Transient features of optical bleaching as studied by photochemical hole burning and fluorescence line narrowing

This paper presents various laser excitation experiments on matrix‐isolated 1,4‐dihydroxyanthraquinone (DAQ). The molecular spectra are studied in two different organic glasses, namely a hydrogen‐bonding matrix of 3:1 EtOH/MeOH and a nonhydrogen‐bonding matrix of 3‐Me‐pentane. The experimental techniques are photochemical hole burning (PHB) and fluorescence line narrowing (FLN). The main difference between the two organic glass matrices is the host‐induced photoreactivity of DAQ in the alcohol matrix and the photostability of DAQ in the pentane matrix. This difference leads to ’’anomalous’’ spectral features in the photoreactive alcohol–DAQ system. In this system, the zero‐phonon transition appears to be more intense at higher temperatures, contrary to the well‐proven theories on electron–phonon coupling. The unusual spectral line shapes are explained as transient features due to the efficient photochemistry of DAQ in hydrogen‐bonding matrices.