阴离子配位抑制偶氮苯型分子镊子热弛豫行为研究

Anion coordination suppressed thermal relaxation of azobenzene based molecular twezzers

偶氮苯型“分子镊子”通过不同波长的光照刺激实现底物的结合与释放,在分子识别、催化和跨膜传输等领域受到广泛关注.其中,热弛豫作为光开关分子最基本的光物理化学行为之一,与底物螯合效应和分子结构的电荷分布相关,其机理研究对设计新型光控体系具有指导意义.阳离子或中性底物与顺式偶氮异构体的螯合作用能够抑制偶氮苯分子的热弛豫速率.然而,阴离子底物配位往往加快其热弛豫速率.这主要是因为阴离子配位使得偶氮双键区域的电荷密度增加,降低了顺式异构体稳定性.为解决这一问题,本文设计了双(苯基邻位二脲)的偶氮苯型配体,利用预组织的多重氢键作用,提高了配体与阴离子配位强度,减弱了电荷密度增加的影响,成功实现了对偶氮苯热弛豫速率的抑制.相比于自由配体,氯离子配位的单螺旋结构的热弛豫速率下降20%,硫酸根离子配位组装的双螺旋结构的热弛豫速率下降50%.

The azobenzene-based molecular tweezers can regulate the uptake and release of substrate upon light irradiation making it extensively studied in the fields of molecular recognition,catalysis,and transmembrane transport.The investigation of thermal relaxation behaviors contributes to understanding the photochemical and photophysical properties of photoswitch molecules and provides design principles of new azobenzene molecules.Strong coordination of cationic or neutral substrates with the cis isomer can suppress the thermal relaxation rate of azobenzene units.However,due to the increased charge density in the azobenzene double bond region,anion coordination typically accelerates the thermal relaxation rate.In this study,azobenzene-based bis-bis(urea)ligands were designed.With enhanced multiple hydrogen bonding interactions,the thermal relaxation rate of azobenzene was successfully suppressed upon anion coordination.Compared with the free ligand,the thermal relaxation rate of chloride-coordinated single helix was decreased by 20%,and the thermal relaxation rate of sulfate-coordinated double helicate was decreased by50%.