<i>π</i> ‐Expanded BODIPYs and Related Analogs as Long‐Wavelength Absorbing Photosensitizers for Green Energy Conversion

Severe environmental issues caused by the use of fossil fuels have prompted the development of alternative, sustainable, and clean energy sources. Solar‐driven chemical processes such as water‐splitting and photocatalysis, as well as solar cells that convert solar radiation into electricity, have attracted considerable attention because solar energy is inexhaustible. Given that visible light accounts for 47%, and nearly 50% of the sunlight spectrum covers the near‐infrared (NIR) and IR regions, photosensitizers with long‐wavelength absorption bands are desirable from the standpoint of efficient light harvesting. To this end, π ‐extended 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐ s ‐indacenes (BODIPYs) have held great promise owing to not only their excellent photophysical properties in the red and NIR regions but also their highly thermal properties. Various synthetic methods, such as metal‐catalyzed coupling, nucleophilic substitution of an aldehyde with pyrroles, and photochemical reactions, enable electronic modification through BODIPY derivatization, according to the working mechanisms of energy devices, including photoelectrochemical cells, dye‐sensitized catalysis for hydrogen production, dye‐sensitized solar cells, organic photovoltaics, and perovskite solar cells. Theoretical and electrochemical studies have supported the use of molecular engineering. This review discusses π ‐expanded BODIPYs and related analogs that have been utilized in energy materials, demonstrating their feasibility as sensitizers for long‐wavelength light.