Self-Assembly of TPPS4 Porphyrin Molecules into Nanorods Investigated by TEM, AFM, STM and UV/VIS Spectroscopy
V. Snitka, R. Rodaite and V. Mizariene
Kaunas University of Technology, LT
self-assembly, porphyrin, scanning probe microscopy
In this work the aggregates of the tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) growth from solution on solid crystalline hydrophilic and hydrophobic substrates were investigated. The spatial structure of TPPS4 deposited on the surface was imaged using Transmission Electron Microscopy (TEM), Scanning Atomic Force Microscopy (AFM). Scanning Tunnelling Microscopy (STM) visualized porphyrin rings structure with molecular resolution. The aggregation of TPPS4 was investigated by UV_VIS spectroscopy. The TEM investigation revealed a 3-dimensional rod and wheel like molecular order of the TPPS4 porphyrin assemblies, while a corresponding shorter and monodisperse oligomer exhibited 2D ribbon-like structure. The TPPS4 porphyrin molecules self-assemble into micrometer-long nanorods and fibers on substrate surface. Their cross section was determined quantitatively by scanning force microscopy. This revealed a typical thickness of two or four molecular layers and a width of tenths of molecule diameter. This indicates that the molecules are fully extended in the ribbons oriented with the conjugated backbone with the 54.7o to the long axis of the rod. We propose here TPPS4 ribbons as polymolecular architectures, which are building blocks of TPPS4 rods and built from the homoassociated porphyrin molecules as revealed by STM. The TPPS4 nanoribbons can find an application in a molecular-scale electronic and nanooptic devices.
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Nanotech 2005 Conference Program Abstract