Water-stable halide coordination polymers with dual self-trapped exciton emissions for dual-mode Hg²⁺ sensing

Metal halide-based materials are an emerging class of optical functional materials used for developing sensors and light-controlled and light-emitting devices. However, most of these materials are moisture-sensitive, which hampers their performance in real applications. In this work, a methylation-functionalized decarboxylase ligand with large steric hindrance was used to construct a two-dimensional acid- and base-stable halide coordination polymer, XCP-1. XCP-1 shows dual broadband emissions with a large full width at half maximum and a large Stokes shift, indicating that self-trapped exciton emissions originated from the deformable crystal lattice of [Pb2I2] centres. XCP-1 also exhibits excitation wavelength-dependent emission spectra and gives red emissions with Commission International de l'Eclairage chromaticity coordinates of (0.64, 0.36), which is close to that of the National Television Standards Committee standard (0.67, 0.33) when excited at 500 nm. Owing to the strong dual self-trapped exciton emissions and unique coordination sites of accessible O atoms, XCP-1 is capable of acting as a luminescent sensor to selectively, reversibly and sensitively detect Hg2+ ions, displaying an efficient dual-mode colorimetric and turn-off sensing strategy.