Electron donor-acceptor (EDA) complex photochemistry has received increasingly attentions, as it enables various of catalyst-free photochemical transformations under visible light irradiation. Despite the remarkable progress in the experimental investigations, a number of fundamental questions about the EDA photochemistry are still ambiguous, such as the origin of visible light absorption, the photochemical and photophysical properties of the EDA complex, as well as the detail mechanism of the radical coupling pathways mediated by EDA complex. To answer these questions, accurate electronic structure calculations at the CASPT2// CASSCF/PCM level of theory were performed to investigate the paradigm example of EDA complex-enabled photoreaction for visible-light-driven dearomative perfluoroalkylation of β-naphthol. The most important finding in this work is that the excitation energy levels of the EDA complex can be controlled by noncovalent interaction. As a result, the stable halogen-bonded complexes can only absorb the UVA irradiation (<380 nm) via either the intra- or inter- molecular charge transfer (CT) excitations, whereas the unstable complexes associated by polar-π or dipole-dipole interactions are capable to be photoactivated by visible light (>500 nm) through the intermolecular CT πσ* excitation. The competitiveness of the radical chain propagation pathway over the radical−radical coupling is also regulated due to the tunable radical concentrations varying the excitation wavelength. In addition, the strong spin–orbit coupling resulting from the heavy atom effect is of critical important to trigger the C-I bond cleavage in the <sup>3</sup>σπ* triplet manifold.

Mechanistic studies on the visible-light induced radical fluoroalkylation enabled by electron donor-acceptor complexes

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ACS Fall 2022

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