Near-Infrared Light Emitting Chromium(III) Complexes - Design and Advanced Applications 2.0

• Applicants: Professorin Dr. Katja Heinze; Dr. Ute Resch-Genger
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 326469115

Based on the knowledge gained in NILE-CHROME and complementary expertise of the applicants in ligand design, coordination chemistry, computational chemistry, photochemistry, quantitative optical spectroscopy, nanotechnology, and design of sensor materials, the ground-breaking objectives of this joint project are to rationally design and establish novel complexes based on earth-abundant chromium(III) – the molecular rubies – in novel applications, unavailable for 3d metal complexes or partially even 4d/5d metal complexes so far. This will involve tuning absorption properties, emission energies, (radiative) lifetimes, and O2 sensitivity to enable applications of molecular rubies beyond those reported so far exploiting theory-guided, rationally designed ligands for homo- and heteroleptic chromium(III) complexes. This will include ligands with six-membered chelate rings for a large ligand field splitting, electron dona¬ting/accepting ligands to target emission energies from orange/red to the NIR, ligands to enhance ligand field absorption (tackling the molar absorption coefficient in the visible) and spin-flip emission (tackling the radiative rate) as well as ligands with a negative charge to partially compensate the chromium(III) ion’s high positive charge. Also, tuning of the phosphorescence lifetime and O2 sensitivity by counter anion association will be explored. The application potential of the novel chromium(III) complexes will be shown for photocatalysis, upconversion (UC), circularly polarized luminescence (CPL), lifetime multiplexing, and singlet oxygen generation.The following objectives will be jointly explored:a) Novel ligand designs and novel synthesis procedures for homo- and heteroleptic chromium(III) complexes.b) Excited state landscape design by quantum chemical calculations with multireference methods (CASSCF-NEVPT2) to predict emission energy shifts of chromium(III) spin-flip emitters and obtain information on intersystem crossing (ISC) rates via density of excited states and spin-orbit couplings. ISC rates will be determined experimentally by fs transient absorption spectroscopy and fs transient X-ray emission spectroscopy. c) Excited state energy and electron transfer catalysis of chromium(III) sensitizers with suitable ground and excited state redox potentials like sensitized [2+2], [3+2] and [4+2] cycloadditions.d) CPL properties of chiral chromium(III) complexes for use in a CPL laser e) Use of chromium(III) complexes with suitable doublet excited state 2E/2T1 energies as donors for sensitized triplet-triplet annihilation upconversion (sTTA-UC) with organic dyes. f) Explore whether chromium(III) complexes in sTTA-UC systems can be sensitized with semiconductor quantum dots. g) Assess molecular rubies as labels for lifetime multiplexing. h) Use differently charged chromium(III) complexes as singlet oxygen photosensitizer in cellular studies and for inducing DNA double strand breaks.

• DFG Programme: Research Grants