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• 作者：Zhongjing Li ; Ekaterina Badaeva ; Angel Ugrinov ; Svetlana Kilina ; Wenfang Sun
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：July 1, 2013
• 年：2013
• 卷：52
• 期：13
• 页码：7578-7592
• 全文大小：979K
• 年卷期：v.52,no.13(July 1, 2013)
• ISSN：1520-510X

文摘

Six new platinum(II) chloride complexes 1鈥?b>6 containing a 6-[9,9-di(2-ethylhexyl)-7-R-9H-fluoren-2-yl]-2,2鈥?bipyridine (R = NO₂, CHO, benzothiazol-2-yl (BTZ), n-Bu, carbazol-9-yl (CBZ), NPh₂) ligand were synthesized and characterized. The influence of the electron-donating or electron-withdrawing substituent at the 7-position of the fluorenyl component on the photophysics of these complexes was systematically investigated by spectroscopic methods and simulated by time-dependent density functional theory (TDDFT). Electron-withdrawing or -donating substituents exert distinct effects on the photophysics of the complexes. All complexes feature a low-energy, broad ¹MLCT (metal-to-ligand charge transfer)/¹ILCT (intraligand charge transfer)/¹蟺,蟺* absorption band (tail) above ca. 430 nm and a major absorption band(s) between 320 and 430 nm, which admix ¹MLCT, ¹蟺,蟺*, ¹ILCT, and/or ¹LLCT (ligand-to-ligand charge transfer) characters. The contributions of different configurations to the major absorption band(s) vary depending on the nature of the substituent. Strong electron-donating or -withdrawing substituents (NPh₂ and NO₂) and the aromatic substituent BTZ cause a pronounced red-shift of the absorption spectra of 1, 3, and 6. All complexes are emissive at room temperature and at 77 K. The emitting excited state is dominated by ³蟺,蟺* character in 1鈥?b>3, with some contributions from ³MLCT in 1 and 2, while the emission is predominantly from the ³MLCT state for 4 and 5 but with some ³蟺,蟺* character. For 6, the emitting state is ³ILCT in nature. With the increased electron-donating ability of the substituent, the ³蟺,蟺* character diminishes while charge transfer character increases. All complexes exhibit broad and strong triplet excited-state absorption (TA) from the near-UV to the near-IR spectral region. The TA band maxima are red-shifted for complexes 1鈥?b>3 (which possess the electron-withdrawing substituents) compared to those of 4鈥?b>6 (which contain electron-donating substituents). All complexes manifest strong reverse saturable absorption (RSA) for a nanosecond laser pulse at 532 nm, which originates from the much stronger triplet excited-state absorption than the ground-state absorption of 1鈥?b>6 in the visible spectral region. The strength of RSA follows this trend: 4 鈮?5 < 1 鈮?3 < 2 < 6, which is primarily determined by the ratio of the triplet excited-state absorption cross section relative to that of the ground-state absorption (蟽_ex/蟽₀) at 532 nm. The 蟽_ex/蟽₀ ratios (116鈥?61) of 1鈥?b>6 at 532 nm are much larger than those of most of the reverse saturable absorbers reported in the literature, with the ratio of 6 (蟽_ex/蟽₀ = 261) being among the largest values reported to date. This makes complexes 1鈥?b>6, especially 6, very promising reverse saturable absorbers.