Abstract:
2, 5-Dibromo-
o-pheneylenedimanine was obtained by the reduction of 4, 7-dibromo-2, 1, 3-benzothiadiazole, and four monoquinoxaline type monomers (M1, M2, M3, M4) were prepared by the reaction of 2, 5-dibromo-
o-pheneylenedimanine with 5, 6-dione-1, 10-phenanthroline, phenanthrenequinone, acenaphthenequinone and benzyl, respectively. Using palladium diacetate (Pd(CH
3COO)
2) and ligand tricyclohexylphosphine as catalyst, four donor-acceptor-donor (D-A-D) type polymers (P1, P2, P3, P4) were prepared by Suzuki coupling alternative copolymerization of 2, 7-bis(4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolan-2-yl)-9, 9-dioctylfluorene (M5) with four monoquinoxaline type monomers, respectively. All monomers and polymers were characterized by FT-IR and
1H-NMR spectra. The optical properties of polymers solution in CHCl
3, at neutral state and when different concentrations of trifluoracetic acid (TFA) was added to the solution, were investigated by UV-Vis and fluorescence spectrometer. The UV-Vis spectra results showed that four D-A-D type polymers had good sensitivity to low concentration of TFA, wherein polymer P1 was sensitive to 2.17×10
-7 mol/L of TFA and polymers P2-P4 were sensitive to 4.32×10
-3 mol/L of TFA. Polymer P1 had better sensitivity to low concentration of TFA than P2-P4, due to the existence of two pyridine rings in quinoxaline unit of polymer P1. The colors of polymers CHCl
3 solution changed significantly after acidified by TFA, a red shift of absorption bands (UV-Vis spectra of polymers P1-P3) followed, and new wide absorption bands on the UV-Vis spectra of P2-P4 appeared. The fluorescence spectra of P1-P4 solution in CHCl
3 were remarkably sensitive to low concentration of TFA, wherein P1 solution (11.0 μg/L) was sensitive to 7.0×10
-10 mol/L of TFA and P2-P4 (32.0, 28.0, 10.0 μg/L) solution were sensitive to 1.73×10
-6, 7.5×10
-7 mol/L and 4.0×10
-6 mol/L of TFA, respectively. The fluorescence spectra intensity of all four polymers decreased to very small value when corresponding concentration of TFA was added to the polymer solution.