Blanca Ros - Academia.edu (original) (raw)

Papers by Blanca Ros

Advanced Materials, Nov 28, 2017

In the specific context of condensed media, the significant and increasing recent interest in the... more In the specific context of condensed media, the significant and increasing recent interest in the α-cyanostilbene (CS) motif [-Ar-CH=C(CN)-Ar-] is relevant. These compounds have shown remarkable optical features in addition to interesting electrical properties, and hence they are recognized as very suitable and versatile options for the development of functional materials. This progress report is focused on current and future use of CS structures and molecular assemblies with the aim of exploring and developing for the next generations of functional materials. A critical selection of illustrative materials that contain the CS motif, including relevant sub-families such as the dicyanodistyrylbenzene (DCS) and 2,3,3triphenylacrylonitrile (TPAN) shows how, driven by the self-assembly of CS blocks, a variety of properties, effects and possibilities for practical applications can be offered to the scientific community, through different rational routes for the elaboration of advanced materials. A survey is provided on the research efforts directed towards promoting the self-assembly of the solid state (polycrystalline solids, thin films and single crystals), liquid crystals, nanostructures and gels with multi-stimuli responsiveness, and applications for sensors, OLED, OFET, solar cell materials or bioimaging purposes.

Physical Review E, Sep 1, 2006

An experimental study of the B 1 -B 2 transition is carried out in a bent-core liquid crystal. Th... more An experimental study of the B 1 -B 2 transition is carried out in a bent-core liquid crystal. The study is essentially based on x-ray measurements as a function of temperature. The B 1 -B 2 transition is extremely unusual and implies a deep structural change from a columnar phase to a lamellar phase. We have found that the B 1 phase in our compound is similar to the so-called B 1 reversed phase, with an additional splay of the polarization in the columns. On approaching the B 2 phase the width of the cross section of the columns increases. The transition is clearly first order, with a large hysteresis though the enthalpy content is very small. A possible mechanism for the transition is briefly sketched.

Journal of Materials Chemistry C, 2019

Looking to understand the supramolecular assemblies that bring together certain molecules to form... more Looking to understand the supramolecular assemblies that bring together certain molecules to form innovative functional materials with high-potential applications, the present review focuses on recent examples of molecular structures that are susceptible of stablishing self-assemblies both in bulk and in solvents. This revision demonstrates that appropriate rod-and V-shaped, disc-like and star-shaped molecules as well as highmolecular-weight compounds, either dendrimers or polymers, exhibit a dual ability. Intermolecular interactions that provide liquid crystalline order in bulk may also manifest in solution and this allows to attain nanomaterials in the form of nanoaggregates. Through bottom-up approaches that involve the self-assembly of molecules driven by hydrogen bonding, π-π stacking, electrostatic or hydrophilic-hydrophobic interactions, appropriate molecules are able to induce a variety of thermotropic mesophases in bulk as well as aggregates with morphologies such as nanoparticles, nanofibers, nanorods or nanotubes in liquid media; including systems in which solvents are immobilized and form gel materials. The aim of this work is to highlight the versatility of mesogenic molecules, that in turn opens the door to a wide number of possibilities, and therefore to help this topic to enter into a more mature period.

Journal of Molecular Liquids, Apr 1, 2018

A new class of molecular architecture made of five conjugated rings carrying terminal methyl or v... more A new class of molecular architecture made of five conjugated rings carrying terminal methyl or variable alkoxy (chain lengths of 4, 6, 8, or 16) substituents at para positions has been synthesized. Among the five rings, two rings are of cyanopyridones utilized as an electron deficient N-heterocycle and blue lumines-cent motif, and the rest of them are phenylene motifs. All the compounds were obtained in good yield and ATR-IR, NMR and Mass spectroscopy confirmed their structures. Furthermore, the compounds were stable up to ≈200 °C and the degradation occurs at higher temperature as evidenced by the TGA analysis. The mesomorphic study reveals that only the compound having very long terminal n-hexadecyloxy substituents showed inlayers liquid crystalline organization as confirmed by POM and variable temperature XRD analysis. Furthermore, the compounds showed intense blue fluorescence in both solution as well as solid state and their fluo-rescence quantum yields are dependent on the length of alkoxy chains. Calculated HOMO/LUMO levels by cyclic voltammetry measurements revealed that the compounds are ambipolar in nature and proposed to be ideal candidates for electroluminescent applications.

Journal of Materials Chemistry C

We have assessed the potential of light-responsive bent-core liquid crystals as candidate materia... more We have assessed the potential of light-responsive bent-core liquid crystals as candidate materials for energy conversion and storage applications, and promoted isothermal phase transitions between columnar and smectic phases.

Physical Review E, 2015

The nature of the nematic-nematic phase transition in the liquid crystal dimer 1 ,9 -bis(4-cyanob... more The nature of the nematic-nematic phase transition in the liquid crystal dimer 1 ,9 -bis(4-cyanobiphenyl-4 -yl) nonane (CB9CB) has been investigated using techniques of calorimetry, dynamic dielectric response measurements, and 2 H NMR spectroscopy. The experimental results for CB9CB show that, like the shorter homologue CB7CB, the studied material exhibits a normal nematic phase, which on cooling undergoes a transition to the twist-bend nematic phase (N TB ), a uniaxial nematic phase, promoted by the average bent molecular shape, in which the director tilts and precesses describing a conical helix. Modulated differential scanning calorimetry has been used to analyze the nature of the N TB -N phase transition, which is found to be weakly first order, but close to tricritical. Additionally broadband dielectric spectroscopy and 2 H magnetic resonance studies have revealed information on the structural characteristics of the recently discovered twist-bend nematic phase. Analysis of the dynamic dielectric response in both nematic phases has provided an estimate of the conical angle of the heliconical structure for the N TB phase. Capacitance measurements of the electric-field realignment of the director in initially planar aligned cells have yielded values for the splay and bend elastic constants in the high temperature nematic phase. The bend elastic constant is small and decreases with decreasing temperature as the twist-bend phase is approached. This behavior is expected theoretically and has been observed in materials that form the twist-bend nematic phase. 2 H NMR measurements characterize the chiral helical twist identified in the twist-bend nematic phase and also allow the determination of the temperature dependence of the conical angle and the orientational order parameter with respect to the director.

Langmuir, 2009

The original publication gave incorrect x-axis labels for Figure and q-values in the text and Fig... more The original publication gave incorrect x-axis labels for Figure and q-values in the text and Figure caption. The x-axis labels for Figure have been corrected as shown below. In the text (left column), the value q = 0.01 nm -1 should be q = 0.1 nm -1 . In the Figure caption, the value q =0.01 nm -1 should be q =0.1 nm -1 .

Journal of Materials Chemistry, 2012

85} were prepared as described elsewhere. Compounds 4. 7 mmol of compound 3 were diluted with 100... more 85} were prepared as described elsewhere. Compounds 4. 7 mmol of compound 3 were diluted with 100 mL of dry DCM. Then, 9 mmol of TEA were added via syringe under argon atmosphere. Then, a solution of 7 mmol of the corresponding acid chloride 2 in dry DCM was added drop wise. The reaction mixture was stirred for 15 hours at room temperature. Then, it was extracted with water and DCM. The organic layer was evaporated, and the crude product was purified by column chromatography on silica gel (Hexanes/Ethyl acetate, 8:2). Compounds 4 are red solids. Yields: 30 %. Rf: 0.3 (silicagel, hexanes/ethyl acetate, 8:2)

Handbook of Liquid Crystals, Feb 26, 2014

The spontaneous orientation of the molecules in mesophases can be explained by the anisotropy of ... more The spontaneous orientation of the molecules in mesophases can be explained by the anisotropy of repulsive forces coupled with the isotropic part of the dispersion interactions. However, it can not be ruled out that, depending on the molecular structure, other molecular interactions can play an important role (e.g. hydrogen bonds, polar forces, charge-transfer processes, etc.). In addition, the interactions between chemically incompatible structures, as well as spatial steric interactions, can determine the structural features of liquid crystal phases. A very attractive example of such a steric interaction concerns molecules with a distinct bent shape, which are the topic of this chapter. VCH Books F o r P e e r R e v i e w 2 Generally speaking, the distinctive liquid crystalline phases promoted by bent-core structures have either a lamellar or a columnar nature, with numerous packing variants and the occurrence of polarity and chirality. Along with these structural characteristics, the remarkable physical properties and phenomena reported for these materials immediately generated great interest. Thus, outstanding work on the relationship between the molecular structure and the properties has been carried out and published. However, very few extensive systematic studies on structure-activity relationships can be cited and this makes it difficult to draw definitive conclusions for many aspects. Nonetheless, detailed reviews concerning the relationship between the chemical structure of bentcore mesogens and their liquid crystalline behavior have been summarized. Interestingly, although different revisions have had fundamentally different aims, they all contribute to show the development of the field in terms of the chemical structure and properties of the bent-core molecules. Research has revealed that the occurrence of the unique polarity and chirality in the mesophases of bent-core molecules strongly depends on the molecular structure and intermolecular interactions. However, many essential questions on the chemical structure-mesomorphism of these compounds remain unanswered. There are three basic structural units in bent-shaped mesogens and these have been the focus of research aimed at designing, modulating and understanding bent-core mesomorphism: the central bent-core (BC), the rod-like lateral structure (LC) that forms the bent-shaped structure of these molecules and the terminal substituents (Figure ). In the following sections we will cover these structural aspects and discuss the most relevant features.

Journal of Applied Physics, 2000

The Pockels effect has been studied in some photopolymers based on chiral smectic C liquid crysta... more The Pockels effect has been studied in some photopolymers based on chiral smectic C liquid crystals. The materials have different degrees of crosslinking, varying from mesogenic side-chain polymers to anisotropic networks. None of them is switchable but there is an important electrooptic response due to a residual molecular motion at low frequencies. In two of the studied materials, the molecular contribution disappears above several kHz and, in these cases, the electronic electrooptic effect has been fully characterized. The electrooptic coefficients are in the range r=1 pm/V. The actual electronic origin of the measured effect has been confirmed by means of comparison with second-harmonic generation data.

Angewandte Chemie, Jun 1, 1991

g = 3.9 auf. Dieses Spektrum steht in Einklang mit anderen fur gemischtvalente Mn"/Mn"'-Komplexe ... more g = 3.9 auf. Dieses Spektrum steht in Einklang mit anderen fur gemischtvalente Mn"/Mn"'-Komplexe erhaltenen Daten" 61. Unerwartel ist die Anwesenheit des dien-Liganden im isolierten Komplex 1. Das fur dessen Herstellung verwendete trien wurde nach Standardmeth~den~~'] gereinigt, wobei gaschromatographisch und massenspektrometrisch kein dien nachzuweisen war. Im Gegensatz dazu enthielt die Mutterlauge, aus der 1 isoliert wurde, signifikante Mengen sowohl des dierials auch des trien-Liganden. Wir vermuten, daB trien unter den durch NH,PF, hervorgerufenen ,,saw ren" Bedinglingen zu einer Imin-Zwischenstufe oxidiert wird, welche clann zu dien hydrolysiert wird. Das I3C-NMR-Spektrum eines CH,CI,-Extrakts der Mutterlauge zeigt Signale von trien und dien. Zusitzlich tritt ein Resonanzsignal irn C-N-Bereich bei 6 = 49.5 sowie ein weiteres bei 6 = 173.2 auf, das dent C-Atom einer Carbonylgruppe zugeordnet werden kann Diese Signale legen nahe, dal3 der von trien abgespaltene C,H,NH,-Rest zu Glycin reagiert hat. Das eigentliche Oxidationsmittel ist Luftsauerstoff, da in Losungen, die unter LuftausschluD zur Reaktion gebracht wurden, kein dien nachgewiesen werden kann. Wir haben gezeigt, daD aus basischeren, ein ihnliches TetraaminC6l enthaltenden Losungen gemischtvalente Mn"'/Mn'"-Komplexe isoliert werden konncn, so daD vermutlich hoheroxidierte Mangankomplexe die Oxidationsreaktion bewirken. Ob diese vor oder nach der Komplexierung mit Mangan stattfindet, 1st offen. Sowoh! Mn"-als auch Mn"'-Zentren sind labil, so daB die Anwesenheit von freiern dien in der Mutterlauge nicht als Hinweis auf eine Oxidation im nicht koordinierten Zustand gewertet werden kann. Die oxidative Dehydrogenierung nicht koordinierter Liganden wurde bei Co"-, Nil'-, und Fe"-Komplexen" nachgewiesen, wobei koordiniertes 0, als Oxidationsmittel genannt wird. In diesem Zusammenhang ist interessant, daD das 0,-freisetzende Zentrum von Photosystem-11-Proben sowohl primire als auch sekundire Amine oxidieren kannfIg1 und jungsten Hinweisen zufolge der Ubergang S, + S, im Photosystem I1 der Oxidation von Histidin entsprichtIZo1. Experimentel/c~s Mn(OAc), (0 5 g. 0.002 mmol) und NaOAc (0.3 g. 0.0036 mmol) werden in Methanol geliist (25 mL) und die Losung wird auf 64°C erhitzt. Nach Zugabe von trien (0.3 g. 0 002 mmol) wird die Losung dunkelgriin. Zugabe von festem NH,PF, (0.5 g. 0.003 mmol) und Erhitzen his zur Auflosung des Feststoffs fuhrt zu einer orangen Losung. Beim Abkiihlen an Luft wird die Losung dunkelrot und iiber Nacht kristallisieren rote Nadeln aus. Bei Durchfuhrung der Reaktion unter LiiftausschluD geht sie nicht iiber die Stufe der orangen Losung hinaus. Korrekte Elementaranalyse. Fur die Strukturanalyse geeignete Kristal-Ic wurden iius der Reaktionslosung erhalten.

Chemistry of Materials, May 30, 2001

ABSTRACT The synthesis and characterization of several mesogenic antiferroelectric gelsobtained b... more ABSTRACT The synthesis and characterization of several mesogenic antiferroelectric gelsobtained by in situ photopolymerization of mixtures of a nonchiral diacrylate and a nonreactive compound with an antiferroelectric SmC*A phaseis described. Along with kinetic aspects from their photopolymerization processes, information has been obtained concerning the dielectric permittivity, spontaneous polarization, optical response to an applied electric field, and the influence that the photopolymerization conditions and the structural characteristics of the network have on these properties. We have found that the polymer network not only stabilizes the antiferroelectric orientation but also alters the electro-optic properties of the liquid crystal.

Journal of Materials Chemistry C, 2014

The mesomorphism of bent-rod dimers with a very long flexible linker strongly depends on the stru... more The mesomorphism of bent-rod dimers with a very long flexible linker strongly depends on the structure of the spacer and the rod-core.

Liquid Crystals, Sep 1, 2004

The synthesis and characterization of the mesomorphic and dielectric properties of a series of ne... more The synthesis and characterization of the mesomorphic and dielectric properties of a series of new imine-based liquid crystalline compounds that exhibit tilted SmC* phases is reported. The presence of an imino linkage within the mesogenic nucleus of these compounds is significant due to the ability of salicylaldimines to coordinate to metals. Structure-activity studies have also been carried out by varying the structural elements in the ligands. The structural variations include changing the length of the chiral chain and incorporating fluorocarbon segments in the achiral terminal chain.

Journal of Materials Chemistry, 2007

Commercial chemicals (reagent grade) were purchased from Aldrich Chemical Co., Fluka or Panreac a... more Commercial chemicals (reagent grade) were purchased from Aldrich Chemical Co., Fluka or Panreac and used without further purification. Solvents were purified and dried by standard techniques. The synthetic procedures leading to the target compounds are outlined in Schemes 2-4. Some of the intermediates used in these syntheses were prepared according to procedures already reported in the literature: 3,4'-dihydroxybiphenyl (1), 1 p-ntetradecyloxyaniline (3), 2 3-[4"-(4"'-n-tetradecyloxybenzoyloxy)benzoyloxy]biphenyl-4'-ol (4), 3 p-n-tetradecyloxybenzoic acid (10) 3 and 4-(4'-n-tetradecyloxy phenylazoxy)benzoic acid (15). 3,4'-[Bis-(4"-formyl)benzoyloxy]biphenyl (2). DCC (1.65 g, 7.5 mmol) was added to a cooled (0 ºC), stirred mixture of 3,4'-dihydroxybiphenyl (1) (0.5 g, 2.7 mmol), pformylbenzoic acid (1.05 g, 6.9 mmol) and DMAP (0.065 mg, 0.27 mmol) and dichloromethane (25 mL) under an argon atmosphere. The reaction mixture was stirred for 30 min at 0 ºC and was allowed to warm up to room temperature. The mixture was stirred for 24 h, the resulting solid was filtered off and the filtrate was evaporated to give a solid, which was purified by flash chromatography on silica gel, using dichloromethane as the eluent, gave the product in 62% yield.

Resumen del trabajo presentado al "16eme Colloque sur les Systemes Anisotropes Auto-organise... more Resumen del trabajo presentado al "16eme Colloque sur les Systemes Anisotropes Auto-organises" celebrado en Strasbourg (Francia) del 3 al 6 de septiembre de 2013.

Liquid Crystals, 2017

Dielectric measurements (Thermally Stimulated Depolarization Currents and Broadband Dielectric Sp... more Dielectric measurements (Thermally Stimulated Depolarization Currents and Broadband Dielectric Spectroscopy) have been performed near the glass transition to study the glass transition on the odd nonsymmetric liquid crystal dimers of the series α-(4-cyanobiphenyl-4´-oxy)-ω-(1-pyreniminebenzylidene-4´oxy) alkanes (CBOnO.Py) with n ranging from 3 to 9. A previous study [S. Diez-Berart et al., Materials 8 (2015) 3334] carried out in CBO11O.Py showed the presence of two glass transition temperatures, attributed to different molecular motions of the terminal groups. The study performed allows us to analyze the molecular dynamics in the rest of the series and determine the role played by the flexible spacer. Parallel and perpendicular orientations of the molecular director with regards to the probe electric field have been investigated. The low and intermediate observed relaxations are explained in the framework of Stocchero's theoretical model [M. Stocchero, J. Chem. Phys. 121 (2004) 8079] for the dielectric behaviour of non-symmetric liquid crystals dimers, as independent end-over-end rotations of each terminal semirigid unit. As the length of the spacer chain in the series of compounds decreases, the different relaxations become progressively more coupled at the glass transition. Numerical simulations of the calorimetric response from the obtained kinetic parameters show good agreement with experimental behaviour.

Metallomesogens

... new materials mainly resemble those already observed for calamitic or columnar mesophases pro... more ... new materials mainly resemble those already observed for calamitic or columnar mesophases produced ... atom clearly depends on the structural character-istics of the new complex ... Other examples of conoscopic characterization have been reported in other, struc-turally different ...