Energy gap dependence of the S2→S1 internal conversion of α,ω-diphenylpolyenes (N=3–8) in solution phase

By using femtosecond and picosecond transient absorption measurement techniques, we have investigated the dynamic behavior of the S2 state of all-trans-α,ω-diphenylpolyenes, from diphenylhexatriene (N=3) to diphenylhexadecaoctaene (N=8), in solution. The S2 state lifetimes, which were determined from the decay of the Sn←S2 absorption band around 700 nm, were similar for N=3–7. The observed small energy gap dependence of the S2→S1 internal conversion rate can be an indication of the large difference in the molecular geometry of the S1 and S2 states.