A family of novel fluorophores with V- and X-shaped skeletons is rationally designed and prepared. Due to the extended cross π-conjugation in the X-shaped ones, their emission wavelengths in both solution and the solid state exhibit considerable bathochromic shifts compared with those of the V-shaped ones. It is found that a heavy intramolecular charge transfer (ICT) effect is the primary element for the mechanofluorochromic (MFC) response of this family, and an appropriate crystallinity of the sample is also indispensible for it to be MFC-active. Additionally, most fluorophores in this family are responsive to pH stimuli and display diverse and reversible changes of emission features. Interestingly, a V-shaped fluorophore exhibits a unique size-dependent emission behaviour, which makes it a distinctive three-color emitter.

A family of V-shaped fluorophores with different numbers and positions of vinyl are rationally designed, using which a largely wide and approximately successive range of solid-state emission wavelengths can be achieved before and after force stimuli. These compounds are intensely emissive and highly mechanofluorochromic (MFC), and many physical properties such as emission wavelengths, quantum yields, intramolecular charge transfer (ICT) extent, solvatochromism, aggregation-induced emission (AIE) activity and time consumed for restoration from amorphous phase are profoundly influenced by the number and site of vinyl groups. However, the emission wavelength shifts under force stimuli seem to be related to neither the number nor the position of vinyl. For a member with double polymorphs, the unqiue molecular pair packing in one of them revealed by X-ray crystallography is presumably responsible for its MFC inertia and the abnormally one-way phase transformation from the stable to the metastable one. Interestingly, a shape-dependent emission of self-assembled crystal with a fractal structure occurs when both of the two polymorphs are fumed in solvent vapor for long time. Moreover, the films made of these V-shaped compounds are successfully developed to be erasable mediums for information storage with robust fatigue resistance.

It is reported that two derivatives of (Z)-3-(quinolin-2-ylmethylene)-3,4-dihydroquinoxalin-2-(1H)-one (1) with a tetraphenylethene (TPE) group introduced at amide N atom of the dihydroquinoxalinone moiety (2) or at phenyl ring of the quinoline fragment (3) are synthesized, and the derivatives exhibit a remarkably enhanced aggregation-induced emission (AIE) activity than the parent. Although both the parent and the derivatives have the characteristic of an excited state intramolecular proton transfer (ESIPT), the AIE mechanism of 2 and 3 is totally different from that of 1. The considerably stronger emission of 3 than that of 2 should be attributed to the unique crystallization-induced emission enhancement (CIEE) effect.

A facile naphthalene-based fluorescence “turn-on” chemodosimeter, 2-((2-(vinyloxy)naphthalen-1-yl)methylene)-malononitrile (MS1), for rapid, selective and sensitive detection of Hg2+ by mercury-promoted hydrolysis of the vinylether group has been reported. The probe displayed a fast response time, and a sensitive fluorescence response (100-fold fluorescence enhancement) to the detection of Hg2+ in aqueous solution.

A family of novel BF2 complexes with (Z)-2-[phenanthridin-6(5H)-ylidene]-1-phenylethanone and its derivatives as ligands were prepared and characterized. The structure–property relationship indicates that photophysical properties of these complexes, which are intensely emissive both in solution and solid state, except for one (C4) with a N,N-dimethylamino group on the phenyl ring, are closely related to the electronic effect of the substituent at the phenanthridinyl or phenyl ring. X-ray crystallography explains the reason for the thoroughly quenched solid-state emission of C4 in view of the molecular packing mode. Powder XRD measurements indicate that the piezofluoro-chromism of the complex (C6) with a tetraphenylethene (TPE) group at the phenanthridinyl ring could be attributed to its morphology-dependent emission. Density functional theory calculations reveal the nature of the solvatochromic effect on complexes C4 and C6.

A new family of (Z)-3-(quinolin-2-ylmethylene)-3,4-dihydroquinoxalin-2(1H)-one derivatives, which exhibit aggregation-induced emission (AIE) activity, is synthesized and characterized. The qualitative structure property analysis reveals that the emission behaviors of these compounds are closely related to the locations of substituents on the molecules. The density functional theory (DFT) calculations elucidate that excited state intramolecular proton transfer (ESIPT) can smoothly occur in these compounds and a following twisted intramolecular charge transfer (TICT) in the lowest excited singlet state should account for their fluorescence quenching in solution. The restriction of such a TICT process in the aggregated state is assumed as the mechanism for their AIE behaviors.

Novel N,O bidentate BF2 complexes were prepared in good to excellent yields through the coordination of (2-quinolin-2-yl)phenol and its derivatives with boron trifluoride etherate under mild conditions. These fluorine–boron complexes exhibited strong fluorescence both in organic solvents and in solid state. Their photophysical properties were thoroughly studied by absorption and fluorescence spectroscopy in various solvents. The electronic and site effects of substituents on phenolic and quinolinyl rings were found to have a profound impact on quantum yields. All these complexes were fully characterized by IR, 1H, 13C, 19F NMR and microanalysis. The high quantum yields and large Stokes shifts make these compounds as potential fluorescent dyes.Graphical abstractNovel N,O bidentate BF2 complexes were prepared in good to excellent yields through the coordination of (2-quinolin-2-yl)phenol and its derivatives with boron trifluoride etherate under mild conditions. These compounds exhibited strong fluorescence both in organic solvents and in solid state. Their photophysical properties were thoroughly studied by UV–visible absorption and fluorescence spectroscopy in various solvents. All these complexes were characterized by infrared (IR) spectroscopy, 1H, 13C, 19F nuclear magnetic resonance (NMR) as well as microanalysis.Highlights► Synthesis of the complexes under very mild conditions. ► Strong fluorescence in solution and in solid state. ► High quantum yields and large Stokes shifts. ► Solvent-dependent absorption and emission behaviors. ► Thorough characterization by IR, 1H, 13C, 19F NMR and microanalysis.

It is surveyed that the amination of the Baylis–Hillman acetates with primary amines can be dramatically promoted in improved yields and shortened reaction time under ultrasound irradiation than those under conventional stirring. The extensive scope of both amines and acetates are screened to investigate the relationship between substituents and their performance in such transformation.

A novel tetracyclic frameworks of dispiropyrrolizidines can be obtained in moderate to good yields via the 1,3-dipolar cycloaddition of azomethine ylides with dipolarophiles derived from aza-Claisen rearrangement of Baylis–Hillman amines. The transformations are highly regioselective and stereoselective, affording the desired compounds in reduced time and increased yields under ultrasound irradiation at room temperature. All the products are confirmed by 1H, 13C NMR, IR and MS spectra, while their molecular structures are elucidated by X-ray crystallography of a selected sample.

A family of novel fluorophores with V- and X-shaped skeletons is rationally designed and prepared. Due to the extended cross π-conjugation in the X-shaped ones, their emission wavelengths in both solution and the solid state exhibit considerable bathochromic shifts compared with those of the V-shaped ones. It is found that a heavy intramolecular charge transfer (ICT) effect is the primary element for the mechanofluorochromic (MFC) response of this family, and an appropriate crystallinity of the sample is also indispensible for it to be MFC-active. Additionally, most fluorophores in this family are responsive to pH stimuli and display diverse and reversible changes of emission features. Interestingly, a V-shaped fluorophore exhibits a unique size-dependent emission behaviour, which makes it a distinctive three-color emitter.

It is reported that two derivatives of (Z)-3-(quinolin-2-ylmethylene)-3,4-dihydroquinoxalin-2-(1H)-one (1) with a tetraphenylethene (TPE) group introduced at amide N atom of the dihydroquinoxalinone moiety (2) or at phenyl ring of the quinoline fragment (3) are synthesized, and the derivatives exhibit a remarkably enhanced aggregation-induced emission (AIE) activity than the parent. Although both the parent and the derivatives have the characteristic of an excited state intramolecular proton transfer (ESIPT), the AIE mechanism of 2 and 3 is totally different from that of 1. The considerably stronger emission of 3 than that of 2 should be attributed to the unique crystallization-induced emission enhancement (CIEE) effect.

(E)-2′-[2-(Benzo[d]thiazol-2-yl)vinyl]-N,N-dimethyl-(1,1′-biphenyl)-4-amine 2, a novel V-shaped molecule (i.e. a half-cut cruciform), and its line-shaped isomer, (E)-4′-[2-(benzo[d]thiazol-2-yl)vinyl]-N,N-dimethyl-[1,1′-biphenyl]-4-amine 4, were successfully prepared via a two-step route of Suzuki coupling and Witting reaction. The much more profound ICT effect on 2 than on 4 means that the former has largely reduced quantum yields in highly polar solvents, in which AIE effect is enhanced for 2 but not for 4. Morphology-dependent fluorochromism in highly contrasted colours induced by mechanical force or surrounding pH stimuli can reversibly occur on 2 but not on 4. X-ray crystallography revealed loose molecular packing caused by the twisted conformation of 2, which is assumed to account for the intense solid-state emission and mechano-chromic activity. An organic solution of 2 and CF3COOH mixture shows potential for use as a security ink without the need for a covering reagent.