Photogeneration of spins and charges in a derivat polyquinolaxine (PQL-type) ladder polymer

ESR studies of photogenerated, thermally generated and native spins in a polyquinoxaline (PQL-type) ladder polymer and monomer are reported. Spins were photogenerated using different light excitation energies, smaller or larger than the bandgap. The results imply long-lived localized photogenerated polarons; their lifetime is described by a two-component exponential decay function. The lifetime dramatically increases with decreasing temperature and strongly depends on the wavelength of the incident light. The two different decay times may be explained by interchain and intrachain recombination of the localized polarons. The decay times are compared with those of the photogenerated charges in a cw photoconductivity study. The similarity of the ESR properties for the photogenerated, thermally generated and native spins in the polymer indicates that these spin species all exhibit polaronic character.