The formation of a slipped cofacial dimer of zinc (II) tripyridylporphyrin in water-soluble polymer

A novel tripyridylporphyrin monomer, 5-[4-[2-(acryloyloxy)ethoxy]phenyl]-10,15,20-tris(4-pyridyl)porphyrin (TrPyP), and its zinc (II) complex (ZnTrPyP) were synthesized. It was copolymerized with acrylamide to prepare water-soluble polymer P(ZnTrPyP-AM). The aggregation behavior of P(ZnTrPyP-AM) in aqueous solution was investigated by UV–visible absorption spectra. The red shift of Q band and the significantly enhanced relative intensity (ɛα/ɛβ) indicated that the ZnTrPyP was axially coordinated. Meanwhile, Soret band of porphyrin split into two bands, suggesting exciton coupling of aggregates. The porphyrin pendants of P(ZnTrPyP-AM) were supposed to form a slipped cofacial dimer and the macromolecular matrix helped to create the well-defined porphyrin aggregates. This finding was helpful for the assembly of artificial light-harvesting systems in aquatic environment to mimic the dimeric structure in natural LHC.