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

Abstract

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 radical-radical cross-coupling reaction, which possesses two doublet-quartet energy gaps, EDQ ≈ 0.2 -0.3 kcal mol -1 and EDQ2 ≈ 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 C under inert atmosphere. Magnetic properties of 3 are characterized by SQUID magnetometry in polystyrene glass and by quantitative EPR spectroscopy. Triradical 3 is evaporated under ultra-high 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 ultra-high 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 longer lifetime.

Thiophene‐Based Double Helices: Radical Cations with SOMO–HOMO Energy Level Inversion†

“…Electrochemistry. Cyclic and square wave voltammetric data for racemic double helices 1-TMS 12 and 2-TMS 8 , using ferrocene as a reference, were obtained according to the following procedure (21,29,30). The double helix 1-TMS 12 (1.49 mg, 0.81 μmol) or 2-TMS 8 (1.61 mg, 1.31 μmol) was evacuated in Schlenk vessel at 60°C overnight and then filled with argon.…”

“…Quantitative EPR spectroscopy for radicals in solutions was carried out using TEMPONE in the identical solvent, as a reference (22,30,35). Typically, the solvent was thoroughly dried DCM.…”

From radical to triradical thin film processes: the Blatter radical derivatives

“…We have previously demonstrated that these spectral features correspond in all three cases to the evaporation and deposition of intact molecules. [15][16][17] We use a specific protocol to assess the intactness. 25 We consider (1) the stoichiometric information from the XPS spectra, (2) the comparison between films and powder XPS spectra (the powder does not undergo evaporation) looking at the shape and the components of the single spectroscopic lines using a best-fit procedure 26 that we have also previously correlated with electron spin resonant (ESR) spectroscopic investigations; 10,15,27,28 (3) the comparison between the experimental and the theoretical curves obtained by DFT calculations.…”

Molecular and Spin Structures of a Through‐Space Conjugated Triradical System

“…Among many types of multi-spin radicals, triradicals with three-fold symmetry have attracted a high level of fundamental interest because their spin-spin coupling modes cannot be determined uniquely due to spin frustration or Jahn-Teller effects. Although a few model systems have been prepared, [8][9][10][11][12][13] studies of isolable three-spin molecules have been limited by their intrinsic instability. This has hindered efforts aimed at gaining a detailed understanding of the fundamental properties of triradicals as well as at developing practical applications.…”