Antimony and Bismuth Complexes as Visible Light Photosensitizers in Catalytic Oxidation Reactions

The unique chemical reactivity offered by photochemistry
has driven
a growing interest in the design of new photocatalysts with diverse
chemical properties. Incorporating heavy atoms into the core of chromophores
presents an excellent opportunity to achieve this by enabling a long-lived
excited state. Herein we report the design, synthesis, and characterization
of new Sb- and Bi-based dipyrrins with a significantly increased stability
in solution, improved luminescent properties, as well as their use
in photocatalysis. Furthermore, the applicability of a new Sb-dipyrrin
photosensitizer ArOMe-Sb-Br is highlighted in the oxidation of different functional groups,
performing especially well in the oxidation of alkenes (TON up to
5500). In addition, the singlet oxygen efficiency was found to be
ΦΔ= 0.76, a value as high as benchmark photosensitizers
such as chlorophyll a and metalloporphyrins. We have
performed further investigations using cyclic voltammetry under light
irradiation with complementary density functional theory (DFT) calculations
to elucidate the redox properties of our new set of heavy pnictogen
dipyrrins. Despite the theoretical and experimental challenges, both
cyclic voltammetry and DFT corroborate the formation of a cationic
complex resulting from light-induced bromide dissociation. Our work
paves the way for exciting new possibilities in light-driven applications
using main-group elements.