Unravelling the Spectroscopic Signatures of Thienoviologen Cyclophanes: A Computational Approach for Water Pollutant Recognition

Water pollution has emerged as a cause for serious concern, with aromatic compounds posing a great threat to marine life and human health. Under these circumstances, detecting and isolating these water pollutants remains a major scientific challenge. Although there are enormous reports on molecular recognition through UV-visible and fluorescence spectroscopy, the scarcity of reports with infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy is intriguing. Herein, we have presented the thienoviologen-based cyclophane as a potential host in recognizing benzenediols and polyaromatic hydrocarbons, with conventional IR and NMR spectroscopic techniques, after confirming the stability of the complexes in water. Integrating classical molecular dynamics simulations and quantum mechanical calculations with the hybrid quantum mechanics/molecular mechanics approach, we unveiled the structure and energetics of the host-guest complexes and their spectroscopic signatures at the molecular level. As the outcome, we found a significant blue shift as high as ~23 cm^-1 in the anthracene complex for the stretching frequency of the C-H bond of the methylene group of the host, while the catechol complex shows 2.3 ppm downfield chemical shift in ¹³C NMR spectra. We hope this work will assist researchers in strategically using the spectroscopic signatures from IR and NMR spectra for molecular recognition.