Divalent benzimidazolium-based axles for self-reporting pseudorotaxanes

Abstract

Mono and (bis)benzimidazoliums were evaluated both experimentally and computationally for their potential as pseudopolyrotaxane axle building blocks. Their aggregation and photophysical 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 photophysical 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.