Formation of Hydrogen-Bonded Supramolecular Assemblies Based on Functionalized Saddle-Distorted Porphyrins

Supramolecular assemblies consisting of porphyrins have been intensively investigated in the light of promising photo-functionality including photoinduced electron transfer, photo-conducting materials, dye-sensitized solar cells, and guest inclusion toward the emergence of novel functions on the basis of unique spatial host-guest arrangements and interactions.

   Along this line, we have developed a series of supramolecular assemblies using the diprotonated form of saddle-distorted dodecaphenylporphyrin (H₂DPP) through intermolecular π-π interaction, such as Porphyrin Nanochannels, which include electron-donating guest molecules.¹ In this presentation, we present formation and characterization of supramolecular assemblies based on H₂DPP derivatives having hydrogen-bonding functional groups and their metal complexes.

   Introduction of carboxyl groups or hydroxyl groups to the meso-phenyl groups of H₂DPP as hydrogen-bonding sites allows us to construct robust and well-organized supramolecular assemblies. A diprotonated tetracarboxyl-DPP derivative (1, Fig. 1a), for example, formed two-dimensional hydrogen-bonding networks (Fig. 1b) to form a porphyrin nanochannel structure, which were reminiscent of that formed by [H₄DPP²⁺]Cl₂ and was persistent up to 150°C, in contrast to that of [H₄DPP²⁺]Cl₂.² To expand the size of the nanochannels, we also introduced 4-carboxylphenyl groups at the 4-positions of the meso-phenyl groups of H₄DPP²⁺.

   A Zn(II) complex of H₂DPP derivatives having hydroxyl groups at the 4-positions of the meso-phenyl groups (2) was prepared to form a dimer bridged by 4,4’-bypyridine.³ The dimer was revealed to form intermolecular hydrogen-bonding network among the hydroxyl groups in the crystal.

In addition to the crystal structures, we will also mention adsorption of gaseous molecules such as N₂ and CO₂ with porous supramolecular assemblies of functionalized H₂DPP derivatives in the solid state.

References

1. (a) R. Harada et al., Chem. Commun. 2005, 716. (b) T. Kojima et al., Chem.–Eur. J. 2007, 13, 8714. (c) T. Nakanishi et al., Chem. Mater. 2008, 21, 7492. (d) S. Fukuzumi et al., Coord. Chem. Rev. 2012, 256, 2488.
2. T. Ishizuka et al. Chem. Commun. 2012, 48, 6481.
3. T. Ishizuka et al. Dalton Trans. 2013, 42, 16073.