Tricolor fluorescence switching in the three crystal polymorphs of tetraphenylethylene modified fluorenone AIEgen

Abstract

Stimuli-responsive organic materials with aggregation-induced emission (AIE) characteristics have become a research hot spot in recent years due to their promising applications in information storage, organic light-emitting semiconductors (OLEDs) and chemosensors. In this study, we employ the molecular design strategy of introducing multiple weak interactions (π–π stacking and hydrogen bonding) and twisted molecular structures into the same molecular system to synthesize a new stimuli-responsive solid-state fluorescence switching molecule, 2,7-bis(4-(1,2,2-triphenylvinyl)phenyl)-9H-fluoren-9-one (TFT), in which the fluorenone and tetraphenyl ethylene moieties are incorporated. By culturing the crystals under different crystallization conditions, three polymorphs of TFT, yellow crystals (Y-TFT), orange crystals (O-TFT) and red crystals (R-TFT), were obtained. All of the three crystals exhibit high luminous efficiency and stimuli-responsive fluorescence switching under the stimuli of temperature, pressure, or solvent vapor. X-Ray single crystal structures, characterization of photophysical properties, powder X-ray diffraction, and theoretical calculations provide in-depth understanding of their phase transition and luminescence behaviors. The different emissions of the three crystal polymorphs originate from the molecular pairs (dimers), molecular layers, and single molecules, respectively. This study presents molecular-level understanding of the relationship between the organic molecular packing characteristics and the resulting optical properties. The simple-preparation, high luminescence efficiency and manageable, reversible tricolor fluorescence switching give TFT the potential to be a ‘‘smart’’ multifunctional luminescence material. In addition, this work also presents a design strategy for smart organic fluorescence switching molecules.