Fluorescein Analogue Xanthene-9-Carboxylic Acid: A Transition-Metal-Free CO Releasing Molecule Activated by Green Light

6-Hydroxy-3-oxo-3<i>H</i>-xanthene-9-carboxylic acid is introduced as the first transition-metal-free carbon monoxide releasing molecule activated by visible light (photoCORM). This water-soluble fluorescein analogue releases carbon monoxide in both water and methanol upon irradiation at 500 nm. When selectively irradiated in the presence of hemoglobin (Hb) under physiological conditions, released CO is quantitatively trapped to form carboxyhemoglobin (COHb). The reaction progress can be accurately monitored by characteristic absorption and emission properties of the reactants and products

Caged Fluoride: Photochemistry and Applications of 4‑Hydroxyphenacyl Fluoride

The quantitative, efficient (Φ = 0.8) photorelease of the fluoride ion upon UV-irradiation in aqueous media is introduced. The 4-hydroxyphenacyl chromophore is simultaneously transformed into UV-transparent 4-hydroxyphenylacetate via a photo-Favorskii rearrangement. The application of this process is demonstrated by photoinduced etching of mica and silicon by AFM

Bambusuril as a One-Electron Donor for Photoinduced Electron Transfer to Methyl Viologen in Mixed Crystals

Methyl viologen hexafluorophosphate (MV²⁺·2PF₆^–) and dodecamethylbambus[6]­uril (BU6) form crystals in which the layers of viologen dications alternate with those of a 1:2 supramolecular complex of BU6 and PF₆^–. This arrangement allows for a one-electron reduction of MV²⁺ ions upon UV irradiation to form MV^+• radical cations within the crystal structure with half-lives of several hours in air. The mechanism of this photoinduced electron transfer in the solid state and the origin of the long-lived charge-separated state were studied by steady-state and transient spectroscopies, cyclic voltammetry, and electron paramagnetic resonance spectroscopy. Our experiments are supported by quantum-chemical calculations showing that BU6 acts as a reductant. In addition, analogous photochemical behavior is also demonstrated on other MV²⁺/BU6 crystals containing either BF₄^– or Br^– counterions

In Search of the Perfect Photocage: Structure–Reactivity Relationships in <i>meso</i>-Methyl BODIPY Photoremovable Protecting Groups

A detailed investigation of the photophysical parameters and photochemical reactivity of <i>meso</i>-methyl BODIPY photoremovable protecting groups was accomplished through systematic variation of the leaving group (LG) and core substituents as well as substitutions at boron. Efficiencies of the LG release were evaluated using both steady-state and transient absorption spectroscopies as well as computational analyses to identify the optimal structural features. We find that the quantum yields for photorelease with this photocage are highly sensitive to substituent effects. In particular, we find that the quantum yields of photorelease are improved with derivatives with higher intersystem crossing quantum yields, which can be promoted by core heavy atoms. Moreover, release quantum yields are dramatically improved by boron alkylation, whereas alkylation in the <i>meso</i>-methyl position has no effect. Better LGs are released considerably more efficiently than poorer LGs. We find that these substituent effects are additive, for example, a 2,6-diiodo-<i>B</i>-dimethyl BODIPY photocage features quantum yields of 28% for the mediocre LG acetate and a 95% quantum yield of release for chloride. The high chemical and quantum yields combined with the outstanding absorption properties of BODIPY dyes lead to photocages with uncaging cross sections over 10 000 M^–1 cm^–1, values that surpass cross sections of related photocages absorbing visible light. These new photocages, which absorb strongly near the second harmonic of an Nd:YAG laser (532 nm), hold promise for manipulating and interrogating biological and material systems with the high spatiotemporal control provided by pulsed laser irradiation, while avoiding the phototoxicity problems encountered with many UV-absorbing photocages. More generally, the insights gained from this structure–reactivity relationship may aid in the development of new highly efficient photoreactions