Modulating organic functional groups in stimuli-responsive luminescent antimony chlorides

Abstract

Stimuli-responsive inorganic–organic hybrid metal halides (IOMHs) have shown great potential in sensing, information encryption and anti-counterfeiting, etc. However, the stimuli-responsive behavior based on the regulation of the functional groups in organic species is still blank in IOMHs. Herein, three zero-dimensional (0-D) antimony-based IOMHs with different functional groups in the organic cations are reported, namely [AOEMIm]₃SbCl₆ (1, AOEMIm = 1-acetoxyethyl-3 methylimidazolium), [HOOCMMIm]₃SbCl₆·3(OOCMMIm) (2, HOOCMMIm = 1-carboxymethyl-3-methylimidazolium) and [HOOCMMIm]₃SbCl₆ (3). Photophysical characterizations show that 1, 2 and 3 exhibit typical self-trapped exciton triplet broadband emission, peaking at 610, 510 and 525 nm under excitation of 365 nm, 375 nm and 345 nm, respectively. Under the H₂O stimulation, the organic groups in the crystal structures undergo a mutual transformation, that is, from acetoxyethyl or carboxyl to a mixture of carboxyl and deprotonated carboxyl. Accordingly, the organic group switching is accompanied by a solid–solid transformation from 1 or 2 to 3 crystals. The intrinsic mechanism for the phase transition is expounded as well. Due to the obvious luminescence change from yellow-green emission (3) to green emission (2), 3 is further applied in the detection of trace water in organic solvents. The water detection limit in tetrahydrofuran (THF) is as low as 0.3% v/v. This study provides a new avenue for the construction of stimuli-responsive IOMHs.