Giant Photoconductivity in NMQ[Ni(dmit)2]

A Semiconductive Nature of Bis(dithiolato)nickelate Radical Salt Exhibiting Broadband Photoconduction

The fractional oxidation state [M(dmit)₂] (dmit^2- = 2-thioxo-1, 3-dithiole-4, 5-dithiolate) salts have long attracted attention in the molecular metal area owing to high conductivity and even superconductivity. In this study, we achieved a mixed-valence salt (1) of [Ni(dmit)₂]^0.5- with monovalent 1,3-N,N-dimethyl-imidazolium (DiMIm⁺) by a solvent evaporation approach under ambient conditions. The mixed valence of [Ni(dmit)₂]^0.5- has been characterized by an analysis of the IR spectrum and crystal structure. In the crystal structure of 1, two [Ni(dmit)₂]^0.5- anions overlap in an eclipsed mode to form a [Ni(dmit)₂]₂^1- dimer, featuring a radical bearing an S = 1/2 spin; the dimeric radicals stack into a column along the b axis, and the adjacent columns connect together via the lateral-to-lateral S···S contacts along the a axis, and through the head-to-head S···S contacts along the [101] direction. Salt 1 shows the magnetic behavior of an S = 1/2 Heisenberg antiferromagnetic uniform linear chain with J/k_B = -47.5(4) K and a semiconducting feature with σ = 2.52 × 10^-3 S cm^-1 at 293 K, 2.32 × 10^-2 S cm^-1 at 373 K, and E_a = 0.22 eV, as well as broadband photoconductivity under irradiation of green and white lights. This study suggests the possibility of designing new photoconductors based on the mixed-valence [Ni(dmit)₂]^0.5- salt.

Modern History of Organic Conductors: An Overview

This short review article provides the reader with a summary of the history of organic conductors. To retain a neutral and objective point of view regarding the history, background, novelty, and details of each research subject within this field, a thousand references have been cited with full titles and arranged in chronological order. Among the research conducted over ~70 years, topics from the last two decades are discussed in more detail than the rest. Unlike other papers in this issue, this review will help readers to understand the origin of each topic within the field of organic conductors and how they have evolved. Due to the advancements achieved over these 70 years, the field is nearing new horizons. As history is often a reflection of the future, this review is expected to show the future directions of this research field.

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 reaction of the bis(1,2-dithiolene) complex [Pd(Me₂timdt)₂] (1; Me₂timdt^•– = monoreduced 1,3-dimethyl-2,4,5-trithioxoimidazolidine) with Br₂ yielded the complex [Pd(Me₂timdt)Br₂] (2), which was reacted with Na₂mnt (mnt^2– = 1,2-dicyano-1,2-ethylenedithiolate) to give the neutral mixed-ligand complex [Pd(Me₂timdt)(mnt)] (3). Complex 3 shows an intense solvatochromic near-infrared (NIR) absorption band falling between 955 nm in DMF and 1060 nm in CHCl₃ (ε = 10700 M^–1 cm^–1 in CHCl₃). DFT calculations were used to elucidate the electronic structure of complex 3 and to compare it with those of the corresponding homoleptic complexes 1 and [Pd(mnt)₂] (4). An in-depth comparison of calculated and experimental structural and vis–NIR spectroscopic properties, supported by IEF-PCM TD-DFT and NBO calculations, clearly points to a description of 3 as a dithione-dithiolato complex. For the first time, a broken-symmetry (BS) procedure for the evaluation of the singlet diradical character (DC) of heteroleptic bis(1,2-dithiolene) complexes has been developed and applied to complex 3. The DC, predominant for 1 (n_DC = 55.4%), provides a remarkable contribution to the electronic structures of the ground states of both 3 and 4, showing a diradicaloid nature (n_DC = 24.9% and 27.5%, respectively). The computational approach developed here clearly shows that a rational design of the DC of bis(1,2-ditiolene) metal complexes, and hence their linear and nonlinear optical properties, can be achieved by a proper choice of the 1,2-dithiolene ligands based on their electronic structure.

The reaction of [Pd(Me₂timdt)₂] (1; Me₂timdt^•− = monoreduced 1,3-dimethyl-2,4,5-trithioxoimidazolidine) with Br₂ yielded [Pd(Me₂timdt)Br₂] (2), which was reacted with Na₂mnt (mnt²⁻ = 1,2-dicyano-1,2-ethylenedithiolate) to give [Pd(Me₂timdt)(mnt)] (3), showing an intense solvatochromic near-infrared (NIR) absorption band. The singlet diradical character (DC), predominant for 1, provides a remarkable contribution to the ground states of 3 and 4. A rational design of the DC of bis(1,2-dithiolene) complexes can be achieved by a proper choice of the 1,2-dithiolene ligands.

Photoconducting Devices with Response in the Visible-Near-Infrared Region Based on Neutral Ni Complexes of Aryl-1,2-dithiolene Ligands

Metal bis(1,2-dithiolene) complexes belonging to the class [Ni(Ar-edt)₂]^x- [Ar-edt^2- = arylethylene-1,2-dithiolate; Ar = phenyl, (1^x-), 2-naphthyl (2^x-); x = 0 and 1] were fully characterized by NMR, UV-visible-near-infrared (UV-vis-NIR), diffuse reflectance, and FT-IR spectroscopy, as well as cyclic voltammetry and single-crystal X-ray diffraction analysis. These complexes have emerged as new photoconducting materials that allowed for the development of a prototype of photodetectors with response in the vis-NIR region. The photodetecting devices showed in some cases quantum efficiencies orders of magnitude higher than those of previously reported 1,2-dithiolene systems.