Final answer:
Aromatic side chains, due to their conjugated π systems, absorb light with lower energy and have excited states closer to the ground state compared to peptide bonds.
Step-by-step explanation:
To determine which absorber exhibits an electronic excited state closer to the ground state, we consider the relative energies of the absorbed electromagnetic radiation. Molecules absorb radiation with wavelengths corresponding to the energy difference (∆E) between their ground and excited states.
A smaller energy difference indicates a closer proximity to the ground state. Aromatic side chains tend to have delocalized electrons due to their conjugated π systems, leading to smaller energy gaps between the ground and excited states compared to peptide bonds.
Therefore, aromatic side chains absorb light with lower energy (longer wavelength) and have excited states closer to the ground state because the electrons require less energy to be excited.
Based on the information provided and molecular spectroscopy principles, the correct answer is B. An aromatic side chain; the absorbed photon energy is lower.
This is because the energy levels of aromatic side chains are more tightly spaced due to the delocalization of electrons, allowing for light absorption at longer wavelengths (lower energy) than the more localized electrons in peptide bonds.