Synthesis and photophysical properties of 6-aryl-2,4-bis(2′-hydroxyphenyl)pyrimidines ligands and their boron fluoride complexes

Abstract

A new family of 6-aryl-2,4-bis(2′-hydroxyphenyl)pyrimidines has been efficiently synthesized and characterized using Suzuki-Miyaura reactions, demonstrating their ability to function as rigid tridentate O^N^O chelating ligands for the preparation of four-coordinate organoboron compounds. Similar to related structures, the uncoordinated compounds do not exhibit fluorescence in either solution or the solid state. The intramolecular hydrogen bonds in their molecular structure promote an excited-state intramolecular proton transfer (ESIPT) process, leading to an excited keto tautomer that deactivates through non-radiative decay. Protonation and boron complexation can successfully inhibit the ESIPT process, resulting in fluorescence recovery, which can be finely tuned by modifying the substituents on the aryl group. Advanced techniques, including X-ray diffraction, density functional theory (DFT), and time-dependent DFT (TD-DFT), provide critical insights into the electronic structure and emission properties. This work offers a deeper understanding of the role of boron chelation in modulating emission properties, opening new avenues for the design of functional fluorescent materials.