Efficient one-pot three-component synthesis of monomethine cyanine dyes with quinoline nucleus and their spectral properties

Abstract

An improved method for the preparation of monomethine cyanine dyes with quinoline nucleus by one-pot three-component using 1-methyl-2-quinolinethione, quaternized 2- or 4-methylheterocyclic compounds and methyl p-toluenesulfonate as starting materials was described. Compared with the traditional methods, the new synthetic method reduced the reaction steps, shortened the reaction time, avoided the separation and purification of the intermediate and reduced cost. The dyes absorbed in the region 478.0-563.0 nm and had molar extinction coefficients of 1.3 × 104 - 9.4 × 104 L mol?1 cm?1. Their fluorescence maxima and Stokes shifts were in the range of 525.2-594.4 nm and 16.2-80.6 nm in different solvents, respectively. From the spectral properties of the dyes in different solvents, it could be found that the ?max of the dyes were shorter in protonic solvents, and showed hypsochromic shifts with the increase of polarity of the solvents.