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Photoinduced electron transfer and geminate recombination in the group head region of micelles
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Image of FIG. 1.
FIG. 1.

Transient absorption spectra at delay following the pump pulse in DTAB micelles. The solid curve is the transient absorption spectrum for ODRB with no DMA acceptors. The curve composed of long dashes is the transient absorption spectrum with DMA present. The curve composed of the short dashes is the difference of the spectra taken with and without acceptors.

Image of FIG. 2.
FIG. 2.

(a) Data taken in DTAB reverse micelles to , a relatively short time period. The Gaussian curve centered at is the instrument response with a full width at half maximum of . The short-dashed curve is the data for ODRB with no DMA acceptors. The solid curve is the excited state decay with DMA. The long-dashed curve is , the normalized charge transfer species concentration. grows in at short time and then decays. (b) The data on a longer time scale. Again, the short-dashed curve is the no acceptor ODRB decay; the solid curve is , and the long-dashed curve is . By there has been substantial geminate recombination, and the remaining geminate recombination slows substantially.

Image of FIG. 3.
FIG. 3.

(a) Forward electron transfer data, , as a function of the DMA acceptor concentration in DTAB micelles. (b) The same data as (a) but on a semilog plot. At short times the decays are nonexponential, but at longer times the decays become approximately exponential. Comparing the decay curve (no acceptors) to the other curves, it is clear that the decays for the samples with acceptors are not the excited state lifetime at long times. (c) The normalized charge transfer state population for the three DTAB micelle samples with acceptors corresponding to the data shown in (a) and (b). The rate and extent of geminate recombination increase as the concentration of acceptors increases.

Image of FIG. 4.
FIG. 4.

Schematic showing the physical model of the micelle with donor (D) and acceptor (A) in the head group region of the micelle. is the angle between the vectors to the centers of the donor and acceptor. See text.

Image of FIG. 5.
FIG. 5.

(a) and (b) show the data for 3 and DTAB samples, respectively. The solid curves are calculated from parameters found in previous experiments that did not have sufficient time resolution to access time .

Image of FIG. 6.
FIG. 6.

Data and fits for the DTAB micelle with the two lowest DMA concentrations [(a) and (b) ]. The fits to the TTAB data are similar in appearance. The values for the parameters obtained from the fits are given in Table I. The quality of the fits is reasonably good.

Image of FIG. 7.
FIG. 7.

The data (circles) and fit are shown for DMA for DTAB. In addition to the data and the fit through the data, the other solid curve is the calculation for DMA using the same parameters that fit the lower two concentrations shown in Fig. 6.

Image of FIG. 8.
FIG. 8.

The radical geminate recombination data, for DMA [(a) circles] and DMA [(b) squares] in DTAB micelles. The solid curves are calculations using a single adjustable parameter. The functional forms of the calculated curves, while not perfect, are certainly quite reasonable, given that there is only a single adjustable parameter. The results are similar in samples with TTAB micelles.

Image of FIG. 9.
FIG. 9.

The radical geminate recombination calculations, , for DMA (short dashes), DMA (long dashes), and DMA (solid) in DTAB micelles. The parameters used are the same as the ones obtained by fitting the experimental curves. curves with higher DMA concentrations exhibit a greater buildup of radicals. The same trend is obtained for calculations in TTAB micelles.


Generic image for table
Table I.

Parameters used to fit the forward electron transfer data.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Photoinduced electron transfer and geminate recombination in the group head region of micelles