The combination of nanomaterials as solid supports and supramolecular concepts has led to the development of hybrid materials with improved functionalities. These "hetero-supramolecular" ideas provide a means of bridging the gap between molecular chemistry, materials sciences, and nanotechnology. In recent years, relevant examples have been reported on functional aspects, such as enhanced recognition and sensing by using molecules on preorganized surfaces, the reversible building of nanometer-sized networks and 3D architectures, as well as biomimetic and gated chemistry in hybrid nanomaterials for the development of advanced functional protocols in three-dimensional frameworks. This approach allows the fine-tuning of the properties of nanomaterials and offers new perspectives for the application of supramolecular concepts.
For the highly selective and sensitive sensing of Hg2+ in water, a new design concept was realized where the selectivity of the probe's binding site is amplified by electronic properties of the chromophore. The molecular architecture of this phenoxazinone-type sensor molecule combines two potential coordination sites via an amino-keto conjugative backbone. These structural prerequisites allow only the most preferred mercuric ion to bind to the dithia dioxa monoaza crown unit, while other heavy, transition, and main group metal ions as well as protons are trapped at the keto group, inducing opposite spectral effects due to interaction with either the donor (Hg2+) or the acceptor group (other cations) of the probe. Besides these advantageous features, the probe operates well within the visible range of the spectrum and displays rather intense molar absorptivities as well as fluorescence quantum yields.
A strategy for the rational design of a new optical sensor material for the selective recognition of long-chain carboxylates in water is presented. The approach relies on the combination of structure-property relationships to single out the optimal molecular sensor unit and the tuning of the sensing characteristics of an inorganic support material. A spacer-substituted 7-urea-phenoxazin-3-one was employed as the signaling moiety and a mesoporous trimethylsilylated UVM-7 (MCM-41 type) material served as the solid support. The sensor material shows the advantageous features of both modules that is absorption and emission in the visible spectral range, a fluorescence red-shift and enhancement upon analyte coordination, and the amplification of noncovalent (binding) and hydrogen-bonding (recognition) interactions in the detection event. Besides these basic results that are related to the design and performance of the sensor material, the paper discusses general aspects of amido-substituted phenoxazinone photophysics and addresses some general features of molecular anion recognition chemistry in aqueous vs nonaqueous media, utilizing steady-state and time-resolved optical as well as NMR spectroscopies. Detailed studies on potentially competing biochemical species and a first access to the schematic model of the response of the sensor material as obtained by a combination of fluorescence lifetime distribution analysis and Langmuir-type fitting of the gross binding constants complement the key issues of the paper.
Four novel borondipyrromethene (BDP) and -diindomethene (BDI) dyes with one or two (dimethylamino)styryl extensions at the chromophore were synthesized and spectroscopically investigated. An X-ray crystal structure shows that the extended auxochrome is virtually planar. All dyes thus display intense red/near infrared (NIR) absorption and emission. The (dimethylamino)styryl group induces a charge-transfer character that entails bright solvatochromic fluorescence, which is only quenched with increasing solvent polarity according to the energy-gap law. The dye with an additional dimethylanilino group at the meso position of BDP shows a remarkable switching of lipophilicity by protonation. Two dyes with an 8-hydroxyquinoline ligand at the meso position display quenched emission in the presence of Hg2+ or Al3+ owing to electron transfer from the excited BDP to the complexed receptor. The BDI dye presents a pH indicator with bright fluorescence and extremely low fluorescence anisotropy.
A new series of boron-dipyrromethene (BDP, BODIPY) dyes with dihydronaphthalene units fused to the beta-pyrrole positions (1a-d, 2) has been synthesised and spectroscopically investigated. All the dyes, except pH-responsive 1d in polar solvents, display intense emission between 550-700 nm. Compounds 1a and 1b with a hydrogen atom and a methyl group in the meso position of the BODIPY core show spectroscopic properties that are similar to those of rhodamine 101, thus rendering them potent alternatives to the positively charged rhodamine dyes as stains and labels for less polar environments or for the dyeing of latex beads. Compound 1d, which carries an electron-donating 4-(dimethylamino)phenyl group in the meso position, shows dual fluorescence in solvents more polar than dibutyl ether and can act as a pH-responsive "light-up" probe for acidic pH. Correlation of the pK(a) data of 1d and several other meso-(4-dimethylanilino)-substituted BODIPY derivatives allowed us to draw conclusions on the influence of steric crowding at the meso position on the acidity of the aniline nitrogen atom. Preparation and investigation of 2, which carries a nitrogen instead of a carbon as the meso-bridgehead atom, suggests that the rules of colour tuning of BODIPYs as established so far have to be reassessed; for all the reported couples of meso-C- and meso-N-substituted BODIPYs, the exchange leads to pronounced redshifts of the spectra and reduced fluorescence quantum yields. For 2, when compared with 1a, the opposite is found: negligible spectral shifts and enhanced fluorescence. Additional X-ray crystallographic analysis of 1a and quantum chemical modelling of the title and related compounds employing density functional theory granted further insight into the features of such sterically crowded chromophores.
A new class of boron-dipyrromethene (BDP or BODIPY) dyes was obtained by phenanthrene fusion to the beta-pyrrole positions, absorbing in the wavelength range of important laser sources. Despite a 'propeller-like' distorted structure in the crystalline state, the chromophore absorbs (log epsilon > or = 5) and fluoresces (Phif > or = 0.8) strongly and can be easily turned into a fluorescence light-up probe. Incorporation into latex beads produces bright and photostable single-dye and Förster Resonance Energy Transfer (FRET) particles for microscopy applications.
Use of functionalized MCM‐41 solids as anion sensing systems has been demonstrated for the first time. The combination of the binding properties of molecular receptors with the structural characteristics of solid, inorganic surfaces leads to remarkably enhanced anion sensing response. The Figure shows a schematic view of a solid surface, with 300 Å diameter holes that are filled with aminoanthracene molecules.
Sending signals: The first core‐modified, expanded porphyrin with polyaromatic units fused to the pyrrole rings absorbs far into the near‐infrared and shows fluorescence that stretches into the second optical window of telecommunication. Doping a polyurethane membrane with the dye yields Hg2+‐responsive optical test strips.
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