Excited state energies and internal conversion in diphenylpolyenes: from diphenylbutadiene to diphenyltetradecaheptaene

Time-resolved and steady-state fluorescence investigations on a series of alpha,omega-diphenylpolyenes have been made. Dual S-1/S-2 fluorescence was observed for polyenes with more than three double bonds in the polyene chain and the intensity and lifetime of the S-1 fluorescence decreased with increasing chain length. The 1B(u) energy was almost inversely proportional to the square root of the total molecular length. A similar dependence was found for the energy of the 1A(g) level, but the length without the phenyl rings was used. The logarithm of the S-1 --> S-0 internal conversion rate in long-chain diphenylpolyenes exhibits a linear dependence on the S-1 energy. The rate in diphenylhexatriene is slightly higher than the value predicted from the linear dependence, while the internal conversion of diphenylbutadiene is much faster due to stronger S-1-S-2 interaction. (C) 1998 Elsevier Science B.V.