Self-Assembly of TPPS_4 Porphyrin Molecules into Nanorods Investigated by TEM, AFM, STM and UV/VIS Spectroscopy

摘要

In this paper we discuss the use of scanning probe microscopy techniques to obtain insight into structural and physicochemical properties of single conjugated (macro)molecules and of their molecular architectures as well as to induce conformational transitions in supramolecular objects with a precision on the molecular scale. The aggregates of the tetrakis (4 -sulfonatophenyl) porphyrin (TPPS_4) growth from solution on solid crystalline hydrophilic and hydrophobic substrates were investigated. The spatial structure of TPPS_4 deposited on the surface was imaged using Transmission Electron Microscopy (TEM), Scanning Atomic Force Microscopy (AFM). Scanning Tunneling Microscopy (STM) visualized porphyrin rings structure with molecular resolution. The aggregation of TPPS_4 was investigated by UV-VIS spectroscopy. The TEM investigation revealed a 3-dimensional rod and wheel like molecular order of the TPPS_4 porphyrin assemblies, while a corresponding shorter and mono-disperse oligomer exhibited 2D ribbon-like structure. The TPPS_4 porphyrin molecules self-assemble into micrometer-long nanorods and fibers on substrate surface. The investigations revealed a typical thickness of two or four molecular layers and a width of tenths of molecule diameter. We propose here TPPS_4 ribbons as polymolecular architectures, which are building blocks of TPPS_4 rods and built from the homo-associated porphyrin molecules as revealed by STM. The TPPS_4 nanoribbons can find an applications in a molecular-scale electronic and nanooptic devices.