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Updated: Dec 17, 2025
Interactive Molecular Model Assembly with 3D Printing
Published on: August 13, 2020
A Chichibabin's Hydrocarbon-Based Molecular Cage: The Impact of Structural Rigidity on Dynamics, Stability, and
Yong Ni1, Fernando Gordillo-Gámez2, Miriam Peña Alvarez3
1Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore.
Abstract:
A three-dimensional π-conjugated polyradicaloid molecular cage -Ph14, consisting of three Chichibabin's hydrocarbon motifs connected by two benzene-1,3,5-triyl bridgeheads, was synthesized. Compared with its linear model compound -Ph4, the prism-like -Ph14 has a more rigid structure, which shows significant impact on the molecular dynamics, stability, and electronic properties. A higher rotation energy barrier for the quinoidal biphenyl units was determined in -Ph14 (15.64 kcal/mol) than that of -Ph4 (11.40 kcal/mol) according to variable-temperature NMR measurements, leading to improved stability, a smaller diradical character, and an increased singlet-triplet energy gap. The pressure-dependent Raman spectroscopic studies on the rigid cage -Ph14 revealed a quinoidal-to-aromatic transformation along the biphenyl bridges. In addition, the ellipsoidal cavity in the cage allowed selective encapsulation of fullerene C70 over C60, with an associate constant of about 1.43 × 104 M-1. Moreover, -Ph14 and -Ph4 exhibited similar redox behavior and their cationic species (-Ph14 and -Ph4) were obtained by chemical oxidation, and the structures were identified by X-ray crystallographic analysis. The biphenyl unit showed a twisted conformation in -Ph4 and remained coplanarity in -Ph14. Notably, molecules of -Ph14 form a one-dimensional columnar structure via close π-π stacking between the bridgeheads.
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