Tweezers-like aromatic molecules and their luminescent properties depending on the structures

Di(hydroxyphenyl)pyrimidine with two anthryl substituents 1a was synthesized and characterized by X-ray crystallography and NMR spectroscopy. The molecule prefers ‘U’-shaped conformation supported by intramolecular O-H···N hydrogen bonds in the solid state and in solution. The CHCl₃-solvated compound binds two CHCl₃ molecules between the two parallel anthryl planes. Hexylation of the OH groups of 1a produces 1c whose diarylpyrimidine core contains these aromatic planes with O···H-C interaction and helical alignment. Compound 1c shows strong emission from the anthryl groups (410 nm, φ = 0.39), while luminescence is not observed for 1a partly due to quenching via PET (photo-induced electron transfer) process.