Achieving Simplified and Tunable Flexibility in Carborane-Based Emitters for Quantitative Vapochromic VOC Sensing

Photoluminescence (PL) sensing of volatile organic compounds (VOCs) represents a convenient and economic detection method toward air pollutants. However, tetraphenylethylene (TPE)-based and recent carborane (Cb)-based sensors retained multiple sites that are responsive to VOC stimulation, making quantitative PL sensing rather challenging. Rendering the simplified and tunable flexibility in the PL sensors is key to achieve the quantitative target. In this work, we proposed a dimeric model of Cb-based emitters to deal with flexibility. Three emissive dibenzothiophene (DBT)-alkynylated carboranes (Cb-1/2/3) were designed and synthesized. Among them, Cb-3 contributed green and green-yellow emission in the crystals, as well as yellow and orange emission in the VOC-incorporated films, together unfolding its vapochromic properties. Crystallographic studies revealed that Cb-3 molecules were invariably dimerized in an interlocked fashion and the redshift in PL was caused by the successive through-space conjugation of DBT moieties. Theoretical calculations verified the thermodynamics stability of Cb-3 dimers and suggested that DBT could individually rotate different angles under the simulation of VOCs. Based on the above findings, we introduced DBT-alkynylated carboranes to detect the VOCs and established linear relationships between the photon energy at the PL maxima and the concentrations of benzene and tetrahydrofuran (THF) vapors. Aside from the successful implementation of quantitative vapochromic sensing, the fast response (6 s) and recovery (3∼5 s), as well as the good reusability, were also evidenced in the sensing of THF vapors.