What an Excited Molecule Does Next: Fluorescence and Phosphorescence · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

What excited molecules do next

Science · Chemistry · ages 19-21
Name ______________________   Date ____________

  1. Why does fluorescence glow at longer wavelength than the driving light?

    • The molecule absorbs twice before emitting
    • Some energy drains as heat before emission
    • The lamp changes colour inside the sample

  2. Which steps of the Jablonski diagram trade photons?

    • Internal conversion and vibrational relaxation
    • Absorption, fluorescence and phosphorescence
    • Crossing to the triplet only

  3. Internal conversion and crossing to the triplet emit photons.

    Circle one:   True   False

  4. Which of two dyes fluoresces more strongly?

    • The floppy, twisting one with broken conjugation
    • The rigid, flat, conjugated one
    • Both glow exactly equally

  5. A dye glows weakly in warm solvent but brightly when frozen in a film. Why?

    • Freezing creates new electrons in the dye
    • Cold light is always brighter than warm light
    • Free rotation opens heat paths, and freezing blocks them

  6. Why is phosphorescence slow?

    • The triplet to singlet step flips spin, which photons forbid
    • Triplet molecules move very slowly
    • Phosphorescence uses heavier photons

  7. A student labels crossing to the triplet as a glowing step. What is the error?

    • Crossing emits the brightest light of all
    • Crossing is a silent heat step with no photon
    • Labels never matter in diagrams

  8. A heavy atom is built into a glowing molecule. What changes, and why?

    • Fluorescence stops because heavy atoms absorb all light
    • Nothing changes, mass never matters
    • Phosphorescence speeds up because spin orbit coupling loosens the spin ban
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Answer key

For grown-ups. Fold this page away before handing over the rest.

What excited molecules do next W1-mt_5AVF6uWed_-s1

  1. Some energy drains as heat before emission · The outgoing photon carries less than the pumping put in.
  2. Absorption, fluorescence and phosphorescence · Those three arrows absorb or emit light. The rest leak heat silently.
  3. False · Both are silent heat steps with no photon.
  4. The rigid, flat, conjugated one · Stiffness blocks heat loss and conjugation favours photons.
  5. Free rotation opens heat paths, and freezing blocks them · Blocking silent routes hands victory to emission.
  6. The triplet to singlet step flips spin, which photons forbid · The spin ban forces the molecule to wait.
  7. Crossing is a silent heat step with no photon · Only absorption, fluorescence and phosphorescence trade photons.
  8. Phosphorescence speeds up because spin orbit coupling loosens the spin ban · Stronger coupling opens the blocked door a little wider.
Worksheet · LightMySky