ANTHRACENE SINGLET QUENCHING BY INDOLES IN MEDIA OF DIFFERENT POLARITIES - MECHANISM AND CHEMICAL PHOTOREACTION

The quenching of excited singlet anthracene by indole derivatives in s olvents of different polarity has been studied using static and time-r esolved techniques. The quenching process is dependent on the nature o f the indole derivative and on the polar properties of the medium. In non-polar solvents photoreaction takes place with unit efficiency in c ompounds which have a hydrogen atom bound to the nitrogen. The efficie ncy decreases in polar solvents and is considerably suppressed in aque ous solvent mixtures. The results here obtained indicate that charge t ransfer is the primary step for the photoreaction in polar solvents. F or compounds with the indolic N-H group, direct hydrogen transfer is t he dominant mechanism in non-polar media. The importance of radical io n formation in these anthracene-indole systems is investigated as a fu nction of the indole structure and solvent polarity.