XVIth IUPAC Symposium on Photochemistry, Helsinki, Finland, July 21-26, 1996, Book of Abstracts, p. 536.
ABSTRACT.
We compared the possibilities of applying of two different kinetic
models for the determination of reaction rate constants in micelles. The
reaction kinetics in micellar solutions were described by analysis of both
computer simulated and experimental data. The pseudophase model considers
micellar solutions as two-phase systems, composed of a bulk phase and a
microphase (pseudophase). It treats the reaction kinetics in these two phases
as if they were two separate homogeneous solutions with particular
concentrations of dissolved species. The microscopic model considers the
compartmentalization of the dissolved molecules over the micelles which are
viewed as individual entities.
Comparative analysis has indicated three different types of
luminescence decay kinetics in micellar solutions in the presence of
quenchers.
(a) When a non-exponential decay is observed, the rate constants for
unimolecular quenching, reactant entry and exit, and intermicellar exchange
can be determined from the experimentally obtained decay only when the
quenching rate exceeds the exit rate.
(b) An essentially monoexponetial decay will be observed if the quenching
rate is much slower than the reactant exit rate. In this situation, the rate
constant for intermicellar quenching can be estimated from the luminescence
decay rate.
(c) If the quencher occupation number is low and the quenching rate is faster
than the reactant exit rate, an essentially monoexponetial decay will also be
observed. Under these conditions, the luminescence decay rate will not yield
information on the quenching rate constant. On the other hand, the rate
constant for reactant entry can be estimated from the decay rate.
The pseudophase model can be used to estimate the reaction kinetics
in micelles only in cases b and c. If the decay deviates insignificantly from an
exponential decay, the accurate determination of the rate constants from
decay data will be virtually impossible by any of the discussed kinetic models.
The values of the intramicellar quenching rate constants estimated
from experimental and simulated data as obtained by the use of the
pseudophase model are close to those obtained by the microphase model.
This work was carried out with the financial support of the European
Union (INTAS Grant No 93-0751), Russian Foundation of Basic Research
(Grant No 95-03775a) and Grant RU.