Shu Chan, Pink Maren, Junghoefer Tobias, Nadler Elke, Rajca Suchada, Casu Maria Benedetta, Rajca Andrzej
Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States.
Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, United States.
J Am Chem Soc. 2021 Apr 14;143(14):5508-5518. doi: 10.1021/jacs.1c01305. Epub 2021 Mar 31.
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.
高自旋（(S = 3/2)）有机三自由基对于几种新兴技术而言可能具有增强的性能，但迄今为止合成的那些通常表现出较小的双重态 - 四重态能隙和/或具有有限的热稳定性及可加工性。我们报道了一种通过钯（0）催化的自由基 - 自由基交叉偶联反应合成的四重态基态三自由基，它具有两个双重态 - 四重态能隙，(\Delta_1\approx0.2 - 0.3)千卡/摩尔和(\Delta_2\approx1.2 - 1.8)千卡/摩尔。该三自由基在室温下四重态基态的占有率超过70%，并且具有良好的热稳定性，在惰性气氛下于(>160)°C开始分解。通过在聚苯乙烯玻璃中的超导量子干涉仪磁强计和定量电子顺磁共振光谱对该三自由基的磁性进行了表征。通过超高真空蒸发该三自由基，在硅衬底上形成完整三自由基的薄膜，高分辨率X射线光电子能谱证实了这一点。约1纳米厚薄膜的原子力显微镜（AFM）和扫描电子显微镜（SEM）图像表明三自由基分子在衬底上形成岛状结构。这些薄膜在超高真空下至少稳定17小时，但在环境条件下4小时后开始分解。滴铸薄膜在空气中不易降解且具有更长的寿命。
