Steady-state quantum yield

From the excited-state conversion rates (ka and kd), it is possible to calculate the ratio of the quantum yields between emission from the twisted and LE states. The ratio of the steady-state quantum yields from the locally excited state (f>LE and the TICT state r/>TI, T for DMABN and other aminobenzonitrile derivatives is described in (1) [12],... 

Haas et al.(m) have examined the fluorescence decay of tyrosine due to different Tyr-Pro conformations in small peptides to elucidate further the nature of the fluorescence change associated with Tyr-92. These peptides have acetyl groups at the amino terminus and /V-mcthylamidc groups at the carboxyl terminus. They found that whereas the dipeptide fluorescence decay requires a double-exponential fit, that of the tripeptide Tyr-Pro-Asn can be fit by a single exponential. By comparison of the average fluorescence decay time and steady-state quantum yield of the peptide to that of A-acetyltyrosine-A-methylamide, they found a relatively greater reduction in the steady-state quantum yield of the peptides. This is attributed to static quenching, which increased from 5 % in the dipeptide to 25 % in the tripeptide. The conformations of these peptides were also examined by NMR, but the results could be interpreted in terms of either cis-trans isomerization or other conformational isomerizations. 

Emission quenching, steady state quantum yield measurements, and flash photolysis studies established that the initiation process could be represented by eqs. 13 or 14, and 15 ... 

Table 2. Charge separation and steady-state quantum yields and recombination rates in the photosensitized reduction of C V2+...

Although the instantaneous quantum yield may generally change with time of irradiation, in conventional experiments at constant light intensity there is often only a short initial period during which the instantaneous quantum yield increases, and then it reaches a constant value. The initial part is called the "induction period." After the instantaneous quantum yield becomes constant, the system is said to be in a stationary or steady state. Under these conditions, it is the steady-state quantum yield which is obtained. Provided that the induction period represents only a small fraction of the total irradiation time and that the quantum yield does then become constant, the overall quantum yield will also be independent of irradiation time and is practically equal to the steady-state quantum yield. 

EXPERIMENTAL QUANTUM YIELD ( ) the number of observed events of a given phenomenon per photon absorbed by the system (see also Overall Quantum Yield, Instantaneous Quantum Yield, and Steady-State Quantum Yield). 

STEADY-STATE QUANTUM YIELD the instantaneous quantum yield in a system after it has attained a constant value in time. 

STEADY-STATE QUANTUM YIELDS FOR CHARGE ACCUMULATION AT 25°C. 

The rdadve steady-state quantum yield of die dentw is given by... 

The increased quantum yield of chlorosome fluorescence in Chlorobium cells under anaerobic conditions is reflected in the fluorescence lifetime data shown in figure 4. In the absence of dithionite (top), the decay was dominated by fast components in fluorescence from both BChl d (760 nm) and BChl a (820 nm). Much longer fluorescence lifetimes were observed when 10 mM Na2S204 was added to the sample (bottom), in agreement with the increase in steady-state quantum yield. 

FIGURE 2. The relationship between the quantum efficiencies of PSl and PS2, i )PSl and PS2, and the steady state quantum yield of C02 assimilation for a barley leaf in 2% 02 air. 

Proton transfer is a fundamental process in both chemistry [1-3] and biology [4]. In particular, proton dissociation namely, proton transfer to solvent, from aromatic dye molecules in their excited electronic state [5] can be easily studied by virtue of their strong fluorescence signal [6]. The older fluorescence measurements did not possess time resolution It was only possible to obtain steady-state quantum yields under conditions of constant illumination [6]. The conventional interpretation of the experimental data assumed a chemical kinetic scheme, such as [3]... 

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