Luminescent Quadrupolar Borazine Oligomers: Synthesis, Photophysics, and Two-Photon Absorption Properties
Luminescent Quadrupolar Borazine Oligomers: Synthesis, Photophysics, and Two-Photon Absorption Properties
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DOI：
10.1002/chem.201502268
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发表时间：
2015-12-07
影响因子：
4.3
通讯作者：
Jaekle, Frieder
中科院分区：
文献类型：
--
作者：
Chen, Pangkuan;Marshall, Ariel S.;Jaekle, Frieder
利用高选择性的硅硼交换反应和锡硼交换反应，通过迭代合成方法，制备了一组单分散的弯曲给体-受体-给体型共轭硼氮低聚物BnNn+1 (n=1-4)，其包含富电子三芳胺给体和缺电子三芳硼烷受体单元。研究了链伸长对电化学、单光子和双光子性质以及激发态光动力学的影响。在400-500 nm范围内，芳胺给体到硼基中心受体的强分子内电荷转移（ICT）导致了高量子产率（Phi(fl) >.5）的发射。溶剂致变色效应导致最短分子（n=1）的溶剂位移约为70 nm，并随着链伸长逐渐减小。低聚物在可见光谱区表现出较强的双光子吸收（2PA）， 2PA截面最大可达1410 GM (n=4)，并且由于长寿命单线态-单线态和自由基阳离子/阴离子吸收而具有宽带激发态吸收（ESA）。激发态动力学也表现出对溶剂环境的敏感性。电化学观察和DFT计算（B3LYP/6-31G*）显示空间分离的HOMO和LUMO水平导致具有强ICT特征的高荧光低聚物。BnNn+1低聚物已被用于检测氰化物阴离子，其缔合常数为log K bbb7。
A set of monodisperse bent donor-acceptor-donor-type conjugated borazine oligomers, BnNn+1 (n=1-4), incorporating electron-rich triarylamine donor and electron-deficient triarylborane acceptor units has been prepared through an iterative synthetic approach that takes advantage of highly selective silicon-boron and tin-boron exchange reactions. The effect of chain elongation on the electrochemical, one-and two-photon properties and excited-state photodynamics has been investigated. Strong intramolecular charge transfer (ICT) from the arylamine donors to boryl-centered acceptor sites results in emissions with high quantum yields (Phi(fl)>0.5) in the range of 400-500 nm. Solvatochromic effects lead to solvent shifts as large as similar to 70 nm for the shortest member (n=1) and gradually decrease with chain elongation. The oligomers exhibit strong two-photon absorption (2PA) in the visible spectral region with 2PA cross sections as large as 1410 GM (n=4), and broadband excited-state absorption (ESA) attributed to long-lived singlet-singlet and radical cation/anion absorption. The excited-state dynamics also show sensitivity to the solvent environment. Electrochemical observations and DFT calculations (B3LYP/6-31G*) reveal spatially separated HOMO and LUMO levels resulting in highly fluorescent oligomers with strong ICT character. The BnNn+1 oligomers have been used to demonstrate the detection of cyanide anions with association constants of log K > 7.