Department of Chemistry, Center for Macromolecular Science and Engineering, University of Florida, Gainesville, Florida 32611, USA.
J Am Chem Soc. 2012 Feb 8;134(5):2599-612. doi: 10.1021/ja207978v. Epub 2012 Jan 31.
We report on the comparison of the electronic and photophysical properties of a series of related donor-acceptor-donor oligomers incorporating the previously known 2H-benzo[d][1,2,3]triazole (BTz) moiety as the acceptor and the recently reported BTzTD acceptor, a hybrid of BTz and 2,1,3-benzothiadiazole (BTD). Although often implied in the polymer literature that BTz has good acceptor character, we show that this moiety is best described as a weak acceptor. We present electrochemical, computational, and photophysical evidence supporting our assertion that BTzTD is a strong electron acceptor while maintaining the alkylation ability of the BTz moiety. Our results show that the identity of the central atom (N or S) in the benzo-fused heterocyclic ring plays an important role in both the electron-accepting and the electron-donating ability of acceptor moieties with sulfur imparting a greater electron-accepting ability and nitrogen affording greater electron-donating character. We report on the X-ray crystal structure of a BTzTD trimer, which exhibits greater local aromatic character in the region of the triazole ring and contains an electron-deficient sulfur that imparts strong electron-accepting ability. Additionally, we examine the transient absorption spectra of BTzTD and BTz oligomers and report that the BTz core promotes efficient intersystem crossing to the triplet state, while the presence of the thiadiazole moiety in BTzTD leads to a negligible triplet yield. Additionally, while BTz does not function as a good acceptor, oligomers containing this moiety do function as excellent sensitizers for the generation of singlet oxygen.
我们报告了一系列相关给体-受体-给体齐聚物的电子和光物理性质的比较，这些齐聚物包含先前已知的 2H-苯并[d][1,2,3]三唑（BTz）部分作为受体和最近报道的 BTzTD 受体，即 BTz 和 2,1,3-苯并噻二唑（BTD）的混合体。尽管在聚合物文献中经常暗示 BTz 具有良好的受体特性，但我们表明该部分最好被描述为弱受体。我们提供了电化学、计算和光物理证据，支持我们的断言，即 BTzTD 是一种强电子受体，同时保持 BTz 部分的烷基化能力。我们的结果表明，在苯并稠合杂环中中心原子（N 或 S）的身份在受体部分的电子接受和电子供体能力中都起着重要作用，其中硫赋予更大的电子接受能力，而氮赋予更大的电子供体特性。我们报告了 BTzTD 三聚体的 X 射线晶体结构，该三聚体在三唑环区域表现出更大的局部芳香性，并含有赋予强电子接受能力的缺电子硫。此外，我们还研究了 BTzTD 和 BTz 齐聚物的瞬态吸收光谱，并报告说 BTz 核促进高效系间交叉到三重态，而 BTzTD 中噻二唑部分的存在导致可忽略不计的三重态产率。此外，虽然 BTz 不作为良好的受体起作用，但包含该部分的齐聚物确实可以作为产生单线态氧的优异敏化剂。
