Fluorescence quenching mechanism

Masuhara H, Shioyama H, Saito T et al (1984) Fluorescence quenching mechanism of aromatic hydrocarbons by closed-shell heavy metal ions in aqueous and organic solutions. J Phys Chem 88 5868-5873... 

Donor-acceptor probes are very useful as fluorescent lables in biochemical assay and sensing based on the fluorescence quenching mechanisms. In a closed state form where the donor and acceptor are close to each other, the fluorescence of the donor (reporter) is highly quenched. In an open state, where the donor and receptor are spaced away from each other due to biochemical reactions, the donor fluorescnece is restored. The changes of the fluorescence intensity of the reporter has been used for DNA detection, immunoassay, enzyme sensing and detection of many other bimolecules. 

One further feature of SERS merits attention at this point. This is the widely recognized fact that strongly fluorescent molecules, whose Raman spectra are obscured by their much stronger and broader fluorescence emission, commonly have their strong fluorescence quenched by adsorption at a SERS-active metal surface. The fluorescence quenching mechanism is presumably closely related to that for the CT effect shown in Fig. 2. 

In order to clear up the mechanism of inactivation of excited states, we examined the processes of quenching of fluorescence and phosphorescence in PCSs by the additives of the donor and acceptor type253,2S5,2S6 Within the concentration range of 1 x 1CT4 — 1 x 10"3 mol/1, a linear relationship between the efficiency of fluorescence quenching [(/0//) — 1] and the quencher concentration was found. For the determination of quenching constants, the Stem-Volmer equation was used, viz. 

Krause, G.H. Behrend, U. (1986). A pH-dependent chlorophyll fluorescence quenching indicating a mechanism of protection against photoinhibition of chloroplasts. FEBS Letters, 200, 298-302. 

The rhodamine B-bound complex of Ir1 (387) shows only minor alterations in the absorption spectrum of bound rhodamine B as opposed to free dye however, its fluorescence is strongly quenched.626 Fluorescence is intense when the rhodamine dye is attached to an Ir111 center. The authors conclude that the excited-state quenching mechanism is via electron transfer. 

El Bissati, K., E. Delphin, N. Murata, A. Etienne, and D. Kirilovsky (2000). Photosystem II fluorescence quenching in the cyanobacterium Synechocystis PCC 6803 Involvement of two different mechanisms. Biochim Biophys Acta 1457(3) 229-242. 

Fluorescence quenching is described in terms of two mechanisms that show different dependencies on quencher concentration. In dynamic quenching, the quencher can diffuse at least a few nanometers on the time scale of the excited state lifetime (nanoseconds). In static quenching, mass diffusion is suppressed. Only those dye molecules which are accidentally close to a quencher will be affected. Those far from a quencher will fluoresce normally, unaware of the presence of quenchers in the system. These processes are described below for the specific case of PMMA-Phe quenched by MEK. 

Lakowicz JR (2006) Mechanisms and dynamics of fluorescence quenching, Chapter 9. In Principles of fluorescence spectroscopy, 3rd edn. Springer, New York... 

Calixarene containing a dioxotetraaza unit, PET-18, is responsive to transition metal ions like Zn2+ and Ni2+. Interaction of Zn2+ with the amino groups induces a fluorescence enhancement according to the PET principle. In contrast, some fluorescence quenching is observed in the case of Ni2+. PET from the fluorophore to the metal ion is a reasonable explanation but energy transfer by electron exchange (Dexter mechanism) cannot be excluded. 

The mechanism for the photoreaction between 133 and cyclohexene can be summarized as in Scheme 8. The initiating electron transfer fluorescence quenching of 133 by cyclohexene resulted in the formation of an w-amino radical-radical cation pair 136. Proton transfer from the 2-position of the cyclohexene radical cation to the nitrogen atom of the a-amino radical leads to another radical cation-radical pair 137. Recombination of 137 at the radical site affords the adduct 134, while nucleophilic attack at the cation radical of 136 leads to another radical pair 138 which is the precursor for the adduct 135. 

---