Chen Kew-Yu, Tsai Hsing-Yang
Department of Chemical Engineering, Feng Chia University, Taichung 40724, Taiwan.
Int J Mol Sci. 2014 Oct 17;15(10):18706-24. doi: 10.3390/ijms151018706.
A series of Schiff bases, salicylideneaniline derivatives 1-4, was synthesized under mild conditions and characterized by 1H NMR, HRMS, UV-Vis and fluorescence spectra, and single-crystal X-ray diffraction. In solid and aprotic solvents 1-4 exist mainly as E conformers that possess an intramolecular six-membered-ring hydrogen bond. A weak intramolecular C-H···F hydrogen bond is also observed in fluoro-functionalized Schiff base 4, which generates another S(6) ring motif. The C-H···F hydrogen bond further stabilizes its structure and leads it to form a planar configuration. Compounds 1-3 exhibit solely a long-wavelength proton-transfer tautomer emission, while dipole-functionalized Schiff base 4 shows remarkable dual emission originated from the excited-state intramolecular charge transfer (ESICT) and excited-state intramolecular proton transfer (ESIPT) states. Furthermore, the geometric structures, frontier molecular orbitals (MOs) and the potential energy curves for 1-4 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations.
在温和条件下合成了一系列席夫碱，即水杨醛苯胺衍生物1 - 4，并通过1H NMR、高分辨质谱（HRMS）、紫外 - 可见光谱和荧光光谱以及单晶X射线衍射对其进行了表征。在固态和非质子溶剂中，1 - 4主要以E构象体形式存在，这些构象体具有分子内六元环氢键。在含氟官能化席夫碱4中还观察到一个弱的分子内C - H···F氢键，它形成了另一个S(6)环 motif。C - H···F氢键进一步稳定了其结构并使其形成平面构型。化合物1 - 3仅表现出长波长的质子转移互变异构体发射，而偶极官能化席夫碱4则显示出源自激发态分子内电荷转移（ESICT）和激发态分子内质子转移（ESIPT）态的显著双重发射。此外，通过密度泛函理论（DFT）和含时DFT计算，对1 - 4在基态和第一单重激发态的几何结构、前沿分子轨道（MOs）和势能曲线进行了充分的合理化分析。
