Optical second order nonlinearities in new chromophores obtained by selective mono-reduction of dinitro precursors

Optical Materials 27 (2004) 91–97 www.elsevier.com/locate/optmat

Optical second order nonlinearities in new chromophores obtained by selective mono-reduction of dinitro precursors F. Cariati a, U. Caruso b, R. Centore b, A. De Maria b, M. Fusco b, B. Panunzi c, A. Roviello b,*, A. Tuzi b a

Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Universit
a degli Studi di Milano, Via Venezian 21, 20133 Milano, Italy b Dipartimento di Chimica, Universit
a degli Studi di Napoli ‘‘Federico II’’, Via Cinthia, 80126 Napoli, Italy c Dipartimento di Scienza degli Alimenti, Universit
a degli Studi di Napoli ‘‘Federico II’’, Via Universit
a 100, 80155 Portici, Napoli, Italy Received 12 June 2003; accepted 17 February 2004 Available online 25 March 2004 Dedicated to Professor Augusto Sirigu on the occasion of his 65th birthday

Abstract Three new push–pull chromophores of potential interest in second order nonlinear optical applications were synthesized and characterized, also by EFISH determination of molecular second order NLO properties. The chromophores contain a phenyl-azo unit coupled with fluorenonic, stilbenic or 1,3,4-thia-diazolic groups and are OH-functionalized to prompt easy covalent insertion in polymer chains. The selective reduction of only one of the two chemically equivalent nitro groups in the starting precursors is the key step of the synthetic pathway affording the chromophores. These show good chemical and thermal stability. The X-ray structural determination of the fluorenone derived chromophore is also reported.
2004 Elsevier B.V. All rights reserved. PACS: 42.70.M,N; 81.20.K Keywords: Nonlinear optics; EFISH measurements; New chromophores synthesis

1. Introduction Polymers with second order nonlinear optical (NLO) properties have been the object of intense investigations owing to the interest for their potential applications in different technologies such as telecommunications, optical information processing and data storage. The bulk NLO properties of these materials originates mainly from the microscopic nonlinearities of the active NLO units in the polymer backbone. Other fundamental aspects are the efficiency and the stability during time of the dipolar molecular orientation obtained through the poling technique. Three crucial points are under investigation: large NLO responses, enduring stability of dipole orientation and low optical loss at operating wavelengths [1–4].

*

Corresponding author. Tel.: +39-081674371; fax: +39-081674090. E-mail address: [email protected] (A. Roviello).

0925-3467/$ - see front matter
2004 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2004.02.011

Second order NLO responses are generally observed in donor–acceptor substituted p-conjugated molecules. The most common strategy in designing NLO active chromophores employs a suitable p-conjugated bridge and efficient donor and acceptor substituents. It is well known [5–7] that molecular first order hyperpolarizability b increases with increasing the length of conjugation path and donor/acceptor strength. Theoretical and experimental studies [8–10] suggest that non-aromatic bridges, such as polyenes, induce larger NLO properties than comparable (in length) aromatic analogues; aromatic rings are anyway inserted in order to ensure good thermal stability. Therefore, the typical choice implies a compromise which involves the presence of both aromatic rings and non-aromatic bridges (e.g. ethylenic or azo). Theoretical and experimental investigations [11–13] have also shown that the azobenzene system ensures values of the hyperpolarizability comparable to that of stilbene and higher than for N-(benzylidene)aniline groups. Other studies [8,14,15]

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F. Cariati et al. / Optical Materials 27 (2004) 91–97

materials with high electroluminescence performance [20–22]. The structures of chromophores have been chosen on the basis of two main considerations. On one hand their features meet several of the requirements above discussed (thermochemically stable heteroaromatic rings, azo and ethylenic bridges etc.) and, in addition, the presence of a common chemical moiety (e.g. the N,Ndialkylamino-phenylazo group) should allow significant cross comparison of NLO activity. On the other hand all the chromophores have a common synthetic origin in that their synthesis (as it will be discussed below) is based on the selective mono-reduction of a dinitro precursor. This reaction could represent a versatile and easy way to the synthesis of large p-conjugated structures functionalized for polymerization.

have also suggested that a further enhancement of NLO activity may be reached by replacing benzene rings with low aromaticity heterocycles. In this work we describe the synthesis and characterization, including NLO properties, of three new push–pull chromophores, F, S, Th (Scheme 1). They have in common a N,N-dialkylamino-phenylazo group and are OH-functionalized to be directly employed in polycondensations. Acetylated model derivatives MF, MS, MTh (Scheme 1) were also synthesized. Chromophore F is characterized by the presence of a fluorenone group. Molecular hyperpolarizability of Nalkylated fluorene derivatives has been measured [16] and compounds containing fluorenone were already used by Mitsubishi Petrochemical Industries [17,18] in the preparation of electrophotographic photoconductors. Chromophore S contains a stilbenic unit whose influence on second order NLO properties has been through investigated in many studies [12], e.g. in the synthesis of side chain oligomers for holographic applications [19]. Chromophore Th presents a 1,3,4thiadiazolic group, already involved in the synthesis of

2. Experimental In this work we report three examples of selective mono-reduction of dinitro symmetric compounds for the synthesis of large p-conjugated push–pull azo chromophores. The synthesis of chromophores was carried out following the route of Scheme 2. The key step is the mono-reduction of a symmetric dinitro compound, followed by diazotization of the amino product and coupling with a commercial aniline. Mono-reduction steps were performed by adapting the Calvin and Buckles method of reduction of 4,40 -dinitrostilbene [23]. In the synthesis of chromophore F the dinitro precursor is a commercial product (2,7-dinitro-9-fluorenone), while for S the synthesis of 4,40 -dinitrostilbene ð1SÞ was performed according to the Walden and Kernbaum method [24] from p-nitrobenzyl chloride in alcoholic potassium hydroxide. 2,5-Bis(4-nitrophenyl)-1,3,4-thiadiazole 1Th was prepared from the corresponding hydrazide with Lawesson reagent.

( CH2 )OR 2 2

NO 2

R1

N

N

N

( CH2 ) OR 2 2

F

R2 = H

MF

R 2 = CCH3

O

R1 = O

S R1 =

O CH

N

R 1=

R2 = H

CH

N

MS

R 2 = CCH3

Th

R2 = H O

S

MTh

R 2 = CCH3

Scheme 1.

×

NO2

NO2

Na 2S

×

NO2

NO2

× 2X

NH 2

2X

1X

NH 2

( CH2 ) OH

NaNO2 NO2 N,N-dihydroxyethylaniline

×

2

N

N

N

X

( CH2 ) OH 2

O

X

( CH2 ) OCCH3

Acetic Anhydride Py

NO2

×

2

N

N

MX X= F, S, Th Scheme 2.

N ( CH2 )2OCCH3 O

F. Cariati et al. / Optical Materials 27 (2004) 91–97

In all cases the mono-reduction gives a push–pull aniline which can be directly converted, in high yield and purity, directly into the final azo-chromophore, OHfunctionalized in order to achieve easy polymerization, by reaction with commercial N,N-dihydroxyethylaniline through the classic scheme of diazotization-coupling. The procedure is a versatile one, as dinitro precursors of various type (aromatic, heteroaromatic, etc) may be prepared in high yield and purity through several chemical routes and with few chemical drawbacks, owing to their eminent chemical stability. Actually, the only limitation to the method rests in the expedience of handling symmetrical dinitro compounds in order to keep at an acceptable level the abundance of the monoreduction product, in consideration of difficulties in separating the mononitro compound from the diamino products and the non-reacted dinitro precursors. Moreover, it is to note that in the case of chromophores F and Th, the mono-reduction reaction is also chemoselective, as demonstrated by the high yield of this step. 1 H NMR spectra were recorded on a Varian XL 300 or 200 MHz. The phase behaviour of all compounds was investigated by differential scanning calorimetry on a Perkin Elmer Pyris apparatus (nitrogen flow, scanning rate 10 K/min) and optical microscopy (Zeiss Axioscop polarizing microscope equipped with FP90 Mettler temperature heating stage). Thermogravimetric analysis was performed with a TA Instruments SDT 2960 Simultaneous DSC-TGA. UV–vis absorption spectra were recorded with a Jasco V-560 Spectrophotometer. The specific synthesis of each chemical product are reported in the Appendix A. 2.1. X-ray analysis Single crystals of MF (form I) were obtained from chloroform/hexane by slow evaporation. Data collection was performed in the x=h scan mode on an Enraf Nonius MACH 3 automated diffractometer, using graphite  No monochromated MoKa radiation (k ¼ 0:71069 A). absorption correction was applied. The structure was solved by direct methods (SHELXS program of the SHELX-97 package [25]) and refined by the full matrix least squares method (SHELXL program of the same package, C, N, O atoms anisotropic). H atoms were placed in calculated positions and refined by the riding model with Uiso equal to Ueq of the carrier atom. Some crystal collection and refinement data are reported in the Appendix A (see Table 1). 2.2. NLO measurements Molecular second order nonlinearities ðlg bvec Þ of chromophores were measured through the EFISH (Electric Field Induced Second Harmonic) technique [26]. Measurements were performed in chloroform

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Table 1 Crystal, collection and refinement data for MF Chemical formula Formula weight T (K) Crystal system Space group  a (A)  b (A)  c (A) a () b () c () 3 ) V (A Z, Dx (g/cm3 ) l (mm1 ) Theta range R1 on F ðI > 3rðIÞÞ R1, wR2 (all data) on F 2 Max peak, hole in the final diff. Fourier map 3 ) (e · A

C27 H24 N4 O7 516.50 293 Triclinic P 1 8.058(1) 8.375(5) 19.773(3) 81.33(3) 86.52(1) 68.87(3) 1230.4(8) 2, 1.394 0.103 2.08–24.96 0.0693 0.2625, 0.2909 0.253, )0.282

solution. The light source was a Q-switched, mode locked Nd3þ -YAG laser with pulse duration of 15 ns at 10 Hz repetition. Laser emission wavelength of 1064 nm was shifted at 1907 nm by stimulated Raman scattering in high-pressure hydrogen cell.

3. Results and discussion Concerning the thermal behaviour of the chromophores, it is to note that a melting point is observed for all the compounds (in some cases polymorphism was also observed), and for three of these a liquid crystalline phase was detected. Chromophore F melts at 267 C (DH ¼ 54 Jg1 ) to isotropic liquid and is thermally stable up to 290 C. The model MF shows solid state polymorphism with two different crystalline phases melting at 181 C (form I) (DH ¼ 75 Jg1 ) and 187 C (form II) (DH ¼ 73 Jg1 ). Both S and MS show a solid–solid transition, at 243 C (DH ¼ 15 Jg1 ) and 151 C (DH ¼ 35 Jg1 ) respectively, and a solid to liquid-crystal transition, at 262 C (DH ¼ 36 Jg1 ) and 167 C (DH ¼ 34 Jg1 ) respectively, as confirmed by the optical observation at the polarizing microscope of the samples. Both the anisotropic liquids show textures characterized by the presence of fan and focal conics, which suggest the mesophase being of the smectic A type. For MS isotropization occurs at 194 C (DH ¼ 9 Jg1 ), while for chromophore S decomposition occurs just after melting to liquid crystalline phase. In particular, the DSC curve of MS is shown, as an example, in Fig. 1. Chromophore Th melts at 290 C with partial decomposition. The corresponding model compound, MTh, shows a solid–solid transition at 185 C

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F. Cariati et al. / Optical Materials 27 (2004) 91–97 Table 2 Selected bond angles () and torsion angles () for MF

Endo

120

140

160

180

200

T/˚C Fig. 1. DSC behaviour of chromophore MS. Heating curve (upper curve) and cooling curve (down curve).

(DH ¼ 6 Jg1 ) and melts to anisotropic liquid at 207 C (DH ¼ 46 Jg1 ). The optical observation of the coexistence of pseudoisotropic regions and focal conics suggests the mesophase being of the smectic A type. Isotropization of the liquid crystalline phase is not detected since the mesophase is stable up to the chemical degradation, which begins at 330 C. Thermogravimetric analysis confirms that the three chromophores show a good thermal stability, their decomposition temperature (taken as the 5% weight loss temperature) being respectively 290 C for F, 305 C for S and 320 C for Th. The X-ray molecular structure of MF (form I) is shown in Fig. 2; selected structural data are reported in Table 2. A planar trigonal geometry is observed around N1, as expected [27], with consequent sp2 hybridization favouring p-donation toward the adjacent phenyl ring. Within the fluorenone moiety, relevant bond angle deformations are observed at C18, C19, C22, and C27 atoms, as a consequence of the pentaatomic ring closure. Owing to deformations, the 4,40 -fluorenone group takes a shape involving some curvature, which is probably

C4–N1–C8 C4–N1–C9 C8–N1–C9 N2–C12–C13 N3–C15–C20 C17–C18–C27 C20–C19–C21 C21–C22–C23 C18–C27–C26 N3–N2–C12–C11 N2–N3–C15–C16

117.4(6) 121.5(6) 121.0(6) 127.1(8) 126.8(8) 130.8(7) 130.5(7) 130.4(6) 131.1(7) 176.0(7) 177.1(7)

reduced by the enlargement of the N3–C15–C20 valence angle. This enlargement (observed also on the corresponding angle C13–C12–N2) is probably due to the repulsion between lone pair on N2 (N3) and ortho hydrogen on C20 (C13) as a result of the planar arrangement of the azobenzene moiety. Phenyl rings (C15–C20) and (C22–C27) are constrained to be coplanar by the five membered ring, while twisted conformations are often observed in biphenyl and triphenyl derivatives [28]. The conformation of the whole p-conjugated system is substantially planar, as inferred by the values of torsion angles for the two only conformational degrees of freedom of the system (i.e. torsion around N2–C12 and N3–C15 bonds). The crystal packing (not shown) is accomplished through parallel placement of long molecular axes and planes, with lateral contacts of the face to face type [29] among p-conjugated rings. Blue solvatochromic effect upon increasing solvent polarity, expected for NLO active p-conjugated molecules, becomes evident from the UV–vis absorption spectra of solutions of MS, MF and MTh in solvents with different polarity (Table 3). UV–vis spectra also show the absence of absorption above 600 nm, which is the SHG generation region of common lasers. In Fig. 3

Fig. 2. Molecular drawing of MF.

F. Cariati et al. / Optical Materials 27 (2004) 91–97

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Table 3 UV–visible absorption data for model chromophores max (DMF)/(L/cm1 · mol1 ) 4

2.6 · 10 4.4 · 104 2.5 · 104

MF MS MTh

kmax (acetone)/nm

kmax (DMF)/nm

kmax (DMSO)/nm

478 448 450

489 459 462

495 469 472

are shown the absorption spectra for the model chromophores in chloroform. Second order nonlinearities of the chromophores have been measured through EFISH technique and are reported in Table 4. The three chromophores have in common some parts of the molecular skeleton, e.g. the 4-(4-dialkylaminophenylazo)phenyl and the 4-nitrophenyl groups, and differ because of the conjugation bridge between these two parts. The values reported in Table 4 are indicative of an NLO activity from medium to medium-high (for instance the lb value reported for the typical NLO chromophore Disperse Red is 580 · 1048 esu at 1.9 lm [30]) and are consistent with the fact that MF has the shortest conjugation length and MTh the longest. In particular, it is worth noticing that the NLO activity of MTh is slightly higher than that of the corresponding oxadiazole compound (lb ¼ 900  1048 esu in the same experimental conditions) [31]. Actually, a significant enhancement of second order nonlinearity on going from oxygen based heteroaromatics to the corresponding sulphur derivatives is expected when the heterocycle is directly attached to the attractor group [14], which is not the present case.

4

c b

Y Axis Title

3

a 2

1

0 400

500

600

X axis title Fig. 3. UV–visible absorption spectra of the three model chromophores in chloroform. Curve a: MF, curve b: MS, curve c: MTh.

In conclusion, the employment of mono-reduction reaction has made possible the synthesis of three new large p-push–pull azo chromophores whose properties have proved satisfactory as concern to their good solubility and thermal stability, as well as their medium-high second order NLO activity. Moreover F, S and Th have been successfully employed in the preparation of polyesters and polyurethanes. A detailed description of the synthesis and properties of polymers will be reported in a forthcoming publication.

Acknowledgements Thanks are due to CIMCF of Universit
a degli Studi di Napoli ‘‘Federico II’’ for X-ray (Nonius MACH3 diffractometer) and NMR facilities. Financial support of MIUR of Italy is also acknowledged.

Appendix A A.1. 2-Nitro-7-amino-9-fluorenone (2F) Sodium sulfide aqueous solution (52 ml), prepared dissolving sodium sulfide nonahydrate (30.0 g) in water (70 ml) and concentrated hydrochloride acid (37%) (10.4 ml), were added, drop-to-drop, to a suspension of 2,7dinitro-9-fluorenone (10.0 g) in hot ethanol (300 ml). Immediately after the first drop was added the suspension became green and then turned progressively to brown during the dripping. Water (70 ml) was added to the reaction mixture and it was kept boiling for 4 min, then it was cooled into an ice/water bath. A black solid was filtered out, washed several times with water and crystallized with N,N-dimethylformamide/ethanol/water (1:1:1.3 by volume) to give 2F (7.6 g, 86%), mp 290 C;dH (300 MHz; DMSO d 6 : Me4 Si) 6.17 (2H, s), 6.79 (1H, dd, J 8.2, 1.8), 6.90 (1H, d, J 1.5), 7.61 (1H, d, J 8.2), 7.71 (1H, d, J 8.2), 8.07 (1H, d, J 1.8 ), 8.38 (1H, dd, J 8.2, 1.8).

Table 4 EFISH data of model chromophores (at 1907 nm) MF MS MT

lg b=ð1048 esuÞ

kmax (CHCl3 )/nm

lg b0 =ð1048 esuÞ

Solvent

510 660 1000

479 447 419

357 488 769

CHCl3 CHCl3 CHCl3

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F. Cariati et al. / Optical Materials 27 (2004) 91–97

A.2. 7-[4-(N,N-dihydroxyethylamino)phenylazo]-2-nitro-9-fluorenone (F) A solution of sodium nitrite (2.2 g) in 11 ml of water was added in 30 min to a suspension of 2F (7.7 g) in 70 ml of water and 9.3 ml of concentrated hydrochloride acid (37%) at temperature of 0–4 C. The mixture was stirred for about 40 min and then slowly poured in a solution, which was kept at room temperature, of N,Ndihydroxyethylaniline (5.8 g) in 4.9 ml of concentrated HCl (aq.) and 35 ml of water, buffered at pH ¼ 4 through addition of sodium acetate. After a reaction period of 40 min, pH was first increased to 7 with sodium hydroxide solution and after to 8 with an aqueous sodium bicarbonate solution. The black/violet precipitate was first washed several times with water, then dried and purified through Soxhlet extraction with tetrahydrofuran to give F (6.7 g, 49%), mp 267 C; dH (300 MHz; DMSO d 6 : Me4 Si) 3.62 (8H, m), 4.93 (2H, t, J 5.1), 6.84 (2H, d, J 9.2), 7.72 (2H, d, J 8.8), 7.80 (1H, d, J 0.9), 7.97 (1H, dd, J 6.6, 1.4), 8.01 (2H, d, J 7.9), 8.14 (1H, d, 1.8), 8.43 (1H, dd, J 7.7, 1.8).

salt of 2S was precipitated by cooling the saturated solution and recovered by filtration; the aqueous solution saturated with the ammonium salt of the dianiline was used to wash three times the mixture of dinitro and 2S hydrochloride to avoid loss of 2S. The whole amount of 2S hydrochloride was collected, dissolved in hot ethanol/ water (1:1) and pH was increased to 8 adding NaOH. 2S (0.4 g, 45%) was recovered from the cold solution, mp 252 C (lit.,19 mp 245 C); dH (300 MHz; DMSO d 6 : Me4 Si) 5.62 (2H, s), 6.61 (2H, d, J 8.2), 7.08 (1H, d, J 16.5), 7.40 (3H, m), 7.77 (2H, d, J 8.8), 8.22 (2H, d, J 8.8). A.5. [4-(N,N-dihydroxyethylamino)phenylazo]-4 0 -nitrostilbene (S) This compound was prepared from 2S (1.0 g) following the same procedure as for F; the product was washed with hot acetone and purified with a Soxhlet extraction with tetrahydrofuran to give S (1.0 g, 57%), mp 262 C; dH (300 MHz; DMSO d 6 : Me4 Si) 3.62 (8H, m), 4.92 (2H, t, J 4.8), 6.90 (2H, d, J 9.2), 7.55 (1H, d, J 15.9), 7.66 (1H, d, J 17.6), 7.83 (6H, m), 7.94 (2H, d, J 8.6), 8.29 (2H, d, J 8.6).

A.3. 4,40 Dinitrostilbene (1S) A.6. 4-Nitro benzoic acid, 2-(4-nitrobenzoyl)hydrazide Potassium hydroxide pellets (4.0 g) were added at room temperature to a solution of 4-nitrobenzyl chloride (27.0 g) dissolved in ethanol (200 ml) and the reaction mixture was kept under vigorous stirring. The progressive formation of a yellow solid took place in a period of 300 . This solid was recovered by filtration. An additional amount of 1S was obtained by two further reaction cycles performed similarly to the first one reusing the same reaction solution and adding two fraction of 4.0 g of KOH. The three fractions were collected and crystallized by N,N-dimethylformamide to give 1S (8.5 g, 40%), mp 302 C (lit., [19] mp 296–305 C); dH (300 MHz; DMSO d 6 : Me4 Si) 7.73 (2H, s), 7.98 (4H, d, J 6.7), 8.32 (4H, d, J 7.3).

Hydrazine monohydrate (3.7 g) were dissolved in tetrahydrofuran (150 ml) and pyridine (45 ml), p-nitrobenzoyl chloride (25 g) was then slowly added at room temperature. The solution progressively changed color from pale yellow to dark red. The reaction mixture was brought at room temperature for 20 min under stirring and then water (1 l) was added. 4-Nitro benzoic acid, 2(4-nitrobenzoyl)hydrazide separated as yellow crystals and was purified by crystallization from N,N-dimethylformamide (10.0 g, 45%), mp 299 C; (200 MHz; DMSO d 6 : Me4 Si) 7.68 (4H, d, J 8.3), 7.89 (4H, d, J 8.1), 10.65 (2H, s). A.7. 2,5-Bis(4-nitrophenyl)-1,3,4-thiadiazole (1Th)

A.4. 4-Amino-40 -nitrostilbene (2S) With an analogous procedure followed for the above reported amino compound, the reaction was performed on 1S (1.0 g), with 5.2 ml of the same sodium sulfide solution in ethanol 95% (40 ml). The reaction mixture was concentrated up to a volume of 20 ml, then water (60 ml) was added and a red compound precipitated. The red solid was then collected on a suction filter and treated with acetone (20 ml). The insoluble fraction was filtered off and the crude product was precipitated with water. It was purified by suspending it in small hot acetone amount and diluite HCl aq. Acetone was distilled off and the unreacted dinitro product was recovered from the warm suspension by filtration, together with a fraction of ammonium salt of 2S. The remaining part of ammonium

4-Nitro benzoic acid, 2-(4-nitrobenzoyl)hydrazide (10.7 g) and Lawesson reagent (15.0 g) were refluxed in acetonitrile (100 ml) for 12 h. The mixture was then poured in 1 M NaOH solution (200 ml) and the precipitate was filtered, washed several times with water and recrystallized from N,N-dimethylformamide to give 1Th (7.4 g, 70%), mp 330 C; (200 MHz; DMSO d 6 : Me4 Si) 7.70 (4H, d, J 7.4), 8.18 (4H, d, J 7.4). A.8. 2-(4-Aminophenyl)-5-(4-nitrophenyl)-1,3,4-thiadiazole (2Th) The same sodium sulfide aqueous solution used for the previous mono-reductions (3.9 ml) was gradually added

F. Cariati et al. / Optical Materials 27 (2004) 91–97

to a boiling solution of 1Th (1.5 g) in N,N-dimethylformamide (40 ml). After few minutes the solution was filtered and poured in water; after crystallization from N,N-dimethylformamide/water 2Th (1.1 g, 80%) precipitated as red-orange compound, mp 281 C; (200 MHz; DMSO d 6 : Me4 Si) 5.99 (2H, s), 6.65 (2H, d, J 7.8), 7.68 (2H, d, J 7.8), 8.25 (2H, d, J 14.4), 8.35 (2H, d, J 13.0). A.9. 2-[4-[[4-(N,N-dihydroxyethylamino)phenylazo]]phenyl]-5-(4-nitrophenyl)- 1,3,4-thiadiazole (Th) This compound was prepared from 2Th (1.8 g) following the same procedure as for F and S. The red precipitate was washed several times with water and finally crystallized from N,N-dimethylformamide/water solution to give Th (1.5 g, 50%), mp 290 C; (200 MHz; DMSO d 6 : Me4 Si) 3.31 (4H, t, J 5.7), 3.64 (4H, t, J 5.8), 6.93 (2H, d, J 8.6), 7.92 (4H, m), 8.24 (4H, m), 8.38 (2H, d, J 11.4). A.10. 7-[4-(N,N-diacetiloxyethylamino)phenylazo]-2-nitro-9-fluorenone (MF), 4-[4- (N,N-diacetiloxyethylamino)phenylazo]-40 -nitrostilbene (MS) and 2-[4-[[4(N,N-diacetiloxyethylamino)phenylazo]]phenyl]-5-(4nitrophenyl)-1,3,4 thiadiazole (MTh) These were prepared for reaction of the appropriate OH-chromofore with acetic anhydride in hot pyridine. MF was crystallized from chloroform/petroleum ether (2,5:1) (53%), mp 181 C; (200 MHz; CDCl3 : Me4 Si) 2.07 (6H, s), 3.75 (4H, t, J 6.1), 4.31 (4H, t, J 6.2), 6.85 (2H, d, J 9.3), 7.74 (2H, m), 7.89 (2H, d, J 9.2), 8.05 (1H, dd, J 9.2, 1.3), 8.21 (1H, d, J 1.4), 8.45 (1H, dd, J 7.4, 1.9), 8.49 (1H, d, J 2.0). Found: C, 61.08; H, 4.52; N, 10.42%. Calc. for C27 H24 N4 O7 : C, 62.80; H, 4.68; N, 10.84%. MS was crystallized from chloroform/eptane (1:1) (61%), mp 167 C; (300 MHz; DMSO d 6 : Me4 Si) 2.04 (6H, s), 3.78 (4H, t, J 5.4), 4.25 (4H, t, J 5.3), 7.00 (2H, d, J 8.8), 7.57 (1H, d, J 16.5), 7.68 (1H, d, J 16.5), 7.85 (6H, m), 7.95 (2H, d, J 8.8), 8.30 (2H, d, J 8.8). Found: C, 65.10; H, 5.48; N, 10.89%. Calc. for C28 H26 N4 O6 : C, 65.11; H, 5.46; N, 10.84%. MTh was purified by column chromatography (florisil, chloroform as eluent) (36%), mp 207 C; (200 MHz; CDCl3 : Me4 Si) 2.08 (6H, s), 3.80 (4H, t, J 5.8) 4.34 (4H, t, J 6.1); 6.95 (2H, d, J 9.0); 7.94 (4H, m); 8.24 (4H, m); 8.38 (2H, d, J 9.2). Found: C, 57.87; H, 4.62; N, 14.51; S, 5.47%. Calc. for C28 H32 N6 O6 S: C, 58.53; H, 4.55; N, 14.62; S, 5.52%.

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References [1] S.W. Nalwa, S. Myata (Eds.), Nonlinear Optics of Organic Molecules and Polymers, CRC Press, Boca Raton, FL, 1997. [2] D.L. Wise, G.E. Wnek, D.J. Trantolo, T.M. Cooper, J.D. Gresser (Eds.), Electrical and Optical Polymer Systems, Marcel Dekker, New York, 1998. [3] L.R. Dalton, A.W. Harper, A. Ren, F. Wang, G. Todorova, J. Chen, C. Zang, M. Lee, Ind. Eng. Chem. Res. 38 (1999) 8. [4] L.R. Dalton, W.H. Steier, B.H. Robinson, C. Zang, A. Ren, S. Garner, A. Chen, T. Londergan, L. Irwin, B. Carlson, L. Fifield, G. Phenlan, C. Kincaid, J. Amend, A. Jen, J. Mater. Chem. 9 (1999) 1905. [5] D.R. Kanis, M.A. Ratner, T.J. Marks, Chem. Rev. 94 (1994) 195. [6] J.J. Wolff, R. Wortmann, Adv. Phys. Org. Chem. 32 (1999) 121. [7] L. Dalton, Adv. Polym. Sci. 158 (2002) 1. [8] Q. Pan, C. Fang, Z. Zhang, Z. Qin, F. Li, Q. Gu, X. Wu, J. Yu, Optical Mat. 22 (2003) 45. [9] D. Li, T.J. Marks, M.A. Ratner, J. Phys. Chem. 96 (1992) 4325. [10] P. Persico, R. Centore, A. Sirigu, M. Casalboni, A. Quatela, F. Sarcinelli, J. Pol. Sci. Part A 41 (2003) 1841. [11] J.O. Morley, J. Chem. Soc. Perkin Trans. 2 (1995) 731. [12] C. VanWalree, O. Franssen, A. Marisman, M. Flipse, L. Jenneskens, J. Chem. Soc. Perkin Trans. 2 (1997) 799. [13] T. Pliska, W. Cho, J. Meier, A. Le Duff, V. Ricci, A. Otomo, M. Canva, G.I. Stegeman, P. Raimond, F. Kajzar, J. Opt. Soc. Am. B 17 (2000) 1554. [14] V.P. Rao, A.K-Y. Jen, J. Chandrasekhar, I.N.N. Namboothiri, A. Rathna, J. Am. Chem. Soc. 118 (1996) 12443. [15] V.P. Rao, A.K-Y. Jen, K.Y. Wang, Polym. Prep. 35 (1994) 130. [16] K. Komatsu, M. Kuniya, Y. Honda, K. Toshikuni, Nonlinear Optics 22 (1999) 173. [17] O. Toyoji, K. Mariko, T. Eiji, U. Takamaso, U. Hideaki, Mitsubishi Petrochemical Co, Japan, Minolta Camera KK, Jpn. Kokai Tokkyo, Koho, 1994. [18] K. Makoto, A. Masafuni, Mitsubishi Chemical Industries, Ltd Japan, Jpn. Kokai Tokkyo, Koho, 1998. [19] O. Haak, C. Jeoung, A. Pawlik, P. Boldt, W. Grahn, F. Kreuzer, H. Leigeber, H. Weitzel, J. Chem. Res. (S) 10 (1998) 630. [20] Y. Kaminorz, B. Schulz, S. Schrader, L. Brehmer, Synth. Met. 122 (2001) 115. [21] S. Hou, A. Gharavi, Macromolecules 35 (2002) 850. [22] B. Schulz, Y. Kaminorz, L. Brehmer, Synth. Met. 84 (1997) 449. [23] M. Calvin, R.E. Buckles, J. Am. Chem. Soc. 62 (1940) 3326. [24] P. Walden, A. Kernbaum, Ber. 23 (1890) 1959. [25] A. Castaldo, R. Centore, A. Peluso, A. Sirigu, A. Tuzi, Struct. Chem. 13 (2002) 27. [26] C.P. Brock, Acta Cryst. 36 (1980) 968, and references therein cited. [27] M.O. Sinnokrot, E.F. Valeev, C.D. Sherrill, J. Am. Chem. Soc. 124 (2002) 10887. [28] L. Dalton, A. Harper, A. Ren, F. Wang, G. Todorova, J. Chen, C. Zhang, M. Lee, Ind. Eng. Chem. Res. 83 (1999) 8. [29] A. Carella, A. Castaldo, R. Centore, A. Fort, A. Sirigu, A. Tuzi, J. Chem. Soc. Perkin Trans. 2 (2002) 1. [30] G.M. Sheldrick SHELX-97, Program for Crystal Structure Determination, University of G€ ottingen, Germany, 1997. [31] I. Ledoux, J. Zyss, J. Chem. Phys. 73 (1982) 203.