Iodide as a Fluorescence Quencher and Promoter—Mechanisms and Possible Implications

Abstract

In this work, Fluorescence Correlation Spectroscopy (FCS) was used to investigate the effects of potassium iodide (KI) on the electronic state population kinetics of a range of organic dyes in the visible wavelength range. Apart from a heavy atom effect promoting intersystem crossing to the triplet states in all dyes, KI was also found to enhance the triplet state decay rate by a chargecoupled deactivation. This deactivation was only found for dyes with excitation maximum in the blue range, not for those with excitation maxima at wavelengths in the green range or longer.Consequently, under excitation conditions sufficient for triplet state formation, KI can promote the triplet state build-up of one dye and reduce it for another, red-shifted dye. This anti-correlated, spectrally separable response of two different dyes to the presence of one and the same agent may provide a useful readout for biomolecular interaction and micro-environmental monitoring studies. In contrast to the typical notion of KI as a fluorescence quencher, the FCS measurements also revealed that when added in micromolar concentrations KI can act as an anti-oxidant, promoting the recovery of photo-oxidized fluorophores. However, in millimolar concentrations 2 KI also reduces intact, fluorescently viable fluorophores to a considerable extent. In aqueous solutions, an optimal concentration of KI of approximately 5 mM can be defined at which the fluorescence signal is maximized. This concentration is not high enough to allow full triplet state quenching. Therefore, as a fluorescence enhancement agent, it is primarily the anti-oxidative properties of KI that play a role.

Distribution of Xanthene Dyes in DPPC Vesicles: Rationally Accounting for Drug Partitioning Using a Membrane Model

“…28 The steady-state fluorescence quenching of the dyes by iodide in an aqueous system fitted well to the Stern-Volmer model, equation 4, as demonstrated in Figure 4a for ERY in water and in DPPC at 30.0 °C, and these data are show as a representative plot for the studied system. All other data curves are presented in the Figure S3 in the Supplementary Information section.…”

Unraveling photoluminescence quenching pathways in semiconductor nanocrystals

“…We conclude that iodine quenches semiconductor NCs in an iodide like fashion. In comparison, in PhI the iodine atom is in its coupled from (as supposed to ionic form) and PhI quenches only via HAE and not via CT, which has been demonstrated by fluorescence correlation spectroscopy [36]. The size-dependent differences in av upon addition of quencher as shown in Figure 1a and b are a direct result of CT-style PL quenching.…”

“…This interaction increases the rate of inter-system crossing into the forbidden triplet state [35]. In addition to the HAE, iodide has been known to form charge transfer complexes (CT) with organic fluorophores [36]. From Raman studies of Iodine adsorbed to graphene surfaces it is known to be reduced to form iodide anions upon charge transfer and form I 3 − and I 5 − with excess neutral I 2 [37], which are both quenching species.…”

Trans–Cis Isomerization of Lipophilic Dyes Probing Membrane Microviscosity in Biological Membranes and in Live Cells

“…[30][31][32] (see SI for details). The setup used for the TRAST experiments is based on a previously described instrument 26,27 with some modifications, providing either a confocal detection or a wide-field microscopy read-out for the live cell measurements (see SI).…”