A novel AIEE pillar[5]arene-based conjugated oligomer as paraquat fluorescence turn-off sensor

A novel linear conjugated oligomer (Co-P[5]TPE) based on pillar[5]arene derivative as recognition group and tetraphenylethylene (TPE) unit as fluorophore was designed and synthesized. The Co-P[5]TPE showed aggregation-induced emission enhancement (AIEE) effect in the mixture of dimethyl sulfoxide (DMSO) and water, reaching the maximum fluorescence intensity while the fraction of water was 30%. In the DMSO/H2O solution (VDMSO/Vwater = 7/3), the oligomer sensor displayed “turn-off” fluorescence response (1–I/I0 = 98.7%) towards paraquat (PQ) over other competitive guests. The detection limit (LOD) was 1.54 × 10−8 M and the Stern-Volmer constant (KSV) was determined as 2.144 × 104 M−1 calculating via fluorescent titration experiments. Therefore, the Co-P[5]TPE has highly selective, sensitive and anti-interference properties for sensing PQ. Moreover, the recognition mechanism was specifically investigated through transmission electron microscopy (TEM), dynamic light scattering (DLS) and theoretical calculations involving frontier orbitals (HOMO and LUMO), electrostatic potential (ESP), and the noncovalent interaction (NCI). The cooperation of host-guest chemistry and photoinduced electron transfer (PET) can achieve fluorescence quenching of the chemosensor Co-P[5]TPE for PQ. In addition, the sensor can be used for PQ detection in practical sample.