Dynamics of Long-lived Polarons in Poly(p-phenylene)-Type Ladder Polymers (LPPP)

The X-band spin 1/2 photoluminescence-detected magnetic resonance (PLDMR) of LPPP films and solutions featuring a high degree of intrachain order and high PL quantum yields (24% in films and 84% in solutions) is described. Excitation at 458 run yields a PL-enhancing polaron resonance at g~2.00 of width ΔH1/2~8G and 4G in films and frozen solutions, respectively. The resonances are assigned to enhanced nonradiative recombination of long-lived polaron pairs, which are singlet exciton quenching centers. Their behavior is consistent with two distinct polaron pair lifetimes or a very broad distribution of lifetimes which are ~10 times longer in solutions than in films. The distinct lifetimes which are ~40 and ~670μs in films and ~370 and ~3300μs in solutions, are discussed in relation to longer-lived intrachain interconjugation segment pairs and shorter-lived interchain pairs. The spectral dependence of the resonance demonstrates that the emission from charge transfer excitons in aggregates of the films is much more spin-dependent than that from single polymer chains of the frozen solutions.