A chemist has synthesized two new dyes based on the molecular structure of plant-based dyes. The lowest energy absorption line for one dye is light in the visible region at 530 nm, the lowest energy absorption line for the other dye is light in the visible region at 645 nm. Based on this evidence, which molecule has the higher 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.

Question

Chemistry

Annika Compton

26 October, 15:59

A chemist has synthesized two new dyes based on the molecular structure of plant-based dyes. The lowest energy absorption line for one dye is light in the visible region at 530 nm, the lowest energy absorption line for the other dye is light in the visible region at 645 nm. Based on this evidence, which molecule has the higher 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.

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Porter Cruz · Answer 1

1. The dye that absorbs at 530 nm.

Explanation:

The dye will absorb light to promote the transition of an electron from the HOMO to the LUMO orbital.

The higher the gap, the higher the energy of transition. The energy can be calculated by E = hc/λ, in which h and c are constants and λ is the wavelength.

The equation shows that the higher the energy, the higher the gap and the lower the wavelength.

Therefore, the dye with absorption at 530 nm has the higher HOMO-LUMO gap.