Enhancement of Light Absorption Ability of Synthetic Chlorophyll Derivatives by Conjugation with a Difluoroboron Diketonate Group

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.

Substituted Methylenation at the 132‐Position of a Chlorophyll‐a Derivative via Mixed Aldol Condensation, Optical Properties of the Synthetic Bacteriochlorophyll‐d Analogs, and Self‐aggregation of Their Zinc Complexes†

“…Especially, the absorbance from 460 to 510 nm was ascribable to the intramolecular charge transfer (CT) transition from a core chlorin p-skeleton to a peripheral aryl group possessing an electronwithdrawing substituent(s) at the 13 2 -methylene terminal (Figure S5 and Table S2). A similar CT band was previously reported for the related chlorins p-conjugated with a difluoroboron diketonate group at the 3-position (58).…”

Synthesis of Cationic Pyridinium‐(Bacterio)Chlorophyll Conjugates Bearing a Bacteriochlorin, Chlorin, or Porphyrin π‐Skeleton and their Photophysical and Electrochemical Properties

“…Typically, the Qy maxima are bathochromically shifted in the order of porphyrin < chlorin < bacteriochlorin. Notably, the peripheral functional groups directly π‐conjugated to the core π‐systems also affect the absorption bands , , , . For example, the introduction of electron‐withdrawing groups at the 3‐position on the molecular y ‐axis moves the Qy maxima to longer wavelengths…”

Syntheses of Chalcone‐Type Chlorophyll Derivatives Possessing a Bacteriochlorin, Chlorin or Porphyrin π‐System and Their Optical Properties

“…Several functional groups are available for peripheral substituents of natural (B)Chls : 3‐acetyl, 3‐vinyl, 7‐formyl, 8‐vinyl, 13‐carbonyl, 17‐acrylate groups and so on. A lot of (B)Chl derivatives possessing a variety of substituents at their peripheral positions have been synthesized by the chemical modification of natural (B)Chls to understand the substitution effects on their optical properties based on several factors : the modification position, π‐conjugation expansion and electronic/steric effects. However, a limited number of reports are available for the substitution effects on (B)Chl derivatives possessing different fundamental π‐systems (bacteriochlorin, chlorin and porphyrin) .…”