Stranius Kati, Iashin Vladimir, Nikkonen Taru, Muuronen Mikko, Helaja Juho, Tkachenko Nikolai
Department of Chemistry and Bioengineering, Tampere University of Technology , 33720 Tampere, Finland.
J Phys Chem A. 2014 Feb 27;118(8):1420-9. doi: 10.1021/jp412442t. Epub 2014 Feb 13.
In this study we have explored the influence of mutual position of chlorin electron donor and fullerene C60 electron acceptor on photoinduced electron transfer. Two zinc-chlorin-aza-[18]crown-6 compounds and three pyrrolidino[60]fullerenes with alkyl aminium and varying coordinative moieties were synthesized and used for self-assembling of a set of complexes via two-point binding. The aza[18]crown6 moieties were connected to chlorins via amide linker either at 13(4) or 17(4) position, hence, being attached on different sides of the chlorin plane. Furthermore, in the former case, the linker holds the crown closely spaced, whereas, in the latter, the linker gives more space and conformational freedom for the crown with respect to the chlorin macrocycle. The coordinative moieties at fullerene site, 3-pyridine, 4-pyridine, and 3-furan, were built by utilizing the Prato reaction. The two-point binding drove the molecules into specific complex formation by self-assembling; aminium ion was chelated by crown ether, while zinc moiety of chlorin was coordinated by pyridine and furan. Such pairing resulted in distinct supramolecular chlorin-fullerene dyads with defined distance and orientation. The performed computational studies at DFT level in solution, with TPSS-D3/def2-TZVP//def2-SVP, indicated different geometries and binding energies for the self-assembling complexes. Notably, the computations pointed out that for all the studied complexes, the donor-acceptor distances and binding energies were dictated by chirality of pyrrolidino ring at C60. The selective excitation of chlorin chromophore revealed efficient emission quenching in all dyads. The ultrafast spectroscopy studies suggested a fast and efficient photoinduced charge transfer in the dyads. The lifetimes of the charge separated states range from 55 to 187 ps in o-dichlorobenzene and from 14 to 60 ps in benzonitrile. Expectedly, the electron transfer rate was found to be critically dependent on the donor-acceptor distance; additionally, the mutual orientation of these entities was found to have significant contribution on the rate.
在本研究中，我们探讨了二氢卟吩电子供体与富勒烯C60电子受体的相互位置对光诱导电子转移的影响。合成了两种二氢卟吩-氮杂-[18]冠-6锌化合物和三种带有烷基铵且配位部分不同的吡咯烷基[60]富勒烯，并通过两点结合用于一组配合物的自组装。氮杂[18]冠-6部分通过酰胺连接基在13(4)或17(4)位与二氢卟吩相连，因此附着在二氢卟吩平面的不同侧。此外，在前一种情况下，连接基使冠紧密间隔，而在后一种情况下，连接基相对于二氢卟吩大环为冠提供了更多空间和构象自由度。富勒烯位点的配位部分，即3-吡啶基、4-吡啶基和3-呋喃基，是通过利用普拉托反应构建的。两点结合通过自组装驱动分子形成特定的配合物；铵离子被冠醚螯合，而二氢卟吩的锌部分由吡啶和呋喃配位。这种配对产生了具有确定距离和取向的独特超分子二氢卟吩-富勒烯二元体系。在溶液中使用TPSS-D3/def2-TZVP//def2-SVP在DFT水平上进行的计算研究表明，自组装配合物具有不同的几何结构和结合能。值得注意的是，计算指出，对于所有研究的配合物，供体-受体距离和结合能由C60处吡咯烷基环的手性决定。二氢卟吩发色团的选择性激发表明所有二元体系中均有有效的发射猝灭。超快光谱研究表明二元体系中存在快速有效的光诱导电荷转移。电荷分离态的寿命在邻二氯苯中为55至187皮秒，在苯甲腈中为14至60皮秒。不出所料，发现电子转移速率严重依赖于供体-受体距离；此外，发现这些实体的相互取向对速率有重大贡献。
