Mirai Tanaka, E. Ohta, Atsushi Sakai
Aug 14, 2013
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0
Influential Citations
25
Citations
Journal
Tetrahedron Letters
Abstract
Abstract The fluorescence (FL) and structural properties of dibenzoylmethanatoboron difluoride ( 1aBF 2 ) and its diisopropyl derivative ( 1bBF 2 ) in the crystalline state were investigated. Both 1aBF 2 and 1bBF 2 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 ( τ 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 1aBF 2 with average τ 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 τ FL = 5.3 ns is likely the emitting species in the crystalline state of 1bBF 2 . 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 1aBF 2 and 1bBF 2 . Specifically, molecules in crystals of 1aBF 2 are aligned having B-on-B and B-on-D overlap with respective short face-to-face distances (3.50 and 3.42 A) while those in 1bBF 2 are aligned in a single B-on-B overlap mode with a longer face-to-face distance (3.82 A).