Synthesis of pyrenocrown ethers as fluorescent sensors and their recognition ability of metal ions

Novel pyrenocrown ethers having different ring sizes were synthesized, and change of fluorescence spectra was investigated upon addition of metal ions. By the addition of Li+ and Na+ ions to 10(-2) M CH3CN solutions of pyreno-15-crown-5 ether (3), excimer/monomer ratio decreased with 3-4 nm longer wavelength shift. Upon addition of Mg2+ and Ba2+ ions to the solution of 3, excimer emission increased with 11-25 nm longer wavelength shift. On the other hand, when these metal ions were added to pyreno-18-crown-6 ether (4), the excimer/monomer ratio monotonically decreased. Addition of Pb2+ ion to solutions of 3 and 4 caused dramatic decrease of both monomer and excimer fluorescence intensity. Inspection of these results indicates that 3 forms 1:1 and 2:1 complexes with respective monovalent and divalent metal ions, whereas 4 forms 1:1 complexes with both monovalent and divalent metal ions. The 1:1 complexes of 3 with monovalent and divalent metal ions emit respective excimer and monomer fluorescence, whereas the 2:1 complexes of 3 emit excimer fluorescence. Monotonical decrease of fluorescence intensity by the addition Pb2+ is attributed to heavy atom effect