Immobilization of cationic zinc(II) complexes of phthalocyanine and unsymmetrical porphyrazine in mesoporous MCM-41 silica, and photo-catalytic activity of the composites

Cationic 2,9,16,23-tetrakis(3-N,N,N-trimethylaminoethyloxy) phthalocyaninatozinc(II) and 20,21-bis(4-N,N,N-trimethylaminophenyl)-4,5,9,10, 14,15-hexakis(4-t-butylphenyl)porphyrazinatozinc(II) were immobilized in MCM-41 silica by the use of an electrostatic interaction with the deprotonated silanol groups of MCM-41. From nitrogen adsorption isotherms, specific surface areas were estimated as 1031 and 702 m².g^-1 for MCM-41 and the composite of 2,9,16,23-tetrakis(3-N,N,N-trimethylaminoethyloxy) phthalocyaninatozinc(II), respectively. From pore-size distribution curves, the maximum pore diameter of MCM-41 and the composite were also estimated as 3.24 and 3.10 nm, respectively. These results revealed that 2,9,16,23-tetrakis(3-N,N, N-trimethylaminoethyloxy)phthalocyaninatozinc(II) was immobilized in the mesopores of MCM-41. While 2,9,16,23-tetrakis(3-N,N,N-trimethylaminoethyloxy) phthalocyaninatozinc(II) formed a dimer with increase in the amount of the complex in the composite, 20,21-bis(4-N,N,N-trimethylaminophenyl)-4,5,9,10,14, 15-hexakis(4-t-butylphenyl)porphyrazinatozinc(II) only slightly formed a dimer in the composite, due to steric hindrance of its peripheral substituents. 1,3-diphenylisobenzofuran was photo-oxidized using the composites as the sensitizer in aerated acetonitrile. The reaction proceeded with singlet dioxygen generated by visible-light irradiation of the sensitizers. While the initial reaction rate with the composite of 20,21-bis(4-N,N,N-trimethylaminophenyl)-4,5, 9,10,14,15-hexakis(4-t-butylphenyl)porphyrazinatozinc(II) increased in proportion to the increase in the amount of the complex, the initial reaction rate with the composite of 2,9,16,23-tetrakis(3-N,N,N-trimethylaminoethyloxy) phthalocyaninatozinc(II) at first increased, but subsequently decreased due to the formation of the photo-inactive dimer.