Synthesis of the quinoxaline-phosphine oxide small molecules (QPSMs)
4-bromo-2,1,3-benzothiadiazole (9.3 mmol) was dissolved in ethanol, then NaBH4 (172 mmol) was added, and the reaction mixture was stirred for overnight at room temperature.
After extraction with diethyl ether, the solvent was removed and dissolved again in acetic acid/ethanol solution with the corresponding α-diketone (11 mmol) to further react at 110oC for overnight. The product was purified by column chromatography on a silica gel using DCM/hexane as eluent.
The final quinoxaline-phosphine oxide small molecule were synthesized by the Suzuki coupling reaction. The previous synthesized molecules (1 mmol) and diphenyl(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)phosphine oxide (1 mmol) were dissolved in toluene and reacted at 90oC for 48 h under N2 atmosphere with addition of Pd(PPh3)4 (5 mol%) and 2M K2CO3. The synthesized small molecules were purified by column chromatography on a silica gel using EA/hexane as eluent.
Figure. 1(a) Chemical structures of QPSMs. (b) Synthetic routes for QPSMs. (c) The optimized geometry, dipole moments, electron density plot from DFT calculation. (d) TGA thermograms, (e) Solid state UV-vis and PL spectra, (f) CV curves, (g) and energy diagrams of QPSMs.
Characterization
1H and 13C nuclear magnetic resonance (NMR) spectra were measured using a JEOL JNM ECP-400 spectrometer. UV-visible absorption spectra were recorded on a Lambda 365 spectrophotometer. Photoluminescence (PL) spectra were measure using LS 55 fluorescence spectrometer. Gas Chromatography/Mass Spectrometer (GC/MS) was analyzed by using Agilent 7890GC/5975C MSD. Thermogravimetric Analysis (TGA) was measured using Q500 instrument. X-ray diffractometry (XRD) was carried out using X’Pert3-Powder (PANalytical). Cyclic voltammetry (CV) measurements were carried out by using a Versa STAT3 (AMETEK, Inc.) with tetrabutylammonium hexafluorophosphate (0.1M, Bu4NPF6) as the electrolyte in anhydrous acetonitrile. For CV measurements, a glassy carbon electrode coated with the polymer and a platinum wire were used as the working and counter electrode, respectively. A silver wire was used as a pseudo-reference electrode with a ferrocene (Fc)/ferrocenium(Fc+) external standard.