Synthesis and Thin Films of Thermally Robust Quartet ( = 3/2) Ground State Triradical.

High-spin ( = 3/2) organic triradicals may offer enhanced properties with respect to several emerging technologies, but those synthesized to date typically exhibit small doublet quartet energy gaps and/or possess limited thermal stability and processability. We report a quartet ground state triradical , synthesized by a Pd(0)-catalyzed radical-radical cross-coupling reaction, which possesses two doublet-quartet energy gaps, Δ ≈ 0.2-0.3 kcal mol and Δ2 ≈ 1.2-1.8 kcal mol. The triradical has a 70+% population of the quartet ground state at room temperature and good thermal stability with onset of decomposition at >160 °C under an inert atmosphere. Magnetic properties of are characterized by SQUID magnetometry in polystyrene glass and by quantitative EPR spectroscopy. Triradical is evaporated under ultrahigh vacuum to form thin films of intact triradicals on silicon substrate, as confirmed by high-resolution X-ray photoelectron spectroscopy. AFM and SEM images of the ∼1 nm thick films indicate that the triradical molecules form islands on the substrate. The films are stable under ultrahigh vacuum for at least 17 h but show onset of decomposition after 4 h at ambient conditions. The drop-cast films are less prone to degradation in air and have a longer lifetime.