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Aggregation‐induced emission luminogens (AIEgens) have been widely investigated due to their promising applications in data storage, organic light‐emitting diodes, and deep tissue bioimaging as compared to conventional fluorophores. In this work, we have designed and synthesized two novel rofecoxib analogues functionalized with different terminal groups (−NH2, −Br) on the benzene ring B. Interestingly, the compound 2 a‐3 with −NH2 substituent shows aggregation‐caused quenching effect whereas the compound 1 b‐3 with −Br group displays aggregation‐induced emission (AIE) property which may be caused by the twisted conformation and restricted – stacking of 1 b‐3 according to the X‐ray single crystal diffraction analysis. These opposite results indicated that the terminal groups could have great influence on the photophysical properties of targets. Moreover, the compound 1 b‐3 exhibited multi‐stimuli response luminescence behaviors under various external stimuli including solvatochromism, mechanochromism and acidochromism. Furthermore, lipid droplets imaging investigation proved the compound 1 b‐3 was capable of achieving specific lipid droplets bioimaging. This work not only presents a better understanding of the structure‐fluorescent property relationship based on the scaffold of rofecoxib, but also provides a new avenue for spectral modulation and the development of new MSR materials. [ABSTRACT FROM AUTHOR]

• p -RBZ, as a new DSE luminogen, has been constructed by integrating the benzothiazolium unit into the rofecoxib scaffold. • A novel insight into the DSE mechanism of p -RBZ is firstly proposed by combining the theoretical calculation and experimental investigation. • The RDG calculation and X-ray crystal data analysis revealed simultaneously that p -RBZ had strong intramolecular π-π interaction, which is mainly responsible for the bright emission in DMSO. • p -RBZ has been demonstrated as a multi-functional material for mechanical-force sensors and lipid droplets imaging probes. There is growing interest in developing dual-state emission luminogens (DSEgens) in the fluorescent materials community due to their bright emission in both dilute solution and the solid state and potential applications in various areas. In this work, we have developed a new dual-state emission (DSE) luminogen by integrating a benzothiazolium unit into the rofecoxib skeleton, namely 5-((Z)-4-(((E)-3-methylbenzo[d]thiazol-2(3H)-ylidene)- amino)benzylidene)-rofecoxib ( p -RBZ). Importantly, by combining theoretical calculations and experimental investigation, a novel insight into the DSE mechanism of p -RBZ is firstly proposed. The reduced density gradient (RDG) calculation and single X-ray data analysis, both revealed that p -RBZ had strong intramolecular π-π interaction between a ring and d ring, which can limit molecular rotation, reduce the rate of non-radiative transition, and enhance luminous efficiency in solution. Meanwhile, the conformation twist of p -RBZ and the highly restricted intermolecular π-π stacking may permit their bright emission in the solid state from the single-crystal X-ray and Hirshfeld surface analysis. Furthermore, p -RBZ displayed apparent solvatochromism, mechanochromism, and lipid droplets-specific imaging properties. These results implied that DSE-active p -RBZ had the potential to be developed as a mechanical-force sensor and lipid droplets imaging probe. [ABSTRACT FROM AUTHOR]

• A new pair of fluorophores (o-PDRF, p-PDRF) which exhibit opposing fluorescence behaviour upon aggregation. • o-PDRF and p-PDRF have been synthesized via a condensation reaction with refocoxib. • p -PDRF with a para-substituted aryl group exhibits ACQ behavior whereas the ortho-substituted isomer o-PDRF exhibits AIE behaviour. • o -PDRF , as an AIE-active compound, shows mechanochromic, acidochromic properties, and its potential application has been demonstrated. Design and syntheses of aggregation-induced emission (AIE) luminescent materials have attracted persistent attention in recent years. Among the various strategies to design novel AIE-active materials, conversion from aggregation-caused quenching (ACQ) to AIE is one of the most efficient because ACQ molecules are capable of being fluorescent in solution already, just not in the aggregated state. In this study, ACQ-to-AIE conversion was realized by regioisomerization of two rofecoxib derivatives named p-PDRF and o-PDRF. For these two compounds, p-PDRF with a piperidine group located on the para-position exhibited typical ACQ behavior while o-PDRF showed characteristic AIE activity when the piperidine group was relocated to the ortho-position. The single-crystal X-ray analysis revealed that the opposite fluorescent behavior in different states was mainly due to different structural conformations and different modes of molecular packing due to regioisomerization. Furthermore, o-PDRF also displayed apparent solvatochromism, mechanochromism, and acidochromism with reversible multi-stimulus behavior. Powder X-ray diffraction analysis indicated that the planarization of twisted structure and the destroy of crystalline structure was responsible for the tuned solid-state fluorescence. Taken together, the data showed that subtle migration of a piperidine group based on the rofecoxib scaffold altered the fluorescent properties of the two compounds significantly and that compound o-PDRF has the potential to be developed as mechanical-force sensors and pH detectors. [ABSTRACT FROM AUTHOR]

In this work, we synthesized a pair of positional isomers by attaching a small electron-donating pyrrolidinyl group at ortho- and para-positions of a conjugated core. These isomers exhibited totally different fluorescent properties. PDB2 exhibited obvious aggregation-induced emission properties. In contrast, PDB4 showed the traditional aggregation-caused quenching effect. Their different fluorescent properties were investigated by absorption spectroscopy, fluorescence spectroscopy, density functional theory calculations and single-crystal structural analysis. These results indicated that the substituent position of the pyrrolidinyl groups affects the twisted degree of the isomers, which further induces different molecular packing modes, thus resulting in different fluorescent properties of these two isomers. This molecular design concept provided a new accurate strategy for designing new aggregation-induced emission luminogens. [ABSTRACT FROM AUTHOR]

• A new AIEgen o-RBZ has been designed and synthesized by integrating the benzothiazole unit into the rofecoxib scaffold. • o-RBZ , as an AIE-active compound, shows an apparent solvatochromic effect, mechanochromic luminescent properties, and LDs specific imaging ability. • The bright emission mechanism in the solid state has been elucidated clearly according to single-crystal X-ray analyses with highly twisted conformation and restricted - stacking of o-RBZ. • The potential application of o-RBZ has been demonstrated as a multi-functional material for mechanical-force sensors and living cell imaging probes. Aggregation-induced emission (AIE) fluorescent molecules with unique photoelectric properties have received extensive attention due to the wide range of applications. In this study, a novel benzothiazole-rofecoxib-based luminogen, o-RBZ , was constructed by integrating the benzothiazole unit into the rofecoxib scaffold. It showed an obvious AIE property, which was investigated and elucidated clearly by systematic experimental and theoretical research. According to single-crystal X-ray and Hirshfeld surface analysis, the highly twisted structure of o-RBZ and restricted-stacking may allow for bright emission in the solid state. Meanwhile, the theoretical calculation revealed that small oscillator strengths (f = 0.06) and a large root mean square deviation (RMSD) were mainly responsible for the large non-radiative transition rate and the suppression of luminous efficacy in DMSO. Furthermore, o-RBZ displayed apparent solvatochromism, mechanochromism, and lipid droplets-specific imaging properties (Pearson's correlative coefficient value of 0.94, low cell cytotoxicity). These findings suggest that AIE-active o-RBZ has the potential to be developed as a multi-functional material for mechanical-force sensors and lipid droplets imaging probes. A novel accurate molecular design strategy was employed to achieve a new AIEgens o-BRZ by constructing a donor-acceptor system on the furanone unit of rofecoxib, and its potential as a multi-functional material have been demonstrated in the area of mechanical-force sensors and living cells imaging probes. [Display omitted] [ABSTRACT FROM AUTHOR]