Higher order fluorescence correlation

The association rate constants were the same within experimental error. The dissociation rate constant for 31 was however an order of magnitude larger than that for 32. The association rate constants determined with fluorescence correlation spectroscopy were similar to the rate constants determined using temperature jump experiments (see above). However, a significant difference was observed for the dissociation rate constants where, for the 1 1 complex, values of 2.6 x 104 and 1.5 x 104s 1 were determined in the temperature jump experiments for 31 and 32, respectively.181,182 The reasons for this difference were not discussed by the authors of the study with fluorescence correlation spectroscopy. One possibility is that the technique is not sensitive enough to detect the presence of higher-order complexes, such as the 1 2 (31 CD) complex observed in the temperature jump experiments. One other possibility is the fact that the temperature jump experiments were performed in the presence of 1.0 M NaCl. 

In fluorescence correlation spectroscopy (FCS) a small volume element or a small area) of a sample is illuminated by a laser beam and the autocorrelation function of fluctuations in the fluorescence is determined by photon counting. From this autocorrelation function the mean number densities of the fluorophores and their diffusion coefficients can be extracted. Measurement and analysis of higher order correlation functions of the fluorescence has been shown to yield information concerning aggregation states of fluorophores ). 

In order to overcome this obstacle, we used a synchronously pumped, mode-locked dye laser, cavity-dumped at 4 MHz and time-correlated single-photon counting detection (18). Because of the higher sensitivity of this experimental system we were able to work at low e, using aqueous rhodamine B solutions with concentrations down to 10" M. To examine the dependence of the fluorescence decays on we chose to work with surface-solution interfaces, so as to minimize the problems associated with inhomogeneous surface coverage, which arise with dry surfaces... 

Another synthetic method for submicrometer fluorescence CdSe/ZnS/PS nanocomposite particles was developed by Joumaa et al. [205]. Submicrometersized particles were synthesized via a mini-emulsion PS process and CdSe/ZnS was coated by PS. Styrene emulsion and mini-emulsion polymerizations were performed in the presence of either TOPO-coated or vinyl-fimctionalized CdSe/ZnS nanocrystals. Both emulsion and mini-emulsion processes were first applied to the incorporation of TOPO-coated CdSe/ZnS nanoparticles. Then, the concentration and type of QD as well as the surfactant concentration were varied in order to investigate the influence of these parameters on the mini-emulsion polymerization kinetics and PL properties of the final particles. The final particle size could be tuned between 100 and 350 nm by varying the initial surfactant concentration. The intensity of luminescence properties increased with the number of incorporated TOPO-coated CdSe/ZnS nanoparticles, and the slight red shift of the emission maximum, induced by the polymerization, was correlated with modification of the medium surrounding the nanoparticles. TOPO-coated CdSe/ZnS nanoparticles showed higher fluorescence intensity than those with a vinyl moiety [205]. 

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