Out-of-equilibrium lattice response to photo-induced charge-transfer in a MnFe Prussian blue analogue

Abstract

Photo-induced structural dynamics in molecular materials often involve two main components; local molecular distortions induced by the self-trapping of electronic excited state and incoherent lattice dynamics due to energy dissipation....

Out-of-equilibrium dynamics driven by photoinduced charge transfer in CsCoFe Prussian blue analogue nanocrystals

“…All these XANES and optical data show that the early response of photoexcited CoFe particles does not depend on the size of the nanocrystals, which agrees with the local nature of the self-trapping process of the photoinduced CT polaron already highlighted in both CoFe and MnFe materials. [36][37][38] As previously discussed in detail for the CoFe PBA, the very rst step of the photoinduced dynamics corresponds to the light-induced excited spin-state trapping process (LIESST) on the Co. The initial photoexcited Co III* (S ¼ 0)Fe II (S ¼ 0) state populates antibonding Co(e g ) states, which drives Co-N bond expansion and the spin transition towards the Co III (S ¼ 2)Fe II (S ¼ 0).…”

“…Understanding and mastering the ultra-fast photoinduced intermetallic CT process is a real challenge because it requires probing the system on the sub-100 femtosecond (fs) timescale of electronic dynamics and molecular motions, as underlined in a recent review by Johansson 34 about ultrafast studies of Fe-Fe, Co-Fe, Mn-Fe, and V-Cr PBAs. 27,28,[35][36][37] We recently used femtosecond X-ray and optical absorption spectroscopies to study the CT process in a photo-excited Co III (S ¼ 0)Fe II (S ¼ 0) material (Fig. 1).…”

“…Time-resolved X-ray diffraction on the picosecond timescale evidenced the macroscopic volume expansion of the RbMnFe crystal due to the structural trapping process, as the small CT polaron associated with the elongation of the Mn-N bonds expands the polymeric M-N-C-M 0 lattice. 37 Here we study out-of-equilibrium dynamics in CoFe nanocrystals on the femtosecond and picosecond timescales. In particular, we are interested in the effect of the size of the crystalline particles on the femtosecond photoinduced CT process and the subsequent macroscopic changes.…”

Exploring Ultrafast Photoswitching Pathways in RbMnFe Prussian Blue Analogue

“…Mn II Fe III CT,f orms as mall-polaron and is responsible for an anisotropic lattice expansion occurring within % 75 ps. [20] However,the crystalline lattice has no time to expand on the sub-ps timescale where Mn À Nb onds elongate.Adistortion is required to accommodates this local lattice expansion, as represented in Figure 5c,a nd the ultrafast MnÀNb ond elongation launches torsion modes Q T in ac oherent way.T he global fit of our data indicates am aximum torsion at t OSC % 50 fs after photoexcitation, which agrees with the bond elongation timescale discussed above.T his is another indication that the Mn À Nb ond elongation, resulting from the Mn(d z 2 )!Mn(d x 2 Ày 2 )o ptical excitation, is the initial process driving the photoinduced Mn III Fe II ! Mn II Fe III CT.…”

Exploring Ultrafast Photoswitching Pathways in RbMnFe Prussian Blue Analogue

“…Indeed, the structural trapping of the CT state, with the ultrafast elongation of the Mn−N bonds around the excited Mn (Figure 1 c) stabilizes CT state over ≈10 μs (Figure 2 b). We have recently shown by time‐resolved X‐ray diffraction that the elongation of the Mn−N bonds along x and y , accompanying the photoinduced Mn III Fe II → Mn II Fe III CT, forms a small‐polaron and is responsible for an anisotropic lattice expansion occurring within ≈75 ps [20] . However, the crystalline lattice has no time to expand on the sub‐ps timescale where Mn−N bonds elongate.…”