Steric hindrance-induced dual fluorescence of congested benzenehexacarboxylates
Steric hindrance-induced dual fluorescence of congested benzenehexacarboxylates
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空间位阻诱导的拥挤苯六羧酸盐的双荧光
DOI：
10.1021/ja00006a011
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发表时间：
1991
影响因子：
15
通讯作者：
S. Takamuku
中科院分区：
文献类型：
--
作者：
N. Yamasaki;Y. Inoue;Taizo Yokoyama;A. Tai;A. Ishida;S. Takamuku
烷基苯四和苯hexacarboxylates被证明在流体溶液中发出微弱的荧光，与完全无荧光的单，二，或三羧酸形成鲜明对比。有趣的是，苯hexacarboxylates与庞大的烷基提供了一种新的双荧光分子系统，涉及不同的机制，从有据可查的准分子形成，质子化/去质子化，或扭曲的分子内电荷转移。因此，异丙基，叔丁基，（-）-庚基，（-）-薄荷基，和1-金刚烷醇的六羧酸酯显示明确的，体积依赖性的双荧光峰，在室温和/或低温下的小和相当大的斯托克斯位移，而六甲酯和相应的四羧酸酯与庞大的烷基从来没有显示这种不寻常的荧光行为。这种双重荧光现象归因于由于相邻的大体积烷基之间的空间位阻而导致的激发态构象弛豫减速。
Alkyl benzenetetra-and benzenehexacarboxylates were shown to fluoresce weakly in fluid solutions, in sharp contrast to entirely nonfluorescent mono-, di-, or tricarboxylates. Interestingly, benzenehexacarboxylates with bulky alkyl groups provide a novel dual-fluorescing molecular system involving a mechanism differing from the well-documented excimer formation, protonation/deprotonation, or twisted intramolecular charge transfer. Thus hexacarboxylates of isopropyl, rert-butyl,(-)-bornyl,(-)-menthyl, and 1-adamantyl alcohols show unambiguous, bulkiness-dependent dual fluorescence peaks with both small and substantially large Stokes shifts at room and/or low temperatures, whereas the hexamethyl ester and the corresponding tetracarboxylates with bulky alkyl groups never show such unusual fluorescence behavior. This dual fluorescence phenomenon is attributed to the decelerated conformational relaxation in the excited state owing to steric hindrance between adjacent bulky alkyl groups.