High-Spin (S = 1) Blatter-Based Diradical with Robust Stability and Electrical Conductivity

• Published in: Journal of the American Chemical Society Vol. 144; no. 13; pp. 6059 - 6070
• Main Authors: Zhang, Shuyang, Pink, Maren, Junghoefer, Tobias, Zhao, Wenchao, Hsu, Sheng-Ning, Rajca, Suchada, Calzolari, Arrigo, Boudouris, Bryan W, Casu, Maria Benedetta, Rajca, Andrzej
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.04.2022
• Subjects: Electric Conductivity; Electron Spin Resonance Spectroscopy - methods; Electrons; Models, Molecular; Molecular Conformation
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.2c01141

Triplet ground-state organic molecules are of interest with respect to several emerging technologies but usually show limited stability, especially as thin films. We report an organic diradical, consisting of two Blatter radicals, that possesses a triplet ground state with a singlet–triplet energy gap, ΔE ST ≈ 0.4–0.5 kcal mol–1 (2J/k ≈ 220–275 K). The diradical possesses robust thermal stability, with an onset of decomposition above 264 °C (TGA). In toluene/chloroform, glassy matrix, and fluid solution, an equilibrium between two conformations with ΔE ST ≈ 0.4 kcal mol–1 and ΔE ST ≈ −0.7 kcal mol–1 is observed, favoring the triplet ground state over the singlet ground-state conformation in the 110–330 K temperature range. The diradical with the triplet ground-state conformation is found exclusively in crystals and in a polystyrene matrix. The crystalline neutral diradical is a good electrical conductor with conductivity comparable to the thoroughly optimized bis­(thiazolyl)-related monoradicals. This is surprising because the triplet ground state implies that the underlying π-system is cross-conjugated and thus is not compatible with either good conductance or electron delocalization. The diradical is evaporated under ultra-high vacuum to form thin films, which are stable in air for at least 18 h, as demonstrated by X-ray photoelectron and electron paramagnetic resonance (EPR) spectroscopies.