Nitrostilbene, structure

Molecules such as 4 -dimethylamino-4-nitrostilbene ( DANS , 1) possess the necessary electronic structure, and have very large p... 

A New Molecular Crystal DEANST. Another example of a low molecular weight compound with a large third-order NLO property is a styrene derivative. By selecting an appropriate -conjugation length and chemical structures of donor and acceptor, several new organic molecular crystals such as stilbene and azo benzene derivatives which exhibit %(3) larger than 10 12 esu can be developed. The %(3) of 4-(N,N-diethylamino)-4 -nitrostilbene (DEANS), an intramolecular CT compound, has been reported in a solution, in a polymer matrix and in a crystalline state(27.29.30). 

Figure 4.5, An 80-keV reflection high-energy electron-diffraction (RHEED) pattern from a single layer of the nitrostilbene molecule shown in Structure 4.1b. The substrate is 111 silicon.

Structures 4.1a and 4.1b. These two molecules, one (a) a hemicyanine and the other (b) a nitrostilbene dye can be used to form an organic superlattice displaying a high coefficient for second harmonic generation (see reference 50). 

Recently, a mixed-substituent polyphosphazene (polymer V) was synthesized and the second-order NLO properties were investigated (17). The nitrostilbene/trifluoroethoxy ratio was approximately 36 64. Due to the low glass transition temperature of V (T - 25 C), the second harmonic signal decayed to zero within a few minutes. However, polymer V is a prototype which offers many opportunities for further tailoring the molecular structure of polyphosphazenes to generate an optimum combination of NLO and physical properties (17). 

Asymmetric derivatives can be synthesized by 4-amino-4 -nitrostilbene-2,2 -disulfonic acid however, their preparation is more expensive, and they show little advantage over the symmetrical compounds. The principal effects of structural variations are changes in solubility, substrate affinity, acid fastness, etc. The bistriazinyl brighteners are anployed principally on cellulosics such as cotton or paper. 2-(Stilben-4-yl)-naphthotriazoles (34, 35) are prepared by diazotization of 4-aminostilbene-2-sulfonic acid or 4-amino-2-cyano-4 -chlorostilbene, coupling with an orthocoupling naphthylamine derivative, and finally, oxidation to the triazole. 

Second-order nonlinear optical properties require noncentrosymmetric structure. On the molecular level this is usually obtained by push-pull systems such as 4-7V,N-dimethylamino-4 -nitrostilbene (DANS) see Fig. 36a. But (/3> and subsequently will be zero if the macroscopic structure of the material is centrosym-metric. Therefore, polymers are usually poled to induce a noncentrosymmetric structure i.e., a high electric field is applied and the polar order is frozen in the glassy state. Problems are the relatively low polar order and its temporal and thermal instability. 

A nitro analog to polyurethane 19 was prepared by triethylamine-catalyzed polycondensation of (N,N-diethanol)-4 - amino-4-nitrostilbene 16 and the chaige transporting diisocyanate 17 (Figure 6). The Xj for 19 was also 316 nm but its absorption extended out to 548 nm. The H NMR spectrum was consistent with the polyurethane structure. The TGA analysis revealed high thermal stability of the polymer, with decomposition beginning at 247. The Tg of polyurethane 19 was... 

The parameters that can be changed at the molecular level are the relative electron affinities of the donor and acceptor groups and the length as well as the nature of the conjugated segment connecting the donor to the acceptor. The chemical structures of some of the NLO chromophores such as 4-(dimethyl-amino)-4 -nitrostilbene (DANS) (a). Disperse Red 1 (b), l-(2 -ethylhexyloxy)-2, 5-dimethyl-4-(4 -nitrophenylazo)benzene (EHDNPB) (c), N,N-diethyl-substituted... 

FDA and urea for few hours [179, 180]. Some of the NLO chromophores [179, 180] used in this method are 2-[3-(2- 4-[bis-(2-hydroxy-ethyl)-amino]-phenyl -vinyl)-5,5-dimethyl-cyclohex-2-enylidene]-malononitrile [179], 4-[N,N-bis(hydroxyethyl)amino]-4 -nitrostilbene [179], 4-[N,N-bis(hydroxyethyl)amino]-4 -nitroazobenzene [179], 4-[N,N-bis(hydroxyethyl)amino]-2 -methyl-4 -nitroazobenzene [179], 4-[N,N-bis (hydroxyethyl) amino]-4 -cyanoazobenzene [179],4-[N,N-bis(hydroxyethyl)amino]-4 -formylazobenzene [180] and 2-[[4-(4-[l,3]dioxolan-2-yl-phenylazo)-phenyl]-(2-hydroxy-ethyl)-amino]-ethanol [180] and their chemical structures are given in figure 34. 

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