Synthesis of pyrazine-linked helicenes improves chiroptical properties, revealing critical frontier orbital effects.
Control of chiroptical responses in π-conjugated molecules is critical for the design of chiral materials. We synthesized terminal π-extended helicenes linked by a pyrazine bridge and investigated their circular dichroism. Extension from naphthalene to tetracene decreased the S0 → S1 dissymmetry factors from 0.027 to nearly zero. TD-DFT calculations and our transition-moment density analysis revealed that frontier orbital localization on the helicene moiety is essential to achieving large g values, clarifying the origin of strong chiroptical activity.
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Zhang et al. (2025) studied this question.
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