Synthesis And Properties Study Of Fluorescence Chemical Sensors With Sequential Recognition Function

Substantial progress has been made in the synthesis of fluorescent sensors for sequential detection of two ions under the same conditions.Notably,the interference from other quenchers in the system can be effectively eliminated,making it more specific for ion detection.In this study,five new fluorescent sensors were designed and synthesized by modifying the parent structure,introducing different recognition groups and adjusting the number of coordination sites and the size of coordination space.Their optical performance and ion detection properties were characterized by ultraviolet-visible spectrophotometry and fluorescence spectrophotometry.The main contents of this study are as follows:?1?Fluorescent sensor 2-?8-??8-methoxyquinolin-2-yl?methoxy?quinolin-2-yl?benzo[d]thiazole?DQT?was synthesized from 2-benzo[d]thiazoline-8-hydroxyquinoline.Its structure was characterized by NMR,ESI-HR-MS and single crystal analysis,and then structural optimization and energy calculations were performed using density functional theory?DFT?.In the CH₃OH/HEPES?9:1,v/v,pH=7.30?buffer system,the sensor DQT showed a fluorescence quenching response toward Ag⁺and Cd²⁺with a detection limit of 0.42?M and0.26?M and a coordination ratio of 1:1,respectively.The complex DQT-Cd²⁺can be used for sequential recognition of S^2-in a pH range of 4-8.?2?The sensor?2E,4E,6E?-2,4,6-tris???4-?5,5-difluoro-1,3,7,9-tetramethyl-5H-4?⁴,5?⁴-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-10-yl?phenyl?amino?methylene?cyclohexane-1,3,5-trione?ML?was synthesized from BODIPY fluorescent chromophore,and its structure was characterized by NMR and ESI-HR-MS.The sensor ML consisted of three recognition sites for sequential recognition of Cu²⁺and HSO₃^-in the CH₃OH/H₂O?99:1,v/v?buffer system.It showed an obvious“on-off”fluorescence quenching response toward Cu²⁺with a detection limit of 0.36?M and a coordination ratio of 1:3.The complex ML-Cu²⁺showed an enhanced“off-on”fluorescence response toward HSO₃^-with a detection limit of 1.4?M.The sensor ML was applicable in the pH range of 4-8.?3?The sensor?E?-2-??2-?benzo[d]thiazol-2-yl?quinolin-8-yl?oxy?-N'-??7-?diethylamino?-2-oxo-2H-chromen-3-yl?methylene?acetohydrazide?TQC?was synthesized from coumarin and 2-benzo[d]thiazolyl-8-hydroxy-quinoline.Its structure was characterized by NMR and ESI-HR-MS,and then structural optimization and energy calculations were performed using DFT.In the DMSO/HEPES?3:2,v/v,pH=7.4?buffer system,the sensor TQC showed an“on-off-on”fluorescence response toward Cu²⁺and PPi and its performance remained stable after 6 cycles.It showed a significant fluorescence quenching response to Cu²⁺with a detection limit of 0.06?M and a coordination ratio of 1:1.The complex TQC-Cu²⁺showed a fluorescence enhancement response to PPi with a detection limit of 0.01?M and a coordination ratio of 2:1.This sensor was applicable in the pH range of 3-8.Notably,the sensor TQC could be used for qualitative detection of Cu²⁺and PPi not only on the test strip,but also in HeLa cells.?4?A novel“off-on-off”fluorescent sensor?E?-N'-?3-?benzo[d]thiazol-2-yl?-2-hydroxy-5-methylbenzylidene?-7-?diethylamino?-2-oxo-2H-chromene-3-carbohydrazide?CHS?was synthesized based on benzothiazole and 7-diethylaminocoumarin-3-carbohydrazide.Its structure was characterized by NMR and ESI-HR-MS,and then structural optimization and energy calculations were performed using DFT.In the DMSO/HEPES?4:1,v/v,pH=7.4?buffer system,sensor CHS could sequentially detect Al³⁺and PPi and its performance remained stable after 4 cycles.At pH=4-8,it showed a fluorescence enhancement response to Al³⁺,and a stable complex CHS-Al³⁺was formed with a 1:1 coordination.This complex showed a fluorescence quenching response to PPi.The detection limit was 0.16?M and 0.18?M,respectively.The sensor CHS could be used for detection of Al³⁺and PPi in HeLa cells.?5?A novel“on-off-on”fluorescent sensor?E?-N'-??7-?diethylamino?-2-oxo-2H-chromen-3-yl?methylene?-6-??quinolin-8-yloxy?methyl?picolinohydrazide?PQC?was synth-esized based on quinoline and 7-?diethylamino?coumarin-3-carbaldehyde.Its structure was characterized by NMR and ESI-HR-MS,and then structural optimization and energy calculations were performed using DFT.In the CH₃OH/HEPES?9:1,v/v,pH=7.23?buffer system,sensor PQC formed a stable complex with Cu²⁺with a detection limit of 0.17?M and a coordination ratio of 1:1 and showed an obvious fluorescence quenching response.The complex PQC-Cu²⁺showed a fluorescence enhancement response to GSH with a detection limit of 0.20?M and a recovery rate of over 80%,and it was applicable in the pH range of6-10.The sensor PQC could be used for test strips and biological imaging in living cells.