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首页> 外文期刊>Chemistry: A European journal >Syntheses and Energy Transfer in Multiporphyrinic Arrays Self-Assembled with Hydrogen-Bonding Recognition Groups and Comparison with Covalent Steroidal Models
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Syntheses and Energy Transfer in Multiporphyrinic Arrays Self-Assembled with Hydrogen-Bonding Recognition Groups and Comparison with Covalent Steroidal Models

机译：自组装有氢键识别基团的多卟啉阵列的合成与能量转移及与共价甾体模型的比较

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A number of new porphyrins equipped with complementary triple hydrogen-bonding groups were synthesized in good yields. Self-assembly was investigated by NMR spectroscopy, dynamic light scattering (DLS), and atomic force microscopy (AFM). These artificial antenna systems were further characterized by stationary and time-resolved fluorescence techniques to investigate several yet unsolved questions on the mechanism of excitation energy transfer (EET) in supramolec-ular systems. For example, the photo-physics of a simple D-U ident to P-A dyad was studied, in which donor D and acceptor A are Zn~(II)- metalated and free-base porphyrins, respectively, and U (uracyl) and P (2,6-diacetamidopyridyl) are complementary hydrogen-bonding groups linked by flexible spacers. In this dyad, the EET occurs with about 20 % efficiency with a lifetime of 14 ps. Reversal of the nonsymmetric triple hydrogen-bonding groups to give a A-U ident to P-D construct results in an EET efficiency of about 25% and a lifetime of 19 ps. Thus, there is a slight directionality of EET mediated by these asymmetric triple hydrogen-bonding units tethered to flexible spacers. In poly-meric systems of the type centre dot centre dot centre dot P-D-P ident to U-A-U ident ot P-D-P centre dot centre dot centre dot, or centre dot centre dot centre dot U-D-U ident to P-A-P ident to U-D-Ucentre dot centre dot centre dot, the EET efficiency doubles as each donor is flanked by two acceptors. Because doubling the probability of photon capture doubles the EET efficiency, there is no energy amplification, which is consistent with the "antenna effect". For these polymeric systems, AFM images and DLS data indicate large rodlike assemblies of a few hundred nanometers, whereas the components form much smaller aggregates under the same conditions. To understand the importance of the flexible hydrogen-bonding zipper, three different covalently bridged D-B-A molecules were synthesized in which the bridge B is a rigid steroidal system and the same ester chemistry was used to link the porphyrins to each end of the steroid. The geometry inferred from molecular modeling of D-B-A indicates geometric similarities between B and some conformations of the - P ident to U- supramolec-ular bridge. Although the EET efficien-cy is a factor of two greater for the steroidal systems relative to the supra-molecular dyads, the rate is 50-80 times slower, but still slightly faster than that predicted by Forster-type mechanisms. Circular dichrosim (CD) spectra provide a conformational sampling of the porphyrin groups appended on the steroidal skeleton, thus allowing an estimation of the orientation factor K for the transition dipole moments, which significantly affects the EET rate. We conclude that the flexible hydrogen-bonded linked systems are adaptive and have variable geometries with foldamers in which the D and A groups can approach well under 1 nm. In these folded conformations, a rapid EET process occurs, probably also involving a Dexter-type exchange mechanism, thus explaining the fast EET relative to the rigid steroidal compounds. This study predicts that it is indeed possible to build large supramolecular antennas and the component design and supramolecular dynamics are essential features that dictate EET rates and efficiencies.
机译：合成了许多具有互补的三氢键合基团的新型卟啉，收率很高。通过NMR光谱，动态光散射（DLS）和原子力显微镜（AFM）研究了自组装。这些人造天线系统还通过固定和时间分辨荧光技术进行了表征，以研究关于超分子系统中激发能传递（EET）机理的几个尚未解决的问题。例如，研究了一个简单的DU身份与PA dyad的光物理关系，其中供体D和受体A分别是Zn〜（II）金属化和游离碱卟啉，以及U（尿嘧啶）和P（2 ，6-二乙酰氨基吡啶基）是通过柔性间隔基连接的互补氢键基团。在这种情况下，EET的效率约为20％，寿命为14 ps。逆转不对称的三重氢键基团以使P-D结构具有A-U身份，其EET效率约为25％，寿命为19 ps。因此，由这些不对称的三氢键合单元连接到柔性间隔基上，介导的EET的方向性很小。在类型为点中心点中心点中心点PDP标识为UAU标识或PDP中心点中心点中心点PDP标识为PAP中心点为UD-Ucentre中心点中心点类型的多点系统中，当每个供体有两个受体时，EET效率翻倍。因为将光子捕获的概率加倍会使EET效率加倍，所以没有能量放大，这与“天线效应”一致。对于这些聚合物系统，AFM图像和DLS数据指示了几百纳米的大型棒状组件，而在相同条件下，这些组件形成的聚集体要小得多。为了理解柔性氢键拉链的重要性，合成了三种不同的共价桥连的D-B-A分子，其中桥B是刚性甾体系统，并且使用相同的酯化学方法将卟啉连接到甾体的每个末端。从D-B-A分子模型推断出的几何结构表明B与B的某些构象之间的几何相似性-识别为U-超分子桥。尽管相对于超分子二倍体，EET效率对于甾体系统而言是高出两倍，但其速度要慢50-80倍，但仍比Forster型机理所预测的快。圆二色谱（CD）光谱对附在甾体骨架上的卟啉基团进行了构象采样，因此可以估算跃迁偶极矩的取向因子K，从而显着影响EET速率。我们得出的结论是，灵活的氢键连接系统具有适应性，并且具有带有折叠器的可变几何形状，其中D和A组可以在1 nm以下接近。在这些折叠的构象中，发生了快速的EET过程，可能还涉及Dexter型交换机制，因此可以解释相对于刚性甾族化合物而言快速的EET。这项研究预测，确实有可能制造大型的超分子天线，并且组件设计和超分子动力学是决定EET速率和效率的基本特征。

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