Photophysical Properties of Platinum(II)−Acetylide Complexes: the Effect of a Strongly Electron-Accepting Diimine Ligand on Excited-State Structure

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• 作者：Christopher J. Adams ; Natalie Fey ; Zoë ; A. Harrison ; Igor V. Sazanovich ; Michael Towrie ; Julia A. Weinstein
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：September 15, 2008
• 年：2008
• 卷：47
• 期：18
• 页码：8242-8257
• 全文大小：437K
• 年卷期：v.47,no.18(September 15, 2008)
• ISSN：1520-510X

文摘

The compounds [Pt(MesBIAN)(CCR)b>2b>] (R = Cb>6b>Hb>4b>−CN-p, <b>1b>; SiMeb>3b>, <b>2b>; Cb>6b>Hb>4b>−CFb>3b>-p, <b>3b>; Cb>6b>Hb>5b>, <b>4b>; Cb>6b>Hb>4b>−CHb>3b>-p <b>5b>) {MesBIAN = bis(mesitylimino)acenaphthene} have been synthesized; the X-ray crystal structure determinations of <b>4b> and <b>5b> and the starting material [Pt(MesBIAN)Clb>2b>] are reported. Chemical oxidation of <b>4b> with diiodine leads to generation of an intermediate platinum(IV) bis(acetylide) diiodide complex, which then couples and reductively eliminates the acetylide ligands as a diyne, leading to the generation of [Pt(MesBIAN)Ib>2b>] <b>6b>. Compound <b>2b> readily forms an adduct <b>2ab> with copper(I) chloride, in which the copper atom is bonded to the two acetylide triple bonds. <b>1−5b> each undergo an irreversible oxidation, and a reversible one-electron reduction to generate a stable anion. ESR studies of <b>1b>^<b>−b>−<b>5b>⁻ show that the unpaired electron is localized mainly on the π* orbital of the coordinated MesBIAN ligand, with about 10% platinum contribution to the singly occupied molecular orbital (SOMO). The compounds show a strong absorption at around 500 nm in the UV/visible spectrum, which is assigned to a “mixed metal−ligand to ligand charge transfer” (MMLL′CT) transition; this assignment is supported by time-dependent density-functional theory (TD-DFT) calculations on <b>5b>. <b>1−5b> emit in the near-infrared region from a ³MMLL′CT excited state, with lifetimes ranging from 8 to 36 ns. Picosecond and nanosecond time-resolved infrared (TRIR) spectroscopy has been used to probe directly the nature and dynamics of the excited state of <b>5.b> The TRIR data show a decrease of the energy of the CC vibration upon excitation, by about 90 cm⁻¹ in comparison to the ground state, and formation of a new, very intense, and very broad band at 1820 cm⁻¹. We propose that the excited-state structure contains some contribution from a pseudo-cumulenic form of the platinum-acetylide moiety, which is supported by TD-DFT calculations. Picosecond TRIR allowed determination of the rate of vibrational relaxation (14 ps) of the vibrationally “hot” electronic excited state of <b>5b> formed upon initial laser excitation.