Imidazole-Based Small Molecule With ESIPT Characteristic: Synthesis And Properties

The inter or intramolecular proton transfer reaction is considered to be one of the most fundamental and important processes in chemistry and biology such as the acid-baseneutralization and catalytic reactions.Among them,excited-state intramolecular process is drawing a great attention because it has an extraordinary Stokes'shift without seft-rebsorption as well as dual fluorescenece emission from enol form and keto form.Nowadays ESIPT molecule have showed amazing research prospects in laser dyes,fluorescent probes,OLEDs and so on.However,the ACQ effect?low emission efficiency in the aggregate state?limits the practical application of ESIPT materials.Thus,to design and synthesize novel classes of highly emissive ESIPT molecules are quite significance.Imidazole is endowed with ambipolar nature,and especially its derivatives have exhibited interesting and tunable photophysical and electrical properties,which lead us to design highly emissive ESIPT molecules with imidazole.In this dissertation,we have presented two kinds ofimidazole-based small molecues with ESIPT characteristic and investigated the relationship between the linkage position,conjugation and luminescent properties of these organic molecules.The detailed work is carried out as follows:?1?We designed and synthesized two isomers constructed by1-phenyl-1H-phenanthro[9,10-d]imidazole?PI?,hydroxyl and tetraphenylethylene?TPE?,abbreviated as m-PITPE and p-PITPE.It is found that they exhibit similar AIE behavior but totally different excited-state intramolecular proton transfer?ESIPT?characteristic,as a result of the different linkage sites of PI on TPE moiety.Theoretical calculations and their different experimental response to F^-demonstrate that only the para-linkage isomer displays ESIPT.The meta-linkage in m-PITPE induces the electron cloud distribution to only locate at the TPE part in the S₁ state,which results in the localized excited state without ESIPT characteristic.?2?We designed a novel imidazole-base derivative with improved molecular conjugation and planarity,and synthesized two ESIPT isomers based this unit.Investigation on their photophysical properties demonstrated they have ESIPT and charge transfer characteristics.The influences between conjugation,space steric and luminescence properties were also studied.In addition,these molecules also showed acid-base stimuli-response behaviors.