Knowledge Bank

Contours of the visible band in copper phthalocyanine (CuPC) and nickel phthalocyanine (NiPC) change sharply as a result of the $\alpha \to \beta$ crystal transformation. The spectra of vanadyl phthalocyanine (VOPC) and metal-free phthalocyanine $(H2PC)$ remained unchanged under all conditions of deposition or heat treatment attempted. The spectrum of $H2PC$ is compared to the polarized spectra of single $crystals.1$ The $\beta$ modifications of both CuPC and NiPC also exhibit spectra whose absorption maxima are consistent with the single crystal $H2PC$ results. Quantitative aspects of Davydov splittings in pure and mixed $\alpha$ and $\beta$ crystals will be discussed.