Elucidation of the relations 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, the authors report the first combined exptl. and d. functional theory (DFT) study 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 anal. 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 sep. 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 examd., 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 coupling of the indole units is a crucial, hitherto unrecognized, structural parameter affecting the electronic absorption properties of 5,6-dihydroxyindole oligomers. Use of exptl. characterized oligomeric scaffolds as a basis for DFT calcns. is a most promising approach to building reliable structural models for studies of eumelanins optical properties.

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 / D'Ischia, Marco; Crescenzi, Orlando; Pezzella, Alessandro; M., Arzillo; Panzella, Lucia; Napolitano, Alessandra; V., Barone. - In: PHOTOCHEMISTRY AND PHOTOBIOLOGY. - ISSN 0031-8655. - STAMPA. - 84:3(2008), pp. 600-607. [10.1111/j.1751-1097.2007.00249.x]

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

D'ISCHIA, MARCO;CRESCENZI, ORLANDO;PEZZELLA, ALESSANDRO;PANZELLA, LUCIA;NAPOLITANO, ALESSANDRA;
2008

Abstract

Elucidation of the relations 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, the authors report the first combined exptl. and d. functional theory (DFT) study 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 anal. 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 sep. 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 examd., 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 coupling of the indole units is a crucial, hitherto unrecognized, structural parameter affecting the electronic absorption properties of 5,6-dihydroxyindole oligomers. Use of exptl. characterized oligomeric scaffolds as a basis for DFT calcns. is a most promising approach to building reliable structural models for studies of eumelanins optical properties.
2008
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 / D'Ischia, Marco; Crescenzi, Orlando; Pezzella, Alessandro; M., Arzillo; Panzella, Lucia; Napolitano, Alessandra; V., Barone. - In: PHOTOCHEMISTRY AND PHOTOBIOLOGY. - ISSN 0031-8655. - STAMPA. - 84:3(2008), pp. 600-607. [10.1111/j.1751-1097.2007.00249.x]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/205141
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