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

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)A(g)(-) symmetry and a planar backbone exhibit a significantly higher diffusion coefficient (34 +/- 10 cm(2) s(-1)) compared to excitons with 1(1)B(u)(+) symmetry (7 +/- 6 cm(2) s(-1)) with a twisted backbone. We also find that exciton transport in the 2(1)Ag(-) state occurs without exciton-exciton annihilation. Both 2(1)A(g)(-) and 1(1)Bu(+) states are found to exhibit subdiffusive behavior. Ab initio GW-BSE calculations reveal that this is due to the comparable strengths of the exciton-phonon interaction and exciton coupling. Our results demonstrate the link between electronic state symmetry, backbone torsion and phonons in exciton transport in pi-conjugated polymers.