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 fluoresc ence was observed for polyenes with more than three double bonds in th e polyene chain and the intensity and lifetime of the S-1 fluorescence decreased with increasing chain length. The 1B(u) energy was almost i nversely proportional to the square root of the total molecular length . A similar dependence was found for the energy of the 1A(g) level, bu t the length without the phenyl rings was used. The logarithm of the S -1 --> S-0 internal conversion rate in long-chain diphenylpolyenes exh ibits a linear dependence on the S-1 energy. The rate in diphenylhexat riene is slightly higher than the value predicted from the linear depe ndence, while the internal conversion of diphenylbutadiene is much fas ter due to stronger S-1-S-2 interaction. (C) 1998 Elsevier Science B.V .