Photodegradation internal conversion

The effect of concentration, temperature, and solvent on the photodegradation of benzothiazolinospiropyrans using flash photolysis has been presented. trans-Cyclo-octene is shown to be the major product in the photolysis of m-cyclo-octene with a quantum yield of 0.34. Hamanoue and co-workers " report on intersystem crossing and lowest triplet states of 4-chromanone, chromone, and flavone and of some nitroanthracene derivatives." For the latter long build-up times for triplet-triplet absorption were observed (72—86 psec) and represent the effect of the rates of internal conversion T aa/ T,). Indirect intersystem crossing to higher levels of the triplet manifold is most important in these systems. 

Figure 6. A. Pathways for photodegradation of riboflavin. B. Pathways for de-activatlon of flavins (FL) In aqueous solution Including reaction with quenchers (Q) and substrates (SH) and energy ( A ) losses through Internal conversion and emission steps.

Several physical interaction mechanisms affect optical absorption. Band shapes of polyatomic molecules are broadened relative to the spectral lines of atoms due to shortening of the lifetime of the excited state. This can be due to internal conversion or to isomerization, photodegradation, spin-orbit coupling or excited discrete states. 

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