Artificial Photosynthetic Reaction Center with a Coumarin-Based Antenna System

• Published in: The journal of physical chemistry. B 2013-09, Vol.117 (38), p.11299-11308
• Main Authors: Garg, Vikas, Kodis, Gerdenis, Liddell, Paul A, Terazono, Yuichi, Moore, Thomas A, Moore, Ana L, Gust, Devens
• Format: Article
• Language: English
• Subjects: Antennas; Applied sciences; Biocompatible Materials - chemistry; Biocompatible Materials - metabolism; Coumarin; Coumarins - chemistry; Direct power generation; Electron Transport; Energy; Energy Transfer; Exact sciences and technology; Excitation; Fullerenes; Natural energy; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosynthetic Reaction Center Complex Proteins - metabolism; Porphyrins; Porphyrins - chemistry; Quantum Theory; Solar energy; Spectrometry, Fluorescence; Sunlight; Time Factors
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp402265e

In photosynthesis, sunlight is absorbed mainly by antenna chromophores that transfer singlet excitation energy to reaction centers for conversion to useful electrochemical energy. Antennas may likewise be useful in artificial photosynthetic systems that use sunlight to make fuels or electricity. Here, we report the synthesis and spectroscopic properties of a molecular hexad comprising two porphyrin moieties and four coumarin antenna chromophores, all organized by a central hexaphenylbenzene core. Light absorbed by any of the coumarins is transferred to a porphyrin on the 1–10 ps time scale, depending on the site of initial excitation. The quantum yield of singlet energy transfer is 1.0. The energy transfer rate constants are consistent with transfer by the Förster dipole–dipole mechanism. A pyridyl-bearing fullerene moiety self-assembles to the form of the hexad containing zinc porphyrins to yield an antenna–reaction center complex. In the resulting heptad, energy transfer to the porphyrins is followed by photoinduced electron transfer to the fullerene with a time constant of 3 ps. The resulting P•+–C60 •– charge-separated state is formed with an overall quantum yield of 1.0 and decays with a time constant of 230 ps in 1,2-difluorobenzene as the solvent.