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_{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 that of diphenyl acetylene. The level inversion of the lowest excited singlet states of dicyano-diphenylbutadiyne was observed. The thermally activated S_{2} ← S_{1} internal conversion was not negligible and the sum of the rate constants of S_{2} → S_{1} and S_{2} ← S_{1} internal conversions was estimated to be about 5 × 10^{11} s^{-1} at room temperature.
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