A Triphenylamine Double‐Decker: From a Delocalized Radical Cation to a Diradical Dication with an Excited Triplet State

Abstract

Triphenylaminium radical cations are well-known for their remarkable stability; furthermore, the oxidation potential is adjustable by the introduction of a series of substituents, in particular, at the para positions. Thus, they are widely used not only as one-electron oxidative reagents but also as catalysts in organic chemistry. [1] Besides such an application as versatile chemical reagents, the ambient stable radical cations generated from triphenylamine (TPA) derivatives could be utilized as spin sources in molecule-based magnetic materials. In fact, a considerable number of TPA-based molecular multi-spin systems have appeared in the literature. However, from the viewpoint of assemblage of the spin sources into the architecture of the reported molecular systems, the spin-spin exchange coupling pathway has been confined to one-and two-dimensionalities, [2] and accordingly, TPA-based multispin systems with three-dimensional (3D) connectivity are rare.In 1985, Neugebauer and co-workers reported the first synthesis of a TPA double-decker 1 (Scheme 1) [3] in which two TPA moieties are directly connected by threefold o,o'-linkage, in association with an interest in intramolecular interaction between two nitrogen lone pairs.[4] In spite of its sensitivity to oxidation and the formation of persistent radical cation, no detailed information was available concerning the electronic structure. Such a cage-like oligo(triphenylamine) can be regarded as a potent building block to afford the opportunity furnishing new TPA-based macromolecular systems with genuine 3D connectivity. Although neither the parent 1 nor its derivatives have been reported since then, [5] an analogue 2 in which two TPA moieties are connected at para positions of all phenyl groups by three meta-phenylenediamine pillars, was successfully prepared in our laboratory.Slow evaporation of a dilute mixed solution (CH 3 OH and CH 2 Cl 2 ) of a pale yellow product 2, which was obtained by using Buchwald-Hartwig cross-coupling reaction [6] between 4,4',4''-tribromo-TPA as a deck and meta-phenylenediamine as a pillar in a ratio of 2:3, [7] gave yellow block crystals suitable for X-ray structure analysis.[21] The crystal belongs to the space group P2 1 , and contains two molecules of 2 per unit cell in which there exist three sites for CH 2 Cl 2 molecules so as to fill spaces between the double-deckers (Supporting Information, Table S1).The X-ray structure of 2 has almost C 3h symmetrical trichetria-like [8] shape when all the methoxy substituents are ignored, and the upper and lower TPA decks adopt almost planar propeller-like conformation (the tilted angles of phenyl rings range from 428 to 538), and moreover, are totally eclipsed (Figure 1). Three meta-phenylenediamine planes are perpendicular to the TPA planes, and therefore, the distance between two TPA decks are estimated to be about 4.9 at the peripheral three nitrogen pairs and 5.8 at the central nitrogen pair, indicating the direct transannular p-p interaction between two TPA decks is virtually ignorabl...

UV-vis and EPR spectroelectrochemical investigations of triarylamine functionalized arylene bisimides

“…All three compounds can be considered as two triarylamine moieties connected by a nonconjugated bridge. The formation of stable dications of diradical character in this type of compounds is known, 49,[63][64][65] however the formation of such paramagnetic moieties in triarylamines connected by a conjugated linker has also been recently reported. 66 Core-functionalized bisimides (B5, B6 and B7) also form stable radical cations which can be electrochemically generated and detected in an EPR spectroelectrochemical experiment.…”

Polymers for electronics and spintronics

“…Very recently Ito et al have synthesized double-and triple-decker molecules which can be regarded as a 1,3,5-benzenetriamine multiple-decker linked by three meta-phenylenes or two locked tetraaza-meta-cyclophanes 514 or two locked hexaazacyclophanes containing m-p-p-bonds alternation. 441 However, tetraazacyclophanes used as building blocks for a belt-shaped polymacrocyclic oligoarylamine showed the most interesting properties. 515 The latter compound is composed of six Scheme 76 Multicyclophane structures.…”

A Chiral Molecular Cage Comprising Diethynylallenes and N‐Heterotriangulenes for Enantioselective Recognition

“…[21][22][23] Precedents of sensing examples involving triarylamines range from the detection of metallic cations, [24] to toxic anions [25] or anions present in chemical weapons, [26] nitroaromatic explosives, [27] biological metabolites, [28] toxic gases, [29,30] and pH determination. [31] Regarding the implementation of triarylamines in both macrocyclic and cage structures, few examples can be tracked down in literature, [32][33][34][35][36][37][38][39] and even scarcer examples are found for their bridged analogues, N-HTAs, whose presence in complexing and sensing processes is limited. [40][41][42][43][44][45] Besides exploring uncharted waters, N-HTA are also of interest given their solid candidacy for next-generation optoelectronic materials, [46][47][48] and properties such as reversible redox chemistry.…”