Structural, dynamical, and photochemical properties ofortho-tetrafluoroazobenzene inside a flexible MOF under visible light irradiation

Abstract

Understanding isomer distribution of tF-AZB inside DMOF-1 as a function of host–guest and guest–guest interaction.

Fundamental Study of the Optical and Vibrational Properties of Fx-AZB@MOF systems as Functions of Dye Substitution and the Loading Amount

“…The density functional tight binding (DFTB) approach 35 , 36 is based on a Taylor series of the Kohn–Sham energy known from density functional theory (DFT) with respect to the equilibrium density, enabling a parametrization of simple tight binding (TB) Hamiltonians 39 with respect to high-level DFT reference data. As in the previous study of E / Z -F4-AZB, 9 the self-consistent charge density functional tight binding (SCC DFTB) 40 , 41 method in conjunction with the 3ob parameter set 42 − 44 as implemented in the DFTB+ package 45 was employed to describe the intermolecular forces under periodic boundary conditions, thereby considering each atom as irreducible. Monkhorst–Pack sampling on a (2 × 2 × 2) grid was employed for the integration along the axes of the Brillouin zone.…”

“…Notably, the dye molecule can also be part of the linker backbone 20 − 23 or can act as a linker pendant group. 24 − 32 To understand the optical characteristics as a function of dye substitution, loading amount, and synthesis temperature, we recently started to investigate differently substituted spiropyrans 16 as well as varying amounts of ortho -tetrafluoroazobenzene (F4-AZB) 9 within the same host matrixes. Both studies showed a significant dependence of the resulting optical properties on the substitution pattern of the inserted guest molecule as well as on the amount being embedded.…”

“…To correlate the experimental results with the interaction between the guest molecules and the host structure, several theoretical investigations have been carried out. Similar to the previous study focused on F4-AZB@DMOF-1, 9 a molecular dynamics (MD) simulation approach describing the system at an elevated temperature was preferred over the calculation of simple minimum structures corresponding to 0 K treatment. Previously, it was shown that the interaction motif of Z -F4-AZB involved only BDC 2– (i.e., terephthalate anion) units associated with a single unit cell of the host structure, forming a square coordination cavity.…”

“…Despite providing a simplified, semiempirical description of the interactions, a DFTB MD simulation approach delivered an accurate description of pristine DMOF-1 when compared to experimental reference data as well as a detailed structural description of E / Z -F4-AZB@DMOF-1 that correlated well with the experimental findings. 9 For this reason, this study employs the same simulation approach to investigate the binding properties of E / Z -F8-AZB and E / Z -F10-AZB embedded in the DMOF-1. In addition to MD simulations of the guest@host systems, the comparison of theoretically and experimentally determined difference infrared (IR) spectra proved to be a valuable tool to correlate the vibrational properties of the individual conformers associated with the photoswitching mechanism.…”

Efficient solid-state photoswitching of methoxyazobenzene in a metal–organic framework for thermal energy storage

“…This has been demonstrated for ortho-functionalised AB derivatives, for which the E and Z isomers have well-separated n-p* bands. 38 However, while this can lead to more efficient photoswitching, including quantitative switching within MOFs, 39 it can also reduce the energy difference between the ground and metastable states, thereby reducing the energy density of the resulting MOST material. 1,37,39,40 The design of both the photoswitch and MOF architecture therefore need to be carefully considered in order to achieve a high degree of conversion as well as a high energy density.…”