Photophysics of 2,4,6,8,10-dodecapentaene vapor

S 1 and S 2 fluorescence and excitation spectra of all- trans -2,4,6,8,10-dodecapentaene vapor have been measured at different N 2 gas pressures from 0 to 800 Torr along with the absorption spectrum. Both S 1 and S 2 fluorescence quantum yields are shown to decrease with increasing excitation energy under the collision free condition, although the decrease of the latter yield is not significant. The difference between the S 1 and S 2 fluorescence lifetimes was demonstrated through the effect of added O 2 gas on the relative fluorescence intensities. Pressure and excitation-energy dependence of the S 1 and S 2 fluorescence yields are interpreted in terms of the relaxation model involving the fast S 2 → S 1 internal conversion followed by vibrational relaxation in the S 1 manifold. Estimates for the rates that characterize the excited-state dynamical behavior of decapentaene vapor have been extracted.