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...

The development of an easily synthesized, modular, and tunable organic photoswitch that responds to visible light has been a long-standing pursuit. Herein we provide a detailed account of the design and synthesis of a new class of photochromes based on furfural, termed donor−acceptor Stenhouse adducts (DASAs). A wide variety of these derivatives are easily prepared from commercially available starting materials, and their photophysical properties are shown to be dependent on the substituents of the push−pull system. Analysis of the switching behavior provides conditions to access the two structural isomers of the DASAs, reversibly switch between them, and use their unique solubility behavior to provide dynamic phase-transfer materials. Overall, these negative photochromes respond to visible light and heat and display an unprecedented level of structural modularity and tunabilty.

We present a one-photon visible light-responsive micellar system for efficient, on-demand delivery of small molecules. Release is mediated by a novel class of photochromic material - donor-acceptor Stenhouse adducts (DASAs). We demonstrate controlled delivery of small molecules such as the chemotherapeutic agent (paclitaxel) to human breast cancer cells triggered by micellar switching with low intensity, visible light.