Toward an Air-Stable Triradical with Strong Spin Coupling: Synthesis of Substituted Truxene-5,10,15-triyl

Abstract

With the aim to achieve air-stable polyradical species manifesting strong spin coupling, synthetic endeavors are made toward triradical molecules featuring a truxene-triyl skeleton. Commonly used steric-hindering side groups such as 2,4,6trichlorophenyl and 9-anthracenyl are both found to be incompetent at stabilizing the targeted truxene triradical, which appears to be elusive from isolation and characterization. Nonetheless, singlecrystal structures of adducts formed by relevant radicals are obtained, which strongly suggests the transient existence of the designed triradicals. Finally, a truxene triradical comprising 1-anthracenyl along with two 9-anthracenyl substituents is successfully isolated and found to exhibit decent stability in air. We propose that because of the smaller dihedral angle assumed by 1-anthracenyl with respect to the plane of truxene-triyl, more effective π-conjugation allows the spin density to be more widely delocalized and distributed to the anthracenyl side groups. Thus, higher stability is gained by the triradical molecule.

Cyclopenta-fused polyaromatic hydrocarbons: synthesis and characterisation of a stable, carbon-centred helical radical

“…The product was obtained as a mixture of isomers; reasonable NMR spectra could thus not be measured. R f = 0.17 5,8,4, difluoren-5-yl (7) Following a published protocol 13 heptacycle 24 (100 mg, 144 µmol) and tBuOK (229 mg, 2.04 mmol), placed in a Schlenk tube, were dissolved under an argon atmosphere in anhydrous THF (7 mL) and the mixture was heated to 60 °C for 16 h. The mixture was cooled to rt, chloranil (160 mg, 649 µg) was added, and after a short stirring (4 min) the mixture was concentrated at reduced pressure. The residue was purified by column chromatography (silica gel, hexane/ CH 2 Cl 2 , 4 : 1) to furnish 7 as a black solid (84 mg, 121 µmol, 84%).…”

“…Neither of the 21 supposable unbranched compounds with seven rings (e.g., 2; all possible structures are given in the ESI) seems to have been synthesized yet, but a branched truxene 4 derivative with a presumed triradical structure has been synthesized and investigated. 13 These and similar persistent organic radicals and diradicals 9b,d,14 are of significant interest due to their redox properties, their possible application as electrode-active materials, 15 and their magnetic behavior. 16 CP-PAHs with two helical arms (5 and 6, which are given in Figure 1 with their closed shell configuration) have similarly been synthesized and investigated.…”

“…, 2 ; all possible structures are given in the ESI†) seems to have been synthesized yet, but a branched truxene derivative 4 with a presumed triradical structure has been synthesized and investigated. 13 These and similar persistent organic radicals and diradicals 9 b,d ,14 are of significant interest due to their redox properties, their possible application as electrode-active materials, 15 and their magnetic behavior. 16…”

Benzo‐Extended Cyclohepta[def]fluorene Derivatives with Very Low‐Lying Triplet States

“…It is worth to mention that 1 – 3 can be easily decomposed by protic solvent, such as methanol and ethanol. For instance, by adding methanol to the CH 2 Cl 2 solution of 1 – 3 , the peak of product [P] + disappeared while a new peak of [P+MeO] + appeared (Figure S61–S63), as monitored by MALDI‐TOF MS, which provide an indirect proof for their open‐shell nature [24] …”

“…For instance, by adding methanol to the CH 2 Cl 2 solution of 1-3, the peak of product [P] + disappeared while a new peak of [P + MeO] + appeared (Figure S61-S63), as monitored by MALDI-TOF MS, which provide an indirect proof for their open-shell nature. [24] Next, the optoelectronic properties of 1-3 were investigated with UV-vis-NIR spectroscopy. As shown in Figure S8, their dihydrogen-precursors 4-6 only showed UV/ Vis absorption below 450 nm.…”