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

Abstract

Controlling the switching efficiency of photoactive hybrid systems is an obligatory key prerequisite for systematically improving the design of functional materials. By modulating the degree of fluorination and the amount being embedded into porous hosts, the E / Z ratios of fluorinated azobenzenes were adjusted as both functions of substitution and the degree of loading. Octafluoroazobenzene (F8-AZB) and perfluoroazobenzene (F10-AZB) were inserted into porous DMOF-1. Especially for perfluoroazobenzene (F10-AZB), an immense stabilization of the E isomer was observed. In complementary molecular dynamics simulations performed at the DFTB (density functional tight binding) level, an in-depth characterization of the interactions of the different photoisomers and the host structure was carried out. On the basis of the resulting structural and energetic data, the experimentally observed increase in the amount of the Z conformer for F8-AZB can be explained, while the stabilization of E -F10-AZB can be directly related to a fundamentally different interaction motif compared to its tetra- and octafluorinated counterparts.

Structural Properties of Metal–Organic Frameworks at Elevated Thermal Conditions via a Combined Density Functional Tight Binding Molecular Dynamics (DFTB MD) Approach

“… 2 − 4 The highly porous, crystalline structure of MOFs enables the trapping of small molecular compounds, resulting for instance in high gas storage capacities 5 − 7 along with a potential activation of guest molecules via the incorporation of catalytically active reaction centers inside the host structure. 8 − 10 More advanced applications focusing on (semi)-conducting properties, 11 the synthesis of photoswitchable functional materials, 12 , 13 and the exploitation of MOFs as carrier matrix in improved drug delivery systems 14 , 15 have recently attracted increased attention.…”

Mechanochemical Loading: An Alternative Route to form Spiropyran@MOF Composite Materials

“…Furthermore, surface adsorption of the SP molecule can be a reason for the roughening process. In previous studies on switch@MOF systems with the photoswitchable part being non‐covalently attached to the host framework, powder X‐ray diffraction (PXRD) has proven to be a powerful tool to trace the successful incorporation of the dye molecule [27,56,62–68] . As a result of the changed electron density of the overall material and the corresponding change of the structure factor, modulations in the reflection intensities are observed upon dye inclusion.…”

“…In previous studies on switch@MOF systems with the photoswitchable part being non-covalently attached to the host framework, powder X-ray diffraction (PXRD) has proven to be a powerful tool to trace the successful incorporation of the dye molecule. [27,56,[62][63][64][65][66][67][68] As a result of the changed electron density of the overall material and the corresponding change of the structure factor, modulations in the reflection intensities are observed upon dye inclusion. Since the dye molecules are non-systematically positioned within the pores, they do not generate a reflection pattern themselves.…”

Optical Characteristics of Spiropyran@MOF Composites as a Function of the Metal–Organic Framework Linker Substitution

“…DCl was added to destroy the host framework, as has been previously reported. 10,12,15,22,23,39 Directly after the addition of DCl, the sample was placed in an NMR glass tube. To determine the composition, characteristic proton signals were integrated and related to each other.…”

“…For fluorinated azobenzenes, liquid-state NMR and IR spectroscopic measurements were found to be powerful tools to determine the photoisomer ratios (E-to-Z ratios) and the nature of interaction with the host scaffold. 23,39 Unfortunately, both methods are not adequate in the case of SPs. In the case of IR spectroscopy, the characteristic signals for the merocyanine form overlap with those of the MOF host and do not allow for a quantitative analysis.…”