Crystal Structure, Spin Polarization, Solid-State Electrochemistry, and High n-Type Carrier Mobility of a Paramagnetic Semiconductor: Vanadyl Tetrakis(thiadiazole)porphyrazine

We report the synthesis, crystal structure, and magnetic,
electrochemical,
and carrier-transport properties of vanadyl tetrakis­(thiadiazole)­porphyrazine
(abbreviated as VOTTDPz) with S = 1/2. X-ray crystal analysis reveals two polymorphs, the α
and β forms; the former consists of a 1D regular π stacking,
while the latter forms a 2D π network. Molecular orbital calculations
suggest a V4+(d1) ground state
and a characteristic spin polarization on the whole molecular skeleton.
The temperature dependence of the paramagnetic susceptibility of the
α form clearly indicates a ferromagnetic interaction with a
positive Weiss constant of θ = 2.4 K, which is well-explained
by McConnell’s type I mechanism. VOTTDPz forms amorphous thin
films with a flat and smooth surface, and their cyclic voltammogram
curves indicate a one-electron reduction process, which is highly
electrochromic, because of a reduction of the porphyrazine π
ring.
Thin-film field-effect transistors of VOTTDPz with ionic-liquid gate
dielectrics exhibit n-type performance, with a high mobility of μ
= 2.8 × 10–2 cm2 V–1 s–1 and an
on/off ratio of 104, even though the thin films are amorphous.