Controlled Molecular Diffusion in Fluorescent Polymer Films for Label‐Free Detection of Volatile Organic Compounds

Aggregation‐induced emission has eliminated the problem of fluorescence quenching in the solid state, making molecules with this property excellent candidates for vapor sensing due to their portability and ease of interpretation. Here, films of polystyrene / 2‐[4‐vinyl(1,10‐biphenyl)‐40‐yl]‐cyanovinyljulolidine copolymers are reported that exhibit aggregation‐induced emission behavior for the detection of toluene, m‐xylene, dichloromethane, and chloroform. After exposure to the analytes, the emission of the copolymers shows significant changes in intensity and spectral shape corresponding to the reduced microviscosity of the molecular environment. However, these changes are similar for different analytes, resulting in low chemical selectivity. Therefore, label‐free selectivity is achieved by controlling the molecular diffusion of the four vapor analytes within the films using the Flory–Huggins solution theory with capping layers of cellulose acetate (CA) and poly(vinyl alcohol) (PVA) polymers. Thin polymer films using moieties displaying aggregation‐induced emission are promising as optical transducers in chemical sensing. This is important for the development of fluorescent vapor sensors. In this work, the authors demonstrate the use of simple diffusion barrier layers to increase the selectivity of the films without the need for chemical labeling.