Fluoride-induced intermolecular excimer formation of bispyrenyl thioureas linked by polyethylene glycol chains

Article abstract of DOI:10.1016/j.tet.2011.08.060

New bispyrenyl thioureas linked by polyethylene glycol (PEG) chains, L1-L3, and methoxy benzene pyrene thiourea, L4, were synthesized. Upon binding with F^- in CHCl₃, L1-L3 exhibited strong excimer emission bands (I_E) and weak monomer emission bands (I_M), while L4 displayed the same intensity of both bands. However, little or no change was observed in fluorescence spectra of L1 upon adding OH^-, AcO ^-, BzO^-, H₂PO₄^-, Cl ^-, Br^-, and I^-. Therefore, only F^- induced the pyrene excimer formation. Job's plots showed 1/1 or 2/2 complexation of L1 with F^-. Ratios of I_E/I_M of L1·F^- complex were dependent on the concentration of L1, implying that the dimerization of L1 proceeded via the intermolecular excimer formation. Among L1-L4, L1 possessed the highest binding constant and sensitivity toward F^- implying the importance of the linking PEG chain. L1 was demonstrated to be an excellent probe for F^- in CHCl₃ with the detection limit as low as 46.2 μg/L.