Advanced Optical Materials

McConney, Michael E.; Rumi, Mariacristina; Godman, Nicholas P.; Tohgha, Urice N.; Bunning, Timothy J.

doi: 10.1002/adom.201900429pmid: N/A

Photoresponsive liquid crystalline photonic materials are a medium in which the self‐regulation of light can occur. Liquid crystals are macroscopically self‐assembling, optically anisotropic materials capable of amplifying photochemical changes and thus are well suited to demonstrate complex light‐driven behavior. This review presents recent progress in liquid crystalline systems exhibiting photoresponsive structural color. More specifically, it surveys progress on liquid crystalline materials and structures with coloration that is the result of the constituents' spatial arrangement (not of presence of dyes or pigments) and for which this arrangement can be externally controlled by light. In cholesteric and blue‐phase liquid crystals, the structural color results from the natural self‐assembly of liquid crystal molecules in periodic structures. Several photochemically driven mechanisms can be exploited to impart color changes to these structures. Photonic liquid crystalline materials can also be generated with directed self‐assembly techniques and subsequent processes can be exploited to create photoinduced changes to their optical properties. After reviewing the recent progress in materials based on natural and directed self‐assembly, these approaches are compared and contrasted. A few interesting examples of more complex behavior are noted, including true autonomous self‐regulation of light flow in liquid crystal systems.

Zhao, Yuda; Ippolito, Stefano; Samorì, Paolo

doi: 10.1002/adom.201970062pmid: N/A

Yang, Meijia; Yuan, Zhongke; Liu, Jie; Fang, Zhengsong; Fang, Long; Yu, Dingshan; Li, Quan

doi: 10.1002/adom.201900069pmid: N/A

Photoresponsive soft actuators with photomechanical energy conversion and flexibility have attracted significant interest in recent years owing to their unique merits of flexibility, contactless operation, and remote control, as well as their multiple technological applications ranging from bionic robotics and biomedical devices to nanomotors. Seeking efficient photoresponsive materials with high energy conversion efficiency and robust mechanical properties and identifying effective photoactuation mechanisms are of paramount significance for the development of advanced photoactuators. Due to their unique optical properties, high mechanical strength, superior electrical and thermal conductivity, good flexibility, and stability, carbon‐based materials are regarded as attractive candidates for high‐performance photoresponsive actuators. Furthermore, easy functionalization or hybridization with other functional species substantially extends the functions of these materials and widens the application scope for photoactuators. Herein, this review summarizes the recent progress of photoactuators based on various carbon‐based soft materials, including 0D, 1D, 2D, and 3D nanocarbons as well as their functional soft composites with other responsive materials. Multiple driving schemes of photoresponsive actuators including photothermal, photomechanical, photoelectronic, and photochemical effects, photoactuating architecture design, and potential technological applications of photoactuators are elucidated. Furthermore, certain future opportunities and challenges in the ever‐flourishing optical‐to‐mechanical energy conversion area are emphasized and discussed.

del Barrio, Jesús; Sánchez‐Somolinos, Carlos

doi: 10.1002/adom.201900598pmid: N/A

Over the last few decades, the demand of polymeric structures with well‐defined features of different size, dimension, and functionality has increased from various application areas, including microelectronics, biotechnology, tissue engineering, and photonics, among others. The ability of light to control over space and time physicochemical processes is a unique tool for the structuring of polymeric materials, opening new avenues for technological progress in different fields of application. This article gives an overview of various photochemical reactions in polymers, photosensitive materials, and structuring techniques making use of light, and highlights most recent advances, emerging opportunities, and relevant applications.

Nocentini, Sara; Martella, Daniele; Parmeggiani, Camilla; Wiersma, Diederik S.

doi: 10.1002/adom.201900156pmid: N/A

Polymer photonics explores manufacturing of polymeric materials in order to create devices for light manipulation at the nanoscale. Available lithographic techniques give access to a truly 3D shaping, which can replicate computer‐aided designs by several methods. Among them, direct laser writing enables nanoscale precision fabrication. This platform allows integration of advanced materials for reconfigurable elements, whose shape and refractive index can be precisely controlled by external stimuli. This Progress Report collects the recent advances in the field of light‐tunable photonics, where polymers are used not only as passive elements for guiding and manipulating light but also to control the optical properties of the devices themselves. This creates dynamic structures with multifunctional performance. Starting from a brief description of light‐responsive materials patterned by direct laser writing (focusing on liquid crystalline networks), examples of integration of photonic materials on different platforms are shown—from simple photonic devices (as lenses or diffraction gratings) to their integration in photonic circuits (as active whispering gallery mode resonator coupled to waveguide). As most of the active materials are demonstrated to be biocompatible, implantable photonic platforms can be foreseen for biomedical applications.

Zhao, Yuda; Ippolito, Stefano; Samorì, Paolo

doi: 10.1002/adom.201900286pmid: N/A

2D materials possess exceptional physical and chemical properties that render them appealing components for numerous potential applications in (opto)electronics, energy storage, sensing, and biomedicine. However, such unique properties are hardly tunable or modifiable. The functionalization of 2D crystals with molecules constitutes a powerful strategy to adjust and modulate their properties, by also imparting them new functions. In this framework, the combination of 2D materials with photosensitive molecules is a viable route for harnessing their light‐responsive nature. The latter takes full advantage of the extremely high sensitivity of 2D materials to subtle changes in the local environment and the capacity of photosensitive molecules to modify their intrinsic properties when exposed to electromagnetic fields. The hybrid molecule–2D materials can preserve the unique optical and electrical properties of 2D layers and can exhibit additional light‐tunable features. In this Progress Report, the protocols that can be pursued for the 2D material functionalization and switching mechanisms in photosensitive systems are reviewed, followed by an in‐depth discussion on their tunable optical properties and their exploitation when integrated in novel photoswitchable electronic devices. The opportunities and associated challenges to be tackled for the development of unprecedented and high‐performance light‐responsive devices are discussed.

Li, Quan; Schenning, Albert P. H. J.; Bunning, Timothy J.

doi: 10.1002/adom.201901160pmid: N/A

Pantuso, Elvira; Filpo, Giovanni; Nicoletta, Fiore Pasquale

doi: 10.1002/adom.201900252pmid: N/A

Stimuli‐responsive polymer membranes have gained particular attention for the ability to tune opportunely their physicochemical properties under the application of an external stimulus. Heat, pH value, ionic strength, pressure, humidity, electric and magnetic fields, antigen/antibody interactions, chemical reactions, and light can be used as triggers for specific responses in polymer membranes. In particular, light is a fascinating stimulus, as it is a green energy, which can be modulated in a precise and convenient way. In addition, it allows remote and contactless interactions without changing the original chemical environment. This review reports recent progresses in light‐responsive polymer membranes with particular attention to chemical groups and responsive mechanisms.

Chang, Victoria Y.; Fedele, Chiara; Priimagi, Arri; Shishido, Atsushi; Barrett, Christopher J.

doi: 10.1002/adom.201900091pmid: N/A

Photoreversible optically switchable azo dye molecules in polymer‐based materials can be harnessed to control a wide range of physical, chemical, and mechanical material properties in response to light, that can be exploited for optical control over the bio‐interface. As a stimulus for reversibly influencing adjacent biological cells or tissue, light is an ideal triggering mechanism, since it can be highly localized (in time and space) for precise and dynamic control over a biosystem, and low‐power visible light is also an inherently gentle, benign, and nondamaging stimulus in a biological environment. Azobenzene‐based dyes in particular are emerging as especially attractive candidates among photoreversible molecules, and soft azobenzene‐containing materials are promising due to their ease of incorporation, and efficient and robust photochemistry and photophysics. This review provides a current survey of the use of photoreversible azo soft materials in cell biology and tissue engineering bio‐interface applications, to afford light control over molecular motion (orientation, flow), by inscribing surface morphological patterns or macroscopically photoactuating surfaces and structures, via three key photophysical and bioactive effects enabled by the azo groups' light‐induced photo‐orientation, topological optical patterning, and photomechanical actuation.

Lu, Fengniu; Nakanishi, Takashi

doi: 10.1002/adom.201900176pmid: N/A

Solvent‐free luminous molecular liquids (LMLs) are a new generation of soft matter which exhibit uncharged, nonvolatile, and fluidic nature and emit intense and homogeneous luminescence in the condensed state. They can be produced readily on the gram scale by modifying luminophores with bulky, flexible, and low‐melting side chains. Their performance can be facilely enriched by blending them with commercially available functional substances. Therefore, since their active optoelectronic properties were perceived a decade ago, LMLs have been regarded as promising contributing components in the burgeoning field of flexible and wearable light‐emitting devices. Recently, richer insights into LMLs have triggered various new applications. Additionally, unexpected phase behavior and photophysical properties have been discovered coincidentally. Therefore, the sensible and sophisticated molecular design principles of LMLs are still being augmented to guarantee predictable, steady, and consistent end‐use performance. This review summarizes the latest developments in LMLs, including molecular design principles, regulation and enrichment of their photophysical properties, and their versatile applications. Additionally, a prediction of the perspectives of LMLs in the near future is presented at the end.