Protic solvents, photodegradation

These results suggest that the photodegradation of a-guaiacoxyacetoveratrone proceeds only via the singlet excited state in aprotic solvents. In protic solvents, about Vs of this photodegradation proceeds through the singlet state and % via the triplet state. 

In an earlier paper (3), we reported that the quantum yield of photodegradation and the triplet state lifetime of I are both significantly higher in a protic solvent. As well, we presented evidence that significant reaction can occur from the first excited singlet state of I, a phenomenon previously unobserved for aromatic ketones. Here... 

Figure 1 Quantum yield of photodegradation for I in dioxane, as a function of mole fraction of added protic solvent.

JA Schmidt, E Goldszmidt, C Heitner, JC Scaiano, AB Berinstain, and LJ Johnston. Photodegradation of a-Guaiacoxyacetoveratrone Triplet-State Reactivity Induced by Protic Solvents, in C Heitner and JC Scaiano, Eds. Photochemistry of Lignocellulosic Materials, Washington, DC American Chemical Society, 1993, p. 122. 

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