Exciton delocalization in a fully synthetic DNA-templated bacteriochlorin dimer

• Published in: Physical chemistry chemical physics : PCCP Vol. 25; no. 41; pp. 28437 - 28451
• Main Authors: Mass, Olga A, Watt, Devan R, Patten, Lance K, Pensack, Ryan D, Lee, Jeunghoon, Turner, Daniel B, Yurke, Bernard, Knowlton, William B
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 25.10.2023; Royal Society of Chemistry (RSC); The Royal Society of Chemistry
• Subjects: BASIC BIOLOGICAL SCIENCES; Chemistry; Computing Methodologies; Dimers; Dipole moments; DNA; Excitation spectra; Excitons; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Light-Harvesting Protein Complexes - chemistry; Modularity; Optoelectronics; Photosynthesis; Photosynthetic Reaction Center Complex Proteins - chemistry; Pigments; Proteins; Quantum computing; Quantum Theory; Room temperature; Structural stability
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp01634j

A bacteriochlorophyll a ( Bchl a ) dimer is a basic functional unit in the LH1 and LH2 photosynthetic pigment-protein antenna complexes of purple bacteria, where an ordered, close arrangement of Bchl a pigments-secured by noncovalent bonding to a protein template-enables exciton delocalization at room temperature. Stable and tunable synthetic analogs of this key photosynthetic subunit could lead to facile engineering of exciton-based systems such as in artificial photosynthesis, organic optoelectronics, and molecular quantum computing. Here, using a combination of synthesis and theory, we demonstrate that exciton delocalization can be achieved in a dimer of a synthetic bacteriochlorin ( BC ) featuring stability, high structural modularity, and spectral properties advantageous for exciton-based devices. The BC dimer was covalently templated by DNA, a stable and highly programmable scaffold. To achieve exciton delocalization in the absence of pigment-protein interactions critical for the Bchl a dimer, we relied on the strong transition dipole moment in BC enabled by two auxochromes along the Q y transition, and omitting the central metal and isocyclic ring. The spectral properties of the synthetic "free" BC closely resembled those of Bchl a in an organic solvent. Applying spectroscopic modeling, the exciton delocalization in the DNA-templated BC dimer was evaluated by extracting the excitonic hopping parameter, J to be 214 cm −1 (26.6 meV). For comparison, the same method applied to the natural protein-templated Bchl a dimer yielded J of 286 cm −1 (35.5 meV). The smaller value of J in the BC dimer likely arose from the partial bacteriochlorin intercalation and the difference in medium effect between DNA and protein. We synthesized a de novo bacteriochlorin and created its dimer covalently attached to DNA. According to the spectral properties evaluated by modeling, the bacteriochlorin dimer showed exciton delocalization comparable to the natural Bchl a dimer.