Photoexdted triplet states

Gloss, G.L., Gautam, R, Zhang, D., Krusic, P.J., Hfll, S.A., and Wassermann, E., Steady-state and time-resolved direct detection EPR spectra of fullerene triplets in Kquid solution and glassy matrixes evidence for a dynamic Jahn-TeUer effect in triplet C60, /. Phys. Chem., 96,5228, 1992. Bennati, M., Grupp, A., Mehring, M., Dinse, K.-P., and Fink, J., Pulsed EPR on the photoexdted triplet state of fullerene, Chem. Phys. Lett., 200, 440,1992. 

Cycloaddition reactions proceed generally via the triplet state. However, the charge transfer interaction may be important for the initial photoexdtation. An example is the 1,2-cydoaddition of maleic anhydride with benzene. The benzene-maleic anhydride complex is the photoabsorbing species (76). 

Figure 3. Time scales on which measurements can be made by photoexdtation and puke radiolysis. For bothy the fastest measurements require pump-probe techniques. The dark regions indicate straighiforward single-shot measurements. Processes having a very long time scale (light areas on the right) require long-lived excited states in photoexcitation, usually triplets, and for both methods may be applicable in special media, such as solids.

In 1977 and 1978 as part of the study of photoexdted state response to geometrically oriented perturbers, my students and I rqiorted the observation of alkali metal ion enhanced fluorescence of a crown ether (l,8-naphtho-21-crown-6) containing an attached naphthalene chromophore 1,2), The approximately 60 percent increase in fluorescence intensity, which was observed in an ethanol glass at low temperatures, correlated with a cation induced decrease in the triplet energy level relative to the fluorescent singlet state and the ground state. The increase in fluorescence was presumably due to a decrease in the intersystem crossing rate relative to the fluorescence rate. 

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