Remarkable difference in fluorescence lifetimes of the crystalline states of dibenzoylmethanatoboron difluoride and its diisopropyl derivative

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• 作者：Mirai Tanaka ; Eisuke Ohta ; Atsushi Sakai ; Yuichi Yoshimoto ; Kazuhiko Mizuno ; Hiroshi Ikeda
• 关键词：Organoboron complex ; Fluorescence ; Excited multimer ; Wave deconvolution ; ¦Ð&ndash ; ¦Ð Stacking
• 刊名：Tetrahedron Letters
• 出版年：2013
• 出版时间：14 August, 2013
• 年：2013
• 卷：54
• 期：33
• 页码：4380-4384
• 全文大小：1065 K

文摘

The fluorescence (FL) and structural properties of dibenzoylmethanatoboron difluoride (1aBF₂) and its diisopropyl derivative (1bBF₂) in the crystalline state were investigated. Both 1aBF₂ and 1bBF₂ in their crystalline states have FL spectra that contain similar emission in the ca. 450-600 nm region, which correspond to emission of green light. However, the FL lifetimes (¦Ó_FL) of these substances in their crystalline states are markedly different. Based on the results of wave deconvolution and decay profile analyses, we tentatively supposed that the FL band of 1aBF₂ with average ¦Ó_FL = 47.7 ns is mainly comprised of FL band from an excited multimer, an emitting domain consisting of three or more molecules. In contrast, an excimer with average ¦Ó_FL = 5.3 ns is likely the emitting species in the crystalline state of 1bBF₂. The results of X-ray crystallographic analyses support the conclusion that these contrasting properties derive from a difference in molecular overlap, especially between the benzene (B) and dioxaborinine (D) rings in the crystalline states of 1aBF₂ and 1bBF₂. Specifically, molecules in crystals of 1aBF₂ are aligned having B-on-B and B-on-D overlap with respective short face-to-face distances (3.50 and 3.42 ?) while those in 1bBF₂ are aligned in a single B-on-B overlap mode with a longer face-to-face distance (3.82 ?).