Exciton Diffusion in Highly-Ordered One Dimensional Conjugated Polymers: Effects of Back-Bone Torsion, Electronic Symmetry, Phonons and Annihilation

Overview & Synopsis

Many optoelectronic devices based on organic materials require rapid and long-range singlet exciton transport. Key factors controlling exciton transport include material structure, exciton-phonon coupling and electronic state symmetry. Here, we employ femtosecond transient absorption microscopy to study the influence of these parameters on exciton transport in one-dimensional conjugated polymers. We find that excitons with 2 1 Agsymmetry and a planar backbone exhibit a significantly higher diffusion coefficient (34 ± 10 cm 2 s-1) compared to excitons with 1 1 Bu + symmetry (7 ± 6 cm 2 s-1) with a twisted backbone. We also find that exciton transport in the 2 1 Agstate occurs without exciton-exciton annihilation. Both 2 1 Agand 1 1 Bu + states are found to exhibit sub-diffusive behaviour. Ab initio GW-BSE calculations reveal that this is due to the comparable strengths of the exciton-phonon interaction