Symmetric anionic polymethine dyes derived from fluorene and its derivatives with electron-acceptor substituents: synthesis and spectral properties

Abstract

Novel anionic polymethine dyes were synthesized from 2,7-bis(phenoxysulfonyl)-, 2,7-dinitro-, and 2,4,5,7-tetranitrofluorenes. The reasons for the complicated shape of their absorption spectra were analyzed: the formation of contact ion pairs, associates, and conformational isomers and electronic effects of substituents. The quantum chemical calculations by the Pariser—Parr—Pople method and nonempirical DFT and TDDFT methods in the B3LYP/6-31G(d,p) basis set revealed that the orbitals of the nitro groups, unlike the orbitals of the SO2OPh groups, are efficiently conjugated with the common chromophore system inducing additional electron transitions.