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

► S1 and S2 fluorescence and excitation spectra of all-trans-dodecapentaene vapor were measured at different pressures. ► Pressure and excitation-energy dependence of the fluorescence yields were interpreted in terms of a relaxation model. ► This model involves the fast S2 → S1 internal conversion followed by vibrational relaxation in S1. ► Estimates for the rates that characterize the excited-state dynamical behavior were extracted.