Energetic and electronic properties of bilirubin photoisomerization products using density functional theory

Document Type : Original Article

Authors

• Maryam Taheri ¹
• Mohammad Taghi Baei ²

¹ Biology Department, Shahrood Branch, Islamic Azad University, Shahrood, Iran

² Department of Chemistry, Azadshahr Branch, Islamic Azad University, Azadshahr, Golestan, Iran

Abstract

The thermodynamic stability and the electronic structures of bilirubin isomers along the photoisomerization process have been studied using the density functional theory and time-dependent density functional theory in aqueous solvent medium. The stability of 4Z,15Z isomer in comparison with other isomers is due to the presence of six intramolecular hydrogen bonds. The most stable bilirubin isomer has the lowest and the most unstable isomer has the highest electron–hole pair binding energy in the S1 excited state. The maximum absorption band for all studied isomers are related to the HOMO→LUMO and HOMO→LUMO+1 electron transfers due to the π→π* charge transfer while the weak peak of UV-Vis spectrum is related to the n→π* charge transfer. The main absorption wavelength in the bilirubin isomers around 400 nm for blue-purple light and its complementary color is yellow-orange.

Keywords

• Photoisomerization
• Bilirubin
• Density Functional Theory
• Time-Dependent Density Functional Theory
• Density of state plot
• UV-Vis spectrum

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