Single photon counting technique fluorescence

Nemzek and Ware [7] have studied the fluorescence decay of 1,2-benzanthracene (and naphthalene) in 1,2-propanediol or purified mineral oil by the single photon counting technique over the temperature range 10—45°C. The fluorescence lifetimes, t0, were measured. In further experiments, which included a heavy atom fluorescence quencher, carbon tetrabromide in concentration [Q] 0.05—0.29 mol dm-3, no longer could the decay be characterised by an exponential with a constant lifetime. However, the decay of fluorescence was well described by an expression of the form... 

Halpern and Ware (97) have measured the fluorescence lifetimes (if) of HFA using the time-correlated single photon counting technique over a wide pressure range (0.1-700 torr) from... 

Figure 16. Decay-associated spectrum resulting from a global analysis of the decay of the porphyrin fluorescence of pentad 22 following excitation of a — lxlO M chloroform solution with a 590-nm laser pulse. Data were obtained using the single photon counting technique, and the instrument response time was 0.035 ns. Decays at 14 different wavelengths were analyzed simultaneously, and the goodness of fit parameter was 1.12.

There are numerous spectroscopic studies of the chromophores bound to the chemically modified silica gel(2-4) but dynamic studies such as fluorescence lifetime measurements are rather limited. In their recent work, Lochmuller and Hunnicutt (5) have employed the time-correlated single photon counting technique and analyzed the non-exponential decays in detail to disclose the complex features of the interfaces through (10-(3-pyrenyl)decyl)dimethylmonochlorosilane chemically bonded to silica as a probe. Unfortunately, however, their method, though sophisticated enough to monitor heterogeneous fluorescence decays, cannot distinguish one microparticle from the other and hence unavoidably follows overall decays. 

Fluorescence decay curves for the pyrenyl emissions were obtained by a time - correlated single photon counting technique. The monoexponentlallty of these curves in both solvent phases is consistent with k4 k3 (l.e., that adiabatic exciplex formation is unlmportant(31)) and allows the decay constants to be equated to the excited state lifetimes. The rate constant for exciplex formation, k3, could be obtained uniquely from Eqn. 23 by assuming that kj+k2 is the Inverse of the fluorescence lifetime of 1 -ethylpyrene (EZ) i 1L- From Arrhenius and Eyring... 

The method s sensitivity can be estimated by following up the previous example. Assuming a fluorescence quantum yield of 0.1 and a spatial collection efficiency of 10 , a population of 5x10 excited molecules leads to 5 X 10 photons reaching the detector per pulse. Single-photon counting techniques easily allow the observation of 0.1-1 photon per pulse. Evidently fluorescence methods can easily be used to probe submil-litorr samples. 

The complexes of 2,3 (sodium salt) and 4 (potassium salt) with P-CD and (2,3,6- tri-0-methyl)-/ -CD were studi using steady-state fluorescence and time-correlated, single-photon counting techniques [52]. The formation of both 1 1 and 2 1 complexes between p-CD and 2,3 was confirmed. Trimethyl- -CD gave evidence only of 1 1 complexes. The fluorescence decay of systems giving exclusively 1 1 complexes was collected at CD concentrations that ensure more than 90% complexation. The analysis performed using a continuous lifetime distribution model... 

Figure 2.16. Fluorescence dec curve for the intact (continuous line) and thiol oxld>7 d (broken line) hemogbbin alpha cliain obtained vith the single photon counting technique Source- Albani J, Alpert D. Krajearski D.T and Szabo. A.G. I98S, FEDS Letters. 182.302-304.

Figure 2.17. Fluorescence decay curve for the intact (continuous line) and thiol oxidized (broken line) hemoglobin beta chain obiained with the single photon counting technique. Source- Albani, J.. Alpert, B., Krajearski. D. T. and Szabo, A. G. 198S, FEBS Letters, 182. 302-.304.

Dynamic fluorescence decay data were collected with the single photon counting technique with a set-up described elsewhere [14]. 

There are a variety of well-known problems associated with the time correlated single photon counting technique (11), the technique most commonly used for measuring fluorescence decays in synthetic polymer systems. Some are seemingly trivial (some filters fluoresce) until one stumbles across them. Others require rather delicate judgment. Among the latter, two problems are particularly noteworthy First, it... 

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