Regioselective photochemical C-OMe bond formation initiated by one-electron transfer and N-OMe bond fragmentation in electron donor-acceptor systems

摘要

Compounds that integrate electron donor-acceptor subunits with N-methoxyisoquinolinium as acceptors and substituted (methoxy)benzenes as donors were synthesized and their luminescent and photochemical properties studied. Photolysis yielded the corresponding photomethoxylation products in a two-step process that involves N-OMe bond scission followed by C-OMe bond formation. Homolysis of the N-OMe bond restores the aromatic isoquinoline nucleus and produces a methoxy radical that can couple to the required ring carbon atom in the benzene cation radical to give the products in a regioselective process controlled by the spin density of the cation radical. This photoprocess involves two different pathways: methoxylation of the acceptor (intracomponent methoxylation) or the donor (intercomponent metoxylation). Both methoxy-transfer pathways are controlled by the donoating ability (redox potential) of the donor subunit, consistent with the emission observed upon excitation of the charge-transfer state in systems that undergo intermethoxylation.