Fluorescence was efficiently

Our study included only observations of the behavior of the CT band and did not consider the IL band, which should appear farther to the UV than the wavelength range in which these experiments were conducted. In our fluid MMA samples, the CT fluorescence was efficiently quenched. 

The subject of delayed fluorescence was discussed in Section 5.2a. It was seen that there are two common types of delayed fluorescence, that arising from thermally activated return from the triplet state to the lowest excited singlet (E-type delayed fluorescence) and that arising from collision of two excited triplet molecules resulting in a singlet excited molecule and a ground state molecule (P-type delayed fluorescence). The P-type delayed fluorescence can be used as a convenient tool for the determination of intersystem crossing efficiencies[Pg.125]

Eukaryotic cells utilize an efficient transport system that delivers macromolecules fast and secure to their destination. In the case of the small GTP binding proteins of the Ras family the modified C-terminus seems to be sufficient for addressing the polypeptide to its target membrane (in the case of Ras itself the plasma membrane). Lipopeptides with the C-terminal structure of N-Ras (either a pen-tamer with a C-terminal carboxymethylation and farnesylation or a heptapeptide with a palmitoyl thioester in addition) and a N-terminal 7-nitrobenz-2-oxa-l,3-diazolyl (NBD) fluorophore were microin-jected into NIH3T3 fibroblast cells and the distribution of the fluorophore was monitored by confocal laser fluorescence microscopy. Enrichment of the protein in the plasma membrane was efficient only for peptides with two hydrophobic modification sites, while the farnesylated but not palmitoylated peptide was distributed in the cytosol.1121... 

The intensity of the fluorescence emission detected at the photodetector stage was plotted as a function of temperature over the same range, and this is shown in Figure 11.22. It falls off rapidly with temperature increase over the whole temperature region. This does not contradict the experimental evidence of Burns and Nathan(56) who showed that the fluorescence quantum efficiency of the ruby fluorescence integrated over the entire band from 620 to 770 nm is independent of temperature (to 5%) in the region from-196 to 240°C, for the emission detected here is only the A-line part of the total fluorescence emission. 

To test the above ideas, Weitz etal.(i2) performed experiments on the fluorescence decay from a thin layer of europium(III) thenoyltrifluoracetonate (ETA) deposited on a glass slide covered with Ag particles approximately 200 A in diameter. The fluorescence decay rate was found to increase by three orders of magnitude in comparison with that of ETA in solid form. In addition to the large increase in decay rate, there was also evidence for an increase in overall fluorescence quantum efficiency. It is not possible from Eq. (8.11) to say anything about the manner in which is partitioned between radiative and nonradiative processes, y should be written in terms of a radiative part yr and a nonradiative part ynr y = yr + y r. Since the radiative rate for dipole emission is given by... 

Detection of the bound PNA is possible via on-column fluorescence detection. Efficient single base-pair discrimination was achieved routinely using that technique, as shown in Fig. 7. The system was optimized to observed a difference of 25°C between the perfect match and single-mismatched PNA probe. The assay should be applicable for clinical research and diagnostics and may be automated as well. 

Once the efficiency of normal fluorescence had been determined, the efficiencies of phosphorescence and delayed fluorescence under the same conditions were derived without reference to any other solution. The ratio of the efficiencies of delayed fluorescence (6) to that of normal fluorescence was simply caculated by comparing the intensities at one of the principal maxima in the spectra, which were, of course, identical in shape. Due correction was made for the phosphorimeter factor (assumed to be 3 for lifetimes greater than 1 msec.) and also for the different instrumental sensitivities at which the two spectra were measured. Phosphorescence efficiencies were determined in a similar manner, except that the spectra first had to be corrected and the areas under the corrected curves compared with those of the corresponding normal fluorescence spectra. The phosphorimeter and instrumental sensitivity factors were then applied as before. 

The intensity of delayed fluorescence was proportional to the square of the rate of absorption of exciting light and the general equation (67) for P-type delayed fluorescence can therefore be applied. If we consider only the 3 X 10-aM solution at temperatures of — 77 °C. and higher, where the proportion of dimer emission is low, and assume that the conversion of triplets to excited- and ground-state singlet is 100% efficient, i.e., kd/(k j + k 0 + kd) = 1, then... 

After extraction, the fluorescent indicator was in the unbound state and gave input to the radiative relaxation. Therefore, the fluorescence lifetime increased and, consequently, the intensity as well. After MIP contacting with the analyte, the non-radiative processes were again efficient compared to the radiative processes and, subsequently, fluorescence was quenched. With steady-state fluorescence spectroscopy the cross-reactivity test towards structurally similar biomolecules was performed that yielded selectivity factors for guanosine, cAMP and cCMP of 1.5, 2.5 and 5.1, respectively. 

Whereas in solution the photoluminescence efficiency (Of) of poly(3-alkylthiophenes) (PATs) is 3(Mf)%, it drastically drops to 1-4% and lower in the solid state due to the increased contribution of nonradiative decay via interchain interactions and ISC caused by the heavy-atom effect of sulfur (97MM4608). Optoelectronic devices of this type of compounds have been studied (98SCI(280)1741 06SM(156)1241). Fibers of poly(3-hex-ylthiophene) for photovoltaic applications have been described (07MI1377). Poly(3-octylthiophene) showed a TTA band at 800 nm (96JPC15309). The photophysical properties of some alkyl and aryl polythiophenes have been studied (03JCP(118)1550). The absorption maximum of poly(3-octylthiophene) is at 438 nm, while the fluorescence was... 

Compound 99 was made more hydrophobic by butylation of the 2-OH and 3-OH groups [88], The prepared CD derivative (100) solubilized 9-anthrylmethyl pivalate (AP) much more effectively than 99 or (3-CD. In the presence of AP, the naphthyl emission (Xex = 314 nm) of 100 was efficiently quenched and intense AP emission was observed. Because essentially all of the light is absorbed by the naphthyl chromophores, the strong AP fluorescence demonstrates that energy transfer occurs efficiently. The naphthyl antenna chromophores of 100 were shown to sensitize a selective photoreaction of AP included in the CD cavity (Scheme 2). The photoirradiation of AP in methanol gives 9-neopentylanthracene... 

A fluorescence decay of the ensemble of many CV molecules on a PMMA film is shown in Fig. 12. The decay was not fitted to a single exponential function and a stretched exponential function, but was well fitted to a biexponential function I(t) = Af exp(-t/xf) + Asexp(—t/ts), where tf and ts are time constants and Af and As are pre-exponential factors. We obtained tf = 0.43 ns and ts = 1.76 ns, and the ratio As/Af = 1.14. Compared with the excited state lifetime of CV (2-3 ps) in methanol and ethanol [5-8,58-68], the fluorescence lifetime of CV on a PMMA film increased more than two orders of magnitude [9-12] thus, so did the fluorescence quantum efficiency. The enhancement of the fluorescence efficiency of CV on a PMMA film made it possible to observe single CV molecules. Figure 13 shows fluorescent spots on a PMMA film on which a drop of 1-nM CV in methanol was spin-coated. The number of fluorescent spots in an image linearly increased with increasing concentration of a CV methanol... 

Synthesis of PP-L-A molecules consisting of bisporphyrin PP linked to a pyromellitimide rather than quinone acceptor A was also reported in [162], For the cofadal bisporphyrin strong quenching of fluorescence was found, while for the side-by-side bisporphyrin relatively weak quenching was observed. Fluorescence quenching data are supported by the direct ps laser studies of PET in PP-L-A molecules with cofacial and side-by-side bisporphyrin. These results show that the proximity of PP and Q is not sufficient for high efficiency of PET. Other factors, such as appropriate geometry of PP play an important role for efficient PET. Note that cofacial bisporphyrin models the special pair electron donor in the reaction centre of photosynthesis. 

Dorr, Lewis, and co-workers found evidence through quenching experiments and flash spectroscopy for a triplex in the system trans-stilbene — amine — benzene — [105]. They quenched singlet excited trans-stilbene with various mono- and diamines and found a steric effect on the quenching constant The a, co-diamines (dabco, diaminoethane, -propane and -butane) quenched the stilbene fluorescence more efficiently than the monoamines, depending on the chain length between the amino groups. This was ascribed to the formation of cyclic radical cations, with a N-N three electron a-bond. In this case, an exciplex between diamine and stilbene is formed. 

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