Wang Chen, Xu Qing-Wen, Zhang Wei-Ning, Peng Qian, Zhao Cui-Hua
School of Chemistry and Chemical Engineering, Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, Shandong University , Jinan 250100, People's Republic of China.
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, People's Republic of China.
J Org Chem. 2015 Nov 6;80(21):10914-24. doi: 10.1021/acs.joc.5b02038. Epub 2015 Oct 8.
A series of organoboron-based biphenyls o,o'-NMe2, o,p'-NMe2, p,p'-NMe2, which contain an electron-donating NMe2 and an electron-accepting BMes2 groups at o,o'-, o,p'-, p,p'-positions of biphenyl skeleton, respectively, as well as o,o'-NBn2, which contains more bulky NBn2 rather than NMe2, were fully characterized to explore the effect of structural modification on the intramolecular charge-transfer emissions. In addition to significant effect of substitution position on photophysical properties, remarkable influence of conformation was also observed for o,o'-substituted compounds. The emission is substantially blue-shifted as conformation changes from the location of NMe2 and BMes2 at same side of biphenyl axis with a close B···N distance, and thus direct B···N electronic interaction in o,o'-NMe2, to the location of NBn2 and BMes2 on two opposite sides in o,o'-NBn2. And o,o'-NMe2 exhibits the longest emission wavelength, but the shortest absorption wavelength, and thus largest Stokes shift among these four organoboron-based biphenyls in both solution and solid state. The theoretical calculations demonstrated that the unique structure of o,o'-NMe2, in which boryl and amino located at the same side of biphenyl axis with close B···N distance and direct B···N electronic interaction, is helpful to stabilize the lowest singly occupied orbital in the exited state.
一系列基于有机硼的联苯，即分别在联苯骨架的邻位、邻 - 对位、对位含有给电子的NMe₂和吸电子的BMes₂基团的o,o'-NMe₂、o,p'-NMe₂、p,p'-NMe₂，以及含有比NMe₂体积更大的NBn₂的o,o'-NBn₂，都经过了全面表征，以探究结构修饰对分子内电荷转移发射的影响。除了取代位置对光物理性质有显著影响外，对于邻位取代的化合物，还观察到了构象的显著影响。当构象从联苯轴同侧的NMe₂和BMes₂位置（B···N距离很近，因此在o,o'-NMe₂中有直接的B···N电子相互作用）转变为o,o'-NBn₂中NBn₂和BMes₂位于两个相对侧时，发射显著蓝移。并且o,o'-NMe₂在这四种基于有机硼的联苯中，在溶液和固态下均表现出最长的发射波长，但最短的吸收波长，因此具有最大的斯托克斯位移。理论计算表明，o,o'-NMe₂的独特结构，即硼基和氨基位于联苯轴同侧且B···N距离很近并有直接的B···N电子相互作用，有助于稳定激发态的最低单占据轨道。
