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

Chem, Eur. J., accepted (2017). DOI: 10.1002/chem.201703220  
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) were prepared and their electronic and magnetic properties in the di(radical cationic) states were investigated. 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 structure of the parent TOT radical cation 3+. The UV-vis spectrum of the di(radical cation) showed characteristic absorptions depending on the connecting pattern. Thus, in the long wavelength region (600-900 nm), 4-2+ exhibited strong and broad characteristic absorptions, while compounds 5-2+ and 62+ exhibited weak absorptions. Notably, in the 450-600 nm region, 5-2+ displayed very similar absorptions (with twice the intensity) to those of 3+, while small changes were observed for 6-2+. We finally investigated the detailed magnetic properties of corresponding di(radical cation)s based on the measurements of electron spin resonance spectra and magnetic susceptibilities measurements. The results indicated the intramolecular exchange interactions with a singlet ground state with a large singlet-triplet (S-T) gap for 4-2+, a singlet ground state with a small S-T gap for 5-2+, and a triplet ground state for 6-2+.