Self-aggregation of synthetic zinc chlorophyll derivatives possessing multi-perfluoroalkyl chains in perfluorinated solvents

Abstract

Zinc 3¹-hydroxy-13¹-oxo-chlorins possessing two, three, four and six perfluorooctyl chains were synthesized from naturally occurring chlorophyll-a. Only the synthetic zinc chlorin possessing six perfluorooctyl chains was directly dissolved in perfluorinated solvents due to its high fluorine content in molecular weight (over 50%). In this solution, visible absorption spectra gave a red-shifted Q_y band at 723 nm (compared to 648 nm in THF) and showed the formation of well-ordered self-aggregates. No monomeric form was observed in the solution from any fluorescence emission spectra from visible absorption spectra. In the aggregate solution, no precipitation occurred during either standing for a long period or heating at 70 °C. This showed that the supramolecular structure was stabilized by F–F interactions on its surface among the perfluorooctyl chains on the 17-position and perfluorinated solvents. The core part of the supramolecular structure was constructed by a special intramolecular bond of Zn⋯O3²-H⋯OC13¹, which was confirmed from resonance Raman spectral analysis.