Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Chem Phys. 2018 Jul 14;149(2):024905. doi: 10.1063/1.5036656.
Aggregated cyanines form ordered supramolecular structures with the potential to transport energy efficiently over long distances, a hallmark of photosynthetic light-harvesting complexes. In concentrated aqueous solution, pseudoisocyanine (PIC) spontaneously forms fibers with a chiral J-band red-shifted 1600 cm from the monomeric 0-0 transition. A cryogenic transmission electron microscopy analysis of these fibers show an average fiber width of 2.89 nm, although the molecular-level structure of the aggregate is currently unknown. To determine a molecular model for these PIC fibers, the calculated spectra and dynamics using a Frenkel exciton model are compared to experiment. A chiral aggregate model in which the PIC monomers are neither parallel nor orthogonal to the long axis of the fiber is shown to replicate the experimental spectra most closely. This model can be physically realized by the sequential binding of PIC dimers and monomers to the ends of the fiber. These insights into the molecular aggregation model for aqueous PIC can also be applied to other similar cyanine-based supramolecular complexes with the potential for long-range energy transport, a key building block for the rational design of novel excitonic systems.
聚集型花青染料可以形成有序的超分子结构，具有在长距离上高效传输能量的潜力，这是光合作用光捕获复合物的标志。在高浓度的水溶液中，假花青（PIC）自发形成具有手性 J 带的纤维，其红移 1600 cm 相对于单体的 0-0 跃迁。对这些纤维的低温透射电子显微镜分析表明，纤维的平均宽度为 2.89nm，尽管目前尚不清楚聚集物的分子水平结构。为了确定这些 PIC 纤维的分子模型，使用 Frenkel 激子模型对计算的光谱和动力学进行了比较实验。结果表明，一种 PIC 单体既不平行也不垂直于纤维长轴的手性聚集模型最能复制实验光谱。这种模型可以通过 PIC 二聚体和单体顺序结合到纤维的末端来物理实现。这些关于水溶液 PIC 分子聚集模型的见解也可以应用于其他类似的基于花青的超分子复合物，这些复合物具有长程能量传输的潜力，是合理设计新型激子系统的关键构建块。
