Spectroscopic Characterization and Mechanistic Studies on Visible Light Photoredox Carbon–Carbon Bond Formation by Bis(arylimino)acenaphthene Copper Photosensitizers

Currently, the most
popular molecular photosensitizers used for
synthetic organic chemistry and energy applications are still the
noble-metal-based ruthenium and iridium complexes that usually require
expensive metal and ligand precursors. In contrast, bis­(arylimino)­acenaphthene
(Ar-BIAN) is an established redox noninnocent π-accepting ligand
that is easily assembled in one condensation step from affordable
and commercially available precursors. Herein, we have developed a
series of Ar-BIAN CuI complexes as visible-light-harvesting
photosensitizers. Notably, one of these panchromatic, homoleptic Ar-BIAN
CuI complexes exhibits a radiative recombination lifetime
that is longer than diffusion-controlled
reactions, as observed by time-correlated single-photon counting spectroscopy.
Ar-BIAN CuI facilitates visible-light-promoted atom-transfer
radical addition reactions via carbon–carbon bond formation
with CBr3 radicals in good yields of up to 75%. Steady-state
and transient absorption spectroscopic measurements, together with
spectroelectrochemical experiments and intermediate isolation studies,
were performed to obtain insights into this photoredox catalysis and
provide guidelines for the general deployment of Ar-BIAN CuI photosensitizers in synthetic organic chemistry and renewable energy
applications.