Multiple Verdazyl Radicals Appended to a Triarylamine Scaffold

We report the synthesis of three triphenylamine-based verdazyl radicals. These include a mono, bis, and tris(verdazyl) at the 4-position(s) of the N–Ar groups, containing one, two, and three unpaired electrons, respectively. Each of these compounds is air stable, and fully characterized using EPR spectroscopy, high-resolution mass spectrometry, infrared spectroscopy, UV/Vis spectroscopy, and cyclic voltammetry. From the UV/Vis absorbance data, the optical absorbance energy gaps were found to be ~2.35 eV for all three verdazyl-containing compounds. Cyclic voltammetry was used to estimate the energy levels of the singly occupied molecular orbitals (SOMOs), which are -4.91 eV, -5.12 eV, and -4.98 eV for mono, bis, and tris(verdazyl) compounds respectively. Spin-spin exchange interactions were observed in the EPR spectra of both the bis and tris(verdazyl)s, leading to additional hyperfine coupling patterns and assignment of the ground states as triplet and quartet, respectively.