Studies of cyanomethylcarbamoyl-bridged anthracene and pyrene fluorophores

Abstract

A series of cyanomethylcarbamoyl-bridged molecular ensembles was synthesized via a facile two-step Strecker-acylation approach. The resulting products are arene–arene dyads, in which anthracene and pyrene are incorporated as fluorogenic units, respectively. The molecular structures and solid-state packing properties of these compounds were characterized by X-ray single-crystal analysis in conjunction with density functional theory (DFT) calculations. Hydrogen bonding interactions and π–π stacking were observed as two key noncovalent forces that dictate supramolecular self-assemblies in the crystalline states, while the types of arene groups in these molecular dyads play a vital role in the solid-state packing motifs, pointing to a way of crystal engineering through bottom-up control. The electronic absorption and fluorescence emission properties of these compounds in the solution phase and solid state were examined. In each of the dyads, the arene group and cyanomethylcarbamoyl groups have little influence on the solution phase absorption and emission behaviors. However, the solid-state fluorescence properties were found to be significantly dependent on the arene groups as well as the crystalline and powdery states. In particular, close face-to-face stacking of the fluorogenic arenes (anthracene and pyrene) in the solid state can be correlated to long-wavelength (green color) luminescence due to the excimer mechanism. Moreover, the cyanomethylcarbamoyl bridge offers a receptor site for binding with fluoride anion through hydrogen bonding. Interactions of these molecular dyads with fluoride anion in polar organic solvents such as DMSO lead to fluorescence turn-off sensing function.