Emission, excitation, and absorption spectra of diphenyltetradecaheptaene (DP7) have been measured in solvents with different polarizabilities, together with the Raman spectrum at room temperature. DP7 exhibits dual fluorescence from the 2 (1)A(g)(S-1) and 1 B-1(u)(S-2) states in room temperature solution. It is shown that the 2 (1)A(g)/1 B-1(u) fluorescence intensity-ratio varies significantly depending on the solvent polarizability. This observation was interpreted on the basis of the coupling strength between the 2 (1)A(g)/1 B-1(u) states which is determined mainly by the 2 (1)A(g)-1 B-1(u) energy separation. Fitting of the spectra with sum of Gaussians reveals a significant difference in Franck-Condon envelop between the 2 (1)A(g) and 1 B-1(u) fluorescence spectra, which is originating from the large difference in the C-C and C=C stretching mode displacements between the 2 (1)A(g) and 1 B-1(u) states. (C) 2003 American Institute of Physics.