Electronic excitation energy excited triplet state

Energy transfer from a donor that is in an electronically excited triplet state to produce an electronically excited acceptor which is also in its triplet state. 

Fig. 1. Schematic energy-level diagram for a dye molecule. Electronic states Sq = ground singlet state = first excited singlet state S2 = second excited singlet state Tj = first excited triplet state T2 = second excited triplet state EVS = excited vibrational states. Transitions A = absorption excited states ...

If the cross-coupling is strong enough this may include a transition to a lower electronic level, such as an excited triplet state, a lower energy indirect conduction band, or a localized impurity level. A common occurrence in insulators and semiconductors is the formation of a bound state between an electron and a hole (called... 

Figure 9.1. Potential energy diagram for the electronic states of ethylene N, ground state (w)2 r(3Biu) first excited triplet state (mr ) V, first excited singlet state (wir ) Z, two-electron excitation (w )2. For the ion C2H + R and R, Rydberg states, /, / ground and excited states. [From Ref. 2(c).]...

Moreover, carotenoids may quench electronically excited states and scavenge free radicals formed in the retina, and therefore protect biomolecules from oxidative damage. Due to the low energy level of the first excited triplet state ( Car), carotenoids (Car) can act as efficient acceptors of triplet state energy from photosensitizers (S) (Equation 15.1), such as all-tra .s-retinal, the photosensitizers of lipofuscin (Rozanowska et al., 1998), or singlet oxygen C02) (Equation 15.2) (Cantrell et al., 2003) ... 

These energy-transfer processes are especially interesting in those chemiluminescence reactions where the primary electronically excited product is formed in its triplet state (autoxidation reactions, radical-ion recombination reactions see Sections III and VIII), although some reactions have been reported to involve direct emission from the excited triplet state 14>. 

If chemiluminescence is to occur, a critical electron-transfer enthalpy value must be exceeded. This value is similar to the energy of the lowest excited triplet state, as was found in the case of fluoranthene 150>, for example. 

An excited triplet state always has a lower energy than that of the corresponding excited singlet state. This is in line with Hund s rule when two unpaired electrons occupy different orbitals, there is a... 

A thermal oxidation of 2,3-dimethyl-2-butene, 16, occurs in NaY when the temperature of the oxygen-loaded zeolite in raised above — 20°C [35], Similar thermally initiated oxidations were not observed for the less electron rich tram-or cix-2-butene. Remarkably, pinacolone was conclusively identified as one of the products of the reaction of 16, This ketone is not a product of the photochemical Frei oxidation (vide supra) and underscores the very different character of these two reactions and the complexity of the oxygen/16 potential energy surface, A rationale for the different behavior could lie in the different electronic states of the reactive oxygen-CT complex in the thermal and photochemical reactions. Irradiation could produce an excited triplet-state CT complex ( [16 O2] ) and/ or ion pair ( [16 02 ] ) with different accessible reaction channels than those available to a vibrationally excited ground-state triplet complex ( [16 "02]) and/... 

An increase in the ion annihilation exergonicity AG to values comparable to the excited triplet-state energies (AG I LT < 0) opens an additional electron transfer channel (T-route). In the simplest case, only one excited triplet 3 A or 3 D becomes accessible. Triplet emission can be directly observed from the ECL systems involving rare earth and transition metal complexes with allowed (due to extensive spin-orbit coupling) triplet-singlet electronic transition. 

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