Heavy-atom free organic photosensitizers for efficient hydrogen evolution with ? > 600 nm visible-light excitation

Water splitting into H2 via artificial photosynthesis represents an appealing strategy for converting solar energy into fuels. However, commonly used photosensitizers are severely limited by precious metal with narrow visible utilization range. Herein, a library of organic photosensitizers was developed by engineering Bodipy with anthryl and aromatic aldehyde (B-1 - B-6) for enhancing intersystem crossing and extending absorption range. Their absorption can cover over 80% visible regions. Impressively, B-3 can absorb lambda > 600 nm visible light to efficiently sensitize nickel-catalyst to produce over 150 mu L H2. This performance was much higher than that with noble-metal photosensitizer Ru(bpy)32+ (bpy = 2,2 '-bipyridine), representing a breakthrough in developing noble-metal-free photocatalytic systems with long-wavelength excitation. Systematical investigations reveal that B-3 with lambda > 600 nm light absorption, long-lived triplet state and superior photochemical stability greatly boost H2 evolution. This work opens an avenue to construct efficient and sustainable catalytic systems by developing organic photosensitizers with long-wavelength excitation.