DOI: 10.1002/chem.201103843 Preparation and Photophysical and Photoelectrochemical Properties of a Covalently Fixed Porphyrin–Chemically Converted Graphene Composite Tomokazu Umeyama, [a, b] Junya Mihara, [a] Noriyasu Tezuka, [a] Yoshihiro Matano, [a] Kati Stranius, [c] Vladimir Chukharev, [c] Nikolai V. Tkachenko,* [c] Helge Lemmetyinen, [c] Kei Noda, [d] Kazumi Matsushige, [d] Tetsuya Shishido, [a] Zheng Liu, [e] Kaori Hirose-Takai, [e] Kazu Suenaga, [e] and Hiroshi Imahori* [a, f, g] Introduction Graphene, a material that has a two-dimensional atomic layer consisting of sp 2 -hybridized carbon, has attracted in- tense interest in recent years owing to its unique structure and electronic and optical properties. [1] In particular, gra- phene is a zero-bandgap semiconductor with high carrier mobilities and concentrations, and shows nearly ballistic transport at room temperature. [2] Several methods have been used to prepare graphene: mechanical exfoliation of graphite, [3] epitaxial growth, [4] chemical vapor deposition (CVD), [5] solvent dispersion of graphite, [6] and reduction of graphene oxide (GO) [7] generated by oxidation of graphite using strong oxidants. [8] Among them, chemical reduction of GO is a feasible technique for access to graphene-based ma- terials on a large scale. [7, 9] Although GO is electrically insu- lating due to the disrupted sp 2 -bonding networks, the reduc- tion treatments can restore the p network significantly and Abstract: Chemically converted gra- phene (CCG) covalently linked with porphyrins has been prepared by a Suzuki coupling reaction between io- dophenyl-functionalized CCG and por- phyrin boronic ester. The covalently linked CCG–porphyrin composite was designed to possess a short, rigid phen- ylene spacer between the porphyrin and the CCG. The composite material formed stable dispersions in DMF and the structure was characterized by spectroscopic, thermal, and microscopic measurements. In steady-state photolu- minescence spectra, the emission from the porphyrin linked to the CCG was quenched strongly relative to that of the porphyrin reference. Fluorescence lifetime and femtosecond transient ab- sorption measurements of the porphy- rin-linked CCG revealed a short-lived porphyrin singlet excited state (38 ps) without yielding the porphyrin radical cation, thereby substantiating the oc- currence of energy transfer from the porphyrin excited state to the CCG and subsequent rapid decay of the CCG excited state to the ground state. Consistently, the photocurrent action spectrum of a photoelectrochemical device with a SnO 2 electrode coated with the porphyrin-linked CCG exhib- ited no photocurrent response from the porphyrin absorption. The results ob- tained here provide deep insight into the interaction between graphenes and p-conjugated systems in the excited and ground states. Keywords: energy transfer · gra- phene · photophysics · porphyri- noids · time-resolved spectroscopy [a] Dr. T. Umeyama, J. Mihara, N. Tezuka, Prof.Dr. Y. Matano, Prof. Dr. T. Shishido, Prof. Dr. H. Imahori Department of Molecular Engineering Graduate School of Engineering Kyoto University, Nishikyo-ku Kyoto 615-8510 (Japan) Fax: (+ 81) 75-383-2571 E-mail : imahori@scl.kyoto-u.ac.jp [b] Dr. T. Umeyama PRESTO Japan Science and Technology Agency (JST) 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan) [c] K. Stranius, Dr. V. Chukharev, Prof.Dr. N.V. Tkachenko, Prof. Dr. H. Lemmetyinen Department of Chemistry and Bioengineering Tampere University of Technology P.O. Box 541, 33101 Tampere(Finland) Fax: (+ 358) 3-3115-2108 E-mail : nikolai.tkachenko@tut.fi [d] Dr. K. Noda, Prof. Dr. K. Matsushige Department of Electronic Science and Engineering Graduate School of Engineering Kyoto University, Nishikyo-ku Kyoto 615-8510 (Japan) [e] Dr. Z. Liu, K. Hirose-Takai, Prof. Dr. K. Suenaga National Institute of Advanced Industrial Science and Technology (AIST) AIST Central 5, Tsukuba, 305-8565 (Japan) [f] Prof. Dr. H. Imahori Institute for Integrated Cell-Material Sciences (WPI iCeMS) Kyoto University Nishikyo-ku, Kyoto 615-8510 (Japan) [g] Prof. Dr. H. Imahori Fukui Institute for Fundamental Chemistry Kyoto University Sakyo-ku, Kyoto 606-8103 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201103843.  2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim Chem. Eur. J. 2012, 18, 4250 – 4257 4250