Pyridyl CO₂ Fixation Enabled by a Secondary Hydrogen Bonding Coordination Sphere

Reversible CO₂ binders under ambient conditions are of significant interest for multiple applications in sensing and capture technologies. In this paper, a general systematic way to evaluate CO₂ receptors with π-systems is put forward. A series of receptors (five pyridine-based and one triazine-based) are evaluated as CO₂ binders in terms of number of hydrogen bonding sites, strength of hydrogen bond donors, and number of nucleophilic sites. The binding of CO₂ to the receptors was probed by computational models, absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and ¹H NMR studies. Multiple solvents with varying ionic strength additives are probed to analyze the effects on CO₂-bound intermediates. The receptors were screened progressively down-selecting through the different analytical techniques arriving at a promising pyridine receptor, which shows evidence of CO₂ binding with each of the analytical techniques. The diaminopyridine motif demonstrates reversible CO₂ binding and has convenient substitution sites for derivatization to incorporate into functional sensor systems.