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Chlorophyll-a derivatives possessing a substituted methylene group at the 13 2 -position were prepared by the mixed aldol condensation of methyl 3-hydroxymethyl-pyropheophorbide-a with aldehydes bearing a methyl, p-nitro/cyanophenyl, or pentafluorophenyl group. Their electronic absorption spectra were dependent on the substituents at the methylene terminal. The Soret bands were broadened by increasing the group electronegativity of the substituents, which was ascribable to the charge transfer from the core chlorin to the peripheral substituent in a molecule. Although their Qy absorption and fluorescence emission bands resembled each other, the emission intensities decreased with an increase in the electronegativity because of intramolecular electron transfer quenching. Some of their zinc complexes self-aggregated in a less polar organic solvent to give red-shifted and broadened absorption bands with intense circular dichroism couplets, which were similar to those of bacteriochlorophyll-c/d aggregates in natural chlorosomes as the main light-harvesting antennas of green photosynthetic bacteria and their models. The J-aggregation was suppressed with an enhancement in the size of the 13 2 -substituents., (© 2022 American Society for Photobiology.)

Chlorophyll(Chl)- a derivatives possessing a zinc center and a C13 2 -alkanoate residue with a terminal pyridyl group were synthesized. Their C13 2 -epimerically pure products were isolated by preparative reverse phase HPLC. The C13 2 -stereochemistry resulted in two directed terminal pyridinyl groups that coordinate with the central zinc atom in each stereoisomeric molecule: α/β-intramolecular axial coordination. The asymmetric axial coordinations mimic the immobilization manner of Chl- a in photosynthetically active proteins. The diastereomerically dependent conformers in solution were characterized by 1D/2D NMR, UV-visible absorption, and fluorescence emission as well as circular dichroism (CD) spectroscopy. The 1 H NMR and DOSY spectra revealed that the stereoselectively intramolecular coordination occurred in less coordinative deuterated chloroform, whereas a highly coordinative deuterated pyridine molecule replaced the terminal pyridine moiety as the axial ligand to form a mixture of α/β-coordinated species. Their optical spectra in pyridine were nearly independent of the C13 2 -stereochemistry and the linkers in the C13 2 -substituents. The CD bands of β-coordinated species in chloroform were more intense than those of the corresponding α-coordinated stereoisomers, indicating that the former had a larger distortion of the chlorin π-plane than the latter. Therefore, the α-coordinated Chl complex is more conformationally stable than the β-complex.

Chlorosomes in the green photosynthetic bacteria are the largest and most efficient light-harvesting antenna systems of all phototrophs. The core part of chlorosomes consists of bacteriochlorophyll c, d, e, or f molecules. In their biosynthetic pathway, a BciC enzyme catalyzes the removal of the C13 2 -methoxycarbonyl group of chlorophyllide a. In this study, in vitro C13 2 -dealkoxycarbonylations of zinc chlorophyll a derivatives bearing a methyl-, ethyl- or propyl-esterifying group and its methyl ester analogs with additional alkyl and hydroxy groups at the C13 2 -position were examined using the BciC enzyme. The BciC-catalyzed reaction activity for the C13 2 -methoxycarbonylated substrate was comparable to that for the ethoxycarbonylated compound; however, depropoxycarbonylation did not proceed. The BciC enzymatic demethoxycarbonylation of zinc methyl C13 2 -alkylated pheophorbides a was gradually suppressed with the elongation of the alkyl chain and finally became inactive for the propyl substrate. The reaction of the C13 2 -hydroxylated substrate (allomer) was accelerated compared to that of the C13 2 -methyl analog possessing a similar steric size, and gave the corresponding C13 2 -oxo product via further air-oxidation. All of the abovementioned enzymatic reactions occurred for one of the C13 2 -epimers with the same configuration as in chlorophyllide a. The above substrate specificities and product distributions indicated the stereochemistry and size of the BciC enzymatic active site (pocket)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

A zinc chlorophyll derivative possessing an oligoethylene glycol ester at the 17-propionate residue was prepared as a model of specific pigments in chlorosomes, such as bacteriochlorophylls-c, d, and e, by chemical modification of naturally occurring chlorophyll-a. The zinc chlorophyll derivative aggregated in aqueous or hexane solutions containing 1% (v/v) ethanol to give red-shifted and broadened Soret/Qy absorption bands with intense circular dichroism signals, indicating the formation of its chlorosome-like J-type self-aggregates. The atomic force microscope images of the self-aggregates prepared in aqueous or hexane solutions showed thin tube-like (ca. 3 nm diameter) or thick rod-like aggregates (> 20 nm diameter), respectively. After standing these solutions for several days, the nanotubes or nanorods further assembled to give ribbon- or bundle-like aggregates, respectively. The latter transformation (tube to ribbon) was triggered by hydrogen bonding between oligoethylene glycol esters located outside of the tubes via water or ethanol molecules. These dynamic supramolecular transformations may also be useful for revealing the growth process of bacteriochlorophyll self-aggregates in a chlorosome.

Zinc bacteriochlorophyll-d analogs possessing a methylene group at the 132-position were prepared by chemical modification of naturally occurring chlorophyll-a. The synthetic 31-epimers were successfully separated by reverse phase HPLC to give diastereomerically pure samples. The stereochemistry of the chiral C31-center in the separated bacteriochlorophyll-d analogs was determined by HPLC analysis of the authentic stereoisomers prepared stereospecifically. Both the epimers were monomeric in tetrahydrofuran to give sharp absorption bands, while they self-aggregated to form chlorosomal oligomers with red-shifted bands in an aqueous Triton X-100 micelle solution. The resulting large oligomers deaggregated by addition of Triton X-100 to give monomeric species. Their aggregation and deaggregation were dependent on the 31-stereochemistry, indicating that each epimer produced self-aggregates that were supramolecularly different. The substitution with the 132-methylene group enhanced their self-aggregation abilities and the stability of their resulting self-aggregates.

Light-harvesting antennas are one of the most important types of apparatus that use solar energy for natural and artificial photosynthesis. Bacteriochlorophyll (BChl) and chlorophyll (Chl) pigments play key roles in absorbing photons from the sun, migrating/transferring the singlet excitation energy, and transferring electrons. Chlorosomes, the main light-harvesting antennas of photosynthetic green bacteria, contain self-aggregates composed of a large number of BChl-c, d, e, and f molecules without any assistance from peptides, and such J-aggregates transfer the harvested energy to BChl-a pigments of baseplate proteins. In building such green bacterial light-harvesting antennas in artificial systems, self-aggregative model compounds of chlorosomal BChl-c-f pigments and their energy transferring systems have been reported to use synthetic (B)Chl derivatives in organic and aqueous solutions. In this study, we report the co-assembly and energy transfer of chlorin and porphyrin model compounds with covalently linked synthetic zinc and free-base (B)Chl heterodimers having different π-skeletons (bacteriochlorin, chlorin, and porphyrin). The co-assemblies of the self-aggregating BChl-d model having a porphyrin π-skeleton with heterodimers were first studied and showed singlet excitation energy transfer from the photoexcited chlorosomal J-aggregates to a free-base bacteriochlorin or chlorin moiety of the heterodimers. The present co-assembly is a good light-harvesting model system that mimics chlorosomes of photosynthetic green bacteria.

Chlorosomes are unique light-harvesting apparatuses in photosynthetic green bacteria. Single chlorosomes contain a large number of bacteriochlorophyll (BChl)-c, -d, -e, and -f molecules, which self-assemble without protein assistance. These BChl self-assemblies involving specific intermolecular interactions (Mg⋅⋅⋅O3 2 -H⋅⋅⋅O=C13 1 and π-π stacks of chlorin skeletons) in a chlorosome have been reported to be round-shaped rods (or tubes) with diameters of 5 or 10 nm, or lamellae with a layer spacing of approximately 2 nm. Herein, the self-assembly of synthetic zinc BChl-d analogues having ester, amide, and urea groups in the 17-substituent is reported. Spectroscopic analyses indicate that the zinc BChl-d analogues self-assemble in a nonpolar organic solvent in a similar manner to natural chlorosomal BChls with additional assistance by hydrogen-bonding of secondary amide (or urea) groups (CON-H⋅⋅⋅O=CNH). Microscopic analyses of the supramolecules of a zinc BChl-d analogue bearing amide and urea groups show round- or square-shaped rods with widths of about 65 nm. Cryogenic TEM shows a lamellar arrangement of the zinc chlorin with a layer spacing of 1.5 nm inside the rod. Similar thick rods are also visible in the micrographs of self-assemblies of zinc BChl-d analogues with one or two secondary amide moieties in the 17-substituent., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Zinc 3-hydroxymethyl-13 1 -oxo-chlorins bearing a variety of primary alkyl groups at the 20-position were prepared as models of bacteriochlorophyll-c by chemical modification of naturally occurring chlorophyll-a. The synthetic chlorophyll-a derivatives self-aggregated in an aqueous Triton X-100 solution to afford large oligomers whose Soret and Qy bands were red-shifted and broadened, compared with the bands of their monomers in tetrahydrofuran. The oligomeric bands are similar to those of bacteriochlorophyll-c self-aggregates in chlorosomes, the main light-harvesting antennae of photosynthetic green bacteria. The 20-alkylation led to bathochromic shifts of the visible Soret maxima in J-type self-aggregates of the synthetic models, while elongation of the 20-alkyl group decreased the chlorosomal Qy maxima due to an increase in steric hindrance. Considering the light-harvesting and energy-transferring processes in a chlorosome, the 20-methylation in bacteriochlorophyll-c would be more suitable for efficient culturing of green bacteria than the 20-ethylation and propylation as well as the 20-unsubstitution in bacteriochlorophyll-d.

Zinc chlorophyll derivatives Zn-1-3 possessing a tertiary amino group at the C3 1 position have been synthesized through reductive amination of methyl pyropheophorbide-d obtained from naturally occurring chlorophyll-a. In a dilute CH 2 Cl 2 solution as well as in a dilute 10 %(v/v) CH 2 Cl 2 /hexane solution, Zn-1 possessing a dimethylamino group at the C3 1 position showed red-shifted UV/Vis absorption and intensified exciton-coupling circular dichroism (CD) spectra at room temperature owing to its dimer formation via coordination to the central zinc by the 3 1 -N atom of the dimethylamino group. However, Zn-2/3 bearing 3 1 -ethylmethylamino/diethylamino groups did not. The difference was dependent on the steric factor of the substituents in the tertiary amino group, where an increase of the carbon numbers on the N atom reduced the intermolecular N⋅⋅⋅Zn coordination. UV/Vis, CD, and 1 H NMR spectroscopic analyses including DOSY measurements revealed that Zn-1 formed closed-type dimers via an opened dimer by single-to-double axial coordination with an increase in concentration and a temperature decrease in CH 2 Cl 2 , while Zn-2/3 gave open and flexible dimers in a concentrated CH 2 Cl 2 solution at low temperature. The supramolecular closed dimer structures of Zn-1 were estimated by molecular modelling calculations, which showed these structures were promising models for the chlorophyll dimer in a photosynthetic reaction center., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Zinc bacteriochlorophyll-d analogs possessing an amino group instead of the original hydroxy group at the C3 1 position were prepared by chemical modification of naturally occurring chlorophyll-a. The synthetic 3 1 -epimers were successfully separated by reverse phase HPLC to give diastereomerically pure samples. The stereochemistry of the chiral C3 1 -center in the separated amines was determined by NMR analysis of their diastereomeric amides as well as by their asymmetric synthesis from authentic stereoisomers. Both the epimers were monomeric in tetrahydrofuran to give sharp electronic absorption bands, while they self-aggregated to form chlorosomal oligomers with the redshifted bands in an aqueous Triton X-100 micelle solution (pH = 6.9). The resulting oligomers deaggregated by addition of p-toluenesulfonic acid to give monomeric N-protonated ammonium species. The aggregation and deaggregation were dependent on the 3 1 -stereochemistry, indicating that each epimer produced supramolecularly different self-aggregates., (© 2016 The American Society of Photobiology.)

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., (© 2014 The American Society of Photobiology.)

Zinc complex of pyropheophorbide-b, a derivative of chlorophyll-b, was covalently dimerized through ethylene glycol diester. The synthetic homo-dyad was axially ligated with two methanol molecules from the β-face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto-carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, (1) H NMR and IR spectra. All the synthetic zinc chlorin homo- and hetero-dyads consisting of pyropheophorbides-a, b and/or d took the above methanol-locked and π-π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo-dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo-dyads partially took such supramolecules. The J-type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads., (© 2013 The American Society of Photobiology.)

When a pyridine solution of zinc methyl 8-vinyl-mesopyropheophorbide-a was irradiated with visible light in the presence of ethanol, ascorbic acid and diazabicylo[2.2.2]octane under nitrogen at room temperature, zinc (7R/S,8E)-8-ethylidene-bacteriochlorin was obtained via 1,4-hydrogenation. The 1,4-photoreduction is similar to the enzymatic reduction of 8-vinyl-chlorophyllides to (E)-8-ethylidene-bacteriochlorins in anoxygenic photosynthetic bacteria producing bacteriochlorophylls-b/g. The resulting zinc 8-ethylidene-bacteriochlorin was readily isomerized to the chemically more stable 8-ethyl-chlorin by further illumination. As a by-product, zinc 8-vinyl-7,8-cis-bacteriochlorin was slightly formed by photoinduced 1,2-hydrogenation of zinc 8-vinyl-chlorin., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Natural chlorophylls (Chls) and bacteriochlorophyll (BChls), which are major pigments in photosynthesis, possess a central Mg (or Zn) in their cyclic tetrapyrrole macrocycles. Removal of the central metal atom from chlorophyllous pigments, called pheophytinization, is a biologically important reaction in that it allows production of the primary electron acceptors in photosystem II(-type) reaction centers and is one of the crucial steps in the Chl degradation pathway. Pheophytinization in processed and postharvest foods derived from vegetables and fruits has attracted considerable attention in agricultural and food chemistry from the viewpoints of maintenance of their color level and evaluation by consumers. In this review, we focus on in vivo demetalation reactions and demetalated products of chlorophyllous pigments. In addition, we summarize kinetic studies on in vitro demetalation of natural (B)Chl molecules and their synthetic analogs under acidic conditions., (Copyright © 2012 Verlag Helvetica Chimica Acta AG, Zürich.)

Photoreaction of zinc methyl 20-substituted meso(pyro)pheophorbide-a prepared by modifying naturally occurring chlorophyll-a in the presence of oxygen molecules gave its C19-C20 oxidative cleavage (1-carbonyl-19-oxo-bilatrienes) as the major products and the regioisomeric C1-C20 cleavage (19-carbonyl-1-oxo-bilatrienes) as the minor products. The resulting zinc complexes of linear tetrapyrroles took a helical conformation and the P-conformers were preferential over the M-stereoisomers due to the presence of their 17S,18S-chiral centers. The helical conformers (diastereomers) of the corresponding nickel complexes were separated by reverse-phase or chiral HPLC and their conformational changes were observed in solution.

Effects of peripheral substituents in the A- and B-rings of the chlorin macrocycle on demetalation of zinc chlorophyll derivatives were examined. The demetalation rate constants of zinc 8-formyl-chlorin (1) were comparable to those of zinc 3-formyl-chlorin (2). Both 1 and 2 exhibited significantly slower demetalation kinetics than the corresponding zinc chlorin 3, which had no formyl group. Comparison of demetalation kinetics between zinc 3-ethyl-chlorin (3) and zinc 3-vinyl-chlorin (4) indicated that the substitution at the 3-position of the chlorin macrocycle from a vinyl to an ethyl group accelerated removal of the central zinc. Activation energies of demetalation of zinc chlorins 1, 2, and 5 possessing a formyl group in the A- or B-ring of the chlorin macrocycle were larger than those of zinc chlorins 3 and 4 lacking a formyl group. These results indicate that the formyl groups in the A- or B-ring provide tolerance to demetalation of chlorin molecules due to their electron-withdrawing effects.

A heterodimer, where zinc pyropheophorbide-a was linked with zinc pyropheophorbide-d through ethylene glycol diester, was prepared, as well as the corresponding homodimers. The synthetic dimers were complexed with methanol in benzene to give folded dimers by mutual Zn...O(Me)-H...O=C13(1) bonding. Such complexes had furthest red (Qy) absorption bands at longer wavelengths than the monomeric species. These red-shifts were ascribable to excitonic coupling of the Qy transition states in the chlorin pi-pi stacking conformer. In the heterodimeric system, a minor band was observed at the shorter wavelength side of the main Qy band. This observation can be explained by an additional contribution of Qy vibronic state to the exciton-coupled states. Based on the experimental results, a pair of chlorophyll(Chl)-d with Chl-a as well as a Chl-d homopair were proposed as dimers in reaction centers of Chl-d dominating cyanobacteria.

Zinc 3(1)-demethyl-bacteriopheophorbides-d possessing various 17-propionate residue (17(2)-COOCH2-) were prepared as models of light-harvesting pigments in major photosynthetic antennae of green bacteria. The synthetic compounds were monomeric in polar organic solvents to give the same visible absorption spectra, but self-aggregated in non-polar organic solvents to afford large oligomers with broadened and red-shifted absorption bands. The peak positions were identical for all the self-aggregates but the widths of the redmost (Qy) bands were dependent upon the substituents. More hydrophobic and less sterically hindered hydrocarbon moieties as the esterifying group sharpened oligomeric Qy bands, giving less inhomogeneous supramolecular structures due to stabilization of the self-aggregates. In the reverse esters (17(2)-CH2OCO-) structurally isomeric to the above compounds, the same optical behavior was observed. Movement of the oxo group from the 17(3)- to 17(5)-position (17(2)-COOCH2--->17(2)-CH2OCO-) slightly increased the widths of self-aggregated Qy bands without change of the peak positions, where minor less self-aggregated components would enhance in the solution due to a little more stabilization of such species by the 17(4)-carbonyl group.

Zinc 3(1)-hydroxy-13(1)-oxo-chlorins possessing two, three, four and six perfluorooctyl chains were synthesized from naturally occurring chlorophyll-a. Only the synthetic zinc chlorin possessing six perfluorooctyl chains was directly dissolved in perfluorinated solvents due to its high fluorine content in molecular weight (over 50%). In this solution, visible absorption spectra gave a red-shifted Q(y) band at 723 nm (compared to 648 nm in THF) and showed the formation of well-ordered self-aggregates. No monomeric form was observed in the solution from any fluorescence emission spectra from visible absorption spectra. In the aggregate solution, no precipitation occurred during either standing for a long period or heating at 70 degrees C. This showed that the supramolecular structure was stabilized by F-F interactions on its surface among the perfluorooctyl chains on the 17-position and perfluorinated solvents. The core part of the supramolecular structure was constructed by a special intramolecular bond of Zn ... O3(2)-H ... O=C13(1), which was confirmed from resonance Raman spectral analysis.

Zinc 3(1)-hydroxy-13(1)-oxo-chlorins possessing various perfluorooctyl groups in the 17-propionate were prepared by modifying naturally occurring chlorophyll-a. The synthetic compound having four perfluorooctyl groups readily self-assembled to form large J-aggregates, which were dissolved in fluorous phases with more ordered supramolecular structures than in a hydrocarbon solvent.

Zinc 3(1)-hydroxy-13(1)-oxo-chlorin possessing a perfluoroheptyl group on the 17-propionate was prepared by modifying chlorophyll a. The synthetic compound self-aggregated in 0.1% (v/v) THF and HCFC225cb (CClF2CF2CHClF) to give similar large oligomers to natural light-harvesting antennae of green photosynthetic bacteria and their models. Visible absorption, circular dichroism, and fluorescence emission spectra showed that F-F interaction between the perfluoroheptyl side chain and the fluorinated solvent (HCFC225cb) stabilized the supramolecular structure. The core part of the supramolecular structure was constructed by a special bond of Zn...O3(1)-H...O=C13(1) and pi-pi stacking, and the 17-propionates were at the peripheral part.

We prepared novel zinc 8-ethyl-8-methyl-7-oxo- and 7-ethyl-7-methyl-8-oxo-bacteriochlorins 1 and 2 possessing substituents characteristic of chlorosomal chlorophylls, exclusively observed in extramembraneous light-harvesting antennas of photosynthetic green bacteria. The electronic absorption spectra of monomeric 1 and 2 in THF were obviously different: the Q(y) maximum of the former was 724 and that of the latter was 683 nm. This observed spectral difference was clearly explained by theoretical ZINDO/S calculation of their energetically minimized molecules. The optical properties of monomeric 1/2 were controlled by the electronic effect of the 7/8-oxo groups. Specific spectral changes in the electronic, CD, and FT-IR absorption spectra by dilution of the monomeric THF solutions of 1/2 with a 100/200-fold volume of cyclohexane showed the formation of chlorosomal self-aggregation species constructed by 13-C=O...H-O(3(1))...Zn and pi-pi stacking. Especially, the red-shift values in the Q(y) band of 1/2 by self-aggregation were 2450/1970 cm(-1), indicating that exciton interaction among the composite molecules in the self-aggregation of 1 was stronger than in those of 2. Molecular model calculations for dodecamers of 1/2 based on a parallel chain arrangement gave partially different supramolecular structures; the specific hydrogen-bonding distances in 2-dodecamer were larger than those of 1-dodecamer, while both coordinations gave the same Zn-O distance. These modeling results showed that 1 was more tightly packed in the self-aggregates to give a larger red-shift value in the Q(y) band by self-aggregation than 2. The difference in the supramolecular structures is mainly ascribable to the steric effect of 8/7-dialkyl groups in self-aggregates of 1/2.

Zinc complex of methyl 3(1)-octadecyl-bacteriopheophorbide-d was prepared from modification of naturally occurring chlorophyll-a. The 3(1)-epimerically pure samples were obtained by HPLC separation and their stereochemistry including the absolute configuration at the secondary alcoholic 3(1)-position was determined by combination of esterification to methoxy(trifluoromethyl)phenylacetate and NMR spectroscopy (Mosher's method). Both the epimers were monomeric in a polar organic solvent and self-aggregated in a non-polar solvent to give oligomers as well as dimers possessing red-shifted visible absorption bands. Visible spectra of the non-polar organic solutions were dependent upon the 3(1)-chirality and such a diastereoselective control on the self-aggregation led to the formation of self-aggregates with different supramolecular structures.

Zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide-a (1), a good model compound of light-harvesting pigments of green photosynthetic bacteria, formed self-aggregates in the presence of octadecyltriethoxysilane and tetraethoxysilane in an aqueous solution to exhibit visible absorption spectra similar to the natural antenna. Base-catalyzed cross-linked polymerization of the additive Si-ORs (R=ethyl and H) afforded the formation of a siloxane network (Si-O-Si) on the surface of the self-assemblies of 1. The resulting microcapsules were stable to tolerate the deaggregation to monomeric 1 by addition of surfactant Triton X-100 more largely than the corresponding micelles before polymerization.

Zinc 3-hydroxymethyl-pyroprotopheophorbides-a esterified with a chiral secondary alcohol at the 17-propionate residue were prepared as bacteriochlorophyll-d analogs. The synthetic zinc 31-hydroxy-131-oxo-porphyrins self-aggregated in an aqueous Triton X-100 micellar solution to give red-shifted and broadened Soret and Qy absorption bands in comparison with their monomeric bands. The intense, exciton-coupled circular dichroism spectra of their self-aggregates were dependent on the chirality of the esterifying groups. The observation indicated that the self-aggregates based on the J-type stacking of the porphyrin cores were sensitive to the peripheral 17-propionate residues. The supramolecular structures of the present J-aggregates as models of bacteriochlorophyll aggregates in natural chlorosomes were remotely regulated by the esterifying groups. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zinc 31-demethyl-bacteriochlorophylls- d with pinacol boronate on B-ring were prepared. • The synthetic analogs self-aggregated in aqueous micelles similar to chlorosome. • The chlorosome-like aggregates exhibited red-shifted and broadened Qy bands. • Exciton-coupled circular dichroism couplets were observed in the red-shifted regions. • The J-aggregation suppressed with an increase in the size of the boron substituents. Zinc 3-hydroxymethyl-131-oxo-bacteriochlorins possessing a variety of pinacol boronates on the B-ring were prepared from chemical modification of naturally occurring chlorophyll- a. The synthetic bacteriochlorophyll- d analogs were dissolved into an aqueous Triton X-100 solution to exhibit red-shifted and broadened electronic absorption bands with reversed S-shape circular dichroism bands, compared with their monomeric bands. The behaviors indicated that most synthetic models possessing a bacteriochlorin π-system self-aggregated inside the aqueous micelles to give similar oligomers as the J-aggregates of bacteriochlorophyll- d bearing a chlorin π-skeleton in major light-harvesting antennas of green photosynthetic bacteria, chlorosomes. The methylboronate self-aggregated more largely than the phenylboroante, and the self-aggregation was suppressed by ortho -substitution on the phenyl ring: phenyl > 1-naphthyl ≫ 9-anthryl and phenyl > 2,6-dimethylphenyl. Along with an increase in the size of the substituents on the boron atom of their boronates, the formation of the chlorosome-like self-aggregates decreased substantially. [ABSTRACT FROM AUTHOR]

Two heterodyads were prepared from the chemical modification of naturally occurring (bacterio)chlorophyll-a and composed of a chlorin π-skeleton linked to a porphyrin or bacteriochlorin π-system. Zinc methyl pyropheophorbide-a, one of the chlorophyll-a derivatives, was covalently linked with its 17,18-didehydrogenated species (zinc methyl pyroprotopheophorbide-a) or its trans-7,8-dihydrogenated analog (zinc methyl pyrobacteriopheophorbide-a as one of the bacteriochlorophyll-a derivatives) through ethylene glycol diester at their 17-propionate residues. In benzene, the central zinc atoms of the synthetic conjugates were coordinated by two methanol molecules which were hydrogen-bonded with the 13-keto-carbonyl groups in a dyad molecule. The methanol locked, y-axis aligned, and slipped cofacial conformers showed two apparent Qy bands at longer wavelengths than those of the composite zinc complex monomers. The red-shifted Qy bands are ascribable to the exciton coupling of the two different π-systems in the folded heterodyad conformers. The synthetic heterodyads could be models of chlorophyll-a/c dimers in the light-harvesting antennas of chromophytes including fucoxanthin–chlorophyll proteins in diatoms and also chlorophyll-a species interacting with bacteriochlorophyll-a or g species in the charge-separating reaction centers of green sulfur bacteria or heliobacteria, respectively. [ABSTRACT FROM AUTHOR]

Zinc bacteriochlorophyll-d analogs possessing a methylene group at the 132-position were prepared by chemical modification of naturally occurring chlorophyll-a. The synthetic 31-epimers were successfully separated by reverse phase HPLC to give diastereomerically pure samples. The stereochemistry of the chiral C31-center in the separated bacteriochlorophyll-d analogs was determined by HPLC analysis of the authentic stereoisomers prepared stereospecifically. Both the epimers were monomeric in tetrahydrofuran to give sharp absorption bands, while they self-aggregated to form chlorosomal oligomers with red-shifted bands in an aqueous Triton X-100 micelle solution. The resulting large oligomers deaggregated by addition of Triton X-100 to give monomeric species. Their aggregation and deaggregation were dependent on the 31-stereochemistry, indicating that each epimer produced self-aggregates that were supramolecularly different. The substitution with the 132-methylene group enhanced their self-aggregation abilities and the stability of their resulting self-aggregates. [ABSTRACT FROM AUTHOR]

Abstract Light-harvesting (LH) antennas are one of the most important apparatuses for photosynthetic organisms to utilize solar energy. The main LH apparatuses in photosynthetic green bacteria are chlorosomes containing baseplate proteins. A chlorosome possesses a large number of bacteriochlorophyll(BChl)- c – f molecules. These BChls are chemically programmed pigments for J -aggregation, which self-assemble in a hydrophobic environment. The BChl- c – f self-assemblies in a chlorosome are primary energy donors, which absorb sunlight, migrate the excitation energy, and transfer it to energy acceptor BChl- a pigments in a baseplate protein. To develop such chlorosomal LH antenna in artificial systems, self-assemblies of synthetic BChl- d analogs and BChl- a derivatives have been used for the energy donors and acceptors, respectively. In this study, we report the co-aggregation of zinc chlorophyll derivatives with chlorosomal self-assemblies. The present system showed singlet excitation energy transfer from energetically donating chlorosomal self-assemblies to energetically accepting zinc chlorophyll derivatives in the solution and solid states. Graphical abstract Image 1 Highlights • Zinc (bacterio)chlorin co-aggregated with biomimetic chlorosomal self-assembly. • Co-aggregate accepted singlet energy from photoexcited chlorosomal self-assembly. • Co-aggregate could be post-prepared like a layer-by-layer technique. [ABSTRACT FROM AUTHOR]

Chlorophylls (Chls) are abundant, naturally occurring pigments that play key roles in light-harvesting and electron/energy transfer in natural photosynthetic apparatus. To demonstrate the idea that Chls are suitable hole transporters, we employed two Chl derivatives, Chl-1 and Chl-2, which self-assembled readily into π-stacking aggregates through a simple spincasting process, in perovskite solar cells (PSCs). The Chl aggregate films exhibit an ultra-smooth film surface, high hole mobility, appropriate energy levels, and efficient hole injection efficiencies that are all key characteristics for efficient hole transporters in PSCs. CH3NH3PbI3− xCl x-based PSCs with these Chls as hole transporters were fabricated and compared with P3HT as a standard hole transporter. PSCs based on Chl-1 and Chl-2 without the use of typical additives, such as 4- tert-butylpyridine and lithium bis(trifluoromethanesulfinyl)imide, gave power conversion efficiencies of 11.44 and 8.06 %, respectively. This research provides a unique way to incorporate low-cost and environmentally friendly natural photosynthetic materials in the development of highly efficient photovoltaic devices. [ABSTRACT FROM AUTHOR]

Systematically synthetic zinc 3-hydroxymethyl-131-oxo-chlorins esterified by different linear alcohols (methanol, 1-propanol, 1-hexanol, 1-dodecanol and 1-octadecanol) at the 17-propionate were self-assembled in the presence of cetyltrimethylammonium bromide in an aqueous solution. These zinc chlorins exhibited red-shifted Qy absorption bands and circular dichroism (CD) signals in the corresponding Qy region after incubation for 17 h, indicating that the zinc chlorins formed self-aggregates like those in natural chlorosomes of green photosynthetic bacteria. Visible absorption and CD spectra of self-aggregates of the zinc chlorins depended on the length of their esterifying alcohols. Zinc chlorins esterified by shorter alcohols gave larger changes in their visible absorption and CD spectra after incubation above 40°C, whereas zinc chlorins esterified by longer alcohols afforded smaller changes. These results indicate that hydrophobic interaction among esterifying chains of chlorin molecules as well as that between the esterifying chains and peripheral surfactants or lipids play an important role in the stability of chlorosomal self-aggregates. [ABSTRACT FROM AUTHOR]

Zinc 21- and 31-hydroxy-13-carbonylhexaethylporphyrins 2 and 3 were synthesized by modifying easily available octaethylporphyrin, and the HPLC-separated regioisomers were fully characterized. The latter compound 31-OH-13-C=O-3, which structurally resembled naturally self-aggregative bacteriochlorophyll-d (31-OH/13-C=O), was preferable to make ordered J-aggregates in the solid film, compared to its regioisomeric 21-OH-13-C=O-2. In contrast, more ordered oligomers were obtained by self-aggregation of zinc porphyrin I possessing the interactive moieties (31-OH, Zn, 13-C=O) at the same positions, which was prepared by modifying natural chlorophyll-a molecule. The difference between self-aggregation of 1 and 3 was ascribable to the methyl and ethyl groups attached at the 2-position neighboring the 3'-OH group which is requisite for self-aggregation; the steric environment around the interactive OH group is important to make highly ordered supra-molecules through strong molecular packings. [ABSTRACT FROM AUTHOR]

The article discusses the zinc 3-hydroxymethyl-poryphins synthesis, which possess carbonyl groups at either 13- or 15-positions for self-aggregate chlorophyll models in green photosynthetic bacteria. It notes that artificial photoactive devices can be made through π-conjugated choromophores self-aggregation ,wherein exciton energy is delocalized well over the supramolecules. The results for its ultraviolet (UV), resonance Raman (RR), and FT-IR spectroscopies are discussed.

Zinc methyl 31-demethyl-17,18-cis-bacteriopheophorbide-d was prepared as a model of naturally occurring bacteriochlorophyll-d. From the absorption spectral analysis, the synthetic cis-chlorin self-aggregated in a non-polar organic solvent to give an oligomer possessing red-shifted and broadened peaks, compared to the non-aggregated form. The red-shifted values by self-aggregation were smaller than those observed in the corresponding trans-isomer, indicating that self-aggregates of the cis-isomer took on more disordered supramolecular structures than those of the trans-isomer. [ABSTRACT FROM AUTHOR]

Abstract: The activity of a methyltransferase, BchU, which catalyzes methylation at the C-20 position of chlorin ring in the biosynthetic pathway of bacteriochlorophyll c, was investigated in vitro. The bchU gene derived from the photosynthetic green sulfur bacterium, Chlorobium tepidum, was overexpressed in Escherichia coli as a His-tagged protein (His6-BchU), and the enzyme was purified. In the presence of S-adenosylmethionine, His6-BchU methylated zinc bacteriopheophorbide d at the C-20 position to give zinc bacteriopheophorbide c. Metal-free bacteriopheophorbide d could not be methylated by the BchU, indicating that the central metal in the chlorin should be required for the recognition by the BchU. [Copyright &y& Elsevier]

Aqueous assemblies of zinc chlorins possessing a nonionic (oligo)oxyethylene, a cationic quaternary ammonium or an anionic sulfonate group were prepared in the presence of a synthetic surfactant. The nonionic zinc chlorin formed aggregates when admixed with a nonionic surfactant such as Triton X-100 to give a highly ordered oligomeric J-aggregate similarly as natural bacteriochlorophyll-c or d does in a chlorosome. In addition, the coassemblies of the cationic zinc chlorin with an anionic surfactant and of the anionic zinc chlorin with a cationic surfactant gave large oligomers of these chlorophyllous pigments. The structures of hydrophilic groups in both the zinc chlorin and surfactant molecules controlled their aqueous coassemblies. [Copyright &y& Elsevier]

Zinc complexes of 21-hydroxy-121/131-oxo-porphyrins were prepared by modifying octaethylporphyrin as models of self-aggregative chlorophylls found in extramembranous antennas of green photosynthetic bacteria. Their visible absorption spectra showed that less hindered interactive groups, such as CH2OH and CHO in a synthetic zinc porphyrin molecule were necessary for their self-aggregation in non-polar organic solvents. Zinc 2-hydroxymethyl-12-formyl-porphyrin self-aggregated to form larger oligomers with red-shifted broad visible bands than the 2,13-regioisomer, indicating that the linear location of OH, Zn and C&z.dbnd;O in a molecule is requisite for similar self-aggregation with natural systems. [Copyright &y& Elsevier]

• Zinc chlorophyll- a derivatives bearing an O -substituted 13-oxime were synthesized. • The energetically stable 131 E -oximes were prepared more than the 131 Z -isomers. • Almost the synthetic oximes formed J -aggregates in an aqueous TX-100 solution. • The 131 Z -oximes gave less red-shifted absorption bands than the 131 E -isomers. • The self-aggregation was dependent on 131 E / Z -stereochemistry and O -substituents. Zinc methyl 3-hydroxymethyl-131-deoxo-pyropheophorbides- a possessing a variety of O -substituted oxime moieties at the 13-position were prepared as models of bacteriochlorophyll- d , which could be found in the main light-harvesting system of green photosynthetic bacteria by chemical modification of naturally occurring chlorophyll- a. The E / Z -stereoisomers of the synthetic O -substituted oximes were successfully separated by silica gel column chromatography. Most of these zinc bacteriochlorophyll- d analogs formed J -type self-aggregates in an aqueous Triton X-100 micelle solution, affording large oligomers whose Soret and Qy bands were red-shifted, compared with those of their monomers in tetrahydrofuran. The self-aggregation was dependent on their E / Z -stereochemistry. Thus, the E -stereoisomers showed the red-shifted electronic absorption bands, which were similar to those of the original bacteriochlorophyll- d bearing the 131-oxo group. On the other hand, the Z -stereoisomers exhibited the less red-shifted absorption bands than did the E -stereoisomers, to give different self-aggregates. In addition, the self-aggregation could be controlled by the size of the O -substituents in the oxime moiety. [ABSTRACT FROM AUTHOR]

• Zinc chlorophyll- a derivatives bearing the 131-alkoxyimino groups was synthesized. • These (131 E / Z)-stereoisomers were separated by silica gel column chromatography. • Less sterically demanding oximes formed J -type self-aggregates in aqueous micelles. • The J -aggregates were destabilized by greater steric bulkiness of the alkoxy group. • The self-aggregates were dependent on the (131 E / Z)-stereochemistry. Zinc complexes of methyl 3-hydroxymethyl-131-deoxo-131-alkoxyimino-pyropheophorbides- a were prepared through the condensation of the 13-keto carbonyl group with several alkoxyamines. The E / Z -stereoisomers of the synthetic alkoximes were successfully separated by silica gel column chromatography. The zinc bacteriochlorophyll- d analogs formed J -type self-aggregates in an aqueous micelle solution to give red-shifted electronic absorption bands, which were similar to those of the original bacteriochlorophyll- d bearing the 131-oxo group. The self-aggregation was largely dependent on the size of the alkoxyimino groups and their E / Z -stereochemistry. [ABSTRACT FROM AUTHOR]

Two-dimensional sheet-like supramolecules have attracted much attention from the viewpoints of their potential application as functional (nano)materials due to unique physical and chemical properties. One of the supramolecular sheet-like nanostructures in nature is visible in the self-assemblies of bacteriochlorophyll-c–f pigments inside chlorosomes, which are major components in the antenna systems of photosynthetic green bacteria. Herein, we report artificial chlorosomal supramolecular nanosheets prepared by the self-assembly of a synthetic zinc 31-methoxy-chlorophyll derivative having amide and urea groups in the substituent at the 17-position. The semi-synthetic zinc chlorophyll derivative kinetically formed dimeric species and transformed into more thermodynamically stable chlorosomal J-aggregates in the solid state. The kinetically and thermodynamically formed self-assemblies had particle-like and sheet-like supramolecular nanostructures, respectively. The resulting nanosheets of biomimetic chlorosomal J-aggregates had flat surfaces and well-ordered supramolecular structures. The artificial sheet-like nanomaterial mimicking chlorosomal bacteriochlorophyll-c–f J-aggregates was first constructed by the model molecule, and is potentially useful for various applications including artificial light-harvesting antennas and photosyntheses. [ABSTRACT FROM AUTHOR]

Zinc methyl 3-devinyl-pyropheophorbides- a bearing a (1-azacycloalkyl)methyl group at the 3-position were prepared by chemically modifying naturally occurring chlorophyll- a. The azacyclobutylated molecules closely dimerized through double coordination of the 31-nitrogen atom to the central zinc atom in 1%(v/v) dichloromethane and hexane to give red-shifted visible absorption and reverse S-shaped circular dichroism (CD) bands. The azacyclopentyl analog formed similarly π–π interacted and A-ring overlapped dimers with relatively weakened and lengthened Zn–N bonds to show less split excitonic bands, and its cofacial and anti-parallel supramolecule giving S-shaped CD bands was inversely twisted by the insertion of a methylene group in the 1-azacycloalkyl moiety. One more methylene insertion as in the azacyclohexyl derivative induced a least coordination ability and no more dimerization, so the compound with the most sterically crowded 31-N was monomeric in the less polar organic solvent. Steric factor at around the 31-nitrogen atom controlled the dimerization and affected the supramolecular structure with excitonically coupling visible absorption and CD bands. Image 1 [ABSTRACT FROM AUTHOR]

The article discusses a study which analyzed the self-aggregation of synthetic zinc 3-hydroxymethyl-purpurin-18 and N-hexylimide methyl esters in an aqueous solution. The aqueous solution used in this study contains 6 percent THF, which is said to be effective for self-aggregation of chlorosomal chlorophylls.

An ω-(m -pyridyl)alkyl group was introduced at the C132-methoxycarbonyl group of methyl pheophorbide- a as a chlorophyll- a derivative by exchange of the esterifying moiety. To avoid allomerization and epimerization of the C132-chiral center in the β-keto-ester moiety, a propyl group was substituted at the C132-position. The free bases were zinc-metalated to give zinc methyl 132-propyl-pheophorbides- a bearing an oligomethylene chain with a pyridyl terminal at the C132-position. Depending on the length of the alkyl chain between the terminal pyridine and C132-carboxylate moieties, the coordination of the m -pyridyl group with the central zinc atom in the stereochemically pure and fixed zinc chlorin–pyridine conjugates occurred in intra- or intermolecular fashions. [Display omitted] • Zinc chlorophyll(Chl)- a derivatives bearing a m -pyridyl terminal were synthesized. • Zn-Chl–pyridine conjugates with an oligomethylene spacer were analyzed in chloroform. • The shortest linkage induced intermolecular Zn–N coordination at high concentration. • Longer spacers allowed intramolecular α-coordination at any concentrations. • The strain on intramolecularly α-coordinated species depended on the linker length. [ABSTRACT FROM AUTHOR]

Zinc 3¹,13¹-dihydroxychlorin lacking an exo-five-membered E-ring was prepared as a model of natural bacteriochlorophyll-d possessing 3¹-OH and 13-C=O groups. The synthetic zinc complex has the 13-CH2OH instead of the 13-C=O and self-aggregated in a nonpolar organic solvent, giving slipped and π-overlapped molecular stackings (J-aggregates) with red-shifted and broadened electronic absorption bands. For the intermolecular interactions among the J-aggregates, coordination bonding of the 3¹-OH (not 13¹-OH) with the central Zn was utilized. [ABSTRACT FROM AUTHOR]

Visible absorption and circular dichroism spectra of zinc chlorophyll derivatives possessing an oligo(oxyethylene) moiety at the 17-propionate in aqueous media were drastically changed by treatment with dichloromethane or chloroform, indicating that dimeric and monomeric species were converted into chlorosome-like large self-aggregates. [ABSTRACT FROM AUTHOR]

Zinc chlorophyll derivatives possessing (multi)-perfluoroalkyl chain(s) in the 17-propionate residue were dissolved in liquid carbon dioxide to form their oligomers (=J-aggregates), while the alkyl-type analog was insoluble in the medium. These results indicated solubilization and stabilization of their supramolecules by an interaction between the perfluoroalkyl substituents and liquid carbon dioxide. [ABSTRACT FROM AUTHOR]

The diketonate group of the peripheral position in chlorophyll derivatives 1 and 2 coordinated ruthenium bisbipyridine to give direct linkages 3-5 of the chlorin ring with the Ru(II) complex. Zinc metalation of the central position in the chlorin ring of free base 3 afforded the Ru-Zn binuclear complex 3-Zn. Because the diketonate group at the C3 position of chlorophyll derivatives coordinated to bulky Ru(bpy)22+, the plane of the diketonate group was twisted from the chlorin p ring in synthetic 3-5 and 3-Zn to lead to a partial deconjugation and a slight blue shift of the longest wavelength electronic absorption band in dichloromethane. A broad metal-to-ligand charge-transfer absorption band derived from the Ru complex was observed around 500 nm, in addition to visible absorption bands from the chlorophyll moiety. Chlorophyll derivatives 3-5 and 3-Zn directly coordinating the ruthenium complex were less fluorescent in dichloromethane than chlorophyll-diketonate ligands 1, 2, and 1-Zn due to the heavy atom effect of the ruthenium in a molecule. The coordination to the ruthenium complex moiety at the peripheral position shifted the electrochemical reduction of the chlorin part in acetonitrile to a negative potential, and the coordination to zinc at the central position decreased the redox potentials. Chemical modification of the bipyridine and diketonate ligands of the ruthenium complexes greatly affected the redox potentials of Ru(II)/(III) and/or Ru(II)/(I) but minimally the redox properties of the chlorin moiety. Substitution with electron-donating groups shifted the former to a negative potential but only barely shifted the latter. The zinc metalation caused no apparent shifts for the redox potentials of the Ru center. [ABSTRACT FROM AUTHOR]

Abstract: Zinc chlorins having a bridged moiety between 3- or 8- and 17-positions were designed as protected chlorophylls at one of π-faces, aiming at the investigation of asymmetric coordination ability towards the central metal. These strapped chlorins were synthesized by the cyclization of the dihydroxylated chlorins with dicarboxylic acid dichlorides under highly diluted conditions. The synthetic zinc chlorins complexed with pyridine as an axial ligand in benzene to form 5-coordinated species. The 1:1 binding constants determined by UV–vis titration method were smaller than those of the corresponding acyclic (unstrapped) compounds. [Copyright &y& Elsevier]

[Display omitted] • Zinc methyl mesochlorophyllide a bearing the (131 S)-hydroxy group was prepared. • A recombinant BciC protein catalytically hydrolyzed the (132 R)-methoxycarbonyl group. • The 132-carboxy-chlorin was first observed as the hydrolyzed product. • The BciC enzyme functions as a hydratase both in vivo and in vitro. • The in vivo resulting β-keto-carboxylic acid is non-enzymatically decarboxylated. Green photosynthetic bacteria with an efficient light-harvesting system contain special chlorophyll molecules, called bacteriochlorophylls c , d , e , in their main antennae. In the biosynthetic pathway, a BciC enzyme is proposed to catalyze the hydrolysis of the C132-methoxycarbonyl group of chlorophyllide a , but the resulting C132-carboxy group has not been detected yet because it is spontaneously removed due to the instability of the β-keto-carboxylic acid. In this study, the in vitro BciC enzymatic reactions of zinc methyl (131 R / S)-hydroxy-mesochlorophyllides a were examined and a carboxylic acid possessing the C132 S -OH was first observed as the hydrolyzed product of the C132-COOCH 3. [ABSTRACT FROM AUTHOR]

As a model of bacteriochlorophyll(BChl)- d specifically found in major light-harvesting antennae (chlorosomes) of photosynthetic green bacteria, zinc methyl 7,8-dihydro-17,18,171,172-tetradehydro-bacteriopheophorbide- d was prepared from naturally occurring BChl- a through the double dehydration of the cis -17,18-diol. The synthetic B-ring reduced Zn-BChl- d analog bearing the 17-acrylate residue in tetrahydrofuran exhibited a more bathochromically shifted Soret band in the monomeric state than its counterpart with the 17-propionate residue, while the former's Qy band slightly moved to a longer wavelength and was somewhat broadened in comparison with the latter's. Compared with the monomeric bands, the acrylated pigment self-aggregated in 1% tetrahydrofuran and hexane to give more red-shifted and broadened Soret and Qy bands at blue-to-green and far-red regions, respectively, which were similar to the J -aggregates of BChl- d in chlorosomes. By contrast, the propionated pigment remained monomeric under the same conditions. These spectral differences were owing to the 17-substitution effect including the π-conjugating and electron-withdrawing 17-acrylate residue. Image 1 • Zinc B-ring reduced bacteriochlorophyll- d analogs were prepared. • The synthetic analog with 17-acrylate residue self-aggregated in a hexane solution. • The self-aggregates showed red-shifted and broadened visible absorption bands. • The 171,172-didehydrogenated π-conjugation enhanced chlorosomal J -aggregation. [ABSTRACT FROM AUTHOR]