Femtosecond Relaxation of Photoexcitations in a Poly(Para-Phenylene)-Type Ladder Polymer

Time-resolved femtosecond pump and probe experiments were conducted on films of poly(para-phenylene)-type ladder homopolymers featuring a high degree of intrachain order. We find stimulated emission in the region of the interband luminescence which is of the same magnitude as the photoinduced absorption. The latter is located energetically below the interband luminescence and therefore does not compete with the stimulated emission. We conjecture this to be an intrinsic property of conjugated polymers of high intrachain order and a narrow distribution of long conjugation lengths. From the decay dynamics we conclude that stimulated emission and photoinduced absorption originate from different species.