title: Molecular photoconductor with simultaneously photocontrollable localized spins.
abstract: UV irradiation reversibly switches a new insulating and nonmagnetic molecular crystal, BPY[Ni(dmit)(2)](2) (BPY = N,N'-ethylene-2,2'-bipyridinium; Ni(dmit)(2) = bis(1,3-dithiole-2-thione-4,5-dithiolato)nickelate(III)), into a magnetic conductor. This is possible because the bipyridyl derivative cations (BPY(2+)) trigger a photochemical redox reaction in the crystal to produce a change of ∼10% in the filling of the Ni(dmit)(2) valence band, leaving localized spins on the BPY themselves. In the dark, almost all of the BPY molecules are closed-shell cations, and most of the Ni(dmit)(2) radical anions form spin-singlet pairs; thus, this material is a diamagnetic semiconductor. Under UV irradiation, a photocurrent is observed, which enhances the conductivity by 1 order of magnitude. Electron spin resonance measurements indicate that the UV irradiation reversibly generates carriers and localized spins on the Ni(dmit)(2) and the BPY, respectively. This high photoconductivity can be explained by charge transfer (CT) transitions between Ni(dmit)(2) and BPY in the UV region. In other words, the photoconduction and "photomagnetism" can be described as reversible optical control of the electronic states between an ionic salt (BPY(2+)/[Ni(dmit)(2)](-), nonmagnetic insulator) and a CT complex (BPY(2(1-δ)+)/[Ni(dmit)(2)]((1-δ)-) (δ ≈ 0.1), magnetic conductor) in the solid state.
authors.affiliation: Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan. tnaito@ehime-u.ac.jp
authors.forename: Toshio
authors.initials: T
authors.lastname: Naito
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Karasudani
authors.forename: Shigeki
authors.initials: S
authors.lastname: Mori
authors.forename: Keishi
authors.initials: K
authors.lastname: Ohara
authors.forename: Kensuke
authors.initials: K
authors.lastname: Konishi
authors.forename: Takahiro
authors.initials: T
authors.lastname: Takano
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Inabe
authors.forename: Sadafumi
authors.initials: S
authors.lastname: Nishihara
authors.forename: Katsuya
authors.initials: K
authors.lastname: Inoue
mesh_terms: D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D055668:Photochemical Processes; D014466:Ultraviolet Rays
chemical_list: D009942:Organometallic Compounds; D009532:Nickel