Four cyclometalated iridium(III) complex-based chemosensors for turn-on response to thiourea in fruit juice and their application in test strips

Excessive thiourea(TU) was demonstrated to be harmful to both environmental system and human body, so it is essential to create selective and sensitive sensors to detect TU. Herein, Four iridium(III) complexes, [(fppy)2Ir(PD)]PF6 (Ir-fppy, fppy = 2-(4-fluorophenyl)pyridine), [(fpiq)2Ir(PD)]PF6 (Ir-fpiq, fpiq = 1-(4-fluorophenyl)isoquinoline), [(dfppy)2Ir(PD)]PF6 (Ir-dfppy, dfppy = 2-(3,5-difluorophenyl)pyridine) and [(dfpiq)2Ir(PD)]PF6 (Ir-dfpiq, dfpiq = 1-(3,5-difluorophenyl)isoquinoline) bearing 1,10-phenanthroline-5,6-dione (PD) as ancillary ligands, were designed and synthesized, and employed as efficient chemosensors to identify thiourea. These iridium(III) complexes exhibited emission peaks between 541 nm and 583 nm with PLQY ranging from 0.12 to 0.26 and lifetime in the range of 2.65–2.74 μs. All the four iridium(III) complexes showed significant turn-on response to TU with low limit of detect on the order of 10−8 M. Furthermore, these iridium(III) complexes-based chemosensors exhibited excellent recoveries toward TU in various juice samples including orange, kiwi fruit and lemon juice. Four complexes-composite test strips showed marker color change after adding TU.