Supramolecular Chiral Properties Of Cyanostilbene Derivative And Its Metal Complexes

Chiral molecular self-assembly is a frontier topic in supramolecular chemistry.The self-assembly structure and chiral characteristics are changeable under different environment due to the existence of multiple intermolecular interactions.Thus,chiral supramolecular materials show good response to external stimuli.With the development of the field,single chiral signal responsive behaviors cannot fulfill the demand of scientists.The combination of chirality and fluorescence not only opens up the study of circular polarized luminescence characteristics of chiral supramolecules,but also broadens the application of materials in optoelectronic display,molecular recognition,biological imaging and other fields.Cyanostilbene is one of the classical fluorophore,which can emit strong fluorescence in aggregation state.In addition,such structure is easy to be synthesized and modified.The introduction of functional groups endows the molecules with a variety of molecular stacking and stimuli responsive behaviors.Therefore,a novel cyanostilbene derivative(CSPP),modified by chiral cholesteryl group and pyridine group,was prepared.The self-assembly structure,fluorescence and supramolecular chirality of CSPP in the gel state are investigated.Meanwhile,the effects of heat,light,acid and metal ions on the chirality and fluorescence of the supramolecular are also explored.Firstly,CSPP was synthesized by modifying cyanostilbene with chiral cholesterol group and pyridine group.The molecule can form a green fluorescent supermolecular gel in ethyl acetate through ?-? interactions.The gel has obvious right-handed helix fiber morphology and strong negative Cotton chiral signal.Under the stimulation of light and acid,the gel collapses accompanied with the destruction of chiral transfer,leading to fluorescence and chirality quenching.This is due to the trans-cis isomerization of cyanostilbene structure and the protonation effect of pyridine group.Under this premise,the light irradiation at 254 nm and the addition of alkali can restore the molecular configuration,contributing to the regeneration of gel,which exhibits strong green emission and chiral signals.Secondly,we studied the fluorescence and chiral properties of CSPP metallogels.We can get four kinds of metallogels(Zn-CSPP,Mn-CSPP,Co-CSPP,Ni-CSPP)by adding a small amount aqueous solution of metal ions(Zn2+,Mn2+,Co2+,Ni2+)to CSPP tetrahydrofuran solution.Due to the existence of a single unoccupied molecular orbital(SUMO)in the three paramagnetic metal ions(Mn2+,Co2+ and Ni2+),the radiation transition of the main molecules is suppressed,the fluorescence of Mn-CSPP,CoCSPP and Ni-CSPP quenches.However,Zn2+ is a diamagnetic metal ion,and there is no SUMO orbit.Therefore,Zn-CSPP can emit strong green fluorescence.Furthermore,we found that Zn-CSPP shows opposite chiral signals with Mn-CSPP,Co-CSPP and Ni-CSPP.Zn-CSPP has obvious right-handed spiral fibre morphology,but Mn-CSPP,Co-CSPP and Ni-CSPP have left-handed spiral fibre morphology.Chiral signal and morphology of four metallogels indicate that the opposite chirality originates from different helix directions.By the addition of different metal ions,molecule has different fluorescence and chiral properties.This part of the work makes cholesteric single chiral molecules have more chiral performance,and promotes the research in the field of supramolecular chiral precise regulation.