Triplet long-range

Oxidative repair is not a unique feature of our Rh(III) complexes. We also demonstrated efficient long-range repair using a covalently tethered naphthalene diimide intercalator (li /0 1.9 V vs NHE) [151]. An intercalated ethidium derivative was ineffective at dimer repair, consistent with the fact that the reduction potential of Et is significantly below the potential of the dimer. Thymine dimer repair by a series of anthraquinone derivatives was also evaluated [151]. Despite the fact that the excited triplets are of sufficient potential to oxidize the thymine dimer ( 3 -/0 1.9 V vs NHE), the anthraquinone derivatives were unable to effect repair [152]. We attribute the lack of repair by these anthraquinone derivatives to their particularly short-lived singlet states anthraquinone derivatives that do not rapidly interconvert to the excited triplet state are indeed effective at thymine dimer repair [151]. These observations suggest that interaction of the dimer with the singlet state may be essential for repair. 

The overlap integrals J (v) which are essential for a Forster long-range dipole-dipole transfer mechanism 56> were obtained from the benzaldehyde phosphorescence spectrum and the absorption spectra of the fluorescers used. A linear relation was observed between the square root of the overlap integrals and the number of excited singlet fluorescer molecules produced per molecule of benzaldehyde triplet, which is a strong argument for the essential role of the proposed transfer mechanism. 

The prominent feature of the triplet curve in the long-range region R > 1.8 A is a double-humped repulsive barrier. This is evidently associated with successive... 

G. L Closs, M. D. Johnson, J. R. Miller, P. Piotrowiak, A Connection between Intramolecular Long-Range Electron, Hole, and Triplet Energy Transfers , J. Am Chem Soc 1989, 111, 3751-3753. 

The Coulombic mechanism would require that both 3D — 3D and 1A —> 3A were allowed transitions, which clearly they are not as both are spin-forbidden processes. Thus, triplet-triplet energy transfer by the long-range Coulombic mechanism is forbidden. 

Phenylquinoxalines (30) turned out to be both fluorescent and phosphorescent emitters [167, 168]. By using these molecules as host, singlet excitons as well as triplet excitons can be transfered by long-range interactions to phosphorescent dopant molecules such as 66. 

H. E. Zemel and B. M. Hoffman, Long-range triplet-triplet energy transfer within metal-substituted hemoglobins, J. Not. Chem. Soc. 103, 1192-1201 (1981). 

In this chapter we discuss three-site systems. We extend the three models treated in Chapter 4 direct correlation, indirect correlation mediated through the adsorbent molecule, and indirect correlation mediated by a chain of communicating subimits. Here, we discuss separately two possible structures of the system, a linear and a triangle arrangement of the sites (Fig. 5.1). Two fundamentally new features are discussed in considerable detail the nonadditivity of the triplet correlation and the possibility of long-range correlations. 

If the long-range interaction 17(1, 3) can be neglected compared with 1/(1, 2), the (direct) triplet correlations can be written as ... 

In writing these equations, it is implicitly assumed that (1) there is no long-range correlation, i.e., = 1 and (2) the triplet correlation can be expressed as the sum... 

We note that in spite of the large differences in the two sets of results reported in Table 5.3, the binding isotherms computed with these three sets of results were almost indistinguishable on the scale of Fig. 5.19. The most important differences between the calculated correlations and those reported by Senear et al. are, first, there is a large negative cooperativity between sites a and c, while Senear et al. assumed from the outset that no long-range cooperativity exists, and second, the triplet correlation is not additive, i.e., neither Sj nor 62 is zero, while Senear et al. assumed from the outset that 82 = 0. 

We stress, however, that these two properties of the free energy of interaction are valid only in very special cases. We have shown in Sections 5.4-5.7, that, in general, the interaction free energies do not conform to this behavior there could be long-range correlations, i.e., [or g(a, c)], that differ from unity, and triplet correlations that differ from the product g(a, b)g(b, c). [There is no known example where the triplet correlation may be written as a sum of pair correlations g a, b) + gib, c), as assumed by Ackers et ai]... 

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