Structurally Constrained Boron-, Nitrogen-, Silicon-, and Phosphorus-Centered Polycyclic π-Conjugated Systems

Abstract

Incorporation of main group elements into the π-conjugated frameworks is a sophisticated strategy to alter the fundamental nature of the parent conjugated πsystems, giving rise to attractive electronic and photophysical properties that are otherwise inaccessible with classic carbon-or metal-based materials. Out of all πconjugated heterocycles, those that are structurally constrained by tethered aryl substituents surrounding the main group center deserve a great deal of attention because not only do they commonly possess the maximum efficiency of π-conjugation and intermolecular interaction, but they also enjoy remarkable thermal and morphological stabilities that are especially crucial for solid-state performances. In certain cases, elucidation of the behavior of such compounds may additionally provide sufficient perspective toward graphene materials doped with main group elements, which are widely considered as potential next-generation optoelectronic materials. In this review, we will specifically focus on historical developments of structurally constrained polycyclic π-electron systems particularly of those with boron, nitrogen, silicon, or phosphorus atoms annulated directly into the center of π-conjugated systems. CONTENTSReview pubs.acs.org/CR

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…[192] Boron-doped polycyclic arenes are gaining more and more attention because of their promising properties and use in organic electronics,l ight-emissive materials,a nd fluorescent sensors. [193,194] Yamaguchi and co-workers have synthesized the first planarized, fully conjugated triarylborane 187 using FeCl 3 -mediated cyclization, which led to the formation of two new bonds between the benzothienyl substituents and an anthracene moiety ( Figure 14). [195] Thes ame group has also used FeCl 3 as an oxidant in the synthesis of alarger PA H containing two boron atoms.…”

A Spherically Shielded Triphenylamine and Its Persistent Radical Cation

“…[10] Exploiting the rich chemistry of aromatic amines,b ack in the 1980s, Hellwinkel and Melan [11] reported an elegant molecular design resulting from the exhaustive introductiono fb ridging units at the ortho-position of triphenylamine, which forces the originally propeller-shaped scaffold into av irtually planar geometry (Figure 1b). [12] Various types of bridged triphenylamines have been reported to date, [12,13] including carbonyl, [14] ether, [5,15,16] thioether, [17] dimethylmethylene, [18,19] and diphenylmethylene bridges [20] as well as triphenylamines with two fused pentagons. [21] It has been demonstrated that Hellwinkel's design principle can be adopted to stabilize N-centered radicalcations by delocalization of the radical over the planarized p-system.…”

Oxoborane Formation Turns on Formazanate‐Based Photoluminescence

“…[14] While heterocycles containing BC [15] or BN [16] bonds with some p character are common, there appear to be no reports of photoluminescence induced by the formation of terminal double or triple bonds to boron.I nt his work, we demonstrate that the formation of the oxoborane (B=O) group transforms normally non-emissiveb oron triarylformazanate complexes into ap hotoluminescent compound. Electron-rich diborenes have also been paired with p-accepting diarylboryls to produce molecules with near-IR photoluminescence.…”