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

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 Mn values of polymers 1 and 2 were 5200 and 8100, and Mw 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 Zn2+ until an equimolar amount and then increased upon the addition of an excess amount of Zn2+, which enabled the detection of Zn2+ over a wider concentration range (10−6–10−4 M) than those of the previously reported Zn2+ sensors. The PL intensity upon the addition of excess Zn2+ was greater in polymer‐2 than in polymer‐1 because the Zn2+‐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+, Cu2+, and Zn2+ was analyzed using the Stern–Volmer and Benesi–Hildebrand methods. Zn2+ sensor