title: Design and Synthesis of Photodissociable Ligands Based on Azoimidazoles for Light-Driven Coordination-Induced Spin State Switching in Homogeneous Solution.
abstract: Light-switchable azoimidazoles were rationally designed and synthesized, and their performance was investigated as photodissociable ligands (PDL) and for spin state switching of Ni porphyrins. The rationally designed ligands exhibit a high photochemical conversion rate (trans → cis > 98%) and no measurable fatigue over a large number of switching cycles at room temperature under air. As compared to the known phenylazopyridines, the phenylazoimidazoles exhibit a much stronger affinity as axial ligands to Ni porphyrin in the binding trans configuration and a low affinity in their cis form. This affinity switching was used to control the coordination number of Ni(2+). Concomitant with the change in coordination number is the change of the spin state from triplet (high spin) to singlet state (low spin). We report on phenylazoimidazole-based PDLs that switch the paramagnetic ratio of the investigated nickel species by up to 70%. Consequently, azoimidazoles exhibit considerably higher switching efficiencies than previously described pyridine-based PDLs.
authors.affiliation: Otto Diels-Institute for Organic Chemistry, University of Kiel , Otto-Hahn-Platz 4, Kiel D-24119, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schütt
authors.affiliation: Otto Diels-Institute for Organic Chemistry, University of Kiel , Otto-Hahn-Platz 4, Kiel D-24119, Germany.
authors.forename: Gernot
authors.initials: G
authors.lastname: Heitmann
authors.affiliation: Otto Diels-Institute for Organic Chemistry, University of Kiel , Otto-Hahn-Platz 4, Kiel D-24119, Germany.
authors.forename: Thore
authors.initials: T
authors.lastname: Wendler
authors.affiliation: Otto Diels-Institute for Organic Chemistry, University of Kiel , Otto-Hahn-Platz 4, Kiel D-24119, Germany.
authors.forename: Bahne
authors.initials: B
authors.lastname: Krahwinkel
authors.affiliation: Otto Diels-Institute for Organic Chemistry, University of Kiel , Otto-Hahn-Platz 4, Kiel D-24119, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Herges