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1. On-demand guest release from MOF-5 sealed with nitrophenylacetic acid photocapping groups

   https://doi.org/10.1039/c9pp00392d  

   Yan, Jingjing; Homan, Rick A.; Boucher, Corrianna; Basa, Prem N.; Fossum, Katherine J.; Grimm, Ronald L.; MacDonald, John C.; Burdette, Shawn C. (December 2019, Photochemical & Photobiological Sciences)

   null (Ed.)

   Recently, we demonstrated that triphenylacetic acid could be used to seal dye molecules within MOF-5, but guest release required the digestion of the framework by treatment with acid. We prepared the sterically bulky photocapping group [bis-(3-nitro-benzyl)-amino]-(3-nitro-phenyl)-acetic acid ( PC1 ) that can prevent crystal violet dye diffusion from inside MOF-5 until removed by photolysis. 

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2. Mechanochemical activation of an indole-fused 2H-benzopyran generates an acidochromic merocyanine dye enabling multicolor chromomorphic materials

   https://doi.org/10.1039/D5PY00746A  

   Sun, Yan; Granados_Razo, Wendy; Luo, Stella M; Osler, Skylar K; Robb, Maxwell J (August 2025, Polymer Chemistry)

   Molecular switches based on the 2H-1-benzopyran (chromene) scaffold have been widely developed for their desirable photochromic and mechanochromic properties. Extended π-conjugation is necessary to stabilize the ring-opened merocyanine dye at room temperature leading to efficient switching under ambient conditions. To this end, naphthopyrans represent a special class of benzo-annulated benzopyrans that have been studied extensively as both photoswitches and more recently as mechanophores, generating intensely colored merocyanine dyes upon exposure to ultraviolet light or mechanical force, respectively. Alternative annulation strategies with judicious heteroatom substitution have also been studied in the photochemistry literature, but the mechanochemistry of 2H-1-benzopyrans has yet to be explored. Here, we report the mechanochemical activation of an indole-fused 2H-1-benzopyran mechanophore that generates a yellow-colored merocyanine dye in polymers that is subsequently transformed to a purple-colored dye upon treatment with acid. Neutralization with base recovers the yellow-colored merocyanine isomer with trans exocyclic alkene geometry through an unusual acid-mediated alkene isomerization. This study expands the repertoire of mechanochromic mechanophores based on (hetero)annulated benzopyrans to enable multicolor chromomorphic behavior in response to both mechanical force and acid for applications in stimuli-responsive polymeric materials with complex switching properties. 

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3. Electrochemical and Biocatalytic Signal‐Controlled Payload Release from a Metal–Organic Framework

   https://doi.org/10.1002/adma.202308640  

   Sterin, Ilya; Hadynski, John; Tverdokhlebova, Anna; Masi, Madeline; Katz, Evgeny; Wriedt, Mario; Smutok, Oleh (December 2023, Advanced Materials)

   Abstract A metal–organic framework (MOF), ZIF‐8, which is stable at neutral and slightly basic pH values in aqueous solutions and destabilized/dissolved under acidic conditions, is loaded with a pH‐insensitive fluorescent dye, rhodamine‐B isothiocyanate, as a model payload species. Then, the MOF species are immobilized at an electrode surface. The local (interfacial) pH value is rapidly decreased by means of an electrochemically stimulated ascorbate oxidation at +0.4 V (Ag/AgCl/KCl). Oxygen reduction upon switching the applied potential to −0.8 V allows to return the local pH to the neutral/basic pH, then stopping rapidly the release process. The developed method allows electrochemical control over stimulated or inhibited payload release processes from the MOF. The pH variation proceeds in a thin film of the solution near the electrode surface. The switchable release process is realized in a buffer solution and undiluted human serum. As the second option, the pH decrease stimulating the release process is achieved upon an enzymatic reaction using esterase and ester substrate. This approach potentially allows the release activation controlled by numerous enzymes assembled in complex biocatalytic cascades. It is expected that related electrochemical or biocatalytic systems can represent novel signal‐responding materials with switchable features for delivering (bio)molecules within biomedical applications. 

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4. Copper-based redox shuttles supported by preorganized tetradentate ligands for dye-sensitized solar cells

   https://doi.org/10.1039/c9dt04030g  

   Rodrigues, Roberta R.; Lee, Joseph M.; Taylor, Natalie S.; Cheema, Hammad; Chen, Lizhu; Fortenberry, Ryan C.; Delcamp, Jared H.; Jurss, Jonah W. (January 2020, Dalton Transactions)

   Three copper redox shuttles ([Cu( 1 )] 2+/1+ , [Cu( 2 )] 2+/1+ , and [Cu( 3 )] 2+/1+ ) featuring tetradentate ligands were synthesized and evaluated computationally, electrochemically, and in dye-sensitized solar cell (DSC) devices using a benchmark organic dye, Y123 . Neutral polyaromatic ligands with limited flexibility were targeted as a strategy to improve solar-to-electrical energy conversion by reducing voltage losses associated with redox shuttle electron transfer events. Inner-sphere electron transfer reorganization energies ( λ ) were computed quantum chemically and compared to the commonly used [Co(bpy) 3 ] 3+/2+ redox shuttle which has a reported λ value of 0.61 eV. The geometrically constrained biphenyl-based Cu redox shuttles investigated here have lower reorganization energies (0.34–0.53 eV) and thus can potentially operate with lower driving forces for dye regeneration (Δ G reg ) in DSC devices when compared to [Co(bpy) 3 ] 3+/2+ -based devices. The rigid tetradentate ligand design promotes more efficient electron transfer reactions leading to an improved J SC (14.1 mA cm −2 ), higher stability due to the chelate effect, and a decrease in V lossOC for one of the copper redox shuttle-based devices. 

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5. Development of GTP-responsive liposomes by exchanging the metal-DPA binding site in a synthetic lipid switch

   https://doi.org/10.1039/d3cc00288h  

   Lou, Jinchao; Hudson, Macy M.; Ancajas, Christelle F.; Best, Michael D. (March 2023, Chemical Communications)

   We report stimuli-responsive liposomes that selectively release encapsulated contents upon treatment with guanosine triphosphate (GTP) over a wide variety of phosphorylated metabolites, validated by fluorescence-based leakage assays. 

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