Synthesis and Spectral Properties of Merocyanine Dyes Derived from Tetranitrofluorene and Heterocycles of Various Electron-donating Ability

Abstract

Syntheses are reported for di-, tetra-, and hexamethine merocyanines derived from 2,4,5,7-tetra-nitrofluorene and heterocyclic fragments with various electron-donating ability. The absorption spectra of these compounds were studied in solvents of different polarities. A quantum-chemical analysis was carried out for the electronic structure and types of electronic transitions of these merocyanines by using the DFT and TDDFT methods in the B3LYP/6-31G(d,p) basis set. The electronic structure of these merocyanines varied from neutral polyene to polymethine and bipolar polyene with increasing electron-donating ability of the heterocyclic fragment and with solvent polarity. These differences were strongly reflected in the position, intensity, and shape of the absorption bands, vinylene shifts, and deviations, as well as the sign of solvatochromic effect.