Oxidative coupling of parent free-base porphyrin or metalloporphyrins on the surface of an aqueous phase in a Langmuir-Blodgett trough yields sheets of free-base porphene (C20N4H2)∞, a regular fully conjugated two-dimensional polymer of monoatomic thickness, composed of fused porphyrin rings. As initially formed, the polymer is doped with positively charged holes and its charge is compensated by a diffuse layer of negative counterions beneath it. Depending on the choice of metal and reaction conditions, single or double sheets of dimensions up to tens of micrometers across are obtained. The structure of porphene was determined using in-situ synchrotron grazing incidence X-ray diffraction, X-ray reflectance, X-ray photoelectron spectroscopy and, after transfer to a solid substrate, by scanning tunneling microscopy and atomic force microscopy. Density functional calculations with periodic boundary conditions agree with the proposed structure and suggest that the most stable tautomer contains a checkerboard arrangement of NH bonds in which their directions alternate from any macrocycle to the four neighbors with which it shares sides.

Properties of porphene, a fully conjugated two-dimensional polymer

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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