Photoinduced Energy and Electron Transfer in a ‘Two‐Point’ Bound Panchromatic, Near‐Infrared‐Absorbing Bis‐styrylBODIPY(Zinc Porphyrin)2 – Fullerene Self‐Assembled Supramolecular Conjugate

• Published in: Chemistry : a European journal 2024-08, Vol.30 (46), p.e202401892-n/a
• Main Authors: Shao, Shuai, Gobeze, Habtom B., De Silva, Imesha W., Schaffner, Jacob, Verbeck, Guido, Karr, Paul A., D'Souza, Francis
• Format: Article
• Language: English
• Subjects: Antennas; BisstyrylBODIPY; Charge separation; Conjugates; Electron transfer; Energy; Energy harvesting; Energy transfer; Fullerenes; Modular systems; Modularity; Molecular cleft; Near infrared radiation; Photoexcitation; Photosynthesis; Porphyrins; Reaction centers; Self-assembly; Two-point binding strategy; Ultrafast energy transfer; Zinc
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202401892

Structurally well‐defined self‐assembled supramolecular multi‐modular donor‐acceptor conjugates play a significant role in furthering our understanding of photoinduced energy and electron transfer events occurring in nature, e. g., in the antenna‐reaction centers of photosynthesis and their applications in light energy harvesting. However, building such multi‐modular systems capable of mimicking the early events of photosynthesis has been synthetically challenging, causing a major hurdle for its growth. Often, multi‐modularity is brought in by combining both covalent and noncovalent approaches. In the present study, we have developed such an approach wherein a π‐extended conjugated molecular cleft, two zinc(II)porphyrin bearing bisstyrylBODIPY (dyad, 1), has been synthesized. The binding of 1 via a ‘two‐point’ metal‐ligand coordination of a bis‐pyridyl fulleropyrrolidine (2), forming a stable self‐assembled supramolecular complex (1 : 2), has been established. The self‐assembled supramolecular complex has been fully characterized by a suite of physico‐chemical methods, including TD‐DFT studies. From the established energy diagram, both energy and electron transfer events were envisioned. In dyad 1, selective excitation of zinc(II)porphyrin leads to efficient singlet‐singlet excitation transfer to (bisstyrly)BODIPY with an energy transfer rate constant, kEnT of 2.56×1012 s−1. In complex 1 : 2, photoexcitation of zinc(II)porphyrin results in ultrafast photoinduced electron transfer with a charge separation rate constant, kCS of 2.83×1011 s−1, and a charge recombination rate constant, kCR of 2.51×109 s−1. For excitation at 730 nm corresponding to bisstyrylBODIPY, similar results are obtained, where a biexponential decay yielded estimated values of kCS 3.44×1011 s−1 and 2.97×1010 s−1, and a kCR value of 2.10×1010 s−1. The newly built self‐assembled supramolecular complex has been shown to successfully mimic the early events of the photosynthetic antenna‐reaction center events. A ‘two‐point’ metal‐ligand coordination approach has been developed to construct a multimodular donor‐acceptor conjugate featuring π‐connected bis zinc porphyrin‐bisstrylBODIPY and bipyridine functionalized fulleropyrrolidine. Upon full characterization of this conjugate by a suite of physico‐chemical and time‐dependent DFT studies, occurrence of ultrafast energy transfer from excited zinc porphyrin to bisstrylBODIPY and electron transfer involving C60 in the conjugate is demonstrated us