Unsymmetrical zinc azaphthalocyanines, peripherally substituted with thiophen-2-yl and 2-functionalized phenoxy groups

Abstract Four targeted octasubstituted zinc azaphthalocyanines (ZnAzaPc), substituted with thiophen-2-yl groups and ortho-substituted phenoxy groups, were obtained by cyclotetramerization of 5-aryloxy-6-(thiophen-2-yl)pyrazine-2,3-dicarbonitriles. Thiophen-2-yl substituents are known to extend the macrocyclic conjugation, and thereby cause red-shifted UV–Vis Q-bands. Peripheral phenoxy groups with bulky ortho substituents are expected to suppress aggregation and thereby improve solubility of these compounds. The reagent Zn(quinoline) 2 Cl 2 was used for one-step syntheses of these ZnAzaPc. Four tetrasubstituted ZnAzaPc, with phenoxy, (2-isopropyloxy)phenoxy, (2-isopropyl)phenoxy or (2- tert -butyl)phenoxy substituents, were obtained as controls from 5-aryloxypyrazine-2,3-dicarbonitriles. The tetra- and octa-substituted ZnAzaPc, 5 and 6 , were obtained in 30–50% yields after purification by chromatography on silica. UV–Vis Q-bands with high molar extinction coefficients (100 000–160 000), were observed at 635 nm for compounds 5 , and at 660–665 nm for 6 . Grass-green solutions were obtained of compounds 6 in most organic solvents, whereas the less soluble compounds 5 gave blue-green solutions. 2D NMR methods were applied in analyses of DMSO- d 6 solutions of ZnAzaPc 5 and 6 . Broad and partly overlapping 1 H NMR signals for some of the compounds indicate some aggregation as well as presence of two or more structural isomers. Molecular ions of ZnAzaPc 5 and 6 were determined by mass spectrometry (MALDI-TOF). Structure analyses of 5-phenoxy-6-(thiophen-2-yl)pyrazine-2,3-dicarbonitrile ( 4a ), and 5-(2-isopropyloxyphenoxy)-6-(thiophen-2-yl)pyrazine-2,3-dicarbonitrile ( 4b ), show the impact on conformation exerted by the bulky isopropyloxy ortho-substituent of the phenoxy group in 4b , and indicates how this substituent hinders the type of disorder found in 4a .