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

Dinuclear alkynylplatinum(II) metallofoldamers with an oligomeric m-phenyleneethynylene backbone have been designed with the incorporation of a sterically undemanding, p-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 center dot center dot center dot Pt and pi-pi 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 center dot center dot center dot Pt and pi-pi stacking interactions has been studied by H-1 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.