Phenothiazine−Pyrene Dyads: Photoinduced Charge Separation and Structural Relaxation in the CT State
Electron donor−acceptor systems with phenothiazine linked directly to pyrene exhibit a dual emission in moderately and very polar solvents. Steady state and time-resolved fluorescence spectroscopy provide evidence that the “blue” and “red” emission bands originate from different species. Fluorescenc...
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Published in | The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 107; no. 45; pp. 9530 - 9541 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
American Chemical Society
13.11.2003
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Online Access | Get full text |
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Summary: | Electron donor−acceptor systems with phenothiazine linked directly to pyrene exhibit a dual emission in moderately and very polar solvents. Steady state and time-resolved fluorescence spectroscopy provide evidence that the “blue” and “red” emission bands originate from different species. Fluorescence excitation spectra show a similar appearance when the emission is monitored either in the red or blue spectral range, but they are slightly shifted against each other. This suggests that different isomers exist with a distinctly different photophysical behavior. Semiempirical (AM1/CI) molecular orbital calculations with a continuum solvent treatment have been used to establish the geometry of the two nearly isoenergetic stereoisomers and to calculate the properties of their excited Franck−Condon states. Geometry optimization of various excited states provides evidence for different internal relaxation coordinates for the phenothiazine-localized S1 state and the charge transfer state S6, on one hand, and the pyrene-localized S2 (S3) state, on the other hand. The relaxed geometries in the excited states of both isomers represent mirror images with identical properties. The different photophysical behavior of the two isomers is most likely caused by the different potential energy curves, or more precisely speaking, by different location and/or heights of the barrier along the reaction coordinates from the locally excited to the geometry-relaxed CT states. |
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Bibliography: | istex:3DED45341558EB5C17966F7C60DB01CDA3FB5D0D ark:/67375/TPS-N7G5S3W9-L |
ISSN: | 1089-5639 1520-5215 |
DOI: | 10.1021/jp036250u |