Fluorescence from centers

Stanley R J and Boxer S G 1995 Oscillations in the spontaneous fluorescence from photosynthetic reaction centers J. Phys. Chem. 99 859-63... 

Examination of the corrected room temperature fluorescence properties of PET yarns revealed an excitation maximum at 342 nm with a corresponding emission maximum at 388 nm. At 77°K, in the uncorrected mode, the fluorescence spectra of PET yarns exhibited a structured excitation having maxima at 342 and 360 nm and a shoulder at 320 nm. At 77°K, PET yarns displayed a structured emission with maxima at 368 and 388 nm. As in solution, the copolymer yarns showed both fluorescence from the terephthalate portion of the polymer and the 4,4 -biphenyldicarboxyl ate portion of the polymer. Excitation at 342 nm produced an emission band centered at 388 nm. This excitation and emission correspond to the PET homopolymer emission. Excitation with about 325 nm light produced an emission with a maximum near 348 nm from the 4,4 -biphenyldicarboxyl ate portions of the polymer. 

Two types of fluorescence spectra are observed in aqueous solution and in the presence of an excess of cadmium ions. In the absence of any stabilizer the fluorescence is characterized by two very weak bands (41), one centered at 450 nm and attributed to the direct recombination of charge carriers (61) from shallow traps, and the other very broad at about 650 nm, which is not clearly attributed. The presence of a stabilizing agent, such as HMP (59,60), makes it possible to increase the sulfide vacancies at the surface resulting in a more intense fluorescence band, centered in the region of 550 nm. This band is attributed to the recombination of... 

V,/V-Dimethylamino)benzonitrile (DMABN) and its derivatives, as a class of organic donor-acceptor compounds, exhibit dual fluorescence, one related to the local excited state ( B band) and the other ascribed to the twisted intramolecular charge transfer (TICT) state ( A band).17 As expected, compound 818 exhibits dual fluorescence, showing two fluorescence bands centered at 350 and 432 nm, which can be ascribed to the corresponding band (from the local excited state) and A band (from the TICT state), respectively. After oxidation of TTF unit in 8, the fluorescence intensity of A band decreases while that of band increases slightly. As expected, further reduction of TTF" + into neutral TTF unit leads to the restoration of the fluorescence spectrum of 8. Therefore, the dual fluorescence spectrum of 8 can be reversibly modulated by redox reactions of TTF unit in 8. 

All three MGd-fluorophores could be observed in imaging studies with Jurkat-T lymphoma cells as a result of the fluorescence produced by the marker fluorophores (Fig. 6). The cells displayed punctate localization predominantly, as would be expected for retention that is primarily in cellular vesicles or lysosomes. Importantly, fluorescence from the MGd core could not be seen under standard CFM conditions. This means that the paramagnetic Gd(lll) center does not quench the fluorescence of the appended fluorophore. ft also highlights the fact that these new conjugates are potentially far more effective as detectable targeting agents then MGd alone. 

Table 11 Spectral and Lifetime Data for Fluorescence from Excited Heteroatom-Centered Radicals at Room Temperature and in Low-Temperature (77 K) Matrices...

Fig. 1. On the left is a simplified energy-level diagram for l Hg+. The 281.5 nm quadrupole "clock" transition can be observed by monitoring the 194 nm fluorescence. If the ion has made a transition from the Si to the 5/2 level the 194 nm flourescence disappears. For the figure on the right, on the horizontal axis is plotted the relative detuning from line center in frequency units at 281.5 nm. On the vertical axis is plotted the probability that the fluorescence from the 6s Si - 6p pi first resonance transition, excited by laser radiation at 194 nm, is on immediately after the 281.5 nm pulse. The electric-quadrupole-allowed S-D transition and the first-resonance S-P transition are probed sequentially in order to avoid light shifts and broadening of the narrow S-D transition. The recoilless absorption resonance or carrier (central feature) can provide a reference for an optical frequency standard. (From ref. 11)...

Turzo, K., Laczko, G., Filus, Z., and Maroti, P. (2000) Quinone-dependent delayed fluorescence from the reaction center of photosynthetic bacteria, Biophys. J. 79, 14-25. 

An alternate assignment of the emitting state in PuFe following 1064 nm excitation would be the 5f state at about 9755 cm . Fluorescence from this state to lower lying levels would be expected to occur centered around 9755, 5205, 4970 and 3960 cm, in poor agreement with the single observed band centered at about 4550 cm . This alternate assignment is therefore rejected. 

Woodbury, N. W. T., and Parson, W. W., 1984, Nanosecond fluorescence from isolated photosynthetic reaction centers of Rhodopseudomonas sphaeroides. Biochim. Biophys. Acta, 767 345n361. 

Fluorescence from a six-coordinate copper(II) complex is quite rare and it is easy to see why from the energy level diagram of Fig. 7. If the CuF center is distorted from an octahedral geometry then the lowest level of the T2g multiplet comes very close in energy to the upper sheet of the E <8) e Jahn-Teller surface. For positive Qg in Fig. 7 this is the z excited state, and will offer an efficient... 

The quantum yield of charge separation in the reaction center is remarkably high. If Rb. sphaeroides reaction centers are excited in the 870-nm absorption band of P, P Qa is formed with a quantum yield of 1.02 0.04 [48]. In accord with the high yield of photochemical products, the yield of fluorescence from P is only about 1 X 10 [49,50]. 

Set the amplifier gains so that the positive fluorescence from each color lies across the center of the range. 

Set up and optimize the flow cytometer as in Basic Protocol 1. UV-excited (360 nm) blue fluorescence (collected with a 450 nm centered bandpass filter) from the Hoechst 33342 dye is proportional with cellular DNA content. To excite MitoTracker Green FM and CMXRosamine stained samples, the argon-ion laser should be tuned to the 488 nm line. To collect fluorescence from MitoTracker Green FM, use a bandpass filter centered around 530 nm for CMXRos use a longpass filter above 630 nm (see Notes 5-8). 

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