Wu Wen-Jie, Li Quan-Song, Li Ze-Sheng
Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of Cluster Science of Ministry of Education, Beijing Key Laboratory for Chemical Power Source and Green Catalysis, School of Chemistry and Chemical Engineering, Beijing Institute of Technology , Beijing 100081, China.
J Phys Chem A. 2017 Feb 2;121(4):753-761. doi: 10.1021/acs.jpca.6b09495. Epub 2017 Jan 18.
Understanding the photochemistry of organoboron compounds is essential to expand optoelectronic applications. In this work, the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combining with density functional theory (DFT) have been employed to investigate the elimination mechanisms of compound 6,7-dihydro-5-benzo[d]pyrido[2,1-f][1,2]azaborininr (B4) on the ground state (S) and the first excited state (S). B4 is one of the 1,2-B,N-heterocycles that undergo competitive thermal elimination and photoelimination depending on the substitution groups on the B atom and the chelate backbone, thus providing a high-selectivity synthesis strategy for luminescent compounds. Since the energy barrier from B4 to BH-pyrido[1,2-a]isoindole (D1) and pyrido[1,2-a]isoindole (A1) on the ground state is lower than that from B4 to 5-benzo[d]pyrido[2,1-f][1,2]azaborininr (C4), the retraction ring reaction is expected to proceed with larger probability than the H elimination upon heating. On the contrary, photoelimination of H may take place easily due to the almost barrierless pathway on the S state. Remarkably, we have located an energetically available conical intersection (S/S)-1, which allows for ultrafast S → S decay and subsequently generation of C4. Our results not only throw light on the experimental observations of the selectivity of thermal elimination and photoelimination but also provide detailed information on the excited state as instructional implications for further synthesis and application of B,N-embedded aromatics.
了解有机硼化合物的光化学对于拓展其光电应用至关重要。在这项工作中，采用了完全活性空间自洽场（CASSCF）及其二阶微扰（CASPT2）方法，并结合密度泛函理论（DFT）来研究化合物6,7-二氢-5-苯并[d]吡啶并[2,1-f][1,2]氮杂硼茚（B4）在基态（S）和第一激发态（S）上的消除机理。B4是1,2-B,N-杂环化合物之一，根据B原子和螯合主链上的取代基团，它会发生竞争性的热消除和光消除反应，从而为发光化合物提供了一种高选择性的合成策略。由于在基态下从B4到BH-吡啶并[1,2-a]异吲哚（D1）和吡啶并[1,2-a]异吲哚（A1）的能垒低于从B4到5-苯并[d]吡啶并[2,1-f][1,2]氮杂硼茚（C4）的能垒，因此预计在加热时缩环反应比氢消除反应更有可能发生。相反，由于在S态上几乎没有能垒的途径，氢的光消除可能很容易发生。值得注意的是，我们找到了一个能量上可行的锥形交叉点（S/S）-1，它允许超快的S→S衰变，随后生成C4。我们的结果不仅揭示了热消除和光消除选择性的实验观察结果，还提供了关于激发态的详细信息，作为对含B,N的芳烃进一步合成和应用的指导意义。
