Direct observation of structural properties and fluorescent trapping sites in macrocyclic porphyrin arrays at the single-molecule level

By utilizing single-molecule defocused wide-field fluorescence microscopy, we have investigated the molecular structural properties such as transition dipole moment orientations and the angular relationship among chromophores, as well as structural distortions and flexibilities depending on the ring size, in a series of cyclic porphyrin arrays bearing close likeness in overall architectures to the LH2 complexes in purple bacterial photosynthetic systems. Furthermore, comparing the experimental results with molecular dynamics simulations, we ascertained site selection for fluorescent trapping sites. Collectively, these experimental and computational results provide the basis for structure-property relationships and energy hopping/emitting processes in an important class of artificial light-harvesting molecular systems widely used in molecular electronics technology.