Band deconvolution analysis of the absorption and magnetic circular dichroism spectral data of ZnPc(-2) recorded at cryogenic temperatures

Absorption, magnetic circular dichroism (MCD), and emission spectra recorded from vitrified solutions of zinc phthalocyanine, ZnPc(-2), are reported. A spectral band deconvolution analysis was performed on the absorption and MCD data using a fitting technique in which identical band parameters are used for both sets of data by the SIMPFIT program. A detailed study of the temperature dependence of the absorption and MCD spectra of ZnPc(-2) shows that a major fraction of the spectral intensity observed at room temperature can be assigned to "hot" bands. This results in a significant discrepancy between the absorption and MCD band widths in spectral data recorded at room temperature. The first spectral band deconvolution of the optical spectra of a main group metal phthalocyanine complex recorded at cryogenic temperatures is reported. The analysis identifies an n → π* transition, at 604 nm, that lies just to the blue of the lowest energy π → π* transition, the phthalocyanine Q band at 671 nm. The B1 and B2 π → π* transitions are assigned to overlapping bands in the 300-430 nm region. The origin of the vibrational bands associated with Q transition is resolved enabling a complete description of the optical spectrum in the UV-visible region to be made. A band at 509 nm in the spectrum of [ZnPc(-1)]⁺ is reassigned as an n → π* transition on the basis of an earlier spectral deconvolution calculation. The results of the spectral deconvolution calculations are compared with results reported for a number of other spectroscopic and theoretical techniques.