I. Radical Recombination in Solvent Cages. II. Quenching of Excited States of Aromatic Molecules Through Exciplex Formation. III. Magnetic Field Effect on Triplet-Triplet Energy Transfer Processes

Citation

Gupta, Amitava (1974) I. Radical Recombination in Solvent Cages. II. Quenching of Excited States of Aromatic Molecules Through Exciplex Formation. III. Magnetic Field Effect on Triplet-Triplet Energy Transfer Processes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7BCX-J566. https://resolver.caltech.edu/CaltechETD:etd-10132005-092659

Abstract

The first section describes experiments on radical recombination rates. From the temperature and solvent dependence of quantities such as escape efficiency from primary solvent cages we deduced that the activation energy of recombination of radical pairs inside the primary cage is zero in all solvents. Some previous data on recombination rates were reinterpreted accordingly, and then we focused our attention on intersystem crossing in radical pairs. Cage efficiencies were determined in a magnetic field relative to zero field values and the significance of these results discussed. The second section describes experiments designed to explore the mechanism of bimolecular quenching processes. Naphthalene fluorescence was quenched by trans-[beta]-ethyl styrene and it was found that this quenching process induces intersystem crossing in naphthalene. The same quencher was used to quench naphthalene triplets and it was observed that a substantial amount of energy wastage (quenching without electronic energy transfer to the quencher) occurs in solvents other than benzene. Energy wastage was also found in quenching of acetophenone triplets by sterically hindered olefins. We obtained kinetic evidence that olefins quench acetophenone triplets through the formation of triplet exciplexes and we estimated its lifetime for the olefin cis-2,2-dimethyl-3-hexene. The third section relates observations that bimolecular ratios of triplet-triplet energy transfer are affected by application of a magnetic field. Efforts were made to further study this field effect using deuterated quenchers and quenchee. A hypothesis has been put forward to explain our data. Other hypotheses have been critically evaluated.

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