화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.113, No.23, 6430-6436, 2009
Electron Transfer in Platinum(II) Diimine-Centered Triads: Mechanistic Insights from Photoinduced Transient Displacement Current Measurements
The consequences of photoexcitation of a platinum diimine bisacetylide complex and its triads with phenothiazine species (McGarrah, J. E.; Eisenberg, R. Inorg. Chem. 2003, 42, 4355-4365) were investigated by the photoinduced transient displacement current (PTDC) method, with the aim of understanding the role of solvent in defining the nature and extent of intratriad electron transfer. PTDC enables reports on the distance of charge separation in photoexcited states. Photoexcition of the triad, Pt(dbbpy)(CCC6H4CH2(PTZ))(2) (where dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine), leads to formation of the (MLCT)-M-3 excited state, which in CH2Cl2 is intramolecularly quenched by PTZ to form a charge-separated (CS) state, Pt(dbbpy(center dot-))(CCC6H4CH2(PTZ) CCC6H4CH2(PTZ(center dot+)); the CS state features a dipole moment oriented in essentially the opposite direction to that of the (ground state. In toluene the last step of charge separation is shut down. In THF these two transient states are equilibrated, approximately as a 1:1 mixture of (MLCT)-M-3 and CS states, causing a complex, but instructive, PTDC response. The PTDC response for Pt(dbbpy)(CCC6H5)(2), on the other hand, is similar in all solvents and shows a negative signal corresponding to a long-lived, and comparatively nonpolar, (MLCT)-M-3 state. The ground-state dipole moment, mu g, weakly increases with solvent polarity. from similar to 11.5 D in toluene to similar to 15.5 D in THF and CH2Cl2.