Probing photoinduced valence tautomerism with femtosecond Medge spectroscopy

Probing photoinduced valence tautomerism with femtosecond M-edge spectroscopy Ryan Ash, Kaili Zhang, Josh Vura-Weis Group, UIUC 6/19/19

What is valence tautomerism (VT)? Why do we care? ¢ Change in electronic configuration in valence orbitals Benzoquinone, -0 ¢ Semiquinone, -1 Catechol, -2 Cobalt dioxolene complexes undergoing VT candidates for optomagnetic switches Kaim, W. ; Schwederski, B. Cooperation of Metals with Electroactive Ligands of Biochemical Relevance: Beyond Metallophyrins. Pure Appl. Chem. 2004, 76, 351– 364.

Overview of photoinduced VT What are the natures and lifetimes of intermediate states? DQ- Co 2+ LS DQ- LMCT? hν, 525 nm DQDQ- Co 3+ LS DQ 2 - Co 2+ HS DQ-

M-edge XAS gives useful info about the oxidation, spin, and ligand field of a metal center Continuum 3 s or 3 p Inner-shell y Sensitive to elementspecific oxidation state, spin state, and ligand field M-edge ra L-edge X- K-edge Valence 2 s or 2 p 1 s XAS 3 d metal M-edges range from 30 -100 e. V – extreme ultraviolet (XUV) photons

Tabletop femtosecond XUV spectrometer N 2 flow 7. 5 mm

Understanding M-edge transitions with crystal field multiplet theory

Crystal field theory case study – Fe 2 O 3 Core-Hole State Ground State … 3 p 5 3 d 6 3 p 6 3 d 5 4 H 4 I Selection rules: ΔL=0, ± 1 ΔS=0 6 P 6 D 6 F … 6 S e-e Repulsion Vura-weis, J et al. Femtosecond M 2, 3 -Edge Spectroscopy of Transition-Metal Oxides: Photoinduced Oxidation State Change in α ‑ Fe 2 O 3. 2013, 3667– 3671.

Crystal field theory case study – Fe 2 O 3 Core-Hole State Ground State … 3 p 5 3 d 6 3 p 6 3 d 5 Selection rules: < f│µ │i ˃ = A 1 ΔS=0 4 H 4 I 6 P 6 T 6 D 6 F 6 E 6 A 2 u+ 1 u +6 T u 6 T 1 u 2 u +6 T 2 u … 6 S e-e Repulsion 6 A 1 g Crystal Field Vura-weis, J et al. Femtosecond M 2, 3 -Edge Spectroscopy of Transition-Metal Oxides: Photoinduced Oxidation State Change in α ‑ Fe 2 O 3. 2013, 3667– 3671.

Applying M-edge spectroscopy to study photoinduced VT

Film deposition and annealing to increase fraction of LS species 170°C, 30 min Co. III

Ground state M-edge spectra confirm increase in LS species upon annealing Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Ground state M-edge spectra confirm increase in LS species upon annealing %LS Co. III (1 A 1 g) %HS Co. II (4 T 1 g) As Deposited 40 60 Annealed 90 10 Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Ground state M-edge spectra confirm increase in LS species upon annealing %Co. III LS (1 A 1 g) %Co. II HS (4 T 1 g) As Deposited 40 60 Annealed 90 10 Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Overview of transient M-edge results λpump: 525 nm Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Overview of transient M-edge results λpump: 525 nm Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Overview of transient M-edge results λpump: 525 nm Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Overview of transient M-edge results λpump: 525 nm Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Data fit to model with parallel relaxation pathways τ2’ Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Data fit to model with parallel relaxation pathways Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Component spectra match simulated spectra of 2 Eg, 4 T 1 g states Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Why are there multiple relaxation timescales? 67 fs 460 fs 640 fs hν 24 ps Ash, R. ; Zhang, K. ; Vura-Weis, J. Chem Rxiv 2019. DOI: 10. 26434/chemrxiv. 8283647 (Submitted)

Overall picture in the Co diquinone VT system 67 fs 460 fs 640 fs hν 24 ps Initially populated Co 2+ HS state Ultrafast ISC to Co 2+ HS state Fast relaxation to ground state when vibrationally hot

Conclusions ¢ Ultrafast M-edge spectroscopy is a useful probe to study dynamics of the metal center of transition metal complexes ¢ Assignment of initial Co 2+ LS state upon photoinduced VT ¢ Fast relaxation back to GS could be problematic for Co VT complexes to be effective switches

Acknowledgements Vura Weis Group Members Prof. Josh Vura-Weis, Kaili Zhang, Liz Ryland, Max Verkamp, Kris Benke, Kori Sye, Aastha Sharma, Yusef Shari’ati, Clare Leahy Funding Sources

OTA of annealed film