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Typical cross-linked polymer networks have rubbery elasticity and do not exhibit thermoplasticity such as linear polymers. However, thermodynamically cross-linked polymer networks exhibit certain t...

We report the design and synthesis of a tetraphenylethene substituted with naphthalimide at the 4, 6 positions, named NI-2TPE. NI-2TPE exhibits strong solvent-dependent emission properties with combined ICT and AIE characteristics in THF–H2O systems. This probe was used directly on test papers to distinguish normal organic solvents using their emission colours under UV light based on its AIE and ICT nature. Thanks to the vinyl group in NI-2TPE, we synthesized a copolymer of NIPAM and NI-2TPE, termed P(NIPAM-co-NI-2TPE). The resulting polymer is highly soluble and fluorescent in water (ΦF = 15.4%). Due to the well-known thermo-responsive character of NIPAM, P(NIPAM-co-NI-2TPE) exhibits an interesting fluorescence change in response to various temperatures. Due to the thermo-induced shrinking of the PNIPAM chain, the fluorescence intensity gradually increased from 20 to 34 °C. As the temperature further increased from 34 to 90 °C, the fluorescence intensity decreased sharply, which was caused by the well-known thermal effects. Furthermore, we synthesized a P(HEA-co-NI-2TPE–TPP acrylate) copolymer, in which HEA is a hydrophilic unit, TPP is a mitochondria label and NI-2TPE a fluorescent probe. The corresponding polymer probe is highly soluble in water with FLQY = 7% and we have further applied this probe as a mitochondria targeted imaging tracker in HeLa cells successfully.

The magical fantasy of decades-old transformer characters is becoming closer to scientific reality, as transformable materials can change their shapes in response to thermal, mechanical, electrical, and chemical stimuli. However, precise and prompt control of plastic shaping remains to be wanted. Photoresponsive materials provide a promising alternative for rapid optomechanical shaping with limited success. Here, we report a new class of photoplastic transformation based on dynamic covalently crosslinked polytriazole (PTA) networks, in which crosslinking points are comprised of photocleaveable hexaarylbiimidazole (HABI). Upon sub-500 nm light irradiation, HABI is dissociated into two triphenylimidazole radicals (TPIRs) followed by spontaneous recombination back to the initial state. This photoswitching effect is demonstrated to generate nonthermal shape change in the PTA-HABI gel network at will upon light stimulus. A unique photoalignment phenomenon has also been discovered which can form oriented nanoscale patterning in the PTA-HABI gel network upon laser irradiation. The solvent-free PTA-HABI elastomer exhibits photoenhanced automatic self-healing properties at temperatures ranging from 25 °C to freezing points, which is attributed to the dynamic equilibrium between TPIRs and HABI. A photoplastic spring is fabricated and exhibits photoswitchable plastic behavior, i.e., a reversible transformation between plastic strain and elastic strain upon light irradiation. HABI-based polymer networks, including solvated gel and solvent-free elastomer, are promising as smart materials for nonthermal photoactivated shape changing, transformation, and self-healing applications.

In this article, we report the design and synthesis of a fluorescent molecular switch based on perylenemonoimide–hexaarylbiimidazole dyad (PMI–N–HABI), which exhibits not only photoswitchable near-infrared (NIR) fluorescence but also photoswitchable electron paramagnetic resonance (EPR) resulting from photo-induced twin radicals. The emission of PMI–N–HABI varies with different polarities of solvents due to the D–π–A molecular architecture, displaying strong NIR emission (715 nm) in methylene chloride with fluorescence quantum yield as high as 0.29. The photo-induced cleavage of the C–N bond between the two imidazole groups produces twin radicals efficiently upon UV irradiation and the colored species recovered to the initial state spontaneously by the collision of the two intramolecular TPIRs in a few seconds, with decay (or fluorescence recovery) half-life time (τ1/2) of 1.3 s in toluene at 297 K. The radical nature of the colored species is verified by EPR measurements. The emission of the perylenemonoimide could be reversibly quenched by the photo-induced radicals through the Forster resonance energy transfer (FRET) mechanism. The fluorescence-switching dye is applied to the optical nanoimaging of polymer nanowires prepared using the typical electrospinning method. The average diameter of about 160 nm is in accordance with the scan electron microscopic (SEM) images. Compared with the traditional SEM technique, we provide a convenient alternative to SEM with practical imaging resolution for polymer nanostructures.

Self-assembly of an amphiphilic photoswitchable fluorescent macrocycle methoxy-tetraethylene glycol-substituted hexaarylbiimidazole-borondipyrromethene can be observed directly under a super-resolution fluorescence microscope, with the nanoscale resolution beyond the optical diffraction limitation.