Metallic Lustrous Porphyrin Foil with an Exceptional Refractive Index

Abstract

Metal-lustrous porphyrin foils, self-standing films of fully πconjugated polymers composed of a glassy porphyrin unit bearing the elastic 3,4,5-tri((S)-dihydrocitronellyloxy)phenyl groups, are disclosed. A remarkable refractive index of 3.04 due to the anomalous dispersion effect of the intense resonance absorption was found for the porphyrin foil of a polymer with a meso-to-meso 1,4-diethynylphenylene-linked backbone (1). Due to the anomalous dispersion effect, the sharp contrast between the intense absorption and specular reflection at the smooth glassy porphyrin foils provides a brilliant noniridescent green metallic luster. On the other hand, the porphyrin foil of a 1,4-diethynyl-2,3,5,6-tetrafluorophenylenelinked polymer with a conformation-locked conjugated backbone via the C−F•••H−C interaction between and the edge-faced porphyrin β-protons (2) results in an insignificant refractive index presumably because of the low dielectric constant of fluorine. Nevertheless, the enlarged π-conjugated domain of 2 forms a stable ground-state biradical, while the open-shell character of 1 is moderate. The study reveals that brilliant metallic luster manifests the considerably delocalized π-system in a relatively bulk and/or macroscopic context rather than the molecular-scale properties.