MONOMETHINE CYANINE DYES CONTAINING BENZ[C,D]INDOLE AND PYRYLIUM END-GROUPS

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 containin g nitrogen heterocycles synthesized so far. Quantum-chemical considera tions show that electronic excitation to the first-singlet-excited sta te is localized in the polymethine fragment and is connected with a co nsiderable decrease in electronic polarizability.