Maximizing the Carrier Mobilities of Metal-Organic Frameworks Comprising Stacked Pentacene Units.

Egbert Zojer,Christian Winkler

doi:10.1021/acs.jpclett.1c01892

Abstract

Charge transport properties of metal–organic frameworks (MOFs) are of distinct interest for (opto)electronic applications. In contrast to the situation in molecular crystals, MOFs allow an extrinsic control of the relative arrangement of π-conjugated entities through the framework architecture. This suggests that MOFs should enable materials with particularly high through-space charge carrier mobilities. Such materials, however, do not yet exist, despite the synthesis of MOFs with, for example, seemingly ideally packed stacks of pentacene-bearing linkers. Their rather low mobilities have been attributed to dynamic disorder effects. Using dispersion-corrected density functional theory calculations, we show that this is only part of the problem and that targeted network design involving comparably easy-to-implement structural modifications have the potential to massively boost charge transport. For the pentacene stacks, this is related to the a priori counterintuitive observation that the electronic coupling between neighboring units can be strongly increased by increasing the stacking distance.

Highlights

Charge transport properties of metal−organic frameworks (MOFs) are of distinct interest forelectronic applications
Metal−organic frameworks (MOFs) are highly porous materials consisting of inorganic nodes connected by organic linkers.[1−3] They are traditionally employed in fields like gas storage,[4−6] catalysis,[7−9] and gas separation.[10,11]
In a recent work on pentacene-containing MOFs, this has been attributed to dynamic disorder,[38−40] as a consequence of frustrated rotations of the pentacene units.[34]. While such effects certainly play a decisive role for charge transport in the intermediate coupling regime often encountered in π-conjugated materials,[38,41,42] we will argue here that for the MOFs studied in ref 34 another complication is that the framework structure enforces a packing of the pentacene units that is far from ideal for the obtained electronic coupling

Summary

Introduction

Charge transport properties of metal−organic frameworks (MOFs) are of distinct interest for (opto)electronic applications. The π-slip between the centers of consecutive pentacene units in the direction parallel to the π-planes increases essentially linearly from 4.06 to 9.07 Å over the considered range of a3 values (see Figure 2e); that is, the observed change in the πslip is more than an order of magnitude larger than that of the π-distance.

Results

Conclusion