Temperature-dependent magnetic circular dichroism of lutetium bisphthalocyanine

Magnetic circular dichroism (MCD) and absorption spectra are reported for t he Q, RV, and IV band regions (6000-19000 cm(-1)) of lutetium bisphthalocya nine in poly(methyl methacrylate) films and Ar matrixes. Weak, temperature- independent MCD of the IV band (similar to 7500 cm(-1)) is consistent with its assignment to the intervalence transition of a delocalized mixed-valenc e system. The temperature-dependent MCD of the Q (similar to 15300 cm(-1)) and RV (similar to 11000 cm(-1)) bands is quantified by moment analysis and interpreted to indicate excited-state spin-orbit splittings due to weak mi xing of metal and ligand pi orbitals. The spectra are semiquantitatively co nsistent with interpretation of these bands as arising from fully allowed t ransitions terminating in exciton coupling states derived principally from pi* <-- pi - excitations of the individual ligands.