Macroscopic alignment and assembly of π-conjugated oligopeptides using colloidal microchannels

B. Li, L. R. Valverde, F. Zhang, Y. Zhou, S. Li, Y. Diao, W. L. Wilson and C. M. Schroeder

ACS Appl. Mater. Interfaces, Just accepted (2017)
ne-dimensional (1-D) supramolecular self-assembly offers a powerful strategy to achieve long-range unidirectional ordering of organic semiconducting materials via non-covalent interactions. Using hierarchical assembly, electronic and optoelectronic materials can be constructed for applications including organic conducting nanowires, organic field-effect transistors (OFETs), and organic light-emitting devices (OLEDs). Despite recent progress, it remains challenging to precisely align and assemble 1-D structures over large areas in a rapid and straightforward manner. In this work, we demonstrate a facile strategy to macroscopically align supramolecular fibers using a templating method based on sacrificial colloidal microchannels. Using this approach, colloidal microchannels are generated on a solid surface using a simple fabrication method, followed by the spontaneous self-assembly of π-conjugated oligopeptides inside large arrays of microchannels triggered by solvent evaporation. Following oligopeptide assembly and removal of sacrificial microchannels, the structural properties of oligopeptide fibers were characterized using atomic force microscopy (AFM), atomic force microscope infrared-spectroscopy (AFM-IR), photo-induced force microscopy (PiFM), fluorescence polarization microscopy, and electron microscopy. These results reveal macroscopic alignment of oligopeptide fibers into ordered structures over millimeter length scales, facilitated by colloidal microchannel templating. In addition, the charge transport properties (I-V curves) of π-conjugated oligopeptides assembled using this method were determined under a wide range of applied voltages using interdigitated array electrodes and conductive AFM. Overall, this work illustrates a simple yet robust strategy to pattern 1-D supramolecular fibers over large areas, thereby offering new routes for assembling materials for organic electronics.