Second harmonic generation in anisotropic stratified media: A generalization of the Berreman method and its application to photonic materials

We have developed a numerical method for calculating the second harmonic generation (SHG) generated by an anisotropic material whose optical properties present an arbitrary modulation in one dimension. The method is based on the Berreman 4x4 matrix formalism, which is generalized to include nonlinear optical phenomena. It can be used under oblique incidences of the input beam, and is valid even when the SHG frequency is close to photonic bands, where the usual slowly-varying-amplitude approximation breaks down. As an example of application, we have studied the SHG performance of ferroelectric and helielectric nematic liquid crystals. The latter present a helicoidal structure that can be distorted under electric field. In the different tests of the method we have analyzed the conditions for the most efficient SHG, and compared with previous results in the case there were any. The obtained results indicate that the present procedure may contribute to improve the structural design and enlarge the variety of nonlinear optical materials for their application in optical devices.Comment: 14 pages, 6 figure

Upgrading the Performance of Cholesteric Liquid Crystal Lasers: Improvement Margins and Limitations

The topic of cholesteric-liquid-crystal lasers is a rapidly expanding research area in the field of soft-matter photonics. The increasing interest in this field is due to the high versatility that these lasers may possibly present and the prospects of giving rise to new miniaturized devices. However, further improvements in their operation capabilities are still required for potential applications. In this paper, we critically analyze the main strategies proposed up to now to optimize their performance. We show theoretically and experimentally that possible innovations in the device structure cannot produce lasers with threshold energies below a certain limit. This limit is determined by the light scattering and absorption losses inside the liquid crystal. Even assuming the case of samples free of defects and perfectly non-absorbing, an intrinsic light scattering, typical of mesogens, still remains. Numerical estimates of the thresholds indicate that these lasers could hardly be driven by compact light sources such as current electroluminescent or light-emitting diodes. Since the improvement possibilities regarding cell architecture seem to be exhausted, the advance must come from the use of new dye molecules. These molecules should show enhanced emission cross-sections and be efficiently integrable within the mesogenic solvent. In addition, the fluorescent systems must present very small quantum yields to triplet states if continuous-wave lasing is sought. In this respect, quantum dots are an alternative to explore for further investigations

Diseño en 3D, análisis hidrodinámico y cálculo del escantillonado de una embarcación de 24 metros de eslora fabricada con materiales compuestos.

Se desarrolla el procedimiento de diseño en 3D de una embarcación de eslora menor de 24 metros y la posterior determinación de su escantillonado siguiendo las indicaciones de la norma internacional ISO 12215 para la construcción de cascos y escantillones de pequeñas embarcaciones. Se analizan también las ventajas y desventajas de la construcción del casco de un velero con fibra de vidrio y fibra natural de lino. Para llevar a cabo el diseño 3D a partir de los planos 2D de la embarcación se ha utilizado el software Rhinoceros. Los cálculos hidrostáticos, hidrodinámicos y el comportamiento en la mar se han estudiado con el programa Maxsurf, ampliamente utilizado en el sector naval

Chiral ferroelectric nematic liquid crystals as materials for versatile laser devices

We present a liquid-crystal laser device based on the chiral ferroelectric nematic phase (NF*). The laser medium is obtained by mixing a ferroelectric nematic material with a chiral agent and a small proportion of a fluorescent dye. Notably, in the NF* phase very low electric fields perpendicular to the helical axis are able to reorient the molecules, giving rise to a periodic structure whose director profile is not single harmonic but contains the contribution of various Fourier components. This feature induces the appearance of several photonic bandgaps whose spectral ranges depend on the field, which can be exploited to build tunable laser devices. Here we report the characterization of home-made NF* lasers that can be tunable under low electric fields and present laser action in two of the photonic bands of the material. The obtained results open a promising route for the design of new and more versatile liquid-crystal based lasers

Self-assembly of bent-core amphiphiles joining the ethylene-oxide/lithium ion tandem

The synthesis, supramolecular self-assembly and structural characterization of a new family of tetraethylene oxide (TEG)-based bent-core compounds and their 1/1 lithium-containing complexes are reported. TEG-based bent-core amphiphiles, even joining the TEG/Li+ tandem, are suitable building-blocks to achieve supramolecular nanostructures, in some cases showing chiral features from achiral molecules either in the mesophase or in solvents. The thermal and liquid crystal behavior of these materials studied by polarizing optical microscopy and X-ray diffraction confirmed that Li-based materials stabilized polar smectic C and helical nanofilament-type mesophases, in contrast to the non-liquid crystalline pure TEG-compounds. Alternatively, both the pure amphiphiles and the lithium-doped materials self-assemble into physical gels in non-polar solvents, displaying three-dimensional networks composed of long fibers with lamellar molecular organizations as shown by transmission electron microscopy and X-ray diffraction. Interestingly, biphenyl- and azobenzene-based bent core amphiphiles aggregate in solvent into chiral nanostructured morphologies with supramolecular trends comparable to their molecular arrangement in their liquid crystalline phases

Soft nanostructures out of star-shaped triazines with flexible amide spacers: liquid crystals with a cubic to columnar transition with memory effect, gels and supramolecular chirality

This work reports the synthesis and characterization of a new family of star-shaped tricarboxamides with C3-symmetry that have flexible amide spacers linking a tris(triazolyl)triazine core with three trialkoxyphenyl groups. The presence of amide groups allows the formation of intermolecular hydrogen bonds that reinforce π-stacking and van der Waals interactions, promoting liquid crystalline behavior, and self-assembly in solvents leading to organogels. As determined by polarized optical microscopy, differential scanning calorimetry and X-ray diffraction on powder samples, all the three reported molecules present a hexagonal columnar (Colh) phase stable at room temperature. Interestingly, they show a transition to a cubic micellar mesophase (BCC) at high temperatures. A mechanism for this transition, which is consistent with the fragmentation of columns to form supramolecular spheres, was elucidated from X-ray studies on aligned samples. Moreover, on cooling from the BCC to the columnar phase a preferential orientation of columns occurs, according to which each cubic domain gives rise to four hexagonal domains. The ability of the synthesized structures to aggregate in solvent media was studied in a variety of organic solvents, and all of them were able to gel 1-octanol at low concentrations. X-ray studies of gels and xerogels were carried out and showed a molecular organization consistent with Colh order. FTIR studies were carried out to analyze the formation of hydrogen bonds and the influence of the length of the flexible spacer in the liquid crystalline state and in the organogels. Furthermore, the presence of a stereogenic center in the flexible amide spacer leads to macroscopic chirality in the liquid crystal state and the organogels in 1-octanol as demonstrated by circular dichroism spectroscopy

Modulating Organic/Inorganic Segregation in Columnar Mesophases

This work reports an uncommon modulation of columnar segregation of metal–organic triphenylene liquid crystals by blending two structurally dissimilar metallomesogens that can self-associate through complementary electron donor–acceptor interactions. The constituent molecules are cis-[PtCl2(CNR)2] (CNR = 2-(6-(4-isocyanophenoxy)hexyloxy)-3,6,7,10,11-pentakisdodecyloxytriphenylene) that displays an organic/inorganic segregated columnar mesophase and [PtCl2(Bipy)] (Bipy = didodecyl 2,2′-bipyridyl-4,4′-dicarboxylate) that shows a lamellar mesomorphism. The phase diagram of this system was constructed using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray scattering data. The phase diagram corresponds to a typical binary system with an intermediate compound (in this case a supramolecular aggregate) of stoichiometry [PtCl2(CNR)2]/2[PtCl2(Bipy)], which is maintained in solution. This species shows an unusual columnar mesophase formed by the stacking of alternating organic/inorganic fragments. Quantum chemical calculations show that the columnar structure is mainly supported by complementary π electron donor–acceptor interactions between each triphenylene group of the isocyanide complex and a platinum-bipyridine molecule. This induces the elimination of the organic/inorganic columnar segregation of the isocyano parent component and constitutes an unconventional example of modulation of organic/inorganic segregation in columnar mesophases by the intercalation of metal complexes into hexaalkoxytriphenylene stacks.This work was sponsored by the Ministerio de Ciencia e Innovación (Project PID2020-118547GB-I00), the Junta de Castilla y León (Project VA224P20), and the Basque Government (Project IT1458-22). E.D. thanks MECD for a FPU grant. The authors thankfully acknowledge the computer resources at Lusitania II and CIERZO-CAESARAUGUSTA III and the Technical support provided by Cénits-COMPUTAEX (FI-2022-1-0009, FI-2022-3-0008), Centro de Supercomputación de Aragón (QHS-2023-3-0005, QH-2023-1-0002) and Red Española de Supercomputación. We thank Dr. S. Ferrero (University of Valladolid) for his help in the NMR titration experiments

Alignment of Palladium Complexes into Columnar Liquid Crystals Driven by Peripheral Triphenylene Substituents

Producción CientíficaMono- and dinuclear ortho-palladated complexes based on a triphenylene-imine ligand that display columnar mesophases (Col) at temperatures close to ambient have been isolated. The mesophase stability is large, and their structures consist of Pd-containing columnar zones supported by fully organic columns formed by the triphenylene moieties.Ministerio de Economía, Industria y Competitividad (CTQ2011-25137)Ministerio de Economía, Industria y Competitividad (MAT2012-38538-C03-02)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Liquid crystalline and nonlinear optical properties of bent-shaped compounds derived from 3,49-biphenylene.

9 pages, 6 figures, 3 tables.The synthesis of different bent-core molecules derived from 3,49-biphenylene bearing azo, azoxy, imine or ester linkages in their lateral structures is reported. Structure–activity relationships for their liquid crystalline behaviour are discussed. SmCP, USmCP and Colob mesophases are found depending on the type and number of these connecting units. The sequence ester#azoxy . imine . azo can be proposed for the mesophase range, with significant differences observed in terms of mesopahase stabilization. SHG studies on these compounds give nonlinear coefficients in the range of 1–8 pm V21. The molecular origin for these values is analyzed semi- uantitatively. It was concluded that the SHG performance of bent-core mesogens in general can still be increased substantially. An approach to improve the properties of these materials is briefly outlined.This work was supported by projects MAT2003-07806-C02 and MAT2006-13571-C02 (CICYT-FEDER) from Spain-EU and by the DGA (Spain) and University of the Basque Country (Project. Nu 9/UPV 00060.310-13562/2001). I. P. and I. A. also thank DGA and the Ministry of Education of Spain, respectively, for grants.Peer reviewe

Synergistic π-π and Pt-Pt interactions in Luminescent Hybrid Inorganic/Organic Dual Columnar Liquid Crystals

Producción CientíficaA new triphenylene-isocyanide CN-C6H4-O-(CH2)6-TriPh, non mesogenic, and their ortho-metallated benzoquinolate (bzq) complexes, [M(bzq)X(CN-C6H4-O-(CH2)6-TriPh)] (M = Pd, Pt; X = Cl, I) and [Pt(bzq)(CN-C6H4-O-(CH2)6-TriPh)2]A (A = NO3−, BF4−, PF6−), all displaying a columnar mesophase, have been prepared. The structure of the mesophase, determined by X-ray diffraction methods, is uncommon and consists of a central column formed by stacking of the organometallic benzoquinoline-platinum fragments, surrounded by six columns in hexagonal disposition formed by stacking of the triphenylene groups. These materials show aggregation-induced phosphorescence based on inter-disk Pt⋯Pt interactions.2017-02-15Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13)Ministerio de Economía, Industria y Competitividad (CTQ2014-52796-P)Ministerio de Economía, Industria y Competitividad (MAT2012-38538-C03-02)Gobierno Vasco (GI/IT-449-10