Morphology-Controlled Self-Assembled Nanostructures of 5,15-Di[4-(5-acetylsulfanylpentyloxy)phenyl]porphyrin Derivatives. Effect of Metal−Ligand Coordination Bonding on Tuning the Intermolecular Interaction

Novel metal-free 5,15-di[4-(5-acetylsulfanylpentyloxy)phenyl]porphyrin H2[DP(CH3COSC5H10O)2P] (1) and its zinc congener Zn[DP(CH3COSC5H10O)2P] (2) were designed and synthesized. Single-crystal X-ray diffraction (XRD) analysis confirmed the tetrapyrrole nature of these two compounds, revealing the existence of metal−ligand coordination bond between the carbonyl oxygen in the aryloxy side chain of meso-attached phenyl group in the porphyrin molecule with the zinc center of neighboring porphyrin molecule in the crystal structure of 2. This intermolecular Zn−O coordination bond induces the formation of a supramolecular chain structure in which the porphyrinato zinc moieties are arranged in a “head-to-tail” mode (J-aggregate), which is in contrast to a “face-to-face” stacking mode (H-aggregate) in the supramolecular structure formed depending on the C−H···π interaction in the crystal of 1. Their self-assembling properties in MeOH and n-hexane were comparatively investigated by scanning electronic microscopy and XRD technique. Intermolecular π−π interaction of metal-free porphyrin 1 leads to the formation of hollow nanospheres and nanoribbons in MeOH and n-hexane, respectively. In contrast, introduction of additional Zn−O coordination bond for porphyrinato zinc complex 2 induces competition with intermolecular π−π interaction, resulting in nanostructures with nanorod and hollow nanosphere morphology in MeOH and n-hexane. The IR and XRD results clearly reveal the presence and absence of such metal−ligand coordination bond in the nanostructures formed from porphyrinato zinc complex 2 and metal-free porphyrin 1, respectively, which is further unambiguously confirmed by the single-crystal XRD analysis result for both compounds. Electronic absorption spectroscopic data on the self-assembled nanostructures reveal the H-aggregate nature in the hollow nanospheres and nanoribbons formed from metal-free porphyrin 1 due to the π−π intermolecular interaction between porphyrin molecules and J-aggregate nature in the nanorods and hollow nanospheres of 2 depending on the dominant metal−ligand coordination bonding interaction among the porphyrinato zinc molecules. The present result appears to represent the first effort toward controlling and tuning the morphology of self-assembled nanostructures of porphyrin derivatives via molecular design and synthesis through introduction of metal−ligand coordination bonding interaction. Nevertheless, availability of single crystal and mole