title: Photoluminescence and trans → cis photoisomerization of aminostyrene-conjugated phenylpyridine C^N ligands and their complexes with platinum(II): the styryl position and the amino substituent effects.
abstract: 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-NR2-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 (Φf and Φtc) of the free ligands and the Pt complexes. In general, the styryl position effect is more significant than the amino substituent effect. The relative Φf and Φtc values are distinct between the free ligands and the corresponding Pt complexes. However, the phenomenon of Φf + 2Φtc ≈ 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 S1 but barrierless in T1. 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.
authors: Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.
authors: Che-Jen
authors: CJ
authors: Lin
authors: Yi-Hung
authors: YH
authors: Liu
authors: Shie-Ming
authors: SM
authors: Peng
authors: Jye-Shane
authors: JS
authors: Yang