Click-enabled tetrazine ionic liquid as advanced material for chemo-selective gas detection via inverse electron-demand Diels-Alder reaction

Abstract

A room-temperature 1,2,4,5-tetrazine ionic liquid (TIL) was synthesized in eight steps with an overall yield of 8.5% as a new functional material for chemoselective target gas detection. The TIL, bearing two electron-withdrawing substituents on the tetrazine ring, served as a reactive probe for alkene and alkyne vapors through the rapid inverse electron-demand Diels-Alder (IEDDA) [4+2] cycloaddition. When thin-coated on a quartz crystal microbalance (QCM), the TIL enabled real-time monitoring of gaseous styrene, strained cycloalkenes, and cyclooctyne with distinct frequency responses and high sensitivity. These results demonstrate that tetrazine-based ionic liquids can act as both reaction media and chemo-sensing elements. This study establishes a concise synthetic route and introduces an IEDDA reaction-based platform for the selective and sensitive detection of unsaturated hydrocarbons.ExperimentalDetailed 1 H and 13 C NMR and HRMS spectra of TIL, the HRMS spectrum of the TIL-styrene adduct (Fig. S1), the QCM measurement protocol, and procedures for in-solution click reactions monitored spectrophotometrically are summarized in the Electronic Supplementary Information (ESI).