Heptazine derivatives have attracted significant interest due to their small S1-T1 gap, which contributes to their unique electronic and optical properties. However, the nature of the lowest excited state remains ambiguous. In the present study, we characterize the lowest optical transition of heptazine by its magnetic transition dipole moment. To measure the magnetic transition dipole moment, the flat heptazine must be chiroptically active, which is difficult to achieve for single heptazine molecules. Therefore, we used supramolecular polymerization as an approach to make homochiral stacks of heptazine derivatives. Upon formation of the supramolecular polymers, the preferred helical stacking of heptazine introduces circular polarization of absorption and fluorescence. The magnetic transition dipole moments for the S1 â S0 and S1 â S0 are determined to be 0.35 and 0.36 Bohr magneton, respectively. These high values of magnetic transition dipole moments support the intramolecular charge transfer nature of the lowest excited state from nitrogen to carbon in heptazine and further confirm the degeneracy of S1 and T1.
Photoclick reactions combine the advantages offered by light-driven processes and classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photo-crosslinking, and protein labeling. Despite these advances, the dependency of most of the photoclick reactions on UV light poses a severe obstacle for their general implementation, as this light can be absorbed by other molecules in the system resulting in their degradation or unwanted reactivity. However, the development of a simple and efficient system to achieve bathochromically shifted photoclick transformations remains challenging. Here, we introduce triplet-triplet energy transfer as a fast and selective way to enable visible light-induced photoclick reactions. Specifically, we show that 9,10-phenanthrenequinones (PQs) can efficiently react with electron-rich alkenes (ERAs) in the presence of a catalytic amount (as little as 5â mol %) of photosensitizers. The photocycloaddition reaction can be achieved under green (530â nm) or orange (590â nm) light irradiation, representing a bathochromic shift of over 100â nm as compared to the classical PQ-ERAs system. Furthermore, by combining appropriate reactants, we establish an orthogonal, blue and green light-induced photoclick reaction system in which the product distribution can be precisely controlled by the choice of the color of light.
The light-induced photocycloaddition of 9,10-phenanthrenequinone (PQ) with electron-rich alkenes (ERA), known as the PQ-ERA reaction, is a highly attractive photoclick reaction characterized by high selectivity, external non-invasive control with light and biocompatibility. The conventionally used PQ compounds show limited reactivity, which hinders the overall efficiency of the PQ-ERA reaction. To address this issue, we present in this study a simple strategy to boost the reactivity of the PQ triplet state to further enhance the efficiency of the PQ-ERA reaction, enabled by thiophene substitution at the 3-position of the PQ scaffold. Our investigations show that this substitution pattern significantly increases the population of the reactive triplet state (3ππ*) during excitation of 3-thiophene PQs. This results in a superb photoreaction quantum yield (ΦP, up to 98%), high second order rate constants (k2, up to 1974 M-1 s-1), and notable oxygen tolerance for the PQ-ERA reaction system. These results have been supported by both experimental transient absorption data and theoretical calculations, providing further evidence for the effectiveness of this strategy, and offering fine prospects for fast and efficient photoclick transformations.
Light-induced 9,10-phenanthrenequinone-electron-rich alkene (PQ-ERA) photocycloadditions are an attractive new type of photoclick reaction, featuring fast conversions and high biocompatibility. However, the tunability of the reaction was hardly investigated up to now. To this end, we explored the influence of substituents on both reaction partners and the reaction rate between the PQs and ERAs. We identified new handles for functionalization and discovered that using enamines as ERAs leads to drastically enhanced rates (>5400â times faster), high photoreaction quantum yields (ΦP , up to 65 %), and multicolor emission output as well as a high fluorescence quantum yield of the adducts (ΦF , up to 97 %). Further investigation of the photophysical and photochemical properties provided insights to design orthogonal reaction systems both in solution and on nanoparticle surfaces for ultrafast chemoselective functionalization by photoclick reactions.
Due to the highly selective nature of singlet oxygen as an oxidant, it has received considerable interest in various areas of (organic) chemistry. Two green light activated hydrazone-based boron difluoride triplet photosensitizers possessing high quantum yields for 1O2 formation are reported. These photostable complexes are promising in applications in synthesis and catalysis.
The development of a responsive fluorescent probe for the detection of a particular biomolecule in a specific site at the desired moment is important in the fields of bioanalysis and imaging, molecular biology and biomedical research. In this work, we report the development of a remote-light activatable nanoprobe for the fluorescence detection of sulphite in pure aqueous solution and its imaging applications in living cells. The nanoprobe, Poly-Cm-SP, is fabricated simply by wrapping photochromic molecules (Cm-SP) into a polymer nanoparticle. Upon alternate UV/Vis light irradiation for several seconds, the Poly-Cm-SP nanoprobe exhibits red/blue fluorescence switch due to the inactive/active FRET processes from coumarins to the SP/MR isomers of the photochromic molecule. In the presence of sulphite, the specific reaction of sulphite with the electron deficit "CîC" bond of the MR isomer occurs, resulting in an inefficient FRET process and thus exhibiting a constant "ON" blue channel fluorescence signal. After UV-light irradiation, the formation of activated Poly-Cm-MRin situ thus enables the detection of sulphite through recording the ratiometric changes of fluorescence signals at both blue and red channels. The Poly-Cm-SP nanoprobe possesses excellent biocompatibility and lysosome distribution capability, allowing it to be used for photochromic imaging and sulphite detection in the lysosomes of living macrophage cells. This work thus offers a new remote-light activatable nanoprobe for the detection and imaging of sulphite in biological systems.
Fluorescent Dyes , Nanoparticles , Fluorescence Resonance Energy Transfer/methods , Fluorescent Dyes/chemistry , Nanoparticles/chemistry , Optical Imaging , Sulfites
Natural systems transfer chiral information across multiple length scales through dynamic supramolecular interaction to accomplish various functions. Inspired by nature, many exquisite artificial supramolecular systems have been developed, in which controlling the supramolecular chirality holds the key to completing specific tasks. However, to achieve precise and non-invasive control and modulation of chirality in these systems remains challenging. As a non-invasive stimulus, light can be used to remotely control the chirality with high spatiotemporal precision. In contrast to common molecular switches, a synthetic molecular motor can act as a multistate chiroptical switch with unidirectional rotation, offering major potential to regulate more complex functions. Here, we present a light-driven molecular motor-based supramolecular polymer, in which the intrinsic chirality is transferred to the nanofibers, and the rotation of molecular motors governs the chirality and morphology of the supramolecular polymer. The resulting supramolecular polymer also exhibits light-controlled multistate aggregation-induced emission. These findings present a photochemically tunable multistate dynamic supramolecular system in water and pave the way for developing molecular motor-driven chiroptical materials.
Nanofibers , Water , Nanofibers/chemistry , Polymers/chemistry , Stereoisomerism
The development of very fast, clean, and selective methods for indirect labeling in PET tracer synthesis is an ongoing challenge. Here we present the development of an ultrafast photoclick method for the synthesis of short-lived 18F-PET tracers based on the photocycloaddition reaction of 9,10-phenanthrenequinones with electron-rich alkenes. The respective precursors are synthetically easily accessible and can be functionalized with various target groups. Using a flow photo-microreactor, the photoclick reaction can be performed in 60 s, and clinically relevant tracers for prostate cancer and bacterial infection imaging were prepared to demonstrate practicality of the method.
A new probe for precise and accurate bioimaging contributes significantly to advancing biomedical research for early disease diagnosis and treatment monitoring. Through wrapping a photochromic molecule (SP-Np-B) within a polymer nanoparticle, a new light-controlled multicolour fluorescence nanoprobe (Poly-SP-Np-B) is developed for precise fluorescence subcellular bioimaging. Poly-SP-Np-B shows an "OFF-ON" red-emitting fluorescence response upon alternate UV/Vis light irradiation. After activation by hydrogen peroxide (H2O2), a green-emitting Poly-SP-Np nanoparticle is generated, thus allowing light-controlled fluorescence response simultaneously, i.e., green and yellow switch upon alternate UV/Vis light irradiation for 10 and 20 s, respectively. Such a "blinking" fluorescence signal change is not possible by only using a photochromic molecule probe (SP-Np-B) with alternate UV/vis light irradiation for over 5 min. Poly-SP-Np-B has large isomerization kinetic constants (kSP-MR = 0.4543 s-1 and kMR-SP = 0.0809 s-1), excellent biocompatibility and lysosome distribution capability, enabling multicolour fluorescence imaging in live cells. With exo-/endogenous H2O2 activation in lysosomes, light-controlled "double-check" fluorescence imaging at the subcellular level is successfully achieved. More specifically, the change in fluorescence imaging is reversible in green, red and yellow channels in live cells upon excitation under alternate UV and visible light. This work thus provides a new strategy to develop switchable photochromic probes for precise fluorescence bioassay and bioimaging.
Hydrogen Peroxide , Nanoparticles , Color , Lysosomes , Optical Imaging
An artificial protein-probe hybrid, Cm-Np-B@BSA, was prepared via host-guest interactions between hydrogen peroxide (H2O2)-responsive Cm-Np-B molecule and bovine serum albumin (BSA). The Cm-Np-B@BSA probe exhibited high sensitivity and selectivity towards H2O2 under physiological conditions and had excellent biocompatibility, allowing for sensitive ratiometric detection and imaging of endogenous H2O2 in live cells.
Fluorescent Dyes/chemistry , Hydrogen Peroxide/analysis , Serum Albumin, Bovine/chemistry , Animals , Cattle , Mice , Molecular Structure , Optical Imaging , Particle Size , RAW 264.7 Cells , Surface Properties
Despite the rapid development of imaging techniques, precise probe localization and modulation in living cells is still a challenging task. Here we show that the simple hybridization between a photochromic fluorescent glycoprobe and human serum albumin (HSA) enables a unique fluorescence "double-check" mechanism for precisely localizing and manipulating probe molecules in living cells. Docking of a carbohydrate-modified naphthalimide (Naph)-spiropyran (SP) dyad to a hydrophobic pocket of HSA produces the glycoprobe-protein hybrid, causing the protein conformation to fold as determined by small-angle X-ray scattering. We show that the Naph and merocyanine (the photoisomer of SP) fluorescence of the resulting hybrid can be reversibly switched by light in buffer solution and in target cells overexpressing the carbohydrate receptor.
Asialoglycoprotein Receptor/analysis , Benzopyrans/chemistry , Fluorescent Dyes/chemistry , Indoles/chemistry , Nitro Compounds/chemistry , Serum Albumin, Human/chemistry , Binding Sites , Fluorescence , Hep G2 Cells , Humans , Hydrophobic and Hydrophilic Interactions , Light , Molecular Docking Simulation , Naphthalimides/chemistry , Optical Imaging/methods , Protein Conformation
Development of powerful fluorescence imaging probes and techniques sets the basis for the spatiotemporal tracking of cells at different physiological and pathological stages. While current imaging approaches rely on passive probe-analyte interactions, here we develop photochromic fluorescent glycoprobes capable of remote light-controlled intracellular target recognition. Conjugation between a fluorophore and spiropyran produces the photochromic probe, which is subsequently equipped with a glycoligand "antenna" to actively localize a target cell expressing a selective receptor. We demonstrate that the amphiphilic glycoprobes that form micelles in water can selectively enter the target cell to operate photochromic cycling as controlled by alternate UV/Vis irradiations. We further show that remote light conversion of the photochromic probe from one isomeric state to the other activates its reactivity toward a target intracellular analyte, producing locked fluorescence that is no longer photoisomerizable. We envision that this research may spur the use of photochromism for the development of bioimaging probes.Fluorescence sensing in biological environments is prone to background signal interference. Here the authors design a photochromic fluorescent glycoprobe for light-controlled photo-switchable cell imaging and photo-activated target recognition, resulting in an increased sensing precision.
Fluorescent Dyes/chemistry , Sulfites/analysis , Cell Line , Hep G2 Cells , Humans , Light , Lysosomes/chemistry , Optical Imaging
We report the synthesis of a water-compatible bis-glycosyl diarylethene using click chemistry that undergoes photochromism and functions as a molecular logic gate.
