Expanded Hexapyrrolohexaazacoronenes. Near-Infrared Absorbing Chromophores with Interrupted Peripheral Conjugation

Gońka, E.; Chmielewski, P. J.; Lis. T.; Stępień, M.
J. Am. Chem. Soc. 2014, 136, 16399-16410 | view at publisher's site

A family of azacoronenes containing up to two saturated bridges at the periphery was synthesized from substituted hexapyrrolylbenzenes using a two-step condensation-aromatization procedure. The introduction of peripheral bridges provides access to nonplanar, sterically crowded systems that display complex reactivity patterns, involving stereospecific aromatization of bridges and nucleophile additions. In spite of the interrupted conjugation on the periphery, the new azacoronenes have easily accessible higher oxidation levels, and a quadruply charged species was chemically generated by reaction with SbCl5. These oxidized species show extensive π-electron conjugation, and are efficient UV-vis-NIR absorbers, active up to ca. 2400 nm. Interruption of peripheral conjugation is shown to induce a tendency towards biradicaloid electron configurations in doubly oxidized species.