Structural and Spectroscopic Study of 6,7-Dicyano-Substituted Lumazine with High Electron Affinity and Proton Acidity
Structural and Spectroscopic Study of 6,7-Dicyano-Substituted Lumazine with High Electron Affinity and Proton Acidity
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高电子亲和力和质子酸性的 6,7-二氰基取代的二甲氧麻嗪的结构和光谱研究
DOI：
10.1021/jp401528c
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发表时间：
2013
期刊：
影响因子：
2.9
通讯作者：
and Tomoyuki Akutagawa
中科院分区：
文献类型：
--
作者：
Ken-ichi Sakai,* Kenta Nagahara;Yuuya Yoshii;Norihisa Hoshino;and Tomoyuki Akutagawa
在C6和C7位置将氰基引入鲁马嗪（蝶啶-2，4-（1H，3H）二酮）中可增强其电子亲和力、质子酸性和在溶剂中的溶解度。结果，6，7-二氰基甲氨嗪（DCNLH 2）与供体如四硫富瓦烯、2，3，5，6-四甲基-1，4-苯二胺和3，3 ′，5，5 ′-四甲基联苯胺形成电荷转移（CT）络合物，并容易从N1氮解离质子以与四丁基铵（TBA+）形成单阴离子盐。CT复合物的晶体结构由混合堆叠组成，其中DCNLH2与供体以面对面的构型相互作用，但它们形成不同的分子间氢键，这取决于供体类型。在TBA+盐中，两个去质子化的DCNLH-单阴离子通过两个中心对称氢键N3-H···O-C2连接形成独特的双阴离子二聚体，该二聚体通过大体积TBA+抗衡阳离子的存在和N1氢键位点处质子的缺失而电子隔离。该二聚体发出黄绿色荧光（荧光量子产率Φ = 0.04）。由于DCNLH-阴离子在水溶液中只显示出微弱的蓝色荧光（Φ <0.01），我们认为二聚体的形成是导致荧光增强的原因，其发射带向低能侧移动。
The introduction of cyano groups into lumazine (pteridine-2,4-(1H,3H)dione) at the C6 and C7 positions enhances its electron affinity, proton acidity, and solubility in solvents. As a result, 6,7-dicyanolumazine (DCNLH2) forms charge transfer (CT) complexes with donors such as tetrathiafulvalene, 2,3,5,6-tetramethyl-1,4-phenylenediamine, and 3,3′,5,5′-tetramethylbenzidine and readily dissociates a proton from the N1 nitrogen to form a monoanionic salt with tetrabutylammonium (TBA+). Crystal structures of the CT complexes consist of mixed stacks in which DCNLH2interacts with donors in face-to-face configurations, but they form intermolecular hydrogen bonds differently depending on the donor type. In the TBA+salt, two deprotonated DCNLH–monoanions form a unique dianionic dimer connected by two centrosymmetric hydrogen bonds, N3–H···O–C2, which is electronically isolated by the presence of bulky TBA+countercations and the absence of a proton at the N1 hydrogen-bonding site. This dimer fluoresces yellowish green (fluorescence quantum yield Φ = 0.04). Because the DCNLH–anion only shows weak blue fluorescence in aqueous solution (Φ < 0.01), we suggest that the dimer formation is responsible for the fluorescence enhancement with a large emission band shift to the low-energy side.