Static and dynamic aspects of the partitioning of naphthalene into
the hydrocarbon phase in aqueous
sodium dodecyl sulfate micelles have been critically examined by
nanosecond time-resolved pulse fluorometry.
It is shown that, in such a system, a properly detailed analysis
of the excited-state decay behavior as a
function of progressive partitioning of the solute into increasing
concentrations of micelles is capable of
revealing and directly quantitating the underlying kinetics of the
reversible transfer of naphthalene in
its excited state between aqueous and micellar phases. The
time-resolved data indicate that, in the aqueous
sodium dodecyl sulfate system, the partition coefficient for
excited-state naphthalene can differ only
marginally from that for the ground state. From the estimate
obtained for the rate coefficient for entry
of excited-state naphthalene into micelles, it would appear that any
barrier to the crossing of excited
naphthalene into the micelle, given that a collision has taken place,
is likely to be rather small. The
contrasting time-resolved behavior of a system in which the basis
lifetime of the fluorescence probe in the
micellar environment is shorter than that in the bulk environment
rather than longer, as in the case
examined experimentally, is also modeled. The effects of quenching
of the fluorescence at the interface
between the micellar and aqueous phases are also examined and discussed
in the context of the aqueous
cetyltrimethylammonium bromide system.