Figures index

From

Optical and Raman Experiments for the Electro-organic Synthesis of Bromothymol Blue and Bromophenol Blue

Achim Habekost

World Journal of Chemical Education. 2025, 13(1), 19-29 doi:10.12691/wjce-13-1-4
  • Figure 1. Reaction scheme of the bromination of thymol blue (left) to bromthymol blue (right)
  • Figure 2. Change of the light intensity at pH=6. A: thymol blue, B: bromothymol blue
  • Figure 3. Top: Thin-film transmission quartz cell with Pt grid as working electrode, Ag/AgCl as reference electrode and Pt as counter electrode. Bottom: Experimental set-up for absorptovoltammetry. From left to right: Potentiostat with connection to the electrodes and trigger cable for triggering the fibre spectrometer, light source (halogen and deuterium light), quartz cell in the cell holder, fibre spectrometer. Fibre connection via two fibres: Light source - cell - fibre spectrometer.
  • Figure 4. Change in the light intensity of thymol blue / bromide as a function of the applied potential from 0.95 V to 1.3 V.
  • Figure 5. Absorptovoltammogram of thymol blue / bromide. Solid line: linear sweep voltammogram (LSV), dashed line: light intensity at 610 nm - 650 nm. Insert: LSV and derived light intensity
  • Figure 6. SERS set-up. From left to right: Raman spectrometer with 785 nm laser, Raman probe with Raman cell. Inside the Raman cell: SPE with connection to potentiostat (right). The potentiostat triggers the Raman spectrometer
  • Figure 7. SERS of thymol blue between 0 and -0.6 V. Insert: Potential-dependent intensity of the transition at 1321 cm-1
  • Figure 8. SERS bromothymol blue between 0 V and -0.6 V. Insert: Potential-dependent intensity of the transition at 1056 cm-1
  • Figure 9. Raman spectra of thymol blue (solid line) and bromothymol blue (dashed line)
  • Figure 10. Extract from the Raman spectra of thymol blue (red), bromothymol blue (blue) and the electrochemically brominated thymol blue (blue, dashed)
  • Figure 11. Linear-sweep voltammetry of phenol red / bromide for different working electrodes: solid line: C-CNT-SPE, dashed line: Au-SPE, dotted line: Pt-SPE
  • Figure 12. Change in the absorption of phenol red / bromide as a function of the applied potential between 0.7 V and 1 V for different working electrodes. Top: Pt, center: Au, bottomt: C-CNT
  • Figure 13. Absorption spectra after 10-60 s electrolysis of thymol blue at 2 V. Red dotted line after 10 s, black dashed line after 60 s. The other curves after 20, 30, 40 and 50 s. The arrows indicate the changes
  • Figure 14. Solid line: Raman spectrum of bromothymol blue, dotted line: after 60 s electrolysis. Bold arrow: C-Br Raman vibration, thin arrow: newly formed Raman transitions