Figures index

From

Fascinating school experiments with fluorescent dyes

Matthias Ducci

World Journal of Chemical Education. 2023, 11(3), 74-79 doi:10.12691/wjce-11-3-9
  • Figure 1. The bleeding chestnut branch: Starting from the cut surface of a chestnut branch dipped in ethanol, blue fluorescent streaks of aesculin appear under UV light (λ = 365 nm). (Photograph: Ducci)
  • Figure 2. Left: The rolled rim vial contains an ethanolic eosin Y solution. If a freshly cut chestnut branch is placed in the solution (middle), the solution fluoresces white within a few minutes (right). (Photographs: Ducci)
  • Figure 3. Scheme of additive colour mixing with the primary colours red, green and blue. The background symbolises the colour perception black (no light).
  • Figure 4. Structural formulae of the fluorescent dyes used.
  • Figure 5. Demonstration of additive colour mixing with fluorescent solutions. In the Erlenmeyer flasks, the solutions fluoresce in the three primary colours. The rolled rim vials contain the mixtures. (Photograph: Ducci)
  • Figure 6. The ammonia fountain experiment with the fluorescent indicator phloxine B (left), quinine and eosin Y (middle) as well as sodium 4-aminonaphthalene-1-sulfonate and phloxine B (right). (Photographs: Ducci)
  • Figure 7. The structural formulae of phloxine B in an acidic (left) and alkaline environment (right). In the alkaline range an aqueous solution of this dye fluoresces orange, whereas in the acidic range the fluorescence is quenched.
  • Figure 8. Structural formula of quinine (left, ) and of sodium 4-aminonaphthalene-1-sulfonate (right).
  • Figure 9. Aqueous sodium 4-aminonaphthalene-1-sulfonate solution as invisible UV ink (left: in daylight, right: under UV light (λ = 365 nm)). (Photographs: Ducci)
  • Figure 10. Reductive cleavage of azorubine in Powerade Wild Cherry using a fabric colour remover containing sodium dithionite. Left: Powerade Wild Cherry, middle: after addition of the colour remover, right: the bottle from the middle under UV light. (Photographs: Ducci)
  • Figure 11. Reaction equation for the reductive cleavage of azorubine with sodium dithionite.
  • Figure 12. The colour solution of a yellow highlighter (top left) containing pyranine fluoresces intensely green under UV light (top right). It can be made invisible by hydrochloric acid (bottom left). Under UV light, the invisible writing fluoresces intensely blue (bottom right). (Photographs: Ducci)
  • Figure 13. The indicator effect of pyranine is based on the reversible deprotonation of the hydroxy group.
  • Figure 14. Ammonia gas sweeping from right to left over a writing made of acid pyranine solution, which is invisible in daylight. (Photograph: Ducci)
  • Figure 15. The alginate beads loaded with fluorescent indicators exhibit a different fluorescent behaviour in the acidic (left), neutral (middle) and alkaline (right) solution. The photograph was taken shortly before the fluorescence in the left vial completely extinguished. (Photograph: Ducci)
  • Figure 16. 2-Naphthol and 5-ASA are fluorescent indicators.