Novel Dimeric o-Carboranyl Triarylborane: Intriguing Ratiometric Color-Tunable Sensor via Aggregation-Induced Emission by Fluoride Anions

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• 作者：Byung Hoon Choi ; Ji Hye Lee ; Hyonseok Hwang ; Kang Mun Lee ; Myung Hwan Park
• 刊名：Organometallics
• 出版年：2016
• 出版时间：June 13, 2016
• 年：2016
• 卷：35
• 期：11
• 页码：1771-1777
• 全文大小：381K
• 年卷期：0
• ISSN：1520-6041

文摘

A dimeric o-carboranyl triarylborane compound (2) with a biphenylene bridge group was prepared and characterized. Also, its solid-state structure was determined via X-ray diffraction. Treatment of 2 with an excess amount of KF in the presence of 18-crown-6 formed a dimer-type potassium salt, [2·F₂][K·18-crown-6]₂; its structure was fully confirmed by multinuclear NMR spectroscopy. UV–vis titration experiments carried out in THF showed that 2 binds fluoride ions with a binding constant (K) of 8.5 × 10⁵ M^–1. The linear decline of the UV/vis absorption of 2 upon titration with fluoride suggested that the triarylborane moieties acted as independent binding sites, which were not affected by each other. Contrary to a single emission (λ_em = 376 nm) of 2 assignable to an intramolecular charge transfer (ICT) transition at 298 K in THF, a broad low-energy emission band was additionally observed at 77 K, which is dominant in the film state. The TD-DFT calculation on the first excited singlet state (S₁) of 2 shows that the low-energy emission band originates from the CT nature between carborane and triarylborane groups. Aggregation-induced emission (AIE) of 2 was clearly confirmed by enhanced photoluminescence intensity (λ_em = 489 nm) upon increasing the water fraction (f_w) in the THF solution of 2, and it further accounts for the intense emission in the solid state. Interestingly, the emission spectrum of a film sample of 2 upon addition of two equivalents of fluoride ion was was mostly similar to that of [2·F₂][K·18-crown-6]₂, indicating that the ICT-based AIE nature of 2 could be red-shifted by fluoride binding.