Bifunctional chromophores

The theoretical models discussed above indicate that the sulfonyl group, although slightly weaker in electron acceptor strength, is indeed a viable alternative to the nitro group. In particular, sulfonyl derivatives of stilbene and azobenzene display large molecular hyperpolarizabilities and can be used as bifunctional chromophores for the construction of materials with nonlinear optical properties. 

The interpretation of the experimental data for the kinetics of photoacid-solvent clusters is complicated by the substantial fragmentation of the clusters after the excited-state reaction. The heat of reaction is often sufficient to allow the evaporation of one or several solvent molecules [14,16]. This difficulty does not arise when the H atom transfer or proton transfer occurs intramolecularly along a solvent wire attached to a bifunctional chromophore. 

Fig.24a-e. Examples of bifunctional chromophores for photorefractive applications a N-2-butyl-2,6-dimethyl-4H-pyridone-4-ylidenecyanomethylacetate (2BNCM) b 1,3-dimethyll-2,2lctramethylene-5- nit roben zirnidazoli ne (DTNBl) c 4- (N,N -diphenylamino)- (P )-nitros-tyrene (DPANST) d 4,4 -di(N-carbazolyl)-4"-(2-N-ethyl-4-[2-(4-nitrophenyl)-l-azo]anili-noethoxyl-triphenylamine (DRDCTA) e carbazole trimer... 

If bifimctional molecules do not form glasses, they can be incorporated into polymer binders. Examples of bifunctional molecules are shown in Fig. 24. DTNBl (molecule (b) in Fig. 24) was doped in PMMA and Cgg was used as a sensitizer. Diffraction efficiencies of 7%, sub-second grating growth times, and net two-beam coupling gain coefficients of 34 cm" were observed in such samples [81]. DPANST (molecule (c) in Fig. 24) was doped into PBMA [84]. Recently, ms response times were reported in photorefractive glasses based on the bifunctional chromophore DRDCTA (molecule (d) in Fig. 24) doped with the plasticizer DOP (molecule (b) in Fig. 23) and Cgg as a sensitizer [89, 90]. 

Eastman Kodak. Its bifunctional chromophore absorbs strongly at 365 nm. Its cross-linking reaction has a quantum yield of 0.1. ... 

Figure 2. Molecular structure of a bifunctional chromophore, 4-(N,N jdipheny lamino)-(P-nitrostyrene).

In conclusion, we first described the one step synthesis of nanoporous organosilica powders functionalized with a Non Linear Optical chromophore in the channel pore (azobenzene diethylphosphonate). These powders have been totally characterized and present a meso-porosity with a wormlike structure. Thin films monofunction-alised with NLO chromophore in the channel pores or bifunctionalized (NLO in the channel pores/erbium salt in the framework) were also prepared in one step and characterized by Grazing Incidence Small angle X-ray Scattering (GISAXS) and X-ray reflectivity. Interestingly, while the monofunctional thin film presents a lamellar structure, the bifunctional one (channel pores/framework)... 

The combined extension of the chromophore and introduction of the alkoxysilane using silyl-styrene 15 is also possible with bifunctional bromides dibromobenzene 23 (n = 0) gave the distyrylbenzene with 2 silane moieties in 16% yield, and the transformation of distyrylbenzene 24 (n = 1) to the 5-ring OPV yielded 33% of 26 (n = 2) after chromatographic separation from 14% of the intermediate with both a bromine and an alkoxysilane. 

The fluorescence of the other chromophore was efficiently but not totally quenched in the bifunctional systems but not at all in equimolar mixtures of the monofunctional models. All phosphorescence, however, occurred from the parabutyrophenone part, indicating very efficient triplet transfer. Bathochromlc shifts and a hyperchromic effect in the longest wavelength band of the absorption spectra are an indication for ground state interaction, which might lead to nonplanar conformations of the molecule playing a role in the excitation transfer. 

A different example of complementarity is explored in this chapter. We report studies of a bifunctional redox protein maquette based on the triple-helix bundle design of Ghadiri, Sasaki, and co-workers (4-S). Attempts to monitor electron transfer from an N-terminal ruthenium tris-bipyridyl excited state were fruitless, since electron transfer could not compete with the excited state decay of the Ru(IP) tris-bpy. However, as described below, replacement of photoactive ruthenium by a radiolytically accessible Co couple has allowed initial exploration of electron transfer in this synthetic protein couple. In turn, photochemistry initiated at the viologen chromophore helped confirm and extend the radiolytic results. 

The principal aim of this research was to obtain new types of linear chains rich in amide bonds and along which asymmetric diketopiperazine chromophores are regularly enchained. The CD curves of polymers compared to that of a model compound tend to exclude any interactions among the chromophores along the polymeric chain. Other polyamides based on diketopiperazines of /-glutamic acid or /-aspartic acid by reaction with a variety of diamines have also been investigated [40]. More recently, Cvescenzi et al. [41] prepared mixed polyamide-polyurethane copolymers by reaction of 3,6-bifunctional 2,5-diketopiper-azine with aliphatic and aromatic diisocyanates... 

Similar cyclic systems with other chromophores are reported [52). Rdated to the cage systems 45 and 46 are the phosphine oxide bifunctional macrocydes such as 48a and 48b [54] (Chart 7.3). These cydophanes were prepared from tris-... 

These examples demonstrate why, besides being fundamental models for elucidating the mechanism of tautomerization phenomena, bifunctional NH/N chromophores can be used for molecular recognition [118], as well as fluorescence indicators of water content [111, 119], microviscosity [111], or as fluorescence probes of hydrogen-bonding environments [112]. 

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