Synthesis, acid-base responsive fluorescence, and ion-selectivity of novel π-conjugated polymers containing coumarin unit in the main chain

Abstract

A two-step synthetic method for four dibromocoumarin monomers (3,7-dibromo-4-methylcoumarin, 3, 6-dibromo-4-methylcoumarin, 3,7-dibromocoumarin, and 3,6-dibromocoumarin) containing von Pechmann reaction for the formation of coumarin ring followed by regioselective bromination at C3 position at monobrominated coumarins was developed. A series of novel coumarin-fluorene π-conjugated copolymers was synthesized by Sonogashira coupling reaction. The polymers exhibited absorption maxima at longer wavelength due to π-π* transition of the main chain, which indicates the expansion of π-conjugated system along the polymer main chain. The polymers showed acid-base responsive fluorescence due to the lactone ring opening-closing property in the main chain accompanied by the addition of alkali and acid. The polymers also exhibited ion selectivity between Na+ and K+ ion.