Photoswitching the fluorescence of nanoparticles for advanced optical applications

The dynamic optical response properties and the distinct features of nanomaterials make photoswitchable fluorescent nanoparticles (PF NPs) attractive candidates for advanced optical applications. Over the past few decades, the design of PF NPs by coupling photochromic and fluorescent motifs at the nanoscale has been actively pursued, and substantial efforts have been made to exploit their potential applications. In this perspective, we critically summarize various design principles for fabricating these PF NPs. Then, we discuss their distinct optical properties from different aspects by highlighting the capability of NPs in fabricating new, robust photoswitch systems. Afterwards, we introduce the pivotal role of PF NPs in advanced optical applications, including sensing, anti-counterfeiting and imaging. Finally, current challenges and future development of PF NPs are briefly discussed.

Developing Anisotropy in Self-Assembled Block Copolymers: Methods, Properties, and Applications

Block copolymers (BCPs) self-assembly has continually attracted interest as a means to provide bottom-up control over nanostructures. While various methods have been demonstrated for efficiently ordering BCP nanodomains, most of them do not generically afford control of nanostructural orientation. For many applications of BCPs, such as energy storage, microelectronics, and separation membranes, alignment of nanodomains is a key requirement for enabling their practical use or enhancing materials performance. This review focuses on summarizing research progress on the development of anisotropy in BCP systems, covering a variety of topics from established aligning techniques, resultant material properties, and the associated applications. Specifically, the significance of aligning nanostructures and the anisotropic properties of BCPs is discussed and highlighted by demonstrating a few promising applications. Finally, the challenges and outlook are presented to further implement aligned BCPs into practical nanotechnological applications, where exciting opportunities exist.

Visible-Light-Driven Photoswitching of Aggregated-Induced Emission-Active Diarylethenes for Super-Resolution Imaging

Photoswitchable fluorescent diarylethenes are promisingly widely applied in the fields of optical memory, all-optical transistors, bioimaging, and super-resolution imaging, and so on. However, they face the problems of fluorescence quenching in an aggregated/solid state, the inadequate fluorescence ON/OFF switching ratio, and the necessity of UV-light irradiation. Herein, we report a novel kind of high-performance diarylethenes with aggregated-induced emission (AIE) by conjugating two diarylethene groups on one AIE-gen (i.e., TPE-2DTE (blue-green fluorescent) and OTPE-2DTE (orange fluorescence)). Their open forms show enhanced fluorescence in the aggregated and solid states. The closed form of TPE-2DTE/OTPE-2DTE was effectively generated upon short-wavelength visible-light (400 nm-450 nm) irradiation, whose fluorescence was dramatically quenched by intra- and inter-molecular energy transfer. Remarkably, 405 nm purple irradiation gives fluorescence ON/OFF ratios of 1196:1 and 1983:1 for TPE-2DTE and OTPE-2DTE, respectively. The reverse process can be accomplished after another longer wavelength irradiation such as 621 nm and shows considerable fatigue resistance. Taking advantage of superior photoswitching properties under visible-light irradiation, TPE-2DTE and OTPE-2DTE were used for super-resolution imaging with a high resolution of sub 50 nm. This work offers guidance to design bright-emitting and high-performance visible-light-controlled diarylethene photoswitches for practical applications.

Super-resolution imaging of self-assembly of amphiphilic photoswitchable macrocycles

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.