Bifunctional Photoacids with Multicolour Emission

• Applicant: Professor Dr. Gregor Jung
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation ; Analytical Chemistry ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445103157

The unique combination of fluorescence spectroscopy and photochemistry is found in the excited-state proton transfer (ESPT) reaction. Based on the intrinsic dual emission of suchlike systems, we recently developed a substrate which shows up to four emission colors in dependence of two orthogonal cleavage sites for two different enzymes. While the enzymatic conversions represent irreversible transformations under realistic conditions, we would like to transfer this promising concept of orthogonal reactivities, encoded by different emission colors, to reversible reactions and would like to compare it to the behavior of non-orthogonal binding sites. The latter system is represented by the photoacidic site, combined with a photobasic moiety.Thermodynamics and kinetics of reversible bond formation and dissociation are probed by NMR-spectroscopy and fluorescence correlation spectroscopy, respectively. These measurements allow for quantifying the extent by which binding on one site influence the binding at the other site. The reversible binding of Lewis-bases to Boron-substituted hydroxypyrene derivatives is expected to act as the orthogonal binding sites. The carboxylated hydroxypyrene derivatives combine photoacidity and -basicity within one molecule. The well-established carboxylate as photobase is complemented by an imine base; this latter compound was recently described as part of a so-called super-photobase. As the ordering of acidities is expected to change upon excitation, ESPT from the hydroxyl-moiety to the basic site via a hydrogen-bonding network can be probed. It is planned to exploit this feature in studying hydrogen-bonding chains in various solvent compositions. Therefore, one major objective of this grant proposal is the preparation of various regioisomers in amounts and solubility which fit to the needs of the various spectroscopy methods.

• DFG Programme: Research Grants