PHOTOINDUCED INTRAMOLECULAR CHARGE-TRANSFER AND TRANS-CIS ISOMERIZATION OF THE DCM STYRENE DYE - PICOSECOND AND NANOSECOND LASER SPECTROSCOPY, HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY, AND NUCLEAR MAGNETIC-RESONANCE STUDIES

The photoexcitation of 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM) induces a large intramolecular charge transfer (ICT) from the dimethylamino electron-donor group to the dicyanomethylene acceptor group. The dramatic effect of the solvent polarity on the absorption and fluorescence spectra on the one hand and the competition between the nonradiative S1 → S0 deactivation and trans → cis isomerization processes on the other hand has been examined. Our results clearly show that DCM isomerization efficiency is very low in the more polar solvents. The S1 → S0 internal conversion may intervene at a torsional angle smaller than 90° before reaching the perpendicular configuration. © 1990 American Chemical Society.