Question

A chemist has synthesized two new dyes based on the molecular structure of plant-based dyes. The lowest energy absorption line for the first dye is light in the visible region at 530 nm. The lowest energy absorption line for the second dye is light in the visible region at 645 nm. Based on this evidence, which molecule has the larger HOMO-LUMO gap?

1. The dye that absorbs at 530 nm
2. There is not enough information given to predict
3. The gap is the same, because they both absorb in visible region
4. The dye that absorbs at 645 nm

Answer 1

1. The dye that absorbs at 530 nm

Step-by-step explanation:

With a larger HOMO-LUMO gap, there's also a higher absorption energy, so this means that the dye with the higher absortion energy has the larger HOMO-LUMO gap.

The relationship between energy and wavelenght can be expressed by the formula E = hc/λ, this means that the lower the wavelenght, the higher the energy is. So the dye that absorbs at a lower wavelenght has a larger HOMO-LUMO gap.