Jahn–Teller Couplings and Exciton Models Reveal Origins of Chiroptical Activity in Symmetric Cyclic π‑Conjugated Systems

Understanding the origin of chiroptical responses in
symmetric
cyclic π-conjugated systems is key to advancing their application
in optoelectronic and spintronic technologies. Here, we document that
such a response is intrinsically nonadiabatic and arises from the
entangled contributions of electronic states and molecular vibrations.
We exploit a comprehensive theoretical framework that unifies localized
exciton coupling and delocalized Jahn–Teller (JT) vibronic
modelstwo traditionally distinct approachesto accurately
predict the ECD spectra of chiral spirobifluorene macrocycles. We
show that using a flexible method to parametrize linear vibronic coupling
(LVC) models in both localized and delocalized representations enables
a direct comparison of excitonic and nonadiabatic effects. We demonstrate
that quantum dynamical simulations on both models reproduce the experimental
ECD spectrum of the D3-symmetric macrocycle
(P,P,P)-1 with high accuracy and reveal that the coupling between nuclear
and electronic motions plays a dominant role in shaping its chiroptical
response. This analysis highlights the critical influence of conical
intersections, exciton–charge transfer interactions, and symmetry-guided
combinations of local transition dipoles. Importantly, the same approach
captures the spectral features of the less symmetric C2 stereoisomer (P,P,M)-1, underscoring the generality of the method.
This dual-framework strategy provides deep mechanistic insight into
the interplay of symmetry, vibronic coupling, and excitonic interactions
and offers a powerful design tool for next-generation chiral materials.