Aggregation and site-selective spectroscopy of matrix-isolated metallophthalocyanines

Absorption, emission and selective excitation spectra are reported for the Q (1Eu↔1A1g) transition of zinc phthalocyanine (ZnPc) in Ar matrices. The dependence of the spectra on the method of sample preparation and subsequent treatment of the matrix are indicative of gas-phase aggregation of ZnPc. A simple matrix-preparation method is described that consistently yields samples dominated by well-isolated monomeric guest molecules. The variations of hole-burning efficiency with sample-preparation method and concentration, as well as its dependence on burn wavelength, indicate a role for inter-chromophore interactions and are consistent with a hole-burning mechanism that involves intermolecular triplet-state charge transfer followed by singlet recombination.