Separately Enhanced Dual Emissions Of Amphiphilic Derivative Of 2-(2’-hydroxylphenyl) Benzothiazole By Host-guest Interaction

The fluorescence of 2-(2’-hydroxyphenyl)benzothiazole(HBT)is widely studied due to its unique excited-state intramolecular proton transfer(ESIPT)effect.ESIPT effect has promoted the development of fluorescent materials,which could be constructed by supramolecular interaction.Cyclodextrins(CD)are often used as hosts to construct supramolecular structures by selective inclusion of fluorescent guest molecules.In this article,we synthesize a fluorescent molecule with the ESIPT effect(denoted by HBT-11),explored its special fluorescence properties and supramolecular complexation with α-cyclodextrin(α-CD),β-cyclodextrin(β-CD)respectively.This line of research supplies a method to separately modulate the emission of two tautomers of HBT derivatives,and makes one step progress to understand the emitting mechanisms of ESIPT chromophores.In order to investigate the emission behavior of HBT-based chromophores in water,we synthesized an amphiphilic derivative of HBT(denoted by HBT-11)terminated with pyridinium group.It was found that the fluorescence behavior of HBT-11 was concentrationdependent.As the concentration is lower than the critical micelle concentration(CMC),HBT-11 shows two emissive bands at 385 and 446 nm,which are assigned to the enol-and keto-emission of the isolated monomers,respectively.These two emissions were separately enhanced by complexation with a-CD and b-CD.The formation of HBT-11/a-CD complexes through multiple hydrogen bonding,and mainly enhanced the keto-emission of HBT-11 at 446 nm.The formation of HBT-11/b-CD complexes by host-guest interaction,and mainly enhanced the enol-emission of HBT-11 at 385 nm.As the concentration is higher than the CMC,a new fluorescence peak appeared at 507 nm,which should be assigned to the emission of aggregated HBT-11.Upon addition of a-CD or b-CD,the intensity of the fluorescence emission located at around 507 nm became relatively weaker than that of the other two isolated emission bands.The complexation between HBT-11 and α-CD(or β-CD),should be strong enough to break the self-assembled aggregates of HBT-11 in aqueous solution.To the best of our knowledge,this is the first time to report the keto-emission of the isolated HBT chromophore.