Rational design of 1, 2, 4, 5-tetraphenyl-1H-imidazole-based AIEgens with tunable intramolecular charge transfer and restricted intramolecular rotation processes for multifunctional sensing.

Aggregation-induced emission fluorogens (AIEgens) with intramolecular charge transfer (ICT) characteristic are widely used in the detection of various analytes owing to their highly tunable fluorescence emission properties. However, facilely synthesis of AIEgens with ICT characteristic for multiple sensing is still rare and limited in use. In this work, two new AIEgens of 1,2-bis(4-alkoxycarbonylphenyl)-4,5-bis(4-methoxyphenyl)-1H-imidazole (AMI) and its hydrolyzed derivative 1,2-bis(4-carboxylphenyl)-4,5-bis(4-methoxyphenyl)-1H-imidazole (CMI) were facilely synthesized with donor-π-acceptor (D-π-A) structures. The tunable ICT and restricted intramolecular rotation (RIR) processes endow them multifunctional sensing performances. AMI could serve as a reversible fluorescent thermometer, in which a positive linear correlation between fluorescence intensities and temperatures from 20 °C to 60 °C was obtained. Meanwhile, owning to the specific interaction between carboxyl groups and Al(III) ions, CMI was successfully served as a "turn-on" fluorescent chemosensor for detecting Al(III) in aqueous solutions under a neutral condition with high sensitivity and selectivity. Mechanism study showed that the formation of aggregation states of coordination polymers between CMI and Al(III) was responsible for the fluorescence enhancement. What is more, the sensing process could be applied for detecting Al(III) in real water samples and on solid test papers, which implied its potential application values. Furthermore, the aggregation-induced emission (AIE) characteristic also made fluorescence emissions of CMI suitable for specific pH sensing. This work provides an efficient strategy for the construction of multifunctional fluorescence chemosensors based on AIEgens.