SUBSTITUTED TETRA-2,3-PYRAZINOPORPHYRAZINES .2. BIS(TRI-N-HEXYLSILOXY)SILICON DERIVATIVES

Dichlorosilicon complexes of substituted tetra-2,3-pyrazinoporphyrazin es were obtained via condensation of 2,3-dicyanopyrazine, 2,3-dicyano- 5,6-diphenylpyrazine, 2,3-dicyanoquinoxaline, 2,3-dicyano-benzo[f]quin oxaline, and 2,3-dicyano-dibenzo[f,h]quinoxaline with silicon tetrachl oride in the presence of urea, quinoline, and tri-n-butylamine. Hydrol ysis of the Si-Cl bond in concentrated H2SO4, followed by treatment wi th 0.01 N NaOH and aqueous NH3, afforded the corresponding dihydroxide s, which were converted to the bis(tri-n-hexylsiloxy)silicon derivativ es 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 sub stituents at the central silicon atom prevent aggregation in organic s olvents, permitting detailed studies on the effects of structural modi fications on the electronic spectra of tetraazaphthalocyanines. Our da ta show that each benzo ring addition, angularly condensed to the tetr a-2,3-quinoxalinoporphyrazine, induces a hypsochromic shift (similar t o 10-15 nm) of the main absorption maximum.