Porphyrin nanofibers of ca. 30 nm in diamgeter with aspect ratios of up to 400:1 were formed through hierarchical assembly by acidifying tetra(<i>p</i>-carboxyphenyl)porphyrin (TCPP) with hydrochloric acid in water, and their resulting morphology, internal molecular arrangement, and the growth mechanisms have been explored. UV-visible absorption spectroscopy and atomic force microscopy (AFM) show that after the carboxylate groups of TCPP were protonated (ca. pH 5), the porphyrins form J-aggregate nanoplatelets. At lower pHs (ca. pH 2), the absorption spectrum of the porphyrin nanofibers shows a collapse of the Q bands, revealing that protonation of the core nitrogens of the porphyrin occurred, yielding TCPP diacids. Once formed, a highly crystalline lattice in the porphyrin nanofibers could be observed using cryogenic transmission electron microscopy (cryo-TEM), with X-ray photoelectronc spectroscopy (XPS) verifying the intercalation of chloride within the porphyrin nanofibers. Fluorescence of the TCPP was observed to be quenched when assembled into nanoplatelets, but was found to be restored when the porphyrins assembled into nanofibers. Circular dichroism (CD) spectroscopy showed that although the porphyrin molecules and nanoplates were achiral, the porphyrin nanofibers exhibited a degree of supramolecular chirality. Photoconductivity of the porphyrin nanofibers was measured by four point probe and two-terminal current voltage (I-V) measurements, which will also be described.

Self-assembly and photophysical properties of porphyrin nanofibers

254th National Meeting (2017)

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