Molecular Design of Chiral Naphthalenediimide-Based Cations for Chiral One-Dimensional Metal Halide Semiconductors with Strong Chiroptical Activity and Amplified Charge Transport Ability

Abstract

Chiral organic–inorganic metal halide semiconductors (MHSs) have emerged as promising materials for chiroptoelectronics, spintronics and ferroelectrics. However, commonly used chiral cations with nonconductive aliphatic and aromatic structures exhibit large energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) relative to those of the inorganic frameworks. This energy mismatch between the chiral spacer and the inorganic sublattice creates a barrier that hinders charge-carrier transport, leading to inefficient out-of-plane charge mobility and strong quantum confinement effects. To address this challenge, we design and synthesize chiral n-type naphthalenediimide (NDI)-based cations, (R)-2-(7-ethyl-1,3,6,8-tetraoxo-3,6,7,8-tetrahydrobenzo[lmn][3,8]phenanthrolin-2(1H)-yl)propan-1-aminium ((R)-NDIEPA+). We successfully tune the LUMO level of (R)-NDIEPA+ to align with that of the inorganic sublattice, and the resulting chiral one-dimensional (1D) (R-NDIEPA)PbI3 MHS demonstrates a type II band alignment that facilitates charge separation, as evidenced by quenched photoluminescence and transient absorption dynamics indicative of ultrafast charge transfer across the organic–inorganic interface. As a result, these materials demonstrate an approximately 7-fold enhancement in electron mobility compared to the chiral 1D MHS incorporating nonconductive aromatic cations. (R-NDIEPA)PbI3 also exhibits a strong circular dichroism (CD) signal, confirming effective chirality transfer from the organic cation to the inorganic framework. These findings underscore the importance of leveraging the electronic properties of chiral organic cations while preserving strong chiroptical activity, highlighting the potential of (R-NDIEPA)PbI3 for chiroptoelectronic applications such as circularly polarized light photodetectors and other spintronic devices.