Type of Publication: | Journal article |
URI (citable link): | http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-78006 |
Author: | Winter, Gerhard; Steiner, Ulrich |
Year of publication: | 1980 |
Published in: | Berichte der Bunsengesellschaft ; 84 (1980), 12. - pp. 1203-1214. - eISSN 0005-9021 |
DOI (citable link): | https://dx.doi.org/10.1002/bbpc.19800841204 |
Summary: |
The influence of heavy atom substituents (Br, I) in the electron donor aniline on the electron transfer reaction with thiopyronine triplet is investigated by flash spectroscopy in solvents of different viscosity and polarity. Triplet quenching constants and radical yields are determined. The results are analysed in terms of decay constants of an intermediate triplet exciplex where the heavy atom substituents significantly enhance the intersystem crossing process leading to singlet ground state formation and thus diminishing the radical yield due to exciplex dissociation. The sensitivity of the radical yield to solvent effects is strongly enhanced by heavy atom substitution though the solvent effects proper on the exciplex dynamics are substituent independent. The heavy atom effect is used to study the solvent cage effect on exciplex dissociation by means of viscosity variation. The exciplex dissociation lifetime is proportional to solvent viscosity, however, it contains a constant contribution which may be attributed to exciplex bonding. By means of the heavy atom probes it is found that increasing solvent polarity intersystem crossing in the exciplex is favored over exciplex dissociation into radicals. A tentative explanation is given in terms of solvent polarity dependence of the electronic energy gap between exciplex and corresponding Franck-Condon ground state.
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Summary in another language: |
Der Einfluß von Schweratomsubstituenten (Br, I) im Elektronendonor Anilin auf die Elektronentransferreaktion mit dem Thiopyronintriplett wurde blitzspektroskopisch in Lösungsmitteln verschiedener Viskosität und Polarität untersucht. Es wurden Triplettlöschkonstanten sowie die Radikalausbeuten bestimmt. Mit Hilfe dieser Ergebnisse wurden relative Zerfallskonstanten eines intermediar gebildeten Triplettexciplexes ermittelt, in dem die Schweratomsubstituenten den zum Singlettgrundzustand führenden Intersystem- Crossing-Prozeß signifikant verstarken und so die Radikalausbeute, die aus der Exciplexdissoziation resultiert, vermindern. Die Empfindlichkeit der Radikalausbeute für Lösungsmitteleffekte wird durch die Schweratomsubstituenten gesteigert, obwohl der eigentliche Lösungsmitteleffekt auf die Exciplexdynamik substituentenunabhängig ist. Mit Hilfe des Schweratomeffekts lässt sich die Variation des Cage-Effektes des Lösungsmittels auf die Exciplexdissoziation bei steigender Lösungsmittelviskositat verfolgen. Die Dissoziationslebensdauer des Exciplexes wächst linear mit der Viskosität, enthält jedoch einen viskositatsunabhängigen Beitrag, der sich der Exciplexbindung zuschreiben lässt. Mit zunehmender Lösungsmittelpolaritat wird der Intersystem-Crossing-Prozeß im Vergleich zur Exciplexdissoziation in Radikale begünstigt. Zur Erklärung wird eine Polaritätsabhängigkeit des Franck-Condon-Faktors des strahlungslosen Prozesses diskutiert.
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Subject (DDC): | 540 Chemistry |
Keywords: | Lösungsmitteleffekte, Photochemie, Schweratomeffekte, Triplettexciplexe |
Link to License: | Attribution-NonCommercial-NoDerivs 2.0 Generic |
WINTER, Gerhard, Ulrich STEINER, 1980. Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short-lived Triplet Exciplexes. In: Berichte der Bunsengesellschaft. 84(12), pp. 1203-1214. eISSN 0005-9021. Available under: doi: 10.1002/bbpc.19800841204
@article{Winter1980Heavy-9711, title={Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short-lived Triplet Exciplexes}, year={1980}, doi={10.1002/bbpc.19800841204}, number={12}, volume={84}, journal={Berichte der Bunsengesellschaft}, pages={1203--1214}, author={Winter, Gerhard and Steiner, Ulrich} }
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