Related Experiment Video
Updated: Jan 14, 2026
08:12
Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films
Published on: September 8, 2017
10.0K
Light-Driven Intraoctahedral Halide Isomerization in Two-Dimensional Mixed Halide Perovskites
Wenxin Mao1,2, Enamul Haque3, Stephanie A Bird4
1Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
Journal of the American Chemical Society
|January 13, 2026
Summary
Two-dimensional metal halide perovskites exhibit light-driven, reversible halide-ion isomerization within single octahedra. This intraoctahedral switching tunes optoelectronic properties, enabling new possibilities for reconfigurable devices.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Quantum Optics
Background:
- Two-dimensional (2D) metal halide perovskites are promising for quantum light emission and neuromorphic computing.
- Their functionality is often linked to quantum confinement and tunable optoelectronic properties.
- Unique opportunities exist for engineering functionality at the subunit-cell level by exploiting distinct halide sites within octahedra.
Purpose of the Study:
- To investigate light-driven, reversible halide-ion isomerization in single-crystalline 2D perovskites.
- To understand the mechanism of intraoctahedral halide switching and its impact on optoelectronic properties.
- To explore the potential of this phenomenon for advanced optoelectronic applications.
Main Methods:
- Hyperspectral imaging
- In situ X-ray diffraction
- First-principles calculations (Density Functional Theory)
Main Results:
- Demonstrated reversible halide-ion isomerization within individual PbX6(4-) octahedra in BA2PbBrxI4-x (x=1-3).
- Observed modulation of the optical bandgap by ~0.1 eV due to intraoctahedral halide site switching.
- Estimated a reversible electronic bandgap shift of up to ~0.5 eV, attributed to valence band character redistribution.
Conclusions:
- Uncovered a mechanism of structurally encoded, site-selective photoisomerization in 2D perovskites.
- Showcased intraoctahedral halide switching as a novel strategy for reconfigurable optoelectronic devices.
- Highlighted potential applications in nonvolatile optical memory and quantum photonics.
Related Concept Videos
02:46Halogenation of Alkenes
18.4K
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
18.4K
01:26Photochemical Electrocyclic Reactions: Stereochemistry
2.2K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
2.2K
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
2.9K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
2.9K
01:17Thermal Electrocyclic Reactions: Stereochemistry
2.5K
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.5K
01:14Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
3.4K
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.
3.4K
02:38Electrophilic Addition to Alkynes: Halogenation
10.0K
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
10.0K