Synthesis, spectral properties, and solvatochromism of merocyanine dyes based on bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate

Di-, tetra-, and hexamethine merocyanines containing heterocyclic fragments with different electron-donor abilities have been synthesized on the basis of bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate. Their electronic absorption spectra in solvents with different polarities have been studied, and their electronic structure and electronic transitions have been analyzed by DFT and TDDFT quantum chemical calculations using B3LYP functional and 6-31G(d,p) basis set. The electronic structure of the synthesized merocyanines changes from neutral polyene to polymethine and dipolar polyene, depending on the electron-donor ability of the heterocyclic fragment, length of the polymethine chain, and solvent polarity. Therefore, these merocyanines display positive, negative, and reverse solvatochromism.