Self‐aggregation of Synthetic Zinc Chlorophyll Derivatives Possessing 3¹‐Hydroxy or Methoxy Group and 13¹‐Mono‐ or Dicyanomethylene Moiety in Nonpolar Organic Solvents as Models of Chlorosomal Bacteriochlorophyll‐d Aggregates

Abstract

Methyl 13(1)-(di)cyanomethylene-pyropheophorbides were synthesized by Knoevenagel reactions of the corresponding 13(1)-oxo-chlorins prepared from modifying chlorophyll-a with malononitrile or cyanoacetic acid. Alternatively, methyl 13(1)-cyanomethylene-pyropheophorbides were produced by Wittig reactions of 13(1)-oxo-chlorins with Ph3P=CHCN. Self-aggregation of zinc complexes of the semi-synthetic chlorophyll derivatives possessing a hydroxy or methoxy group at the 3(1)-position was examined in 1%(v/v) tetrahydrofuran or dichloromethane and hexane by electronic absorption and circular dichroism spectroscopy. Although intermolecular hydrogen-bonding between the 3(1)-hydroxy and 13(1)-oxo groups of bacteriochlorophylls-c/d/e/f was essential for their self-aggregation in natural light-harvesting antenna systems (=chlorosomes), zinc 3(1)-hydroxy-13(1)-di/monocyanomethylene-chlorins self-aggregated in the less/lesser polar organic solvents to form chlorosome-like large oligomers in spite of lacking the 13(1)-oxo moiety as the hydrogen-bonding acceptor. Zinc 3(1)-methoxy-13(1)-dicyanomethylene-chlorin gave similar self-aggregates regardless of lack of both the 3(1)-hydroxy and 13(1)-oxo groups. The present self-aggregation was ascribable to stronger coordination of the 3(1)-oxygen atom to the central zinc than the conventional systems, where the electron-withdrawing cyano group(s) increased the coordinative ability of the central zinc through the chlorin π-system.

Hydroquinone redox mediator enhances the photovoltaic performances of chlorophyll-based bio-inspired solar cells

“…Figure 1a shows the chemical structures of Chl-A and Chl-D, which were derived from the natural Chl- a 6 . Chl-A and Chl-D are easy to synthesize with high synthetic yields of approximately 80% and 70%, respectively 26 – 28 . Natural Chl- a was extracted from a commercial cyanobacterium, Spirulina geitleri .…”

Push–pull pyropheophorbides for nonlinear optical imaging

“…[35][36][37][38] The effects of chemical modification of the -system of 1a on its optical properties have been explored in several studies. [39][40][41][42][43][44][45][46] The electronic absorption spectrum of 1a is characteristic of chlorins, and is dominated by two absorption bands, one in the high-energy region at the border of the UV (Soret band) and one in the far-red visible region (Q band). Absorption in the far-red region is useful for onephoton techniques because photo-damage is reduced at these energies compared to shorter wavelengths.…”