Monomethine cyanine dyes containing benz[c,d]indole and pyrylium end-groups

Abstract

Asymmetric monomethine cyanine dyes with benz[c,d]indole and pyrylium end-groups were prepared. The dyes absorb in the region 633–688 nm and are among the most deeply coloured monomethine cyanine dyes containing nitrogen heterocycles synthesized so far. Quantum-chemical considerations show that electronic excitation to the first-singlet-excited state is localized in the polymethine fragment and is connected with a considerable decrease in electronic polarizability.