1. Self-Darkening Sunglasses
A Reversible Chemical Reaction

2. Glasses that darken in sunlight and
become clear in ordinary room light

3. Example of a Reversible Chemical Reaction
Self-darkening sunglasses use a reversible chemical reaction called “photochromic”
Photochromic is derived from photo, meaning light, and chromic meaning color
- a change in color with light

4. Napthopyran Molecule Colorless Form Weak Bond
Absorbs only Ultraviolet Light, not Visible Light

5. UV Light Breaks the Weak Bond and Electrons Shift Positions
Napthopyran Molecule
Effect of UV Light
Ultraviolet
Light
UV Light Breaks the Weak Bond
and Electrons Shift Positions

6. Napthopyran Molecule Dark Colored Form Molecule changes shape after
new bonds are formed
New molecule form absorbs
long wavelength visible light

7. Reversible Photochromic Reaction
of Napthopyran
Sunlight
Colorless
Form
Dark Colored
Form
No Sunlight