Molecular Photonics Laboratory, School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom.
J Org Chem. 2010 Mar 19;75(6):2018-27. doi: 10.1021/jo1000803.
A series of compounds containing two boron dipyrromethene (Bodipy) units has been synthesized and fully characterized in which the spacer between the two Bodipy groups is varied from dibenzothiophene (BD1), to dibenzofuran (BD2), to 9,9-dimethylxanthene (BD3), and finally to diphenyl ether (BD4 and BD5). For BD1-BD4 the Bodipy units adopt, to varying degrees, cofacial conformations that allow for systematic variations of both the mutual orientation and the mean separation of the two Bodipy residues. In the remaining dimer, BD5, the Bodipy units are well-separated and cannot come into close proximity. Single-crystal X-ray structures have been determined for BD1-BD3 and reveal that the "bite angle" between the two Bodipy residues decreases progressively along the series with individual values of 41.33(5) degrees, 36.95(6) degrees, and 8.57(3) degrees. Detailed (1)H and (19)F NMR studies for BD3 and BD4 show the methylene protons to be diastereotopic due to restricted rotation of the two Bodipy groups. For BD4 conformational rocking is invoked to explain the variable-temperature NMR spectra, whereby the methyl and methylene groups become inequivalent. Cyclic voltammetry indicates reversible oxidation and reduction of the Bodipy groups. However, the close proximity of the Bodipy groups in BD3 and BD4 results in two well-resolved waves in the anodic region, and slight splitting of the cathodic wave. Peak splitting is attributed to charge delocalization. Spectroelectrochemical measurements at a fixed oxidative potential reveal an optical intervalence charge-transfer (IVCT) absorption band. This IVCT band is attributed to electron exchange between the cofacially arranged neutral and mono-oxidized Bodipy units. Various levels of exciton coupling are observed for BD1-BD4, but not BD5 since here the Bodipy groups remain isolated.
已经合成了一系列含有两个硼二吡咯甲川（Bodipy）单元的化合物，并对其进行了充分的表征，其中两个 Bodipy 基团之间的间隔物从二苯并噻吩（BD1）、二苯并呋喃（BD2）、9,9-二甲基芴（BD3），最后到二苯醚（BD4 和 BD5）。对于 BD1-BD4，Bodipy 单元在不同程度上采用共面构象，允许两个 Bodipy 残基的相互取向和平均分离进行系统变化。在剩余的二聚体 BD5 中，Bodipy 单元彼此分离且无法接近。BD1-BD3 的单晶 X 射线结构已确定，结果表明两个 Bodipy 残基之间的“咬合角”沿系列逐渐减小，分别为 41.33(5)度、36.95(6)度和 8.57(3)度。详细的（1）H 和（19）F NMR 研究表明，BD3 和 BD4 的亚甲基质子因两个 Bodipy 基团的受限旋转而呈现出不等的构象。对于 BD4，构象摇摆被用来解释变温 NMR 谱，其中甲基和亚甲基基团变得不等价。循环伏安法表明 Bodipy 基团可发生可逆氧化还原。然而，BD3 和 BD4 中 Bodipy 基团的接近导致在阳极区域出现两个很好分辨的波，并且阴极波稍微分裂。峰分裂归因于电荷离域。在固定氧化电势下的光谱电化学测量揭示了光学离域电荷转移（IVCT）吸收带。该 IVCT 带归因于共面排列的中性和单氧化 Bodipy 单元之间的电子交换。对于 BD1-BD4，观察到不同程度的激子耦合，但对于 BD5 则没有观察到，因为在这里 Bodipy 基团仍然是孤立的。
