Highly Twisted Fenestrindane-Based Porous Nanographenes

Two fenestrindane-based porous nanographenes containing four polyaromatic macrocycles in a highly twisted, basically S₄-symmetric conformation were synthesized and characterized by NMR spectroscopy and mass spectrometry. Stepwise π-extension at the periphery of the fenestrindane core by a sequence of eightfold Suzuki-Miyaura cross-coupling, fourfold Scholl cyclodehydrogenation and another eightfold Suzuki-Miyaura reaction affords the porous nanographene precursors in good yields. In the last step, fourfold intramolecular Yamamoto coupling generates the porous nanographenes in 17-18 %-yield. Their optical and electronic properties were studied by UV/Vis and fluorescence spectroscopy and cyclic voltammetry. DFT calculations revealed structural details of the macrocycles. The surprisingly weak binding of these porous structures with chloride ions (K≈10 M^-1) is attributed to their highly twisted conformation. The title compounds represent the first porous nanographenes based on the [5.5.5.5]fenestrane motif and, at the same time, they consist of a fenestrane-like polyarylene network.