Solvent-dependent intramolecular charge transfer dual fluorescence of p-dimethylaminobenzanilide bearing steric ortho,ortho-dimethyl substituents at amido aniline
作者:Xuan Zhang、Yun-Bao Jiang
DOI:10.1039/c1pp05208j
日期:2011.11
Intramolecular charge transfer (ICT) dual fluorescence was observed in various organic solvents with p-dimethylaminobenzanilide (DMBA) derivatives bearing ortho-methyl (DMOMBA) and ortho,ortho-dimethyl (DMDMBA) substituents at amido aniline moiety. Ab initio calculation and absorption spectral data indicated that high steric hindrance was introduced by the ortho,ortho-dimethyl substitutions. It was found that, with DMDMBA, the CT emission initially shifted to the red with increasing solvent polarity from cyclohexane (CHX, 480 nm) to diethyl ether (DEE, 520 nm), similar to those of DMBA derivatives with the ortho-, meta- or para-methyl substitutions at amido aniline moiety. However, there is a characteristic blue-shift of the long wavelength emission between DEE and tetrahydrofuran (THF, 424 nm) then a bathochromic shift again in highly polar solvent acetonitrile (ACN, 484 nm). The unusual solvent-dependent CT emission was ascribed to two competitive CT channels. One is benzanilide (BA)-like CT, whose CT reaction occurs from amido aniline to benzoyl moiety in nonpolar solvent CHX and DEE; the other one is p-dimethylaminobenzamide (DMABA)-like, whose CT reaction occurs from dimethylamino to benzanilide moiety in highly polar solvent THF and ACN. These findings revealed the steric effect plays an important role in the ICT process, which may alter the properties of the electron donor and/or acceptor, but also change the reaction potential.
在酰胺苯胺部分带有邻甲基 (DMOMBA) 和邻,邻二甲基 (DMDMBA) 取代基的对二甲氨基苯甲酰苯胺 (DMBA) 衍生物的各种有机溶剂中观察到分子内电荷转移 (ICT) 双荧光。从头计算和吸收光谱数据表明,邻,邻二甲基取代引入了高空间位阻。结果发现,对于 DMDMBA,随着溶剂极性从环己烷 (CHX,480 nm) 到乙醚 (DEE,520 nm) 的增加,CT 发射最初转向红光,与具有邻位、间位的 DMBA 衍生物类似。氨基苯胺部分的-或对甲基取代。然而,DEE 和四氢呋喃(THF,424 nm)之间的长波长发射存在特征性蓝移,然后在高极性溶剂乙腈(ACN,484 nm)中再次出现红移。不寻常的溶剂依赖性 CT 发射归因于两个竞争性 CT 通道。一类是苯甲酰苯胺(BA)类CT,其CT反应是在非极性溶剂CHX和DEE中由酰胺基苯胺生成苯甲酰基部分;另一种是类对二甲氨基苯甲酰胺(DMABA),其在高极性溶剂THF和ACN中发生从二甲氨基到苯甲酰苯胺部分的CT反应。这些发现揭示了空间效应在ICT过程中发挥着重要作用,它可能会改变电子供体和/或受体的性质,但也会改变反应电位。