Pt^II Diimine Chromophores with Perfluorinated Thiolate Ligands: Nature and Dynamics of the Charge-Transfer-to-Diimine Lowest Excited State

The synthesis of new Pt^II diimine complexes bearing perfluorinated thiolate ligands, Pt^II(NN)(4-X-C₆F ₄-S)₂, where NN = 2,2′-bipyridine or 1,10-phenanthroline and X = F or CN, is reported, together with an investigation of the nature and dynamics of their lowest excited states. A combined UV-vis, (spectro)electrochemical, resonance Raman, and time-resolved infrared (TRIR) study has suggested that the HOMO is mainly composed of thiolate(φ)/S(p)/Pt(d) orbitals and that the LUMO is largely localized on the φ* (diimine) orbital, thus revealing the {charge-transfer-to-diimine} nature of the lowest excited state. An enhancement of the thiolate ring vibrations, C-F vibrations, and the vibration of the CN-substituent on the thiolate moiety was observed in the resonance Raman spectra, whereas no such enhancement was seen for the nonfluorinated analogues. Thus, the introduction of fluorine substituents on the thiolate moiety probably leads to a more pronounced contribution of the intrathiolate modes to the HOMO compared to the analogous complexes with nonfluorinated thiolates. Furthermore, the introduction of the p-CN group into the thiolate moiety has allowed the dynamics of the lowest excited state of Pt(bpy)(4-CN-C₆F ₄-S)₂ to be monitored by picosecond TRIR spectroscopy. The dynamics of the lowest {charge-transfer-to-diimine} excited state are governed by ca. 2-ps vibrational cooling and 35-ps back electron transfer.