Self-Darkening SunglassesSelf-Darkening Sunglasses

A Reversible Chemical ReactionA Reversible Chemical Reaction

Glasses that darken in sunlight andGlasses that darken in sunlight andbecome clear in ordinary room light become clear in ordinary room light

Example of a ReversibleExample of a ReversibleChemical ReactionChemical 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

Napthopyran MoleculeNapthopyran MoleculeColorless FormColorless Form

Absorbs only Ultraviolet Light, not Visible Light Absorbs only Ultraviolet Light, not Visible Light

Weak Bond

Napthopyran MoleculeNapthopyran MoleculeEffect of UV LightEffect of UV Light

UltravioletUltravioletLightLight

UV Light Breaks the Weak BondUV Light Breaks the Weak Bondand Electrons Shift Positionsand Electrons Shift Positions

Napthopyran MoleculeNapthopyran MoleculeDark Colored FormDark Colored Form

Molecule changes shape afterMolecule changes shape afternew bonds are formednew bonds are formed

New molecule form absorbsNew molecule form absorbslong wavelength visible lightlong wavelength visible light

Reversible Photochromic ReactionReversible Photochromic Reactionof Napthopyranof Napthopyran

SunlightSunlight

No SunlightNo Sunlight

ColorlessColorlessFormForm

Dark ColoredDark ColoredFormForm