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| - Slow Interfacial Electron Hole Transfer of a trans-Stilbene Radical Cation Photoinduced ina Channel of Nonacidic Aluminum Rich ZSM-5 Zeolite
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| - trans-Stilbene (t-St) is incorporated as an intact molecule without solvent in the medium size channel ofnonacidic aluminum rich Na6.6ZSM-5 zeolite with Na6.6(SiO2)89.4(AlO2)6.6 formula per unit cell. The interactionbetween Na+ cation and t-St occurs through one phenyl group facially coordinated to the Na+ cation near theO atoms binding Al atoms. The similarity between Raman spectra of t-St in solution and occluded in Na6.6ZSM-5 shows that the motion of t-St in the channel approaches at room temperature the isotropic limitcharacteristic of a liquid. The laser UV (266 nm) photoionization generates a primary t-St•+-electron pair asa fast phenomenon. These charge carriers exhibit lifetimes that extend over less than 1 h at room temperatureand disappear according to two parallel competitive ways: direct charge recombination and electron transfer.This subsequent electron-transfer takes place between the electron deficient radical cation (t-St•+) and theelectron donor oxygen atom of the zeolite framework. The aluminum rich Na6.6ZSM-5 zeolite hinders efficientlythe charge recombination and promotes the electron transfer to generate a very long electron−hole pair whichexceeds several hours at room temperature. A one laser Resonance Raman experiment using exciting lineswithin the contour of the unique three band visible absorption spectrum characterizes the ground state ast-St@ZSM-5•+•-. The three UV bands at 512, 558, and 613 nm correspond to a vibrational progression of the1600 cm-1 mode (C−C stretching) in the excited state. A two laser resonance Raman experiment characterizesthe excited-state as a t-St•+@ZSM-5•- radical cation electron pair.
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