Structural Engineering of Chiral Naphthalene-Based Sandwich Emitters: Circularly Polarized Luminescence and Modulation of Charge-Transfer Mechanisms

Constructing chiral multichannel through-space charge
transfer
(TSCT) emitters presents a significant challenge due to difficulties
in synthesis and the need for chiral resolution. Herein, two chiral
multinaphthalene compounds, (S,S)-2,3-NpE and (S,S)-1,8-NpE, were synthesized via a one-pot nucleophilic
aromatic substitution. Their photophysical, chiroptical, and structural
properties were systematically investigated. UV–vis and fluorescence
studies revealed significant charge transfer-based absorptions and
emissions. Chiroptical studies confirmed strong Cotton effects and
circularly polarized luminescence (CPL) with high emission dissymmetry
factors of 6.4 × 10–3, exhibiting remarkable
chirality transfer from naphthalene-based structures to spatial charge
transfer emission. Single-crystal structural analysis demonstrated
a unique sandwich-like molecular architecture, highlighting the role
of molecular geometry in enabling TSCT. Time-dependent density functional
theory calculations provided nuanced insights into the excited-state
electronic structures. Frontier molecular orbital and hole–electron
analyses unveiled distinct excitation mechanisms: (S,S)-2,3-NpE demonstrated a hybridized
locally excited and charge transfer (HLCT) character, while (S,S)-1,8-NpE predominantly
exhibited TSCT. These findings emphasize the importance of precise
structural design in tuning charge transfer and photophysical behaviors,
paving the way for future exploration of functionalized chiral materials.

构建手性多通道空间电荷转移（through-space charge transfer, TSCT）发光体面临着重大挑战，其根源在于合成难度较高且需要进行手性拆分。本文通过一锅法亲核芳香取代反应，合成了两种手性多萘化合物：(S,S)-2,3-NpE与(S,S)-1,8-NpE。研究团队对这两种化合物的光物理、手性光学以及结构性质进行了系统表征。紫外-可见吸收与荧光光谱研究表明，其存在显著的基于电荷转移的吸收与发射行为。手性光学研究证实，该类化合物具有较强的科顿效应（Cotton effect）与圆偏振发光（circularly polarized luminescence, CPL），其发射不对称因子高达6.4 × 10^-3，展现出从萘基结构到空间电荷转移发射的高效手性传递过程。单晶结构分析表明，该类化合物具有独特的类三明治分子构型，凸显了分子几何结构对实现空间电荷转移的关键作用。含时密度泛函理论计算为激发态电子结构提供了细致深入的解析。前线分子轨道与空穴-电子分析揭示了两种化合物截然不同的激发机制：(S,S)-2,3-NpE兼具杂化局域激发-电荷转移（hybridized locally excited and charge transfer, HLCT）特性，而(S,S)-1,8-NpE则主要表现出空间电荷转移行为。本研究结果凸显了精准结构设计在调控电荷转移与光物理行为中的重要性，为后续功能化手性材料的探索铺平了道路。