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oai:figshare.com:article/34027663 2026-09-29T21:03:31Z category_1 category_4 category_915 category_7 category_16 category_873 category_39 category_734 category_64 portal_63 item_type_6 month_year_09_2026

Ultrafast Site-Selective Excitation Pathways Governing Short-Lived Photoinduced Spin States in a Cyanide-Bridged Fe–Cr Spin-Crossover System Kazuki Nakamura (589803) Valentin Spitale (25139038) Grégory Taupier (4865785) Nicolas Godin (20617937) Daiki Kobayashi (414250) Shintaro Akagi (14639056) Shin-ichi Ohkoshi (1396678) Hiroko Tokoro (1678819) Eric Collet (1591651) Biophysics Biochemistry Physical Sciences not elsewhere classified Medicine Physiology Chemical Sciences not elsewhere classified Ecology Biological Sciences not elsewhere classified Cancer mm ’ ct metal charge transfer ir spectroscopic studies 2 </ sub ultrafast structural relaxation photoexcitation indeed generates high ligand field excitation pathways generate crossover material csfe metastable hs state hs state decays hs </ sub ls </ sub iii </ sup thermal spin transition hs state material consists crossover system ultrafast site ultrafast light whereas excitation results reveal preventing long flipped site counteracting pressure cooperative switching combining optical bridged network bridged lattice always ls 5 ps 200 fs We study the ultrafast light-induced excited spin state trapping (LIESST) process in a cyanide-bridged Fe–Cr spin-crossover material CsFe^II[Cr^III(CN)₆]·1.3H₂O. This material consists of an original Fe^II–NC–Cr^III units, responsible for the thermal spin transition (ST) of the low ligand field Fe ST site from a low-spin (LS) Fe^II_LS to a high-spin (HS) Fe^II_HS states. Although electronic structures suggest that a metastable HS state can be reached by photoexcitation, no LIESST to this HS state has yet been observed using conventional techniques. In addition, part of the units exhibits a thermally driven cyanide flip toward the Fe^II_LS–CN–Cr^III sites, where Fe is always LS by the high ligand field. By combining optical and IR spectroscopic studies, we investigated whether light excitation is ineffective in inducing the LIESST or whether it causes the cyanide flip. Our results reveal that photoexcitation indeed generates the HS state, but its lifetime is limited to a few picoseconds by ultrafast structural relaxation. Excitation at 800 nm predominantly triggers a Fe-centered d–d transition at the ST site, whereas excitation at 530 nm induces metal-to-metal charge transfer (MM’CT) at both ST and flipped sites. For the ST site, both excitation pathways generate the HS state within less than 200 fs, which launches coherent torsional motion of the cyanide-bridged network, and this HS state decays to a LS state within 3.5 ps. In contrast, at the flipped site, 530 nm excitation selectively populates a transient MM’CT Fe^III_LS–Cr^II*, which decays without inducing spin state switching nor cyanide flipping. Overall, the photoinduced HS state rapidly decays, due to the counteracting pressure of the rigid cyanide-bridged lattice, preventing long-lived LIESST and cooperative switching. 2026-09-29T00:00:00Z Text Journal contribution 10.1021/acs.chemmater.6c01993.s001 https://figshare.com/articles/journal_contribution/Ultrafast_Site-Selective_Excitation_Pathways_Governing_Short-Lived_Photoinduced_Spin_States_in_a_Cyanide-Bridged_Fe_Cr_Spin-Crossover_System/34027663 CC BY-NC 4.0