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.

以取代六吡咯基苯为原料，通过两步缩合-芳构化过程，合成了一类在边缘带有至多两个饱和桥连基团的氮杂蔻烯（azacoronenes）。边缘桥连基团的引入可获得非平面、空间位阻拥挤的体系，此类体系展现出复杂的反应模式，包括桥连基团的立体专一性芳构化以及亲核加成反应。尽管外围共轭被中断，但所合成的新型氮杂蔻烯具有易于达到的更高氧化态，且通过与五氯化锑（SbCl5）的化学反应可得到四电荷物种。这些氧化态物种展现出广泛的π电子共轭特性，是高效的紫外-可见-近红外（UV–vis–NIR）吸收体，其吸收活性可延伸至约2400 nm。研究表明，外围共轭的中断会使双氧化物种呈现出双自由基型电子构型的趋势。