Steric group enforced aromatic cyclic trimer conformer in tripodal molecules

Abstract

A family of tripodal molecules (1-6) with/without steric ethyl groups at the central benzene scaffold and with furan/thiophene/pyridyl group at the 2-position of the benzimidazolyl unit was synthesised. Compounds 1-6 were characterized by elemental analysis and NMR spectroscopy. Compounds 1, 3, and 5 were further characterized by single crystal X-ray diffraction analysis. The molecular structures of 1 and 4 were optimized using density functional theory (DFT) calculations. X-ray and < sup > 1 < /sup > H NMR studies reveal that the introduction of three ethyl groups into a central benzene scaffold of furan/thiophene/pyridyl substituted benzimidazolyl based tripodal molecules enhances the edge-to-face C-H⋯π interactions, thereby favouring the aromatic cyclic trimer motif, in solution and the solid state. The unsubstituted central benzene scaffold allows the furan/thiophene substituted benzimidazolyl units in the tripodal molecules to move freely thereby weakening the edge-to-face C-H⋯π interactions between the aromatic cyclic trimer motif. Molecular modelling calculations indicate that the energy minimized structures of the tripodal molecules adopt a symmetric cyclic aromatic motif conformation.