Anthraquinone (AQ) has been long identified as a highly promising lead structure for various applications in organic electronics. Considering the enormous number of possible substitution patterns of the AQ lead...

In functional materials, the understanding of the interactions between the individual components is essential for further development. One example for such materials are guest@host systems, with a metal−organic framework (MOF) as the host matrix. These porous compounds consist of metal nodes and organic linker molecules and are therefore inorganic−organic hybrid materials. Combining MOFs with photoswitchable dyes such as spiropyrans (SPs) resulted in new functional materials with fascinating properties. To obtain such materials with technologically relevant properties, knowledge of the individual adjusting screws to modulate, for example, the optical response is obligatory to further push material's design. Within this work, we systematically studied the optical properties of a nitro-substituted SP inside an MIL-68(In) series as a function of linker substitution. In particular, 1,3,3-trimethylindolino-6′-nitrobenzopyrylospiran ( SP-Nitro) was non-covalently attached into the pores of MIL-68(In) with the terephthalate linker molecule being functionalized either with a Br-, NH 2 -, or a NO 2group. Three different hybrid systems were obtained, exhibiting both photochromic and solvatochromic response. The observed optical characteristics were found to strongly depend on the substitution pattern of the linker molecule. Based on the resulting structural and dielectric properties of the substituted terephthalic acid molecules calculated at B3LYP and MP2 levels, the observed UV/vis reflectance spectra were directly correlated with the out-of-plane rotation of the carboxyl group in the vicinity of the respective substituent.

Electrochemical capture of carbon dioxide (CO 2 ) using organic quinones is a promising and intensively studied alternative to the industrially established scrubbing processes. While recent studies focused only on the influence of substituents having a simple mesomeric or nucleophilicity effect, we have systematically selected six anthraquinone (AQ) derivatives (X-AQ) with amino and hydroxy substituents in order to thoroughly study the influence thereof on the properties of electrochemical CO 2 capture. Experimental data from cyclic voltammetry (CV) and UV–Vis spectroelectrochemistry of solutions in acetonitrile were analyzed and compared with innovative density functional tight binding computational results. Our experimental and theoretical results provide a coherent explanation of the influence of CO 2 on the CV data in terms of weak and strong binding nomenclature of the dianions. In addition to this terminology, we have identified the dihydroxy substituted AQ as a new class of molecules forming rather unstable [X-AQ-(CO 2 ) n ] 2– adducts. In contrast to the commonly used dianion consideration, the results presented herein reveal opposite trends in stability for the X-AQ-CO 2 •– radical species for the first time. To the best of our knowledge, this study presents theoretically calculated UV–Vis spectra for the various CO 2 -AQ reduction products for the first time, enabling a detailed decomposition of the spectroelectrochemical data. Thus, this work provides an extension of the existing classification with proof of the existence of X-AQ-CO 2 species, which will be the basis of future studies focusing on improved materials for electrochemical CO 2 capture.