Tuning Chiroptical Properties of Two-Dimensional Hybrid Perovskites through Organic Spacer and Halide Composition.

Two-dimensional (2D) chiral hybrid organic-inorganic perovskites (HOIPs) have emerged as promising materials for optoelectronic and spintronic applications owing to their tunable electronic structures and chiroptical properties. Here, we investigate the effects of organic spacer and halide composition on chiroptical properties of 2D HOIPs using circular dichroism (CD) spectroscopy and density functional theory (DFT) calculations. A blue shift in excitonic transitions is observed from methylbenzylamine (MBA) to 1-cyclohexylethylamine (CHEA) with increasing steric factor and with halide substitution from I to Br. The highest dissymmetry factor, gCD = 2.7 × 10-3, is obtained for (R/S-MBA)2PbBr4, whereas (R/S-CHEA)2PbI4 exhibits the value 1.6 × 10-4. DFT calculations reveal that bromide-based systems exhibit stronger charge transfer, enhanced molecule-halide reactions, and greater lattice distortions, while MBA promotes stronger electronic coupling than CHEA. These effects facilitate more efficient transfer of chirality from the organic spacer to the inorganic framework, thereby governing the observed chiroptical response.