Divalent Benzimidazolium-Based Axles for Self-Reporting Pseudorotaxanes

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 and fluorescence spectroscopy, and time-dependent density functional theory. Their photophysical behavior 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.