Synthesis,Characterization And Properties Of Triazole-based Pyridinium Salts

Pyridinium salt is an important class of six-membered nitrogen heterocyclic compounds.Due to special physical and chemical properties,such as aromaticity,basicity,and electrophilic effects,pyridinium salt compounds are not only important intermediates for organic synthesis but also play a vital role in the field of non-linear optical materials and biological aspects.Therefore,it is of great theoretical significance and application value to design and synthesize novel pyridinium salts with versatility.Nitrogen-rich triazole groups are a five-membered system.It has good reactivity and biological activity.It can be used as an intermediate in organic synthesis,which forms a conjugated system with other structures to increase the fluorescence properties of the whole molecule.However,to the best of our knowledge,triazole-based pyridinium salts have never been reports so far.The specific research contents are as follows:?1?Synthesis and characterization of triazole-based pyridinium salts.Three kinds of?-monosubstituted triazole-based pyridinium salts 3a³c and four kinds of?-dissubstituted triazole-based pyridinium salts 3d³g were designed and synthesized by the reaction of pyrylium salts with 3-amino-1,2,4-triazole.The structure of seven molecules was characterized by ¹H NMR,¹³C NMR,MS and X-ray analysis.Compounds 3a³c have relatively strong chemical reactivity compared to 3d³g.The UV-vis absorption spectra and the photoluminescent?PL?spectra show that 3a,3d and 3e have weak blue fluorescence,3b and 3c have strong yellow fluorescence,and 3f and 3g show strong blue fluorescence.And the range of the PL peaks is 400-550 nm.The seven compounds show different solvent effects.And in the mixed solvent of ethanol/water with different water contents,3b,3c and 3e exhibit typical aggregation-caused quenching?ACQ?,3g exhibites typical aggregation-induced emission enhancement?AIEE?.?2?Study on anion recognition of triazole-based pyridinium salts.It was found that the3f and 3g fluorescence quenched in the presence of F^-and AcO^-.The recognition mechanism between the acceptors 3f and 3g with anions was studied by NMR titration,fluorescence lifetime,and UV-vis absorption spectra,which indicates that the reason of fluorescence quenching is hydrogen bonding and electrostatic interaction between the host and the guest.?3?Study on photocyclization of triazole-based pyridinium salts.By testing the PL spectra of compounds 3a³g under light irradiation,the stability of seven compounds under illumination was investigated.The fluorescence emission intensity of 3a³c increased significantly with the increasing of illumination time,which may have a photocyclization.The structure of photocyclization products was speculated using MS and orbital energy levels of HOMO-LUMO.Compounds 4a and 4b were synthesized by the photocyclization reaction of triazole-pyridinium salts.Compounds 4a and 4b have good fluorescence properties,and the fluorescence intensity does not change in different polarity of the solvents.