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

Abstract

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.