Versatile Strategy To Access Fully Functionalized Benzodifurans: Redox-Active Chromophores for the Construction of Extended π-Conjugated Materials

An efficient synthetic approach to construct a fully substituted benzo[1,2-b:4,5-b′]difuran (BDF) 2a via base-catalyzed double annulations is presented. Compound 2a can readily undergo Suzuki, Heck, and Sonogashira coupling reactions to afford in good yields a manifold of extended π-conjugated BDF derivatives, e.g., with pyridine termini (4−6) and with different spacers. These are highly luminescent materials that undergo two reversible one-electron oxidations. Remarkably, their photophysical and electrochemical properties can be largely tuned by methylation or protonation. Consequently, they can function as pH-dependent fluorescence switches. Finally, the observed electronic properties are explained on the basis of density functional theory.

本文报道了一种高效合成方法，可通过碱催化双环化反应构建全取代苯并[1,2-b:4,5-b′]二呋喃（benzo[1,2-b:4,5-b′]difuran, BDF）2a。化合物2a可便捷地发生铃木-宫浦（Suzuki）、赫克（Heck）及薗头（Sonogashira）偶联反应，以良好收率得到一系列拓展型π共轭BDF衍生物，例如带有吡啶端基（4~6）以及不同间隔基的衍生物。此类化合物均为高发光材料，可经历两次可逆单电子氧化过程。值得注意的是，其光物理与电化学性质可通过甲基化或质子化手段实现大幅调控。因此，它们可作为pH响应型荧光开关发挥功能。最后，本文基于密度泛函理论（density functional theory）对所观测到的电子性质进行了解释。