Exciton exothermic

If E is greater than the electron affinity E of the accepter, then the photoinduced forward electron-transfer reaction will be exothermic. This approach can be used to determine the E for both singlet and triplet excitons from the corresponding singlet and triplet state oo values. A similar calculation of an acceptor exciton s electron affinity ( ) may be made, to assess whether acceptor exciton-dissociation... 

After a photon has excited the conjugated polymer to form an exciton, the C60 accepts one electron due to its high electron affinity and establishes the anion Cg0. What is left on the polymer chain is a cation radical, i.e., a positive polaron, as depicted in Fig. 1.14, which is a mobile charge carrier that can move along the polymer backbone. This transfer is an exothermal reaction, where energy from the system is released. 

Another interesting finding based on the thermodynamic data is the low A fH0A (-28.9 kcal/mol or -121.0 kj/mol) of the Ca/CsF system. The combined used of Ca and CsF should conceptually construct a novel cathode configuration in OLEDs. Our device studies in Section 5.5 have clarified this presumption. The device performances are also dependent of other factors, e. g. they may be deteriorated by exciton quenching that arise from the gap-state formation over a rather thick interface region due to the highly exothermic reaction between the Ca and CsF. 

Fig. 5 Diffusional intermolecular singlet fission, (a) Energy diagram of singlet fission via a [T-T] intermediate. In TIPS-pentacene (13) formation of two triplet excitons is exothermic whilst for TIPS-tetracene (14) this process is endothermic, reflected in the respective triplet yields for the two molecules (b). (c) Schematic depicting the collision of TIPS-pentacene in solution to form the excimer intermediate. Adapted from ref, 28,...

Despite fission being orders of magnitude slower than the solid state in this diffusion-limited system, fission was equally efficient. The triplet exciton yield determined from the relative extinction coefficients of the triplet and singlet excitons was 197%. Such a high yield indicates that once the molecules collide in solution, fission proceeds rapidly in this exothermic system. Indeed the observed rate of triplet formation in the concentrated solution suggests that fission occurs as fast as the diffusional timescales allow the rise of the triplet exciton absorption had a 500 ps time constant, reaching 30% of the expected diffusion limit for the system. 

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