Charge-transfer dynamics and nonlocal dielectric permittivity tuned with metamaterial structures as solvent analogues

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by Prof. Jeong Weon Wu  (jwwu@ewha.ac.kr)

Department of Physics​

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​Charge separation and recombination are two sides of the same coin, which impact numerous applied and fundamental phenomena in electronics, magnetism, biology and photosynthesis, as well as chemistry. Understanding and artificially tuning charge transfer dynamics are then of the greatest importance. Optical spectroscopy techniques have equipped researchers with powerful tools to probe charge exchanges between donors and acceptors with sub-picosecond time resolution over a wide spectral range. Interfaces, solvents, as well as atomic or molecular organization and engineering are among the triggers which scientists investigate and rely on to gain control over charge transfer dynamics. Here, we evidence that charge transfer dynamics can be altered by multi-layered hyperbolic metamaterial substrates. Taking triphenylene:perylene diimide dyad supramolecular self-assemblies as a model system, we reveal longer-lived charge transfer states in the presence of hyperbolic metamaterial structures, with both charge separation and recombination characteristic times increased by factors of 2.4 and 1.7, that is, relative variations of 140 and 73%, respectively. To rationalize these experimental results in terms of driving force, we successfully introduce image dipole interactions in Marcus theory. The nonlocal effect herein demonstrated is directly linked to the number of metal-dielectric pairs, can be formalized in the dielectric permittivity, and is presented as a solid analogue to local solvent polarity effects. This model and extra P3HT:PC₆₀BM results show the generality of this nonlocal phenomenon and that a wide range of kinetic tailoring opportunities can arise from substrate engineering. This work paves the way toward the design of artificial substrates to control charge transfer dynamics of interest for applications in optoelectronics and chemistry.

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​Transient absorption measurements of annealed dyad molecule thin films. Time resolved ΔT/T spectra probed at 725 nm monitoring ia plotteed. a, the formation and b, the disappearance of the anionic PerDi (inset : semilog plots with inverted scale illustrating the single exponential recovery behaviour). Colored curves are exponential fits (a, b).

* Related article
Kwang Jin Lee, Yiming Xiao, Jae Heun Woo, Eunsun Kim, David Kreher, André-Jean Attias, Fabrice Mathevet, Jean-Charles Ribierre, Jeong Weon Wu & Pascal André, "Charge-transfer dynamics and nonlocal dielectric permittivity tuned with metamaterial structures as solvent analogues", Nature Materials, 16, 722 (2017)