Non-Aufbau spiro-conjugated quinoidal & aromatic charged radicals

Abstract

We have studied electron acceptor and electron donor spiroconjugated dimers based, respectively, on bis(benzoquinoidal tetracyano carbon-bridged para-phenylene-vinylene) and on bis(benzo-aromatic bis(aryl)amino carbon-bridged paraphenylene-vinylene)s. Of the latter, two molecules either with identical units of carbon-bridged para-phenylene-vinylene or featuring a carbon-bridged para-phenylene-vinylene and a fluorene unit are considered. The radical forms of their charged species have been studied to explore the existence of SOMO-HOMO energy level inversion. It turns out that the radical trianion of the quinoidal and the radical cation of asymmetric aromatic show non-Aufbau SOMO-HOMO energy property. Spiro-conjugation and accumulation of electron-electron repulsion in the trianion and para-phenylene-vinylene/fluorene segmentation or localization of the frontier orbitals in the cation both explain the “anomalous” electronic configurations. Quantum chemical calculations and UV-Vis-NIR absorption spectroscopy have been used.