Giant Photoconductivity in NMQ[Ni(dmit)₂]

Abstract

The simple molecular salt NMQ[Ni(dmit) 2 ] (NMQ = N-methylquinolinium, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) functions as a diamagnetic insulator with an activation energy E a (dark) of 0.20 eV. However, at 300 K, it exhibits ca. 40 times higher conductivity (σ UV ) under UV irradiation [(375 Ϯ 5) nm, 15.7 mW cm -2 ] than it does under dark conditions (σ dark ). The ratio σ UV /σ dark rapidly increases with decreasing temperature and reaches ca. 880 at 200 K. From the temperature dependence of σ UV , the activation energy

Direct Control of Spin Distribution and Anisotropy in Cu-Dithiolene Complex Anions by Light

“…The remaining species is optically doped to have excited carriers, like photoconductors. "Giant photoconductivity", which possibly originates from reversible melting of charge order, has been observed by UV irradiation upon a related molecular crystalline salt [33]. The advantage of this photochemical or optical method lies in the fact that control of the crystal structure is not required at any level.…”

Dye-Sensitized Molecular Charge Transfer Complexes: Magnetic and Conduction Properties in the Photoexcited States of Ni(dmit)2 Salts Containing Photosensitive Dyes

“…This implies that CT transition occurs between cations and anions under UV-irradiation. As the CT transitions between two different components in solids produce net photocarriers and photoexcited spins at the same time [10][11][12]16], the observed photoresponse in ESR spectra accounts for the observed photoresponse in electrical behavior mentioned above. The g-values of a part of the spins on the N atoms (#3 (N) in the dark conditon in Table A2 were markedly enhanced compared with those of isolated spins on the bipyridine derivatives (g~2.00 for N atoms), indicating strong interaction with the spins having larger g-values such as those in heavy atoms and transition metals, i.e., indicating strong interaction between cations and anions.…”

“…Based on the discussion thus far, the overall relaxation time of photoexcited spins on the cations and anions is unusually prolonged to produce the observed photoresponse in ESR and conduction. Such prolonged relaxation times have been observed only in the CT complexes containing bipyridine derivatives with apparently mixed-stacking structures [10][11][12]. The mechanism can be related to the characteristic or advantage in this kind of molecular CT complexes such as CT interactions with photosensitive dyes, which would stabilize the photoexcited states.…”

“…In fact, such examples have been recently reported [10][11][12]16]. It has been demonstrated that metallic and paramagnetic properties can be realized in some CT complexes containing bipyridyl derivatives and π-acceptor molecules under UV irradiation.…”

Diradical Character of Neutral Heteroleptic Bis(1,2-dithiolene) Metal Complexes: Case Study of [Pd(Me2timdt)(mnt)] (Me2timdt = 1,3-Dimethyl-2,4,5-trithioxoimidazolidine; mnt2– = 1,2-Dicyano-1,2-ethylenedithiolate)

“…The interest of the scientific community toward bis­(1,2-dithiolene) metal complexes has been continuously increasing during the past few decades, − accompanied by a growing number of applications relying on the superconducting, − photoconducting, − magnetic, and linear and nonlinear optical properties − of this class of compounds. Bis­(1,2-dithiolene) complexes [M­(R 2 C 2 S 2 ) 2 ] q − of d 8 metal ions M x + , such as Ni II , Pd II , Pt II , and Au III , feature peculiar properties, , such as molecular planarity and the ability to exist in well-defined oxidation states q typically ranging between x – 4 and x – 2, − also assuming fractional charges in nonintegral oxidation state (NIOS) salts. , The redox noninnocence of the 1,2-dithiolene ligands (Scheme ) renders it difficult to partition the charge of the complexes between the ligands L and the central metal ion M x + . , …”