Chiral Molecular Carbon Imides: Shining Light on Chiral Optoelectronics

Abstract

Chiral molecular carbon imides (CMCIs) represent a kind of chiral π-conjugated molecules that are typically designed and synthesized by introducing helical chirality. This approach creates a stereogenic axis, rather than a traditional chiral center or chiral axis with saturated bonds, resulting in chiral conjugated helices (CCHs). CMCIs have garnered significant attention due to their flexible synthesis (annulative π-extension strategies), tailor-made structures (chiral polycyclic π-conjugated frameworks), and diverse properties (optical, electronic, magnetic, and biochemical characteristics related to chirality). Furthermore, CMCI systems exhibit unique chiroptical properties, including circular dichroism (CD) and circularly polarized luminescence (CPL), which have elevated them as emerging stars among chiral organic functional molecules. Benefiting from their large conjugation planes and excellent electron-withdrawing ability, CMCIs often display outstanding electron mobility, high electron affinity, and strong light absorption or emission capabilities, making them valuable in various organic semiconductor applications. Their unique chiroptical properties and excellent semiconducting abilities position CMCIs as key players in the emerging field of chiral optoelectronics. Additionally, the appropriate packing modes and efficient charge transfer in solid-state CCHs provide excellent platforms for applications in chiral-induced spin selectivity (CISS) and topological quantum properties.

In this Account, we present a comprehensive overview of three representative types of CMCIs: single-strand CCHs (ss-CCHs), double-strand CCHs (ds-CCHs), and multiple-strand CCHs (ms-CCHs). We focus on their rational design strategies, fundamental chiroptical properties, and chiral optoelectronic applications, particularly in circularly polarized organic photodetectors (CP-OPDs). We also discuss key parameters for evaluating chiroptical performance, such as the luminescence dissymmetry factor (g_lum) and photoluminescence quantum yield (Φ_PL), and explore how the magnetic transition dipole moment (m), together with the electric transition dipole moment (μ), influence g_lum and Φ_PL. Through this review, we highlight successful strategies to enhance chiroptical responses, such as improvements in molecular symmetry, heteroannulation, and the introduction of multiple chiral centers. We also delve into the intrinsic correlation between chiral structure and excited-state parameters, supported by theoretical calculations. By emphasizing the judicious structure evolution of high-efficiency circularly polarized photoluminescence (CPPL) in solutions based on these CCHs, we offer perspectives on the future development of circularly polarized electroluminescence (CPEL) emitters and their potential applications in circularly polarized organic light-emitting diodes (CP-OLEDs), which would be more practical for future displays and photonic technologies. Finally, we emphasize the promising prospects of CCHs in multi-functional spin-polarized optoelectronic devices, aiming to achieve room-temperature, long-distance spin transport by leveraging the unique chiral-induced spin selectivity (CISS) effect and outstanding optoelectrical performance.