Highly optically responsive divalent benzimidazolium-based axles as self-reporting pseudorotaxanes

Mono and (bis)benzimidazoliums were evaluated both experimentally and computationally for their potential as building blocks of pseudopolyrotaxane axles. Their aggregation and optical behavior, along with their potential to form a [2]pseudorotaxane with dibenzyl-24-crown-8, was studied through the synergistic application of 1D/2D and diffusion ordered NMR spectroscopy, mass spectrometry, ultraviolet-visible & fluorescence spectroscopy, and time-dependent density functional theory. Their unique optical behaviour was measured and modeled as a function of protonation state, solvent, and concentration. The axles show strong solvochromaticism and a very pronounced concentration-dependent optical profile, including self-quenching when a pseudorotaxane is formed. This axle with multiple recognition sites, has the potential to form pseudorotaxanes with tunable optical behavior