2D hyperbranched conjugated polymer for detecting TNT with excellent exciton migration

• Published in: Sensors and actuators. B, Chemical Chemical, 2017-01, Vol.238, p.48-57
• Main Authors: Ma, Xiao-Shuang, Cui, Yue-Zhi, Ding, Yun-Qiao, Tao, Fu-Rong, Zheng, Bing, Yu, Run-Hui, Huang, Wen
• Format: Article
• Language: English
• Subjects: Addition polymerization; Conjugated polymers; Detection; Electron transfer; Exciton migration; Excitons; Fluorescence; Hyperbranched; Migration; Molecular orbitals; Polymers; Quenching; Sensors; TNT; Trinitrotoluene
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2016.07.025

Compared with linear conjugated polymers, 2D hyperbranched conjugated polymers afford multi-dimensional transport pathways for exciton migration, meaning that an exciton formed on one chromophore of the hyperbranched conjugated polymer can be quenched by an analyte interacting with a second chromophore. In addition, the electrons can transfer rapidly from the LUMO (lowest unoccupied molecular orbital) of hyperbranched conjugated polymers to that of TNT. This gives rise to the potential for sensing response amplification and the superior performance of hyperbranched conjugated polymers. [Display omitted] •The 2D hyperbranched conjugated polymer P2 was synthesized and used as a sensor for detecting TNT.•Thermal stability, solubility, sensitivity and thermodynamic driving force of the hyperbranched conjugated polymer were improved.•The quenching speed of P2 positively correlates with the rate of electron transfer.•Hyperbranched conjugated polymers afford multi-dimensional transport pathways for exciton migration.•Quantum-chemical calculations were performed to study the binding mode of sensors and TNT. Efficient migration of excitons in conjugated polymers is important for sensor devices. In this study, we make use of pyridine and styrene as the sensing units to design the two-dimensional hyperbranched conjugated polymer P2 (poly(2,3,5,6-styrylpyrazine)s) and the one-dimensional linear conjugated polymer P1 (poly(2,5-styrylpyrazine)s) along with their two corresponding model compounds (M1, M2) to study the orbital energies of LUMO (the lowest unoccupied molecular orbital) and HOMO (the highest occupied molecular orbital). Interestingly, comparing with the Stern-Volmer constants (Ksv) of P1 (Ksv=2.49×104M−1), P2 shows excellent sensibility (Ksv=6.84×104M−1) in the presence of TNT (2,4,6-trinitrotoluene), indicating that super quenching effect may get involved in P2. The superior fluorescent quenching performance of P2 could be explained by the following theories: (i) hyperbranched conjugated polymers afford multi-dimensional transport pathways for excitons to migrate; (ii) The LUMO of P2 is closer to that of TNT molecules; (iii) Quenching speed is positively correlated with the rate of electron transfer. In addition, the fluorescence lifetimes of the polymers are almost constant as the TNT concentration increased, indicating that the sensing mechanism could be static quenching.