Porphyrins. XV. Vapor absorption spectra and stability: Phthalocyanines

Abstract

Vapor absorption spectra in the range 800-200 mμ are given for free base phthalocyanine (H2Pc), MgPc, TiOPc, VOPc, CrPc, FePc, CoPc, NiPc, CuPc, ZuPc, SnCl2Pc, and PbPc. Electronic bands Q, B, N, L, C characteristic of the ring are found in the regions 660 mμ (15 200 cm-1), 320 mμ (31 300 cm-1), 275 mμ (36 400 cm-1), 245 mμ (40 800 cm-1), 210 mμ (47 600 cm-1), respectively. Vacuum UV spectra of H2Pc and ZnPc are given in the region 200-145 mμ and show nearly constant diffuse absorption with two broad bands at 180 mμ (55 600 cm-1) and 160 mμ (62 500 cm-1) and no evidence of Rydberg spectra. The main bands are nicely accounted for by SCMO-PPP-CI calculations. In addition VOPc, CrPc, FePc, CoPc, NiPc, SnCl2Pc, and PbPc show extra bands. For NiPc these are interpreted in terms of d-π* transitions predicted by extended Hückel theory. The vapor spectra are usually blue shifted several hundred cm-1 with respect to solution spectra in DMSO and 1-chloronaphthalene. Only the vapors VOPc, CoPc, NiPc, CuPc, ZnPc are completely stable; the others decompose more or less quickly. Data are given to provide estimates of vapor pressure which average ∼0.1 Torr at 500°C. Solution spectra of H2Pc and CuPc were studied up to 300°C. The bands generally broaden and shift a few mμ to the red but the Qy of H2Pc broadens abnormally and shows no wave-length shift. © 1970.