Self-Assembled Hybrids Composed of Block Copolymer/Porphyrin-Metal Complex via Hydrogen Bonding

Macroscopically homogeneous hybrids comprising a block copolymer/porphyrin-metal complex were prepared by mixing a polystyrene-b-poly(4-vinylpyridine) (SP) block copolymer and a porphyrin metal complex with carboxyl groups. The selective and uniform incorporation of a porphyrin metal complex into the poly(4-vinylpyridine) phase of a nanophase-separated structure was achieved by hydrogen bonding between the pyridyl groups of the poly(4-vinylpyridine) block and the carboxyl groups of the porphyrin- metal complex. The phase-separated structures of the hybrids were observed by multiple structural observation tools. The morphology transition depends on the amount of the porphyrin-metal complex added. Furthermore, increasing the amount of added porphyrin-metal complex was found to lead to its precipitation. This result was attributed to a molar amount of pyridyl groups in the poly(4-vinylpyridine) block that was insufficient for hydrogen bonding compared with the amount of carboxyl groups on the porphyrin-metal complex. The precipitation of the porphyrin-metal complex was also affected by the molecular weight of the poly(4-vinylpyridine) block and was observed even when the molar ratio of pyridyl groups to carboxyl groups was larger than unity, suggesting there were still some free pyridyl groups that could be hydrogen-bonded with carboxyl groups. This result could be explained in terms of the effective concentration of the porphyrin-metal complex in solutions during solvent casting.