Spectroscopic studies of phthalocyanines and their clusters with small molecules

van der Waals clusters of free base phthalocyanine (H2Pc) and magnesium phthalocyanine (MgPc) with small hydrocarbons [CnH2n+2(n=1,2,3)], hydrogen bonding solvents (H2O, MeOH, EtOH), and CO2 are studied in the gas phase using supersonic molecular jet spectroscopy. Fluorescence excitation spectra of the cluster systems are characterized in the 000 regions of the cluster S1←S0 transitions. Forbidden low frequency cluster chromophore out-of-plane vibronic transitions are induced by clustering in the majority of the cluster systems studied. This low frequency motion is characterized using an out-of-plane normal coordinate analysis on the H2Pc moiety. Calculations of the binding energy and ground state geometry for the clusters are carried out employing Lennard-Jones (6-12-1) and hydrogen bonding (10-12-1) potentials. Comparison between the calculations and experiments allow for the identification of specific configurations responsible for the cluster vibronic transitions observed. The cluster vibronic spectra and theoretical calculations suggest that stable H2Pc and MgPc solvation sites are located over the phthalocyano core and not over peripheral ring centers. The H2Pc/hydrocarbon cluster experimental and calculational results parallel those obtained for benzene and N-heterocycle/hydrocarbon clusters studied previously. The H2Pc and MgPc/alcohol cluster spectra and calculated geometries suggest that the solvent OH group is intimately involved in the intermolecular interactions and contributes significantly to the observed spectroscopic shifts.