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

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.
Despite 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 toward biradicaloid electron configurations in doubly oxidized
species.