Energy transfers in weakly interacting oligothiophenes

The optical properties of oligothiophene inclusion compounds in perhydrotriphenylene are reported. Excitonic effects are suppressed due to the large inter-molecular distances imposed by the host crystal. In a mixture of quinquethiophene and terthiophene inclusion compounds we observe very efficient long range energy transfers from the short to the long oligomer. Foerster theory indicates that quite large critical distances are involved in this system, thanks to the parallel relative orientation of the molecules within the channels of the host crystal. The fast rise times (shorter than 40 ps) of quinquethiophene excited state population, observed with time-resolved photoluminescence studies, suggest the presence of sizeable contributions from energy transfers among terthiophene molecules.