Efficient water reduction by ruthenium-picolinate dye-sensitized photocatalyst under red light illumination

To utilize a wider region of the solar spectrum for solar-fuel production, we newly synthesized a heteroleptic Ru (II)-picolinate complex, [Ru(H4dpbpy)2(pic)]+ (Rupic; H4dpbpy = H4dpbpy = 2,2 '-bipyridine-4,4 '-diphosphonic acid, Hpic = picolinic acid) as a red light-absorbing molecular photosensitizer. Rupic exhibited metal-to-ligand charge-transfer (MLCT) absorption and emission (lambda abs and lambda em = 491 and 711 nm, respectively) over a longer wavelength region than that observed with the bipyridine derivative [Ru(H4dpbpy)2(bpy)]2+ (Rubpy, bpy = 2,2 '-bipyridine). The Ru(III)/Ru(II) redox potential of Rupic (Eox = +1.07 vs NHE) was approximately 0.27 V more negative than that of Rubpy, owing to the weaker ligand field strength of pic than that of bpy. Moreover, as expected, owing to the red-light absorption ability of Rupic, the photocatalytic H2 evolution reaction activity of the Rupic-sensitized Pt-TiO2 nanoparticles (apparent quantum yield, AQY - 3 %) under red light illumination (lambda = 625 +/- 35 nm) was significantly higher than that of its Rubpy-sensitized analog (AQY - 0.5 %). These results indicate the superior photosensitizing performance of the Ru(II)-picolinate complex for H2 production under sunlight illumination.

Automated summary

To enhance solar-fuel production, a new heteroleptic Ru (II)-picolinate complex, Rupic, was synthesized as a red light-absorbing molecular photosensitizer. Rupic exhibited metal-to-ligand charge-transfer absorption and emission over a longer wavelength region than its bipyridine derivative, Rubpy. The Rupic-sensitized Pt-TiO2 nanoparticles showed significantly higher photocatalytic H2 evolution reaction activity under red light illumination compared to Rubpy-sensitized analog, indicating the superior photosensitizing performance of Rupic for H2 production under sunlight.