Construction of a Long-Range Quantitative Fluorescence Sensor for Multiple Amine Vapors by π···π Aggregates of Carborane

Abstract

The exploitation of small molecules as fluorescence sensors represents a minimalistic solution toward the sensing of hazardous volatile organic compounds (VOCs). Compared with the conventional aggregation-induced emitting sensors, the carborane (Cb)-based sensors have exhibited multiple advantages and improved quantitative fluorescence (QF) sensing abilities toward the gaseous VOCs. However, in the current Cb-based sensors, the localization of a single responsive site toward VOCs remains less focused, which results in a bias in the trace detection and short-range testing windows. In this work, we synthesized two pyrene-alkynylated carboranes (Py-1 and Py-2) and investigated their photophysical properties in different cases. We found that Py-1 and Py-2 in the films were consistently self-assembled through π···π aggregation of pyrenylethynyl moieties. Theoretical modeling showed that the highly emissive π···π aggregates were thermodynamically stable and their responsive sites toward VOCs were localized on the electron-poor phenyl or fluorenyl groups. As a result, the Py-1 and Py-2 films showed remarkable emission-off sensibilities toward NEt3 vapors via a major route of photoinduced electron transfer. The optimized QF sensor Py-2 showed linear emission-off response toward three types of static amine vapors in long concentration ranges (1.78–90 g/m3 at most), and the limit of detection could be lowered to 99 mg/m3 in the in situ sensing.