Arturo Jiménez-Sánchez

Synthesis and crystal structures of a series of Schiff bases: a photo-, solvato- and acidochromic compound

Seven Schiff base derivatives of 4-dimethylamino-trans-cinnamaldehyde were synthesized in good yield. The structures of all new derivatives were established by IR, 1H, 13C NMR and HRMS experiments and three of them were corroborated by X-ray diffraction studies. Analysis of the supramolecular structures evidenced the presence of strong intermolecular hydrogen bonds (O–H⋯N) which promote the formation of molecular chains. The linear properties of this series of chromophores were investigated by UV-Vis and fluorescence spectroscopy in solution and in the solid state. The results revealed interesting photochromic properties for compound 2a promoted by a hydrogen bonding interaction in the solid state, which was established by absorption and emission spectra. Further evidence of the specific interactions that take place in compound 2a was obtained by studying the solvent effects observing a solvato- and acidochromic behavior.

Optical properties of two fluorene derived BODIPY molecular rotors as fluorescent ratiometric viscosity probes

BODIPY-derived molecular fluorescent rotors are one of the most useful families of fluorescent probes for the quantitative measurement of microviscosity. Here, we report the photophysical properties of two molecular rotors as ratiometric viscosity sensors, meso-(4-(9H-fluoren-2-yl)ethynyl)phenyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (1) and meso-(5-(9H-fluoren-2-yl)ethynyl)thiophen-2-yl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (2) having two independent chromophores; one (fluorene) is not influenced by viscosity and is used to determine concentration properties, and the other chromophore (BODIPY) acts as a molecular rotor. The fluorescence ratiometric calibration against microviscosity for the most sensitive probe (1), was obtained in a wide linear dynamic range. The sensitivity of the spectroscopic observables for 1 and 2 towards solvent viscosity and the typical analytical interfering solvent polarity and polarizability parameters were investigated by means of two different solvent scales, namely Lippert–Mataga and Catalan, finding consistent results. Quantum chemical calculations were conducted to analyze the probe mechanism in terms of Natural Transition Orbitals (NTOs) and the spatial extent of charge transfer excitations.

Strong Dipolar Effects on an Octupolar Luminiscent Chromophore: Implications on their Linear and Nonlinear Optical Properties.

Design parameters derived from structure-property relationships play a very important role in the development of efficient molecular-based functional materials with optical properties. Here, we report on the linear and nonlinear optical properties of a fluorene-derived dipolar system (DS) and its octupolar analogue (OS), in which donor and acceptor groups are connected by a phenylacetylene linkage, as a strategy to increase the number of delocalized electrons in the π-conjugated system. The optical nonlinear response was analyzed in detail by experimental and theoretical methods, showing that, in the octupolar system OS, the dipolar effects induced a strong two-photon absorption process whose magnitude is as large as 2210 GM at infrared wavelengths. Solvatochromism studies were implemented to obtain further insight on the charge transfer process. We found that the triple bond plays a fundamental role in the linear and nonlinear optical responses. The strong solvatochromism behavior in DS and OS was analyzed by using four empirical solvent scales, namely Lippert-Mataga, Kamlet-Taft, Catalán, and the recently proposed scale of Laurence et al., finding consistent results of strong solvent polarizability and viscosity dependence. Finally, the role of the acceptor groups was further studied by synthesizing the analogous compound 2DS, having no acceptor group.

Acid–base and coordination properties of 2-phenyl-3-hydroxy-4-quinolones in aqueous media

The acid–base and coordination properties of 2-phenyl-3-hydroxy-4(1H)-quinolone (1) and 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone (2) were characterized by potentiometric, UV-Visible and fluorescence titrations in water containing 5 or 30% vol MeCN and in a micellar solution of a cationic surfactant. The first dissociation constants (pKa1) corresponding to OH deprotonation of 1 and 2 are about 10 and ligand 1 undergoes a second NH deprotonation with a pKa2 about 12, which is reduced to 10.4 in the presence of a cationic surfactant. More detailed complexation studies were performed with more soluble ligand 1, which forms stable complexes of 1:1 and 1:2 compositions with Fe(III), Cu(II), Zn(II), Pb(II) and Me2Sn(IV) cations in neutral solutions. The most unusual behavior is observed with Zn(II), which strongly promotes NH deprotonation of ligand 1 with formation of the Zn(L)22− complex at a pH about 8. The formation of this complex is confirmed by the results of 1H NMR titrations in DMSO-d6. Binding of all cations is accompanied by the appearance of a new absorption band in the range 385–405 nm with concomitant disappearance of the band at 350–360 nm in the free ligand. Interactions of 1 and 2 with Zn(II) and Me2Sn(IV) are accompanied by strong and selective fluorescence enhancements with the blue shift of the emission bands allowing ratiometric detection of these cations. Complexation with transition and heavy metal ions as well as with lanthanides induces fluorescence quenching. Ligand 2 is characterized by X-ray crystallography.