title: Solvent-Controlled Doublet Emission of an Organometallic Gold(I) Complex with a Polychlorinated Diphenyl(4-pyridyl)methyl Radical Ligand: Dual Fluorescence and Enhanced Emission Efficiency.
abstract: A paramagnetic, luminescent organometallic gold(I) complex AuI(C6F5)(PyBTM), where PyBTM is a photostable fluorescent polychlorinated diphenyl(4-pyridyl)methyl radical, was prepared, and its crystal and electronic structures and magnetic and optical properties were investigated. Magnetic studies using electron spin resonance spectroscopy and a superconducting quantum interference device magnetometer indicated the existence of S =1/2spin per molecule, with the spin density distributed mainly on the PyBTM ligand. The complex exhibited fluorescence in CHCl3with emission peak wavelength (λem) of 619 nm and the absolute fluorescence quantum yield (ϕem) of 0.04, confirming that AuI(C6F5)(PyBTM) is the first luminescent organometallic complex with a coordinated luminescent radical. Solvent-dependent unique luminescent characteristics were observed in halogenated solvents (CCl4, CHCl3, CH2Cl2, and ClCH2CH2Cl). ϕemdecreased, and λemshifted to longer wavelengths as the polarity (dielectric constant) of the solvent increased. Notably, the complex in CCl4displayed fluorescence with ϕem= 0.23, which was quite high in radicals, while showed dual fluorescence in CH2Cl2and ClCH2CH2Cl with lifetimes of around 1 and 7 ns for two emissive components. Density functional theory (DFT) and time-dependent (TD)-DFT calculations indicated that the fluorescence occurred from an interligand charge transfer (CT) excited state in CCl4, in which the C6F5and PyBTM moieties acted as electron donor and acceptor, respectively, while the fluorescence was centered at the PyBTM ligand in the other three solvents. This method, i.e., the formation of an interligand CT state, to enhance ϕemis distinctly different from the methods reported previously. The present study revealed that a coordination bond is available for forming emissive CT excited states that lead to high ϕem, providing a novel method with greater capability for realizing highly emissive radicals.
authors.affiliation: Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Yasuyo
authors.initials: Y
authors.lastname: Ogino
authors.affiliation: Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Tetsuro
authors.identifier: http://orcid.org/0000-0001-8391-4526
authors.initials: T
authors.lastname: Kusamoto
authors.affiliation: Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Hattori
authors.affiliation: Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Shimada
authors.affiliation: Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Mizuho
authors.initials: M
authors.lastname: Tsuchiya
authors.affiliation: Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Yoshinori
authors.identifier: http://orcid.org/0000-0002-6155-2357
authors.initials: Y
authors.lastname: Yamanoi
authors.affiliation: Division of Physics, Faculty of Pure and Applied Sciences, Tsukuba Research Center for Interdisciplinary Materials Science (TIMS) &, Center for Integrated Research in Fundamental Science and Engineering (CiRfSE), University of Tsukuba , Tsukuba, Ibaraki 305-8571, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Nishibori
authors.affiliation: Japan Synchrotron Radiation Research Institute (JASRI) , Sayo-gun, Hyogo 679-5148, Japan.
authors.forename: Kunihisa
authors.initials: K
authors.lastname: Sugimoto
authors.affiliation: Department of Chemistry, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishihara