Self-Organization of Self-Assembled Tetrameric Porphyrin Arrays on Surfaces
T Milic, Jayne C. Garno, T. Saab, G Smeureanu, J Batteas, Charles M. Drain
The incorporation of designed self-assembled supramolecular structures into devices requires deposition onto surfaces with retention of both structure and function. This remains a significant challenge and presents a barrier to developing devices with these types of materials. To examine the role of peripheral groups in the organization of self-assembled multiporphyrinic arrays on surfaces, square and trapezoidal tetrameric porphyrin arrays with peripheral tert-butyl-phenyl or dodecyloxy-phenyl functionalities were investigated using various spectroscopies and atomic force microscopy. The orientation and length of the peripheral alkyl substituents influences the resultant structures on surfaces. The tert-butyl-phenyl substituted square forms discrete columnar stacks, which assemble in a vertical direction via π-stacking interactions among the macrocycles.. The tetrameric array with dodecyloxyphenyl groups forms a continuous film via van der Waal s interactions among the peripheral hydrocarbon chains. In addition, the supermolecules with liquid-crystal-forming moieties also form 3D crystalline structures on surfaces. These observations clearly demonstrate that the number, position and nature of the peripheral groups, as well as supramolecular dynamics, are of key importance to the 2D and 3D organization of assemblies such as porphyrins on surfaces.