Probing Triplet State Properties of Organic Chromophores via Design and Synthesis of Os(II)-Diketonate Complexes: The Triplet State Intramolecular Charge Transfer

We report the probe of specific triplet state properties of organic chromophores that are otherwise inaccessible in low viscous solution. The prototypical example demonstrated here is [Os(CO)₃(Cl)(NDP)] (1) ((NDP)H = 2-naphthyl-7-dimethylanilino-1,3-propanedione), which, upon electronic excitation, undergoes intramolecular charge transfer in both S₁ and T₁ manifolds of NDP. The dipolar changes in S₁ and T₁ monitored via the solvatochromism for both fluorescence and phosphorescence were deduced to be 18.0 and 11.9 D, respectively. The appreciable difference in the dipolar change can be qualitatively rationalized by different extents of charge-transfer character between S₁ and T₁ states. The results led to the probe of other reactions in triplet manifold feasible.