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

Abstract

Understanding the interactions between the single components of hybrid systems is essential to drive the development of advanced functional materials. A prerequisite for this is the systematic variation of the building blocks of such compounds. Focusing on spiropyran@metal–organic framework (MOF) composite materials with noncovalently attached spiropyran dyes, both the host scaffold and the dye molecules can be systematically tuned. In this work, a broad substitution pattern was applied to systematically elucidate the characteristics of the resulting hybrid materials as a function of the supplemental substitution on spiropyran. The newly developed 12 composites exhibit substitution and host-dependent optical characteristics, which are particularly affected by the substitution of the 6′-position on the chromene ring. Through the favorable combination of the MOF host’s polarity and an adequate strength of the spiropyran’s indolinedonor–chromeneacceptor pair, reversible conversion between photoisomers is efficiently accomplished, especially for nitro-substituted spiropyrans inside MIL-68­(In).

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

“…The composition of the obtained F8-AZB x @DMOF-1 systems was performed via liquid-state NMR spectroscopy following the procedure previously described for diarylethenes, 11 , 12 spirooxazines, 17 spiropyrans, 16 F4-AZB, 9 and fulgides 18 inside different MOF hosts. For this, the respective compound was digested in DMSO- d 6 and DCl.…”

“…Metal–organic framework consist of metal cations or metal-oxo clusters, which are linked by an organic molecule with at least two functional groups to form networks with potential voids. Various photochromic dyes were incorporated into MOFs as noncovalently bound guests, including stilbenes, azobenzenes and functionalized derivatives, − diarylethenes, , spiropyrans, − spirooxazines, fulgides, or donor–acceptor Stenhouse adducts (DASAs) . For all resulting composites, photoswitching was enabled in the solid state, which makes these systems very interesting for further implementation as functional materials.…”

“…For all resulting composites, photoswitching was enabled in the solid state, which makes these systems very interesting for further implementation as functional materials. Notably, the dye molecule can also be part of the linker backbone − or can act as a linker pendant group. − To understand the optical characteristics as a function of dye substitution, loading amount, and synthesis temperature, we recently started to investigate differently substituted spiropyrans as well as varying amounts of ortho -tetra­fluoro­azobenzene (F4-AZB) 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.…”

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

“…Using this approach, solid-state photoswitching has been demonstrated for AB derivatives 13–22 as well as other molecules including dithienylethenes, 23–27 2-phenylazopyridine, 28 and spiropyrans. 29–35…”

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

“…To overcome this problem, various studies on the embedment of the photoswitch as a guest molecule into a porous metal–organic framework (MOF) have been performed. − MOFs are inorganic–organic hybrid materials with potential voids . Within the last few years, several studies with a photoactive molecule being non-covalently attached into the porous framework have been published. − These so-called switch@MOF systems show fascinating functionalities, which vary from solid-state photoswitching, − solvatochromism, enantioselectivity switching, selective gas-uptake and release, and even conduction . Recently, Heinke and co-workers have exploited an azobenzene-functionalized MOF as an electronic nose .…”