Crown-ether coordination compounds with unusual structural and optic properties (Crown I)

• Applicant: Professor Dr. Claus Feldmann
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511091465

The coordination chemistry of metal cations with crown ethers has long been known and has led to a large number of compounds. Typically, cations and crown ethers are chosen so that cation diameter and opening diameter are well matched. The extensive coordination chemistry has led to some spectacular compounds, and the high selectivity of coordination even allows quantitative determinations that have found their way into analytical chemistry and sensor technology. If cations are coordinated, which, in principle, exhibit luminescence, the corresponding crown-ether coordination compounds may also exhibit luminescence, but so far the luminescence has been weak or only observed at low temperatures.With our preliminary work, we have recently shown that cations that are too small with respect to the ring opening diameter of the crown ether lead to diverse coordination and structural chemistry (e.g., Mn2+ in 18-crown-6). Surprisingly, such compounds can also exhibit outstanding fluorescence properties, which include quantum yields close to 100% (at room temperature), nonlinear optical (NLO) properties, and efficient photoluminescence excitation after frequency bisection. Based on this unexpected discovery, this project aims to synthesize new crown-ether coordination compounds (e.g., with Pr3+, Eu2+/3+, Tb3+, Sm3+, Ho3+, Tm2+/3+) with outstanding luminescence properties and to understand the background of the unusual luminescence properties. Synthesis under chiral conditions will be used to specifically prepare enantiomerically pure crown-ether coordination compounds with NLO properties and to develop a new class of NLO materials. In addition to luminescent compounds, the concept of cations being too small with respect to the ring-opening diameter of the crown ether shall finally be transferred to compounds with metal-metal bonds and lead to a new cluster chemistry.

• DFG Programme: Research Grants