Lab 4: Chemiluminescence

Luminol

• When luminol is oxidized (by sodium hypochlorite or hydrogen peroxide), it transitions to an excited state. The energy released as electrons return to their ground state results in the emission of blue light.

• The concentration of luminol directly influences the intensity and duration of the emitted light. Higher concentrations typically lead to brighter luminescence.

Sodium Hydroxide (NaOH)

• strong base

• By increasing the pH of the solution, sodium hydroxide facilitates the removal of labile hydrogen atoms from luminol, resulting in a negatively charged nitrogen atom.

• This negative charge allows for effective interaction with carbonyl groups, crucial for the subsequent oxidation reaction that leads to luminescence.

• The basic conditions enhance the overall reaction kinetics, promoting faster electron transitions and thus affecting the brightness and duration of the light emitted.

Sodium Hypochlorite- Bleach

• oxidizing agent

• oxidize luminol, leading to the formation of excited-state intermediates that emit light.

• The efficiency of sodium hypochlorite in oxidizing luminol determines the intensity and duration of the emitted light. If the oxidizing agent is too weak or used in insufficient quantity, the luminescence will be diminished.

Potassium Ferricyanide

• A catalyst that can accelerate reactions.

• The presence of this metal complex not only increased the reaction rate but also affected the color of the emitted light. The interaction between luminol and ferricyanide produced a more complex emission spectrum, resulting in a blend of blue and green light that transitioned to yellow when fluorescein was added.

Hydrogen Peroxide (H₂O₂)

• Another oxidizing agent that can promote luminescence.

• When hydrogen peroxide is mixed with luminol and sodium hydroxide, it can generate a reaction similar to that with sodium hypochlorite.

• However, in the absence of a catalyst, the reaction is slower and may not produce noticeable luminescence initially. This was observed in Experiment 3, where minimal light was detected without the presence of a catalyst (like iron in blood).

• When blood (containing hemoglobin) was introduced, hydrogen peroxide acted in concert with the iron to accelerate the reaction and produce a strong luminescent glow.

Fluorescein

• A dye added to change the color of emitted light.

• In Experiment 2, fluorescein was used to alter the visual outcome of the reaction by adding a green hue to the emitted light.

• The interaction between fluorescein and the blue light emitted by luminol resulted in a yellowish color due to the mixing of different wavelengths. This demonstrates how additional compounds can affect the perceived color of luminescence and emphasizes the complex interplay of light emissions in chemiluminescent reactions.

Key findings

• The role of sodium hydroxide in forming a negatively charged nitrogen atom, facilitating the reaction with carbonyl groups in luminol.

• The impact of temperature on reaction rates, where higher temperatures lead to increased luminescence duration.

• The influence of potassium ferricyanide as a catalyst, which altered both the reaction speed and the wavelengths of emitted light.