(Invited) The Interplay of Conformation and Electronic Structure in Metal Organic Frameworks
Authors: Pramudya Yohanes , Kozlowska Mariana , Heidrich Shahriar , Krstić Marjan , Haldar Ritesh , Neumann Tobias , Schlöder Tobias , Zhang Qiang , Symalla Franz , Hassan Zeinab Mohamed , Liu Xiaojing , Heinke Lars , Woell Christof , Wenzel Wolfgang 
Published: December 2020

Metal organic frameworks (MOFs) have emerged as a versatile class of designer crystals with tunable properties. Due to their vast chemical composition space and key importance of molecular structure and organization on their electronic properties, modelling and simulation are essential to understand and to optimize MOF functionality. Here, we show that multiscale models that combine structural simulations with electronic structure calculations can be used to explain the origin of the photophysical and conducting behavior of MOF films as the function of their nano/microscale morphology and to tune the specific property by predictive crystal engineering.

Using the density functional theory formalism and our in-house ab initio method, we investigate efficient excited-state transport properties of porphyrin SURMOF [1] and photoconduction of MOF with embedded acceptors like C60 [2]. We predict the charge transport and mobility in polycyclic aromatic hydrocarbons based on the surface-anchored metal-organic frameworks (SURMOF) as a function of the type of the organic linker. We show the reason for the improved conductivity as derived from the spatially ordered structure of a material and confirm the charge transfer anisotropy through the detailed analysis of the transfer rates for electron and hole transport.

To achieve unprecedented PL quantum yields for crystalline core-substituted naphthalenediimides (cNDIs) MOF, we determined the optimal alignment of chromophoric linkers to yield highly emissive J-aggregates [3]. We tuned the molecular alignment of linkers by introducing adjustable “steric control units” (SCUs) controlling the excitonic coupling and computationally screened the large library of handle-equipped MOF chromophoric linkers and for the best SCUs.

Together with experimental observations, we prove that ab initio calculations enable valuable predictions of new promising candidates for emitting and/or semiconducting organic materials made in spatially ordered fashion in the SURMOF. Our data demonstrates the feasibility of MOF-based crystal engineering approaches that can be universally applied to tailor the materials properties.

References:

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[2] X. Liu, M. Kozlowska, T. Okkali, D. Wagner, T. Higashino, G. Brenner-Weiß, S. M. Marschner, Z. Fu, Q. Zhang, H. Imahori, S. Bräse, W. Wenzel, C. Wöll, L. Heinke, Photoconductivity in Metal-Organic Framework Thin Films, Angew. Chem. Int. Ed, 2019, 58, 9590-9595.

[3] R. Haldar, A. Mazel, M. Krstić, Q. Zhang, M. Jakoby, I. A. Howard, B. S. Richards, N. Jung, D. Jacquemin, S. Diring, W. Wenzel, F. Odobel, C. Wöll, A de novo strategy for predictive crystal engineering to tune excitonic coupling, Nat. Commun., 2019, 10, 2048-2054.