Highly Efficient One-Dimensional Triplet Exciton Transport in a Palladium−Porphyrin-Based Surface-Anchored Metal−Organic Framework
Adams, M. / Kozlowska, M. / Baroni, N. / Oldenburg, M. / Ma, R. / Busko, D. / Turshatov, A. / Emandi, G. / Senge, M. / Haldar, R. / Wöll, C. / Nienhaus, U. / Richards, B. / Howard, I. (2019)
ACS Appl. Mater. Interfaces, 2019, 11, 15688−15697
- Date: April 2019
Efficient photon-harvesting materials require easy-to-deposit materials exhibiting good absorption and excited-state transport properties. We demonstrate an organic thin-film material system, a palladium−porphyrin-based surface-anchored metal−organic framework (SURMOF) thin film that meets these requirements. Systematic
investigations using transient absorption spectroscopy confirm that triplets are very mobile within single crystalline domains; a detailed analysis reveals a triplet transfer rate on the order of 1010 s−1. The crystalline nature of the SURMOFs also allows a thorough theoretical analysis using the density functional theory. The theoretical results reveal that the intermolecular exciton transfer can be described by a Dexter electron exchange mechanism that is
considerably enhanced by virtual charge-transfer exciton intermediates. On the basis of the photophysical results, we predict exciton diffusion lengths on the order of several micrometers in perfectly ordered, single-crystalline SURMOFs. In the presently available samples, strong interactions of excitons with domain boundaries present in these metal−organic thin films limit the diffusion length to the diameter of these two-dimensional grains, which amount to about 100 nm. Our results demonstrate high potential of SURMOFs for light-harvesting applications.