The Effects of the Coordination Environment on the Self-Trapped Exciton in Hybrid Organic–Inorganic Copper(I) Halides

Abstract

Hybrid organic–inorganic copper(I) halides are promising light-emitters due to their structural diversity and tunable optical properties. However, the role of Cu(I) coordination environments in the formation of self-trapped exciton (STE) and their impact on luminescence remains underexplored. Here, we investigate the influence of Cu(I) coordination, ranging from linear [CuX₂] to tetrahedral [CuX₄] (X = Cl, Br, I), with varying connection types. First-principles excited-state calculations reveal that linear configurations undergo significant structural distortion, including elongation of Cu–X bonds, while planar and tetrahedral configurations exhibit Cu–Cu distance compression, enhancing 4s–4s interactions and leading to large Stokes shifts. Additionally, we demonstrate how variations in connectivity and structural motifs within similar coordination environments critically affect luminescent behavior. These insights offer valuable guidance for the rational design of efficient Cu(I)-based light emitters, emphasizing the synergistic effects of both coordination geometry and connectivity.