Tuning of Aggregation Enhanced Emission and Solid State Emission

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Tuning of Aggregation Enhanced Emission and Solid State Emission from 1,8-Naphthalimide Derivatives: Nano-Aggregates, Spectra and DFT Calculations Ashish Kumar Srivastava, Avinash Kumar Singh, and Lallan Mishra J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b05355 • Publication Date (Web): 13 Jun 2016 Downloaded from http://pubs.acs.org on June 20, 2016

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The Journal of Physical Chemistry

Tuning of Aggregation Enhanced Emission and Solid State Emission from 1,8-Naphthalimide Derivatives: Nano-Aggregates, Spectra and DFT Calculations Ashish Kumar Srivastavaa, Avinash Singhb and Lallan Mishraa* a

Department of Chemistry (Centre of Advanced Study), Institute of Science, Banaras Hindu University, Varanasi-221005, India

b

Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India

1 ACS Paragon Plus Environment


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ABSTRACT

Four

new

1,8-naphthalimide

benzo[de]isoquinolin-2-ylmethyl)-benzoic

based

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compounds,

acid

(LH),

4-(1,3-Dioxo-1H,3H4-(1,3-Dioxo-1H,3H-

benzo[de]isoquinolin-2-ylmethyl)-benzoic acid methyl ester (LMe), 4-(1,3-Dioxo-1H,3Hbenzo[de]isoquinolin-2-ylmethyl)-benzoyl benzo[de]isoquinolin-2-ylmethyl)-benzoic

chloride acid

(LCl)

hydrazide

and (LN)

4-(1,3-Dioxo-1H,3Hare

synthesized

and

characterized using spectral data and X-ray crystallography. They form nano-aggregates in aqueous-DMF solution and exhibited aggregation enhanced emission (AEE). The nanoaggregates are characterized using their SEM and AFM images. The emission intensity follows the order as LH˃LMe˃LCl˃LN. Their photophysical properties are recorded both in solution and in the solid-state and are correlated with the nature of benzoic acid derivatives owing to the combinatorial effect of π–π stacking, intermolecular and intramolecular interactions. The DFT calculations empower the understanding of their molecular and cumulative electronic behaviors. Antiparallel dimeric interactions in the solid-state extend a herringbone arrangement to LH and 2D channel and stair like arrangement for LCl and LN respectively.

Introduction The design and synthesis of organic compounds as luminescent materials have been fascinating owing to their extensive and useful applications.1-3 The concentration dependent and aggregation induced quenching of the fluorescence arise due to the formation of excitons/excimers, resulting in nonradiative decay of their excited states.4 The design and synthesis of new luminescent materials which can aggregate and emit efficiently is considered as an overcome of such quenching processes. The concept of aggregation-induced emission (AIE) and aggregation-induced emission enhancement (AIEE) was propounded independently by Tang5-7 and Park8-11 respectively. The advent of their discovery empowered the development of


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advance luminescent materials for sensing,12-14 biomedical,15-18 and solid state lighting19-21 applications.

Several

organic

compounds

like

siloles,22,23

1-cyano-trans-1,2-bis-(4-

methylbiphenyl)ethylene,24 thienyl-azulene,25 arylethene26 and naphthalimide27 were developed and displayed intense emission in the solid state. Among them, 1,8-naphthalimide derivatives displayed wide dimension of properties in their aggregated state yet their solid state properties are least explored.28-30 Aggregation induced emission and solid state emission runs parallel to each other. In general, compounds bearing 1,8-naphthalimide group show strong tendency to form intermolecular π–π stacking interactions and display strong intramolecular charge transfer (ICT) which can diminish the emission in their condensed states.31,32 The design and synthesis of metal–organic frameworks based on 1,8-naphthalimide was exploited by Reger et al. as π- π stacking synthons.33 It turned out to be suitable candidate for optoelectronic and semiconductor applications.34 Although, 1,8-naphthalimides have been well studied in coordination complexes yet their true potentials are still to be explored. Systematic changes made in their molecular frameworks can screen and identify suitable materials which can control different molecular and cumulative properties.35 A dyad of tetraphenylethylene–naphtalimde has been integrated as luminogen and its property is dictated by pendant groups tetraphenylethylene (TPE).36 Similarly, in another dyad of naphtalimde–styryl, it is styryl moiety which govern its property.37 As a consequence, design principle was improved by Thilagar et al.38 and 1,8-naphthalimides bearing flexible substituents with weaker ICT features

met the demand of aggregation enhanced

emission (AEE). In principle, intramolecular rotations of bulky groups, regardless of their conjugation or non-conjugation, they consume energy and extinguish excited state. However, molecules to some extent with bent structures hamper the π–π stacking interaction in the aggregated state. In an analogous approach, systematic changes in intermolecular effects through



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structural alterations may provide a general path of development of 1,8-naphthalimide derivatives with aggregation enhanced emission. Thus, based on the precedence, we were enthused to design and synthesize simple and novel compounds of type LH, LMe, LCl and LN and characterize them by full battery of physiochemical techniques including their single crystal X-ray crystallography. As expected, these newly synthesized compounds formed nanoaggregates in aqueous-DMF solution most likely assisted by complementary H-binding besides π–π stacking interactions through their tricyclic1,8-naphthalimide core. They also emitted in the solid states. The systematic investigation of the compounds unveiled a number of intriguing outcomes and provided an insight into the origin of such behaviours. The observed photophysical property of synthesized compounds was well substantiated by optimized structures of monomers and corresponding dimers using DFT calculation. The present manuscript is targeted to provide an understanding of the aggregation enhanced emission tuned from newly synthesized compounds bearing1,8-naphthalimide group. Experimental Section All reagents and solvents were obtained from commercial sources. The elemental analyses were performed on Carbo-Erba elemental analyzer 1108. The infrared spectra of the compounds were recorded on a Varian 3100 FT-IR spectrometer (4000-400 cm−1) using KBr disks. The 1H NMR / 13

C NMR spectra were recorded using a Jeol 300 MHz instrument. Chemical shifts were reported

in parts per million (ppm) relative to internal TMS (0ppm). ESI-Ms of LMe was measured on Amazon SL and of LH, LCl and LN were measure on Waters UPLC-TQD Mass spectrometer. Single crystal X-ray diffraction data for compounds were collected on an Oxford Diffraction Xcalibur CCD diffractometer at 293 K using Mo Kα radiation. The structures were solved by direct methods using SHELXS-97 and refined on F2 by full matrix least squares technique using


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SHELXL-97.39,40 Drawings were carried out using MERCURY,41 and special computations were carried out with PLATON.42 All non hydrogen atoms were refined anisotropically. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre (CCDC) as deposition Nos. CCDC 1033906(LH), 1034179 (LCl) and 1034178(LN). Copies of the data can be obtained, free of charge, on application to the CCDC, 12 Union Road, Cambridge CB2 lEZ, U.K. (fax:þ 44 (1223) 336 033; e-mail:[email protected]). UV−visible absorption spectra were recorded at room temperature in DMF solution (2×10-5 M) on Jasco V-630 spectrophotometer; however, solid state UV-visible absorption spectra were recorded on Horiba Jobin Yuvon spectrophotometer. The emission spectra at room temperature as well as at variable temperatures were recorded on Horiba Jobin Yuvon fluorescence spectrophotometer. Time resolved fluorescence data were obtained using a picoseconds pulsed diode laser based time-correlated single photon counting (TCSPC) instrument from IBH (United Kingdom). The samples for SEM and AFM samples were prepared using drop-casting method and using 2×10-5 M solutions of compounds in DMF/water media and solutions were then evaporated to dry the samples. The nano aggregates thus obtained were characterized using Scanning Electron Microscope (SEM, EVO/18 reaseach) and Atomic Force Microscope (NTMDT Moscow) instruments. UV-visible and Fluorescence Spectral Measurements The stock solution of the compounds was prepared separately in DMF (1×10-4 M). An aliquot (400µL) was taken and added with an appropriate amount of DMF and water to adjust the desired solvent composition and made the final concentration of 2×10-5 M in each case. Corresponding solutions were allowed to equilibrate at room temperature for 1h before their



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spectral measurements. The emission from compounds at variable-temperatures were measured using corresponding solutions in DMF:water media (v/v,2:8 for LH, 3:7 for LMe, 2:8 for LCl and 4:6 for LN) at 60°C to -10°C and allowed to equilibrate for 5 min at the desired temperatures before each measurement. All emission measurements were carried out at λex=330 nm. The quantum yields were calculated using quinine sulfate (1×10-1 M) H2SO4, ʎex=350 nm, Φs=57.7%) solution as reference using43 equation: Φu=Φs(Afu/Afs)[As(ʎex)/Au(ʎex)](ηu/ηs)2 where, Φ=quantum yield, u=sample to be measured, s=standard sample, Afu=integrated area under normalized emission spectra, η=refractive index of the solvent, As=absorbance area at excitation wavelength. Computational Calculation The ground state configurations of the compounds and their corresponding dimers were optimized by DFT calculations using Gaussian-09 software over a Rock cent Os cluster IBM Blade server.44 The molecular level interactions were studied using B3LYP/6-31G(d,p) functional model and basis set.45 Vertical electronic excitations based on B3LYP optimized geometries were computed using time-dependent density functional theory (TD-DFT)46 and Gabedit, a graphical user interface was used for drawing the spectra.47 Result and Discussion The synthetic strategy of compounds is shown in Scheme 1 where as their synthesis and characterization details are described in S1 and S2. The method of life-time measurement is provided in S3. The 1H and

13

C NMR spectra of the compounds are shown in Figures S1- S4,

where as their ESI-MS spectra are displayed in Figures S5- S8. IR spectra of LH showed major peaks at 2543-3071, 1659 cm-1 and 1591 cm-1 assigned to ν(O-H), νas(COOH) and νs(COOH) respectively. The infrared spectra of LMe, LCl and LN showed peaks at 1721, 1769 and 1698


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cm-1 assigned to ν(C=O) vibrations of -H3CO-C=O, Cl-C=O and H2N-C=O respectively. The 1H NMR spectrum of LH displayed a peak at δ=12.88 ppm assigned to carboxylic acid proton. The 1

H NMR spectrum of LMe showed a peak at δ=3.87 ppm owing to -OCH3 protons. The NH2 and

NH protons of LN appeared at δ=4.47 ppm and δ=9.69 ppm respectively. The N-CH2 protons of the compounds appeared at δ=5.27-5.33 ppm while their phenyl protons were displayed at δ= 7.39-8.49 ppm. These spectral data were further supported by their ESI-MS and single crystal Xray data. However, X-ray crystallography of LMe could not be performed due to its poor diffraction. A summary of the crystallographic data are given in Table 1 and selected bond lengths and bond angles are shown in Table S1. The parameters describing the selected secondary interactions are presented in Table 2. Molecular Structure of Compounds Compounds LH and LN were crystallized from DMF solvent whereas LCl was crystallized from dichloromethane (DCM) and their crystals were found triclinic with space group as P-1. The crystal of LH consists of one molecule of LH along with a molecule of DMF as shown in Figure 1(a).

The

complete

molecular

system

adopts

a

bent

shape

and

dihedral

angle

(C(023)−C(019)−C(013)−N(001)) was found as 94.88°. The bent shape minimizes the steric hindrance between hydrogen atoms of methylene unit and oxygen atoms of 1,8 naphthalimide core. The distance between hydrogen atoms of methylene unit H(01A)C(013)···O(1) is 2.37 Å and H(01B)C(013)···O(2) is found as 2.35 Å. It contains one O−H···O interactions and five C−H···O interactions in which one O−H···O interaction comes from crystallized DMF molecule and resulted into the structure as depicted in Figure 1(b). Unlike LH, asymmetric unit of LCl contains a molecule of LCl without any solvent molecule as shown in Figure 2(a). This molecule also adopts a bent shape with dihedral angle C(015)−C(011)−C(014)−N(001) of 75.38°. The bent



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shape again supported the stabilization of this molecule. The distance between hydrogen atoms of methylene unit H(01 A)C(014)···O(1) is 2.37 Å and H(01B)C(014)···O(2) was found 2.35 Å. The molecule LCl has type 1 trans Cl···Cl interaction with C(020)-Cl(1)-Cl(1) (θ1=θ2=148.57°)48,49 as shown in Figure 2(b). The four C−H···O interactions and one C−H···Cl interaction in LCl resulting into two dimensional channels as shown in Figure 2(c). The molecule LN also adopts a bent shape with dihedral angle (C(010)−C(008)−C(013)−N(001)) of 83.59° and the distance between hydrogen atoms of methylene unit H(01A)C(013)···O(1) and H(01B)C(013)···O(2) was found as 2.37 Å is 2.35 Å respectively as shown in Figure 3(a). The molecule LN comprises three classical hydrogen bonds and two C−H···O interactions and it is resulted in stair like arrangement as shown in Figure 3(b). Additionally, LH exhibits face to face antiparallel π···π stacking interaction between its naphthalimide core separated at a distance of 3.709 Å as depicted in Figure 4(a). However, compounds LCl and LN exhibited slipped π···π stacking interactions at a distance of 3.763 Å and 3.524 Å as shown in Figure 4(b) and in Figure 4(c) respectively. Thus, it was interesting to observe intermolecular interactions lead the foundations of herringbone arrangement50 in LH, two dimensional channels in LCl and stair like arrangement in LN. SEM and AFM Analysis The SEM images of the compounds displayed cubic shape nano-aggregates for LH and LCl, spherical nano-aggregates for LMe and flower like morphology for LN as displayed in Figure 5. SEM images of LH and LCl were found crystalline in nature, whereas globular aggregates were found for LMe. LN displays crystalline to flower-like morphology.

These morphologies

supported the formation of nano-aggregates of average size 250-350nm. Their AFM images as


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depicted in Figure 6 also gave similar morphology with almost similar range of size of the nano aggregates. Photophysical Properties of LH, LMe, LCl and LN in Solution The measurement of photophysical properties of the compounds were carried out by the incremental addition of water (up to 80%) in their corresponding solutions in DMF. The absorption spectra of LH, LMe, LCl, and LN recorded in pure DMF solution (2×10-5 M each) showed bands at ʎmax =334 - 335 nm as shown in Figures 7(a), 7(b), 7(c) and 7(d) respectively. On the addition of water in their DMF solutions, absorbance decreased (except LN) with concomitant bathochromic shift by1- 9 nm (Table 3). This observation is found in consistence with the earlier report assigned to J-type aggregation.51-53 The emission from these compounds recorded in DMF solution displayed emissions at ʎem =384-386 nm as shown in Figures 8(a), 8(b), 8(c) and 8(d) for LH, LMe, LCl and LN respectively. The origin of these emissions are considered from their 1,8 naphthalimide ring in view of earlier reports.54,55 However, on addition of excess water to their corresponding solutions (keeping final concentration constant at 2×10-5 M), the resultant solutions displayed 1.5 fold - 2.0 fold enhanced emission in the order of LH˃LMe˃LCl˃LN (Figure 8 and Table 3). Their images recorded in DMF solution with the incremental addition of water and illuminated by UV light are shown in Figure 9. Intensities of fluorescence images support the order of emission as shown in Table 3. As shown in Table 3, maximum emission from LH and LCl was observed on the addition of water up-to 80%. However, for LMe and LN maximum emission was observed at 70% and 40 % water-DMF mixture respectively. A bar diagram showing the variation of emission intensity from all compound versus the water content is depicted in Figure 10. This variation was found consistent



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with the earlier report for AEE characteristic.56 The quantum yields of compounds in DMF with and without water have also been calculated and are shown in Table 4. In order to support that emission enhancement is aggregation induced; the effect of the temperature on the emission displayed from the corresponding solution of the compounds in water-DMF mixture has also been investigated. As shown in Figure 11, emission intensity decreases with increase in the temperatures and vice versa. The decrease in the temperature of a solution can restrict intra molecular motion/rotations (RIR/RIM) processes57 and consequently increase the emission intensity whereas increase in the temperature can relax the rotation or intra molecular motion resulting a decrease in emission intensity. The RIR process is likely to be affected by the viscosity of the solvent. Greater is the viscosity of the solvent, slower would be the intramolecular rotation/motion, and concomitantly intense would be the emission from compounds. Thus, the effect of a viscous solvent (glycerol) on the emission intensity from the compounds has been investigated. Emission spectra of the compounds were recorded by the incremental addition of the glycerol. The fluorescence intensity from all compounds increases on the addition of 50 to 60% volume fraction of glycerol (Figure S9). This is attributed to the high viscosity of the solution that restricted intramolecular rotation leading to the closure of nonradiative decay channel, hence, making the molecules more emissive.58 Photophysical Properties of LH, LMe, LCl and LN in Solid State The absorption spectra of the compounds recorded in the solid state are shown in Figure S10. The emission spectra of the compounds recorded in their solid state and excited at the absorption band ʎex=360 nm (Figure 12), displayed emissions at 457, 456, 450 and 442 nm for LH, LMe, LCl and LN respectively. As compared to their emissions at ʎem =384 - 386 in DMF solution,


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the emissions from solid state shifted to longer wavelength and was found comparable to the emissions from their aggregates in aqueous-DMF solution. Such a red-shift can be attributed to the closely packed intermolecular interactions in the solidstate. It helped to form a band-structure in the solid-state and lower the effective cumulative band gap in the condensed states of organic compounds (DFT computation studies, vide infra). The compound with maximum intermolecular interaction resulted with the lowest emission intensity while compounds involving minimum intermolecular interactions resulted with the highest emission intensity. In view of earlier report, π···π interaction in the solid state, could also contribute to the larger shift in the wavelength.59 Slipped stacking interactions and C−H···O/ C−H···N has also been considered important for the solid state emission with large bathochromic shift.60,61 This provides favourable factors that eliminate self-quenching and enhance their solid fluorescence. The optimal recipe for π···π stacking units as well as intermolecular C−H···O interactions are observed in LH, trans arrangement in LCl showing Cl···Cl interaction and classical hydrogen bonds in LN may be considered as an effective combinations of molecular interactions attributing to the significant aggregation induced emission observed strongly in the solid state of the molecules. The Emission Life-Time Studies The life-time measurement of compounds in DMF could not be completed as decay curves did not deconvolute. Therefore, it was carried out in the solid state by fitting the time resolved curves (Figure 13). The emission life time for the compounds was obtained based on their biexponential function. The data and are given in Table 5. In case of LH and LMe, majority of the molecules (57% for LH and 66% for LMe) undergo with slower decay- rate where as in other



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compounds, majority of the molecule follow a faster decay -rate (84 % for LCl and 82 % for LN). The life-time observation supports the extent of aggregation observed in the compounds. Theoretical Discussion Theoretical calculations on these compounds have been carried and they support the experimental data. The optimized geometries of the compounds are given in Figure 14.

The

dihedral angles obtained from the ORTEP diagrams {Figures 14(a) LH, 14(b) LCl and 14(c) LN} of the corresponding compounds have been compared with their corresponding optimized structures {Figures 14(d) LH, 14(e) LMe, 14(f) LCl and 14(g) LN}. The optimized structures are also found non-planar and their HOMO-LUMO’s of compounds have been depicted in Figure 15. The compounds contain CH2 group which connects the 1,8-naphthlimide ring with benzene carboxylic acid and its derivatives, they will be unable to attain a coplanar geometry, and instead the overall structure is bent. In addition to this, non classical hydrogen bonds from hydrogen atoms of methylene group also help to restrict the geometry in bent shape. But in case of LCl and LN, although the geometries are bent but sufficient electro negativity of –COCl and NHNH2 group displace the HOMO from 1,8-naphthalimide group to –COCl and -CONHNH2 groups respectively. This could be attributed to stronger emission from LH and LMe as compared to emission from LCl and LN in both aggregated and solid state. In addition to this, TD-DFT calculations have also been carried out to investigate their electronic transitions. For LH, LMe, LCl and LN the bands at 329.88 nm, 329.96, 330.50 nm and 330.20 are dominated by the HOMO-4→LUMO and HOMO→LUMO, HOMO-4→LUMO and HOMO→LUMO, HOMO→LUMO and HOMO-6→LUMO and HOMO→LUMO transitions respectively. The calculated UV-visible spectra of the compounds are shown in Figure S11. They could be compared very well with their corresponding experimentally observed spectra. To understand the


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nature of the interactions in dimers of these compounds, ground state (B3LYP/6-31G(d), gaseous state) geometry optimizations of the model systems named D1, D2, D3 and D4 have been carried out and are shown in Figure 16 where as their corresponding HOMO, LUMO are shown in Figure 17. The HOMO–LUMO gaps in the dimeric structural models from D1–D4 were found to be lower than those of the corresponding monomers (Table 6). It could be attributed to combined effect of the destabilisation of the occupied MOs (i.e., HOMOs) and the weaker stabilisation of the virtual unoccupied MOs (i.e., LUMOs). The lowering of the HOMO–LUMO gaps in these model systems directly corroborates the red shifted emission bands arising from 1,8naphthalimide ring in their aggregated states. Conclusion 1,8-Naphthalimide anchored with four benzoic acid derivative via methylene group provides simple and interesting compounds which exhibit different types of nano-aggregates in waterDMF media. These aggregates display enhanced emission. Several interesting supramolecular structures are formed by the weaker secondary interactions. These interactions also support the aggregation processes. They emit enhanced emission in both aggregated and in the solid states. The DFT and TD-DFT calculations empowered the data to corroborate their experimentally observed photophysical properties. Associated content Supporting information The 1H and

13

C NMR of synthesized compounds, table of bond length and bond angle,

emission spectra with various glycerol content, solid state UV-visible spectra and method of determination of life-time are provided in supplementary information.



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AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]

Funding Sources ACKNOWLEDGMENT AKS is thankful to UGC-BSR RFSMS (Award no- F.5/105/2007/BSR), New Delhi, India for Junior and senior research fellowships. Prof. Anindya Datta, Department of Chemistry, IIT Bombay, India is gratefully acknowledged for his help in the measurement of life time of the compounds.


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Scheme 1. Synthetic scheme of LH, LMe, LCl and LN



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Table 1. Crystallographic data for compounds LH, LCl and LN

Compounds

LH

LCl

LN

Formula

C23H20N2O5

C20H12ClNO3

C20H15N3O3

Weight

404.41

349.76

345.35

Space group

P-1

P-1

P-1

a [Å]

7.1869(7)

7.3863(13)

7.2393(14)

b [Å]

10.4125(11)

8.2034(12)

8.2113(17)

c [Å]

13.9921(16)

13.638(2)

13.890(2)

α [deg]

99.407(10)

107.497(13)

82.844(15)

β [deg]

99.754(9)

91.679(13)

82.043(15)

γ [deg]

98.226(8)

95.166(14)

79.855(17)

ρcald [Mgm−3]

1.340

1.482 Mg/m^3

1.432

V [Å3]

1002.24(18)

783.5(2)

800.7(3)

Z

2

2

2

Index ranges

-7≤h≤9

-10≤h≤10

-8≤h≤8

-12≤k≤14

-11≤k≤11

-9≤k≤9

-18≤l≤14

-18≤l≤18

-16≤l≤15

R1a [I > 2σ(I)]

R1 = 0.0626, R1 = 0.0686, R1 = 0.0805, wR2 = 0.1576 wR2 = 0.1747 wR2 = 0.1467

wR2

R1 = 0.1128,

R1 = 0.1054,

R1 = 0.2936,

b (all data)

wR2 = 0.1922

wR2 = 0.2137

wR2 = 0.2488

GOF on F2

1.054

1.028

0.966


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Table 2. Selected parameters of secondary interactions

LH D–H---A

D-H

H---A

D---A

D-H---A

Symmetry codes

C(012)—H(1)---O(1)

0.93

2.44

3.3040

156

2-x,-y,1-z

C(021)—H(2)---O(4)

0.94

2.52

3.3367

147

2-x,-y,-z

C(039)—H(03B)--O(2)

0.96

2.29

3.2080

161

C(011)—H(12)---O(2)

0.96

2.48

2.8249

101

C(011)—H(12)---O(5)

0.96

2.60

3.3607

136° 358.00

C(013)— H(01A)---O(1)

0.97

2.38

2.704

98.37

C(013)— H(01B)---O(2)

0.97

2.37

2.690

98.42

C(012)—H(012)---Cl(1)

0.93

2.62

3.0393

108

C(014)—H(01B)---O(2)

0.97

2.36

2.6939

100

C(015)—H(015)---O(2)

0.93

2.52

3.2078

131

C(019)—H(019)---O(2)

0.93

2.44

3.3408

163

1-x, 2-y,1-z

C(02)—H(022)---O(3)

0.93

2.60

3.5259

179

x,1+y,1+z

C(014)—H(01A)---O(1)

0.97

2.37

2.694

98.32

N(003)—H(42)---O(002)

0.86

2.51

3.0983

126

-1-x,2-y,1-z

N(003)—H(42)---N(5)

0.86

2.50

3.1051

128

-x,2-y,1-z

N(5)—H(51)---N5(003)

1.02

2.54

3.2067

315

-x,2-y,1-z

C(010)—H(010)---O(005)

0.93

2.48

3.1981

134

-1+x,y,z

C(013)—H(01B)---O(004)

0.97

2.35

2.7190

102

C(013)—H(01A)---O(005)

0.97

2.38

2.6734

96.56

121'

LCl

LN



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Page 18 of 48

Table 3. Absorption and emission spectral data of compounds

compounds

λa

λb Solnc

IA/Is

Solnc

Aggtd

Aggtd

LH

335(0.32)e

344(0.25)e 385e

394e

2.05e

LMe

344(0.13)f

345(0.82)f

384f

395f

1.82f

LCl

335(0.24)e

343(0.18)e 385e

395e

1.65e

LN

334(0.16)g

340(0.19)g 385g

391g

1.51g

a

Absorption maximum. bEmission maximum. cSolution (in DMF). dAggregate. eAggregate in water -DMF mixture with 80 vol% water. fAggregate in water -DMF mixture with 70 vol% water. gAggregate in water -DMF mixture with 40 vol% water Ratio of PL peak intensities of aggregate (IA) and solution (IS). Value in parentheses indicates corresponding absorbance value.


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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


Table 4. Quantum yield variation with different fractions of water [Φ (0% water), Φ1 to Φ8 (10, 20, 30……80% water) with respect to quinine sulphate

Compounds Φ

Φ1

Φ2

Φ3

Φ4

Φ4

Φ5

Φ6

Φ7

Φ8

LH

0.253

0.276

0.302

0.344

0.391

0.416

0.467

0.471

0.481

0.501

LMe

0.216

0.245

0.267

0.283

0.315

0.336

0.358

0.376

0.393

0.381

LCl

0.263

0.280

0.293

0.314

0.345

0.367

0.382

0.391

0.422

0.431

LN

0.238

0.257

0.291

0.313

0.342

0.281

0.273

0.277

0.273

0.276



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Table 5. Fluorescence life-times of compounds in the solid state

compounds

τ1

τ2

a1

a2

b

χ2

LH

7.8

15.6

0.43

0.57

1.04

LMe

6.9

22.4

0.34

0.66

1.09

LCl

2.8

10.9

0.84

0.16

1.17

LN

1.4

4.4

0.82

0.18

1.14

τ1 and τ2 are biexponential lifetimes of compounds in solid state. a1 and a2 are the amplitudes of that component at the wavelength at which decays are recorded. bReduced χ2 value


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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


Table 6. Energy of FMO’s of compounds and their dimers (Energies are given in eV unit)

Model

HOMO

LUMO

HOMO-LUMO gap

LH

6.61

2.46

4.15

LMe

6.60

2.54

4.05

LCl

6.76

2.16

4.15

LN

6.59

2.51

4.07

D1

6.59

2.77

3.88

D2

6.61

2.61

4.00

D3

6.75

2.81

3.94

D4

6.57

2.76

3.81



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Figure 1. (a) Moleecular structture (ORTE EP) and (b) Packing P diaagram of LH H (herringboone like) (a)

(b)


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Figure 2. (a) Moleecular struccture (ORTE EP diagram m) of LCl (b b) Compounnd LCl show wing type 1 trans Cll···Cl interacction (c) Paacking diagrram of LCl

(a))

(b))

(c)

23 3 ACS Paragon Plus Environment


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Page 24 of 48

Figure 3. (a) Mollecular struccture (ORT TEP diagram m) and (b) Packing P diaagram of LN L (steps off stair aree arranged in i anti-paralllel manner)). (a)

(b b)


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Figure 4. π···π staacking diagrrams of (a) LH (b) LCl and (c) LN N are show wing distancces between n tri-cycliic core.



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Page 26 of 48

Figure 5. SEM images of nano -aggregates of LH, LMe, LCl and LN (2×10-5M DMF/water 2:8 v/v for LH, 3:7 v/v for LMe, 2:8 v/v for LCl and 4:6 v/v for LN).


Page 27 of 48

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Figure 6. AFM images of nano-aggregates of LH, LMe, LCl and LN (2×10-5 M, DMF/water 2:8 v/v for LH, 3:7 v/v for LMe, 2:8 v/v for LCl and ,4:6 v/v for LN).



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Page 28 of 48

-55 Figure 7. UV-visibble absorption spectra of (a) LH (b) LMe (c) LCl and (d) LN in DMF(2×10 D

M) (blaack color) an nd DMF-waater(2:8, v/v v)(red colorr).


Page 29 of 48

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Figure 8. Emissionn spectra off (a) LH (b) LMe (c)) LCl and (d d) LN (2×10-5 M DMF F/water 2:8, v/v).



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Page 30 of 48

Figure 9. The fluorescence images of compounds with different fractions of water (fw) under Uv-illumination


Page 31 of 48

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


Figure 10. A bar diagram showing variation in emission intensity of compounds on the incremental addition of water to the solution of compounds in DMF.



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

Figure 11. Emisssion spectraa showing effect of

Page 32 of 48

increasing g temperatuure (Left image) i and d

decreassing temperaature( rightt image) on PL peak inntensity of 2×10-5 M L LH, LMe, LCl L and LN N (from top t to bottoom) in DM MF/water(2:8 8) solution upward arrrow showss increase in i emission n intensity y and downnward arrow w shows deccrease in em mission inten nsity.


Page 33 of 48

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


Figure 12. Emission spectra of LH, LMe, LCl and LN in solid state (λex= 330 nm).



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Page 34 of 48

Figure 13. Fluoresscence life-ttime decay curve in pow wdered statte


Page 35 of 48

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Figure 14. Comparison of dihedral angles between the X-ray structures of (a) LH (b) LCl and (c) LN and optimized structures (d) LH (e) LMe (f) LCl and (g) LN.



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Page 36 of 48

Figure 15. FMOs of compounds with their energy value in eV (a) LH (b) LMe (c) LCl and (d) LN


Page 37 of 48

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


Figure 16. Optimized geometries of Dimers (a) LH (b) LMe (c) LCl and (d) LN {H atoms are omitted for the sake of clarity of images}



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Page 38 of 48

Figure 17. FMO’s of dimmers of (a) LH (b) LMe (c) LCl and (d) LN.


Page 39 of 48

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