Department of Chemistry & Chemical Engineering, Xi'an University of Arts and Science, Xi'an, Shaanxi 710069, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2012 Nov;97:352-8. doi: 10.1016/j.saa.2012.06.017. Epub 2012 Jun 17.
The photophysical properties of 4-(2-dimethylaminoethyloxy)-N-octadecyl-1,8-naphthalimide (DON) consisting of donor and acceptor units were investigated in different solutions. Changing from a non-polar to a polar solvent increased the solvent interaction and both the excitation and emission spectra were shifted to longer wavelength and intensity decreased through taking advantage of twisted intramolecular charge transfer (TICT). Density functional theory (DFT) calculations and spectral analyses revealed that such fluorophores were capable of sensing protons by intramolecular charge transfer (ICT). Empirical and quantum mechanical calculations showed that the electron donating effect of the dimethylamino group decreased the change in dipole moment on excitation which resulted in a fluorescence quantum yield remarkably enhanced as the solvent polarity increased. In alkaline media the fluorescence of DON was quenched owing to photoinduced electron transfer being disabled in acidic media. The pK(a) of the 1,8-naphthailimide dye was 6.70, which defines the dye as a highly efficient "off-on" switch. DON exhibited a typical aggregation-induced emission enhancement (AIEE) behavior that it is virtually nonemissive in organic solvent but highly luminescent in water, as a result of the restriction of free intramolecular rotation of a C-N bond and the non-planar configuration in the aggregate state. The hydrophobicity of octadecyl group provided DON with a fluorescent response to water based on AIEE and the water-dependent spectral characteristics of DON, and the AIEE of DON caused by the effect of water and formation of J-aggregation states. In the range of 0-79.8% (v/v), the fluorescence intensity of DON in acetone solution increased as a linear function of the water content. The optimum detection limits were of 0.011%, 0.0021%, and 0.0033% of water in acetone, ethanol, and acetonitrile, respectively. Satisfactory reproducibility, reversibility and a short response time were realized.
4-(2-二甲氨基乙氧基)-N-十八烷基-1,8-萘酰亚胺（DON）由给体和受体单元组成，其光物理性质在不同溶液中进行了研究。从非极性溶剂变为极性溶剂会增加溶剂相互作用，通过利用扭曲的分子内电荷转移（TICT），激发和发射光谱都移向更长的波长，强度降低。密度泛函理论（DFT）计算和光谱分析表明，此类荧光团能够通过分子内电荷转移（ICT）感应质子。经验和量子力学计算表明，二甲氨基的供电子效应降低了激发时偶极矩的变化，导致荧光量子产率随着溶剂极性的增加而显著增强。在碱性介质中，由于在酸性介质中光诱导电子转移被禁用，DON 的荧光被猝灭。1,8-萘酰亚胺染料的 pK(a)为 6.70，这表明该染料是一种高效的“开-关”开关。DON 表现出典型的聚集诱导发射增强（AIEE）行为，即在有机溶剂中几乎不发光，但在水中高度发光，这是由于 C-N 键的自由分子内旋转受限和聚集态的非平面构型所致。十八烷基的疏水性使 DON 具有基于 AIEE 的对水的荧光响应，以及 DON 对水的依赖的光谱特性，以及 DON 由于水的影响和 J-聚集态的形成而产生的 AIEE。在 0-79.8%（v/v）范围内，DON 在丙酮溶液中的荧光强度随含水量呈线性增加。在丙酮、乙醇和乙腈中，DON 的最佳检测限分别为 0.011%、0.0021%和 0.0033%的水。实现了令人满意的重现性、可逆性和短的响应时间。
