A versatile new class of organic photochromic molecules that offers an unprecedented combination of physical properties including tunable photoswitching using visible light, excellent fatigue resistance, and large polarity changes is described. These unique features offer significant opportunities in diverse fields ranging from biosensors to targeted delivery systems while also allowing non-experts ready synthetic access to these materials. In the field of adaptable and responsive materials, the ability of organic photochromic compounds to reversibly undergo changes in spectral absorption, volume, and solubility is of particular importance for applications in energy storage and chemical sensing and for controlling the conformation and activity of biomolecules.1 These switches are particularly valuable because their property changes are triggered by light, the most widely available, non-invasive, and environmentally benign external stimulus. Significantly, light also provides unique opportunities for spatial and temporal resolution.Among the classes of organic photochromic materials, azobenzenes, spiropyrans and diarylethenes have received the most attention because of their excellent performance and broad utility. Specifically, azobenzene has been extensively employed for its change in volume, resulting from a trans to cis isomerization, upon irradiation.2 Similarly, the change in spectral properties of spiropyrans and diarylethenes upon photoswitching has been exploited in a number of applications, 3 with spiropyran exhibiting the added benefit of a solubility switch, or a conversion from a hydrophobic to a hydrophilic form, upon irradiation. 4 Despite their ubiquity and broad utility, these privileged classes of photochromes typically all require the use of high-energy UV light to trigger their photochemical reactions. This hinders their potential use in biomedical applications and material science because UV light can be damaging to healthy cells and results in degradation for many macromolecular systems. Fatigue resistance is also a primary concern for UV-based photochromic switches.A common design principle to address this problem is to make synthetic modifications to these known classes of photochromic compounds that enable the use of visible light.5 Herein, we describe a conceptually different approach in which we designed a new class of visible light activated photochromes, termed donor−acceptor Stenhouse adducts (DASAs).6 These derivatives switch from a conjugated, colored, and hydrophobic form to a ring-closed, colorless, and zwitterionic structure on irradiation with visible light and have high fatigue resistance under ambient conditions ( Figure 1). In addition, the potential of this photoswitch in materials science is highlighted through the synthesis of a functional amphiphile that displays light-mediated micelle disassembly and cargo release.Our interest in the cascade rearrangements of activated furans 7 and a pioneering report by Honda 8 played a critical role in our development of t...

A facile approach to unique 3D, patterned polymer brushes is based on visible‐light‐mediated controlled radical polymerization. The temporal and spatial control of the polymerization allows the patterning of polymer brushes from a uniform initiating layer using a simple photomask (see picture). Furthermore, gradient polymer brushes, patterned block copolymers, and complex 3D structures can be obtained by modulating light intensity.

Block copolymer lithography holds promise as a next-generation technique to achieve the sub-20 nm feature sizes demanded by semiconductor roadmaps. While molecular weight and block immiscibility have traditionally been used to control feature size, this study demonstrates that macromolecular architecture is also a powerful tool for tuning domain spacing. To demonstrate this concept, a new synthetic strategy for cyclic block polymers based on highly efficient "click" coupling of difunctional linear chains is developed, and the thin film self-assembly of cyclic polystyrene-block-polyethylene oxide (cPS-b-PEO) is compared with the corresponding linear analogues. The reduced hydrodynamic radii of the cyclic systems result in ~30% decrease in domain spacing over the corresponding linear polymers.

A modular and general method based on a photomediated ATRA reaction for the spatially controlled functionalization of surfaces with visible light is reported. The ability to control reactivity with light intensity combined with the orthogonality of ATRA chemistry allows well-defined chemically differentiated monolayers and complex nonlinear chemical concentration gradients to be easily prepared. Use of light to mediate these reactions permits spatial regulation and the generation of unique, multifunctional chemical gradients.

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Ein einfacher Zugang zu gemusterten 3D‐Polymerbürsten basiert auf einer durch sichtbares Licht angeregten radikalischen Polymerisation. Die zeitliche und örtliche Kontrolle der Polymerisation ermöglicht die Musterung der Polymerbürsten ausgehend von einer einheitlichen Initiatorschicht durch eine einfache Photomaske (siehe Bild). Durch Änderung der Lichtintensität können unter anderem gemusterte Polymerblöcke und komplexe 3D‐Strukturen aufgebaut werden.

Controlled radical polymerizations have significantly impacted the field of polymer science by facilitating the synthesis of polymers with greater control over molecular weight, structure, and dispersity (Ð). As these synthetic techniques continue to evolve, more degrees of control can be realized via external regulation. Recent work has demonstrated external regulation of a controlled radical polymerization process with light using a photoredox Ir‐catalyst. While light offers many advantages as a stimulus for polymerization, scaling up presents unique challenges such as shallow and uneven penetration of light through the reaction medium, which negatively impacts the rate of polymerization. This work addresses some of the challenges associated with scaling up light‐mediated controlled radical polymerizations by employing a continuous flow microreactor and selecting appropriate reactor materials for oxygen sensitive reactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2693–2698

Three-dimensional (3D) nanostructures were obtained by the directed formation of multilayer block copolymer (BCP) thin films. The initial step in this strategy involves the assembly and cross-linking of cylinder-forming polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) BCP, in which 1.5 mol % of reactive azido (-N(3)) groups were randomly incorporated along the styrene backbone. Significantly, assembly of thin films of lamellar-forming BCPs on top of the underlying cross-linked cylindrical layer exhibited perpendicular orientations of microdomains between lamellae and cylinder layers. From the theoretical calculation of free energy in the multilayers, it was found that the nematic interactions between polymer chains at the interface play a critical role in the perpendicular orientation of lamellae on the cross-linked cylinder layers. Removal of the PMMA domains then affords nonsymmetrical nanostructures which illustrate the promise of this strategy for the design of well-defined 3D nanotemplates. It was also demonstrated that this structure can be effectively used to enhance the light extraction efficiency of GaN light-emitting diodes. Furthermore, we anticipate that such 3D nanotemplates can be applied to various areas, including advanced BCP nanolithography and responsive surface coating.