The semiconductive properties of a series of pyrenyl polyenes of the type R-(CH=CH)n-R, are studied as a function of the adsorption of different amount of a vapour. With regard to the compensation temperature (T0) the compounds are divided into two groups. For compounds which have odd number of double bonds,T0 is infinite and in compounds having even number double bonds,T0 is finite.T0 for II2 is higher while that of II4 is lower than the experimental temperature. DifferentT0 for the compounds having odd or even number of double bonds suggests a physical basis for the compensation rule, which we believe, is related to the molecular and crystalline structure of the compounds
