Synthesis and optoelectronic properties of 2,6-bis(2-anilinoethynyl)pyridine scaffolds

Abstract

A series of sixteen bisphenylureas based on a 2,6-bis(2-anilinoethynyl)pyridine scaffold have been synthesized for use as potential anion sensors. Prior work with one of these receptors revealed a distinct fluorescence response in the presence of a suitable anion source with specificity towards chloride anion. This study demonstrates that the fluorescent properties of these receptors can be tuned through the systematic variation of the pendant functional groups.

“Off-on” aggregation-based fluorescent sensor for the detection of chloride in water

“…S N Ar reaction of 3 with 2-dimethylaminoethanol and potassium carbonate produces 1 in 67% yield. Previous results with similar pyridine receptors 18–20 demonstrated a positive fluorescent response to chloride and other anions upon the protonation of the host. The addition of more than two equivalents of trifluoroacetic acid (TFA) in acetonitrile provides the final water-soluble chloride sensor, denoted here as “ 1 + ” (the plus sign symbolizes only the protonated state of the receptor, not the charge of the receptor complex).…”

Ion and Molecular Recognition Using Aryl–Ethynyl Scaffolding

“…For example, in our studies, changing the appended groups alters the electron density within an anion sensor and thus the nature of the fluorescent response from different anionic guests (see below). [25, 26] …”

Synthesis and solid-state structures of a macrocyclic receptor based on the 2,6-bis(2-anilinoethynyl)pyridine scaffold

“…17–22 Interestingly, phenylurea derivatives substituted with electron-withdrawing groups (e.g., 1a , Fig. 2) displayed an “off-on” response in the presence of chloride, which typically quenches fluorescence.…”

“…Counterintuitively, higher yields of 4 were obtained by first protonating 3 with anhydrous HCl followed by the addition of phosgene (as a solution in toluene), presumably due to slower reaction kinetics and reduced oligomerization. Unstable 4 was concentrated under reduced pressure to remove excess phosgene and HCl and subsequently reacted with previously reported 2,6-bis(2-anilinoethynyl)pyridine core 5 17,22 to afford the desired macrocycle 1c in low yield.…”

“…What is still unclear is why electron-withdrawn phenyl ureas display an “off-on” response in the presence of chloride. 19,22 One would presume that quenching to some degree would be observed and investigation into this behaviour is ongoing.…”