TIME-RESOLVED PHOTOACOUSTIC CALORIMETRY OF TRIPHENYLETHYLENES AND TETRAPHENYLETHYLENES - DO S-0 AND T-1 ENERGY SURFACES CROSS

We have studied triphenylethylene, tetraphenylethylene and one derivat ive of the latter employing time-resolved photoacoustic calorimetry (P AC). We report relaxed triplet energies and triplet lifetimes. These e xperiments show that a fourth independent parameter can be extracted f rom PAC data by appropriate experimental design. The results with tetr aphenylethylene are compared to data for thermal geometric isomerizati on of substituted tetraphenylethylenes. The comparison shows that So a nd T-1 energy surfaces of arylalkenes do not always cross.