Vibronic spectra of solutions and sols of copper phthalocyanine

Optical spectra of solutions and sols prepared from finely dispersed crystalline copper phthalocyanine (CuPc) were studied. The CuPc preparation was demonstrated to contain an admixture of an amorphous phase. The amorphous phase proved to be soluble in dioxane and heptane with the formation of a true molecular solution of CuPc. It was found that CuPc molecules are absorbed by polyethylene, polypropylene, polycaproamide, and cellulose triacetate films. The optical spectrum of individual CuPc molecules was demonstrated to differ substantially from those of particles of the pigment. It featured intense vibronic bands belonging to three π → π* transitions typical of aromatic structures and a series of bands characteristics of n → π* transitions involving nitrogen atoms (<29000 cm −1 ) but showed no absorption bands characteristic of dispersions of the pigment in the visible spectrum (400–800 cm −1 ). It was revealed that the Q-band (λ = 670 nm), assigned in the literature to individual CuPc molecule, in reality belongs to CuPc associates.