Related Experiment Video
Updated: Aug 15, 2026

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
A computational study of the excited states of bilirubin IX
Giovanni Granucci1, Marina Mazzoni, Maurizio Persico
1Dipartimento di Chimica e Chimica Industriale, Università di Pisa, v. Risorgimento 35, I-56126, Pisa, Italy.
Abstract:
We have determined the lowest excited states of bilirubin IX by TD-DFT calculations. The lowest pair of excited states, S(1) and S(2), turn out to be of charge-transfer (CT) nature. Although DFT based methods tend to underestimate the energy of CT states, the small oscillator strengths we have computed indicate that such states may actually exist in this spectral region, but would have escaped spectroscopic detection. The next pair of excited states, S(3) and S(4), account for the most prominent spectral feature of bilirubin. They can be accurately described by the exciton coupling model, as we show by a thorough analysis of wavefunctions and properties. This finding therefore supports the interpretation of bilirubin photoisomerization behaviour, based on the exciton coupling model.
Related Concept Videos
Jaundice
UV–Vis Spectroscopy: Molecular Electronic Transitions
Deactivation Processes: Jablonski Diagram
Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation
UV–Vis Spectroscopy of Conjugated Systems
One of the factors influencing λmax is the extent of conjugation in the...
¹H NMR: Complex Splitting
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
