Photophysical Properties of Diphenylacetylene and Diphenylbutadiyne Derivatives in Solution Phase

By using the femtosecond and picosecond transient absorption measurement techniques, we have investigated diphenylacetylene, diphenylbutadiyne, and their methoxy and cyano derivatives in the solution phase. Both the rapid S$\text{}_{2}$ → S$\text{}_{1}$ 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 that of diphenyl acetylene. The level inversion of the lowest excited singlet states of dicyano-diphenylbutadiyne was observed. The thermally activated S$\text{}_{2}$ ← S$\text{}_{1}$ internal conversion was not negligible and the sum of the rate constants of S$\text{}_{2}$ → S$\text{}_{1}$ and S$\text{}_{2}$ ← S$\text{}_{1}$ internal conversions was estimated to be about 5 × 10$\text{}^{11}$ s$\text{}^{-1}$ at room temperature.