Realizing metalloporphyrin functionalization of 4-vinylpyridine copolymer via axial coordination reaction

Cobalt tetra(para-chlorophenyl)porphyrin (CoTCPP) and zinc tetraphenyl porphyrin (ZnTPP) were linked on the side chains of the copolymer of 4-vinylpyridine (4VP) and styrene (St), P(4VP-co-St), via axial coordination reactions, respectively, and the metalloporphyrin-functionalized macromolecules, CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), were prepared. Their chemical structures were characterized by FTIR and 1H NMR. The spectral properties of the two macromolecular axial coordination complexes were mainly studied, and their photophysical behavior were discussed in depth. The experimental results show that the metalloporphyrin-functionalized macromolecules, CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), can be prepared favorably through axial coordination reaction with the side pyridine groups of the copolymer P(4VP-co-St) as ligands. The two complexes have characteristic spectra similar to that of the small molecular metalloporphyrins, CoTCPP and ZnTPP, respectively. At the same time, they also display the characteristic spectroscopic property of axial coordination complexes: the electronic adsorption spectra of CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St) red-shifted obviously as compared to that of CoTCPP and ZnTPP, and the fluorescence emission of ZnTPP-P(4VP-co-St) blue-shifted apparently with respect to that of ZnTPP. For CoTCPP-P(4VP-co-St) and ZnTPP-P(4VP-co-St), some polymer effects were found: (1) the bonding degree of the small molecular metalloporphyrin, CoTCPP or ZnTPP, on the side chains of the copolymer P(4VP-co-St) has a limit value because of the steric hindrance and there is a bonding degree difference between the actual value and the theoretical value; (2) for ZnTPP-P(4VP-co-St), slight energy transfer between adjacent ZnTPP units on an identical macromolecule occurs, leading to slight static quench of the fluorescence emission as the bonding density of ZnTPP units on the side chains of the copolymer P(4VP-co-St) reaches a certain value.