Electronic Structures of Metal Complexes Possessing Stacking Configurations of Conjugated Macrocycles

Abstract

Electronic structures of multilayered phthalocyanine (H₂pc) complexes, including phthalocyaninato lanthanide double-decker complexes (dimers), triple-decker complexes (trimers), their radicals, and a tetramer biradical, were investigated through spectroscopic measurements, synthesis of new complexes and theoretical calculations. (1) Excited states of double-decker phthalocyaninato complexes were described using exciton-type and charge-resonance-type excitations. Assignments were given for split Q bands and B bands of lanthanide and tin phthalocyaninate dimers. (2) A new soluble crown-ether substituted trimer was synthesized to obtain detailed spectroscopic data. Previously unknown absorption bands were found in near IR region. The changes in the electronic spectra from a monomeric phthalocyaninato complex through the trimeric complex were accounted for. (3) In order to describe electronic structure of molecular assembly systems in a manner where roles of component units are explicitly represented, localized orbitals (LOs) defined to have a maximum population on a unit were used. The LOs were employed for CI calculations, thereby contributions of intra- and inter-ligand excitation s in excited states of the dimer and trimer were elucidated. Orbital energy changes on respective macrocycies of the dimer and trimer were evaluated using the LOs. (4) A hole in a radical species of the dimer was concluded to be delocalized over the macrocycles by a comparison of electronic spectra of a newly synthesized hetero-dimer, [Lu (nc) (pc) ] (H₂nc: naphthalocyanine), and two homo-dimers. Based on the hole delocalization, a description of ground and excited states of the dimer radicals was given. (5) A trimer radical generated by chemical oxidation showed an intense band at 5000 cm^-1. Energy ratio of the band to the counterpart of the dimer (ca.1/√2 ) as well as the difference of the behavior of the hole was explained. The model also correctly predicted the presence of a single intense band in Q-band region. (6) From a newly synthesized crown-ether substituted dimer radical, a supramolecular structure consisting of two dimer radicals was generated. It was shown from electronic and ESR spectra that the supramolecular structure was in biradical state where the two holes are localized on respective dimer sites.