Solvent-Directed Self-Assembly of (Aqua)Zinc Phthalocyanine in Crystal Solvates and Its Manifestation in Optical Properties

Abstract

A series of 1:1 (aqua)zinc phthalocyanine solvates with polar aprotic solvents was obtained. The X-ray single diffraction study assisted with DFT calculations showed that coordinated water and solvent molecules determine the crystal structure via strong hydrogen bonding, with three fundamentally different structural motifs being formed: a doubly H-bonded supramolecular synthon, which alternates with classical π–π interactions between shifted phthalocyanine fragments, and a solvent-assisted motif with bifurcated hydrogen bonds and negligible π–π intermolecular interactions, which is exceptional for phthalocyanines. H-Bonded dimers in all crystals are very rigid owing to the directionality of hydrogen bonds and their relatively high energy, while π–π supramolecular fragments are flexible and depend on the volume and the properties of the solvents, with a slipping distance ranging from 1.5 to 4.7 Å. The solvent-dependent supramolecular arrangement has a great influence on the molecular structure of (aqua)zinc phthalocyanine and the optical properties of the crystals, which were investigated by visible absorption spectroscopy.