Insight into the Properties of Heteroleptic Metal Dithiolenes: Multistimuli Responsive Luminescence, Chromism, and Nonlinear Optics

Abstract

A comprehensive investigation of the functional properties of heteroleptic Donor-M-Acceptor dithiolene Bu4N[M II (L1)(L2)] complexes is presented (M = Pd, Pt). The acceptor L1 consists in the chiral (R)-(+)α-methylbenzyldithio-oxamidate: (R)-α-MBAdto; the donor L2 is the 2-thioxo-1,3-dithiole-4,5-dithiolato (dmit) in 1 (Pd), and 2 (Pt), the 1,2dicarbomethoxyethylene dithiolate (ddmet) in 3 (Pd), and 4 (Pt), or the[4′,5′:5,6][1,4]dithiino[2,3-b]quinoxaline-1′,3′dithiolato (quinoxdt) in 5 (Pd), and 6 (Pt). L1 is capable to undergo proton exchange and to promote crystals formation in noncentrosymmetric space groups. L2 has different molecular structures while maintaining similar electrodonating capability. Thanks to the ligands' synergy, 1-6 behave as H + and Ag + switchable linear chromophores. Moreover, the compounds exhibit H + -switchable second-order NLO response in solution, which is maintained in the bulk for 1, 3 and 4 when embedded into PMMA poled matrix. 5 and 6 show unique anti-Kasha H + and Ag + tunable colored emission originating from the quinoxdt ligand. The correlation between the electronic structure and properties is performed through Density Functional Theory (DFT) and time-dependent DFT calculations.

Introduction of a mesityl substituent on pyridyl rings as a facile strategy for improving the performance of luminescent 1,3-bis-(2-pyridyl)benzene platinum(ii) complexes: a springboard for blue OLEDs

“…53,54,58,64,65 The C1-Pt1-Cl1 axis is almost linear [179.6(1)1], whereas N11-Pt1-N31 is more distorted at 161.9(1)1, as a consequence of the chelate ring strain. The torsion angle between the mesityl groups and the pyridines is 62.7/60.7(5) and 61.6(5)/61.7 (5). Interestingly, the shortest PtÁ Á ÁPt distance is 8.59 Å (Fig.…”

“…Platinum complexes have attracted much attention for many applications such as nonlinear optics, 1–6 bioimaging, 7–14 sensing, 15–17 and electroluminescent devices. 18–38 Indeed, among a large number of organometallic materials, phosphorescent platinum( ii ) complexes have gained interest due to the important spin–orbit coupling associated with the metal which promotes intersystem crossing, and therefore the emission of light from triplet excited states, a behavior that is further improved by the presence of platinum–carbon bonds.…”

Progress and perspectives on strategies to control photochemical properties in Metallo-Dithiolene Donor-Acceptor systems

“…showing the capability of the novel derivatives to respond to external stimuli (protons, silver ions, and light-irradiation) to obtain multifunctional linear and nonlinear chromophores will be presented [31][32][33][34][35]. Promising and less promising results in the production of 2 nd NLO-active materials where chromophores are embedded into polymeric PMMA (PolyMethylMethAcrylate) poled films or form crystals belonging to non-centrosymmetric point groups are also here shortly discussed.…”

“…During the cooling process and after the removal of the electric field, the SHG signal is monitored as a function of time and temperature, to check whether or not reorientation of the chromophores within the polymeric matrix occurs in the explored time and temperature range. This technique has been employed on thin films of [NiA2-Dn] (A2 = Bz2pipdt, n = 3-6) [33] and of Bu4N[PdA1D1]; Bu4N[PdA1D4] and Bu4N[PtA1D4] [35] dispersed in PMMA matrix. The SHG signals, negligible at room temperature, reach a maximum value as the temperature is increased around Tg of the PMMA and the electric field applied.…”

“…Commonly d 8 metal heteroleptic dithiolene complexes do not exhibit luminescent properties, neither in solution at room temperature nor in glassy solvents at 77 K, with the exception of those containing the quinoxdt donor (D2). It has been found that both the homoleptic radical [Pt(D2)2] - [40] and heteroleptic [PtA1D2] - [35] and [PtA2D2] [32] complexes are emissive in solution at room temperature and, remarkably, the observed emission falls above the energy of the lowest-energy absorption, pointing to an "anti-Kasha" behaviour [41,42] (Kasha's Rule: The level of a given multiplicity is the lowest excited level of that multiplicity). The origin of this peculiar emissive behaviour is ascribed to the D2 ligand and in particular to the sequence and localization of the FOs as calculated from density functional theory (DFT) and schematized in Figure 11a.…”