Spectroscopy and electron dynamics of polynuclear lanthanide and transition metal complexes (multi-lanthanide) (C05)

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The aim of the project in the second funding period is to synthesise an unprecedented family of [2x2] metalgrid complexes, to investigate their spin-dependent electron dynamics by spectroscopic methods, and toachieve active control over their cooperative magnetic properties. For this purpose, we will develop a newtype of grid-ligand that is stabilizing the metal ions - either a transition metal or a lanthanide - on their specificpositions. In particular, the backbone of the employed ligand family will allow controlling the overall-charge ofthe resulting grid complex and therefore also the number of counter ions. This may lead to neutral unchargedgrid complexes which potentially will be suitable for sublimation processing. Moreover, for FeII the ligandsystem is designed to access different conformational isomers, allowing to investigate and to compare theintrinsic cooperativity of the spin state switching process. We will separate the resulting two grid-types eitherby fractionated crystallization or more promising by ¿freezing¿ the two conformational isomers by chemicalsynthesis. This will prevent isomerisation allowing the separation of the isomers using columnchromatography. The control over the cooperative magnetic properties of these compounds will be achievedby following two main strategies:(i) Deposition of the complexes on magnetic substrates;(ii) Control of the spin state transition by optical triggers.The first approach (i) is to choose various ferromagnetic substrates (Fe, Co, Ni, magnetic oxides), to modifythe strength of the magnetic coupling with the spin centres of the deposited complexes. Different strengths ofthe magnetic coupling will inevitably influence the transition temperature of the high-spin (HS) and low-spin(LS) state transition, giving us control over the overall spin transition process. The second approach (ii) willtarget the selective optical excitation of the HS-LS transition in dynamical pump-probe spin-resolvedphotoemission experiments. Here, the wavelength of the optical pump pulse will be tuned to excite the HSLStransition, while the probe pulse will be selective to the specific spin state of the grid complexes depositedon the various ferromagnetic surfaces. Such experiments will thus give access to the fundamentaltimescales involved in the HS-LS transition, opening the way to the active control of the spin transition inmetal grid complexes deposited on magnetic surfaces by tailored optical excitation.