Femtosecond transient absorption studies of diphenylpolyenes. Direct detection of S2 → S1 radiationless conversion in diphenylhexatriene and diphenyloctatetraene

Femtosecond transient absorption studies of diphenyloctatetraene (DPO), diphenylhexatriene (DPH), diphenylbutadiene (DPB), and 1,4-diphenyl-1,3-cyclopentadiene (DPCP) were performed in cyclohexane solution at room temperature using 390 nm excitation and probe wavelengths of 720 and 780 nm. Fast decay components observed in DPH and DPO are attributed to absorption by initially excited S2 with decay rates of ∼ 450–600 fs assigned to S2 → S1 internal conversion processes. No comparable fast decay components were observed in DPB and DPCP.