Recent progress in the development of organic dye based near-infrared fluorescence probes for metal ions

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials.

Aliphatic polyesters and polycarbonates are a class of biorenewable, biocompatible, and biodegradable materials. One of the most powerful methods for accessing these materials is the ring-opening polymerization (ROP) of cyclic monomers. Here we report that the deprotonation of ureas generates a class of versatile catalysts that are simultaneously fast and selective for the living ring-opening polymerization of several common monomers, including lactide, δ-valerolactone, e-caprolactone, a cyclic carbonate, and a cyclic phosphoester. Spanning several orders of magnitude, the reactivities of several diaryl urea anions correlated to the electron-withdrawing substituents on the aryl rings. With the appropriate urea anions, the polymerizations reached high conversions (∼90%) at room temperature within seconds (1–12 s), yielding polymers with narrow molecular weight distributions (Đ = 1.06 to 1.14). These versatile catalysts are simple to prepare, easy to use, and exhibit a range of activities that can be tuned ...

Urea Anions: Simple, Fast, and Selective Catalysts for Ring-Opening Polymerizations.

Anion coordination chemistry: From recognition to supramolecular assembly

UV/vis absorption titrations have been used to investigate the formation of H-bonded complexes between anionic H-bond acceptors (HBAs) and neutral H-bond donors (HBDs) in organic solvents. Complexes formed by three different HBDs with 15 different anions were studied in chloroform and in acetonitrile. The data were used to determine self-consistent HBA parameters (β) for chloride, bromide, iodide, phosphate diester, acetate, benzoate, perrhenate, nitrate, triflimide, perchlorate, hexafluorophosphate, hydrogen sulfate, methyl sulfonate, triflate, and perfluorobutyl sulfonate. The results demonstrate the transferability of H-bond parameters for anions between different solvents and different HBD partners, allowing reliable prediction of anion recognition properties in other scenarios. Carboxylates are the strongest HBAs studied, with β parameters (≈ 15) that are significantly higher than those of neutral organic HBAs, and the non-coordinating anion hexafluorophosphate is the weakest acceptor, with a β param...

http://pubs.acs.org/doi/pdf/10.1021/jacs.7b02008

H-Bond Acceptor Parameters for Anions

Anion binding with urea and thiourea derivatives

The importance of anion receptors is a reflection of the ubiquitousness of anions, their functions in biological and industrial processes, as well as their behaviour as pollutants. In the immense field of anion receptor chemistry which has expanded greatly in the past few decades, one of the most prominent binding sites is (thio)urea. The simple synthesis of diverse (thio)urea derivatives, their possibility to form two H-bonds with anions and a promising selectivity with anions of complementary geometry are factors that gave rise to a plethora of studies reporting new organic molecules with different properties and applicability. This review includes the most important examples of (thio)urea receptors from the very beginning, until present. Many authors have used (thio)urea moieties in the computer-aided design of anion sensors, which was then followed by their synthesis, and utilization in the photophysical characterization of host–guest systems, and studies in the transport of ions and ion pairs through membranes. These endeavours led to their successful utilization in the fields of crystal engineering and development of functional materials. Characterization of supramolecular systems and investigations of the complexation thermodynamics has been conducted by use of different analytical and physico-chemical methods. Consequently, it is highly beneficial to summarize all aspects of anion recognition by (thio)ureas within one review article. This critical review containing 386 references classifies (thio)urea derivatives, published from 1990 to 2015, with respect to the complexity of the receptors and the number of urea groups in the molecule.

Anion Binding with Urea and Thiourea Derivatives

[4-(2-Pyrrolyl)phenyl]pyridines 2–4 were synthesized and their photophysical properties and reactivity in phototautomerization reactions investigated by fluorescence spectroscopy and laser flash photolysis (LFP). The pKa for the protonation of the pyridine nitrogen in 2–4 was determined by UV–vis and fluorescence titration (pKa = 5.5 for 4). On excitation in polar protic solvents, 2–4 populate charge-transfer states leading to an enhanced basicity of the pyridine (pKa* ≈ 12) and enhanced acidity of pyrrole (pKa* ≈ 8–9) enabling excited-state proton transfer (ESPT). ESPT gives rise to phototautomers and significantly quenches the fluorescence of 2–4. Phototautomers 2-T and 4-T were detected by LFP with strong transient absorption maxima at 390 nm. Phototautomers 2-T and 4-T decayed by competing uni- and bimolecular reactions. However, at pH 11 the decay of 4-T followed exponential kinetics with a rate constant of 4.2 × 106 s–1. The pyridinium salt 4H+ forms a stable complex with cucurbit[7]uril (CB[7]) wit...

/pdf/phototautomerization-in-pyrrolylphenylpyridine-terphenyl-2i63jpg3aq.pdf

Phototautomerization in pyrrolylphenylpyridine terphenyl systems.

ortho-, meta- and para-Hydroxymethylaniline methyl ethers 3–5-OMe and acetyl derivatives 3–5-OAc were investigated as potential photocages for alcohols and carboxylic acids, respectively. The measurements of photohydrolysis efficiency showed that the decaging from ortho- and meta-derivatives takes place efficiently in aqueous solution, but not for the para-derivatives. Contrary to previous reports, we show that the meta-derivatives are better photocages for alcohols, whereas ortho-derivatives are better protective groups for carboxylic acids. The observed differences were fully disclosed by mechanistic studies involving fluorescence measurements and laser flash photolysis (LFP). Photoheterolysis for the para-derivatives does not take place, whereas both meta- and ortho-derivatives undergo heterolysis and afford the corresponding carbocations 3-C and 4-C. The ortho-carbocation 4-o-C was detected by LFP in aqueous solution (λmax = 410 nm, τ ≈ 90 μs). Moreover, spectroscopic measurements for the meta-acetyl ...

/pdf/hydroxymethylaniline-photocages-for-carboxylic-acids-and-37nrfwi5t9.pdf

Vesna Blažek Bregović

Papers

Anion binding with urea and thiourea derivatives

Anion Binding with Urea and Thiourea Derivatives

Phototautomerization in pyrrolylphenylpyridine terphenyl systems.

Hydroxymethylaniline Photocages for Carboxylic Acids and Alcohols

Anthracene adamantylbisurea receptors: switching of anion binding by photocyclization