Enhancement of Light Absorption Ability of Synthetic Chlorophyll Derivatives by Conjugation with a Difluoroboron Diketonate Group. Issue 29 (15th June 2016)

• Record Type: Journal Article
• Authors: Kinoshita, Yusuke; Kitagawa, Yuichi; Tamiaki, Hitoshi
• Is Part Of: Chemistry. Volume 22:Issue 29(2016)
• Page Start: 9996
• Page End: 10001
• Publication Date: 2016-06-15
• Subjects: absorption -- charge transfer -- chromophores -- enols -- porphyrinoids; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201601882
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The enhancement of the light absorption ability of synthetic chlorophyll derivatives is demonstrated. Chlorophyll derivatives directly conjugated with a difluoroboron 1, 3‐diketonate group at the C3 position were synthesized from methyl pyropheophorbide‐ d through Barbier acylmethylation of the C3‐formyl moiety, oxidation of the C3‐carbinol, and difluoroboron complexation of the diketonate. Electronic absorption spectra in a diluted solution showed that the synthetic conjugates gave an absorption band at λ =400–500 nm, with a Qy band shifted to a longer wavelength of λ ≈700 nm. DFT calculations demonstrated that the absorption bands and redshifts were ascribable to the coupling of the LUMO of chlorin with that of the difluoroboron diketonate moiety. The introduction of a pyrenyl group at the C3 3 ‐position of the conjugate afforded an additional charge‐transfer band over λ =500 nm, producing a pigment that bridged the green gap in standard chlorophylls. Abstract : Bridging the green gap : Chlorophyll derivatives directly conjugated with a difluoroboron 1, 3‐diketonate group at the C3‐position were synthesized. The LUMO of the chlorin π‐system electronically interacted with the π* orbital of the boron complex to afford a redshifted Q band and broadened and split Soret bands. A novel charge transition from the boron moiety to chlorin was stabilized to give an absorption band in the visible region (see figure).