Synthesis, Spectral Characteristics and DFT Studies of the New Dye 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) in Different Solvents.

The photophysical parameters such as electronic absorption spectra, molar absorptivity(ε), fluorescence spectra and fluorescence quantum yield (φf) of a new dye namely 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) were determined in different solvents. The electronic absorption are less sensitive to medium polarity. A bathochromic shift was observed in emission spectra(ca. 50 nm) upon increase of solvent polarity, which indicates that the singlet excited state (S1) of DMMF is more polar than the singlet ground state (So). Solid crystals of DMMF exhibit intense yellow fluorescence maximum at 550 nm with bandwidth equal 64 nm upon excitation at wavelength 365 nm. The change in dipole moment value (Δμ) was calculated by using the variation of Stokes shift with solvent polarizability (Δf) (Lippert - Mataga plot) and was found to be 7.22 and 5.5 Debye for higher and lower energy of So - S1 (π-π*) H-1 → L and So - S1 (π-π*) H → L, respectively. These results show that, the excited state is more polar than the ground state. The net photochemical quantum yields of photodecomposition of DMMF (φc) were calculated as 7.2 × 10(-5), 1.14 × 10(-4), 1.44 × 10(-4) and 2.11 × 10(-4) in different solvents such as MeOH, CH2Cl2, CHCl3 and CCl4, respectively. DFT/TD-DFT methods were used to study the geometric and electronic structures of DMMF in different solvents. A good agreement was found between the experimental and theoretical results.