The Mechanism of Triplet-Energy Transfer in Solution: the Quenching of Excited-State Benzophenone by Transition-Metal Chelates

Citation

Foss, Robert Paul (1963) The Mechanism of Triplet-Energy Transfer in Solution: the Quenching of Excited-State Benzophenone by Transition-Metal Chelates. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/16RT-DR28. https://resolver.caltech.edu/CaltechETD:etd-03252009-151617

Abstract

The quenching of triplet-state benzophenone by transition-metal chelates of acetylacetone, dipivaloylmethane and dibenzoylmethane is studied in detail. Compounds with both diamagnetic and paramagnetic ground state configurations and with square planar and octahedral structural configurations are used in this investigation. The most extensively studied chelates are the octahedrally complexed acetylacetonate and dipivaloylmethide complexes of iron, chromium, cobalt and aluminum. Detailed molecular orbital calculations considering the π-orbital interaction between the ligand π-orbital system and the d-atomic orbitals centered on the metal atom are performed on these chelates. The calculated spectra of the chelates agree well with the observed. Quenching experiments show no correlation between the paramagnetic susceptibility of the chelates and their quenching efficiency. Furthermore, no correlation between quenching efficiencies and the energies of the low energy ligand field transitions is observed. A correlation is obtained, however, between the quenching efficiencies of the chelates and the calculated and observed π-π* transition energies. A steric effect, introduced by the ligands, is observed between corresponding sets of dipivaloylmethide and acetylacetonate chelates. Both the energy correlation and the steric effect may be explained by a general mechanism for triplet energy transfer in solution which is given in this thesis. Quenching of singlet benzophenone by the dibenzoylmethide chelates of iron and chromium is also observed. A possible explanation of these results is given.

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