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Two donor–acceptor cruciform luminophores MB-CACEB and DFB-CACEB , which show unique intramolecular charge transfer (ICT) process originating from electron-donors 9,9-Dimethyl-9,10-dihydroacridine units and electron-acceptors dicyanovinylbenzene moieties, are designed and synthesized. Owing to the presence of the large steric hindrance between the four surrounding substituents attaching to the central benzene ring, MB-CACEB and DFB-CACEB adopt the spatial conformation with high degree of distortion, which endows the two compounds with aggregation-induced emission (AIE) properties, effective solid-state luminescence and high contrast mechanofluorochromic (MFC) behavior. Upon external force stimuli, the emission color of MB-CACEB and DFB-CACEB solid powders changes from initial bright yellow-green (535 nm and 537 nm) to orange (604 nm) and red (628 nm), respectively, thus large spectral red-shifts of 69 nm and 91 nm are obtained. PXRD and spectral results suggest that the remarkable MFC phenomenon comes from the planarization of the molecular conformation and subsequent planar intramolecular charge transfer (PICT) during the process of destruction of the crystals in the as-prepared samples by external force. Moreover, compared to MB-CACEB , DFB-CACEB shows more significant MFC behavior, this is because DFB-CACEB possesses the larger distortion degree and the stronger ICT process than that of MB-CACEB. Image 1 • Two twisted donor–acceptor π-conjugated cruciform luminophores showing unique ICT properties were prepared. • They exhibited evident AIE characteristics and effective solid-state luminescence efficiency. • They showed high contrast MFC behavior tuning by the substitution groups in molecules. [ABSTRACT FROM AUTHOR]

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. Image 1 • Two twisted X-shape cruciform luminophores exhibiting unique ICT properties were prepared. • They exhibit evident AIE characteristics and effective solid-state emission. • They show high contrast MFC behavior, which is tuned by degree of distortion of molecular conformation and ICT degree. [ABSTRACT FROM AUTHOR]

New D-A type cruciform luminophore TFMB-CBCEB bearing electron-donor carbazole unit and electron-acceptor dicyanovinylbenzene segment was designed and prepared. The results show that the emission wavelengths of TFMB-CBCEB are strongly affected by solvent polarity, indicating intramolecular charge-transfer (ICT) transitions. Interestingly, TFMB-CBCEB exhibits AIE behavior with high α AIE of 405 and high solid-state luminescence efficiency of up to 0.810. Moreover, TFMB-CBCEB shows remarkable mechanofluorochromic (MFC) properties. When the as-prepared samples are subjected to grinding, the emission of TFMB-CBCEB red-shifts by 32 nm from the blue regions (λ max = 566 nm) to the orange regions (λ max = 598 nm). The changes of fluorescence emission induced by grinding can be restored by solvent-fuming and regenerated by grinding, suggesting excellent reversibility in the switching processes. PXRD analysis revealed that the MFC mechanism of TFMB-CBCEB attributed to the crystalline-amorphous phase transformation between the original and ground states. Meanwhile, the red-shift in the PL spectra upon grinding comes from the extension in molecular conjugation caused by planarization of molecular conformation and subsequent planar intramolecular charge transfer (PICT) process. Image 1 • The twisted donor–acceptor π-conjugated cruciform luminophore TFMB-CBCEB showing unique ICT properties was prepared. • TFMB-CBCEB exhibited evident aggregation-induced emission characteristics and high solid state efficiency. • TFMB-CBCEB showed reversible mechanofluorochromic behavior with a spectral red-shift of 32 nm. [ABSTRACT FROM AUTHOR]

Two donor–acceptor cruciform luminophores MB-CTPEEB and DFB-CTPEEB with twisted molecular conformations have been prepared. It was found that both cruciforms showed unique intramolecular charge transfer (ICT) emission due to the existence of tetraphenylethene with electron-donating ability and dicyanovinylbenzene with electron-withdrawing ability. Moreover, MB-CTPEEB and DFB-CTPEEB bear obvious aggregation-induced enhanced emission (AIEE) properties and good solid state fluorescence emission with high solid state luminescence efficiency of 0.633 and 0.783, respectively. In particular, both luminophores exhibited substituent-dependent reversible mechanofluorochromic (MFC) behavior. Under external force stimuli, the emission color of DFB-CTPEEB powders changes from initial bright yellowish green (517 nm) to final orange (583 nm), thus large spectral shift of 66 nm, which originates from the planarization of the molecular conformation and subsequent planar intramolecular charge transfer (PICT) caused by destruction of the crystals in the as-prepared samples under external force, is obtained. By sharp contrast, MB-CTPEEB exhibits no MFC behavior. The reason is that MB-CTPEEB possessed less twisted molecular conformation and weaker ICT degree than that of DFB-CTPEEB , which endows the MB-CTPEEB molecules with strong intermolecular forces and close packing, the small deformability and relative weak PICT ability under external force. Image 1 • Two twisted donor–acceptor π-conjugated tetraphenylethene-containing cruciform luminophores showed unique ICT properties. • They exhibited evident AIEE characteristics and high solid state luminescence efficiency. • They showed different MFC behavior, which was effected by degree of distortion of molecular conformation and ICT degree. [ABSTRACT FROM AUTHOR]

Two D-A type cruciform luminophores FB-CTPAEB and DFB-CTPAEB were designed and prepared. The two compounds exhibited unique intramolecular charge-transfer (ICT) and solid-state fluorescence behavior. The results show that both compounds exhibit AIEE behavior and high solid-state luminescence efficiency (up to 0.693 and 0.442, respectively). Moreover, FB-CTPAEB and DFB-CTPAEB show remarkable mechanofluorochromic (MFC) properties. Once the as-prepared samples were subjected to grinding, the emission of the two cruciform luminophores was red shifted by 52 nm and 46 nm, correspondingly, their fluorescence colors changed from yellow and reddish orange to red, respectively. The fluorescence emission changes induced by grinding can be restored by solvent-fuming and regenerated by grinding. PXRD analysis revealed that the MFC behavior of FB-CTPAEB and DFB-CTPAEB came from the transformation between crystalline and amorphous states upon external stimuli. Meanwhile, the extension in molecular conjugation caused by planarization of molecular conformation and subsequent planar intramolecular charge transfer (PICT) process were responsible for the red-shifts in the PL spectra. Image 1 • Two twisted donor–acceptor π-conjugated cruciform luminophores showing unique ICT properties were prepared. • The two cruciform luminophores displayed aggregation-induced emission characteristics and high solid state efficiency. • They possessed high contrast mechanofluorochromic behavior with good reversibility. [ABSTRACT FROM AUTHOR]

Two D-A type cruciform luminophores MODCS-TPE and FMDCS-TPE were successfully prepared via a two-step route involving Suzuki cross-coupling and Knoevenagel condensation reactions, and their intramolecular charge-transfer (ICT) and solid-state fluorescence were studied in detail. The results show that MODCS-TPE and FMDCS-TPE exhibit AIE behavior with high solid state fluorescence efficiency of 0.321 and 0.312. Interestingly, MODCS-TPE and FMDCS-TPE exhibit both typical AIE behavior with the AIE factors of 138 and 51and high contrast MFC effects. Once grinding had been performed, the emission of the two cruciform luminophores was red shifted by 34 nm and 44 nm from the blue regions (λ max = 471 nm and 478 nm) to the green and yellowish green regions (λ max = 505 nm and 522 nm), respectively. Moreover, the mechanochromic switching behavior was reversible and repeated many times without any fatigue in the grinding-heating (for MODCS-TPE) or grinding-fuming (for MODCS-TPE and FMDCS-TPE) fluorochromic process. The mechanism of MFC behavior that the transformation between crystalline and amorphous states upon external stimuli is revealed by PXRD and DSC analysis, and the large red-shifts induced by grinding originate from extended conjugation and subsequent planar intramolecular charge transfer (PICT) after grinding. Image 1 • Two twisted π-conjugated cruciform luminophores MODCS-TPE and FMDCS-TPE showing unique ICT properties were synthesized. • MODCS-TPE and FMDCS-TPE exhibited AIE characteristics and high solid-state luminescence efficiency. • MODCS-TPE and FMDCS-TPE showed high contrast reversibable mechanofluorochromic properties. [ABSTRACT FROM AUTHOR]