Ana B. Descalzo

Dihydronaphthalene‐Fused Boron–Dipyrromethene (BODIPY) Dyes: Insight into the Electronic and Conformational Tuning Modes of BODIPY Fluorophores

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.

Red/Near‐infrared Boron–Dipyrromethene Dyes as Strongly Emitting Fluorophores

We present an overview of the state of the art in long‐wavelength boron–dipyrromethene (BODIPY) fluorophores, focusing on strategies to shift the absorption and emission bands into the red/near‐infrared (NIR) range of the spectrum. This report also discusses chemical modifications of the chromophoric core to obtain analyte‐responsive fluorophores, including examples of pH and metal ion indicators. Finally, we present a new series of phenanthrene‐fused BODIPY dyes, emitting with high efficiency in the red/NIR region of the spectrum, as well as discussing potential applications thereof as probes.

Mesoporous silica materials with covalently anchored phenoxazinone dyes as fluorescent hybrid materials for vapour sensing

Mesoporous silica matrices functionalized with a fluorescent solvatochromic dye have been employed as optical sensor materials for volatile organic compounds. Re-functionalisation of the polar silica surface of the parent solid by passivation of the silanol groups with hexamethyldisilazane yielded a hydrophobic hybrid sensory material with improved performance in terms of the spectroscopic response, the detectable polarity range of organic vapours, response times and reversibility, and minimized interference from environmental humidity. Polar vapours such as methanol and acetone for instance are indicated by a shift in absorption of ca. 40 and 30 nm, and a ca. 10-fold fluorescence enhancement. With the present system, acetone vapours can be detected down to 300 ppmV.

On the Signalling Pathways and CuII‐Mediated Anion Indication of N‐meso‐Substituted Heptamethine Cyanine Dyes

Join or attack: meso-Cyclam-substituted heptamethine cyanine dye 1 responds very differently to the presence of metal ions and protons. Whereas the former are embraced in a host-guest complex, the latter attack the cyanine pi system (see picture). In the presence of Cu(II), 1 selectively forms near-infrared absorbing aggregates in buffered solution that allow the determination of citrate by using colourimetry.Three mid-chain rigidified heptamethine cyanine dyes substituted with dimethylamino or cyclam groups at the meso position of the polymethine chain have been prepared and studied both experimentally and theoretically with respect to their spectroscopic response toward protons and various metal ions. Despite a potentially rich conformational ground-state chemistry, the spectroscopic studies revealed that the behaviour of the dyes is in agreement with Kuhns classic polymethine dye theory. Coordination of metal ions and protonation of the alkyl amino groups in the cyclam moiety accordingly lead to moderate bathochromic shifts in absorption and reduced Stokes shifts. In contrast, protonation of the dimethylamino-substituted derivatives occurs at the polymethine chain, transforming the heptamethine into a trimethine-type chromophore with concomitant gigantic spectral blueshifts. In the presence of Cu(II) in buffered aqueous solution, the cyclam-substituted dye selectively forms near-infrared absorbing aggregates. The latter allow the determination of citrate under realistic conditions by changes in absorption at wavelengths greater than 800 nm, which results from a disruption of the aggregates when citrate binds to Cu(II). The copper ions thus act as mediators in a signalling reaction that constitutes a colourimetric displacement assay.

Optimization of the Coupling of Target Recognition and Signal Generation

Fluorescent reporters that literally “light up” upon binding of a target species are particularly interesting from an analytical point of view. This contribution introduces the main signaling concepts in fluorescent probe research, discusses strategies toward their optimization in terms of signal output, and highlights the wealth of alternative protocols that has been realized in the past two decades to create signaling systems with luminescence amplification features.