Excited ions charge transfer

The insight of photoinitiation is complicated. Even when CT absorption is observed, the initiation process may not start from a charge transferred state or form ion-radicals. An alternative mechanism is triplet excitation via charge transfer absorption. Namely, when the CT excited level is higher than the triplet level, a considerable amount of the CT excitation would be converted to the triplet state. The TMPD+-naphthalene pair fits in this case (20). Conversely, the contribution of CT might be predominant even when the CT interaction in the ground state is not observed. As shown in Eqs. (14) and (16), charge transfer interaction will not take part in photoexcitation but occurs in the excited state. Possible reaction mechanismus may be explained as follows. 

Here A(aq+ ) denotes the solvent-to-ion charge-transfer excited state, and A(aq ) is the hypothetical state of the A ion with the solvent molecules reorganized in the configuration appropriate for A+(aq). Term AG is a work term analogous to AG. Values of AG calculated from the cycle are shown in Table VIII. 

Red emission in lamps is due to YtOvEu. Excitation involves charge transfer transition from O2- ions to Eu3+ and then emission occurs due to f-f transitions in Eu3+ ions. 

Charge transfer complexes received much attention in the early decades of the twentieth century [75] and again in the 1950s and 1960s [76]. They would prove to be of particular importance because the excitation of charge transfer absorptions allows the unambiguous generation of intimate radical ion pairs. 

Fig. 12. Relative velocity dependence of metal ion charge transfer and excitation collisions with N2.

Similar photoinduced dimerizations and ligand substitutions in the presence of additives such as triphenylphosphine are observed with ion-pairs salts of Mn(CO)s and V(CO)6" with cobaltocenium or other cationic acceptors such as Ph2Cr", pyr-idinium, quinolinium, etc [118]. Most importantly, all photochemical transformations of the various carbonyl metallate salts are initiated by actinic light that solely excites the charge-transfer absorption bands of the contact ion pairs whereas local excitation of the separate ions is deliberately excluded. 

These reactions can be attributed to the excitation of charge-transfer states. High-energy UV irradiation (A < 200 nm) leads to high-quantum-yield photoreduction of Ru(III) amine complexes. Another photoredox-induced substitution is the result of exciting the intervalence charge-transfer band of the ion pair. ... 

The temperature dependence of collisional energy transfer in the photoisomerization of cycloheptatriene has been discussed.19 The reactions of singlet methylene with butadiene,20 the excitation of charge-transfer complexes of C2H4-02-Ar mixtures at low temperatures,21 and the photodissociation of the perfluoroallyl cation22 have been reported. The product of the last reaction is the CF3+ ion, and the threshold wavelength for its production is 295 nm. 

Metal ion can form complex through coordination with unsaturated compounds such as olefin. Through coordination with metal ion, two olefins can be positioned in close proximity, and olefin photochemistry may be caused upon irradiation at longer wavelengths by exciting the charge-transfer band of the resultant complex. Evers and Mackor investigated the intramolecular [2-h2] photocycloaddition of diene 148, which is photochemi-cally catalyzed by copper(l) trifluoromethanesulphonate. In the presence of the copper... 

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