Chromophoric chain β-substituted hemicyanines: Effect of the nature of substituents on optical properties

Abstract

As a part of the project undertaken to study the effect of substitution, a number of chain β-substituted hemicyanines have been synthesised by condensing 4,4′-bis(dimethylamino)benzophenone with variously 6-substituted quinaldinium alkyl iodides. Absorption and photosensitisation of the dyes have been recorded. Contrary to the earlier observation that chain β-substitution in hemicyanine causes hypsochromic shifts in absorption, the dyes under report have shown uniform bathochromic shifts, which confirms the authors' previous findings. Further, these dyes absorb at longer wavelengths and are better sensitisers than their β-phenyl and β- p-nitrophenyl analogues. Progressively weightier hetero-6-halosubstitutions have led to progressive bathochromic shifts and extended extrasensitisations, irrespective of the nature of the β-substituents. Ethoquaternised hemicyanines have been found to absorb at longer wavelengths and to exhibit greater photosensitisation than their methoquaternised analogues.