Core-Structure-Dependent Luminescence of Thiolato-Bridged Copper(I) Cluster Complexes

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• 作者：Kotaro Shimada ; Atsushi Kobayashi ; Yuriko Ono ; Hiroki Ohara ; Tatsuya Hasegawa ; Tetsuya Taketsugu ; Eri Sakuda ; Soichiro Akagi ; Noboru Kitamura ; Masako Kato
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：July 28, 2016
• 年：2016
• 卷：120
• 期：29
• 页码：16002-16011
• 全文大小：559K
• 年卷期：0
• ISSN：1932-7455

文摘

Thiolato-bridged dinuclear, tetranuclear, and hexanuclear Cu(I) complexes [Cu₂(P^∧S)₂(PPh₃)₂], [Cu₄(P^∧S)₄(CH₃CN)₂], and [Cu₆(P^∧S)₆] (abbreviated as Cu₂, Cu₄, and Cu₆, respectively, P^∧S = 2-(diphenylphosphino)benzenethiolate, PPh₃ = triphenylphosphine) were synthesized and characterized by elemental analyses and single-crystal X-ray diffraction measurements. These complexes had {Cu₂S₂}, {Cu₄S₄}, and {Cu₆S₆} cluster cores and exhibited strong luminescence at room temperature in solid states. Different luminescence properties were observed depending on the core structure. Cu₂, Cu₄, and Cu₆ exhibited blue-green (λ_max = 482 nm, Φ_em = 0.52), green (λ_max = 526 nm, Φ_em = 0.19), and yellow (λ_max = 553 nm, Φ_em = 0.49) luminescence, respectively, at 298 K in the solid state; among them, only Cu₆ showed luminescence thermochromism. Different radiative rate constants at room temperature and 78 K derived from the emission lifetimes and quantum yields indicate that the luminescence from Cu₂ and Cu₄ at room temperature originated from thermally activated delayed fluorescence (TADF), whereas the luminescence at low temperatures was attributed to the phosphorescence. The temperature dependence of the emission lifetimes was successfully analyzed by the singlet–triplet two-state model with an energy difference (ΔE_S1-T1) of 547 and 775 cm^–1 for Cu₂ and Cu₄, respectively. Based on the time-dependent density-functional theory calculations, the origin of the luminescence for Cu₂ and Cu₄ was attributed to the charge transfer from the cluster core to the ligand. Moreover, the small values of ΔE_S1-T1 for Cu₂ and Cu₄ were supported by the excited state calculations. On the other hand, the emission origin of Cu₆ was attributed to the phosphorescence from the triplet cluster-centered (³CC) excited state in which the electron is located on a bonding in-phase orbital constructed from the 4s/4p orbitals of the Cu atoms because only Cu₆ contains trigonal-planar Cu(I) ions in the cluster.