Synthesis of Aza-m-Xylylene Diradicals with Large Singlet鈥揟riplet Energy Gap and Statistical Analyses of Their EPR Spectra

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• 作者：Arnon Olankitwanit ; Maren Pink ; Suchada Rajca ; Andrzej Rajca
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：October 8, 2014
• 年：2014
• 卷：136
• 期：40
• 页码：14277-14288
• 全文大小：632K
• ISSN：1520-5126

文摘

We describe synthesis and characterization of a derivative of aza-m-xylylene, diradical 2, that is persistent in solution at room temperature with the half-life measured in minutes (鈭?0鈥?50 s) and in which the triplet ground state is below the lowest singlet state by >10 kcal mol^鈥?. The triplet ground states and 螖E_ST of 2 in glassy solvent matrix are determined by a new approach based on statistical analyses of their EPR spectra. Characterization and analysis of the analogous diradical 1 are carried out for comparison. Statistical analyses of their EPR spectra reliably provide improved lower bounds for 螖E_ST (from >0.4 to >0.6 kcal mol^鈥?) and are compatible with a wide range of relative contents of diradical vs monoradical, including samples in which the diradical and monoradical are minor and major components, respectively. This demonstrates a new powerful method for the determination of the triplet ground states and 螖E_ST applicable to moderately pure diradicals in matrices.