Wu YL Bures F Jarowski PD Schweizer WB Boudon C Gisselbrecht JP Diederich F 2010 Novel donor- and/or acceptor-substituted cross-conjugated carbocycles based on quinoids or expanded quinoids, with radiaannulene perimeters, were prepared and investigated to validate proaromaticity as a concept for reducing HOMO-LUMO gaps in push-pull chromophores. Analyses of IR, (1)H NMR, and UV/Vis/NIR spectra in conjunction with molecular structures determined by X-ray diffraction show that these push-pull quinoids have significant charge-separated ground states. This feature results in small optical gaps (near IR region) and diatropic magnetic environments inside the carbocycles, as suggested by nucleus-independent chemical shift (NICS) calculations. The NICS results, together with the bond-length analysis of the quinoid spacers, provide strong support that proaromaticity, that is, aromatized zwitterionic mesomeric contributions in the ground state, is effective. A push-pull tetrakis(ethynediyl)-expanded quinoid chromophore represents the first proaromatic radiaannulene. https://sonar.ch/global/documents/167697 eng info:eu-repo/semantics/altIdentifier/doi/10.1002/chem.201001051 info:eu-repo/semantics/altIdentifier/pmid/20648493 Chemistry (Weinheim an der Bergstrasse, Germany). - 2010 Proaromaticity: organic charge-transfer chromophores with small HOMO-LUMO gaps. http://purl.org/coar/resource_type/c_6501