Spectral hole burning in conjugated organic polymers

Persistent and transient hole-burning (HB) at 4.2 K have been applied to study the intrinsic properties of electronic excitations of a ladder type π-conjugated poly(para-phenylene) in solution. Narrow spectral holes less than 1 meV wide have been detected. The dependencies of the HB efficiency on the burning dose and wavelength and doping the samples by electron scavenger are interpreted in terms of a photoreaction related to the so-called two-level-systems, specific low-energy excitations characteristic for disordered materials. At transient HB an additional hole broadening was observed which stems from the triplet energy transfer under conditions of lack of correlation of site energies of the singlet and triplet states of chromophores.