Contrasting Solid-State Fluorescence of Diynes with Small and Large

Recommend Documents