Stilbazolium salts

The possible redistribution of the electronic density in these compounds as typical push-pull systems depends on the solvent polarity. When the electron transition 

FIGURE 6.1 Chemical diagram of substituted stilbazolium salts. 

Source Kolev, T.S., B.B. Koleva, M. Spiteller, H. Mayer-Figge, and W.S. Sheldrick, 2008, DyesPigm., 79 7-13. (With permission.) 

In the case of l-methyl-4-[2-(4-hydroxyphenyl)ethenyl)]pyridinium] hydrogen-phosphate in an ethanohwater solvent mixture (1 1), two bands at 386 nm and 492 nm are observed. The observation of two maxima in acetonitrile as well as the spectral 

With respect to the development of new materials with potential NLO applications, compounds with quinoide-like forms, obtained after the deprotonation of the OH-group in the 4 -position, can be reasonably studied because a significant batho-chromic effect is observed (Table 6.2). Negative solvatochromism is observed with lowering of the solvent polarity and a shifting of occurs within 170 to 210 nm. 

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The desire to increase P values above those of molecules used in the earliest materials has led to the exploration of organic compounds as the active components of second order NLO devices. Considerable effort has been expended in the synthesis and analysis of candidate molecules, which are largely donor-acceptor substituted conjugated n systems. (2) Examples of compound classes whose members display large nonresonant P include azo dyes, stilbenes, polyenes, merocyanines, stilbazolium salts, and quinoid... 

Closely related to cyanine dyes are stilbazolium salts that are based on the styryl scaffold. Stilbazolium dyes are a class of fluorescent, lipophilic cations that have been used as mitochondrial labeling agents and membrane voltage-sensitive... 

Fig. 5.4 Selected aldehyde (9) and picolinium building blocks (10) for the combinatorial synthesis of stilbazolium salts.

Photoaddition - Micellar aggregates of alkylated -stilbazolium salts in water form only head-to-head photodimers, with a preference for the jj/n-isomer, suggesting a significant degree of order within the aggregates. Preferential... 

A-Alkylpyridinium salts 20 with alkyl chains from 14 to 22 carbon atoms andp substituents such as methyl, phenyl, and styryl groups (stilbazolium salts) with Cl", Br", I", BPh ", and C H SOj" counteranions were prepared by Ster et al. [27]. The stability of the SmA phase increased with the size of the anion, but no mesophase was observed with heptyl sulfonate. 

Quina and Whitten (5,6) studied the photodimerization, photoisomerization and excimer fluorescence of stilbazolium derivatives in homogeneous solution, CTAB micelles, monolayer assemblies, and the solid state. The photoproducts of /V-(1-Octadecyl)-4-stilbazolium salts (CisStzX, where X is the counterion) were found to be extremely dependent upon the molecular environment. In acetonitrile, CisStzX exhibits a weak structureless fluorescence with a maximum peak at 430nm. Irradiation of a nearly saturated solution results in trans- cis isomerization without evidence of bimolecular interactions occurring. Prolonged irradiation of the CisStzX solution results in cyclization to the corresponding azaphenathrene salt from c/s-CisStzX. The photochemical behavior of CisStzX in CTAB micelles was found to be quite similar to that observed in homogeneous solution. Trans- cis isomerization with eventual cyclization occurs upon irradiation. No dimerization was observed. 

This chapter deals with the properties of the excited states of 1,2-diary lethylenes in general, with the effects caused by specific variation of reaction conditions on photochemical cis trans isomerization in condensed phase, and with the reaction mechanisms. In particular, the influence of substitution on the properties of excited states involved in cis trans isomerization in solution is examined. Besides various substituted stilbenes (which have been most extensively studied), styrylpyridines (StPs, azastilbenes) including some of their positively charged derivatives (quaternary stilbazolium salts), dipyridylethylenes (DPEs), styrylnaphthalenes (StNs), their pyridine analogues (NPEs), and some related compounds, such as dinaphthylethylenes (DNEs), are surveyed. Results on photochemical cis ttrans isomerization of stilbenes and other 1,2-diarylethylenes under direct (Section II) and sensitized (Section III) irradiation conditions are summarized, as well as their photophysical excited singlet and triplet state properties (Section IV) and some selected side reactions (Section V). The mechanistic section (Section VI) describes several photochemical isomerization routes. Characteristic photophysical and photochemical aspects of specific classes of substituted stilbenes are discussed and mechanistic schemes are critically examined with reference to their experimental basis. 

Ionic chromophores in which the packing is mainly driven by the stronger Coulomb interactions among ions are an approach [25-28]. Relevant results have been obtained with Af-methyl-stilbazolium salts or IV-phenyl-piridinium salts. In particular, DAST (4-dimethylamino-A-methylstilbazolium 4-toluene-sulphonate) is presently known as one of the best organic nonlinear optical crystal (SHG efficiency 1,000 times urea). 

Stewart, K. R. Preparation of high melting point stilbazolium salts as second harmonic generators. U.S. Patent 5292888, 1994 Chem. Abstr. 1994, 120, 270132. 

In this section we will demonstrate the applicability of the CS-NLC method for investigation of the effect of protonation on the symmetry of the molecules and the IR spectroscopic properties. In this respect, the CS-NLC method has also been successfully applied for the elucidation of organic dyes, in particular different dicy-anoisophorones, anyles, merocyanine dyes, and corresponding stilbazolium salts. 

The role of the effect of the substituents on the spectroscopic characteristics of the stilbazolium salts has been elucidated in detail using the corresponding derivatives, where the OH and OCH3 groups are at the 2-position and/or 3-position (Fignre 6.1). The role of the N-aliphatic fragment has also been studied. 

FIGURE 6.4 Resonance forms in the 2-OH substituted stilbazolium salts depending on the pH values. 

Yang, Z., M. Wdrle, L. Mutter, M. Jazbinsek, and P. Gunter. 2007. Synthesis, crystal structure, and second-order nonlinear optical properties of new stilbazolium salts. Cryst Growth Des. 7 83-86. 

Ruiz, B., Z. Yang, V. Gramlich, M. Jazbinsek, and P. Gunter. 2006. Synthesis and crystal structure of a new stilbazolium salt with large second-order optical nonlinearity. J. Mater. Chem. 16 2839-2842. 

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