Steady-state emission

Models which assume uniform mixing throughout the volume of a three-dimensional box are useful for estimating concentrations, especially for first approximations. For steady-state emission and atmospheric conditions, with no upwind background concentrations, the concentration is given by... 

Fig. 45. (a) Introduction of M(phen)31 complex into DNA oligomers, (b). Steady-state emission spectra of modified oligonucleotides in 0.01 m sodium phosphate buffer, pH 7.0, 0.1 NaCl. Top Ru(phen)3+-modified 20-mer duplex (solid line), a 1 1 mixture of non-comple-mentary Ru(phen)3+- and Os(phen)g+-modified 20-mers (- -) and a 20-mer duplex containing Ru(phen)g+ and Ps(phen)3+groups on different strands separated by one base pair (---). Bottom 20-mer duplex with 5 -terminal Rufphen) (solid line), and Ru(phen)jf/Os(phen)3 -containing analog (---). Reproduced with permission from Ref. (157). Copyright 1998, American Chemical Society. 

S02 emitted from the modulated bed goes through a minimum after switching to the S03/S02 mixture. Lowest values are obtained 2 min after the composition change for the sulfur burning feed and they are about 8% of the steady-state emission, whereas for the smelter effluent feed, the lowest emission is about 13% of the steady-state value. Evidently, a cycle period of 4 to 5 min would be optimum for the conditions used, yielding a performance some 10% better than that shown at r = 10 in Table II. 

Neither the electronic absorption nor the emission spectrum of Re2Cl8 changes in the presence of the quenchers, and no evidence for the formation of new chemical species was observed in flash spectroscopic or steady-state emission experiments. The results of these experiments suggest that the products of the quenching reaction form a strongly associated ion pair, Re2Cl8 D+. 

Situation 1 Steady state emission before peak. Situatbn 2 Peak approx 30 kg Chlorine in 3 minutes. Situation 3 Peak approx 200 kg Chlorine in 3 minutes. 

Figure 25.5 plots the results of the same experiments with a lower active chlorine concentration. Compared to the 170 g L1 of hypochlorite solution, the emission peaks here are lower with a 30% reduction. The same effect is seen with the steady-state emission experiments, with a higher hypochlorite concentration giving higher emission values under the same process conditions. 

Steady-state emission Decreased Strongly decreased... 

Measurement of steady-state emission anisotropy. Polarization spectra... 

For isotropic motions in an isotropic medium, the values of the instantaneous and steady-state emission anisotropies are linked to the rotational diffusion coefficient Dr by the following relations (see Chapter 5) ... 

Steady state emission polarization measurements reflect the time over which the excited species remains rigidly bound to DNA, yielding some idea of the movement and orientation of the luminophore in the DNA microenvironment. 

The steady-state emission of beryl has been previously studied. The broad band at 720 nm is connected with Fe ", while the relatively narrow bands at 480 and 570 nm are ascribed to Mn " in tetrahedral and octahedral coordination, respectively. Cr " emission was connected with narrow i -lines at 680 and 682 nm (Tarashchan 1978 Kuznetsov and Tarashchan 1988). 

Steady-state emission and excitation spectra are measured for the dimethyl terephthalate and three polyesters in four solvents. The polymers have the repeating unit ABm, where A is -CO— C6H4— COO-, B is -(CH2—CH2—0)m- and m - 1,2,3. An RIS treatment of the unperturbed polymers identifies the conformations that should be conducive to excimer formation by nearest-neighbor aromatic rings. The population of such conformations is maximal in the polyesters in which m = 2. 

Steady-state fluorescence spectroscopy has also been used to study solvation processes in supercritical fluids. For example, Okada et al. (29) and Kajimoto and co-workers (30) studied intramolecular excited-state complexation (exciplex) and charge-transfer formation, respectively, in supercritical CHF3. In the latter studies, the observed spectral shift was more than expected based on the McRae theory (56,57), this was attributed to cluster formation. In other studies, Brennecke and Eckert (5,31,44,45) examined the fluorescence of pyrene in supercritical CO2, C2HSteady-state emission spectra were used to show density augmentation near the critical point. Additional studies investigated the formation of the pyrene excimer (i.e., the reaction of excited- and ground-state pyrene monomers to form the excited-state dimer). These authors concluded that the observance of the pyrene excimer in the supercritical fluid medium was a consequence of increased solute-solute interactions. 

Figure 2. Normalized steady-state emission spectra for 10 /tM PRODAN in normal liquids. Xejt = 351 nm.

Steady-State Experiments. Figure 3 shows a series of density-dependent steady-state emission spectra for 100 /zM pyrene in COj. The long wavelength, structureless excimer emission is clearly evidenced. (Again, at this concentration in a normal... 

Steady-State Fluorescence. The fluorescence characteristics of PRODAN are extremely sensitive to the physicochemical properties of the solvent (38). As benchmarks, the steady-state emission spectra for PRODAN in several liquid solvents are presented in Figure 1. It is evident that the PRODAN emission spectrum red shifts with increasing solvent polarity. This red shift is a result of the dielectric properties of the surrounding solvent and the large excited-state dipole moment (ca. 20 Debye units) of PRODAN (38). It is the sensitivity of the PRODAN fluorescence that will be used here to investigate the local solvent composition in binary supercritical fluids. 

Figure 1. Steady-state emission spectra for 10 /xM PRODAN in cyclohexane (- - ), acetonitrile (------), methanol (-----) and water (------).

Figure 2. Steady-state emission spectra for 10 ftM PRODAN in pure CO2...

The time-resolved emission spectra were reconstructed from the fluorescence decay kinetics at a series of emission wavelengths, and the steady-state emission spectrum as described in the Theory section (37). Figure 4 shows a typical set of time-resolved emission spectra for PRODAN in a binary supercritical fluid composed of CO2 and 1.57 mol% CH3OH (T = 45 °C P = 81.4 bar). Clearly, the emission spectrum red shifts following excitation indicating that the local solvent environment is becoming more polar during the excited-state lifetime. We attribute this red shift to the reorientation of cosolvent molecules about excited-state PRODAN. 

Optical rotations, accurate within 0.003°, were measured on Perkin-Elmer 241 and 141 polarimeters using a 1 dm cell. All reported rotations (from which residual rotations from solvent impurities have been subtracted) are the difference between solution and pure solvent measurements. Uncorrected steady-state emission spectra were obtained from room temperature samples on a Perkin-Elmer MPF-2A or Spex Fluorolog spectrofluorometer. 

Figure 59 (Top) Steady-state emission spectra (Xexc = 450 nm) of adsorbed monolayers of Coum-PAH and Fl-PAH polycations, PdTAPP+, and the coadsorbed coumarin-flu-orescein-porphyrin triad. (Bottom) Emission spectra of a similar triad containing PdT-SPP4, with and without an added viologen electron acceptor layer. (From Ref. 43a. Copyright 1999 Elsevier Publications.)...

In general, a thorough spectroscopic study, as routinely carried out in the group of Prof. Dr. Dirk M. Guldi by means of steady-state emission/absorption measurements and time-resolved techniques in numerous solvents, sheds light onto the photophysical processes following photoexcitation of these systems. Equally, a detailed description of the employed spectroscopic methods will be given in the next sections. 

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