Synthesis of Zinc Chlorophyll Homo/Hetero-Dyads and their Folded Conformers with Porphyrin, Chlorin, and Bacteriochlorinπ-Systems

Bio-based porphyrins pyropheophorbide a and its Zn-complex as performing visible-light photosensitizers for free-radical photopolymerization

A chlorophyll a derivative, namely pyropheophorbide a (Pyro), and the corresponding zinc (II) complex (Zn-Pyro) were used for the first time as performing visible-light photosensitizers (PS) for free-radical photopolymerization (FRP)...

Intramolecular interaction of synthetic chlorophyll heterodyads with different π-skeletons

Covalently linked zinc chlorin and zinc porphyrin/bacteriochlorin heterodyads formed methanol-locked conformers with red-shifted Qy bands as models of Chl-a and Chl-c/BChl-a(or g) dimeric species, respectively, in photosynthetic apparatuses.

Heterodimers of zinc and free-base chlorophyll derivatives co-assembled in biomimetic chlorosomal J-aggregates

Free-base chlorophyll derivatives covalently linked with their zinc complex accepted singlet excitation energy from chlorosomal self-aggregates in their co-assembly.

Push-pull pyropheophorbides for nonlinear optical imaging

Pyropheophorbide-a methyl ester (PPa-OMe) has been modified by attaching electron-donor and -acceptor groups to alter its linear and nonlinear optical properties. Regioselective bromination of the terminal vinyl position and Suzuki coupling were used to attach a 4-(N,N-diethylaminophenyl) electron-donor group. The electron-acceptor dicyanomethylene was attached at the cyclic ketone position through a Knoevenagel condensation. Four different derivatives of PPa-OMe, containing either electron-donor or electron-acceptor groups, or both, were converted to hydrophilic bis-TEG amides to generate a series of amphiphilic dyes. The absorption and emission properties of all the dyes were compared to a previously reported push-pull type porphyrin-based dye and a commercial push-pull styryl dye, FM4-64. Electrochemical measurements reveal that the electron donor group causes a greater decrease in HOMO-LUMO gap than the electron-acceptor. TD-DFT calculations on optimized geometries (DFT) of all four dyes show that the HOMO is mostly localized on the donor, 4-(N,N-diethylaminophenyl), while the LUMO is distributed around the chlorin ring and the electron-acceptor. Hyper-Rayleigh scattering experiments show that the first-order hyperpolarizabilities of the dyes increase on attaching either electron-donor or -acceptor groups, having the highest value when both the donor and acceptor groups are attached. Two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) images of the bis-TEG amide attached dyes in lipid monolayer-coated droplets of water-in-oil reveal that the TPEF and SHG involve transition dipole moments in different orientations.

What can we learn from artificial special pairs?

Plants and photosynthetic bacteria obtain their energy from sunlight or surrounding radiation. Their photosynthetic membranes are composed of a much elaborated series of antenna molecules based on chlorophylls or bacteriochlorophylls, carotenoids playing multiple roles, various electron transport accessories, and central special pairs. The latter components are the most difficult to mimic with exactitude because the structure−property relationship depends on many factors including interplanar distance, slip angle, substituents, metal, and axial ligand. To this list of factors to control with quasi-perfection, one should also add the thermal activation (i.e., temperature). Over the past 15 years or so (2001–2013), an intensive collaboration with Professor Roger Guilard (Université de Bourgogne, Dijon) dealt with elucidating the role of each parameter to provide the best design of artificial special pairs capable of responding or behaving like the natural special pairs, namely with regards with the antenna effect. The latest feature is one of the defence mechanisms slowing down the rate for the primary electron transfer from the special pair to the electron transport accessories. This review highlights the advances in this challenging area of mimicry of the photophysical events in biological systems, namely the artificial special pairs designed in our laboratory for the antenna processes.