Tubular All‐Benzene Nanocarbon with Evolving Excited‐State Chirality

Molecular nanocarbons with precisely defined conjugated scaffolds can provide an ideal platform for investigating mechanistic insights into photophysical properties. Here, we report the synthesis and time-resolved spectroscopic characterization of two isomeric tubular all-benzene nanocarbon (TANC) molecules, named meso- and chiral-TANC, respectively. Structurally, they feature triple covalent linkages, with different connectivity, between coaxially stacked cycloparaphenylene units. While meso-TANC maintains conformational rigidity, chiral-TANC shows photo-induced dynamic helicity. Femtosecond transient absorption (TA) and time-resolved circularly polarized luminescence (TRCPL) spectroscopy demonstrate that chiral-TANC undergoes ultrafast relaxation accompanied by untwisting motions within 8 ps upon photoexcitation, establishing the direct correlation between photo-induced conformational evolution and chiroptical dynamics in heteroatom-free, fully conjugated molecules.