Benzoate Ester Functionalized Phenylenediamine Derivatives: Synthesis, Crystal Structure and Optical Properties

Abstract Methyl benzoate functionalized phenylenediamine derivatives with the methoxycarbonyl groups at the ortho ‐, meta ‐ and para ‐positions of amino group were synthesized via palladium‐catalyzed Buchwald‐Hartwig reaction and copper‐catalyzed Ullmann amination. Crystallographic analysis unraveled the presences of intra‐ and intermolecular hydrogen bonds in compounds bearing NH groups. Spectroscopic investigation revealed that compounds with amine protected by phenyl showed varied emissions with relatively stronger intensity in solution and in solid state than those of the unprotected ones. All the compounds demonstrated aggregation induced enhanced emissions in THF/water, some of which exhibited tunable emissions according to the water contents. Theoretical calculations unveiled that compound with intramolecular hydrogen bond possessed twisted structure and could undergo one proton transfer process in the excited state, which were essential to its low fluorescence intensity in solution and enhanced emission in the solid state.