Fluorescence turn‐off and turn‐on sensors of Zn²⁺ based on π‐conjugated poly(aryleneethynylene)s comprising alloxazine‐6,9‐diyl and 2,7‐diethynylene‐9,9‐dialkylfluorene units

Abstract

π-Conjugated poly(aryleneethynylene)s, polymer-1 comprising alloxazine-6,9-diyl and 2,7-diethynylene-9,9-dihexylfluorene units and polymer-2 comprising alloxazine-6,9-diyl and 2,7-diethynylene-9,9-bis(hexaethylene glycol monomethyl ether)fluorene units, were synthesized via Pd-complex-catalyzed condensation reactions. The M n values of polymers 1 and 2 were 5200 and 8100, and M w values were 24,900 and 69,700, respectively. The onset wavelengths of the polymers were longer wavelength than that of the monomer in the UV-vis spectra, confirming the π-conjugated system along the polymer chain. The photoluminescence (PL) of the polymers decreased with the addition of Zn 2+ until an equimolar amount and then increased upon the addition of an excess amount of Zn 2+ , which enabled the detection of Zn 2+ over a wider concentration range (10 À6 -10 À4 M) than those of the previously reported Zn 2+ sensors.The PL intensity upon the addition of excess Zn 2+ was greater in polymer-2 than in polymer-1 because the Zn 2+ -alloxazine complex in polymer-2 was stabilized by its interaction with the oligoether side chain. The difference in the PL response of the polymers to metal ions such as Cu + , Cu 2+ , and Zn 2+ was analyzed using the Stern-Volmer and Benesi-Hildebrand methods.