S2(11Bu) fluorescence of diphenyldecapentaene vapor

Fluorescence and fluorescence excitation spectra of diphenyldecapentaene (DP5) vapor have been measured in the presence of an added buffer gas and compared with those of diphenyloctatetraene (DP4) vapor. It is shown that DP5 vapor exhibits the weak S2(11Bu) fluorescence in addition to the S1(21Ag) fluorescence. The S2/S1 fluorescence intensity ratio is found to be significantly higher for DP5 than for DP4. This observation is interpreted in terms of the intensity borrowing of S1 from S2. The excitation origin of the S2 state of DP5 vapor is observed at wavenumbers about 700 cm−1 higher than that estimated previously.