Engineering nanometre-scale coherence in soft matter

Abstract

Electronic delocalization in redox-active polymers may be disrupted by the heterogeneity of the environment that surrounds each monomer. When the differences in monomer redox-potential induced by the environment are small (as compared with the monomer-monomer electronic interactions), delocalization persists. Here we show that guanine (G) runs in double-stranded DNA support delocalization over 4-5 guanine bases. The weak interaction between delocalized G blocks on opposite DNA strands is known to support partially coherent long-range charge transport. The molecular-resolution model developed here finds that the coherence among these G blocks follows an even-odd orbital-symmetry rule and predicts that weakening the interaction between G blocks exaggerates the resistance oscillations. These findings indicate how sequence can be exploited to change the balance between coherent and incoherent transport. The predictions are tested and confirmed using break-junction experiments. Thus, tailored orbital symmetry and structural fluctuations may be used to produce coherent transport with a length scale of multiple nanometres in soft-matter assemblies, a length scale comparable to that of small proteins.

Using coherence to enhance function in chemical and biophysical systems

“…Is coherent charge transport important in disordered molecular systems? This is a question that has been examined in the context of conjugated materials for solar energy conversion 56 and charge transport along DNA strands 82 .…”

Thermopower of molecular junctions: Tunneling to hopping crossover in DNA

“…Alternatively, in Ref. 79 charge transport in DNA was simulated using a stochastic Schrödinger equation while taking into account temporal and spatial fluctuations in electronic parameters. In other methods, one explicitly includes the interaction of transport charges with selected DNA vibrational modes using e.g.…”

When can time-dependent currents be reproduced by the Landauer steady-state approximation?

“…In Ref. 47, the authors argue that in order to have coherent transport the molecular orbitals responsible for the transport across the junction must be delocalized. In light of the results presented here, it becomes clear that this statement is not entirely precise as, in the absence of fluctuations, transport through a junction with localized states will be well described by the Landauer approach.…”

“…What leads to the disagreement between Landauer and TD-NEGF in Ref. 47 is that the noise can strongly change the magnitude of the steady-state current by changing the degree of localization of the states involved in the transport.…”