Exciplex modeling

Intermolecular exciplex model (endo orientation) Favored... 

Finally, steric effects have been observed to play a significant role in controlling the dia-stereoselectivity of the arene-alkene cycloadditions. Elaboration of this aspect of the reaction again rests on an exciplex model and will be provided in the context of synthetic plications where it has been most frequently encountered. 

Studies with model compounds have demonstrated that photodehydrochlorination is sensitized by jj-cresol triplets via a charge-transfer exciplex intermediate in which the alkyl chloride is the electron acceptor (15). The detailed mechanism suggested for this process (15) is outlined in Equations 11 and 12. 

Nitro substituted stilbenes have been used as models in stUbene cis trans-isomerization studies. It had been reported previously, that cis -v benzene solution, and a photostationary state of 99.5% trans isomer had been reached 132) ... 

According to the model for [2+2] cycloaddition shown in Fig. 2, it should be possible to reach the pericyclic intermediate upon irradiation of the cycloadduct. If a common intermediate is attained from the cycloaddition and cycloreversion processes, then the sum of the quantum yields for the two processes should equal unity. This has, in fact, been observed to be the case for several exciplex and anthracene excimer systems (49b,52). Stereospecific cycloreversion of stilbene dimers 11 and 12 to t-1 has been observed to occur upon 254 nm... 

An important issue in the nature of the excited states in stacks of DNA bases is whether or not the states extended over a number of the bases are neutral Frenkel excitons or if they carry some degree of charge transfer character (exciplex or excimer).3 [2-4] A purely excitonic model neglects configurations... 

The theory of geminate recombination experienced a similar evolution from primitive exponential model and contact approximation [19,20], to distant recombination carried out by backward electron transfer [21], However, all these theories have an arbitrary parameter initial separation of reactants in a pair, / o. This uncertainty was eliminated by unified theory (UT) proposed in two articles published almost simultaneously [22,23], UT considers jointly the forward bimolecular electron transfer and subsequent geminate recombination of charged products carried out by backward electron or proton transfer. The forward transfer creates the initial condition for the backward one. This is the distribution of initial separations in the geminate ion pair/(ro), closely analyzed theoretically [24,25] and inspected experimentally [26,27], It was used to specify the geminate recombination kinetics accompanied by spin conversion and exciplex formation [28-31], These and other applications of UT have been covered in a review published in 2000 [32],... 

The importance of bioexcimers (bioexciplexes) in the photochemistry of biological compounds has been also emphasized. Computation of potential energy curves modeling the complex pheophytin-quinone shows the relevance that stabilization caused by the formation of rr-stacked excited dimers, that is, excimers (exciplexes) and the corresponding presence of conical intersections, have to provide... 

The exciplex or CIP is treated as a dipole of radius q and dipole moment p. The last term in Eq. (15) describes the energy of this dipole, based on the Kirkwood-Onsager model (assuming formation of a spherical complex) [14]. Thus, an exciplex or CIP is stabilized by Coulombic interactions and by solvation. The solvation energy is expected to be favored by increasing solvent polarity and a large dipole... 

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