Visible Light Absorption and Long-Lived Excited States in Dinuclear Silver(I) Complexes with Redox-Active Ligands

Abstract

Well-defined dinuclear silver­(I) complexes have been targeted for applications in catalysis and materials chemistry, and the effect of close silver–silver interactions on electronic structure remains an area of active inquiry. In this study, we describe the synthesis, structure, and photophysical properties of dimeric silver complexes featuring a redox-active naphthyridine diimine ligand. Unusually for silver­(I), these complexes display absorption features in the visible region due to metal–metal to ligand charge transfer (MMLCT) transitions, which arise from the combination of close silver–silver interactions and low-lying ligand π* orbitals. The complexes’ photophysical properties are explored via a combination of spectroscopic and computational studies, revealing MMLCT excited state lifetimes that exceed 1 μs. These results portend previously unforeseen applications of silver­(I) dimers in visible light absorption and excited state reactivity.

Ditopic Phosphide Oxide Group: A Rigidifying Lewis Base to Switch Luminescence and Reactivity of a Disilver Complex

“…56 As indicated by the NMR data, the dinuclear and nonsymmetrical structure of 1 persists in solution. The lowtemperature (193 K) 31 P{ 1 H} spectrum in CD 2 Cl 2 displays six signals, two of which overlap (Figure S3). This pattern complies with six nonequivalent phosphorus nuclei found in the crystal structure.…”

“…In contrast to 2 and 3, which adopt higher symmetry in solution compared to that in the solid, boronated complex 4 shows an opposite behavior. In fluid medium, 4 yields a noncentrosymmetric species that is manifested by four 31 P NMR signals with a 1:1:1:3 ratio of integral intensities at 193 K (Figure S6). The low-field part of the spectrum resembles that of 1 and suggests that the phosphide-oxide (PO) groups occupy inequivalent positions around the disilver core.…”

“…The NMR spectra for hydrohalogenated derivatives 2 and 3 are nearly identical and show three multiplets having the same integral intensity that is consistent with the idealized C 2 molecular symmetry and the equivalence of − P 3 O ligands. Both compounds are less fluxional at 298 K than 1, which is corroborated by relatively insignificant changes in the 31 P spectra observed upon cooling to 193 K (Figure S5). The proton spectra for 2 and 3 contain a broad signal at δ = 15.3 ppm, which reaffirms the presence of an acidic O•••H−O hydrogen atom.…”

“…Another way to influence the energies of electronic transitions, responsible for the absorption and emission, is to introduce metal–metal interactions, which are frequently found among silver­(I) compounds . Argentophilic contacts can induce cluster-centered (CC), metal-perturbed ligand-to-ligand (LLCT), or metal/metal-to-ligand charge transfer (MMLCT) transitions, thus having a strong impact on the excited state dynamics and optical properties. − The sensitivity of charge transfer excited states to weak Ag···Ag bonding together with the variable coordination number of the silver­(I) ion provides a basis for the design of appealing thermo-/mechano-responsive and sensing systems. ,,,− Notably, despite high quantum yields of TADF/phosphorescence (up to 0.95) having been reported for some silver­(I) clusters, ,− , the presence of Ag···Ag contacts does not necessarily lead to dramatic enhancement of spin–orbit coupling (SOC), as the rates of radiative decay k r for these species are often rather moderate and vary from ca. 10 3 to 10 5 s –1 under ambient conditions, reaching values of 1.6 × 10 5 s –1 for some cases of 3 CC excited states .…”

Copper and Zinc Complexes of 2,7-Bis(6-methyl-2-pyridyl)-1,8-naphthyridine─A Redox-Active, Dinucleating Bis(bipyridine) Ligand

“…The Cu atoms sit out of the plane of the naphthyridine core by 0.835–0.999 Å. This falls at the upper end of the range observed in the two known examples of [Cu 2 L 2 ] 2+ helicates with 2,7-diimine-1,8-naphthyridine ligands (0.530–0.997 Å). , M 2 L 2 helicate structures are known for a small number of Cu I 2 , and Ag I 2 , 2,7-disubstituted-1,8-naphthyridine complexes with weakly coordinating anions. To accommodate the strained helical geometry, a wider range of Cu–N bond lengths (1.9920(18)–2.1317(19) Å) and more acute bidentate N–Cu–N angles (78.62(8)–79.52(8)°) are seen compared to those of the monometallic bipyridine analogue [Cu 2 (dmbp) 2 ]PF 6 (dmbp = 6,6′-dimethyl-2,2′-bipyridine) (2.0248(9)–2.0472(9) Å, 81.13(4)–81.59(3)°) …”