Deuterated Molecular Ruby with Record Luminescence Quantum Yield

effectively eliminates non-radiative decay pathways, such as photosubstitution, back-intersystem crossing, and trigonal twists. In the absence of energy acceptors, such as dioxygen, the remaining decay pathways are energy transfer to high energy solvent and ligand oscillators, namely OH and CH stretching vibrations. Selective deuteration of the solvents and the ddpd ligands probes the efficiency of these oscillators in the excited state deactivation. Addressing these energy-transfer pathways in the first and second coordination sphere furnishes a record 30 % quantum yield and a 2.3 millisecond lifetime for a metal complex with an earth-abundant metal ion in solution at room temperature.