TRIPLET EXCITON FORMATION DUE TO INTERACTION BETWEEN SINGLET EXCITONS IN POLYDIACETYLENE

The time-resolved spectroscopy in polydiacetylene single crystals (PDA-MADF {poly-1-[3-(methylamino)phenyl]-4-[3,5-bis(trifluoromethyl)phenyl]-1,3-butadiyne}) on femtosecond and picosecond time scales was -performed. The time dependence of the photoinduced reflectance change in PDA-MADF exhibits three components with lifetimes approximately 200 fs, 1-2 ps, and much greater than 200 ps. These components are assigned to the free B-1(u) excitons, self-trapped excitons, and triplet excitons. From the excitation intensity dependence of the reflectance change, a significant role of bimolecular interactions between singlet excitons for the formation of triplet excitons is clarified. A model of the mechanism of triplet exciton formation after the creation of singlet excitons is proposed.