Supramolecular Organization of Solid Azobenzene Chromophore

Subscriber access provided by READING UNIV

Article

Supramolecular Organization of Solid Azobenzene Chromophore Disperse Orange 3, Its Chloroform Solutions and PMMA-Based Films Timur I. Burganov, Sergey A. Katsyuba, Tatiana A. Vakhonina, Anastasia V. Sharipova, Olga D. Fominykh, and Marina Yu. Balakina J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b10543 • Publication Date (Web): 03 Jan 2018 Downloaded from http://pubs.acs.org on January 9, 2018

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 C 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 18 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

Supramolecular Organization of Solid Azobenzene Chromophore Disperse Orange 3, Its Chloroform Solutions and PMMA-Based Films Timur I. Burganov, Sergey A. Katsyuba,* Tatiana A. Vakhonina, Anastasiya V. Sharipova, Olga D. Fominykh, Marina Yu. Balakina

A.E. Arbuzov Institute of Organic and Physical Chemistry of Kazan Scientific Centre of RAS, Arbuzov str. 8, 420088, Kazan, Russia

ACS Paragon Plus Environment

The Journal of Physical Chemistry 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

ABSTRACT Quantum chemical modelling in combination with vibrational and electronic absorption spectroscopy has delivered the detailed information about supramolecular organization of azochromophore 4-amino-4′-nitroazobenzene, DO3, its solutions and blends with PMMA polymer of various concentrations. It is shown that the neat chromophore contains both antistacked forms and hydrogen bonded associations of the “head-to-tail” type, while separate DO3 molecules dominate in diluted solutions of DO3 in chloroform. In PMMA/DO3 films with low concentrations of the chromophore, DO3 is mainly H-bonded to C=O moieties of PMMA matrix, while in the blends with high concentrations of DO3 molecules the latter form hydrogen bonds both with PMMA and with each other. Infrared, Raman and UV-vis spectroscopic markers of isolated DO3 molecules and various modes of their supramolecular associations are revealed.


Page 2 of 18

Page 3 of 18 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


INTRODUCTION

One of the key tasks in the design of nonlinear-optical (NLO) polymers is the translation of molecular nonlinearity of organic chromophores to the macroscopic NLO response of the material.1,2 To exhibit NLO response, chromophores should be non-centrosymmetrically arranged in the polymer matrix what is achieved by their orientation in the electric field applied to the material heated to temperature close to the glass-transition temperature.2 Retention of the fieldinduced ordering is necessary for the long-term stability of NLO response. One of the means to provide the relaxation stability of chromophores arrangement is the non-covalent bonding between chromophores and polymer matrix3-5 and/or between chromophores themselves. Both experimental and theoretical research give evidence to the formation of chromophores clusters of the “head-to-tail” type where electron donor groups of one chromophore interact with the electron acceptor groups of the other via hydrogen bonds (HBs), which results in the essential enhancement of the NLO response, this effect being a cooperative one.6-11 Another example of selforganization is the formation of π-stacked structures with either co-directed or anti-parallel dipole moments of chromophores.6,12-15 In the clusters of the latter type centrosymmetric arrangement annihilates the NLO activity. In the co-directed species the chromophores are shown to be mutually shifted, the shift degree determining the NLO characteristics of such structures. For the clusters with strongly shifted chromophores the increase of the molecular NLO response is predicted.14,15 Evidently the design of new NLO materials should include the account of the possibility of the abovementioned non-covalent interactions. Various molecular aggregates can be revealed by spectroscopic study. However to distinguish between different types of non-covalent interactions in the material some spectral features should be detected, which could be used as spectroscopic markers of the interaction of the definite type. The main objective of the present work is to reveal possible modes of supramolecular associations of NLO azochromophore 4-amino-4′-nitroazobenzene (or Disperse Orange 3, DO3). DO3 push-pull dye (Figure 1) contains primary amine in its structure, which enables the DO3 molecules to form HBs with each other and/or with polymer matrix containing HB-acceptor functionalities. Thus, both stacked and H-bonded species should be expected for the DO3 dye, both of which are important for the retention of the orientational order of the chromophores, obtained during poling. To our knowledge, no information on the supramolecular organization of neat DO3, its solutions in organic solvents or in polymer matrices is available. We also intend to identify infrared (IR), Raman and electronic absorption (UV-vis) spectroscopic markers of the above modes of the intermolecular associations that can be used in the development of various DO3-based materials.

EXPERIMENTAL AND THEORETICAL METHODS ACS Paragon Plus Environment


Materials. DO3 was synthesized according to procedure described in.16 Spectroscopic Methods. Raman spectra were registered at room temperature on a BRUKER RAM II module (using a Ge detector operating at liquid nitrogen temperature) attached to a BRUKER VERTEX 70 FTIR spectrometer in the range 10-4000 cm-1 with an optical resolution of 4 cm-1. Raman scattering radiation was collected in a back-scattering configuration. 1024 scans were averaged for each spectrum. A Nd:YAG laser with a wavelength of 1064 nm and power of 150-250 mW was used as the excitation source. The samples were inserted in a standard glass cell. Electronic absorption (UV-vis) spectra were recorded at room temperature on a Perkin-Elmer Lambda 35 spectrometer using 10 mm quartz cells. Absorption spectra were registered with a scan speed of 480 nm/min, using a spectral width of 1 nm. All samples were prepared as solutions in CHCl3 and THF, with the concentrations ranging from ~10–5 to ~10−4 mol/ L. IR spectra were recorded on a FTIR spectrometer Bruker Vector-22 in the 400 – 4000 cm-1 range at optical resolution of 4 cm-1. Solid samples were prepared as KBr pellets. Solutions in CHCl3 with concentrations raging from ~10-6 to 10-2 mol·L-1 were prepared in 0.1 mm KBr cells. Films Preparation Thin polymer films containing 5 wt.%, 10 wt.%, 20 wt.% , 30 wt.% and 40 wt.% of the DO3 were prepared by spin-coating from 7% solution of PMMA-based composite material in cyclohexanone on glass plates; the samples were kept in vacuum drying oven at room temperature for 10–16 h followed by a soft baking at 50 °C for 2 h. Computational Procedures. All calculations were carried out using the Jaguar suite of programs.17 Following full geometry optimizations (tight criterion was used), harmonic vibrational frequencies and Raman activities were calculated with the use of Density Functional Theory (DFT) employed in this study, corresponding to hybrid functional B3LYP18 with the D3 London dispersion correction in the Becke-Johnson sampling scheme (indicated by “-D3” appended to the functional name)19,20 and Grimme’s GGA functional including dispersion corrections B97D.21 As demonstrated elsewhere,22,23 B3LYP offers the cost effective choice for the computation of IR and Raman spectra of organic molecules. In particular, the relative Raman activities for the bands in the frequency range ν≤ 2300 cm-1 are better predicted by this hybrid functional than by second order Moller-Plesset perturbation theory (MP2).22 As inclusion of diffuse orbitals on heavy atoms is important for simulations of Raman and IR spectra,22-24 calculations were carried out with the 631++G** and 6-311++G** basis sets.25-28 Static Raman activities were computed in the double harmonic approximation, ignoring cubic and higher force constants and omitting second and higher order dipole moment and polarizability derivatives. For comparison of computed and experimental ACS Paragon Plus Environment

Page 4 of 18

Page 5 of 18 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


spectral curves the following procedure was applied: i) the calculated Raman activities (S) were converted, prior to the comparison with the experiment, to the corresponding Raman intensities (I) with the use of Eqn (1), derived from the intensity theory of Raman scattering 29; ii) the computed frequencies and relative Raman intensities were plotted with a Lorentzian broadening (f.w.h.m. = 15 cm-1 was taken from the experimental Raman spectra). f (ν 0 − ν n ) 4 S n , (1)   − hc ν n   ν n 1 − exp    kT    where f is suitably chosen common normalization factor for all the intensities, ν0 is the exciting In =

laser wave number, νn is the wave number and Sn is Raman activity of the n-th vibrational mode, c, h and k are fundamental constants, T is the temperature. Both B97D/6-31++G** and B3LYP-D3/6-311++G** computations produced qualitatively similar results, but Raman spectra simulated at B3LYP-D3/6-311++G** level better match the corresponding experimental spectra (vide infra), and for this reason only the results of B3LYPD3/6-311++G** computations are discussed in the paper. For the electron excitation energies the def2-TZVP30 AO basis set along with the range-separated CAM-B3LYP functional31 were used. Linear response time-dependent density functional theory (TD-DFT)32-34 has been employed to compute the vertical excitation energy (i.e., absorption wavelengths) and oscillator strength for the ground state optimized geometries in the gas phase. The spectra were broadened by Gaussian functions with a half-width at 1/e height of 0.4 eV. No energy shift has been applied. Implicit treatment of media effects within the framework of polarizable continuum model (PCM)35 was employed, with chloroform parameters for PCM being used.

RESULTS AND DISCUSSION Possible Dimers Formed by DO3 Chromophores In the absence of X-ray structural information for DO3 crystal, four variants of possible intermolecular association of DO3 molecules were regarded, viz., with parallel, shifted parallel and anti-parallel arrangement of chromophores, and also head-to-tail (htt) dimer bound by HBs between NH2 moiety of one DO3 molecule and NO2 group of another molecule (Figure 1).

(a)



(b)

(c)

(d)

Figure 1. Quantum chemically optimized structures of dimers formed by DO3 chromophores: headto-tail (a), parallel (b), shifted parallel (c), and anti-parallel (d) arrangement.

Simulated electronic absorption spectra of shifted form (c) differ both from the spectrum of DO3 monomer, and from the spectra of all other dimers (a), (b) and (d), which are similar to each other in positions of the absorption maxima (Figure 2). 1,1

1.1

expt monomer

1.0

expt (a)

1,0

0.9

0,9

0.8

0,8

0.7

0,7

0.6

0,6

a.u.

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

Page 6 of 18

0.5

0,5

0.4

0,4

0.3

0,3

0.2

0,2

0.1

0,1

0.0

0,0

250

300

350

400

450 500 λ, nm

550

600

650

700

250

300


350

400

450

500

λ, nm

550

600

650

700

Page 7 of 18

1,1

1,1

expt (b)

expt (c)

1,0

0,9

0,9

0,8

0,8

0,7

0,7

0,6

a.u.

a.u.

1,0

0,6

0,5

0,5

0,4

0,4

0,3

0,3

0,2

0,2

0,1

0,1

0,0

0,0

250

300

350

400

450 500 λ, nm

550

600

650

700

250

300

350

400

450

500

550

600

650

700

λ, nm

1.1

expt (d)

1.0 0.9 0.8 0.7

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


0.6 0.5 0.4 0.3 0.2 0.1 0.0

250

300

350

400

450 500 λ, nm

550

600

650

700

Figure 2. Experimental (black lines) in CHCl3 and calculated (red lines) UV-vis spectra of DO3: monomer, head-to-tail (a), parallel (b), shifted parallel (c), and anti-parallel (d) arrangement.

Simulated IR spectrum of htt dimer (a) differs essentially from the spectra of both the monomeric molecule, and of other dimers (b) (c) and (d) (Figure 3). HB between NH2 and NO2 groups of two DO3 molecules forming htt dimer (a) results in strong redistribution of IR intensities of bands of NH2 symmetrical and antisymmetrical stretching vibrations (νsNH2 and νasNH2, respectively), while impact of stacking dimerization of DO3 on the IR spectra is quite moderate. Simulated Raman spectra of DO3 and dimers (a), (b) and (d) are dominated by very strong bands of stretching vibrations (ν) of conjugated nitro-, azo-, and benzene-moieties (Figure 4). The bands

νsNO2 (~1330 cm-1), νC-NH2 (~1300 cm-1) and νC-NO2 (~1100 cm-1) are sensitive to the type of dimerization of DO3, which can be used for analytical purposes (vide infra).



monomer 3504

(a) 3406

3509 3417

(b)

3494

(c) 3395

3507

(d) 3477

3404 3359 3388 3300

3350

3400

3450

3500

3550

3600

ν, cm

-1

Figure 3. Bands of NH2 stretching vibrations in the simulated IR spectra of DO3: monomer, headto-tail (a), parallel (b), shifted parallel (c), and anti-parallel (d) arrangement. The computed frequencies are scaled by factor of 0.97 to provide the best agreement of νscaled(NH2) of the monomer with the corresponding experimental frequencies in IR spectrum. 1321 1302

(a)

(a)

(b)

(b)

1297

(c)

1301

1337 1333

(c)

1296

(d)

(d)

(monomer)

(mon)1298

1329 1332 1344

*

(1)

(1)

(2)

(2) 1000

1100

1200

1300

1400

1500

1600

-1

ν, cm

1700 1250

1302

13 13 10 2 13 0 38

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 18

1300

1350

ν, cm-1

Figure 4. Raman spectra of DO3: the simulated spectra of monomer and dimers with head-to-tail (a), parallel (b), shifted parallel (c), and anti-parallel (d) arrangement are scaled according to Ref.36: νscaled = Aνcomputed + B, where A = 0.9395, B = 55.36 cm-1. Experimental spectra of the powder sample (2) and the solution in CHCl3 of c ~ 10-2 mol·L-1 (1). The band of CHCl3 is marked with asterisk. ACS Paragon Plus Environment

Page 9 of 18

Experimental Spectra of Solid DO3 and DO3 Solutions in CHCl3 The most pronounced solvent effects in the experimental IR spectra of DO3 are found in the region of ca. 3400-3500 cm-1 (Figure 5). νs(NH) νas(NH)

(a)

3495 3401 3412

(b) 3412

3508

(c) 3506

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


(d) (e) 3100

3412 3200

3300

3400

3500

ν, cm

3600

3700

3800

3900

-1

Figure 5. IR spectra of DO3 as solid sample in KBr (a) and in solutions of CHCl3 (b-e) with different concentrations: b) c = 2.4·10-5 mol·L-1; c) c = 2.4·10-4 mol·L-1; d) c = 1.2·10-3 mol·L-1; e) c = 1.2·10-2 mol·L-1 Relative IR intensity of bands νsNH2 and νasNH2, I(νsNH2)/I(νasNH2), amounts to ca. 7 in the spectrum of solid sample, and varies from ca. 4 to ca. 2 in the spectra of progressively diluted chloroform solutions (Figure 5). According to our quantum chemical computations (Figure 3), I(νsNH2)/I(νasNH2) for htt dimer is much higher than that for isolated DO3 molecule or stacked dimers (b), (c) and (d). This strongly suggests that htt forms of DO3 dominate in the solid sample, and the abovementioned decrease of I(νsNH2)/I(νasNH2) found in the experimental IR spectra of chloroform solutions should be assigned to the process of destroying of these H-bonded forms upon dilution of the dye solutions. Similar conclusions can be drawn on the grounds of analysis of Raman spectra, which is based on comparison of frequencies and intensities of very strong bands νsNO2 (~1330 cm-1), νC-NH2 (~1300 cm-1) and νC-NO2 (~1100 cm-1). The computed frequency of νsNO2 varies from 1321 cm-1 for htt-dimer (a) to 1329-1337 cm-1 for all other forms of DO3 arrangement (Figure 4). This suggests that the band at 1320 cm-1 in the experimental spectrum of solid DO3 should be assigned to htt-dimer (a). Indeed, this band disappears from the spectra registered for chloroform solutions at ACS Paragon Plus Environment


concentrations of ca. 10-2 mol⋅L-1 (Figure 4). The latter spectra perfectly match the spectrum published for such a solution of ca. 10-5 mol⋅L-1 concentration,36 which should correspond mainly to monomeric DO3 solvated by chloroform. Moreover, Raman spectrum quantum chemically simulated for isolated DO3 molecule perfectly matches both the published and our own spectra registered for the diluted solutions of DO3 (Figure 4). It should be noted though, that simulated Raman spectra of stacking dimers (b) and (c) are rather similar to the spectrum of isolated DO3 molecule. Thus, the existence of these forms in the DO3 solutions cannot be excluded on the basis of the Raman spectra analysis. In contrast, the computed Raman spectrum of antistacking dimer (d) differs from the spectra of monomeric DO3 or dimers (b) and (c). For the former species the band νC-NO2 at ca. 1100 cm-1 is essentially stronger than the neighboring band at ca. 1140 cm-1, while the opposite is true for the latter forms. Another specific feature of the simulated Raman spectrum of the form (d) is the higher intensity of νC-NH2 band at ca. 1300 cm-1 relative to νsNO2 band (~1330 cm-1). In contrast, νsNO2 band is stronger than νC-NH2 band in the computed spectra of all other species (Figure 4). Relative intensities of bands at 1105 / 1140 cm-1, and at 1310 / 1338 cm-1 in the experimental spectrum of solid DO3 are close to unity (Figure 4 (2)), and drop to much smaller values in the spectrum of DO3 solution (Figure 4 (1)). This strongly suggests that solid DO3 contains essential portion of the anti-stack dimer (d) of DO3, which disappears upon dilution of DO3 in chloroform, in parallel with disappearance of its htt form (a). Further details are delivered by comparison of the experimental absorption spectrum of highly diluted DO3 solution in chloroform with the spectra quantum chemically simulated for isolated DO3 molecule and its various associations (Figure 2). Clearly, the registered spectrum matches the corresponding computed spectrum of the monomer much better than the spectra simulated for stacking dimers with parallel (b) and shifted parallel (c) arrangements, which suggests that at concentration of ca. 10-4-10-3 mol⋅L-1 the stack forms (b) and (c) are practically completely destroyed. Summarizing the results of joint analysis of IR, Raman and UV-vis spectra of solid DO3 and its solutions supported by quantum chemical computations, we can conclude that the neat chromophore contains both H-bonded associations and antistacked dimers, though a coexistence of monomeric and stacked forms with parallel/shifted-parallel arrangement cannot be excluded. The diluted solutions of DO3 in chloroform unable to formation of pronounced HBs are dominated by separate DO3 molecules surrounded by the solvent.

Spectra of Guest-host Systems Formed by DO3 Chromophores and PMMA Polymer. IR spectra of thin films consisting of DO3 dispersed in PMMA are presented in Figure 6. Positions of IR bands νsNH2 and νasNH2 remain the same in the spectra of the samples with low ACS Paragon Plus Environment

Page 10 of 18

Page 11 of 18 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


concentrations of DO3, being essentially different from the positions found in the spectra of solid DO3 and its solutions. As the concentrations increase, the bands steadily approach the positions registered in the IR spectrum of the solid chromophore. This suggests that DO3 molecules in the films of low concentrations of the chromophore are H-bonded to the PMMA matrix rather than to each other. At concentrations exceeding 10 wt. % the blends show phase separated crystalline domains of DO3 dispersed in a continuous PMMA-rich phase,37 and the bands of these domains, overlapping with the bands of DO3 “dissolved” in this latter phase, result in the shift of the enveloping contours of IR bands νsNH2 and νasNH2.

1% 5% 40% 50% solution in CHCl3 KBr 3200

3300

3400

3500

ν, cm

-1

3600

3700

3800

Figure 6. Experimental IR spectra of DO3: in PMMA matrix with different concentrations of DO3 chromophore (from 1 to 50%), in solution of CHCl3 and in KBr. The above conclusions are strongly supported by analysis of absorption spectra of thin films consisting of DO3 dispersed in PMMA (Figure 7), which almost coincide irrespective of DO3 concentration in the blend. The absorption maxima (434 nm) are red-shifted both relative to the ACS Paragon Plus Environment


spectrum of DO3 solution in chloroform (414 nm, Figure 2), and relative to the spectrum simulated for htt dimer (422 nm, Figure 2 (a)). This suggests that the bands of DO3 molecules H-bonded via their NH2 groups are red-shifted relative to the molecules free from HBs, and the red shift depends on the HB acceptors participating in the H-bonding. Indeed, the spectrum simulated for the DO3 molecule H-bonded to Me(C=O)OMe, taken as a simplest model of PMMA HB-acceptor moieties, is slightly red-shifted relative to the simulated spectrum of htt dimer, and perfectly matches the experimental spectra of DO3-PMMA films (Figure 8).

normalized spectra 1.8

1% 5% 20% 40%

1.6 1.4

1% 5% 20% 40%

1.0 0.9 0.8

1.2

0.7

1.0

0.6

a.u.

a.u.

0.8

0.5 0.4

0.6

0.3

0.4

0.2

0.2

0.1 0.0 300

350

400

450

500

550

600

650

λ, nm

350

400

450

λ, nm

500

550

600

Figure 7. UV-vis experimental absorption spectra of PMMA/DO3 films with different percentage of chromophore (from 1% to 40%). expt PMMA (40%) expt PMMA (5%) calc PMMA model cacl HTT

1,0

0,8

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

Page 12 of 18

0,6

0,4

0,2

0,0

350

400

450

500

550

600

650

700

λ, nm

Figure 8. Calculated electronic absorption spectra of the model H-bonded DO3 with Me(C=O)OMe molecule (calc model PMMA) and head-to-tail dimer (calc HTT) with experimental spectra of DO3 (40 wt. % and 5 wt. %) dispersed in PMMA polymer matrix (expt PMMA). ACS Paragon Plus Environment

Page 13 of 18 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


Summarizing the results of joint analysis of the experimental spectra of PMMA/DO3 films supported by quantum chemical computations, we can conclude that at low concentrations of the chromophore it is mainly H-bonded to C=O moieties of PMMA matrix, while in the blends with high concentrations of DO3 molecules the latter form H-bonds both with PMMA and with each other.

CONCLUSIONS Quantum chemical modelling in combination with experimental IR, Raman and UV-vis spectroscopy of DO3 azochromophore, its solutions and blends with PMMA polymer of various concentrations has delivered the detailed information about supramolecular organization of neat DO3, its solutions in chloroform and in the polymer matrices. It is shown that the neat chromophore contains both antistacking forms, and H-bonded associations of “head-to-tail” form. The diluted solutions of DO3 in chloroform predominantly contain separate DO3 molecules. In PMMA/DO3 films with low concentrations of the chromophore, DO3 is mainly H-bonded to C=O moieties of PMMA matrix, while in the blends with high concentrations of DO3 molecules the latter form Hbonds both with PMMA and with each other. This conclusion is particularly valuable, since it gives guidelines on the use of H-bonds in the retention of the chromophores orientational order formed during poling, which is necessary for providing long-term stability of the NLO response of the polymer material. The obtained structural information has allowed to reveal spectroscopic markers of isolated DO3 molecules and various modes of their supramolecular associations. Namely, NH2 stretching modes of isolated DO3 molecules in CHCl3 solutions are characterized by IR bands at ca. 3410 and ca. 3510 cm-1, the former being of more than two-fold intensity relative to the latter. Formation of the “head-to-tail” H-bonded dimers is reflected in increase of the relative intensity to ca. four, while Hbonding of NH2 moieties to C=O groups of PMMA shifts the bands to ca. 3375 and ca. 3440 cm-1, respectively. The Raman band of NO2 stretchings at ca. 1320 cm-1 should be regarded as a “signature” of the “head-to-tail” H-bonded form. High intensity of Raman bands νC-NO2 at ca. 1100 cm-1 and νC-NH2 at ca. 1300 cm-1 relative to the respective closest-neighboring strong bands is indicative of anti-stacking arrangement of DO3 molecules. Finally, monomeric DO3 molecules in CHCl3 solution absorb at 414 nm, while their forms H-bonded to C=O groups of PMMA absorb at ca. 434 nm.

AUTHOR INFORMATION ACS Paragon Plus Environment


Corresponding Author *[email protected] [email protected] [email protected] [email protected] [email protected] [email protected]

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT This study was supported by Russian Foundation for Basic Research (grant No 15-03-04423-a).

REFERENCES (1)

Organic Electro-Optics and Photonics: Molecules, Polymers, and Crystals. L.R. Dalton, P. Günter, M. Jazbinsek, O.-P. Kwon, Ph.A. Sullivan: Materials Research Society and Cambridge University Press, 2015, 300 p.

(2) Burland, D.M.; Miller, R.D.; Walsh, C.A. Second-order Nonlinearity in Poled-polymer Systems, Chem. Rev. 1994, 94, 31–75. (3)

Möncke, D., Mountrichas, G., Pispas, S., Kamitsos, E.I. Orientation Phenomena in Chromophore DR1-containing Polymer Films and Their Non-linear Optical Response. Mater. Sci. Eng., B 2011, 176, 515-520

(4)

Priimagi, A.; Cattaneo, S.; Ras, R.H.A.; Valkama, S.; Ikkala, O.; Kauranenc, M. Supramolecular Guest–host Systems: Combining High Dye Doping Level with Low Aggregation Tendency, Proc. of SPIE 2006, 6331, 63310L

(5)

Priimagi, A. Vapaavuori, J. Rodrigue, F.J., Faul, C.F.J., Heino, M.T., Ikkala, O., Kauranen, Kaivola, M. Hydrogen-Bonded Polymer-Azobenzene Complexes: Enhanced Photoinduced ACS Paragon Plus Environment

Page 14 of 18

Page 15 of 18 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


Birefringence with High Temporal Stability Through Interplay of Intermolecular Interactions, Chem. Mater. 2008, 20, 6358-6363 (6)

Di Bella, S.; Ratner, M. A.; Marks, T. J. Design of Chromophoric Molecular Assemblies with Large Second-Order Optical Nonlinearities. A Theoretical Analysis of the Role of Intermolecular Interactions. J. Am. Chem. Soc. 1992, 114, 5842–5849.

(7)

Yokoyama, S.; Nakahama, T.; Otomo, A.; Mashiko, S. Intermolecular Coupling Enhancement of the Molecular Hyperpolarizability in Multichromophoric Dipolar Dendrons. J. Am. Chem. Soc. 2000, 122, 3174–3181.

(8)

Ray, P.C.; Lesczinsky, J. Nonlinear Optical Properties of Highly Conjugated Push-Pull Porphyrin Aggregates: Role of Intermolecular Interaction. Chem. Phys. Lett. 2006, 419, 578583.

(9)

Terenziani, F.; Mongin, O.; Katan, C.; Bhatthula, B.K.G.; Blanchard-Desce M. Effects of Dipolar Interactions on Linear and Nonlinear Optical Properties of Multichromophore Assemblies: A Case Study. Chem. Eur. J. 2006, 12, 3089–3102.

(10) Yamamoto, Y. Programmed Self-Assembly of Large π-Conjugated Molecules into Electroactive One-Dimensional Nanostructures. Sci. Technol. Adv. Mater. 2012, 13, 033001– 033016. (11) Balakina, M.Yu., Fominykh, O.D. The Quantum-Chemical Study of Small Clusters of Organic Chromophores: Topological Analysis and Nonlinear Optical Properties, Int. J. Quant. Chem. 2008, 108, 2678-2692 (12) Keinan, S.; Ratner, M. A.; Marks, T. Self-Assembled Electrooptic Superlattices. A Theoretical Study of Multilayer Formation and Response Using Donor-Acceptor, HydrogenBond Building Blocks. J. Chem Mater 2004, 16, 1848-1854 (13) Cheng, W. D.; Wu, D. S.; Zhang, H.; Li, X. D.; Chen, D. G.; Lang, Y. Z.; Zhang, Y. C.; Gong, Y. J. First Principle Treatments on Site- and Size-Dependent Super-Molecular Interactions and Nonlinear Optical Properties of Polymer of 2-Methyl-4-Nitroaniline. J. Phys. Chem. B 2004, 108, 12658- 12664. (14) Suponitsky, K.Y., Masunov, A.E. Supramolecular Step in Design of Nonlinear Optical Materials: Effect Of π⋯π Stacking Aggregation on Hyperpolarizability, J. Chem. Phys. 2013, 139, 094310 (15) Fominykh, O.D.; Sharipova, A.V.; Balakina, M.Yu. The Choice of Appropriate Density Functional for the Calculation of Static First Hyperpolarizability of Azochromophores and Stacking Dimers. Int J. Quant. Chem. 2016, 116, 103–112. (16) Shulyndin, S.V.; Vakhonina, T.A.; Ivanova, N.V.; Gubanov, E.F.; Ustyugov, A.N.; Fominykh, O.D.; Estrina, G.A.; Rozenberg, B.A.; Zuev, M.B. Synthesis and Properties of ACS Paragon Plus Environment


Epoxyamine Oligomers and Prepolymers with Nonlinear-Optical Azobenzene Chromophores. Polymer Science - Series A. 2005, 47, 808-819. (17) Schrödinger Release 2015-4: Jaguar, version 9.0, Schrödinger, LLC, New York, NY, 2015. (18) Becke, A.D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648–5652. (19) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements HPu. J. Chem. Phys. 2010, 132, 154104–154119. (20) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the Damping Function in Dispersion Corrected Density Functional Theory. J. Comp. Chem. 2011, 32, 1456–1465. (21) Grimme, S. GGA-Type Density Functional Constructed with a Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787–1799. (22) Zvereva, E. E.; Shagidullin, A. R.; Katsyuba, S. A. Ab initio and DFT Predictions of Infrared Intensities and Raman Activities. J. Phys. Chem. A. 2011, 115, 63–69. (23) Katsyuba, S. A.; Zvereva, E. E.; Burganov, T. I. Is There a Simple Way to Reliable Simulations of Infrared Spectra of Organic Compounds? J. Phys. Chem. A 2013, 117, 6664– 6670. (24) Katsyuba, S. A; Vandyukova, E. E. Scaled Quantum Mechanical Computations of Vibrational Spectra of Organoelement Molecules, Containing the Atoms P, S, and Cl. Chem. Phys. Lett. 2003, 377, 658−662. (25) Hehre, W.J.; Ditchfield, R.; Pople, J.A. Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules. J. Chem. Phys. 1972, 56, 2257−2261. (26) Hariharan, P.C.; Pople, J.A. The Influence of Polarization Functions on Molecular Orbital Hydrogenation Energies. Theor. Chim. Acta 1973, 28, 213−222. (27) Clark, T.; Chandrasekhar, J.; Spitznagel, G.W.; Schleyer, P.V.R. Efficient Diffuse FunctionAugmented Basis Sets for Anion Calculations. III. The 3-21+G Basis Set for First-Row Elements, Li−F. J.Comput. Chem. 1983, 4, 294−301. (28) Frisch, M.J.; Pople, J.A.; Binkley, J.S. Self-consistent Molecular Orbital Methods 25. Supplementary Functions for Gaussian Basis Sets. J. Chem. Phys. 1984, 80, 3265–3269. (29) Keresztury, G. Raman Spectroscopy: Theory; Handbook of Vibrational Spectroscopy, vol.1; Chalmers, J.M.; Griffiths, P.R., Eds.; John Wiley and Sons: Chichester, UK, 2002. (30) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H To Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys., 2005, 7, 3297−3305.


Page 16 of 18

Page 17 of 18 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


(31) Yanai, T.; Tew, D.; Handy, N. A New Hybrid Exchange-Correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett., 2004, 393, 51-57. (32) Gross, E. U. K.; Dobson, J. F.; Petersilka, M.; Nalewajski, R. F.; Ed.; Density-Functional Theory of Time-Dependent Phenomena, Springer: Heidelberg, Germany, 1996. (33) Casida, M. E.; Chong, D. P., Ed., Recent Advances in Density Functional Methods; World Scientific: Singapore, 1995; Vol. 1. (27), 155–192. (34) Furche, F. On the Density Matrix Based Approach to Time-Dependent Density Functional Response Theory, J. Chem. Phys., 2001, 114, 5982–5992. (35) Barone, V.; Cossi, M. Quantum Calculation of Molecular Energies and Energy Gradients in Solution By A Conductor Solvent Model, J. Phys. Chem. A 1998, 102, 1995-2001. (36) Minisini, B.; Messager, G.; Piyanzina, I.; Delorme, N.; Bardeau, J.-F., Vibrational Analysis of [4-[(E)-Phenylazo] Phenyl]Ethanol Based on the Comparison between the Experimental and DFT Calculated Raman Spectra, J. Struct. Chem. 2014, 55, 843–851. (37) Orofino, A. B.; Camezzana, M. F.; Galante, M. J.; Oyanguren, P. A.; Zucchi, I. A. Effects of Block Copolymer Self-Assembly on Optical Anisotropy in Azobenzene-Containing PS-BPMMA Films, Nanotechnology, 2012, 23, 115604–115609.



Table of Contents Graphic


Page 18 of 18

Supramolecular Organization of Solid Azobenzene Chromophore

Recommend Documents