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 S-2 State of all-trans-alpha, omega-diphenylpolyenes, from diphenylhexatriene (N = 3) to diphenylhexadecaoctaene (N = 8), in solution. The St state lifetimes, which were determined from the decay of the S-2 <-- S-2 absorption band around 700 nm, were similar for N = 3-7. The observed small energy gap dependence of the S-2 --> S-1 internal conversion rate can be an indication of the large difference in the molecular geometry of the S-1 and S-2 states. (C) 1999 Published by Elsevier Science B.V. All rights reserved.