Wurster‐Type Nanographenes as Stable Diradical Dications

Abstract

Three new and stable diradical dications based on the 4,10-dibromoanthanthrone have been synthesized and characterized. In their dicationic state, the amines show a biradical character in the ground state. Their magnetic properties have been investigated by NMR and EPR spectroscopies. The dicationic salts shows strong and broad optical absorption in the near-infrared region. The main driving force to obtain a ground state biradical is the high steric hindrance that prevents planarization of the diphenylamines with the anthanthrone aromatic core. The radical cations are isolated in two perpendicular π-systems as demonstrated by X-ray diffraction structures. This work provides a new bridging unit in the search for biradical bis(triarylamines) salts.

Wurster‐Type Anthanthrene Polyradicaloid Cations

“…Compared with single molecule 1 in solution, the oxidation potential for P1 was found to be much higher (0.80/0.98 and 1.16/1.32, respectively), which is the opposite of what is expected for a polymer with an extended conjugation. Indeed, as shown in our previous study, the diradical dications are not conjugated with the anthanthrene core, making them isolated from the linear conjugation in the polymer. Yet, in such a case, the oxidation potentials should not show such a large discrepancy with the monomeric unit.…”

“…But, the peaks associated with the now neutral TBPA, i.e., tris(4‐bromophenyl)amine, were not discernible in the spectra. This is in sharp contrast to what is observed with molecule 1 ·+ and 1 2+ since it was possible to quantify the number of transferred electrons from the oxidant with the peak integration associated with the neutral tris(4‐bromophenylamine) . It is probable that a rapid reduction/oxidation process with TPBA is faster than the NMR timescale, producing very large peaks of low intensity, which are lost in the baseline.…”

“…The synthesis of P1 is presented in Scheme . Compound 1 was synthesized in three steps in 60% overall yield according to a previously reported method . Starting from 4,10‐dibromoanthanthrone, imine condensation on the 6 and 12 positions using 4‐octyloxyaniline and titanium tetrachloride was performed.…”

“…It was found that this structural change can occur by heating in solution or by applying pressure in the solid state. Pursuing isoelectronic structures, we have reported the synthesis and characterization of three new anthanthrene‐based bis(triarylamines) (Scheme C) . It was demonstrated that because of the same high steric hindrance that is present in the all‐carbon system, the doubly oxidized anthanthrene has two isolated radical cations (D).…”

Graphene‐like Molecules with Four Zigzag Edges

“…[9] Despite all these studies,t here are very limited reports on GLMs with four zigzag edges (see examples in Figure 1d)and so far,the experimental studies on this type of molecule have been limited to the small-size anthanthrene (FZ1';F igure 1d)d erivatives. [10] Extension along the two short zigzag edges of the anthanthrene molecule will result in large-size GLMs with four zigzag edges (FZ2' and FZ3'). Studies on their electronic properties will help to better understand the effect of the edge structure on the properties of GLMs.Herein, we report the synthesis of their derivatives, FZ1, FZ2, and FZ3, in which all the reactive zigzag edges are kinetically protected by bulky aryl groups to ensure sufficient stability as well as solubility (Scheme 1).…”