Structural effects on the electronic absorption properties of 5,6-dihydroxyindole oligomers: the potential of an integrated experimental and DFT approach to model eumelanin optical properties

Photochemistry and Photobiology
Marco d'IschiaVincenzo Barone

Abstract

Elucidation of the relationships between structural features and UV-visible absorption properties of 5,6-dihydroxyindole oligomers is an essential step towards an understanding of the unique optical properties of eumelanins. Herein, we report the first combined experimental and density functional theory (DFT) investigation of the 5,6-dihydroxyindole oligomers so far isolated. 2,2'-Biindolyl 2 and the 2,4'-biindolyl 3 absorb at longer wavelengths relative to 2,7'-biindolyl 4 and their spectra were well predicted by DFT analysis. The absorption bands of 2,4':2',4''- and 2,4':2',7''-triindolyls 5 and 6 also fall at different wavelengths and can be interpreted by DFT simulations as being due to a combination of two main separate transitions. Tetramer 7, in which two 2,4'-biindolyl units are linked through a 2,3'-connection, exhibits a broad chromophore extending over the entire UV range without well defined absorption maxima. Within the dimer-tetramer range examined, three key points emerge: (1) an increase in oligomer chain length does not result in any regular and predictable bathochromic shift; (2) a marked broadening of the absorption bands occurs when going from the monomer to the tetramer structure; and (3) the mode of coupli...Continue Reading

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Citations

Dec 2, 2009·Photochemistry and Photobiology·Dana N Peles, John D Simon
Apr 10, 2008·Pigment Cell & Melanoma Research·John D Simon, Małgorzata Rózanowska
Jul 11, 2012·Nanoscale Research Letters·Guido MulaAlessandro Pezzella
Nov 1, 2012·Journal of Biological Inorganic Chemistry : JBIC : a Publication of the Society of Biological Inorganic Chemistry·Emanuele FerrariLuigi Casella
Jun 2, 2017·The Journal of Physical Chemistry. B·Paulami Ghosh, Debashree Ghosh
Oct 24, 2014·Accounts of Chemical Research·Marco d'IschiaMarkus J Buehler
Mar 19, 2009·Angewandte Chemie·Marco d'IschiaTadeusz Sarna
Jul 30, 2017·International Journal of Molecular Sciences·Elisa PinnaGuido Mula
Apr 14, 2015·Journal of Materials Chemistry. B, Materials for Biology and Medicine·Giuseppe VitielloGiuseppina Luciani
Jun 15, 2018·International Journal of Molecular Sciences·Lucia PanzellaKenzo Koike
Sep 27, 2008·The Journal of Physical Chemistry. B·John D SimonDana N Peles
Oct 23, 2008·The Journal of Organic Chemistry·Hung A DuongChristina L L Chai
Jul 16, 2014·The Journal of Physical Chemistry. B·Louise H FornanderBengt Nordén

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