Investigation of thermochromic photoluminescent, dielectric and crystal structural properties for an inorganic-organic hybrid solid of [1-hexyl-3-methylimidazolium][PbBr₃]

The thermochromic photoluminescence, dielectric and impedance spectra, as well as temperature dependent crystal structures were investigated for the hybrid solid of [1-hexyl-3-methylimidazolium][PbBr₃] (1). The hybrid crystal, belonging to a monoclinic system with the space group P2₁/c, is composed of one-dimensional [PbBr₃]_∞ chains where the neighboring PbBr₆ coordination octahedra are connected via face-sharing mode; the organic cations are incorporated in the space of the inorganic chains. The dynamic motion of the cations strongly influences the dielectric and emission features of 1. The platform-type dielectric anomaly, accompanied by a thermal event, occurs at an onset temperature of around 250 K, which is related to the alkyl chain swing motion. The dielectric relaxation appears at temperatures above 240 K and results from the alkyl chain swing motion and imidazole ring libration motion. Another fascinating feature of 1 is its dual emissions, arising from the π ← π∗ transition within the imidazole ring and the exciton luminescence of the [PbBr₃]_∞ semiconducting chain. The two emission bands have different sensitivities to temperature, leading to 1 showing photoluminescent thermochromism, which may have a potential application in thermosensitive devices.