Thermally Ultrarobust S=1/2 Tetrazolinyl Radicals: Synthesis, Electronic Structure, Magnetism, and Nanoneedle Assemblies on Silicon Surface

Open-shell organic molecules, including S = 1/2radicals, may provide enhanced properties for several emerging technologies;however, relatively few synthesized to date possess robust thermalstability and processability. We report the synthesis of S = 1/2 biphenylene-fused tetrazolinyl radicals 1 and 2. Both radicals possess near-perfect planar structures basedon their X-ray structures and density-functional theory (DFT) computations.Radical 1 possesses outstanding thermal stability asindicated by the onset of decomposition at 269 degrees C, based on thermogravimetricanalysis (TGA) data. Both radicals possess very low oxidation potentials<0 V (vs. SCE) and their electrochemical energy gaps, E (cell) approximate to 0.9 eV, are rather low. Magnetic propertiesof polycrystalline 1 are characterized by superconductingquantum interference device (SQUID) magnetometry revealing a one-dimensional S = 1/2 antiferromagnetic Heisenberg chain with exchangecoupling constant J '/k approximate to-22.0 K. Radical 1 in toluene glass possessesa long electron spin coherence time, T (m) approximate to 7 mu s in the 40-80 K temperature range, a propertyadvantageous for potential applications as a molecular spin qubit.Radical 1 is evaporated under ultrahigh vacuum (UHV)forming assemblies of intact radicals on a silicon substrate, as confirmedby high-resolution X-ray photoelectron spectroscopy (XPS). Scanningelectron microscope (SEM) images indicate that the radical moleculesform nanoneedles on the substrate. The nanoneedles are stable forat least 64 hours under air as monitored by using X-ray photoelectronspectroscopy. Electron paramagnetic resonance (EPR) studies of thethicker assemblies, prepared by UHV evaporation, indicate radicaldecay according to first-order kinetics with a long half-life of 50 +/- 4 days at ambient conditions.

Automated summary

The synthesis of S = 1/2 biphenylene-fused tetrazolinyl radicals with near-perfect planar structures, outstanding thermal stability, and low oxidation potentials is reported. These radicals possess good magnetic properties and long electron spin coherence time, making them promising for potential applications in molecular spin qubits.