Cluster-quenched fluorescence

Y. Nosenko, A. Kyrychenko, R. P. Thummel, J. Waluk, B. Brutschy, and J. Herbich, Fluorescence quenching in cyclic hydrogen bonded complexes of I // pyrrolo[3,2 hjquinoline with methanol Cluster size effect. Phys. Chem. Chem. Phys. 9, 3276 3285 (2007). 

The silver clusters can be applied as fluorescent probes to retrieve information about the chemical environment. There are reported three classes of sensors based on silver clusters. First, we discuss silver cluster sensors of which the fluorescence quenches in the presence of the analyte. Second, we discuss a sensor in which fluorescent clusters are formed only in presence of the analyte. Finally, we discuss the shift in the absorption and fluorescence bands of silver clusters while sensing the chemical environment. 

What is not discussed at length are photophysical phenomena in SCF solvents (e.g. fluorescence quenching, triplet-triplet annihilation, charge transfer, and exiplex formation) which have been extensively used to probe SCF properties, in general, and have been especially informative regarding the existence of clusters (solvent-solute and solute-solute) and their effect on reactivity. Absorption and fluorescence spectroscopy (both steady state [21-33] and time resolved [34-40], vibrational spectroscopy [41-44] pulse radiolysis, [45] and EPR [46,47] have all been utilized in this regard. 

Fluorescence and fluorescence excitation spectra, and fluorescence quantum yields of the fullerene clusters are different from those of the fullerene monomers. The excitation and absorption spectra of the fullerene clusters are in good agreement [80]. The observed fluorescence yields of fiillerenes decrease significantly upon the formation of clusters. This is opposite to the trend of increasing transition probabilities as measured by the integrated molar absorptivities. The lower fluorescence yields for the fullerene clusters are likely due to more efficient excited state nonradiative decays. One possible mechanism is the quenching of photoexcited fiillerenes by neighboring fullerene molecules in the clusters with excimer-like interactions [82]. However, no flillerene-fiillerene excimer emissions have been observed. 

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