Synthesis of Luminescent Platinum(II) 2,6-Bis(N-dodecylbenzimidazol-2′-yl)pyridine Foldamers and Their Supramolecular Assembly and Metallogel Formation

Abstract

Dinuclear alkynylplatinum(II) metallofoldamers with an oligomeric m-phenyleneethynylene backbone have been designed with the incorporation of a sterically undemanding, π-conjugated, and hydrophobic 2,6-bis(N-dodecylbenzimidazol-2'-yl)pyridine pincer ligand. The complex with the optimal chain length has been found to exhibit gelation behavior via stabilization by noncovalent Pt···Pt and π-π stacking interactions in the hierarchical architecture constructed from the single-turn helix. The chain lengths of the complexes have been found to be a critical determinant for their gelation behavior, conformations, and morphologies. Such a gelation process has been found to undergo a cooperative assembly mechanism according to the nucleation-elongation model. Their self-assembly via the Pt···Pt and π-π stacking interactions has been studied by 1H NMR, 2D ROESY NMR (ROESY = rotating-frame Overhauser spectroscopy), electronic absorption, and emission spectroscopy, and density functional theory calculations have provided further insights into the folded state geometry of this class of metallofoldamers.