Thiele, Chichibabin and Müller hydrocarbons are considered as classical Kekulé diradicaloids. Herein we report the synthesis and characterization of acyclic diaminocarbene (ADC)-based Thiele, Chichibabin, and Müller hydrocarbons. The calculated singlet–triplet energy gaps are ΔE_S–T = −27.96, −3.70, −0.37 kcal mol⁻¹, respectively, and gradually decrease with the increasing length of the π-conjugated spacer (p-phenylene vs. p,p′-biphenylene vs. p,p′′-terphenylene) between the two ADC-scaffolds. In agreement with the calculations, we also experimentally observed the enhancement of paramagnetic diradical character as a function of the length of the π-conjugated spacer. ADC-based Thiele's hydrocarbon is EPR silent and exhibits very well resolved NMR spectra, whereas ADC-based Müller's hydrocarbon displays EPR signals and featureless NMR spectra at room temperature. The spacer also has a strong influence on the UV-Vis-NIR spectra of these compounds. Considering that our methodology is modular, these results provide a convenient platform for the synthesis of an electronically modified new class of carbon-centered Kekulé diradicaloids.

中文翻译：

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基于无环二氨基卡宾的锡尔，奇奇巴宾和穆勒碳氢化合物

Thiele，Chichibabin和Müller碳氢化合物被认为是经典的Kekulé双自由基。本文中，我们报告了基于无环二氨基卡宾（ADC）的Thiele，Chichibabin和Müller烃的合成和表征。计算出的单重态-三重态能隙分别为ΔE _S–T = −27.96，−3.70，−0.37 kcal mol ^-1，并且随着π共轭间隔基长度的增加而逐渐减小（对苯撑vs. p，p '亚联与p，p两个ADC支架之间的′′′-三亚苯基）。与计算结果一致，我们还通过实验观察到顺磁性双自由基特性随π共轭间隔基长度的增加而增强。基于ADC的Thiele烃是无EPR的，并具有很好的分辨NMR光谱，而基于ADC的Müller的烃在室温下可显示EPR信号和无特征的NMR光谱。间隔物对这些化合物的UV-Vis-NIR光谱也有很大的影响。考虑到我们的方法是模块化的，这些结果为合成电子修饰的新型以碳为中心的Kekulédiradicaloids提供了便利的平台。