Luminescent copper(I) complexes as vapochromic sensors for volatile organic compounds: integrating two distinct sensing mechanisms in a single platform

Abstract

We propose a strategy for the design of coordination complexes capable of sensing volatile organic compounds (VOCs) through integrating two distinct sensing mechanisms on the base of a single platform. The first mechanism, emission switching via ligand-enabled, VOC-induced structural distortion, relies on the incorporation of a flexible structural component into the ligand architecture. This design enables sensing of weakly coordinating VOC molecules through the reversible distortion of the molecular and crystal structure. The second mechanism, emission quenching via VOC-driven labile ligand displacement, relies on the tuning of the ligand coordination strength: it should be sufficient for stable complex formation yet allow for dissociation in the presence of VOCs with stronger electron-donating properties. To illustrate this strategy, we report the synthesis of mononuclear copper(I) complexes, [CuL(PPh3)2](PF6)·nSolv and [CuL(XantPhos)](PF6)·nSolv (where L is LH or LMe; LH = 2-(benzylthio)-4-(1H-benzotriazol-1-yl)pyrimidine, LMe = 2-(benzylthio)-4-(1H-benzotriazol-1-yl)-6-methylpyrimidine), which exhibit a visually detectable luminescence response to MeCN and CH2Cl2 vapours. For these complexes, the response to MeCN is associated with the reversible decoordination of L, while the response to CH2Cl2 stems from the reversible uptake of solvent molecules into the crystal lattice. The successful integration of these two orthogonal sensing pathways within a single family of compounds renders them unique examples of rationally designed bifunctional copper(I)-based VOC sensors.