Fluorescence efficiency

A number of drawbacks in the application of the 0PA/2-ME reagent system include the instability of the fluorescent isoindole derivative (5-7) the use of the noisome reagent 2-mercaptoethanol the low and solvent-dependent fluorescence efficiencies (8,9) of the isoindole and—perhaps the most limiting—the effective restriction of the OPA assay to primary aliphatic amines and to amino acids. 

Perhaps most encouraging in these discoveries was the observation that NDA/CN worked equally well for derivatization of dipeptides and higher homologues of the primary amino acid series. Again, a stable, fluorescent, isolatable derivative was obtained. One of the most important initial findings was the high fluorescence efficiency of the CBI adduct (12). Tables 1 and 2 list the efficiencies for a representative group of mono-, di-, and tripeptides and a limited comparison of the CBI efficiencies with the more traditional OPA (8) and dansyl (9) derivatives, respectively. 

As noted, the fluorescence efficiencies of the CBI adducts are invariably greater than those of OPA or dansyl analogs, generally ranging from 0.4 to 0.8, with the exception of the bis-CBI adduct of... 

If reaction time is kept short, however, the derivatization process can be intercepted at the mono-adduct form, which is sufficiently fluorescent for assay purposes. It should be noted that the fluorescence efficiencies of the CBI adducts are relatively insensitive to the water content of the solvent mixture (11,12) in contrast with earlier reports on the dansyl derivatives, which lose an order of magnitude of efficiency in aqueous-based solvent systems(9). 

Table IX. Fluorescence Efficiencies ( j,), Chemiluminescence Efficiencies ( . ), and Emission Maxima (A. ) for...

As shown in Fig. 4, the fluorescent intensity increased with the DCM concentration. This means that the fluorescence efficiency remains constant at high... 

To perform structural research on a food stuff into which a colorant is incorporated, special properties of fluorescing molecules are exploited fluorescence efficiency, fluorescence lifetime, fluorescence quenching, radiationless energy (Foerster) transfer, stationary or time-dependent fluorescence polarization and depolarization." Generally, if food colorants fluoresce, they allow very sensitive investigations which in most cases cannot be surpassed by other methods. 

Thus we see that in molecules possessing ->- 77 excited states inter-combinational transitions (intersystem crossing, phosphorescence, and non-radiative triplet decay) should be efficient compared to the same processes in aromatic hydrocarbons. This conclusion is consistent with the high phosphorescence efficiencies and low fluorescence efficiencies exhibited by most carbonyl and heterocyclic compounds. 

Different substituents on the carboxy-functionalized fluorescein can be introduced to produce marked alterations in the absorbance and fluorescence emission wavelengths, as well as in other physical properties. The selective substitution of chlorine for aromatic hydrogen has been found to increase fluorescence efficiency and to narrow emission and absorbance maxima when compared with fluorescein 48, which is useful in multicolor imaging. 

In conclusion, we stress that the complementary NLO characterization techniques of pump-probe, Z-scan, and 2PF allow for the unambiguous determination of nonlinear optical processes in organic materials. The important molecular parameters of 2PA cross section, fluorescence efficiency, reorientation lifetimes, excited state cross sections, etc. can be determined. 

Battad JM, Wilmann PG, Olsen S, Byres E, Smith SC, Dove SG, Turcic KN, Devenish RJ, Rossjohn J, Prescott M (2007) A structural basis for the pH-dependent increase in fluorescence efficiency of chromoproteins. J Mol Biol 368 998-1010... 

In fluorescence spectroscopy, the orientation distribution of the guest probe is not necessarily identical to the actual orientation of the polymer chains, even if it is added at very small concentrations (i.e., a probe with high fluorescence efficiency). As a matter of fact, it is generally assumed that long linear probes are parallel to the polymer main chain, but this is not necessarily the case. Nevertheless, if the relation between the distribution of the probe axes and those of the polymer axes is known, the ODF of the structural units can be calculated from that of the probe thanks to the Legendre s addition theorem. Finally, the added probe seems to be mainly located in the amorphous domains of the polymer [69] so that fluorescence spectroscopy provides information relative to the noncrystalline regions of the polymeric samples. 

Cx electronically excited product) depends on the efficiency es of the production of excited product molecules, and on the efficiency of the excited product molecules (or other molecules present in the reaction mixture) in transforming excitation energy into light. In most of the chemiluminescence reactions investigated so far this efficiency is identical with the fluorescence efficiency of the molecules concerned, so that... 

Therefore a low chemiluminescence quantum yield can be due to the fact that the fluorescence efficiency of the product molecules is high but the chemical efficiency of the reaction producing excited molecules is low, or the reverse, or that ifies and n are both low. 

Hydrazide chemiluminescence has been investigated very intensively during recent years (for reviews, see 1>, p. 63, 2>, 90>). Main topics in this field are synthesis of highly chemiluminescent cyclic diacyl hydrazides derived from aromatic hydrocarbons, relations between chemiluminescence quantum yield and fluorescence efficiency of the dicarboxylates produced in the reaction, studies concerning the mechanism of luminol type chemiluminescence, and energy-transfer problems. 

E. H. White and coworkers 12> stated that the fluorescence efficiency of the dicarboxylate formed in the general reaction is not the factor... 

Another rather striking example demonstrates that the fluorescence efficiency of the respective dicarboxylates is not the most important factor in determining the chemiluminescence efficiencies of the hydrazides 9.10-diphenylanthracene-2.3-dicarbonic acid 25 has a fluorescence efficiency of about 0.9 (as has the parent compound 9.10-di-phenylanthracene) 94>. The corresponding hydrazide 26, however, gives a quantum yield of 48% that of luminol only (in DMSO/t-BuOK/ O2) 95) although 3-aminophtalic acid has a fluorescence efficiency of about 0.3 only. 

Table 1. Chemiluminescence and fluorescence efficiencies of some substituted phthalic hydrazides (after Brundrett, Roswell, and White 12>)...

This is not due to the relatively extended aromatic system in 25, for C. C. Wei and E. H. White 96> recently succeeded in synthesizing the benzoperylene compound 27 which is the most efficient hydrazide yet known with a chemiluminescence quantum yield of 7.3 % (in DMSO/ t-BuOK/02). The corresponding dicarboxylate has a fluorescence efficiency of 14% and emits at 420 and 450 nm which matches the chemiluminescence emission of 27 9 ). 

Dialkylamino phthalic acids resulting from the chemiluminescence reaction of 4-dialkylamino-phthalic hydrazides cannot easily form a tris anion because deprotonation of the amino group is impossible. They should therefore not exhibit such a strong decrease in fluorescence efficiency at higher pH values. This can actually be concluded from the pH dependence of the chemiluminescence of the 4-dialkylamino-phthalic hydrazides and related compounds 97>. 

The ultraviolet spectrum of the monosodium salt of luminol shows the absorptions of both the mono- and the dianion of luminol on addition of potassium tert. butylate the equilibrium is shifted to the dianion109). On the other hand, even small quantities of water shift the equilibrium back to the monoanion. The luminol dianion Lum2< ) was found to have a higher fluorescence efficiency than the monoanion. Absorption and fluorescence data for luminol, Lum< > and Lum2< > are listed in Table 4. 

B, C reactants Dx electronically excited product A acceptor molecule with high fluorescence efficiency... 

Photon emission must be a favorable deactivation process of the excited product in relation to other competitive nonradiative processes that may appear in low proportion (Fig. 3). In the case of sensitized CL, both the efficiency of energy transfer from the excited species to the fluorophore and the fluorescence efficiency of the latter must be important. 

Several processes may compete with fluorescence for deactivation of the lowest excited singlet state. As a result only a fraction of the molecules formed in the lowest excited singlet state, < )/, actually fluoresce. <()/ is called the quantum yield or fluorescence efficiency. It is usually a fraction but may be unity in some exceptional cases and is related to the probabilities (rate constants) of fluorescence (kf) and competitive processes (kd) by... 

A wide variety of different classes of fluorescent molecules has been investigated in the peroxyoxalate chemiluminescent systems. Among those screened were fluorescent dyes such as rhodamines and fluoresceins, heterocyclic compounds such as benzoxazoles and benzothiazoles, and a number of polycyclic aromatic hydrocarbons such as anthracenes, tetracenes, and perylenes. The polycyclic aromatic hydrocarbons and some of their amino derivatives appear to be the best acceptors as they combine high fluorescence efficiency with high excitation efficiency in the chemiluminescent reaction [28],... 

The same authors studied the CL of 4,4,-[oxalylbis(trifluoromethylsulfo-nyl)imino]to[4-methylmorphilinium trifluoromethane sulfonate] (METQ) with hydrogen peroxide and a fluorophor in the presence of a, p, y, and heptakis 2,6-di-O-methyl P-cyclodextrin [66], The fluorophors studied were rhodamine B (RH B), 8-aniline-l-naphthalene sulfonic acid (ANS), potassium 2-p-toluidinylnaph-thalene-6-sulfonate (TNS), and fluorescein. It was found that TNS, ANS, and fluorescein show CL intensity enhancement in all cyclodextrins, while the CL of rhodamine B is enhanced in a- and y-cyclodextrin and reduced in P-cyclodextrin medium. The enhancement factors were found in the range of 1.4 for rhodamine B in a-cyclodextrin and 300 for TNS in heptakis 2,6-di-O-methyl P-cyclodextrin. The authors conclude that this enhancement could be attributed to increases in reaction rate, excitation efficiency, and fluorescence efficiency of the emitting species. Inclusion of a reaction intermediate and fluorophore in the cyclodextrin cavity is proposed as one possible mechanism for the observed enhancement. 

While retaining much of the substituted PT character (e.g., good hole-transport properties and stability), these materials exhibit significantly improved fluorescence efficiency in the solid state (cl>Pi up to 29%) that leads to (hllof UP to 0.1% for ITO/453/Ca PLED (Table 2.6). Other widely studied thiophene copolymers with aromatic 9,9-disubstituted fluorene units were already described above in Section 2.3. 

While the linear absorption and nonlinear optical properties of certain dendrimer nanocomposites have evolved substantially and show strong potential for future applications, the physical processes governing the emission properties in these systems is a subject of recent high interest. It is still not completely understood how emission in metal nanocomposites originates and how this relates to their (CW) optical spectra. As stated above, the emission properties in bulk metals are very weak. However, there are some processes associated with a small particle size (such as local field enhancement [108], surface effects [29], quantum confinement [109]) which could lead in general to the enhancement of the fluorescence efficiency as compared to bulk metal and make the fluorescence signal well detectable [110, 111]. 

Substituent groups have a marked effect on the fluorescence quantum yield of many compounds. Electron-donating groups such as -OH, -NH2 and -NR.2 enhance the fluorescence efficiency, whereas electron-withdrawing groups such as -CHO, -C02H and -N02 reduce the fluorescence quantum yield, as shown by naphthalene and its derivatives in Table 4.3. 

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