Unexpected Boost in Activity of a Cu(I) Photosensitizer by Stabilizing a Transient Excited State.

In this study, we present a slight but surprisingly successful structural modification of the previously reported heteroleptic Cu(I) photosensitizer ([(xantphos)Cu(biipo)]PF; = 16-benzo-[4',5']-isoquinolino-[2',1':1,2]-imidazo-[4,5-]-[1,10]-phenanthrolin-16-one). As a key feature, bears a naphthalimide unit at the back, which is directly fused to a phenanthroline moiety to extend the conjugated π-system. This ligand was now altered to include two additional methyl groups at the 2,9-positions at the phenanthroline scaffold.