Efficient stimulated emission due to bimolecular annihilation reduction in oligothiophene dioxide thin films

We have studied the optical properties of a thienyl-S, S-dioxide oligothiophene under strong excitation. No stimulated emission is observed in neat films due to singlet-singlet bimolecular annihilation, with a bimolecular constant of A=(4.5 +/- 0.5)x10(-11) cm(3) s(-1). On the contrary we show that strong stimulated emission is observed if the active molecule is blended to an inert polymer [poly(bisphenol A carbonate] (PC) even for a PC content as low as one PC molecule every 500 active molecules. We suggest that small PC quantities modify the film superamolecular packing, thus reducing the bimolecular recombination efficiency. These results are expected to be quite general and could allow a considerable extension of the number of molecules showing stimulated emission for organic laser applications.