Modulation of Semiconducting Behavior and a Change in Morphology upon Gelation of a Peptide Appended Naphthalenediimide

Abstract

A dipeptide appended naphthalenediimide (NDI) are self-assembled in aqueous phosphate buffer medium of pH 7.5 to form nanovesicular structures. Interestingly, these molecules are assembled to form hydrogels in presence of glucono-δ-lactone (at pH 4.7) or Ru3+ solution (at pH 4.6). The gel formation is associated with a sharp morphological change from nanospheres to nanofibrous network structure and this nanofibrous network is responsible to trap many solvent molecules to form hydrogels. These gels and aggregates are well characterized by different spectroscopic and microscopic tools including UV-vis absorption and fluorescence spectroscopy, Fourier transformed infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD), rheological studies and high resolution transmission electron microscopic (HR-TEM) studies. The peptide appended NDI was found to form J-aggregate as it is evident from the UV-vis absorption studies of the aggregated species. Upon excitation at 384 nm wavelength, the glucono-δ-lactone based hydrogel shows a greenish blue fluorescence and similar fluorescence is observed for the aggregates of NDI appended peptide in aqueous buffer medium at pH 7.5. The soluble aggregates and both gels (obtained from the treatment of glucono-δ-lactone and Ru3+) show wonderful current conduction and photo-switching properties. Interestingly, the photo-conductivity and the gain in photocurrent values are enhanced in the GDL and Ru3+ mediated gels by several orders. This indicates that the morphological change from nanovesicles to ordered network of fibers have an important role in the enhancement of photocurrent gain in photo switching experiments.