Computational Studies on the Excited States of Luminescent Platinum(II) Alkynyl Systems of Tridentate Pincer Ligands in Radiative and Nonradiative Processes

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• 作者：Wai Han Lam ; Elizabeth Suk-Hang Lam ; Vivian Wing-Wah Yam
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：October 9, 2013
• 年：2013
• 卷：135
• 期：40
• 页码：15135-15143
• 全文大小：433K
• 年卷期：v.135,no.40(October 9, 2013)
• ISSN：1520-5126

文摘

Platinum(II) alkynyl complexes of various tridentate pincer ligands, [Pt(trpy)(C鈮R)]⁺ (trpy = 2,2鈥?6鈥?2鈥?terpyridine), [Pt(R鈥?bzimpy)(C鈮R)]⁺ (R鈥?bzimpy = 2,6-bis(N-alkylbenzimidazol-2鈥?yl)pyridine and R鈥?= alkyl), [Pt(R鈥?bzimb)(C鈮R)] (R鈥?bzimb = 1,3-bis(N-alkylbenzimidazol-2鈥?yl)benzene and R鈥?= C₄H₉), have been found to possess rich photophysical properties. The emission in dilute solutions of [Pt(trpy)(C鈮R)]⁺ originated from a triplet alkynyl-to-tridentate pincer ligand-to-ligand charge transfer (LLCT) excited state, with mixing of a platinum-to-tridentate pincer ligand metal-to-ligand charge transfer (MLCT) excited state, while that of [Pt(R鈥?bzimb)(C鈮R)] originated from a triplet excited state of intraligand (IL) character of the tridentate ligand mixed with a platinum-to-tridentate ligand MLCT character. Interestingly, both emissions were observed in [Pt(R鈥?bzimpy)(C鈮R)]⁺ in some cases. In addition, [Pt(R鈥?bzimb)(C鈮R)] displayed a photoluminescence quantum yield higher than that of [Pt(R鈥?bzimpy)(C鈮R)]⁺. Computational studies have been performed on the representative complexes [Pt(trpy)(C鈮Ph)]⁺ (1), [Pt(R鈥?bzimpy)(C鈮Ph)]⁺ (2), and [Pt(R鈥?bzimb)(C鈮Ph)] (3), where R鈥?= CH₃ and Ph = C₆H₅, to provide an in-depth understanding of the nature of their emissive origin as well as the radiative and nonradiative processes. In particular, the factors governing the ordering of the triplet excited states and radiative decay rate constants of the emissive state (³ES) have been examined. The potential energy profiles for the deactivation process from the ³ES via triplet metal-centered (³MC) states have also been explored. This work reveals for the first time the potential energy profiles for the thermal deactivation pathway of square planar platinum(II) complexes.