摘要
The synthesis, electronic spectra, photochemical properties, and DFT calculations of four phenylpyridine (ppy)-derived C^N ligands and their cyclometalated [(C^N)Pt(II)(acac)] (C^N = trans-n-(4-NR 2 -styryl)-2- phenylpyridine, where n = 3′ or 4 and R = Me or Ph, and acac = acetylacetonate) complexes are reported. The results allow one to address the effects of the styryl position (n = 3′ or 4) and the amino N-substituents (N-Me or N-Ph) on the photoluminescence and trans → cis photoisomerization quantum efficiencies (φ f and φ tc ) of the free ligands and the Pt complexes. In general, the styryl position effect is more significant than the amino substituent effect. The relative φ f and φ tc values are distinct between the free ligands and the corresponding Pt complexes. However, the phenomenon of φ f + 2φ tc ≈ 1.0 is observed for all cases in solutions at room temperature. This phenomenon is interpreted by the conventional one-bond-twist mechanism for photoisomerization, which is an activated process in S 1 but barrierless in T 1 . We conclude that ca. 50% of the C=C bond torsion in the excited-state manifold leads to the cis isomer and the excited-state deactivations are dominated by fluorescence and trans → cis isomerization for both the ligands and the complexes. © 2012 American Chemical Society.