Fluoranthene-o-Carborane Dyad: Exploring Thermochromism and Mechanochromism in Crystalline Systems

Abstract

Fluoranthene, an important subclass of polycyclic aromatic hydrocarbons (PAHs), has continued to attract considerable attention in the fields of synthetic organic chemistry and materials science. However, due to the strong π-π intermolecular interactions resulting from highly planar π-π conjugated structures, they usually suffer from aggregation caused quenching (ACQ) in the solid state, which limits their further applications. In this study, SOF and DOF are synthesized via a modified nickel-catalyzed Kumada coupling reaction using o-carborane with three-dimensional clusters and 3-bromofluoranthene as the starting materials. The structural characteristics, luminescent properties, and stimuli-responsive behavior of these compounds are systematically investigated through single crystal structure analysis, UV-vis absorption spectroscopy, fluorescence spectroscopy, and DFT theoretical calculations. For SOF, the formation of excimers is identified as the primary cause of thermochromism. The DOF exhibits excellent properties of aggregation-induced emission (AIE) and the quantum yields as high as 18.75% in the solid state. Additionally, the transformation from crystalline to amorphous is the primary reason for the significant mechanochromism of DOF. The nearly perpendicular packing is beneficial for thermochromism, while anti-parallel packing is likely to cause mechanochromism. These results suggest that o-carborane can play a distinctive role in precisely regulating the emission properties and stimulus response.