title: A computational study of the excited states of bilirubin IX.
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.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, v. Risorgimento 35, I-56126, Pisa, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Granucci
authors.forename: Marina
authors.initials: M
authors.lastname: Mazzoni
authors.forename: Maurizio
authors.initials: M
authors.lastname: Persico
authors.forename: Alessandro
authors.initials: A
authors.lastname: Toniolo
mesh_terms: D001663:Bilirubin / Q000737:chemistry*; D003198:Computer Simulation; D015394:Molecular Structure; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D001663:Bilirubin