Excited-state levels and relaxation processes of chromone and 6-fluorochromone vapors

Emission and excitation spectra of chromone and 6-fluorochromone have been measured in the vapor phase at different temperatures and pressures along with the absorption spectra. The emission is shown to consist of the 3(n, π*) phosphorescence accompanied by weak S1(n, π*) delayed fluorescence. It is inferred from the temperature dependence of the phosphorescence intensity that the 3(n, π*) state is located at energies below the 3(π, π*) state for chromone and 6-fluorochromone vapors. The relaxation processes in the vapor phase are discussed based on the pressure and excitation energy dependence of the relative phosphorescence yields. The data include the vibrational analyses of the emission spectra based on the results of the DFT calculations at the B3LYP/6-311 + G(p, d) level.