An inorganic application of transient direct current photoconductivity: corroboration of a charge-transfer assignment for the luminescing states of Pt(dpphen)(ecda)1.

Transient direct current photoconductivity (TDCP) is an experimental technique capable of providing information about the sign and magnitude of differences in dipole moment, μ, for the ground state versus an excited state of an uncharged molecular chromophore in solution.2 Briefly, the technique utilizes a static, external electric field to achieve partial orientation of dipolar molecules, as shown in Scheme 1. If photoexcitation leads to a change in dipole moment, the molecules will become either more completely (increase in μ) or less completely (decrease in μ) oriented by the field. In either case, the change, together with the accompanying rotational motion (see Scheme 1), is equivalent to a transient flow of positive charge toward a negative electrode and vice versa. The charge flow will persist until the rotational reorientation is finished, and then it will reverse when the molecule returns to its ground electronic state. The reorientation and associated buildup of charge can be tracked by monitoring the transient photovoltage generated across the TDCP cell. Braun and Smirnov, in particular, have shown how the TDCP methodology can be utilized to (a) evaluate the degree of photoinduced charge transfer, (b) measure net electron-transfer distances, and/or (c) monitor excited-state rotational correlation times for various light-absorbing organic compounds.2 To the best of our knowledge, however, the technique has yet to be applied to inorganic systems. An illustrative application to a representative diimine, dithiolate complex of Pt(II) is the focus of this Note.