McMasters D R, Wirz J
Contribution from the Institut für Physikalische Chemie der Universität Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
J Am Chem Soc. 2001 Jan 17;123(2):238-46. doi: 10.1021/ja0004377.
Two Kekulé hydrocarbons, 2,2-dimethyl-2H-benzo[cd]fluoranthene (1) and its benzannellated analogue 2,2-dimethyl-2H-dibenzo[cd,k]fluoranthene (2), were generated photochemically from two different photoprecursors each and investigated spectroscopically in cryogenic matrices by UV-vis, fluorescence, and EPR and in solution using ns flash photolysis and chemical trapping experiments. Hydrocarbon 1 is a ground-state singlet species, whereas compound 2 has a triplet ground state, the first such neutral Kekulé hydrocarbon. This difference, which is supported by density functional calculations, has profound influence on the spectroscopy and reactivity of the two compounds. Using the results of the spectroscopic measurements, trapping experiments, and density functional calculations, the singlet-triplet gap for 1 is estimated to be 2.3-2.8 kcal mol(-1), with the singlet the ground state, and 0.8-1.3 kcal mol(-1) for 2, in favor of the triplet.
两种凯库勒烃，2,2 - 二甲基 - 2H - 苯并[cd]荧蒽（1）及其并苯类似物2,2 - 二甲基 - 2H - 二苯并[cd,k]荧蒽（2），分别由两种不同的光前驱体通过光化学方法生成，并在低温基质中通过紫外 - 可见光谱、荧光光谱和电子顺磁共振光谱进行研究，同时在溶液中使用纳秒闪光光解和化学捕获实验进行研究。烃1是基态单重态物种，而化合物2具有三重态基态，这是首个此类中性凯库勒烃。这种差异得到密度泛函计算的支持，对这两种化合物的光谱和反应性有深远影响。利用光谱测量、捕获实验和密度泛函计算的结果，估计1的单重态 - 三重态能隙为2.3 - 2.8千卡·摩尔⁻¹，基态为单重态，而2的单重态 - 三重态能隙为0.8 - 1.3千卡·摩尔⁻¹，三重态为基态。
