Singlet-triplet decay rates

Pig. 1). The magnetic field mixes the m= 0 triplet and singlet states and, as a result, the m= 0 triplet decay rate is increased to... 

Figure 4.11 shows a summary of the triplet states kinetics with the intersystem crossing between excited singlet state and the triplet state and the triplet decay rate. 

Figure 1. Schematic representation of the electronic energy levels of a molecule showing the ground singlet state So, the first excited singlet state Si, and the lowest triplet state T. For each electronic state, several levels in the vibrational progression are shown. Laser excitation pumps the (0-0) transition with energy hv. The intersystem crossing rate from the singlet manifold to the triplets is h,x, and the triplet decay rate is kj = Fluorescence emission shown as dotted lines originates...

Cycloalkenes.—Total decay rates of excited singlet states of 1-phenylcycloalkenes have been measured, dissected into component rates for fcj, k., and kf, and compared with corresponding rates of triplet decay a parallel was found between the singlet and triplet decay rates, and a relationship observed between molecular flexibility and internal conversion. ... 

Fig. 12.2. FRET calculator. (A) Table of input parameters arbitrary concentration and time units. The rate constants selected for singlet decay (kdd = kd, excluding FRET see Eq. (12.1)) and for FRET (kt = kt) are the same, corresponding to a FRET efficiency E = 0.5. The acceptor has been assigned quite different parameters, except for triplet decay (kT — ki). The data are plotted for the indicated time scales (10, 150). (B) specification of desired output signals (see Fig. 12.1 b) xl, sg = excited donor ground state...

Singlet oxygen decays to the ground-state triplet oxygen at a rate which is strongly dependent on the solvent.122 Measured half-lives range from about 700 ps in carbon... 

When monitoring the transient due to triplet carbenes is difficult because of the inherent weak nature of the bands and/or severe overlapping with the absorption bands of the parent diazo compounds, it is more convenient to follow the dynamics of the triplet carbene by measuring the rate of the products formed by reaction of triplet carbenes with quenchers such as radicals (Section 5.3) and carbonyl oxides (Section 6.5). In this case, note that the observed rate constant (feobs) of a triplet carbene reaction is the sum of the decay rate constants of the triplet. These may include decay via an associated but invisible singlet with which the triplet is in rapid equilibrium. Thus in general. 

For most aryl azides, the rate constants of singlet nitrene decay and product formation (triplet nitrene and/or ketenimine) are the same. Thus, in all these phenyl-nitrenes cyclization to substituted benzazirines is the rate-limiting step of the process of isomerization to ketenimine, as is the case for the parent phenylnitrene. The only known exception, o-fluorophenylnitrene, will be discussed in the next section. 

The problem of the decay of exciplexes arises directly from their stability. There is no simple and unambigous relation between the electron donor ability of an excited complex A, electron withdrawing property of its reaction partner Q, and the decay rate constant kq. This experimental observation may be understood on the basis of two deactivation pathways of exciplexes (A — Q) a spin-forbidden conversion to the singlet ground state (GS) molecules A and Q, e.g. for a triplet exciplex 3(A — Q)... 

Gidley, D.W., Rich, A., Sweetman, E. and West, D. (1982). New precision measurement of the decay rates of singlet and triplet positronium. Phys. Rev. Lett. 49 525-528. 

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