Time-correlated single-photon counting studies

1 Time-Correlated Single-Photon Counting Studies 

A single photon fluorometer consists of the following subsystems an optical spectrometer (including a pulsed light source), a data acquisition system (consisting of timing electronics) and a data analyser (composed of a computer with re-convolution software). Birch and Imhof [16] have widely published on instrumentation design and analytical methods. 

The data analysis software is used to extract the kinetic information in a given system from the experimental intensity decay curve. The recorded decay curve of emission intensity, I t), is generally synthesised by means of an exponential re-convolution function of the form  

---

The fluorescence of 2AP is strongly quenched by nucleic acid bases [17, 18, 24-29]. Time-correlated single-photon counting studies have shown that the interactions of 2AP with different nucleic acid bases significantly decrease the 2AP fluorescence hfetime [17, 24-29]. While the fluorescence lifetime of free 2AP in aqueous solution is about 10 ns, in double-stranded DNA the 2AP hfetimes are reduced to 30-50 ps. This effect has been used extensively to study the dynamics of mismatched base pairs [19, 21, 25, 30], local changes in dynamics of DNA molecules produced by their binding to the active sites of polymerases [26, 31-33], stacking interactions at abasic... 

Time correlated single photon counting studies give the rise and decay times for the various emissions and excitations for these clusters. These data are presented in Table 5-3 and Figure 5-12. For 6a1 excitation, t,vR is measured in the rise times of the (F emission and the decay of 6a1 emission. For P and P excitation, the rise times measured involve both IVR and VP because 0° emission is observed from 4EA. 

Figure 2.28 (a) Time-correlated single photon-counting studies of fluorescence from oxazine on a thin-... 

D. J. S. Birch, R. E. Imhof and C. Guo, Fluorescence decay studies using multiplexed time-correlated single-photon counting application to aminotetraphenylporphyrins, /. Photochem. Photobiol. A Chem. 42, 223-231 (1988). 

Time-correlated single photon counting (TCSPC) [28] is one of the most sensitive methods for studying time-resolved emission. In this technique, single photon events are detected after excitation and a statistical distribution of photons representing the decay of the excited state is built up over time. 

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. 

The bimolecular reaction dynamics of geminate recombination or acid-base neutralization have until recently been studied with time-resolved techniques probing electronic transitions. Time-resolved fluorescence using time-correlated single photon counting detection is limited to a time resolution of a few picoseconds. UV/vis pump-probe experiments, in principle, may have a time resolution of a few tens of femtoseconds, but may be hampered by overlapping contributions of... 

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... 

Recent simulation studies find that the SD in SCF, CHF3, and CO2 is also biphasic in nature. The fast component of the total solvation energy here decays with a time constant of about a picosecond. The other component relaxes at a rate with time constant in the tens of picosecond regime. A set of recent experimental studies employing a time-correlated single-photon counting technique has, however, indicated that the slow component has a time constant of about 50-70 ps, which is much slower than that observed in the above simulation, and probably was missed in later studies [9]. 

We have studied the microsecond and nanosecond kinetics of the D1/D2 reaction centre by time correlated single photon counting and transient absorption spectroscopy. Stabilisation of the reaction centre has been necessary to establish the kinetics correctly. 

We have also performed time resolved studies (time correlated single photon counting dispersed emission spectroscopy) on all of the above emission spectral features. An example of the data typically obtained is presented in Figure 4. This figure shows that the decay... 

---