Starting materials: (S)-(−)-1-(1-naphthyl)ethylamine (≥99%, Sigma–Aldrich), lead bromide (PbBr2, ≥98%, Sigma–Aldrich chemicals), hydrobromic acid (HBr) (48 wt.% in H2O, >99.99%, Sigma–Aldrich), diethyl ether (Anhydrous (≥99, Fisher Chemical, stabilized with BHT), 2-methoxyethanol (anhydrous, 99.8%, Sigma–Aldrich)
Product: (S-NEA)2PbBr4
Description: lead (II) bromide (90 mg, 0.24 mmol) was dissolved in 1.0 mL of concentrated hydrobromic acid by heating at 90 °C for <5 min. The solution was cooled to room temperature and 2.4 mL DI water was slowly added. (S)-(-)-1-(1-napthyl)ethylamine (78 µL, 0.48 mmol) was then added and the mixture was dissolved in a sealed vial at 90 °C overnight while stirring. The solution was cooled to room temperature at a rate of 1 °C h−1 in an aluminum heating block. The (S-NEA)2PbBr4 crystals were collected via vacuum filtrations and the crystals were washed with 20 mL of diethyl ether three times. The crystals were then dried overnight in a vacuum oven at 55 °C, 150 Torr.
Method: Circular dichroism spectroscopy
Description: Circular dichroism (CD) measurements were performed on thin films of S‑NPB and R‑NPB, which are known to exhibit measurable excitonic CD features. The CD spectra display opposite polarities for the S and R enantiomers, consistent with their reversed polar distortions and spin textures. The measured CD reflects contributions from the lowest exciton as well as the interband continuum, and shows a clear correlation between structural chirality, spin‑texture reversal, and CD sign reversal in the thin films.