Temperature-dependent magnetic circular dichroism of lutetium bisphthalocyanine

Magnetic circular dichroism (MCD) and absorption spectra are reported for the Q, RV, and IV band regions (6000-19000 cm(-1)) of lutetium bisphthalocyanine 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-valence 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 mixing of metal and ligand pi orbitals. The spectra are semiquantitatively consistent with interpretation of these bands as arising from fully allowed transitions terminating in exciton coupling states derived principally from pi* <-- pi - excitations of the individual ligands.