title: Ultrafast deactivation of bilirubin: dark intermediates and two-photon isomerization.
abstract: Bilirubin is a neurotoxic product responsible for neonatal jaundice, which is generally treated by phototherapy. The photoreaction involves ultrafast internal conversion via an elusive intermediate and Z-E isomerization with minor yield (less than 3% in solution). The structure of the intermediate remains unclear. Here, the combination of UV-vis and mid-IR ultrafast transient absorption spectroscopy reports a comprehensive picture of the mechanism and provides essential structural information about the intermediate species. Thus, spectral dynamics during the earliest ps unveils a wavepacket travelling from the Franck-Condon region to the crossing point with a dark state. The latter shows a tighter molecular skeleton than the ground state and decays with 15 ps time constant. Remarkably, the relative contribution of a non-decaying component increases linearly with pump energy, suggesting that Z-E isomerization could also be triggered by two-photon excitation. Implications for the photochemistry of protein-bound open tetrapyrroles are discussed.
authors.affiliation: Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS) and Department of Physical Chemistry, Universidade de Santiago de Compostela, C/Jenaro de la Fuente s/n, E-15782 Santiago de Compostela, Spain. luis.lustres@usc.es.
authors.forename: Carlos
authors.initials: C
authors.lastname: Carreira-Blanco
authors.affiliation: Fachbereich Physik, Technische Universität Kaiserslautern, Erwin Schrödinger Straße, Building 46, D-67663 Kaiserslautern, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Singer
authors.affiliation: Fachbereich Physik, Technische Universität Kaiserslautern, Erwin Schrödinger Straße, Building 46, D-67663 Kaiserslautern, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Diller
authors.affiliation: Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS) and Department of Physical Chemistry, Universidade de Santiago de Compostela, C/Jenaro de la Fuente s/n, E-15782 Santiago de Compostela, Spain. luis.lustres@usc.es.
authors.forename: J
authors.initials: J
authors.lastname: Luis Pérez Lustres
mesh_terms: D001663:Bilirubin / Q000737:chemistry*; D007536:Isomerism; D017785:Photons; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001663:Bilirubin