Phosphorescence from the T2(n, π∗) state observed for 4-hyroxybenzaldehyde in a p-dichlorobenzene matrix

T2(n, π∗) phosphorescence has been observed for 4-hyroxybenzaldehyde along with T1(π, π∗) phosphorescence in a partially translucent 1,4-dichlorobenzene host upon increasing temperature. Quantitative analysis of the steady-state emission spectra and emission decay profiles measured as a function of temperature provides estimates for the excited-state energies and rate constants that characterize the excited-state dynamical behavior of 4-hydroxybenzaldehyde. It is shown that the successive occurrence of the T1(π, π∗) and T2(n, π∗) phosphorescence is caused by the thermal repopulation from the T1 state.