Spin-dependent delayed luminescence from nongeminate pairs of polarons in ∏-conjugated polymers

We measured cw photoinduced absorption (PA) and spin- 1 2 PA- and photoluminescence detected magnetic resonance (PADMR and PLDMR, respectively) in films of two representative p-conjugated polymers; poly(phenylene-vinylene) and polythiophene. From the dependences of the polaron PA and PLDMR on the laser excitation intensity we conclude that the PLDMR is due to spin-dependent delayed luminescence from nongeminate pairs of polarons. Our findings imply that spin-dependent exciton formation in polymer lightemitting diodes leads to enhanced emission efficiency.