THE INDOLE NUCLEUS TRIPLETSTATE LIFETIME AND ITS DEPENDENCE ON SOLVENT MICROVISCOSITY

The dependence of the phosphorescence hfetune of indole and some of its derivatives on the microwscosity of both aqueous and organic sohent mbtures has been determined from 10' to 104 poise. The accompanying change by a factor of over 100 in the intrinsic decay of the excited triplet state was found to be insenslhve both to pola.rity of the sotvent and proton exchange at the ring rutrogen. The high sensitivity to fluidity makes triplet lifetimes a natural probe of local flexibility in protein structure