Electrospun blends comprised of poly(methyl methacrylate) and ethyl(hydroxyethyl)cellulose functionalized with perichromic dyes.

Ethyl(hydroxyethyl)cellulose (EHEC) was modified with 4-(2- (pyridin-4-yl)vinyl) phenol (PBM) and 4- [4-(dimethylamino)styryl]pyridine (DMASP), which are precursors of two well-known perichromic/fluorescent dyes, Brooker's merocyanine (BM) and 4- [4-(dimethylamino)styryl]-1-methypyridinium iodide (DSMI). The EHECs were mixed with poly(methyl methacrylate) (PMMA) to allow electrospinning and the nanofibers obtained were characterized by scanning electron microscopy, fluorescence microscopy, ATR-FTIR spectroscopy, thermogravimetry analysis, differential scanning calorimetry and fluorescence spectrophotometry and the absolute quantum yield and contact angle were determined. The PMMA/EHEC blends formed hydrophilic nanofibers, with high water absorption, in contrast to the pure PMMA nanofibers. PMMA/EHEC-PBM nanofibers exhibited cyan emission when excited in the UV region and PMMA/EHEC-DMASP showed intense green emission under excitation with laser in the blue region. Electrospinning of PMMA/modified EHEC in the proportion of 5:2 (wt/wt) provided nanochain-like nanofibers, which were verified by confocal microscopy. The potential for the use of the electrospun PMMA/EHEC-PBM nanofibers in the detection of CN- in water was demonstrated.

Thermohalochromism of phenolate dyes conjugated with nitro-substituted aryl groups.

The cationic halochromism and thermohalochromism of four phenolate dyes conjugated with aryl moieties substituted with one or two nitro groups were investigated in the presence of organic (tetra-n-butylammonium bromide and benzyltriethylammonium chloride) and inorganic (sodium perchlorate) salts, in hydrogen-bond donating (water, 1-propanol, 1-butanol and 2-propanol) and hydrogen-bond accepting (acetonitrile and dimethylsulfoxide) solvents. Although a positive halochromic response was observed in water for tetraalkylammonium salts, their thermohalochromic behavior was negligible. A negative halochromic behavior was observed for the dyes in all solvents, when the added cation was Na+. Plots of Δλmaxvs. c (Na+) allowed the apparent association constants for the solvated phenolate-cation pair to be estimated. In most cases, a positive thermohalochromism was observed in the range of 25-50°C, exceptions being the more sterically hindered phenolate dyes in the less polar solvents 2-propanol and acetonitrile. The observed variations were rationalized by invoking the effect of temperature on the phenolate-cation, phenolate-solvent and cation-solvent interactions.

Structure-behavior study of a family of "hybrid cyanine" dyes which exhibit inverted solvatochromism.

The inverted solvatochromism of twenty dyes containing an electron-donor phenolate conjugated with an electron-withdrawing nitro-substituted phenyl ring was analyzed in terms of the dye structure and substituents. Structural factors that increased the difference between the electrophilicities of the donor and acceptor moieties, or the donor-acceptor strength of the phenolate dyes, also increased the sensitivity of the dyes to solvent-polarity changes and red-shifted their solvatochromic absorption bands.

Reverse solvatochromism in solvent binary mixtures: a case study using a 4-(nitrostyryl)phenolate as a probe.

A 4-(nitrostyryl)phenolate was synthesized and its use in pure solvents revealed a reversion in solvatochromism. Solutions of a dye in binary solvent mixtures, using as components the solvents in the region of the occurrence of the reversion, provided the first case in the literature of reverse solvatochromism in a binary mixture.

Synthesis and Solvatochromism of Substituted 4-(Nitrostyryl)phenolate Dyes.

4-(Nitrostyryl)phenols 2a-9a were synthesized, and by deprotonation in solution, the solvatochromic phenolates 2b-9b were formed. Their absorption bands in the vis region of the spectra are due to π-π* electronic transitions, of an intramolecular charge-transfer nature, from the electron-donor phenolate toward the electron-acceptor nitroarene moiety. The frontier molecular orbitals and natural bond orbitals were analyzed for the protonated and deprotonated forms. The calculated geometries are in agreement with X-ray structures observed for 4a, 6a, and 8a. The HOMO-LUMO energy gaps suggest that, after their deprotonation, an increase in the electron delocalization is observed. In the protonated compounds, the HOMO is primarily localized over the phenol ring and the C═C bridge. After deprotonation, it extends toward the entire molecule, including the NO2 groups. The solvatochromism of each dye was studied in 28 organic solvents, and it was found that all compounds exhibit a reversal in solvatochromism, which is interpreted in terms of the ability of the media to stabilize their electronic ground and excited states to different extents. The Catalán multiparameter equation is used in the interpretation of the solvatochromic data, revealing that the most important contribution to the solute/solvent interaction is the hydrogen-bond donor acidity of the solvent.

A simple protocol for the visual discrimination of natural cyclodextrins in aqueous solution using perichromic probes.

Three synthesized compounds, 4-(4-nitrostyryl)phenol, 2,6-dibromo-4-(2,4-dinitrobenzylideneamino)phenol and 2,6-dichloro-4-(2,4-dinitrobenzylideneamino)phenol, were deprotonated to generate the perichromic dyes 2b, 3b and 4b, respectively. These dyes were used as probes to investigate the micropolarity of natural cyclodextrins (CyDs) and it was observed that they interact differently with the CyDs according to the molecular structure of the dye and the diameter of the CyD. The solvatochromic bands of the dyes that interacted with the CyDs were bathochromically shifted, suggesting that the probes were transferred to the hydrophobic interior of the CyD in aqueous solution. Dyes 2b and 4b were found to be very selective for α-CyD and γ-CyD, respectively, while ß- and γ-CyD changed the color of the solution of compound 3b. These dyes were then successfully used in a simple assay that allows the naked-eye discrimination of natural CyDs in aqueous solution, without the need for expensive techniques.