Fluorescence decay times

Birch D J S and Imhof R E 1977 A single-photon counting fluorescence decay-time spectrometer J. Phys. E Sol. Instrum. 10 1044-9... 

Table V. Materials Used as Standards for Fluorescence Decay Time, r...

For the investigation of triplet state properties a laser flash photolysis apparatus was used. The excitation source was a Lambda Physik 1 M 50A nitrogen laser which furnished pulses of 3.5 ns half-width and 2 mJ energy. The fluorescence decay times were measured with the phase fluorimeter developed by Hauser et al. (11). 

We are able to measure the ratio p/ F and the fluorescence decay time of the deuterated and undeuterated... 

Lippitsch M.E., Pusterhofer J., Leiner M.J.P., Wolfbeis O.S., Fibre optic oxygen sensor with the fluorescence decay time as information carrier. Anal. Chim. Acta 1988 205 1. 

Optical sensors for oxygen measurement are attractive since they can be fast, do not consume oxygen and are not easily poisoned. The most common method adopted in construction is based on quenching of fluorescence from appropriate chemical species. The variation in fluorescence signal (I), or fluorescence decay time (x) with oxygen concentration [O2] is described by Stem-Volmer equation91 ... 

The first photoelectric fhiorimeter was described by Jette and West in 1928. The instrument, which used two photoemissive cells, was employed for studying the quantitative effects of electrolytes upon the fluorescence of a series of substances, including quinine sulfate [5], In 1935, Cohen provides a review of the first photoelectric fluorimeters developed until then and describes his own apparatus using a very simple scheme. With the latter he obtained a typical analytical calibration curve, thus confirming the findings of Desha [33], The sensitivity of these photoelectric instruments was limited, and as a result utilization of the photomultiplier tube, invented by Zworykin and Rajchman in 1939 [34], was an important step forward in the development of suitable and more sensitive fluorometers. The pulse fhiorimeter, which can be used for direct measurements of fluorescence decay times and polarization, was developed around 1950, and was initiated by the commercialization of an adequate photomultiplier [35]. 

Fluorescence Lifetimes. The fluorescence decay times of TIN in a number of solvents (11.14.16.18.19), low-temperature glasses (12.) and in the crystalline form (15.) have been measured previously. Values of the fluorescence lifetime, Tf, of the initially excited form of TIN and TINS in the various solvents investigated in this work are listed in Table III. Values of the radiative and non-radiative rate constants, kf and knr respectively, are also given in this table. A single exponential decay was observed for the room-temperature fluorescence emission of each of the derivatives examined. This indicates that only one excited-state species is responsible for the fluorescence in these systems. 

The fluorescence decay time, calculated for the 400 nm emission of TIN in PMMA films, decreases from 1.3 0.2 ns to 0.20 0.02 ns as the concentration of TIN is increased from 0.07 mole% to 1.1 mole% respectively. This is further evidence that the TIN molecules are involved in a concentration-dependent, self-quenching... 

The fluorescence decay time is one of the most important characteristics of a fluorescent molecule because it defines the time window of observation of dynamic phenomena. As illustrated in Figure 3.2, no accurate information on the rate of phenomena occurring at time-scales shorter than about t/100 ( private life of the molecule) or longer than about 10t ( death of the molecule) can be obtained, whereas at intermediate times ( public life of the molecule) the time evolution of phenomena can be followed. It is interesting to note that a similar situation is found in the use of radioisotopes for dating the period (i.e. the time constant of the exponential radioactive decay) must be of the same order of magnitude as the age of the object to be dated (Figure 3.2). 

M. Vogel, W. Rettig, R. Sens, and K. H. Drexhage, Structural relaxation of rhodamine dyes with different N-substitution patterns A study of fluorescence decay times and quantum yields. Chem. Phys. Lett. 147,452-460 (1988). 

From a practical point of view the consequences of TOF dispersion are important only for short intrinsic fluorescence decay times of to < 1 nsec. Figure 8.15 shows an example with to = 50 psec and realistic optical constants of the substrate. The intensity maximum in Fb(t) is formed at At 30 psec after (5-excitation. After this maximum, the fluorescence decays with an effective lifetime of r ff = 100 psec that increases after long times to t > > 500 psec. The long-lived tail disappears as soon as there is some fluorescence reabsorption, and for Ke = K there is practically no difference to the intrinsic decay curve (curve 3 in Figure 8.15). 

A. T. Augousti, K. T. V. Grattan, and A. W. Palmer, A laser-pumped temperature sensor using the fluorescence decay time of alexandrite, J. Lightwave Technol. LT-5,759-762 (1987). 

There are many molecular interactions which influence the fluorescence decay times. The measured fluorescence lifetime r is usually shorter than the radiative lifetime tr because of presence of other decay rates which can be dependent on intramolecular processes and intermolecular interactions (Figure 10.3). The measured fluorescence lifetime (r) is given by the inverse of the total rate of dynamic processes that cause deactivation from the excited (mostly singlet Si) state... 

R. A. Lampert, L. A. Chewter, D. Phillips, D. V. O Connor, A. J. Roberts, andS. R. Meech, Standards for nanoseconds fluorescence decay time measurements, Anal. Chem. 55, 68-73 (1983). 

T. Bosselmann, A. Reule, and J. Schroder, Fibre-optic temperature sensor using fluorescence decay time, Proc. of 2nd Conf. on Optical Fibre Sensors (OFS 84), SPIE Proceeding 514, 151-154 (1984). 

V. Fernicola and L. Crovini, Two fluorescent decay-time thermometers, in 7th Int. Symp. Temp., Toronto, Canada, April 30, 1992, American Institute of Physics, Washington, D.C., 1992. 

Haas et al.(m) have examined the fluorescence decay of tyrosine due to different Tyr-Pro conformations in small peptides to elucidate further the nature of the fluorescence change associated with Tyr-92. These peptides have acetyl groups at the amino terminus and /V-mcthylamidc groups at the carboxyl terminus. They found that whereas the dipeptide fluorescence decay requires a double-exponential fit, that of the tripeptide Tyr-Pro-Asn can be fit by a single exponential. By comparison of the average fluorescence decay time and steady-state quantum yield of the peptide to that of A-acetyltyrosine-A-methylamide, they found a relatively greater reduction in the steady-state quantum yield of the peptides. This is attributed to static quenching, which increased from 5 % in the dipeptide to 25 % in the tripeptide. The conformations of these peptides were also examined by NMR, but the results could be interpreted in terms of either cis-trans isomerization or other conformational isomerizations. 

D. R. James, J. R. Turnbull, B. D. Wagner, W. R. Ware, andN. O. Petersen, Distributions of fluorescence decay times for parinaric acids in phospholipid membranes, Biochemistry 26, 6272-6277 (1987). 

K. H. Drexhage, Influence of a dielectric interface on fluorescence decay time, J. Lumin. 12, 693-701 (1970). 

Most common lock-in amplifiers can be operated at frequencies ranging from a few Hz up to 100 kHz. This fact is important in analyzing the temporal evolution of optical signals for example, fluorescence decay time measurements. Although this particular application of lock-in amplifiers is beyond the scope of this section, it is instructive to mention that this can be done by tuning the relative phase (the time delay) between the signal intensity and the reference signal provided by the chopper. 

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