Synthesis and Magnetic Properties of Trioxytriphenylamine Dimers in their Di(radical cationic) States

Three structural isomers of trioxytriphenylamine (TOT) dimers, 4,4′′′-bis(2,2′:6′,2“:6”,6-trioxytriphenylamine) (4), 3,3′′′-bis(2,2′:6′,2“:6”,6-trioxytriphenylamine) (5), and 3,4′′′-bis(2,2′:6′,2“:6”,6-trioxytriphenylamine) (6), have been prepared and their electronic and magnetic properties in their di(radical cationic) states have been investigated. These di(radical cationic) species can be handled under ambient conditions because of their high stability under aerated conditions even in solution. The X-ray crystal structure analysis demonstrated that the TOT moieties of all the di(radical cation)s have planar structures similar to that of the parent TOT radical cation 3+. The UV/Vis spectra of the di(radical cation)s show characteristic absorptions depending on the connecting pattern. Thus, in the long-wavelength region (600–900 nm), 42+ exhibits strong and broad characteristic absorptions, whereas compounds 52+ and 62+ exhibit weak absorptions. Notably, in the 450–600 nm region, 52+ displays very similar absorptions (with twice the intensity) to 3+, whereas small differences were observed for 62+. Finally, we investigated in detail the magnetic properties of the corresponding di(radical cation)s by electron spin resonance spectroscopy and magnetic susceptibility measurements, which indicated intramolecular exchange interactions with a singlet ground state and a large singlet–triplet (S–T) gap for 42+, a singlet ground state and a small S–T gap for 52+, and a triplet ground state for 62+.