A cross-shaped organic framework: a multi-functional template arranging chromophores†

This work explores the use of a cross-shaped organic framework that is used as a template for the investigation of multi-functionalized chromophores. We report the design and synthesis of a universal cross-shaped building block bearing two bromines and two iodines on its peripheral positions. The template can be synthesized on a gram scale in a five-step reaction comprising an oxidative homo-coupling macro-cyclization. The formed scaffold was selectively functionalized via Suzuki cross-coupling reactions with methoxynaphthalene, naphthalimide and BODIPY derivatives, yielding a library of cross-shaped and chromophore-decorated model compounds, all of which were fully characterized. The formed racemic bis- and tetra-substituted crosses were resolved via chiral stationary phase HPLC, and assignment of the enantiomers was done via comparison of experimental and simulated electronic circular dichroism spectra as well as enantiomer single-crystal analysis. Additionally, the hybrid naphthalimide/BODIPY chromophore was found to be acting as an intramolecular Förster energy resonance transfer pair, which was investigated in more detail. With this easy-to-functionalize universal building block, we believe it might prove to be useful in the study of different sets of chromophores.