Chirality Remote Control in Nanoporous Materials by Circularly Polarized Light

Journal of the American Chemical Society, vol. 143, pp. 7059–7068

Abstract

The ability to dynamically control chirality remains a grand challenge in chemistry. Although many molecules possess chiral isomers, lacking their isolation, for instance during photoisomerization, results in racemic mixtures with suppressed enantiospecific chiral properties. Here, we present a nanoporous solid in which chirality and enantioselective enrichment is induced by circularly polarized light (CPL). The material is based on photoswitchable fluorinated azobenzenes attached to the scaffold of a crystalline metal–organic framework (MOF). The azobenzene undergoes trans -to- cis -photoisomerization upon irradiation with green light and reverts back to trans upon violet light. While each moiety in cis conformation is chiral, we show the trans isomer also possesses a nonplanar, chiral conformation. During photoisomerization with unpolarized light, no enantiomeric enrichment is observed and both isomers, R - and S - cis as well as R- and S - trans, respectively, are formed in identical quantities. In contrast, CPL causes chiral photoresolution, resulting in an optically active material. Right-CPL selectively excites R - cis and R - trans enantiomers, producing a MOF with enriched S -enantiomers, and vice versa . The induction of optical activity is reversible and only depends on the light-handedness. As shown by first-principle DFT calculations, while both, trans and cis, are stabilized in nonplanar, chiral conformations in the MOF, the trans isomer adopts a planar, achiral form in solution, as verified experimentally. This shows that the chiral photoresolution is enabled by the linker reticulation in the MOF. Our study demonstrates the induction of chirality and optical activity in solid materials by CPL and opens new opportunities for chiral resolution and information storage with CPL.

Authors 9

1. Anemar Bruno Kanj

   Karlsruhe Institute of Technology

   Affiliation as printed

   Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

2. Jochen Bürck

   Karlsruhe Institute of Technology

   Affiliation as printed

   Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

3. Nina Vankova

   Technische Universität Dresden

   Affiliation as printed

   Fakultät für Chemie und Lebensmittelchemie, TU Dresden, Bergstraße 66c, 01062 Dresden, Germany

4. Chun Li

   Karlsruhe Institute of Technology

   Affiliation as printed

   Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

5. Dragos Mutruc

   Humboldt-Universität zu Berlin

   Affiliation as printed

   Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany

6. Abhinav Chandresh

   Karlsruhe Institute of Technology

   Affiliation as printed

   Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

7. Stefan Hecht Aachen DWI - Leibniz Institute for Interactive Materials Institute of Technical and Macromolecular Chemistry

   Humboldt-Universität zu Berlin · DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI-Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, 52074 Aachen, Germany

   Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany

   Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Worringer Weg 2, 52074 Aachen, Germany

8. Thomas Heine

   Helmholtz-Zentrum Dresden-Rossendorf · Technische Universität Dresden

   Affiliation as printed

   Fakultät für Chemie und Lebensmittelchemie, TU Dresden, Bergstraße 66c, 01062 Dresden, Germany

   Forschungsstelle Leipzig, Helmholtz-Zentrum Dresden-Rossendorf, Permoserstraße 15, 04318 Leipzig, Germany

9. Lars Heinke corresponding

   Karlsruhe Institute of Technology

   Affiliation as printed

   Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany