Successive occurrence of the T1(π, π*) and T2(n, π*) phosphorescence and the S1(n, π*) fluorescence observed for p-cyanobenzaldehyde in a solid matrix

Successive occurrence of the T1(π,π*) and T2(n, π*) phosphorescence and S1(n, π*) fluorescence has been observed clearly for p-cyanobenzaldehyde (p-CNB) in a translucent p-dichlorobenzene host crystal upon increasing the temperature. Quantitative analysis of the steady-state emission spectra and emission decay profiles measured as a function of temperature provides estimates for the energies and rate constants that characterize the excited-state dynamical behavior of p-CNB. It is shown that the successive occurrence of the emission is caused by the thermal depopulation of the T1 state.