Marriage of Aggregation-Induced Emission and Intramolecular Charge Transfer toward High Performance Film-Based Sensing of Phenolic Compounds in the Air

Film-based fluorescence sensing is recognized as one of the most optimized techniques for trace analysis of chemicals in the air after the invention of ion mobility spectrometry. The performance of the technique is highly dependent on the design of the film. This paper reports a new fluorescent film which shows unprecedented and discriminative sensing performance to the presence of phenol, o-cresol, m-cresol, and p-cresol in the air with an ultralow detection limit as low as 0.4, 0.3, 10, and 0.8 ppt, respectively. The film was designed via combination of the advantages of aggregation-induced emission (AIE) and those of intramolecular charge transfer (ICT), where the former provides the opportunity to avoid the widely encountered aggregation-caused quenching (ACQ) effect and the latter allows sensitive sensing of the microenvironment change of the film. The biggest challenge of the design is to find a fluorophore possessing both AIE and ICT effects. Fortunately, a newly synthesized biphenyl derivative of o-carborane capped with azetidine moiety (BZPCarb) shows the properties as expected. Importantly, the fluorophore is photochemically stable, a prerequirement for multiple uses of a film device. In addition, the nonplanar structure of the fluorophore is also favorable for film sensing as it could form porous films owing to screening of dense stacking of the molecules. It is the merits that make BZPCarb-based film show outstanding sensing and discriminative performances. Based on the fluorophore and the design, a conceptual high-performance fluorescent vapor sensor for phenolic compounds was developed.