Revealing Hot and Long-Lived Metastable Spin States in the Photoinduced Switching of Solvated Metallogrid Complexes with Femtosecond Optical and X-ray Spectroscopies

Abstract

An atomistic understanding of the photoinduced spin-state switching (PSS) within polynuclear systems of d 4 -d 7 transition metal ion complexes is required for their rational integration into light-driven reactions of chemical and biological interests. However, in contrast to mononuclear systems, the multidimensional dynamics of the PSS in solvated molecular arrayshave not yet been elucidated, due to the expected complications associated to the connectivity between the metal centers and the strong interactions with the surroundings. In this work, the PSS in a solvated triiron(II) metallogrid complex is characterized using transient optical absorption and X-ray emission spectroscopies on the femtosecond timescale. The complementary measurements reveal the photoinduced creation of energy-rich (hot) and longlived quintet states, whose dynamics differ critically from their mononuclear congeners. This finding opens major prospects for developing novel schemes in solution-phase spin chemistry that are driven by the dynamic PSS process in compact oligometallic arrays. TOC GRAPHICSKEYWORDS molecular squares, photophysics, time-resolved X-ray techniques, light-induced processes, ultrafast phenomena, spin-state switching.

Metal-to-metal communication during the spin state transition of a [2 × 2] Fe(ii) metallogrid at equilibrium and out-of-equilibrium conditions

“…[31][32][33] Additionally, a combination of transient optical-infrared absorption and X-ray emission spectroscopy in solution has demonstrated that strongly linking several metal centres into metallogrids can be developed as an efficient synthetic strategy to increase the lifetime of the photoinduced metastable spin-state. 34,35 However, the aforementioned studies do not provide information on the complex pathway from molecular to materials scales accompanying the non-stationary photoinduced spin transition, while temperature dependent studies at equilibrium conditions only provide partial information on the structural changes. A general picture of the structural changes that accompany the equilibrium and out-of-equilibrium spin transition in the solid state of oligometallic systems is essential to understanding their structure-property relationships, which is necessary to design new materials with bi-or multistability in a targeted approach.…”

Fundamental Characterization, Photophysics and Photocatalysis of a Base Metal Iron(II)‐Cobalt(III) Dyad

“…Still, the final proof for the existence of such an MC state has to be proven by more sensitive methods like ultrafast X‐ray emission spectroscopy. [33] …”

An Alternate [2×2] Grid Constructed Around TiO4N2 Units

“…[9][10][11][12][13] Metallosupramolecular grids [14][15][16] are a particular class of self-assembled architectures that have attracted major interest due to their redox, magnetic or spin-state transition properties. [17][18][19][20][21][22][23][24][25] The construction of such metal ion arrays is based on the mutual recognition of directional ligands (L) and metal ions (M) leading to an orthogonal arrangement of the ligands at each metal corner. The [2 × 2] grids (Figure 1) are archetypes of this family of molecules.…”

“…Thus, an impressive variety of self‐assembled metallo‐architectures have been reported including linear and circular helicates, [3,4] topological non‐trivial molecules, [5–7] metallo‐squares, [8] cages or giant spheres [9–13] . Metallosupramolecular grids [14–16] are a particular class of self‐assembled architectures that have attracted major interest due to their redox, magnetic or spin‐state transition properties [17–25] . The construction of such metal ion arrays is based on the mutual recognition of directional ligands (L) and metal ions (M) leading to an orthogonal arrangement of the ligands at each metal corner.…”