The exciton diffusion length in a nematically organized meso-tetra(4-n-butylphenyl)porphyrin (TnBuPP) layer was found to exceed 40 nm at a temperature of 90 K and to be equal to 22 ± 3 nm at 300 K. The exciton diffusion coefficient decreases from ≥3.1 × 10−6 m2/s at 90 K to (2.5 ± 0.5) × 10−7 m2/s at 300 K. This thermal deactivation is attributed to exciton motion via a band mechanism. The motion of an exciton is not limited by polaronic effects; that is, the deformation of the atomic lattice around the exciton. The absence of polaronic self-trapping implies that the exciton diffusion coefficient can be enhanced by improvement of structural order and rigidity of the material.
Huijser, A., Savenije, T. J., Meskers, S. C. J., Vermeulen, M. J. W., & Siebbeles, L. D. A. (2008). The mechanism of long-range exciton diffusion in a nematically organized porphyrin layer. Journal of the American Chemical Society, 130(37), 12496-12500. https://doi.org/10.1021/ja803753y