AbstractThe 1,2‐diphcnylethyl radical and derivatives were generated from photolysis of tran‐f‐stilbene and its derivatives 1–13 with secondary amines as quenchers. The 1,2‐diphenylelhyl radicals that escaped from the solvent cage were trapped by 2‐methyl‐2‐nitrosopropane (MNP) and were detected by the HPLCEPR method. The yield of the spin adduct is greater for tertiary amines. The smaller yields of the spin adduct formed from secondary amines are ascribed to greater reactivities of the 1,2‐diphenylethyl and dialkylamino radicals within