Supramolecular self-assembly of porphyrinic materials by design. Non-centrosymmetric architectures of the 5-(3′-pyridyl)-10,15,20-tris(4′-carboxyphenyl) and 5-(2′-quinolyl)-10,15,20-tris(4′-hydroxyphenyl) porphyrins

Abstract

This study reports the design of polarized porphyrin network motifs sustained by mixed hydrogen bonding algorithms, aiming at the synthesis of non-centrosymmetric supramolecular architectures. It is based on suitably functionalized porphyrin scaffolds with mixed proton–donor and proton–acceptor groups that exhibit reduced C₂/C_2v point symmetry, in relation to the square-planar tetra-substituted 4′-carboxyphenyl, 4′-hydroxyphenyl or 4′-pyridyl porphyrin derivatives (D_4h) widely utilized in the construction of porphyrin framework solids thus far. Representative examples are provided by supramolecular self-assembly of the free-base 5-(3′-pyridyl)-10,15,20-tris(4′-carboxyphenyl)-porphyrin (1) and 5-(2′-quinolyl)-10,15,20-tris(4′-hydroxyphenyl) porphyrin (2) moieties. In both cases, each porphyrin building block is connected to neighboring species in a cooperative but asymmetric manner by a combination of O–H⋯O and O–H⋯N inter-porphyrin hydrogen bonds, where optimization of the O–H⋯N interactions involves molecules related by twofold screw symmetry. This induces the formation of two-dimensionally networked arrays characterized by polarized intermolecular organization and by corrugated surfaces. Stacking of these layers along the normal direction is characterized by either translation or twofold screw symmetry, affording non-centrosymmetric crystal lattices with solvent species incorporated within the interporphyrin voids.