Monomethine cyanines

The symmetrical dye, bis-(3-methyl-4-phenylthiazole)monomethine cyanine (not mentioned by Mills), has also been identified, and its formation is explained by the enamine character of 20 (Scheme 27). 

The monomethine cyanines with a methyl group on the chain (Table 2113) are prepared in a basic medium from a 2-alkyl-substituted thiazolium by condensation of an electrophilic reagent. 

Likewise, quantum mechanical calculation succeeds in giving a theoretical explanation of some facts that the resonance theory could not explain, for example, why bis(pyridine-2)monomethine cyanine and bis(pyridine-4)monomethine cyanine possess the same lowest energy transition contrary to the 2,2 - and 2,4 -quinoline monomethine dyes, together with a molecular coefficient extinction lower than that of the 4,4 -quinoline dye (11). Calculation shows also that there is no theoretical reason for observing a relationship between and pK in a large series of dyes with different nuclei as it has been postulated, even if limited observations and calculations in short homogeneous series could lead to this conclusion (105). 

TABLE 2113. MONOMETHINE CYANINES WITH SUBSTITUENT ON THE CHAIN... 

Some weak electrophilic reagents, which are usually inert toward azoles, also react with quaternized azoles. Diazonium salts yield phenylhydrazones (Scheme 48) in a reaction analogous to the Japp-Klingemann transformation of /S-keto esters into phenylhydrazones in the dithiolylium series illustrated the product has bicyclic character. Cyanine dye preparations fall under this heading (see also Section 4.02.1.6.5). Monomethine cyanines are formed by reaction with an iodo quaternary salt, e.g. Scheme 49. Tri- and penta-methinecar-bocyanines (384 n = 1 and 2, respectively) are obtained by the reaction of two molecules of a quaternary salt with one molecule of ethyl orthoformate (384 n = 1) or/S-ethoxyacrolein acetal (384 n =2), respectively. 

The 2-methyl-4,9-dioxo-4,9-dihydrothiazolo[4,5-.g]quinoline was first quar-temized with methyl iodide on pyridine nitrogen and then treated with IV-methyl-quinolinium-4-yl salt, affording monomethine cyanine dyes 41 to study solva-tochromism, acid-base properties, and antimicrobial activities (95MI1). 

Bis-fsopropylidene or benzylidene derivatives of 2,2 dioxo-A-3,3 biselena-zoi-5,5 inylidene bis hydrazones, table of products. 253 Bis(pyridine-2)monomethine cyanine. 

Ethylbenzothiazole-2) (3-ethyl-4-one-thiazole-5) dimethine-3-ethyi-4 phenyl thiazole-2] monomethine cyanine. 28... 

Me thy l-4-phenylthiazole-2)( 3-methyl-thiazole-2)monomethine cyanine iodide, 26... 

Methyl-4-phenyl thiazole-2)( 1-methyl quinoline-4)monomethine cyanine iodide, formation. 40... 

Imino-3p-nitrophenyl-4-phenyl-A4-selenazoiine, preparation, 229 2-Iminoseienazolidin-4-ones, benzoylation, on imino nitrogen, 270 preparation, 269 table of products, 263 2-Iminoseienazolines, prototropic equilibrium, U.V. spectra, 231 Indolenine. 2-alkylmercapto, in synthesis of monomethine cyanine bases,... 

When N-ethylated-a-picoline, y-picoline, and lepidine were reacted with the ethoxy cation 75, instead of the expected cyanines of type 136 or 137 the products were dicationic species, whose structures were assigned to be bis(diphenylcyclopropenium)-monomethine cyanines, e.g. 142105 ... 

Treatment of l-methyltetrazolo[5,l-tf]isoindolium perchlorate 49 with acyl chlorides and triethylamine in dioxane as solvent affords a mixture of the 5-acyl-l-methyltetrazolo[5,l-tf]isoindoles 50 and the monomethine cyanine dye 51 (Equation 2) <2004T195>. 

Ogul chansky TYu, Losytskyy MYu, Kovalska VB, Yashchuk VM, Yarmoluk SM (2001) Interactions of cyanine dyes with nucleic acids. XXIV. Aggregation of monomethine cyanine dyes in presence of DNA and its manifestation in absorption and fluorescence spectra. Spectrochim Acta A Mol Biomol Spectrosc 57 1525-1532... 

Closely related are the cyanine dyes, for example cyanine (62) itself, which is formed from the ethiodide salts of lepidine and 4-iodoquinoline in the presence of base (Scheme 51). Analogous monomethine cyanines can have the quinoline nuclei linked 2,2 (pseudocyanines) and 2,4 (isocyanines). Quinaldine ethiodide on condensation With ethyl orthoformate gives the 2,2 -linked trimethine cyanine (carbocyanine) (63), known as pinacyanol (Scheme 51). 

Reaction of the quaternized salts of 4-ethoxycarbonyl-3,5-dimethyl-f-phenylpyttolo(furo or thieno)[2,3-c]pyrazole 34 with the iodomethane quaternary salts of pyridine, quinoline, and isoquinoline in ethanol with catalytic piperidine gave 3-[4(f)]-monomethine cyanine dyes (e.g., 35). Additionally, 3-[2(4)]-trimethine cyanine dyes and 4-[2(4)]-di-3[2(4)]-tri-mixed methine cyanine dyes (e.g., 36 and 37, respectively) were similarly prepared from the intermediates derived by reaction of 34 with triethyl orthoformate in the presence of piperidine (Scheme 8) <2002CCS106f>. 

Similar substitutions can also occur with hydrogen as leaving group if a suitable oxidant is present this usually is the cationic substrate itself (Scheme 14). The products are also in this case monomethine cyanine dyes (66HCA2046 73KGS1004 74KGS49). 

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