Photo-magnetic transitions: Spin crossover molecules Amandine Bellec - PowerPoint PPT Presentation

Photo-magnetic transitions: Spin crossover molecules Amandine Bellec amandine.bellec@univ-paris-diderot.fr Laboratoire Matériaux et Phénomènes Quantiques (Université Paris Diderot/CNRS) Sept 2018 Amandine Bellec – ESM 1

Molecular switch External stimuli: Light, temperature, pressure, electric field Change in the molecular material properties: - Electronic - Magnetic - Optical - Mechanical Property Bistability: Ability to be observed in two different macroscopic states in hysteretic region depending on the history External stimuli Sept 2018 Amandine Bellec – ESM 2

Ingredients for magnetic properties Open shell: - transition metal (d-orbitals) - lanthanide (f-orbitals) - molecular radical SCO compounds Fe 4 Molecular radicals Prussian blue analogues Dy(cp) 2 Sept 2018 Amandine Bellec – ESM 3

Outline - Spin crossover compounds - Introduction - Thermal transition - Light induced transition - SCO on surface - Prussian blue analogues - Molecular radicals Sept 2018 Amandine Bellec – ESM 4

Ligand field • Transition metal ion (d 4 to d 7 – Cr, Mn, Fe, Co) surrounded by organic ligands d-orbitals (n=3, l=2) d xy d x2-y2 d z2 d yz d zx • Octahedral symmetry e g 3 Δ O /5 Δ O d-orbitals 2 Δ O /5 t 2g Central ion Ligands Sept 2018 Amandine Bellec – ESM 5

Jahn-Teller distorsion Compression along z Elongation along z O h d z2 d x2-y2 d z2 , d x2-y2 d x2-y2 d z2 d xy d xz ,d yz d xy d xy , d xz ,d yz d xz ,d yz Sept 2018 Amandine Bellec – ESM 6

Spin crossover molecules Fe II : [Ar] 3d 6 4s 0 HS LS T, P, h  S=0 S=2 Δ O : ligand field Δ O LS > Π Δ O HS < Π Π : pairing energy Central ion Ligands Volume change: 2-6% Sept 2018 Amandine Bellec – ESM 7

SCO: effect of ligand functionalization Fe II [HB(Pz) 3 ] 2 Fe II [HB(3,5-Me 2 Pz) 3 ] 2 Fe II [HB(PPz) 3 ] 2 LS < 350K SCO around 190 K HS blocked Sept 2018 Amandine Bellec – ESM 8

UV-Vis absorption spectroscopy [Fe(ptz) 6 ](BF 4 ) 2 HS MLCT process LS nm 1000 500 333 250 6 e g 0 L 0 5 e g 0 L 1 t 2g t 2g d-d transitions Hauser et al., Top. Curr. Chem., 234, 155 (2004) Marino et al., Angew. Chem. Int. Ed., 53, 3863 (2014) Sept 2018 Amandine Bellec – ESM 9

SQUID measurements SQUID on polycrystalline powder Fe II (pap-5NO 2 ) 2 Iasco et al., Inorga. Chem., 54, 1791 (2015) Sept 2018 Amandine Bellec – ESM 10

Outline - Spin crossover compounds - Introduction - Thermal transition - Light induced transition - SCO on surface - Prussian blue analogs - Molecular radicals Sept 2018 Amandine Bellec – ESM 11

Thermal transition To have the stable spin state, minimization of the Gibbs free energy : Enthalpy: • LS more symmetric • Volume variation: 2-6% : LS favored Δ H around 10 kJ.mol -1 Sept 2018 Amandine Bellec – ESM 12

Thermal transition Entropy: Intramolecular dominates the intermolecular contribution • • Electronic contribution, due to the spin: Vibrational contribution: As longer M-L bonds for the HS : HS favored SCO transition when: Transition temperature: SCO driven by the entropy term High temperature: high spin - Low temperature: low spin Sept 2018 Amandine Bellec – ESM 13

Molecules without interaction • Assembly of molecules in HS and LS exhibiting SCO transition x fraction of HS • No interaction between the molecules ( 1-x ) fraction of LS • Additional term of mixing entropy Δ H = 10.2 kJ.mol -1 Δ S = 53.8 J.mol -1 . K -1 Sept 2018 Amandine Bellec – ESM 14

Cooperativity in SCO crystals, films Cooperativity Ridier et al ., Solid State Sciences, 74, A1 (2017) Sept 2018 Amandine Bellec – ESM 15

Slichter and Drickamer model C. Slichter and H. Drickamer, J.Chem. Phys., 56, 2142, (1972) Δ H = 10.2 kJ.mol -1 Δ S = 53.8 J.mol -1 . K -1 Weak cooperativity Smooth transition Abrupt transition Strong cooperativity 1 st order transition, hysteresis Sept 2018 Amandine Bellec – ESM 16

Thermal transition in crystal Optical microscopy on single micro-crystals of [{Fe(NCSe)(py) 2 } 2 (m-bpypz)] Cooling down Heating up http://dx.doi.org/10.1021/acs.jpcc.7b02816 Traiche et al ., J. Phys. Chem. C,121, 11700 (2017) Sept 2018 Amandine Bellec – ESM 17

Outline - Spin crossover compounds - Introduction - Thermal transition - Light induced transition - SCO on surface - Prussian blue analogs - Molecular radicals Sept 2018 Amandine Bellec – ESM 18

Light induced transition Light induced excited spin state trapping (LIESST): Discovered in 1984, for [Fe(ptz) 6 ](BF 4 ) 2 T<50K, LS to HS transition under light H 3 C N N N N ptz: propyltetrazol Decurtins et al. , Chem. Phys. Lett., 105, 1 (1984) Sept 2018 Amandine Bellec – ESM 19

Light induced transition Light induced excited spin state trapping (LIESST): For [Fe(ptz) 6 ](BF 4 ) 2 Here d-d transition Real et al., Dalton Trans., 12, 2062 (2005) Hauser et al., Top. Curr. Chem., 234, 155 (2004) Sept 2018 Amandine Bellec – ESM 20

Intermediate states For [Zn 1-x Fe x (ptz) 6 ](BF 4 ) 2 (x=0.1) at 120K 2 ps 40 ps Excitation pulse: 100 fs, 830 nm Probe: 300 nm Reverse LIESST: evidence of the intermediate state, sequential double intersystem crossing Marino et al., Angew. Chem. Int. Ed., 53, 3863 (2014) Sept 2018 Amandine Bellec – ESM 21

Excited phonon modes By ultra-fast dynamics: pump-probe experiments X-ray pulse ~ 30 fs (XANES), laser pulse ~ 50 fs (optical reflectivity and transmission) MLCT process 160 fs 50 fs 900 fs 6 e g 0 L 0 5 e g 0 L 1 t 2g t 2g Breathing mode Bending mode Period 300 fs, damping 160 fs Bend ligand and N-Fe-N angles, period 390 fs http://link.aps.org/doi/10.1103/PhysRevLett.113.227402 Cammarata et al., Phys. Rev. Lett., 113, 227402 (2014) Sept 2018 Amandine Bellec – ESM 22

Cooperativity Different time scales: - Local photo excitation + swelling (few 100 fs) - Elastic step: volume change + strain propagation (0.1 to 50 ns) - Thermal conversion (50 µs) 950 x 270 x 35 nm 2 7.5 x 0.64 x 0.21 µm 2 300 x 200 x 15 µm 2 Bertoni et al., Nat. Mater., 16, 606 (2016) Sept 2018 Amandine Bellec – ESM 23

Cooperativity: mechanoelastic model h  threshold: Above x HS Self-amplification of the photoconversion Lattice expansion due to volume change Bertoni et al., Nat. Mater., 16, 606 (2016) Sept 2018 Amandine Bellec – ESM 24

Self-amplification mechanism Bertoni et al., Nat. Mater., 16, 606 (2016) Sept 2018 Amandine Bellec – ESM 25

Non-adiabatic multiphonon relaxation Below 50 K: Tunneling process between HS and LS Temperature increase: -> population of the vibronic states -> increase of the tunneling rate Above 100K: thermally activated Rate for a series of Fe II molecules Hauser et al., Top. Curr. Chem., 234, 155 (2004) Sept 2018 Amandine Bellec – ESM 26

T LIESST Measuring the temperature at which the system relaxes Procedure: At 10K, light on until the saturation is reached Light off, ramping up of the temperature at 0.3 K min -1 Chastanet et al., Chem 2 , doi: 10.28954/2018.csq.07.001 (2018) Sept 2018 Amandine Bellec – ESM 27

T LIESST Measuring the temperature at which the system relaxes Procedure: At 10K, light on until the saturation is reached Prussian blue analogues Light off, ramping up of the temperature at 0.3 K min -1 Fe(L)(CN) 2 T LIESST = 130 K Hayami et al., Inorg. Chem., 40, 3240 (2001) Chastanet et al., Chem 2 , doi: 10.28954/2018.csq.07.001 (2018) Sept 2018 Amandine Bellec – ESM 28

Photo-excitation in the thermal hysteresis [Fe(pyrazine){Pt(CN) 4 }] Δ H = 25 kJ.mol -1 Laser pulse: Δ S = 84 J.mol -1 . K -1 532 nm, 4ns, 11 mJ.cm -2 Γ = 7.11 kJ.mol -1 Above P th = 5 mJ.cm -1 , LS to HS transition at 301 K Bonhommeau et al., Angew. Chem., 44, 4069 (2005) Bonhommeau et al., Polyhedron, 28, 1610 (2009) Sept 2018 Amandine Bellec – ESM 29

Ligand Driven - Light induced spin change (LD-LISC) Modulation of the ligand field strength by photochemical reaction on the ligand Styrylpyridine cis -stpy trans -stpy Show different behavior depending on the stpy conformation Boillot et al., Inorg. Chem., 35, 3975 (1996) In solution at RT: Photoisomerisation inducing a spin state change Boillot et al., New J. of Chem., 23, 176 (1999) Sept 2018 Amandine Bellec – ESM 30

Ligand-driven coordination-induced spin-state switching (LD-CISSS) Not SCO But change of the coordination sphere Venkataramani et al., Science, 331, 445 (2011) Sept 2018 Amandine Bellec – ESM 31

Outline - Spin crossover compounds - Introduction - Thermal transition - Light induced transition - SCO on surface - Prussian blue analogues - Molecular radicals Sept 2018 Amandine Bellec – ESM 32

Displays Initial state: LS (pink) When temperature increase: transition from LS to HS (white) Kahn et al. , Science, 279, 5347 (1998) Létard et al ., Top Curr. Chem, 235, 221 (2004) Sept 2018 Amandine Bellec – ESM 33

Applications for molecular electronics/spintronics Thin films (10 to 100nm): Conduction depending on the spin state Lefter et al ., Adv. Mater., 28, 7508 (2016) Depending on the spin state modification of the mobility in the graphene Stretching induced conversion to HS and an increase of conduction Dugay et al ., Nano Lett., 17, 186 (2017) Fresenda et al ., Nano Lett., 16, 4733 (2016) SCO for monolayer or single molecules in direct contact with metal? Sept 2018 Amandine Bellec – ESM 34