title: 4-(8-quinolyl)amino-7-nitro-2,1,3-benzoxadiazole as a new selective and sensitive fluorescent and colorimetric pH probe with dual-responsive ranges in aqueous solutions.
abstract: Fluorescent and colorimetric pH probe possess many advantages including rapid response time, nondestructive testing, and excellent pH sensitivity. However, they usually cannot be utilized simultaneously in both acidic and basic pH ranges. In this study, a new selective and sensitive fluorescent and colorimetric pH probe, 4-(8-quinolyl)amino-7-nitro-2,1,3-benzoxadiazole (1), was designated and synthesized. The optical probe exhibited dual-responsive pH ranges to both acidic and basic aqueous solutions. When the solution pH was gradually increased from 8.5 to 13.3, the absorption spectra of 1 showed an obvious hyperchromicity, accompanied with a red shift of the absorption band at 340 nm, a blue shift of the absorption band at 482 nm, and a distinct color change from orange to violet pink to yellow. Within the pH range from 2.2 to 0.2, the fluorescent spectra of 1 showed a "turn-on" response signal to solution pH. In order to understand the response mechanism of the probe to solution pH, the probe molecule was split into two parts, 8-aminoquinoline (2) and 4-amino-7- nitro-benzofurazan (3). UV-vis absorption and fluorescent experiments of 2 and 3 indicated that both are sensitive optical pH probes. Furthermore, the NMR experiment of 1 was explored in basic and acidic conditions. The results indicated that the colorimetric responses of 1 to pH under basic condition should be attributed to the deprotonation of the imino group on the quinolyl ring, and the fluorescent recognition of 1 to pH under acidic condition was probably due to the protonation of the nitrogen atoms from the benzofurazan and quinolyl rings.
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Xutian
authors.initials: X
authors.lastname: Li
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Haipeng
authors.initials: H
authors.lastname: Liang
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Zhaowei
authors.initials: Z
authors.lastname: Huang
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Tang
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Chen
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Liting
authors.initials: L
authors.lastname: Yang
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China; Guangzhou Key Laboratory of Materials for Energy Conversion and Storage, PR China. Electronic address: mlj898021@aliyun.com.
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Ma
authors.affiliation: School of Chemistry and Environment, South China Normal University, Shipai, Guangzhou 510631, PR China.
authors.forename: Yuhai
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Technology Development Center for Polymer Processing Engineering of Guangdong Colleges and Universities, Guangdong Industry Technical College, Guangzhou 510300, PR China.
authors.forename: Baiping
authors.initials: B
authors.lastname: Xu
mesh_terms: D000143:Acids / Q000737:chemistry; D000468:Alkalies / Q000737:chemistry; D003124:Colorimetry / Q000379:methods*; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015335:Molecular Probes / Q000138:chemical synthesis / Q000737:chemistry*; D055620:Optical Phenomena; D010069:Oxadiazoles / Q000138:chemical synthesis / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry*
chemical_list: D000143:Acids; D000468:Alkalies; D005456:Fluorescent Dyes; D015335:Molecular Probes; D010069:Oxadiazoles; D012996:Solutions; D014867:Water
keywords: 2,1,3-Benzoxadiazole; Aminoquinoline; Colorimetric pH probe; Dual-responsive range; Fluorescent pH probe