Diimidazolium Halobismuthates [Dim]₂[Bi₂X₁₀] (X = Cl^–, Br^–, or I^–): A New Class of Thermochromic and Photoluminescent Materials

Abstract

We present a novel family of polyhalide salts of Bi(III) with the general formula [Dim][BiX], where Dim is the diimidazolium cation (CHN) and X is Cl, Br, or I. Single-phase materials are easily obtained by means of a mild solution chemistry method performed at room temperature. This [Dim][BiX] family exhibits a crystal structure based on halobismuthate [BiX] dimers, built by distorted {BiX} octahedra interconnected by edge sharing, and sandwiched between two diimidazolium cations. The optical band gaps displayed by these materials (1.9-3.2 eV) allow their classification as semiconductors. Additionally, the three halides display photoluminescence with emission in the visible range. The behavior of [Dim][BiI] is particularly interesting, as it shows an optical band gap of 1.9 eV, a broad band photoluminescence emission, and a relatively long emission lifetime of 190 ns. Moreover, the iodide and bromide compounds also exhibit a reversible solid state thermochromism, being the first example of a bromobismuthate with this property. The diimidazolium cations play an important structural role by stabilizing the crystal structure and balancing the charges of the [BiX] dimers. Furthermore, density functional theory calculations suggest that they play a key role in the thermochromic behavior. Therefore, compounds [Dim][BiX] (X = Cl, Br, or I) represent a very versatile family in which the optical band gap can be tuned by changing the halide or temperature. This makes them promising new materials for different optoelectronic applications, in particular for obtaining new solar absorbers.

Antisolvent‐assisted Crystallization of Centimeter‐sized Lead‐free Bismuth Bromide Hybrid Perovskite Single Crystals with X‐ray Sensitive Merits

“…The thermal stability of (PDA)BiBr 5 was then studied via thermogravimetric and differential scanning calorimetry measurements (Figure S1). Obviously, it begins to lose weight at ∼558 K due to the sublimation of pentamethylenediamine cation (Figure S1a), and then loses all its mass before 1000 K, showing higher stability than the reported bismuth halide perovskites [21,22] . Besides, no apparent thermal anomalies were observed in the DSC curve (Figure S1b), suggesting no phase transition during the heating and cooling process.…”

[((R)-C8H12N)4][Bi2Br10] and [((S)-C8H12N)4][Bi2Br10]: Chiral Hybrid Bismuth Bromides Templated by Chiral Organic Cations

“…41 The band gaps of the reported chiral compounds are similar to those of other various organic–inorganic halide materials. 30,42−44 Because the band gaps of a series of halides compounds are varied by changing the constituting halides (Cl – , Br – and I – ), the related materials can be used in optoelectronic devices by controlling the stoichiometry of halide anions.…”

Halogen‐ and Counterion‐Modulated Photochromic and Photoluminescence Properties of Haloargentate Hybrids

“…The photoluminescence spectra obtained at room temperature for compounds 1–5 are shown in Figure . The maximum emission peaks of 1–5 are mainly centered at 476, 493, 476, 490 and 494 nm (λ ex = 395, 390, 399, 381 and 399 nm), respectively, and simultaneously affected by the type of halogen and Ag ··· Ag distance, which can be assigned to the mixture of halide‐to‐metal charge transfer and metal‐centered states modified by Ag ··· Ag interactions within [Ag 2 X 3 ] n n– chains. [13a], …”