Reversible light-controlled fluorescence switch of block polymer-grafted carbon dots and cellular imaging

A novel type of aggregation-induced emission (AIE) nanoparticles, which are carbon dots (CDs) grafted with block polymer of tetraphenylethylene, spiropyran and N-isopropylacrylamide (CD-g-poly((TPE-co-SPA)-block-NIPAM)), was synthesized. The CD-g-poly((TPE-co-SPA)-block-NIPAM) nanoparticles can emit weak cyan fluorescence in tetrahydrofuran, while showing AIE-enhanced cyan fluorescence in water and solid film. The fluorescence of the CD-g-poly((TPE-co-SPA)-block-NIPAM) nanoparticles can reversibly transform cyan to red with UV/visible light irradiation, and functioned as a reversible fluorescence photoswitch. Importantly, the CD-g-poly((TPE-co-SPA)-block-NIPAM) nanoparticles have low cytotoxicity and, therefore, can be used for imaging in living cells.

Dissipative aggregation-induced emission behaviour of an amino-functionalized tetraphenylethene using a pH oscillator

A dissipative aggregation-induced emission (DAIE) system is successfully fabricated by coupling a stimuli-responsive AIE luminogens (AIEgens) with a pH oscillator. The novel DAIE system exhibits reversible, autonomous and sustainable AIE behaviour. Moreover, the DAIE behaviour can be regulated with the system temperature. The novel strategy will boost the development of bioinspired intelligent systems for real-world applications.

A Mechanochromic and Photochromic Dual-Responsive Co-assembly with Multicolored Switch: A Peptide-Based Dendron Strategy

In this contribution, we report a unique co-assembly composed of pyrene and spiropyran that were linked separately at the focal point of the same peptide-based dendron (Phe-Glu), in which the dendrons offer driving forces for the coaggregation. A series of co-assemblies with different weight ratios (Py-Phe-Glu/SP-Phe-Glu) were prepared and the morphology could be tuned. It is found that the resulting stable co-assembled organogel is double switchable triggered by light and heat. TEM revealed that, in the xerogel, Py-Phe-Glu formed rigid rod nanofibers with large diameters and acted as a rigid sketelon where the gracile interwoven fibrous structure of SP-Phe-Glu grew. More interestingly, the original powder of the co-assembled xerogel (1.0 mg/0.1 mg) not only displayed a sequential high-contrast tricolored switch from dark blue to bright cyan and to red under external force but also presented multistate accessible photochromic properties. Such mechanochromic and photochromic behaviors of the xerogel are mainly due to the transition of different excimers of pyrene and the force/photoinduced ring-opening reaction of spiropyran. It is rarely reported that self-assembled soft materials achieve mechanochromic and photochromic dual-responsive behaviors with a high-contrast multicolored switch. We believe the co-assembly strategy based on polypeptide dendrons can be extended to other systems for establishing novel intelligent fluorescent materials.

Tetraphenylethene-Induced Free Volumes for the Isomerization of Spiropyran toward Multifunctional Materials in the Solid State

Solid-state photochromic materials with reversible and adjustable optical properties are very appealing because of their wide prospects in advanced functional materials. Yet, it remains a significant challenge to develop such materials in the solid state. In this study, a tetraphenylethene derivative (SP-TPE-SP)-based solid-state photoswitch, which exhibits reversible photochromism in the solid state, was constructed. Efficient photoswitching between SP-TPE-SP and its photoisomer MC-TPE-MC is assisted by the large free volumes caused by the nonplanar molecular structures of the TPE1 moieties and the intramolecular π-π stackings between the two MC moieties. The free volumes are large enough to allow for the transport of HCl gas molecules for an acidochromic response. Furthermore, the morphology of the SP-TPE-SP solid surface can be regulated by ultraviolet light irradiation. The contact angles of the SP-TPE-SP solid surface can be decreased, changing from 97 to 82°. Therefore, SP-TPE-SP with a rather simple molecular structure is appealing for advanced multifunctional materials.

Highly sensitive switching of solid-state luminescence by controlling intersystem crossing

The development of intelligent materials, in particular those showing the highly sensitive mechanoresponsive luminescence (MRL), is desirable but challenging. Here we report a design strategy for constructing high performance On–Off MRL materials by introducing nitrophenyl groups to molecules with aggregation-induced emission (AIE) characteristic. The on–off methodology employed is based on the control of the intersystem crossing (ISC) process. Experimental and theoretical investigations reveal that the nitrophenyl group effectively opens the nonradiative ISC channel to impart the high sensitivity and contrast On–Off behavior. On the other hand, the twisted AIE luminogen core endows enhanced reversibility and reduces the pressure required for the luminescence switching. Thin films can be readily fabricated from the designed materials to allow versatile applications in optical information recording and haptic sensing. The proposed design strategy thus provides a big step to expand the scope of the unique On–Off MRL family.

The development of intelligent materials, in particular those showing the highly sensitive mechanoresponsive luminescence (MRL), remains challenging. Here the authors report a strategy for constructing high performance On-Off MRL materials by introducing nitrophenyl groups to molecules with aggregation-induced emission characteristic.