Time-Resolved Study of 1,8-Naphthalic Anhydride and 1,4,5,8-Naphthalene-tetracarboxylic Dianhydride

We investigate the excited electronic states of 1,8-naphthalic anhydride (NDCA) and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) by time- and frequency-resolved electronic spectroscopy in the gas phase using picosecond lasers and by femtosecond time-resolved transient absorption in cyclohexane. The experiments are accompanied by calculations that yield the energy of the excited singlet and triplet states as well as by surface hopping dynamics simulations and calculations of spin–orbit couplings that give insight into the photochemistry. The origin of the A 1A1 ← X 1A1 (ππ*) transition in isolated NDCA was found at 30 260 cm–1, and several low-lying vibrational bands were observed. The lifetime drops sharply from 1.2 ns at the origin to around 30 ps at an excess energy of 800 cm–1. Both internal conversion (IC) and intersystem crossing (ISC) are possible deactivation pathways as found in coupled electron–nuclear dynamics simulations. In cyclohexane solution, two time constants were observed. Deactivation of the initially excited state by ISC seems to dominate as supported by computations. For NTCDA we observed a gas phase lifetime of 16 ps upon excitation at 351 nm.