AbstractThe Stern‐Volmer constant of 40 quenchers was determined at 366 nm for poly(vinyl phenyl ketone) photolysis in benzene and dioxane solution at room temperature. Aromatic hydrocarbons, dienes and olefins were used as quenchers. A procedure for quantitative separation of the screening effect of quenchers absorbing at irradiation wavelength was elaborated. The correctness of this procedure was checked using 2‐hydroxy‐5‐methyl benzophenone over the concentration range 0‐10−3mole/1. The values of the Stern‐Volmer constants lay within the range 0‐250 1./mole, expressing changes of the rate constant of quenching. Stern‐Volmer constants were found to be constant for naphthalene, its alkyl, halogen derivatives and esters at about 70 1./mole, that of 1‐naphtyl amine 1‐ and 2‐naphtol being, however, substantially higher. Electron‐deficient olefins were equally effective as dienes. There has not so far been found a parameter to characterize unambiguously the quenching efficiency of t