Searching for new borondifluoride beta-diketonate complexes with enhanced absorption/emission properties using ab initio tools

The rational design of fluorophores with enhanced absorption/emission properties increasingly relies on theoretical chemistry, as new ab initio methods suited for electronically excited-states reduce the gap between calculated and experimental results. In this framework, Time-Dependent Density Functional Theory (TD-DFT) emerges as an attractive option as it often provides accurate results at a moderate computational cost. Here, we perform a TD-DFT-SOS-CIS(D) study of a panel of 18 borondifluoride beta-diketonate complexes that can be classified as: curcuminoids, hemicurcuminoids, their ethynylene analogues, and 2'-hydroxy-chalcones. First, we reproduce the experimental 0-0 energies with refined models considering the impact of vibrational and solvent effects, the latter through both linear response and two-state specific approaches. We also evaluate the impact of double excitations by using the SOS-CIS(D) scheme to correct the TD-DFT estimates. In addition, we carry out a vibronic simulation for a representative system. Next, we analyze the obtained key structure-property relationships leading to pronounced bathochromic shifts, and finally, based on the obtained results, we propose a panel of related compounds looking for systems with absorption and emission maxima located at longer wavelengths.