Hemicyanine dyes

In hemicyanine dyes one of the charge-carrying terminal atoms of the methine chain forms part of a heterocyclic ring. The lowest vinylogous hemicyanine dyes (cyclomethine dyes) do not contain a methine chain, and the donor and acceptor groups are in the same ring system. 

Cyclomethine Dyes can be prepared by condensing N-heterocyclic carbonyl compounds with secondary amines. Intensely colored products such as 4 are obtained by condensing 3-phenylpyrazoline with compounds such as /V-cthyl-naphtholactam. This compound dyes polyacrylonitrile a brilliant, lightfast yellow. Orange-red dyes are obtained by condensing acridone with secondary amines [6], 

Dimethinehemicyanine Dyes and their aza analogues are important for dyeing polyacrylonitrile. Most of the dyes that color polyacrylonitrile in greenish to reddish-yellow shades belong to this class. 

Enamine Dyes are obtained by condensation of heterocyclic methylene- a) -aldehydes with aromatic amines in an acid medium. Technically important dyes contain 1,3,3-trimethyl-2-methyleneindoline-a)-aldehyde as aldehyde component [7], C.I. Basic Yellow 11, the condensation product formed with 2,4-dimethoxyan-iline, is of particular importance (see 3.8.4). This compound dyes polyacrylonitrile a lightfast, brilliant, greenish-yellow shade. 

The low molecular mass bases of enamine dyes can be sublimed by means of a thermohead from a transfer ribbon onto a receiving material and serve as yellow components for producing color copies in sublimation transfer printing [14], 

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Cao X, Tolbert RW, McHale JL, Edwards WD (1998) Theoretical study of solvent effects on the intramolecular charge transfer of a hemicyanine dye. J Phys Chem A 102(17) 2739-2748... 

Pillai ZS, Sudeep PK, George Thomas K (2003) Effect of viscosity on the singlet-excited state dynamics of some hemicyanine dyes. Res Chem Intermed 29(3) 293-305... 

Ephardt H, Fromherz P (1993) Fluorescence of amphiphilic hemicyanine dyes without free double-bonds. J Phys Chem 97(17) 4540-4547... 

Hubener G, Lambacher A, Fromherz P (2003) Anellated hemicyanine dyes with large symmetrical solvatochromism of absorption and fluorescence. J Phys Chem B 107(31) 7896-7902... 

Fast-response probes (response times less than milliseconds) styrylpyridinium and annellated hemicyanine dyes, merocyanine dyes, and 3-hydroxychromone dyes... 

Fig. 2 Examples of the structures of a few fast-response electric filed sensitive dyes N-(4-sulpho-butyl)-4-(4-(4-(dipentylamino)phenyl)butadienyl)pyridinium inner salt (RH421, a styrylpyridinium dye), ANNINE 5 (an annellated hemicyanine dye), merocyanine 540, and N-[(4 -dimethylamino)-3-hydroxy-6-flavonyl mcthyl-N,N-trimcthyl ammonium (F4N1, a 3-hydroxychromone dye)...

Hemicyanine dyes, 9 257 Hemihedrite, 6 471t Hemiisotactic micro structures, 16 108 4,6-Hemiketals, 24 595 Hemimicelle formation, 24 142 Hemins, 14 552... 

In the hemicyanine dyes, one of the charged terminal atoms is part of a heterocyclic ring, and the other is a nitrogen atom directly linked to the methine chain (5). 

The hemicyanine dyes can be represented by structure (5). They may be considered as cyanines in which a benzene ring has been inserted into the conjugated chain. Hemicyanines provide some bright fluorescent red dyes for polyacrylonitrile. 

Triazene Dyes. If diazonium salts of N-heterocyclic amines are coupled to A-alkyl anilines, e.g., diazotized 2-aminoinomethoxybenzothiazole to A-methyl-4-nitroaniline, a triazene is obtained. A cationic triazene dye (16, diazadimethine-hemicyanine dye) is formed by subsequent A-alkylation, and dyes polyacrylonitrile a very lightfast yellow shade [39],... 

Dithiopheno-tetrathiafulvalene, Ci0H4S6 Ethylene-1,2-dithiolate, [C2H2S2]2 Ethylenedithiotetrathiafulvalene, CgH6S6 Field cooled Critical field Hemicyanine dye... 

Wang LY, Zhang XG, Shi YP et al (2004) Microwave-assisted solvent-free synthesis of some hemicyanine dyes. Dye Pigment 62 21-25... 

Figure 11. Hemicyanine dye with a sterically hindered bridge which gives it a twisted chromophore.

Theoretical methods have also been applied to other classes of 1,3-dithioles. Ab initio molecular dynamics geometry optimization of a C6o-2-thiono-l,3-dithiole cycloadduct took into account the superposition of all possible molecular conformations with weighting factor and multiple interactions <1999PRB9229>. Semi-empirical quantum-chemical calculations (PM3) were used to elucidate the role of counterions in five complex anions (M = Ni, Pd, Cu, Cd, Hg) formed from 4,5-dimercapto-l,3-dithiole-2-thione and combined with a hemicyanine dye <2000JMC625>. 

The Langmuir-Blodgett deposition technique shows excellent promise for the assembly of films with noncentrosymmetric ordering and Coo symmetry. A system that was reported recently (3i) is shown in Figure 6.11. In this system, monolayers of the hemicyanine dye and the nitrostilbene... 

Fig. 17.16 Synthesis of benzimidazolium hemicyanine dyes. Reagents and conditions (a) triethyl orthoacetate, H+, toluene, reflux (b) KOH, Mel, acetone (c) Tf20, poly(4-vinylpyridine), DCM (d) 4, DCM (e) 48% HBr, 65°C (f) 2-chlorotrityl alcohol resin sequentially treated with thionyl chloride in DCM and ethylene diamine in DCM (g) 8, HATU, DIPEA, 30% DMF/DCM (h) R-CHO (96-aromatic aldehydes), pyrrolidine, NMP (i) 5% TFA/DCM...

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