Proton coupled electron transfer (PCET) helps to facilitate multi-electron catalytic processes such as water oxidation and carbon dioxide reduction. Moreover, optical excitation can result in more thermodynamically favorable acid/base process and redox behavior for excited states, creating opportunities for PT, ET, PCET reactions not accessible in the ground state. However, short excited state lifetimes of the reactive chromophore (&lt; 1 µs) will serve to limit the range of reactions that can occur. In Ru(II) complexes with pyrene linked to a diimine ligand, an excited state equilibrium between 3MLCT and 3pyrene has been shown to sustain longer lifetimes (~20us in degassed CH3CN). Here, the photoreaction of [Ru(pyr-bpy)2(bpy-OH)]2+ (pyr-bpy = 4-(1”-pyreneyl)-2,2’-bipyridine; bpy-OH = 4-hydroxy-2,2’-bipyridine) and various proton acceptors (pyridine derivatives) is reported. Transient absorption (TA) experiments clearly demonstrate that excited state PCET happens between excited [Ru(II)(bpy-OH)]2+ and MQ+ (N-methyl-4,4’-bipyridinium) and that excited state PT occurs between excited [Ru(II)(bpy-OH)]2+ and substituted pyridine derivatives. Excited state PT (ESPT) products are detected even in reactions with weak proton acceptors. Cage escape efficiencies for ESPT are investigated and display an interesting relationship with pyridinium pKa values. Further investigations about excited state back proton transfer will be discussed as well.

Bimolecular excited state proton transfer and electron transfer of Ru(II) diimine chromophores exhibiting intramolecular reversible energy transfer

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