ESKIMO-Pro-IRON - Excited State Kinetic Modelling and Properties Tuning of Iron Complexes

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The shortage and increasing prices of noble metals makes the substitution of such elements by abundant and preferably biocompatible base metals an important scientific challenge. Especially in photochemical applications, where sunlight is a sustainable source of energy, base metals as key element will tremendously increase the level of sustainability, as the non-renewable resource depletion is significantly lowered. With the present proposal, we want to contribute to this global aim by employing the most abundant transition metal – iron – in photochemistry. Within the first funding period of the PP 2102, the ESKIMO project achieved significant progress in novel ligands employing 5- and 6-ring chelates for excited state tuning, achieving high octahedricity and MLCT lifetime elongation in iron(II) complexes. A novel type of MC excited state reactivity was demonstrated and a bichromophoric approach was explored. A major breakthrough was achieved by realizing an iron(III) complex showing unprecedented dual emission, a record MLCT lifetime and bimolecular reactivity. This plethora of new results were understood by thorough theoretical and spectroscopic methods such as range-separated DFT functional tuning, ultrafast transient absorption and emission and synchrotron X-ray spectroscopy. Up to date, 17 publications resulted from the first funding period.Consequently, this continuation proposal aims at further exploration and extension of the different achieved results. Novel low-spin iron(II) and iron(III) complexes of tridentate ligands with long-lived excited 3MLCT (3MC/5MC) / 2LMCT states will be prepared by application of the reservoir effect and new ligand designs with tailor-made donor/acceptor properties. The excited state landscape of these complexes including all relevant excited states and photoinduced dynamics will be investigated on all timescales from femto- to microseconds by new approaches in optical and X-ray spectroscopy and theoretical methods. The developed complexes will be exploited in photochemical applications and novel luminescent materials.Within these overarching aims, the project hits the core of the priority program’s thematic focus as molecular emitters and sensitizers based on abundant metals to replace rare and precious metal centres are developed by rational approaches gained by understanding electronically excited states in iron complexes. With ultrafast transient absorption spectroscopy, ultrafast X-ray spectroscopy and scattering methods and quantum chemical calculations and dynamics, dynamic environmental effects will be accessible to gain a holistic view on all relevant processes.