A theoretical exploration of the nonradiative deactivation of hydrogen-bond complexes: Isoindole-pyridine and quinoline-pyrrole

Abstract

The second order approximate Moller-Plesset (MP2) and coupled cluster (CC2) methods have been employed to investigate the geometry, electronic transition energies and photophysics of the isoindole-pyridine and quinoline-pyrrole complexes. The most stable geometry of both isoindole-pyridine and quinoline-pyrrole complexes has been predicted to be a perpendicular structure. It has also been found that the first electronic transition in both complexes is responsible for UV absorption owing to its 1ππ∗ nature, while a charge transfer 1ππ∗ state governs the nonradiative relaxation processes of both complexes. In this regard, excited state intermolecular hydrogen/proton transfer (ESHT/PT) via the charge transfer electronic states plays the most prominent role in non-radiative deactivation. In the HT/PT reaction coordinate, the minimum potential energy profile of the lowest CT-1ππ∗ state predissociates the local 1ππ∗ state, connecting the latter to a curve crossing with the S0 state. At the region of this curve crossing, the S0 and CT state become degenerate, enabling the 1ππ∗ state to proceed as the predissociative state and finally direct the excited system to the ground state. © 2015 The Royal Society of Chemistry.