Chiral Recognition Of Monoalcohols By Amide-Linked Trisporphyrinate Or Bispophyrinates

Porphyrins are considered to be one of the most useful chromophores for using exciton coupling circular dichroism?ECCD?spectroscopy to determine the absolute configuration of chiral substrates.In the visible region,the intense Soret band provides the basis for their satisfactory chirogenic performance and it couldn't be interrupted by other small oranic molecule.In the past few years,many researches were concentrated on the bisporphyrins and bidentate guests,a few of them were about monodentate guests,such as mono-amines.There were few of studies on mono-alcohols because of their lower binding ability to metals.In this paper,we designed a benzene tricarboxamide-linked trisporphyrinate?[Zn₃-BTATPP]?to conduct chiral recognition of mono-alcohols.[Zn₃-BTATPP]has two“spaces”surrounded by three porphyrin moieties.Upon coordinating with a chiral guest,the tree porphyrin chromophores become mutually twisted and form a stable conformation because they encompass the guest in the binding fence,and the chirality of the guest is detected by CD spectroscopy.[Zn₃-BTATPP]has shown extremely high CD sensitivity for a chiral mono-alcohol 1-?1-naphthyl?ethanol,at?M level,which is at least two orders of magnitude lower concentration than other mono-alcohols and three orders than previous reports.The crystal structure of the complex formed between[Zn₃-BTATPP]and S-1-?1-naphthyl?ethanol indicates that there are many weak interactions to stabilize the host-guest complex,such as coordination interactions,hydrogen bonding,?-?and C-H---?interactions etc.UV-vis and CD spectroscopic studies suggest the corresponding binding constant K₁ is over 10⁵ M^-1,which is the largest for a chirality induction process involving porphyrin and mono-alcohol systems.The well complementarity size of the host-guest complex enhances the sensitivity greatly and makes it possible to determine the ee values for 1-?1-naphthyl?ethanol at low concentration.The DFT optimized structure and the corresponding TDDFT calculations were consistent with experimental results.In the other part,three new m-phthalic diamide-linked bisporphyrins were used to determine the absolute configuration of mono-alcohols.They all performed great recognition ability and had similar CD strength comparing with other systems,but weaker than the above trisporphyrinate.The studies on the chiral recognition mechanism are under investigation.