Three-arm star-shaped aniline derivatives: Tunable photoluminescence, aggregation-induced emission and reversible acid-base vapor fluorescence response

The aggregation-induced emission (AIE) molecules demonstrate unique luminous performance in aggregation state, which shows great potential in optoelectronic devices, chemical sensors, bioimaging and so on. Linear aniline derivatives own excellent photoelectric properties, good processing properties, outstanding designability and pH sensitivity. Most reported linear aniline derivatives are typical aggregation caused quenching (ACQ) molecules. One commonly adopted strategy to achieve ACQ-AIE conversion of aniline derivatives is introducing functional groups onto the backbone of aniline chain, which requires multi-step synthesis and post-processing. Herein, we propose a novel "one-step" strategy to achieve the ACQ-AIE conversion of the aniline derivatives through varying the molecular geometry and modification of functional groups on the backbone of the aniline. A series of aniline derivatives in three-arm star-shaped structure was then designed by adjusting the position of aniline units. Furthermore, derivatives containing terminal groups with different electron-withdrawing abilities, including methoxy, bromine, phenyl and cyanophenyl groups, were synthesized in succession. The absorption and emission behaviors of the derivatives could be effectively adjusted. All the synthesized derivatives exhibit AIE behaviors, implying that the ACQ-AIE conversion of aniline derivatives through structural adjustment was feasible. Theoretical simulation was further used to calculate the electronic and geometric structures of the derivatives. The results proved that the distorted conformation was responsible for the AIE characteristics. In addition, the powder of four derivatives showed a reversible fluorescence response to acid-base vapor which indicated potential for anti-counterfeiting applications.