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dc.creatorFraelich, Margaret R.
dc.date.accessioned 2007-08-21T01:43:03Z
dc.date.available 2007-08-21T01:43:03Z
dc.date.issued 1994
dc.identifier.urihttps://hdl.handle.net/1911/19088
dc.description.abstract Lifetimes of the lowest triplet electronic states of C$\sb{60}$ and C$\sb{70}$ have been studied in room temperature benzene solution. The lowest energy triplet state (T$\sb1$) of each species was formed by intersystem crossing from a laser-excited singlet state. Transient triplet-triplet absorption spectroscopy was then used to measure the decay kinetics of the triplet state. The data were analyzed using an expanded kinetic model of C$\sb{60}$ and C$\sb{70}$ triplet relaxation in solution. This model includes not only unimolecular $\rm T\sb{1}\rightarrow S\sb0$ radiationless relaxation, but also three bimolecular quenching processes: triplet-triplet annihilation, oxygen quenching and self-quenching. Under experimental conditions that suppress these bimolecular quenching processes, the exponential lifetimes of T$\sb1$ are found to be $\rm 133\ \mu s\ for\ C\sb{60}\ and\ >2.2\ ms\ for\ C\sb{70}$. Triplet C$\sb{60}$ and C$\sb{70}$ are self-quenched with rate constants of $\rm 1.5\ x\ 10\sp{7}\ M\sp{-1}s\sp{-l} and\ 8.5\ x\ 10\sp{7}\ M\sp{-1}s\sp{-l}$, respectively. Triplet-triplet annihilation occurs with bimolecular rate constants of $\rm 5.4\ x\ 10\sp{9}\ M\sp{-l}s\sp{-l}\ for\ C\sb{60}\ and\ 1.2\ x\ 10\sp{10}\ M\sp{-l}s\sp{-l}\ for\ C\sb{70}$. Mixed solutions of C$\sb{60}$ and C$\sb{70}$ are found to exhibit unusual kinetics. A kinetic model featuring efficient and reversible electronic excitation transfer between nearly isoenergetic triplet states is quantitatively successful in accounting for the observed behavior. Energy transfer rate constants for each energy transfer step have been determined from data spanning a range of sample compositions. The deduced values are $\rm 2.4\ x\ 10\sp{9}\ M\sp{-l}s\sp{-l}$ for energy transfer from $\rm C\sb{60}(T\sb{1})\ to\ C\sb{70}(S\sb{0})\ and\ 2.1\ x\ 10\sp{9}\ M\sp{-1}s\sp{-1}$ for energy transfer from $\rm C\sb{70}(T\sb{1})\ to\ C\sb{60}(S\sb{0}).$ These values imply that T$\sb1$ excitation requires only 103 $\pm$ 30 cm$\sp{-1}$ more energy for C$\sb{60}$ than for C$\sb{70}$. The long unimolecular lifetimes and rapid energy pooling may permit more efficient scheme for fullerene photochemistry and optical limiting.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subjectPhysical chemistry
dc.title Triplet state kinetics of buckminsterfullerene and carbon(70) in solution
dc.type.genre Thesis
dc.type.material Text
thesis.degree.department Chemistry
thesis.degree.discipline Natural Sciences
thesis.degree.grantor Rice University
thesis.degree.level Doctoral
thesis.degree.name Doctor of Philosophy
dc.identifier.citation Fraelich, Margaret R.. "Triplet state kinetics of buckminsterfullerene and carbon(70) in solution." (1994) Diss., Rice University. https://hdl.handle.net/1911/19088.


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