Bathochromic shift of the Q-bands of octakis(p-t-butylbenzyloxy)phthalocyanines with magnesium(II), nickel(II) and copper(II) in a solvent mixture of chloroform and acetic acid

1,4,8,11,15,18,22,25-octakis(p-t-butylbenzyloxy)phthalocyanine complexes of magnesium(II), nickel(II) and copper(II) were prepared by refluxing the propanol solution of 3,6-di(p-t-butylbenzyloxy)phthalonitrile in the presence of magnesium turnings. The complexes showed intense Q-bands between 740 and 750 nm in chloroform. The magnesium(II) complex showed an additional weak band at 807 nm in chloroform, while the nickel(II) and copper(II) did not. The Q-band of the magnesium(II) species was red-shifted with increase of acetic acid in the solvent mixture of chloroform and acetic acid; 745, (765, 807) and (810, 868 nm) in chloroform, 0.1% (v/v) acetic acid and 60% (v/v) acetic acid, respectively. The magnesium(II) complex has bands at 900 and 999 nm in trifluoroacetic acid. In the solvent mixture of 1% (v/v) acetic acid, the red-shift of the Q-band was larger for the magnesium(II) derivative, a little for the nickel(II) and scarcely for the copper(II), respectively. The shift was explained by protonation of the external nitrogen atoms of the phthalocyanine ring.