ISSN:
1573-4846
Keywords:
xerogels
;
pyrene
;
decay associated spectra
;
oxygen quenching
;
multiple domain types
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Steady-state and time-resolved fluorescence spectroscopy are used to determine the local microheterogeneity surrounding pyrene molecules sequestered within tetramethylorthosilicate-derived xerogels. After compensation for the intrinsic background emission from the xerogel, we find that the pyrene intensity decay kinetics are best described by a two-term rate law. This is consistent with the pyrene molecules distributing primarily into two microenvironments. Under ambient conditions, the individual pyrene microenvironments exhibit excited-state fluorescence lifetimes that differ by ∼100 ns. However, the pyrene I1 to I3 band ratios that are associated with each microenvironment are statistically equivalent to one another. These results show that the local dipolarity surrounding these pyrene microenvironments are similar, but the decay rates associated with each microenvironment are very different. The longer-lived pyrene species (Environment #1) constitutes ∼1/2 of the total fluorescence and it exhibits an O2 quenching sensitivity (Ksv1) of (5.19 ± 0.52 × 10−3 %O2 −1 and a bimolecular quenching constant (kq1) of (2.30 ± 0.23) × 104 %O2 −1 s−1. Environment #2, associated with the shorter-lived pyrene species, exhibits an O2 quenching sensitivity (Ksv2) of (2.31 ± 0.16) × 10−2 %O2 −1 and a bimolecular quenching constant (kq2) of (2.11 ± 0.23) × 105 %O2 −1 s−1. These results are interpreted as follows: Environment #1 consists of pyrene molecules sequestered within a relatively rigid siloxane network wherein non-radiative decay pathways are lessened, but these pyrene molecules are not quenched readily by O2. Environment #2 consists of pyrene molecules adsorbed onto surface silanols within the xerogel. These pyrene molecules are quenched by the silanols and they are simultaneously more accessible to O2 compared to Environment #1.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1008717207199
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