含手性亚胺侧基聚苯乙烯衍生物的设计及其在酸碱诱导下的手光响应性质

以N-(2-羟基-1-萘基)亚甲基-(S)-α-苯基乙胺为模型分子,考察了脱质子前后该手性Schiff碱溶液手光性质的变化,利用DFT计算探讨手光信号反转机理.结果表明,手光反转源于分子内氢键的断裂与形成及伴随的C—C单键旋转所引起的构象转变,且前后2种构象处于拟对映关系.这一发现意味着通过单键旋转操控分子构象转变可作为构建手性开关的一种有效途径.在此基础上设计、合成了苯乙烯型手性功能单体(VNP)及相应的光学活性聚合物.由于邻位基团的协同效应,聚合物的手光性质对酸碱刺激表现出比单体更灵敏的响应性和可重复性.当循环加入H+和OH-时,聚合物溶液的CD信号(382 nm处的Cotton效应)以"ON"-"OFF"方式发生可逆转变,以此为输出信号可无损耗重复至少5次,实现了通过酸碱调控的无损输出的新型聚合物基手性开关.此外,基于该手性开关体系构建了典型的"禁阻"(IHIBIT)分子逻辑门.

DESIGN OF AN OPTICALLY ACTIVE POLYSTYRENE BEARING IMINE PENDANTS AND ITS ACID/BASE-TRIGGERED CHIROPTICAL SWITCH PROPERTY

The chiroptical properties of N-(2-hydroxy-1-naphthyl)methylidene-(S)-α-phenylethylamine(s-1) were studied as a model of chiral molecular switches.The Schiff base exhibited a pH-responsive chiroptical inversion behavior as a result of breaking and forming of the intramolecular hydrogen bonding and accompanying C—C single bond rotation far away from the chiral center.DFT computation results showed that both two preferred conformers of s-1 and its deprotonated species are stereochemically quasi-enantiotropic.On the basis of these findings we designed a chiral styrene-type monomer(VNP) containing imine linkage and synthesized corresponding polymers through RAFT technique.It was found that the chiroptical properties of PVNPs are highly sensitive to acid/base stimulus.The addition of acid produced an intensive Cotton effect at 382 nm for the THF solution of polymer,which is probably derived from the dissymmetric spatial arrangement of interacting chromophores in adjacent pendent groups due to the protonation of imine moiety.Furthermore,the CD signal can be totally reversed with addition of base.Chiroptical signals remained consistent after five acid-base reaction cycles,proving that a robust polymer-based chiroptical switch was established.This promising new type of chiroptical switches is relatively unique as it does not involve any covalent bond formation/breakage or conformational transition of polymer main chains and thus possess distinct advantages,such as fast switching rate,high reversibility and fatigue resistance as well as the nondestructive readout.Using such a reversible and reproducible chiral switching system,we designed the IHIBIT molecular logic gate that might have potential uses in information processing at molecular level.