Supramolecular Chemistry Based On Crown Ether Derivatives

Crown ether and its derivatives is one kind of the most widely used hosts in supramolecular chemistry.Here we studied the substituent effects on the complexation between dibenzo-24-crown-8-based cryptand and paraquat derivatives and the application of functionalized crown in fluorescence chemosensor.Dibenzo-24-crown-8-based cryptand 1 forms 1:1 inclusion complexes with three paraquat derivatives,P1,P2,and P3,as demonstrated by proton NMR spectroscopy and X-ray analysis. However,it was found that methyl-substituted paraquat derivatives,P2 and P3,can bind cryptand 4 more strongly than non-methyl-substituted paraquat derivative P1.The association constants(K_a)were determined in acetone by using a UV-Vis titration method to be 5.0×10³ M^-1for 4·P1,1.0×10⁵ M^-1for 4·P2,and 1.2×10⁵ M^-1for 4·P3,respectively.In the solid state,4·P2 and 4·P3 have similar T-type inclusion complexation conformations,which are very different from the pseudorotaxane-type complexation conformation of 4·P1.Theoretical calculations were done to explain these experimental results.A bis(m-phenylene)-32-crown-10-based host to which are covalently attached two pyrene groups as fluorescence chromophores was designed and synthesized.Its complexations with paraquat(PQ)and diquat(DQ)were studied by proton NMR,ESI mass spectrometry and UV-Vis spectroscopy.Its chemosensor behavior to PQ and DQ was revealed by fluorescence emission spectroscopy.This new host can function as a fluorescence chemosensor for PQ and DQ due to the inhibition of photoinduced electron transfer between the bis(m-phenylene)-32-crown-10 moiety and the pyrene groups by the addition of PQ(or DQ).An AB monomer based on bis(m-phenylene)-32-crown-10-based cryptand of supramolecular polymer and its template compound based on simple crown ether were designed and synthesized.