Large Aromatic Hydrocarbon Radical Cation with Global Aromaticity and State-Associated Magnetic Activity

Abstract

The stable radical cation of large aromatic hydrocarbons remains a challenge, due to the recessive aromatic character and high reactivity. Here we report the design, synthesis, and characterization of new aromatic π-radical cations from one π-electron oxidation of baytwisted dibenzoperopyrene derivatives. Experimental observations and theoretical calculations revealed that these π-radical cations had significant resonance hybrid structures, advantageous to the spin-and charge-delocalizations over the molecular backbones and emerging global aromaticity in the distorted π-system. Therefore, they are thermodynamically stable even without fully steric protection of all C−H bonds on the carbon skeleton and can be well characterized and studied routinely at ambient conditions. Moreover, the π-radical cation materials demonstrated readily formed magnetic molecule aggregates in the solution phase, while in powder states cationic monoradical characters were manifested and in the crystalline state intermolecular through-space interactions were popular. The phenomenon of varied magnetic activity in different states is experimentally investigated by various spectral means and X-ray crystallographic analysis, assisted by DFT calculations. Our study provides an insight into the resonance hybrid effects in the design of stable large aromatic hydrocarbon radical cations and demonstrates state-associated magnetic activities for π-radical cations, which are necessary in applications as magnetic materials.

Synthesis and Structural Elucidation of Bisdibenzocorannulene in Multiple Redox States

“…Ther oom-temperature electron spin resonance (ESR) spectrum of the radical anion in powders exhibited afeatureless one-line (g e = 2.0028) at 293 K. Thes ignal intensity increased gradually with decreasing temperature (Figure 5a), similar to those observed in typical monoradicals, [23] showing al inear correlation relative to temperature-dependent ESR intensity.N otably,E SR spectra of the dication in both solution and solid states showed an intense signal with g e = 2.0026, indicating an open-shell carbon-rich species.C ooling led to adecrease of ESR intensities,which nearly disappeared when the temperature dropped to 183 K(Figure 5b), suggesting asinglet open-shell diradical ground state for the dication ((BDBCCC) 2+ ). Fitting of the IT-T data by using the Bleaney-Bowers equation [24] gave asinglet-to-triplet energy gap (DE S-T )o fÀ3.7 kcal mol À1 (Figure 5b), comparable to the calculated result (À3.59 kcal mol À1 )b ased on the optimized structure of the dication.…”

Stable Quadruple Helical Tetraradicaloid with Thermally Induced Intramolecular Magnetic Switching

“…50,51 In addition, fine-tuning of the above parameters in a molecular species can lead to a molecule with two or more accessible magnetic states. Thus, the properties exist in two or more interchangeable phases [52][53][54][55] modulated by external stimuli (temperature, pressure, light, etc. ), which are highly desirable for the development of organic magnetic switching materials.…”

Laser Desorption Ionization of Large Condensed Polycyclic Aromatic Hydrocarbons in Petroleum Pitch and Thermally Treated Products

“…We speculate that C 37 H 15 + is from direct laser ionization of the corresponding radical PAH with a possible structure shown in Figure . It should be pointed out that the existence of radical PAHs in soot from high-temperature combustion of hydrocarbons has been well-studied and documented. − These type of species were also observed in various interstellar research by the mid-infrared spectral characteristics of the PAHs. − Low levels of stable PAH radicals in coal and petroleum asphaltenes have been confirmed experimentally by a combination of non-contact atomic force microscopy (nc-AFM) and electron spin resonance (EPR) spectroscopy. − …”