Optical and ESR studies on dimerization of metallotetra-crowned phthalocyanines

Abstract

The cation and solvent induced dimerization of free base tetra-crowned phthalocyanine (H₂tCRPc) and its metal derivatives (Ag²⁺ and VO²⁺) have been studied by optical and ESR methods. Dimerization induces a blue shift of Q and Soret bands in the optical spectrum with a reduction in intensity. The exciton formalism accounts for the spectral blue shift upon dimerization. ESR studies reveal the formation of a cofacial dimer with axial symmetry upon the addition of cations. The measured zero-field splitting values in parallel and perpendicular regions suggest that the two paramagnetic centres are separated by 4.9 Å in VOtCRPc and 4.8 Å in AgtCRPc. In the micellar medium, the dimerization effects are observed only in 0.1 M SDS, while the tetra-crowned phthalocyanines remain aggregated in 0.1 M CTAB and in 5% TX-100.