Isomeric organic–inorganic indium bromide single crystals with delayed and dual colour emission

Hybrid metal halides attract significant attention in materials science, chemistry, and photonics due to their attractive structural, electronic, and optical properties. However, zero-dimensional (0D) hybrid indium halides are still in their infancy. We report the first isomeric 0D indium halide single crystals showing green and delayed yellow emissions. Single-crystal X-ray structures reveal that these emissions originate from crystals with the molecular formula (C10H22N2)4In4Br20, consisting of organic ligands, InBr6 octahedra, and InBr4 tetrahedra. While both crystals carry eight corner-sharing and two face-sharing InBr6 octahedra, the four face-sharing InBr4 tetrahedra in the green-emitting isomer and two inner InBr4 tetrahedra in the yellow-emitting isomer mark the crystal isomerism, leading to distinct optical properties. The green-emitting crystals exhibit short excitonic lifetimes, whereas the radiative recombination in the yellow-emitting crystals is delayed by several hundred nanoseconds and redshifted, indicating a self-trapped exciton behaviour with a large Huang-Rhys factor and high activation energy. The structural and optical properties of the isomeric single crystals offer insights into the importance of developing 0D metal halides with multi-colour and delayed emission for sensors, LEDs, and displays.