Photoexcited Triplet State of Oxotitanium(IV) Tetraphenylporphyrin Studied by ESR and Laser Photolysis. Proton-Induced Quenching of the Triplet State

Article abstract of DOI:10.1021/j150645a011

Absorption spectroscopic studies of TPPTi=O (oxotitanium(IV)tetraphenylporphyrin) in ethanol solution at room temperature revealed that TPPTi=O is in equilibrium with TPPTi=O(EtOH) in which an ethanol molecule, EtOH, is coordinated in the axial position of TPPTi=O.ESR spectra of the triplet TPPTi=O in ethanol, MTHF (2-methyltetrahydrofuran), and toluene solutions were measured at 77 K.The zero-field splitting parameter, D, of TPPTi=O(EtOH) was found to be smaller than that of TPPTi=O free from axial ligand.Laser photolysis studies of acid ethanol solution of TPPTi=O at room temperature showed that the triplet TPPTi=O is efficiently quenched by proton with a rate constant of 3.4 x 1E9 M^-1 s¹.The result suggests that the Ti=O bond in the triplet TPPTi=O is polarized like Ti^δ+=O^δ-.