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CMP
Credit: Jack Hobhouse

Gabriel Moise

Long Term Visitor

Sub department

  • Condensed Matter Physics

Research groups

  • Quantum spin dynamics
gabriel.moise@physics.ox.ac.uk
Clarendon Laboratory, room 262
  • About
  • Publications

The impact of spin–orbit coupling on fine-structure and spin polarisation in photoexcited porphyrin triplet states

Journal of Magnetic Resonance Elsevier 355 (2023) 107546

Authors:

Gabriel Moise, Ashley J Redman, Sabine Richert, William K Myers, Ibrahim Bulut, Pernille S Bolls, Michel Rickhaus, Jibin Sun, Harry L Anderson, Christiane R Timmel

Abstract:

The photoexcited triplet states of porphyrins show great promise for applications in the fields of opto-electronics, photonics, molecular wires, and spintronics. The magnetic properties of porphyrin triplet states are most conveniently studied by time-resolved continuous wave and pulse electron spin resonance (ESR). This family of techniques is singularly able to probe small yet essential details of triplet states: zero-field splittings, g-anisotropy, spin polarisation, and hyperfine interactions. These characteristics are linked to spin–orbit coupling (SOC) which is known to have a strong influence on photophysical properties such as intersystem crossing rates. The present study explores SOC effects induced by the presence of Pd2+ in various porphyrin architectures. In particular, the impact of this relativistic interaction on triplet state fine-structure and spin polarisation is investigated. These properties are probed using time-resolved ESR complemented by electron-nuclear double resonance. The findings of this study could influence the future design of molecular spintronic devices. The Pd2+ ion may be incorporated into porphyrin molecular wires as a way of controlling spin polarisation.
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Magnetic sensitivity of cryptochrome 4 from a migratory songbird

Nature Springer Nature 594:7864 (2021) 535-540

Authors:

Jingjing Xu, Lauren Jarocha, Tilo Zollitsch, Marcin Konowalczyk, Kevin Henbest, Sabine Richert, Matthew Golesworthy, Jessica Schmidt, Victoire Déjean, Daniel Sowood, Marco Bassetto, Jiate Luo, Jessica Walton, Jessica Fleming, Yujing Wei, Tommy Pitcher, Gabriel Moise, Maike Hermann, Hang Yin, Haijia Wu, Rabea Bartoelke, Stefanie Kaesehagen, Simon Horst, Glen Dautaj, Patrick Murton, Angela Gehrckens, Yogarany Chelliah, Joseph Takahashi, Karl-Wilhelm Koch, Stefan Weber, Ilia Solov'yov, Can Xie, Stuart Mackenzie, Christiane Timmel, Henrik Mouritsen, Peter Hore

Abstract:

Night-migratory songbirds are remarkably proficient navigators1. Flying alone and often over great distances, they use various directional cues including, crucially, a light-dependent magnetic compass2,3. The mechanism of this compass has been suggested to rely on the quantum spin dynamics of photoinduced radical pairs in cryptochrome flavoproteins located in the retinas of the birds4,5,6,7. Here we show that the photochemistry of cryptochrome 4 (CRY4) from the night-migratory European robin (Erithacus rubecula) is magnetically sensitive in vitro, and more so than CRY4 from two non-migratory bird species, chicken (Gallus gallus) and pigeon (Columba livia). Site-specific mutations of ErCRY4 reveal the roles of four successive flavin–tryptophan radical pairs in generating magnetic field effects and in stabilizing potential signalling states in a way that could enable sensing and signalling functions to be independently optimized in night-migratory birds.
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EPR of photoexcited triplet state acceptor porphyrins

Journal of Physical Chemistry C American Chemical Society 125:21 (2021) 11782-11790

Authors:

Ashley Redman, Gabriel Moise, Sabine Richert, Erin Viere, William Myers, Michael Therien, Christiane Timmel

Abstract:

The photoexcited triplet states of porphyrin architectures are of significant interest in a wide range of fields including molecular wires, non-linear optics and molecular spintronics. Electron paramagnetic resonance (EPR) is a key spectroscopic tool in the characterization of these transient paramagnetic states singularly well suited to quantify spin delocalization. Previous work proposed a means of extracting the absolute sign of zero-field splitting (ZFS) parameters, D and E, and triplet sublevel populations by transient continuous wave, hyperfine measurements, and magnetophotoselection. Here, we present challenges of this methodology for a series of meso-perfluoroalkyl substituted zinc porphyrin monomers with orthorhombic symmetries, where interpretation of experimental data must proceed with caution and the validity of the assumptions used in the analysis must be scrutinized. The EPR data are discussed alongside quantum chemical calculations, employing both DFT and CASSCF methodologies. Despite some success of the latter in quantifying the magnitude of the ZFS interaction, the results clearly provide motivation to develop improved methods for ZFS calculations of highly delocalized organic triplet states.
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Spin delocalization in the radical cations of porphyrin molecular wires: A new perspective on EPR approaches

Journal of Physical Chemistry Letters American Chemical Society 10 (2019) 5708-5712

Authors:

G Moise, L Tejerina, M Rickhaus, Harry Anderson, Christiane Timmel

Abstract:

The spin delocalization in the radical cations of a series of ethyne-linked oligoporphyrins was investigated using EPR spectroscopy. The room-temperature spectral envelope for these oligomers deviates significantly from the benchmark N–0.5 trend in line width expected for a completely delocalized spin density, in contrast to the butadiyne-linked analogues measured previously. Here, we show, using DFT calculations and complementary low-temperature ENDOR measurements, that this deviation is primarily driven by a more pronounced inequivalence of the 14N spins within individual subunits for the ethyne-linked oligoporphyrins. Once this 14N inequivalence is taken into consideration, the room-temperature and ENDOR spectra for both butadiyne-linked and ethyne-linked oligomers, up to N = 5, can be simulated by similar static delocalization patterns. This work highlights the importance of EPR in exploring such spin delocalization phenomena while also demonstrating that the N–0.5 trend should not be interpreted in isolation but only in combination with careful simulation and theoretical modeling.
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EPR of lanthanide complexes: exploring the consequences of ligand induced anisotropy

255th National Meeting and Exposition of the American Chemical Society American Chemical Society (2018)

Authors:

K Fisher, Gabriel Moise, Alice Bowen, Christiane Timmel, Stephen Faulkner, A Kenwright
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