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.