Uncommon Optical Properties and Silver‐Responsive Turn‐Off/On Luminescence in a Pt^II Heteroleptic Dithiolene Complex

Abstract

Complex [Pt(iPr pipdt)(Quinoxdt)] (iPr pipdt=1,4-diisopropyl-piperazine-2,3-dithione; Quinoxdt=[1,4]dithiino[2,3-b]quinoxaline-2,3-dithiolate) exhibits a remarkable green emission at 570 nm (room temperature), which is above the lowest excited state. The complex is characterized by negative solvatochromism as well as a high second-order polarizability. Addition of Ag ions induces 1) hypsochromic shift of the lowest frequencies and 2) reversible quenching of luminescence. The corresponding Ni and Pd complexes have also been prepared and investigated to assist interpretation of optical properties within the triad. Computational studies based on DFT and time-dependent DFT highlight the electronic properties of [Pt(iPr pipdt)(Quinoxdt)]. The preferential site of interaction between the Pt complex and incoming Ag is evidenced by the shape of the Fukui functions, pointing to the thiolic sulfur and platinum atoms as the most reactive sites towards a soft cation. Calculated optical properties are in agreement with experimental findings. This study sheds light on the structure-property relationship for this class of compounds.

An excursion in the second-order nonlinear optical properties of platinum complexes

“…A related platinum-dithiolene complex (15), bearing a quinoxaline-dithiolate and diisopropylpiperazine-dithione as donor and acceptor ligands, respectively, also shows a significant µβ1.907EFISH value (-4280 × 10 -48 esu). As expected from the above presented dithiolene complexes, substitution of Pt by Ni (µβ1.907EFISH value = -1490 × 10 -48 esu) or Pd (µβ1.907EFISH value = -1970 × 10 -48 esu) leads to a lower response [65].…”

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

“…More specifically, the HOMO is mainly localized on the dithiolate system, whereas the LUMO is mainly localized on the dithio-oxamidate fragment, in agreement with previous findings for similar systems. 10,11,12,19,23,26 there is a good agreement between the calculated and experimental visible spectra for all of the compounds (Figure S11). The low energy absorption band can be associated almost exclusively to an HOMO→LUMO transition (Tables S2-S6).…”

“…This phenomenon was ascribed to a change in the nature of the involved energy levels, where the formerly emissive quinoxdt-based LUMO+1 changed to a metal -sulphur orbital with antibonding character in presence of silver. 23 Instead, in 6 the overall sequence of MOs is not affected by the interaction with Ag + . As a consequence, the observed blue shift is consistent with the increase of the energy gap between the involved energy states (Figure 7d and S17).…”

Anti-Kasha Conformational Photoisomerization of a Heteroleptic Dithiolene Metal Complex Revealed by Ultrafast Spectroscopy

“…In the former, the electron density is mainly centered on the quinoxaline moiety (LUMO + 1), whereas in the latter, it is mainly localized on the MBAdto moiety (LUMO). 15,16 The internal conversion (IC) between these two states is therefore characterized by a strong ligandto-ligand CT (LL'CT) character. This condition should slow down the IC process to ∼10 ps, 15 making the radiative decay of the higher excited state detectable.…”

“…Recently, novel platinum dithiolene complexes, both homo-and hetero-leptic, with quinoxdt (=[4′,5′:5,6]­[1,4]­dithiino­[2,3- b ]­quinoxaline-1′,3′dithiolato) − have shown a peculiar anti-Kasha behavior displaying photoluminescence only upon excitation of the higher electronic states and no emission when exciting in the lowest electronic absorption band . In heteroleptic d 8 -metal dithiolene complexes (Figure S1) fine modulation of ligands affords planar and low-energy-gap chromophores consisting of a π-acceptor (A) and a π-donor (D) ligand connected in a square-planar coordination by the metal, working as a suitable dπ-bridge for the D–A charge transfer (CT) transition.…”