Synthesis, characterization, and preliminary fluorescence study of a mixed-ligand bis(dicarbollyl)nickel complex bearing a tryptophan-BODIPY FRET couple

•Design of a bichromophoric nickelacarborane for the conformational assignment of the nickelacarborane core by fluorescence spectroscopy.•Multistep synthesis and characterization of Ni(III) and Ni(IV) nickelacarboranes bearing tryptophan/BODIPY FRET couple.•Possible energy transfer through the nickelacarborane core revealed during the preliminary fluorescence study.

In continuation of our work on nickelacarborane-based nanomolecular devices, the design and synthesis of a bis(dicarbollyl)nickel complex, in both formal Ni(III) and Ni(IV) oxidation states, bearing two fluorophore molecules capable of fluorescence resonance energy transfer (FRET) was performed. The FRET couple with a small Förster radius (R0 of 26 Å) consisted of tryptophan and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY). Each fluorophore was connected to the nickelacarborane core by a rigid linker containing two pairs of alternating ethynyl and para-phenylene groups, which created a specific distance (l) between the fluorophore molecules depending on the conformation of the nickelacarborane core. The presence (13 Å < l < 39 Å) or absence (l > 39 Å) of energy transfer in the designed system provides insight into the conformational changes of nickelacarboranes in solution. The target nickelacarboranes were prepared via a multistep organic/organometallic synthesis. The structures and compositions of the intermediates and final products were established by a combination of spectroscopic methods and X-ray structure analysis. A preliminary fluorescence study of the prepared nickelacarboranes was performed.

Graphical abstractThe design and synthesis of bis(dicarbollyl)nickel complexes bearing two fluorophore molecules capable of fluorescence resonance energy transfer was performed. The FRET couple with R0 of approximately 26 Å consisted of tryptophan and BODIPY. The target compounds were prepared via a multistep organic/organometallic synthesis and their fluorescence spectra were studied.Figure optionsDownload full-size imageDownload as PowerPoint slide