Optically active self-assembled pi-conjugated peptides

A major challenge in bioorganic electronics lies in the development of soft, deformable, and (opto)electronically active materials that can assemble into hierarchical structures. We use molecular design and engineering to develop new materials for organic electronics and photonics. In this talk, I discuss recent work that focuses on optically active, pi-conjugated peptides that can be engineered for precise supramolecular assembly. We consider both the kinetics and thermodynamics of assembly using a combination of experiments and modeling. Pi-conjugated peptides are guided to assemble under reaction- or diffusion-dominated conditions, such that the morphology and properties of assembled peptide fiber networks can be controlled by kinetics. A combined spectroscopy-microrheology technique is used to study the sol-gel transition of these materials during assembly, which enables direct measurement of modulus and photophysical properties during gelation. In situ confocal fluorescence microscopy and in situ fluorescence lifetime imaging microscopy (FLIM) are used to characterize peptides during the assembly process. We further demonstrate a facile strategy to macroscopically align supramolecular fibers using a templating method based on sacrificial colloidal microchannels that does not require photolithography. The structural and chemical properties of oligopeptide fibers are characterized using AFM-infrared spectroscopy (AFM-IR), photoinduced force microscopy (PiFM), fluorescence polarization microscopy, and electron microscopy. In addition, the charge transport properties of pi-conjugated peptides are determined under a wide range of applied voltages. Overall, this work illustrates simple yet robust strategies to pattern 1-D supramolecular fibers over large areas, thereby offering new routes for assembling functional organic materials.