SUBSTITUENT EFFECTS OF HEXAPHENYLBENZENE DERIVATIVES ON AGGREGATION-INDUCED EMISSION AND THEIR APPLICATIONS AS CHEMOSENSORS

Abstract

Typical flurophore molecules usually display aggregation caused quenching emission (ACQ) but a recent discovery on the aggregation-induced emission (AIE) leads to new designs of fluorescent sensor. In this work, we would like to report the systematic study of the substituent effects toward emission in the aggregation state of hexaphenylbenzene (HPB) derivatives and their application as chemosensor. Firstly, we compared photophysical properties between the aggregation state and the solution state of five different HPB derivatives HPB-2Me, HPB-2OMe, HPB-2Cl and HPB-2NAP. In high content of water, HPB-2Me, HPB-2OMe and HPB-2NAP showed AIE effect while HPB-2Cl gave no change in fluorescence intensity. Secondly, we synthesized two novel oligophenylene-based pyrene derivatives (FL1 and FL2) in good yields (86-96%). Comparison study of photophysical properties of both compound toward aggregate effect suggested that FL1 showed maximum fluorescence intensity in 60% water in THF (aggregate state) while FL2 displayed no significant change in fluorescence signal. The aggregate state FL1 exhibited specific response towards the picric acid over other nitroaromatic compounds. The detection limit was determined to be 0.880 µM. Finally, we prepared new hexaphenylbenzenes (HPBs) containing imine moiety [SW (4-6)] for metal ions detection. The addition of Al3+ to SW2 resulted in the strong enhancement as orange emission while the SW (4-6) showed selective turn-on fluorescence toward Zn2+ ion in different degrees. Moreover, the detection limits of SW4 and SW5 toward Zn2+ ion were calculated to be 0.160 µM and 0.035 µM, respectively which are lower than drinking water permission concentration by world health organization (WHO). The complex between SW5 and Zn2+ was investigated by NMR titration, Job’s plot, SEM and DLS technique suggesting the formation of nano aggregates in 2:1 complex ratio. We were able to detect Zn2+ in living cell using SW5 and also the emissive SW5-Zn2+ complex can selectively detect organophosphate pesticides, Diazinon in ppm level.