Lemniscular [16]Cycloparaphenylene: A Radially Conjugated Figure-Eight Aromatic Molecule

A cycloparaphenylene-based
molecular lemniscate (CPPL) was obtained
in a short synthesis involving masked p-phenylene
equivalents. The strained figure-eight geometry of CPPL is sustained
by the incorporated 9,9′-bicarbazole subunit, which also acts
as a stereogenic element. The shape of the distorted [16]­cycloparaphenylene
nanohoop embedded in CPPL is accurately approximated with a Booth
lemniscate. The structure of CPPL, investigated using NMR and Raman
spectroscopic methods, revealed strain-dependent features, consistent
with the variable curvature of the ring. The electronic and optical
properties of CPPL combine features more characteristic of smaller
cycloparaphenylenes, such as a reduced optical bandgap and red-shifted
fluorescence. CPPL was resolved into enantiomers, which are configurationally
stable and provide strong chiroptical responses, including circularly
polarized luminescence.