Rethinking Uncaging: A New Antiaromatic Photocage Driven by a Gain of Resonance Energy

Compact Molecular Conformation of Prodrugs Enhances Photocleaving Performance for Tumor Vascular Growth Inhibition

Highly spatiotemporal-resolved photomodulation demonstrates promise for investigating key biological events in vivo and in vitro, such as cell signaling pathways, neuromodulation, and tumor treatment without side effects. However, enhancing the performance of photomodulation tools remains challenging due to the limitations of the physicochemical properties of the photoactive molecules. Here, a compact, stable intramolecular π-π stacking conformation forming between the target molecule (naproxen) and the perylene-based photoremovable protecting group is discovered to confine the motion of the photolabile bond and then enhance the photocleavage quantum yield. In conjunction with a red-absorbing photosensitizer, the photocleavage wavelength is extended to the red region via triplet-triplet annihilation. In particular, the triplet lifetime of the prodrug can be extended via the linked steric hindrance to improve the conversion yield via TTA. Using the new photomodulation tool, it is precisely photoreleased cyclooxygenase-2 inhibitors for tumor vascular growth suppression in vivo. In combination with cisplatin, over 90% efficient inhibition of malignant breast tumors is observed via the synergistic tumor treatment strategy. These findings provide a new concept for the rational design of efficient photocleavage and have implications for photomodulating cell signaling pathways in tumor therapy, as well as laying a solid foundation for the development of phototherapeutic approaches.

Wavelength-Selective Xanthene-Based Monochromophoric Photoremovable Protecting Groups for Tuning Soft Matter Material Properties

Photocontrolled deprotection of specific functional groups has garnered significant interest over the past two decades. Notably, the selective deprotection of distinct groups based on wavelength has emerged as a prominent focus in recent research. The achievement of this objective has primarily involved the utilization of linker-based bichromophoric systems and diverse cocktail mixtures of photoresponsive protecting groups (PRPGs), each responsive to varying wavelengths of light. Herein, we present the first wavelength-selective monochromophoric system based on a hydroxanthene moiety, enabling the wavelength-selective release of two distinct functionalities under 450 and 600 nm light, respectively. The mechanism of the wavelength-selective photodegradation was thoroughly investigated by 1H NMR, UV-vis, and fluorescence spectroscopy, suggesting a proton-coupled electron transfer mechanism in the first photorelease step and electron transfer based arylmethyl type of photorelease in the second step. The utility of the xanthene-based wavelength-selective PRPGs was demonstrated in the multistep degradation of microparticles and dual-color tuning of polymer chain architecture, thus opening an avenue to design advanced photoreactive wavelength-controlled systems for applications in soft matter materials.

3-Substituted 2-Aminonaphthalene Photocages for Carboxylic Acids and Alcohols; Decaging Mechanism and Potential Applications in Synthesis

3-Hydroxymethyl-2-aminonaphthalene photocage (photoremovable protecting group) 2 was synthesized and transformed to different ethers and esters to investigate the applicability to decage alcohols and carboxylic acids, respectively. The photoelimination of carboxylic acids takes place relatively efficiently (ΦR = 0.11) upon excitation with near-visible light, contrary to the elimination of alcohols. The scope of the decaging of both alcohols and esters was demonstrated on several examples, including aliphatic and aromatic substrates, carbohydrates, and nonsteroidal anti-inflammatory drugs. The photophysical properties of the photocage and its models, methyl ether 4a and acetyl ester 5a, were investigated. The fluorescence quantum yields (Φf = 0.40-0.002) were found to be reversely proportional to the efficiency of elimination of OH, alcohols, or carboxylic acids. The decaging photochemical reaction mechanism was investigated experimentally by transient absorption techniques with time scales from femtoseconds to seconds and computationally on the TD-DFT level of theory. The photoelimination of carboxylates takes place directly in the singlet excited state by a homolytic cleavage producing a radical pair within 1 ns. The subsequent electron transfer gives rise to aminonaphthalene carbocation and the carboxylate. A wide scope of substrates that can be decaged relatively efficiently with near-visible light and the chromo-orthogonal compatibility of aminonaphthalene and aniline derivatives render these photocages potentially applicable in organic synthesis or biology.

meso-Methyl BODIPY Photocages: Mechanisms, Photochemical Properties, and Applications

meso-methyl BODIPY photocages have recently emerged as an exciting new class of photoremovable protecting groups (PPGs) that release leaving groups upon absorption of visible to near-infrared light. In this Perspective, we summarize the development of these PPGs and highlight their critical photochemical properties and applications. We discuss the absorption properties of the BODIPY PPGs, structure-photoreactivity studies, insights into the photoreaction mechanism, the scope of functional groups that can be caged, the chemical synthesis of these structures, and how substituents can alter the water solubility of the PPG and direct the PPG into specific subcellular compartments. Applications that exploit the unique optical and photochemical properties of BODIPY PPGs are also discussed, from wavelength-selective photoactivation to biological studies to photoresponsive organic materials and photomedicine.

Inactivation of Competitive Decay Channels Leads to Enhanced Coumarin Photochemistry

In the development of photolabile protecting groups, it is of high interest to selectively modify photochemical properties with structural changes as simple as possible. In this work, knowledge of fluorophore optimization was adopted and used to design new coumarin‐ based photocages. Photolysis efficiency was selectively modulated by inactivating competitive decay channels, such as twisted intramolecular charge transfer (TICT) or hydrogen‐bonding, and the photolytic release of the neurotransmitter serotonin was demonstrated. Structural modifications inspired by the fluorophore ATTO 390 led to a significant increase in the uncaging cross section that can be further improved by the simple addition of a double bond. Ultrafast transient absorption spectroscopy gave insights into the underlying solvent‐dependent photophysical dynamics. The chromophores presented here are excellently suited as new photocages in the visible wavelength range due to their simple synthesis and their superior photochemical properties.