PHOTOPHYSICAL PROPERTIES OF DIPHENYLACETYLENE AND DIPHENYLBUTADIYNE DERIVATIVES IN SOLUTION-PHASE

By using the femtosecond and picosecond transient absorption measureme nt techniques, we have investigated diphenylacetylene, diphenylbutadiy ne, and their methoxy and cyano derivatives in the solution phase. Bot h the rapid S-2 --> S-1 internal conversion in the subpicosecond time scale and the triplet formation in the tens of picosecond region were observed for diphenylbutadiyne and its methoxy derivatives, while the dynamic behavior of dimethoxy-diphenylacetylene was quite similar to t hat of diphenylacetylene. The level inversion of the lowest excited si nglet states of dicyano-diphenylbutadiyne was observed. The thermally activated S-2 --> S-1 internal conversion was not negligible and the s um of the rate constants of S-2 --> S-1 and S-2 <-- S-1 internal conve rsions was estimated to be about 5x10(11) s(-1) at room temperature.