Non-Radiative Deactivation in Isolated Quinoline.

Abstract

The photophysics of the S₂ ¹(ππ*) state of the polycyclic aromatic nitrogen-containing hydrocarbon (PANH) quinoline is investigated in a free jet using a picosecond laser system. A [1 + 1] multiphoton ionization spectrum yields the S₂ origin at around 32 200 cm^-1 and reveals several vibronic bands. In time-resolved experiments, quinoline is then excited between 312.2 and 279.7 nm. Probe wavelengths of 351 and 263.5 nm are employed. The dynamics is monitored by time-resolved photoelectron imaging. The images reveal a short-lived band at high electron kinetic energies with a ps lifetime and a band at lower electron kinetic energies that shows an offset at long delay times. In comparison with previous work, the offset is assigned to ionization from the T₁ state. Lifetimes decrease from 45 ps at the S₂ origin to 11 ps at +3550 cm^-1. Most likely, the S₂ ¹(ππ*) state deactivates by internal conversion to the S₁ ¹(nπ*) state, followed by intersystem crossing to the triplet manifold.