On the ambiguity of 1,3,2-benzodiazaboroles as donor/acceptor functionalities in luminescent molecules
作者:Lothar Weber、Johannes Halama、Kenny Hanke、Lena Böhling、Andreas Brockhinke、Hans-Georg Stammler、Beate Neumann、Mark A. Fox
DOI:10.1039/c3dt52836g
日期:——
A series of 1,3-bis(perfluoroaryl)-2-(hetero)aryl-1,3,2-benzodiazaboroles, 1,3-FAr2-2-Ar-1,3,2-N2BC6H4 (Ar = Ph, FAr = C6F55; Ar = Ph, FAr = 4-C5F4N 6; Ar = Ph, FAr = 4-NCC6F47; Ar = 2-C4H3S, FAr = C6F58; Ar = 2-C4H3S, FAr = 4-C5F4N 9; Ar = 2-C4H3S, FAr = 4-NCC6F410), were synthesised by cyclocondensation of the adducts PhBBr2·PPh3 or 2-thienylBBr2·PPh3 with N,N′-bis(perfluoroaryl)-o-phenylenediamines in the presence of 2,2,6,6-tetramethylpiperidine. Similar treatments of the PPh3 adducts of 4-(1′,3′-diethyl-1′,3′,2′-benzodiazaborolyl)-phenyldibromoborane with the corresponding diamines gave rise to the push–pull compounds, C6H4(NEt)2B-1,4-C6H4-B(NFAr)2C6H4 (FAr = C6F511; 4-C5F4N 12) and C6H4(NEt)2B-2,5-C4H2S-B(NFAr)2C6H4 (FAr = C6F513; 4-C5F4N 14). The X-ray structures of 8, 11, 12 and 13 were determined. Electronic structure calculations reveal that the LUMOs are located at the perfluoroaryl groups in 5–14; thus the fluorinated benzodiazaborolyl groups are considered as electron-withdrawing moieties. These moieties differ from alkylated benzodiazaborolyl groups which are regarded as donors. The emission spectra for 5–14 show charge transfer bands with significant solvatochromism and large Stokes shifts (6100–12 500 cm−1 in cyclohexane and 8900–15 900 cm−1 in CH2Cl2). The emissions of the benzodiazaboroles, 5–10, arise from a different charge transfer (CT) process to the local charge transfer (LCT) process typically found in many fluorescent benzodiazaboroles. This novel remote charge transfer (RCT) process involving the perfluoroaryl groups is supported by CAM-B3LYP computations. The push–pull systems 11–14 here give fluorescent emissions with moderate to high fluorescence quantum yields (65–97%) that arise from the usual LCT process only.
一系列 1,3-双(全氟芳基)-2-(杂)芳基-1,3,2-苯并二硼烷,1,3-FAr2-2-Ar-1,3,2-N2BC6H4(Ar = Ph,FAr = C6F55;Ar = Ph,FAr = 4-C5F4N 6;Ar = Ph,FAr = 4-NCC6F47;Ar = 2-C4H3S,FAr = C6F58;Ar = 2-C4H3S,FAr = 4-C5F4N 9;Ar = 2-C4H3S,FAr = 4-NCC6F410)的加合物 PhBBr2-PPh3 或 2-thienylBBr2-PPh3 与 N,N′-双(全氟芳基)-邻苯二胺在 2,2,6,6-四甲基哌啶存在下进行环缩合而合成。4-(1′,3′-diethyl-1′,3′,2′-benzodiazaborolyl)-phenyldibromoborane 的 PPh3 加合物与相应的二胺进行类似处理后,产生了推拉化合物 C6H4(NEt)2B-1,4-C6H4-B(NFAr)2C6H4 (FAr = C6F511;4-C5F4N 12)和 C6H4(NEt)2B-2,5-C4H2S-B(NFAr)2C6H4 (FAr = C6F513; 4-C5F4N 14)。测定了 8、11、12 和 13 的 X 射线结构。电子结构计算显示,5-14 中的 LUMO 位于全氟芳基上,因此氟化苯并二唑硼烷基团被认为是电子吸收分子。这些分子与被视为供体的烷基化苯并二氮硼酰基不同。5-14 的发射光谱显示电荷转移带具有明显的溶解色和较大的斯托克斯偏移(环己烷中为 6100-12 500 cm-1,CH2Cl2 中为 8900-15 900 cm-1)。苯并二氮硼化合物 5-10 的发射来自不同的电荷转移(CT)过程,与许多荧光苯并二氮硼化合物中常见的局部电荷转移(LCT)过程不同。这种涉及全氟芳基的新型远程电荷转移(RCT)过程得到了 CAM-B3LYP 计算的支持。推拉系统 11-14 发出的荧光具有中等到较高的荧光量子产率(65-97%),而这些荧光量子产率仅来自通常的 LCT 过程。