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

Time-resolved and steady-state fluorescence investigations on a series of α,ω-diphenylpolyenes have been made. Dual S1/S2 fluorescence was observed for polyenes with more than three double bonds in the polyene chain and the intensity and lifetime of the S1 fluorescence decreased with increasing chain length. The 1Bu energy was almost inversely proportional to the square root of the total molecular length. A similar dependence was found for the energy of the 1Ag level, but the length without the phenyl rings was used. The logarithm of the S1→S0 internal conversion rate in long-chain diphenylpolyenes exhibits a linear dependence on the S1 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 S1–S2 interaction.