Ground-state electron spin polarization (ESP) is generated in radical elaborated (bpy)Pt(CAT-NN) and (bpy)Pt(CAT--MePhMe-NN) (bpy = 5,5'-di--butyl-2,2'-bipyridine, CAT = 3--butylcatecholate, -Ph = -phenylene, NN = nitronylnitroxide). Photoexcitation produces an exchange-coupled, three-spin, charge-separated doublet S (S = chromophore excited spin singlet configuration) excited state that rapidly decays to a T (T = chromophore excited spin triplet configuration) excited state. The SQ-bridge-NN bond torsions affect the magnitude of the excited state exchange interaction (), which determines the T-T energy gap. Ground state ESP is dependent on the magnitude of , and we postulate that this results from differences in T and T state mixing. Mechanisms that lead to the rapid transfer of the excited state ESP to the ground state are discussed. Although subnanosecond T state lifetimes are measured optically in solution, the ground state ESP decays very slowly at 20 K and is observable for more than a millisecond.
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