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.

Regulating the Optoelectronic Properties of Nickel Dithiolene by the Substituents: A Theoretical Study

Dithiolene-based complexes show great potential to be applied as materials for organic optoelectronic devices. In this study, we theoretically designed a series of complexes based on nickel dithiolene and its substituted derivatives, the optoelectronic properties of which were comparatively studied by density functional theory (DFT)/time-dependent density functional theory (TD-DFT). The results show that the charge injection property of nickel dithiolene complexes can be significantly improved with introduction of electron-withdrawing groups. The charge transportation property of nickel dithiolene depends on the conjugation degree of the system. The energy gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are determined by the substituents, which makes the maximum absorption wavelength red-shift from the visible to the near-infrared (NIR) region. The electron density difference graph shows that the electron transition from the ground state to the first excited state is assigned to π-π* transition mainly from HOMO to LUMO. The regularity of substituent effect revealed by us in this study will shed light on the application of nickel dithiolenes as potential optoelectronic materials.

Structural tailoring of the NIR-absorption of bis(1,2-dichalcogenolene) Ni/Pt electrochromophores deriving from 1,3-dimethyl-2-chalcogenoxo-imidazoline-4,5-dichalcogenolates

Bis(1,2-dithiolene) and (1,2-diselenolene) Ni and Pt complexes with 2-chalcogenoxo-imidazoline-4,5-dichalcogenolates show intense NIR electrochromism tunable by structural modifications.