When exposed to UV light, single crystals of the vinyl azides 3-azido-1-phenylpropenone (1a), 3-azido-1-(4-methoxy­phenyl)­propenone (1b), and 3-azido-1-(4-chloro­phenyl)­propenone (1c) exhibit dramatic mechanical effects by cracking or bending with the release of N2. Mechanistic studies using laser flash photolysis, supported by quantum mechanical calculations, show that each of the vinyl azides degrades through a vinylnitrene intermediate. However, despite having very similar crystal packing motifs, the three compounds exhibit distinct photomechanical responses in bulk crystals. While the crystals of 1a delaminate and release gaseous N2 indiscriminately under paraffin oil, the crystals of 1b and 1c visibly expand, bend, and fracture, mainly along specific crystallographic faces, before releasing N2. The photochemical analysis suggests that the observed expansion is due to internal pressure exerted by the gaseous product in the crystal lattices of these materials. Lattice energy calculations, supported by nanoindentation experiments, show significant differences in the respective lattice energies. The calculations identify critical features in the crystal structures of 1b and 1c where elastic energy accumulates during gas release, which correspond to the direction of the observed cracks. This study highlights the hitherto untapped potential of photochemical gas release to elicit a photomechanical response and motility of photoreactive molecular crystals.

A new photo-uncaging platform to guide drug delivery with enhanced therapeutic effect.

As one of the most important minerals in the body, potassium is vital for the heart and neurons. Methods that can noninvasively and accurately monitor changes in potassium balances would benefit disease diagnoses as well as offer insight into pathologies. Among the sensing approaches, fluorescent probes serve as a unique detection method for its simplicity, tunable detection range, and bioimaging ability. The design of new probes with highly selective K + receptors and transduction functionality remains a challenge that is motivated by numerous sensing and detection applications. In this minireview, fluoroionophores are summarized that undergo transduction, producing fluorescence signals when interacting with, e. g., potassium ions. The properties of ionophores (afford selective interaction with potassium) and fluorophores (generate signal read-out) are discussed. Molecular structure design and sensing mechanisms are included along with cell imaging applications. The selectivity towards K + and the absorption/ emission characteristics of the probes are of particular interest.

Chemoresistance is one of the major challenges for cancer treatment, more recently ascribed to defective mitochondrial outer membrane permeabilization (MOMP), significantly diminishing chemotherapeutic agent‐induced apoptosis. A boron‐dipyrromethene (BODIPY) chromophore‐based triarylsulfonium photoacid generator (BD‐PAG) was used to target mitochondria with the aim to regulate mitochondrial pH and further depolarize the mitochondrial membrane. Cell viability assays demonstrated the relative biocompatibility of BD‐PAG in the dark while live cell imaging suggested high accumulation in mitochondria. Specific assays indicated that BD‐PAG is capable of regulating mitochondrial pH with significant effects on mitochondrial membrane depolarization. Therapeutic tests using chlorambucil in combination with BD‐PAG revealed a new strategy in chemoresistance suppression.

Photoacid generators (PAGs) are organic compounds that can generate protons (H+) upon irradiation with certain wavelengths of light. In this work, we designed and synthesized the first BODIPY-based PAGs with D–A and D−π–A conjugation structures and achieved green and red LED light-induced acid generation. By the use of red-light absorbance, red-LED-triggered cationic polymerization was demonstrated as a proof-of-concept application of these PAGs.