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.