Multi-stimuli responsive fluorescence switching behaviours of AIE polymers for acid-base vapour sensing and highly sensitive ferric ion detection

Novel aggregation-induced emission (AIE) polymers, i.e., P1-SP and P2-SP , consisting of AIEgenic tetraphenylethylene (TPE) and photochromic spiropyran (SP) units are reported. Both P1-SP and P2-SP exhibit excellent AIE behaviours of TPE moieties in near-aqueous solutions THF/H 2 O (95% water) and solid states with strong cyan and blue emissions at 494 and 477 nm, respectively. Upon acidification, the close forms of P1-SP and P2-SP can be opened and switched to open P1-MCH + and P2-MCH + structures of protonated merocyanine (MCH + ), resulting in fluorescence quenching of TPE units through corresponding intramolecular charge transfer (ICT) and Förster resonance energy transfer (FRET) processes. The fluorescence recovery of TPE can be monitored by the neutralization of P1-MCH + and P2-MCH + with base solutions under ambient/visible light attributed to the re-close P1-SP and P2-SP structures, which led to respective turn-off ICT and FRET phenomena. Distinct fluorescence quenching behaviours of P1-SP and P2-SP can be observed under various stimuli, including acid conditions and ferric ion interactions, which are also confirmed by theoretical studies. Moreover, P1-SP and P2-SP can be utilized as fluorescence quenching sensors for nanomolar level detections of ferric ion (LOD = 166 and 110 nM for corresponding P1-SP and P2-SP ) with excellent selectivities in near-aqueous solutions and paper test strips. Additionally, the interesting visible and fluorescence colour changes of coated cellulosic papers, blended PMMA films and powder forms based on P1-SP and P2-SP under multi-external stimuli (acid-base vapour and visible light/heating processes) are also explored in this report. • Novel aggregation-induced emission (AIE) polymers based on tetraphenylethylene (TPE) and spiropyran (SP) for fluorescence sensors were fabricated. • Multi-stimuli responsive fluorescence switching behaviours of AIE polymers were investigated under external stimuli (various water contents and acid/base treatments). • Highly sensitive and excellent selective Fe 3+ detection in near-aqueous media and test strips were achieved based on fluorescence quenching mechanisms via intramolecular charge transfer (ICT) and Förster resonance energy transfer (FRET) processes. • Interesting visible and emission colour changes of AIE polymers in solid states were also explored under multi-external stimuli.