INTRAMOLECULAR CHARGE TRANSFER AND PHOTOISOMERIZATION OF THE DCM STYRENE DYE: A THEORETICAL STUDY
- 化学化工－已发表论文 
Structures and properties of the low-lying states in 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl)-4H-pyran (DCM) have been investigated theoretically. Calculations show that the dimethylamino and dimethylanilino twisted conformations of DCM on the potential energy surface of the first excited state (S-1) have relatively high stabilities and remarkable intramolecular charge transfers (ICT). Both structures can serve as candidates for the red-shifted emissive state in polar solvent. In particular, the dimethylanilino twisted ICT state has been predicted to have a dipole moment increment of 20 Debye with respect to the ground state by CASSCF calculations, in good agreement with the suggested experimental values. The optimized geometry of the S-1 state exhibits a long central CC bond of 1.458 angstrom, which makes the trans-cis isomerization quite facile through intramolecular rotation around the central CC bond on the S-1 potential surface. The S-1 state is a precursor to the formation of the ICT emissive state and photoinduced trans cis isomerization. The S-1/S-0 crossing in polar solvent and avoid-crossing in the gas phase as well as in non-polar solvent are involved in the trans-cis isomerization process. The presence of an early S-1/S-0 crossing in the strong polar solvent reduces the isomerization efficiency.