NIR Dyes Based on [M(R,R′timdt)₂] Metal‐Dithiolenes: Additivity of M, R, and R′ Contributions To Tune the NIR Absorption (M = Ni, Pd, Pt; R,R′timdt = Monoreduced Form of Disubstituted Imidazolidine‐2,4,5‐trithione)

Abstract

With the aim of preparing new dyes for Q‐switching and/or mode‐locking Nd‐based lasers, such as Nd:YLF and Nd:YAG (emission wavelengths 1053 and 1064 nm, respectively), the syntheses of about 30 new neutral dithiolenemetal complexes belonging to the class [M(R,R′timdt)2] have been carried out [M = Ni (4a−c; 4g−j), Pd (5a−j), Pt (6a−j); R,R′timdt = monoreduced form of disubstituted imidazolidine‐2,4,5‐trithione]. The examination of the effects induced on the intense NIR absorption by changing M, R, and R′ has allowed for the recognition of the additive contributions (Δλ) of the central metal ion and of the substituents to the λM,R,R′max position of the NIR absorption maximum, which is in the region of 1000 nm. The high Δλ values due to aromatic substituents have been elucidated by means of Hybrid‐DFT calculations performed on the model compound [Ni(H2timdt)(Ph,H‐timdt)]. Both the λM,R,R′max values and the molar extinction coefficients vary with the solvent. Complex 5f [M = Pd, R = p‐F‐C6H4, R′ = m,m,p‐(MeO)3‐C6H2] shows that it has been possible to exactly match the emission wavelength of the Nd:YLF and Nd:YAG lasers in chloroform and toluene, respectively (by choosing the appropriate combination of metal ion and substituents). The highest extinction coefficient ever observed for a metal‐dithiolene (120000 M−1·cm−1 at 1034 nm in toluene) is also reported for complex 6g [M = Pt, R = p‐F‐C6H4, R′ = naphthyl]. Time‐resolved absorption dynamics measurements on 5f have also been carried out by means of pump‐probe experiments, with a picosecond Nd:YAG Q‐switched and mode‐locked laser. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A Theoretical Investigation of the Donor Ability of [M(R,R′timdt)2] Dithiolene Complexes towards Molecular Diiodine (M = Ni, Pd, Pt; R,R′timdt = Formally Monoreduced Disubstituted Imidazolidine‐2,4,5‐trithione)

“…[16Ϫ24] Hybrid-DFT [18,19,23] and very recent TD-DFT calculations [21,24] confirmed that the tight HOMOϪLUMO energy gap is responsible for the low-energy NIR transition falling at about 1000 nm (extinction coefficients as high as 120000 …”

“…[17] Synthesis of [M(R,RЈtimdt) 2 ]·nI 2 Adducts: The dithiolene complexes [M(R,RЈtimdt) 2 ] (M ϭ Ni, Pd, Pt; R ϭ RЈ ϭ Et; R ϭ Me, RЈ ϭ iPr) were synthesised as reported previously. [18,19,23] They (15Ϫ30 mg) were then reacted with weighed amounts of diiodine in 1:1, 1:2, 1:5, and 1:10 molar ratios, in 30 mL of CHCl 3 /hexane mixtures (1:3 v/v) according to the procedure described previously for the reaction between 8 and Br 2 . [22] The stoichiometric ratios of the final products summarised in Scheme 1 were calculated on the basis of the elemental analyses.…”

“…[40] Thus, the energy of the NIR transition can be estimated as the one-electron energy difference ∆ε between the HOMO and the LUMO. [18,19,21,23,24] At any rate, although the previous calculations accounted nicely for the spectroscopic and electrochemical properties of the title dithiolene complexes, the MϪS bond lengths were systematically overestimated. Subsequently, we reported relativistic TD-DFT calculations which highlighted how the trend in the metalϪsulfur distances is affected by relativistic effects.…”

“…[23] In addition, contrary to most dithiolene complexes, and in particular to their dmit analogues, neutral [M(R,RЈtimdt) 2 ] complexes behave as donors towards molecular acceptors, and some of the authors of this paper have reported the reaction between [Ni(iPr 2 timdt) 2 ] (7) and molecular diiodine, leading to the CT adducts 7·2I 2 2 ]) has been reported, [18] while the reactivity of Pt dithiolene complexes towards diiodine has not been explored to date. In order to rationalize the donor ability of neutral [M(R,RЈtimdt) 2 ] complexes, we have now carried out a study on the products of the reactions between [M(Et 2 timdt) 2 ] and [M(Me,iPrtimdt) 2 ] (M ϭ Ni, Pd, Pt) and molecular I 2 in several molar ratios (Scheme 1).…”

“…A few years ago, we reported [18,19,23] DFT [33,34] calculations performed with the Gaussian 98 package [35] on [M(H 2 timdt) 2 ] model complexes [M ϭ Ni (10), Pd (11), Pt (12); R ϭ RЈ ϭ H in Scheme 1] using the three-parameter [36] hybrid B3LYP functional (based on the gradientcorrected Becke exchange functional [37] along with the Lee, Yang and Parr correlation functional [38] ), and the LanL2DZ basis set (BS) with Effective Core Potentials (ECP) [39] for the central metal ion. With the results of these calculations it was possible to explain the trend in the NIR absorption maxima experimentally found on changing the central metal ion [λ max (Ni) ഠ λ max (Pt) Ͻ λ max (Pd)], and the electrochemical behaviour of [M(R,RЈtimdt) 2 ] complexes compared to other neutral dithiolenes, such as 1Ϫ3 and 4Ϫ6.…”