Initial Photochemistry of Bilirubin Probed by Femtosecond Spectroscopy

Abstract

Bilirubin is a breakdown product from heme catabolism, and reduced excretion of bilirubin can lead to jaundice. Phototherapy is the most common treatment for neonatal jaundice, a condition frequently encountered in newborn infants. Knowledge of the photochemistry of bilirubin, which is dominated by (ultra)fast components, is necessary for the profound understanding of the processes in phototherapy. Here, we report results from femtosecond fluorescence upconversion measurements on bilirubin and half-bilirubin model compounds, as well as pump-probe absorption measurements on bilirubin. A fast component of ca. 120 fs in the multiexponential fluorescence decay, being only visible in the bilirubin molecule, is interpreted as exciton localization within the molecular halves. The slower components of several hundreds of femtoseconds and a few picoseconds, occurring in bilirubin and the half-bilirubin model, are interpreted as relaxation to a (twisted) intermediate, which decays further with ca. 15 ps to the ground state.

Ultrafast deactivation of bilirubin: dark intermediates and two-photon isomerization

“…The mechanism is found to be consecutive: the shortlived Franck-Condon state forms a weakly fluorescent intermediate which decays to the ground state with a 15 ps time constant. In contrast to previous proposals, [16][17][18] the intermediate shows stronger CQC bonds than the ground electronic state, indicating that the molecular structure is not twisted.…”

“…Upon optical excitation, BR deactivates rapidly by internal conversion with almost negligible quantum yields for all other possible deactivation routes at room temperature. 11,12,16 fs spectroscopy [16][17][18] revealed that the deactivation process extends from the 100 fs to the 50 ps time-scales and could be facilitated by a conical intersection in Scheme 1 Three-dimensional structure of bilirubin IXa (left). Dipoledipole coupling (V ) of the localized endo and exo S 1 states explains the lowest bright states of bilirubin (right).…”

“…the neighbourhood of the Franck-Condon region. 19 The observation was explained by consecutive mechanisms 16,18 invoking a ''partially twisted'' structure from a dark excited state. The latter could be localized in a single dipyrridone moiety, 18 have charge transfer character, 20 or result from pp*-np* mixing, 16 but experimental evidence is still lacking.…”

Isomerization and Aggregation of the Solar Cell Dye D149

“…Twisting of double bonds in the excited state is a very well-known mechanism for fast deactivation, with great relevance in biological processes, such as light detection by retinal in the visual protein rhodopsin 24 or phototherapy of neonatal jaundice. 25 Many of the observed reactions happen on a very fast time-scale, hundreds of femtoseconds to a few picoseconds. In the case of stilbene, for example, a barrierless excited state reaction is observed with time constants of ca.…”

Enhanced photocatalytic performance of molecularly imprinted hydroxyapatite thin film for bilirubin degradation

“…However, it has been suggested that it is toxic when the amount of BR in the body exceeds the binding capacity of albumin, extra free BR binds and deposits to various tissues. Its deposition and accumulation in tissues will cause disorders in the metabolism of BR and induce various diseases . Hydroxyapatite (HAP) (Ca 10 (PO 4 ) 6 (OH) 2 ), a main constituent of bones and teeth, has been used for purification and separation of biological molecules owing to its excellent biocompatibility, slow biodegradation, good mechanical stability, great adsorption and photocatalysis property .…”