Fluorescence diminishing

Sensitization of Ybm luminescence by tetraphenylporphyrinate 5c (TTP, fig. 12) is demonstrated by a dramatic drop in the quantum yields of the 1S i -level fluorescence of this species from 0.06% for [Lu(TTP)acac] to less than 3 x 10 3% for the Ybm derivative. In parallel, the quantum yield of the 1S2-level fluorescence diminishes from 0.15% (Lum) to 0.01% (Ybm). No quantum yield for the metal-centered luminescence is given in this initial work, but t(2F5/2) is reported to be equal to 5 ps (Tsvirko et al., 1980). The quantum yield of [Nd(TTP)acac] has been determined in benzene and is equal to 0.025% (Shushkevich et al., 1981). The latter authors have also measured the quantum yields of [Yb(OEP)acac] (0.045%) and [Yb(2c)acac] (0.054%) in the same solvent and undertaken a careful study of the polarization of Ndm and Ybm emission bands and discussed it with respect to the symmetry of the complexes. In order to improve the photophysical properties of [Er(TPP)acac] the complex has been dispersed at concentrations of 5, 17, 28, and 37 wt% into thin films of n-conjugated... 

Smalley and co-workers have probed intramolecular vibrational relaxation by viewing the yields and the time-dependence of the fluorescence from Sj in alkylated benzenes. They focus attention on those ring modes whose vibrational frequencies are unshifted by alkylation these are vibrations with nodes at the alkylated ring carbon atom. The absorption lines are sharp, but as the alkyl chain is lengthened, the emission spectrum develops a broad relaxed component, while the intensity of the sharp unrelaxed resonance fluorescence diminishes in intensity as the intensity of the relaxed spectrum increases. The time-dependence of the relaxed and unrelaxed emission is found to be a single exponential decay, so unfortunately, the rapid intramolecular dephasing decay has not yet been followed. 

Concerning the fluorescence relay mechanism, the fluorescence enhancement can be attributed to the suppressed PET by the putative B-N bonding, yet the fluorescence diminishment was not rationalized. Thus, a detailed understanding of the sensing mechanism is still open to question. ... 

Figure 5. Above images reptesent preliminary results of the calcium sensor experiments. Arrows denote regions of increased flutnescence detected with the calcium green-modified NSOM tips as calcium diffiised through the pores. Over time, the fluorescence diminishes due to equilibration of calcium levels across the membrane and photobleaching of the tip-bound dye.

Pyruvate is determined by setting the pH to a more acidic value (pH 7.4) to favor production of lactate. The NADH is then consumed, and the fluorescence diminishes with the pyruvate concentration, which can be measured from 0.2 to 1 pM. The presence of the equilibrium means that the response of the optical sensor is non-linear for both lactate and pyruvate. 

This effect, which can also be produced if fluorescent substances are applied to the chromatogram by spraying or dipping after development, is an absorption effect and not a quenching process in the true sense of the word. It is correct to refer to fluorescence or phosphorescence diminishing. The more absorbant sample molecules there are present in the zone the darker this will appear (Fig. 4B). 

On occasion it will be observed that the fluorescence response for substances in TLC will be far less than expected froa measurements made in solution, will occur at different excitation and emission wavelengths than in solution, and may diminish over time at varying rates [10,19,20,173,180]. Adsorption onto the sorbent layer provides additional nonradiatlve pathways for the. . 

A laser beam highly focused by a microscope into a solution of fluorescent molecules defines the open illuminated sample volume in a typical FCS experiment. The microscope collects the fluorescence emitted by the molecules in the small illuminated region and transmits it to a sensitive detector such as a photomultiplier or an avalanche photodiode. The detected intensity fluctuates as molecules diffuse into or out of the illuminated volume or as the molecules within the volume undergo chemical reactions that enhance or diminish their fluorescence (Fig. 1). The measured fluorescence at time t,F(t), is proportional to the number of molecules in the illuminated volume weighted by the... 

D is the output gray scale value after amplification8 in the donor channel (gd) of the sum of the fraction (F ) of donor fluorescence in the donor channel and the fraction (i ) of acceptor fluorescence in the donor channel. The fluorescence of donors depends on the number of donor molecules (No) diminished by... 

As the pH increases, the concentration of the base form of phenol red increases, resulting in increased energy transfer from eosin to phenol red and in a diminished fluorescence intensity of eosin. Thus, changes in the absorption of phenol red as a function of pH are detected as a change in the fluorescence signal of eosin. 

Jiang and Zhu (2001) reported on the synthesis of poly(p-carboxyphe-noxy succinic monoester anhydride) and poly(p-carboxyphenoxy adipic monoester anhydride) (PCPSM and PCPAM), and the copolymer P(CPAM-CPSM) as polymeric antimicrobial prodrugs for diseases such as malaria and hepatitis B. They also reported that PCPSM exhibits strong fluorescence, the intensity of which increases linearly with its molecular weight (Jiang et al., 2001a,b). They showed that when co-polymerized the fluorescence is maintained, though diminished approximately in proportion to the copolymer composition. 

Taylor and Zeitlin [43] described an X-ray fluorescence procedure for the determination of total sulfur in seawater. They studied the matrix effects of sodium chloride, sodium tetraborate, and lithium chloride and show that the X-ray fluorescence of sulfur in seawater experiences an enhancement by chloride and a suppression by sodium that fortuitously almost cancel out. The use of soft scattered radiation as an internal standard is ineffective in compensating for matrix effects but does diminish the effects of instrument variations and sample inhomogeneity. 

Triprolidine hydrochloride in 0.1M sulfuric acid has an excitation maximum at 305 nm and an emission maximum at 445 nm. The fluorescence is much diminished in hydrochloric acid and almost non-existent in distilled water. 

The squaraine rotaxanes based on the macrocycle 16b exhibit intense NIR absorption and emission maxima, and it should be possible to develop them into molecular probes for many types of photonic and bioimaging applications. In contrast, the squaraine fluorescence intensity is greatly diminished when the dye is encapsulated with macrocycle 18. The fluorescence is restored when a suitable anionic guest is used to displace the squaraine dye from a pseudorotaxane complex, which indicates that the multicomponent system might be applicable as a fluorescent anion sensor. 

---