"Among the natural light-harvesting (LH) techniques, people of green sulfur and nonsulfur photosynthetic bacteria are outstanding for the reason that they lack the support of the protein matrix. Rather, these so-called chlorosomes are based solely on ""pigments"". They are self-assembled bacteriochlorophyll c, d, and e derivatives, which consist of a chlorophyll blog post skeleton bearing a 3(1)-hydroxy functional group. Chemists take into account the latter as an critical structural unit to direct the formation of light-harvesting self-assembled dye aggregates with J-type excitonic coupling. The intriguing properties of chlorosomal J-type aggregates, particularly narrow red-shifted absorption bands, compared with monomers and their capacity to delocalize and migrate excitons, have inspired extreme research pursuits toward synthetic analogues within this field.
The ultimate purpose of this exploration area will be the development of (opto-)electronic devices based on the architectural principle of chlorosomal LH systems. On this regard, the challenge is to develop tiny, functional setting up blocks with suitable substituents that are preprogrammed to self-assemble across different length scales and also to emulate functions of organic LH systems or to comprehend totally new functions beyond those found in nature. In this Account, we highlight our achievements in the past decade with semisynthetic zinc chlorins (ZnChIs) as model compounds of bacteriochlorophyllsuseful handbook obtained in the naturally most abundant chlorin precursor: chlorophyll a.
To start, we discover how supramolecular strategies involving pi-stacking, hydrogen bonding, and metal-oxygen coordination is usually made use of to design and style ZnChI-based molecular stack, tube, and liquid crystalline assemblies conducive to charge and power transport. Our style and design principle is depending on the bioinspired functionalization with the 3(one)-position of ZnChI having a hydroxy or methoxy group; the former provides rise to tubular assemblies, whereas the latter induces stack assemblies. Functionalization from the 17(2)-position with esterified hydrophilic or hydrophobic chains, dendron-wedge substituents, and chromophores having complementary optical properties such as PAK1 naphthalene bisimides (NBIs) is utilized to modulate the self-assembly of ZnChI dyes. The resulting assemblies exhibit enhanced charge transport and vitality transfer skills.
We now have applied UV/vis, circular dichroism (CD), fluorescence spectroscopy, and dynamic light scattering (DLS) to the characterization of those assemblies in answer. Additionally, we now have studied assembly morphologies by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), and cryogenic-TEM. Crystallographic approaches this kind of as powder X-ray and solid-state NMR have already been made use of to describe the exact long- and short-range packing of dyes in these assemblies. Ultimately, practical properties this kind of as charge and energy transport are actually explored by pulse radiolysis time-resolved microwave conductivity (PR-TRMC), conductive AFM, and time-resolved fluorescence spectroscopy. The design and style ideas mentioned within this Account are critical actions toward the utilization of these elements in biosupramolecular electronics and photonics within the future."