Irradiation of a polycrystalline mixture of diphenylamine (1) and trans-stilbene (2) caused addition reaction to give an adduct (3) with C-N bond and two adducts (4) and (5) with C-C bond. Similar photoaddition reaction of 1 with phenanthrene (6) in the solid state produced an adduct (7) with C-N bond and another adduct (8) with C-C bond. These photoadditon reactions proceed at the interface of the two component crystallites.