Colour is usually due to the presence of chemical compounds that interact with light (can be due to scattering/refraction etc.). The colouring of rocks is often due to transition metals.

\(\beta\)-Carotene is a carotenoid, and gives an orange colour

• •

  Present in leaves of all plants

• •

  Absorb solar energy, which is the transferred to chlorophyll

• •

  Light reflected lacks a certain wavelength

• •

  Carotenoids absorb visible light

• •

  Due to the presence of a conjugated system

  • –

    Long chain of alternate single and double bonds

  • –

    Pi orbitals overlap

  • –

    Delocalisation spreads over whole chain

  • –

    Reduces energy gap between ground and excited state to visible range