Structural effects of bispyrenyl ureas linked by polyethylene glycol and ethyne spacers towoed anion binding abilities

Abstract

Anion sensors possessing bispyrenyl derivatives have been designed and synthesized. Compound L1 containing amide groups for binding anions and benzyl ring as spacer was synthesized in 41% yield. Compound L2 containing thiourea groups as anion binding sites and polyethyleneglycol chains linked with benzyl ring as spacer was synthesized in 51% yield. Compound L3 containing urea as anion binding sites and ethyne as spacer could not be synthesized. Therefore, we have studied the anion abilities of L1 and L2 using fluorescence spectrophotometry. Compound L1 did not interact with any anions as suggested by an insignificant change of the emission spectra. Emission spectra of compound L2 changed from monomer band (410 nm) to excimer band (515 nm) upon addition of anions. The order of intensity ratio between excimer and monomer bands (IE/IM) in L2 varied as F- > OH- >> AcO- > BzO- > H2PO4- > Cl- > Br-≈ I-. Due to a smaller size and more basicity of F-, it could form H-bonding interactions with protons of N-H thiourea of L2. A large amount of F- and OH- induced the deprotonation of N-H thiourea while AcO- formed H-bonding interactions only. Complexation of L2 and F- occurred via intermolecular pyrene stacking while that of L2 and AcO- as well as OH- occurred via intramolecular pyrene stacking.