Photophysical studies of anion-induced colorimetric response and amplified fluorescence quenching in dipyrrolylquinoxaline-containing conjugated polymers

The dipyrrolylquinoxaline (DPQ)-containing monomer and polymers were synthesized and employed as chromogenic and fluorescent chemosensors for inorganic anions. We have found that in the presence of fluoride or pyrophosphate, the receptors do not form hydrogen bonds between the pyrrole protons and anions. The colorimetric responses and fluorescence quenching in these chemosensors are indeed the result of deprotonation of the N-H proton. The anion selectivity is primarily determined by the relative basicity of anions. The sensitivity of DPQ-based chemosensor was found to display a 34-fold enhancement by incorporation into the conjugated polymer. The anion-induced deprotonation generates low-energy, non-fluorescent trapping sites and is responsible for the signal amplification where the quenching of the excited state occurs from the deprotonated DPQ site in the network by rapid exciton migration along the polymeric backbone.