A Compendium of Methodically Determined Ground- and Excited-State Properties of Homoleptic Ruthenium(II) and Osmium(II) Photosensitizers

Abstract

The one-pot synthesis of a total of 32 ruthenium(II) and osmium(II) photosensitizers bearing substituted 2,2’-bipyridines, 1,10-phenanthrolines, and diaza ligands is reported. Whereas most of these photosensitizers were already reported in the literature, the present study offers extensive datasets of ground- and excited-state properties highly desirable for future development in e. g., machine learning, artificial intelligence, and photoredox catalysis. All photosensitizers absorbed light intensely in the visible part of the spectrum, with the Os(II) photosensitizers absorbing further into the red part. Excited-state lifetimes and photoluminescence quantum yields were generally larger for Ru(II) photosensitizers than for Os(II) analogs, which agrees with the energy gap law. The excited-state redox potentials were determined for all investigated photosensitizers covering a range of −0.21 to −1.35 V vs. SCE for excited-state oxidation and 0.14 to 1.48 V vs. SCE for excited-state reduction. A procedure for counterion exchange to generate the corresponding PF₆⁻, Cl⁻, BF₄⁻, NO₃⁻, OTf⁻, ClO₄⁻, and BAr^F− is reported for six photosensitizers. The synthetic ease, detailed report of fundamental photophysical properties, and a broad range of excited-state redox potentials open opportunities for systematic investigations in several applications and further streamline developments in photoredox catalysis.