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Iodide as a Triplet State Promoter and Quencher –Mechanisms and Possible Implications
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.ORCID iD: 0000-0003-3200-0374
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this work, Fluorescence Correlation Spectroscopy(FCS) was used to investigate the effects of potassium iodide(KI) on the electronic state population kinetics of arange of organic dyes in the visible wavelength range. Apartfrom a heavy atom effect promoting intersystem crossing tothe triplet states in all dyes, KI was also found to enhancethe triplet state decay by a charge-coupled deactivation.This deactivation was only found for dyes with excitationmaximum in the blue range, not for those with excitationmaxima at wavelengths in the green range or longer. Consequently,under excitation conditions sufficient for tripletstate formation, KI can promote the triplet state build-up ofone dye and reduce it for another, red-shifted dye. The anticorrelated,spectrally separable responses of two dyes to thepresence of one and the same agent are likely to provide auseful readout for biomolecular interaction and micro-environmentalmonitoring studies. In contrast to the typicalnotion of KI as a fluorescence quencher, the FCS measurementsalso revealed that when added in micromolar concentrationsKI can act as an anti-oxidant, promoting the recoveryof photo-oxidized fluorophores. However, in millimolarconcentrations KI also reduces intact, fluorescently viablefluorophores to a considerable extent. In aqueous solutions,an optimal concentration of KI of approximately 5 mM canbe defined at which the fluorescence signal is maximized.This concentration is not high enough to allow full tripletstate quenching. Therefore, as a fluorescence enhancementagent, it is primarily the anti-oxidative properties of KI thatplay a role.

Keyword [en]
Fluorescence correlation spectroscopy, FCS, triplet state, iodide, quenching
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-12342OAI: oai:DiVA.org:kth-12342DiVA: diva2:309808
Note
QC20100617Available from: 2010-04-12 Created: 2010-04-08 Last updated: 2010-06-17Bibliographically approved
In thesis
1. Photo-induced dark states influorescence spectroscopy – investigations & applications
Open this publication in new window or tab >>Photo-induced dark states influorescence spectroscopy – investigations & applications
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on investigations of transient dark states of fluorescentmolecules using spectroscopic techniques. The main purpose is to show andconvince the reader that transient dark states are not always a nuisance, butalso represent an additional source of information. Several studies with fluorescencecorrelation spectroscopy were performed, all related to non-fluorescentstates such as triplet state or isomerized states.Photobleaching is one of the main problems in virtually all of the fluorescencetechniques. In this thesis, mechanisms that retard photobleaching arecharacterized. Several compounds, antioxidants and triplet state quenchers,which decrease photobleaching, are studied, and guidelines for achieving optimalfluorescence brightness using these compounds are presented.Triplet state quenching by several compounds was studied. Detailed investigationsof the fluorescence quencher potassium iodide demonstratedthat for some of fluorophores, except of quenching, there is fluorescence enhancementmechanism present. In agreement with the first publication inthis thesis, antioxidative properties were found to play an important role inthe fluorescence enhancement. Quenching of the triplet state is proposedas a tool for monitoring diffusion mediated reactions over a wide range offrequencies.Specially designed fluorophores combining high triplet yields with reasonablefluorescence brightness and photostability were characterized forpossible applications in novel super-resolution imaging techniques based onfluorescence photoswitching. Except of benefits for imaging techniques, photoinducedswitching to non-fluorescent states could be used for monitoringmolecular diffusion, which was also demonstrated in this thesis.Studies of the triplet state kinetics of fluorophores close to dielectric interfaceswere performed using fluorescence spectroscopy. The analysis of thetriplet state kinetic can provide information about the local microenvironmentand electrostatic interactions near dielectric interfaces.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. vii, 111 p.
Series
Trita-FYS, ISSN 0280-316X ; 2010:20
Keyword
fluorescence correlation spectroscopy, triplet state, isomerisation, photobleaching, quenching, diffusion, total internal reflection, interface
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-12372 (URN)978-91-628-8108-5 (ISBN)
Public defence
2010-04-29, FA31, Albanova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100414Available from: 2010-04-14 Created: 2010-04-12 Last updated: 2011-01-20

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