In 1974, the metal-to-ligand charge transfer (MLCT) excited state,
[Ru(bpy)3]2+*, was shown to undergo electron transfer
quenching by methylviologen dication (MV2+), inspiring a new approach
to artificial photosynthesis based on molecules, molecular-level phenomena, and
a “modular approach”. In the intervening years, application of synthesis,
excited-state measurements, and theory to [Ru(bpy)3]2+*
and its relatives has had an outsized impact on photochemistry and photophysics.
They have provided a basis for exploring the energy gap law for nonradiative
decay and the role of molecular vibrations and solvent and medium effects on
excited-state properties. Much has been learned about light absorption,
excited-state electronic and molecular structure, and excited-state dynamics on
timescales from femtoseconds to milliseconds. Excited-state properties and
reactivity have been exploited in the investigation of electron and energy
transfer in solution, in molecular assemblies, and in derivatized polymers and
oligoprolines. An integrated, hybrid approach to solar fuels, based on
dye-sensitized photoelectrosynthesis cells (DSPECs), has emerged and is being
actively investigated.