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

High-spin (S = 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 3, synthesized by a Pd(0)-catalyzed radicalradical cross-coupling reaction, which possesses two doublet-quartet energy gaps, Delta E-DQ approximate to 0.2-0.3 kcal mol(-1) and Delta E(DQ)2 approximate to 1.2-1.8 kcal mol(-1). The triradical has a 70+% population of the quartet ground state at room temperature and good thermal stability with onset of decomposition at >160 degrees C under an inert atmosphere. Magnetic properties of 3 are characterized by SQUID magnetometry in polystyrene glass and by quantitative EPR spectroscopy. Triradical 3 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 similar to 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.

Automated summary

This paper presents a quartet ground state triradical synthesized by a Pd(0)-catalyzed radicalradical cross-coupling reaction. The triradical has small doublet-quartet energy gaps, good thermal stability, and can form stable thin films on silicon substrate. These thin films show onset of decomposition after 4 hours under ambient conditions but have a longer lifetime than drop-cast films.