High Second-Order NLO Response Exhibited by the First Example of Polymeric Film Incorporating a Diimine–Dithiolate Square-Planar Complex: The [Ni(o-phen)(bdt)]

Abstract

A novel square-planar diimine−dithiolate nonlinear optical (NLO) chromophore, the complex [Ni(ophen)(bdt)] (1), is reported in this paper (o-phen = dianion of 1,2-phenylendiamina; bdt =1,2-benzenedithiolate). This compound has been fully characterized by single-crystal X-ray diffraction, UV−vis−NIR spectroscopy, cyclic voltammetry, DFT, and TD-DFT calculations. 1 crystallizes in the P 21 space group and shows an almost planar molecule. The cyclic voltammetry measurements present an irreversible anodic peak at 0.87 V and reversible and quasi-reversible reduction waves at −0.35 and −1.13 V, respectively. A medium-intense (ε = 1.91 × 10 4 mol −1 dm 3 cm −1 ) absorption with a maximum at 728 nm appears in the UV−vis−NIR spectrum. The molecular secondorder NLO properties of 1 have been measured by the electric field induced second-harmonic generation technique in DMF solution, giving values of −1000 × 10 −48 esu for μβ 1.907 and −356 × 10 −48 esu for μβ 0 . Furthermore, remarkable solid-state responses have been measured for polymeric films of 1. Indeed, this complex has been embedded into poly(methyl methacrylate) poled films showing high NLO response (d 33 = 1.90 ± 0.38 pm/V), higher than those previously reported for similar push−pull metal complexes. Moreover, 1 represents the first example of a diimine−dithiolate chromophore incorporated into a NLO-active film.

Design of nickel donor–acceptor dithiolenes for 2nd order nonlinear optics: an experimental and computational study

“…[3][4][5] Square-planar heteroleptic d 8 -metal-dithiolene complexes, have been shown to work as tunable second-order NLO chromophores. [6][7][8][9][10][11] The requirement to obtain this property is achieved with the presence of two ligands occurring in formally different oxidation states, one reducing (dianionic = dithiolate, electron Donor = D), and the other oxidizing (neutral = dithione or diimine, electron Acceptor = A), with the metal (M) acting as a -bridge. These noncentrosymmetric molecules (D-M-A), exhibit an absorption peak in the visible spectral region, which is tunable with the HOMO-LUMO energy gap.…”

“…To overcome this drawback, NLO chromophores are embedded into polymeric poled films. 11,14,42 To obtain a sufficiently stable second-harmonic generation (SHG) signal of thin films, chromophores are required to possess suitable properties (good solubility, thermal stability, no aggregation for stacking) to be incorporated homogeneously in the host matrix of poled film and remain so within the time. To meet these requirements, we are investigating square-planar heteroleptic d 8 -metaldithiolene 6,[12][13][14][15] characterized by remarkable high negative molecular first hyperpolarizability both at the molecular level and in the bulk.…”

Static and Dynamic Electron Correlation in the Ligand Noninnocent Oxidation of Nickel Dithiolates

“…Metal dithiolates are highly tunable , and have a wide range of applications and properties, including catalysis in water splitting and olefin transformations, − proton-coupled electron transfer, nonlinear optical responses, and molecular conductivity and magnetization. − We examine the oxidation series of bis­(ethylene-1,2-dithiolato) nickel or [Ni­(edt) 2 ] (−2,–1,0) , where edt is ethylene dithiolate ligand (Figure ), which is paradigmatic of other more substituted nickel dithiolate complexes. , …”