Strategy to Attain Remarkably High Photoinduced Charge- Separation Yield of Donor−Acceptor Linked Molecules in Biological Environment via Modulating Their Cationic Moieties Ning Cai, †,‡,¶ Yuta Takano, †,¶ Tomohiro Numata, §,∥ Ryuji Inoue, § Yasuo Mori,* ,∥ Tatsuya Murakami, †,⊥ and Hiroshi Imahori* ,†,# † Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan ‡ School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China § Department of Physiology, Graduate School of Medical Sciences, Fukuoka University, Nanakuma 7-45-1, Johnan-ku, Fukuoka 814-0180, Japan ∥ Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan ⊥ Department of Biotechnology, Faculty of Engineering, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan # Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan *S Supporting Information ABSTRACT: A series of ferrocene−porphyrin−fullerene linked triads (TC1, TC2, and TC4) possessing different numbers of cationic moieties were designed and prepared to achieve a high photoinduced charge-separation (CS) yield in a biological environment. In a solution, TC1, TC2, and TC4 demonstrated the formation of their nanoaggregates. Among the new triads, TC4 possessing the four cationic moieties exhibited the formation of a long-lived charge-separated state with the highest CS yield (86%) ever reported in cell membrane-like lipid bilayers, which is consistent with the largest change in the cell membrane potential of PC12 cells via the photoinduced CS under green light illumination. The highest CS yield in the biological environment can be rationalized by the well-tailored balance in hydrophobicity and hydrophilicity of TC4. This finding provides a strategy to improve greatly the photoinduced charge-separation yield of donor− acceptor linked molecules in the biological environment and also will be informative for extracting the full potential of the photoinduced charge-separated state toward biological applications. ■ INTRODUCTION Photoinduced electron-transfer (PET) reactions are a key process occurring in natural photosynthesis and organic photovoltaics. 1−4 PET between an electron donor and an acceptor results in formation of the corresponding donor radical cation and acceptor radical anion which can induce local electric field or drive oxidation and reduction reactions, respectively. 5 Recent synthetic efforts have been devoted to establishing highly efficient artificial donor−acceptor (D−A) systems in which PET is optimized in terms of a photoinduced charge- separation (CS) yield and lifetime toward efficient conversion of light energy into chemical or electrical energy in organic solvents or in solid films. 6,7 In comparison, few PET reactions of synthetic compounds were studied in biocompatible mediums, such as highly polar aqueous solutions or lipid bilayers. 8−14 Taking into account the importance of PET in a biological environment, especially photoinduced CS in photo- synthetic reaction centers and potential applications of PET to control biological functions, 15−17 nanomaterials and organic compounds that utilize PET reactions have recently captured considerable attention. 14,18,19 The exclusive use of PET is also expected to reduce undesirable side effects which would diminish the therapeutic effects, e.g., generation of harmful singlet oxygen by photoinduced energy transfer (PEN). 20 Nevertheless, the preceding CS yield and lifetime in D−A systems have not yet been sufficiently high and long, respectively, to utilize full potential of PET in artificial and biological membranes, although they have been achieved in solutions. 21,22 For instance, to the best of our knowledge, the Received: May 10, 2017 Revised: July 6, 2017 Article pubs.acs.org/JPCC © XXXX American Chemical Society A DOI: 10.1021/acs.jpcc.7b04466 J. Phys. Chem. C XXXX, XXX, XXX−XXX