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The Symmetry of Two-Photon Excited States as Determined by Time-Resolved Fluorescence Depolarisation Experiments
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
2007 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 111, no 45, 11531-11539 p.Article in journal (Refereed) Published
Abstract [en]

A new experimental and theoretical approach is presented for the quantitative determination and assignment of the two-photon absorption tensor of fluorophores dissolved in liquid solutions. Two linearly independent time-resolved fluorescence anisotropies and the two-photon polarization ratio were determined from experiments based on using the time-correlated single photon counting technique. The data were analyzed in a global manner under the assumption of prevailing diffusive molecular reorientations and when accounting for the influence of rapid unresolved reorientations. The method has been applied in fluorescence studies of perylene, two-photon excited at 800 nm. The analysis suggests that the two-photon transition is mediated via vibronic coupling including at least two vibrations of different symmetry, and also that the first singlet excited electronic state acts as a dominating intermediate state.

Place, publisher, year, edition, pages
2007. Vol. 111, no 45, 11531-11539 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97540DOI: 10.1021/jp074506gISI: 000250809400018PubMedID: 17944444OAI: oai:DiVA.org:uu-97540DiVA: diva2:172528
Available from: 2008-09-18 Created: 2008-09-18 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Two-Photon Excited Fluorescence Depolarisation: Experimental and Theoretical Development
Open this publication in new window or tab >>Two-Photon Excited Fluorescence Depolarisation: Experimental and Theoretical Development
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We have studied fundamental aspects of time-resolved two-photon excited fluorescence depolarisation. The thesis presents experimental as well as theoretical progress. We show that a multi-photon induced instrumental response function obtained from a suspension of gold nanoparticles is appropriate for the analysis of two-photon excited fluorescence decays obtained using time-correlated single photon counting detection. Theoretical expressions have been derived for the fluorescence anisotropy decay obtained upon two-photon excitation of various molecular systems in liquid solutions: a) an anisotropic rigid rotor that undergoes rotational diffusion in the presence of ultrafast unresolved restricted reorientations, e.g. librations. b) a molecular group covalently attached to a stationary macromolecule, and undergoing local reorientation in a uniaxial ordering potential. A new approach to the analysis of two-photon excited fluorescence depolarisation experiments was developed, which combines data obtained by using linearly and circularly polarised excitation light, in a global manner. In the analysis, knowledge about unresolved reorientations was obtained from one-photon excitation studies of the corresponding systems. By means of this procedure it has been possible to obtain quantitative information about the molecular two-photon absorption tensor for perylene and two of its derivatives. Thereby the symmetry of the final excited and intermediate vibronic states could be assigned. The analysis reveals that the two-photon transition studied with the 800 nm laser exhibits mixed character. An important finding from the experiments was that the two-photon absorption tensor appears to be solvent dependent. Furthermore, the thesis presents the first theoretical treatment of two-photon excited donor-donor energy migration in the presence of molecular reorientation and which applies the extended Förster theory. Explicit expressions for molecules that belong to the point groups D2h, D2 and C2v are given. Preliminary experiments are finally also reported on a two-photon excited donor-donor energy migration system consisting of a bisanthryl-bisteroid.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2008. 78 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 552
Keyword
Two-photon excitation, Fluorescence, Fluorescence depolarisation, Fluorescence anisotropy, Time-correlated single photon counting, Gold nanoparticles, Rotational diffusion, Excited state symmetry, Extended Förster theory, Orientation correlation functions, Donor-donor energy migration (DDEM)
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-9285 (URN)978-91-554-7282-5 (ISBN)
Public defence
2008-10-10, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, 752 37 UPPSALA, Uppsala, 10:15
Opponent
Supervisors
Available from: 2008-09-18 Created: 2008-09-18Bibliographically approved

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Ryderfors, LinusMukhtar, Emad

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