Tetraphenylethene functionalized rhodamine dye for fluorescence detection of HCl vapor in the solid state

A tetraphenylethene functionalized rhodamine sensor RbTPE has been synthesized by the condensation of tetraphenylethene-aldehyde and rhodamine B hydrazide. RbTPE exhibited an aggregation-induced emission effect in the THF/water system, and displayed high selectivity and sensitivity for HCl vapor in the solid state. The solid-state emission of RbTPE can be reversibly switched between blue and red due to the stronger protonation of the rhodamine amino group by HCl. A satisfactory nonlinear relationship was observed upon exposure to HCl vapor in the range of 0–500 ppm, and the detection limit was as low as 20 ppm. After exposing the post-test product RbTPE–HCl to NH3 vapor for a few minutes, the spirolactam ring closed and the signals restored, which showed that RbTPE could be used as a “naked-eye” and reversible sensor for detecting HCl and NH3.