A volumetric three-dimensional digital light photoactivatable dye display

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

A Nonlinear Photochromic Reaction Based on Sensitizer-Free Triplet-Triplet Annihilation in a Perylene-Substituted Rhodamine Spirolactam

Nonlinear photochromic reactions that work with weak incoherent light are important for molecular operations with high spatial resolution and multiple photofunctions based on single molecules. However, nonlinear photochromic compounds generally require complex molecular design, restricting accessibility in various fields. Herein, we report nonlinear photochromic properties in a perylene-substituted rhodamine spirolactam derivative (Rh-Pe), which is synthesized from rhodamine B in facile procedures. Direct excitation of Rh-Pe produces the triplet excited state via the charge-transfer (CT) state. The triplet excited state causes triplet-triplet annihilation to bring the generation of the intensely colored ring-open form with nonlinear behavior. Furthermore, green- and red-light-induced photochromism was achieved in Rh-Pe using triplet sensitizers, although Rh-Pe can be directly excited only by ultraviolet and blue light. Our findings are expected to contribute to the development of photofunctional materials showing nonlinear behavior and low-energy light responsivity.

Development of a solid-supported light-triggered nitric oxide donor

Nitric Oxide (NO) photocleavable donors are useful tools for interrogating nitric oxide signalling and have potential use in photopharmacological applications. There is currently intensive research into newer methods to improve NO release and kinetic profiles. Herein, we report the design and synthesis of a solid-supported photocleavable NO donor synthesized by ligating an N-nitroso photocleavable nitric oxide derivative to a TentaGel® polymer resin bead. Illumination with 365 nm light released nitric oxide that could be tracked via a turn-on fluorescence response (λex = 450 nm, λem = 545 nm) and measured using the Griess assay and diaminorhodamine derivatives. These beads were further shown to be compatible with living A549 cells and had the ability to deliver greater concentrations of nitric oxide to cells proximal to a bead versus cells at more distal locations within the same well.

Vertically spliced tabletop light field cave display with extended depth content and separately optimized compound lens array

Tabletop three-dimensional light field display is a kind of compelling display technology that can simultaneously provide stereoscopic vision for multiple viewers surrounding the lateral side of the device. However, if the flat panel light field display device is simply placed horizontally and displayed directly above, the visual frustum will be tilted and the 3D content outside the display panel will be invisible, the large oblique viewing angle will also lead to serious aberrations. In this paper, we demonstrate what we believe to be a new vertical spliced light field cave display system with an extended depth content. A separate optimization of different compound lens array attenuates the aberration from different oblique viewing angles, and a local heating fitting method is implemented to ensure the accuracy of fabrication process. The image coding method and the correction of the multiple viewpoints realize the correct construction of spliced voxels. In the experiment, a high-definition and precisely spliced 3D city terrain scene is demonstrated on the prototype with a correct oblique perspective in 100-degree horizontal viewing range. We envision that our research will provide more inspiration for future immersive large-scale glass-free virtual reality display technologies.

Ultrafast Response Organic Photoswitch Materials and Their Application in Volumetric 3D Display

Volumetric three-dimensional (3D) display technology based on static screens is a crucial branch of 3D displays. The essential component in volumetric 3D displays is selectively excitable display media that can generate voxels at any position. Here, we synthesized a series of organic photoswitch materials to meet the specific requirements of 3D display mediums. In these photoswitch solutions, voxels are activated ultrafast within tens of picoseconds at the intersection of two control lasers and faded rapidly within tens of milliseconds when switching light is turned off. An experimental volumetric 3D display system utilizing an organic photoswitch solution as a screen is demonstrated. The system not only achieves a dynamic 3D display but also enables 360° viewing. The volumetric 3D display system can display true 3D images without auxiliary glasses and is expected to be applicable in fields as diverse as virtual reality, medical imaging, architectural design, and military visualization.

360-degree directional micro prism array for tabletop flat-panel light field displays

Tabletop light field displays are compelling display technologies that offer stereoscopic vision and can present annular viewpoint distributions to multiple viewers around the display device. When employing the lens array to realize the of integral imaging tabletop light field display, there is a critical trade-off between the increase of the angular resolution and the spatial resolution. Moreover, as the viewers are around the device, the central viewing range of the reconstructed 3D images are wasteful. In this paper, we explore what we believe to be a new method for realizing tabletop flat-panel light field displays to improve the efficiency of the pixel utilization and the angular resolution of the tabletop 3D display. A 360-degree directional micro prism array is newly designed to refract the collimated light rays to different viewing positions and form viewpoints, then a uniform 360-degree annular viewpoint distribution can be accurately formed. In the experiment, a micro prism array sample is fabricated to verify the performance of the proposed tabletop flat-panel light field display system. One hundred viewpoints are uniformly distributed in the 360-degree viewing area, providing a full-color, smooth parallax 3D scene.

Luminescent Materials for Volumetric Three-Dimensional Displays Based on Photoactivated Phosphorescence

True three-dimensional (3D) displays are the best display technologies and their breakthrough is primarily due to advancements in display media. In this paper, we propose two luminescent materials for a static volumetric 3D display based on photoactivated phosphorescence. The luminescent materials include (1) dimethyl sulfoxide (DMSO)/1-methyl-2-pyrrolidinone (NMP) or tetramethylene sulfoxide (TMSO) as the solvent and photochemically-deoxygenating reagent; (2) a metal phthalocyanine complex as the sensitizer; (3) a phosphorescent platinum complex as the emitter. The metal phthalocyanine complex, PdPrPc (PdBuPc), absorbs the light beam of 635 nm and the solvent scavenges the sensitized singlet oxygen. Light beams pass through a deoxygenated zone. The phosphorescent emitter, PtNI, absorbs the 440 nm light beam and phosphoresces only in the deoxygenated zone generated by the sensitizer. Phosphorescent voxels and high-contrast 3D images are well-defined at the intersection of 635 and 440 nm light beams.

Spirocyclic rhodamine B benzoisothiazole derivative: a multi-stimuli fluorescent switch manifesting ethanol-responsiveness, photo responsiveness, and acidochromism

Multi-stimuli fluorescent switching materials have been extensively employed in chemistry, biochemistry, physics, and materials science. Although rhodamine-based spirolactams have been specifically considered for metal ion sensing by photoluminescence, only some of them manifest photochromic behavior, and further development of rhodamine B (RHB)-based photochromic materials is required. RHB and its cyclic amides are advantageous in various sensing applications owing to their colorimetric responses to external stimulation. Hence, the current work reports a novel multifunctional active molecular material (3',6'-bis(diethylamino))-2-(5-nitrobenzo[c]isothiazol-3-yl)spiro[isoindoline-1,9'-xanthen]-3-one (RHBIT) by linking rhodamine B with 3-amino,5-nitro[2,1]benzoisothiazole (ANB) in a facile synthetic pathway; that perceives both emission color change and switching between off-on states. RHBIT shows acidochromism, photochromism, and pH sensitivity accompanied by unique ethanol responsiveness, with potential applications in anti-counterfeiting and drug delivery. Notably, RHBIT is highly acid sensitive and reverts to the ring-closed form on treatment with triethylamine (base), visible with the naked eye amidst colorless-pink-colorless transformations. On short UV irradiation, RHBIT provides a two-fold rise in the lifetime for the ring-open form in CHCl₃ and DCM compared to the spirolactam (closed form). DFT and TDDFT studies provide electronic characterization for the absorption spectra of the open and closed forms. Using the photoresponsive feature of RHBIT, an information protection application has been enacted via a rewritable platform.

Exploring the Structural Space of Chemiluminescent 1,2-Dioxetanes

Chemiluminescent molecules which emit light in response to a chemical reaction are powerful tools for the detection and measurement of biological analytes and enable the understanding of complex biochemical processes in living systems. Triggerable chemiluminescent 1,2-dioxetanes have been studied and tuned over the past decades to advance quantitative measurement of biological analytes and molecular imaging in live cells and animals. A crucial determinant of success for these 1,2-dioxetane based sensors is their chemical structure, which can be manipulated to achieve desired chemical properties. In this Perspective, we survey the structural space of triggerable 1,2-dioxetane and assess how their design features affect chemiluminescence properties including quantum yield, emission wavelength, and decomposition kinetics. Based on this appraisal, we identify some structural modifications of 1,2-dioxetanes that are ripe for exploration in the context of chemiluminescent biological sensors.

Shining Transparent Displays with Stable Narrow-Band Blue-Emitting Phosphor in Layered Film

Transparent displays (TDs) rendering "levitating" images on screen have appeared as an emerging technology toward augmented/mixed reality applications. However, the traditional phosphor design and screen construction have severely limited the TD performance owing to the lack of efficient narrow-band blue emitters and stable screen structure. Herein, the novel narrow-band (full width at half maximum: 32 nm) NaLi₃ SiO₄ :Eu²⁺ phosphor with a peak at 467 nm as a key blue emitter is explored, and it is sandwiched in layered film as a unique screen design. The devised screen features decent transparency, high emission color purity, and good reliability, and the TD prototype renders "floating" static images and vivid animation with broad viewing angle (15°-165°) and large color gamut (97% of National Television Standards Committee). Spectroscopic and microstructural characterizations reveal the TD superior performance originates from synergistic contributions of moderate crystal field effect (ε_c  ≈ 1.13 eV; ε_cfs  ≈ 1.60 eV), weak vibronic coupling (S ≈ 3; ħω ≈ 285 cm^-1 ), and limited thermal ionization of 5d electrons (E_a  ≈ 0.43 eV) for NaLi₃ SiO₄ :Eu²⁺ emission and layered architecture for screen film. These findings establish fundamental guidelines for narrow-band emitting materials design and shine light on superior TD innovative development.

Synthesis and Optical Characterization of a Rhodamine B Spirolactam Dimer

Amide derivatives of xanthene dyes such as rhodamine B are useful in a variety of sensing applications due to their colorimetric responses to stimuli such as acidity changes and UV light. The optical properties of these molecules can be influenced by intermolecular associations into dimeric structures, but the exact impact can be hard to predict. We have designed a covalently linked intramolecular dimer of the dye rhodamine B utilizing p-phenylenediamine to link the two dyes via amide bonds. The doubly closed spirolactam version of this dimer, RSL₂, is isolated as a colorless solid. Under acidic conditions or UV exposure, RSL₂ solutions develop a pink color that is expected for the ring-opened form of the molecule. However, nuclear magnetic resonance (NMR) and single-crystal diffraction data show that the equilibrium still prefers the closed dimer state. Interestingly, the emission profile of RSL₂ shows solvatochromic blue fluorescence. Control studies of model compounds with similar structural motifs do not display similar blue fluorescence, indicating that this optical behavior is unique to the dimeric form. This behavior may lend itself to applications of such xanthene dimers to more sophisticated sensors beyond those with traditional binary on/off fluorescence profiles.

Visible Light Chemical Micropatterning Using a Digital Light Processing Fluorescence Microscope

Patterning chemical reactivity with a high spatiotemporal resolution and chemical versatility is critically important for advancing revolutionary emergent technologies, including nanorobotics, bioprinting, and photopharmacology. Current methods are complex and costly, necessitating novel techniques that are easy to use and compatible with a wide range of chemical functionalities. This study reports the development of a digital light processing (DLP) fluorescence microscope that enables the structuring of visible light (465-625 nm) for high-resolution photochemical patterning and simultaneous fluorescence imaging of patterned samples. A range of visible-light-driven photochemical systems, including thiol-ene photoclick reactions, Wolff rearrangements of diazoketones, and photopolymerizations, are shown to be compatible with this system. Patterning the chemical functionality onto microscopic polymer beads and films is accomplished with photographic quality and resolutions as high as 2.1 μm for Wolff rearrangement chemistry and 5 μm for thiol-ene chemistry. Photoactivation of molecules in living cells is demonstrated with single-cell resolution, and microscale 3D printing is achieved using a polymer resin with a 20 μm xy-resolution and a 100 μm z-resolution. Altogether, this work debuts a powerful and easy-to-use platform that will facilitate next-generation nanorobotic, 3D printing, and metamaterial technologies.

BODIPYs with Photoactivatable Fluorescence

The borondipyrromethene (BODIPY) chromophore is a versatile platform for the construction of photoresponsive dyes with unique properties. Specifically, its covalent connection to a photocleavable group can be exploited to engineer compounds with photoswitchable fluorescence. The resulting photoactivatable fluorophores can increase their emission intensity or shift their emission wavelengths in response to switching. Such changes permit the spatiotemporal control of fluorescence with optical stimulations and the implementation of imaging strategies that would be impossible to replicate with conventional fluorophores. Indeed, BODIPYs with photoactivatable fluorescence enable the selective highlighting of intracellular targets, the nanoscaled visualization of sub-cellular components, the real-time monitoring of dynamic events and the photochemical writing of optical barcodes.

Seeking Illumination: The Path to Chemiluminescent 1,2-Dioxetanes for Quantitative Measurements and In Vivo Imaging

Chemiluminescence is a fascinating phenomenon that evolved in nature and has been harnessed by chemists in diverse ways to improve life. This Account tells the story of our research group's efforts to formulate and manifest spiroadamantane 1,2-dioxetanes with triggerable chemiluminescence for imaging and monitoring important reactive analytes in living cells, animals, and human clinical samples. Analytes like reactive sulfur, oxygen and nitrogen species, as well as pH and hypoxia can be indicators of cellular function or dysfunction and are often implicated in the causes and effects of disease. We begin with a foundation in binding-based and activity-based fluorescence imaging that has provided transformative tools for understanding biological systems. The intense light sources required for fluorescence excitation, however, introduce autofluorescence and light scattering that reduces sensitivity and complicates in vivo imaging. Our work and the work of our collaborators were the first to demonstrate that spiroadamantane 1,2-dioxetanes had sufficient brightness and biological compatibility for in vivo imaging of enzyme activity and reactive analytes like hydrogen sulfide (H₂S) inside of living mice. This launched an era of renewed interest in 1,2-dioxetanes that has resulted in a plethora of new chemiluminescence imaging agents developed by groups around the world. Our own research group focused its efforts on reactive sulfur, oxygen, and nitrogen species, pH, and hypoxia, resulting in a large family of bright chemiluminescent 1,2-dioxetanes validated for cell monitoring and in vivo imaging. These chemiluminescent probes feature low background and high sensitivity that have been proven quite useful for studying signaling, for example, the generation of peroxynitrite (ONOO^-) in cellular models of immune function and phagocytosis. This high sensitivity has also enabled real-time quantitative reporting of oxygen-dependent enzyme activity and hypoxia in living cells and tumor xenograft models. We reported some of the first ratiometric chemiluminescent 1,2-dioxetane systems for imaging pH and have introduced a powerful kinetics-based approach for quantification of reactive species like azanone (nitroxyl, HNO) and enzyme activity in living cells. These tools have been applied to untangle complex signaling pathways of peroxynitrite production in radiation therapy and as substrates in a split esterase system to provide an enzyme/substrate pair to rival luciferase/luciferin. Furthermore, we have pushed chemiluminescence toward commercialization and clinical translation by demonstrating the ability to monitor airway hydrogen peroxide in the exhaled breath of asthma patients using transiently produced chemiluminescent 1,2-dioxetanedione intermediates. This body of work shows the powerful possibilities that can emerge when working at the interface of light and chemistry, and we hope that it will inspire future scientists to seek out ever brighter and more illuminating ideas.

Xolography for linear volumetric 3D printing

The range of applications for additive manufacturing is expanding quickly, including mass production of athletic footwear parts¹, dental ceramics² and aerospace components³ as well as fabrication of microfluidics⁴, medical devices⁵, and artificial organs⁶. The light-induced additive manufacturing techniques⁷ used are particularly successful owing to their high spatial and temporal control, but such techniques still share the common motifs of pointwise or layered generation, as do stereolithography⁸, laser powder bed fusion⁹, and continuous liquid interface production¹⁰ and its successors^11,12. Volumetric 3D printing^13-20 is the next step onward from sequential additive manufacturing methods. Here we introduce xolography, a dual colour technique using photoswitchable photoinitiators to induce local polymerization inside a confined monomer volume upon linear excitation by intersecting light beams of different wavelengths. We demonstrate this concept with a volumetric printer designed to generate three-dimensional objects with complex structural features as well as mechanical and optical functions. Compared to state-of-the-art volumetric printing methods, our technique has a resolution about ten times higher than computed axial lithography without feedback optimization, and a volume generation rate four to five orders of magnitude higher than two-photon photopolymerization. We expect this technology to transform rapid volumetric production for objects at the nanoscopic to macroscopic length scales.

Annular sector elemental image array generation method for tabletop integral imaging 3D display with smooth motion parallax

One of the important features of tabletop 3D displays is the annular viewing area above the display system. In this paper, we propose an annular sector elemental image array (ASEIA) generation method for the tabletop integral imaging 3D display to form the annular viewing zone with smooth motion parallax. The effective pixels of the elemental images are distributed as annular sector, and they are mapped from the perspective images captured by the ring-shaped camera array. Correspondingly, the viewing sub-zones can be formed with an annular sector configuration and can be seamlessly stitched by using the time division scheme. Compared with the previous approach with rectangular elemental image array (EIA) distribution, the number of viewing sub-zones is decreased from 360 to 10 for the same effect of smooth motion parallax. Meanwhile, rendering efficiency is improved. The experimental results show that the proposed method is feasible to produce 360-degree continuous viewpoints in an annular viewing zone.

Regiodivergent Synthesis of Bis(4-oxycoumarin)-based Dioxabicycles: Exploration of [4 + 4] (Heterocyclo)reversion/addition and 1,5-Hydrogen Shift Photochromism

Two isomeric dioxabicyclic molecular skeletons were constructed by employing the concepts of divergent synthesis. A base-mediated and an acid-catalyzed pseudo-three-component reaction of two equivalents of 4-hydroxycoumarin and (Z)-3-chloro-3-phenylacrylaldehyde yielded the corresponding bis(4-oxycoumarin)-based 2,6- and 2,8-dioxabicycles, respectively. The prepared colorless 2,6-dioxabicycles turned red upon UV irradiation and underwent the reverse reaction when exposed to visible light. The photochromism was proposed to proceed via a sequential [4 + 4] (heterocyclo)addition/reversion and 1,5-hydrogen shift on the basis of photogenerated product-trapping experiments.

Planarization-Induced Activation Wavelength Red-Shift and Thermal Half-Life Acceleration in Hydrazone Photoswitches

The optimization and modulation of the properties of photochromic compounds, such as their activation wavelengths and thermal relaxation half-lives (τ1/2), are essential for their adaptation in various applications. In this work, we studied the effect of co-planarization of the rotary fragment of two photochromic hydrazones with the core of the molecule on their switching properties. The Z and E isomers of both compounds exhibit red-shifted absorption bands relative to their twisted versions, allowing for their photoswitching using longer wavelengths of light. Additionally, the thermal half-lives of both hydrazones are drastically shortened from hundreds of years to days.

Dual-View Integral Imaging 3D Display Based on Multiplexed Lens-Array Holographic Optical Element

We propose a dual-view integral imaging 3D display based on a multiplexed lens-array holographic optical element (MHOE). A MHOE is a volume holographic optical element obtained by multiplexing technology, which can be used for dual-view integral imaging 3D display due to the angle selectivity of the volume HOE. In the fabrication of the MHOE, two spherical wavefront arrays with different incident angles are recorded using photopolymer material. In the reconstruction, two projectors are used to project the elemental image arrays (EIA) with corresponding angles for two viewing zones. We have developed a prototype of the dual-view integral imaging display. The experimental results demonstrate the correctness of the theory.

Visible light photoredox catalyzed thiophosphate synthesis using methylene blue as a promoter

A novel efficient method for the synthesis of thiophosphate derivatives catalyzed by methylene blue with blue light irradiation under an air atmosphere is described.