High contrast mechanochromic luminescence of aggregation-induced emission (AIE)-based 9,9-dimethyl-9,10-dihydroacridine-containing cruciform luminophores

Abstract

Two twisted D–A type cruciform luminophores DMTCS-AC and DBTCS-AC displaying rigid cross-conjugated structures with two conjugated donor and acceptor moieties intersecting at the central benzene core have been synthesized. Due to the existence of electron donor 9,9-dimethyl-9,10-dihydroacridine and electron acceptor dicyanodistyrylbenzene, both cruciforms show unique intramolecular charge transfer (ICT) emission. Moreover, both DMTCS-AC and DBTCS-AC bear highly twisted molecular conformations, which endow them with obvious aggregation-induced emission (AIE) properties and high contrast mechanofluorochromic (MFC) behavior. Under external force stimuli, the emissions of DMTCS-AC and DBTCS-AC powders changes from initial bright orange regions (586 nm and 599 nm) to the final red region (655 nm) and far red/near-infrared (FR/NIR) region (678 nm). PXRD and spectral results suggest that the remarkable MFC phenomenon originates from extension of the planarization of molecular conformation and subsequent planar intramolecular charge transfer (PICT) during the process of destruction of the crystals in the as-prepared original samples by external force. Moreover, the more significant MFC behavior of DBTCS-AC relative to DMTCS-AC is due to its the larger distortion degree and the stronger ICT process than that of DBTCS-AC.