Synthesis and spectrophotometric study of acidic and complexation properties of 5,15-bis(4′-methoxyphenyl)-2,8,12,18-tetramethyl-3,7,10,13,17,20-hexaethylporphyrin and 5,15-bis(4′-methoxyphenyl)-10,20-diphenyl-2,8,12,18-tetramethyl-3,7,13,17-tetraethylporphyrin in acetonitrile