Substituted tetra-2,3-pyrazinoporphyrazines .2. Bis(tri-n-hexylsiloxy)silicon derivatives

Dichlorosilicon complexes of substituted tetra-2,3-pyrazinoporphyrazines were obtained via condensation of 2,3-dicyanopyrazine, 2,3-dicyano-5,6-diphenylpyrazine, 2,3-dicyanoquinoxaline, 2,3-dicyano-benzo[f]quinoxaline, and 2,3-dicyano-dibenzo[f,h]quinoxaline with silicon tetrachloride in the presence of urea, quinoline, and tri-n-butylamine. Hydrolysis of the Si-Cl bond in concentrated H2SO4, followed by treatment with 0.01 N NaOH and aqueous NH3, afforded the corresponding dihydroxides, which were converted to the bis(tri-n-hexylsiloxy)silicon derivatives via reaction with tri(n-hexyl)silane in 3-picoline (2,4,6-collidine) in the presence of tri-n-butylamine. The axial tri-n-hexylsiloxy substituents at the central silicon atom prevent aggregation in organic solvents, permitting detailed studies on the effects of structural modifications on the electronic spectra of tetraazaphthalocyanines. Our data show that each benzo ring addition, angularly condensed to the tetra-2,3-quinoxalinoporphyrazine, induces a hypsochromic shift (similar to 10-15 nm) of the main absorption maximum.