Azaanalogs of phthalocyanine: Syntheses and properties

Structural data, nomenclature, synthetic routes and spectral properties of the majority of known azaanalogs of phthalocyanines are presented. Among the synthetic procedures, the preparation and purification of both lipophilic and water soluble azaphthalocyanines are described. The physico-chemical properties of these compounds are strongly influenced by the presence of exocyclic nitrogen atoms, which are more basic than the meso atoms of the porphyrazine macroring. This increased basicity of the azaanalogs, compared with the corresponding phthalocyanines, explains their tendency to form stable hydrates and their specific affinity for protons in acidic media. The hypsochromic shift of the Q-band in the electronic spectra of the azaanalogs of phthalocyanine, naphthalocyanine and anthracyanine, resulting from the aza substitution in the fused benzo rings, is shown to depend on the number and position of the heterocyclic N atoms in the macrocycle. The effect of aza substitution on the absorption spectra becomes more pronounced in the case of linearly annelated azaphthalocyanines. In contrast, sequential linear annelation alone induces a strong bathochromic displacement of the Q-band. The recent data concerning the angular annelation of octaazanaphthalocyanine suggest that each angularly condensed benzo ring contributes to a hypsochromic shift of the main absorption maximum of 10-15 nm. Such data are essential in the design of new phthalocyanine related compounds with 'tuned' absorption maxima and selected solubility, as substrates for new materials.