Morphology-driven absorption and emission colour changes in liquid-crystalline, cyclometallated platinum(ii) complexes

Platinum(II) complexes of 1,3-bis(2-pyridyl)benzene containing two alkyl chains are unexpectedly mesomorphic and capable of changing absorption and emission colour depending on the phase obtained after thermal treatment

Luminescence modulation in liquid crystalline phases containing a dispiro[fluorene-9,11′-indeno[1,2-b]fluorene-12′,9′′-fluorene] core

International audienceA luminescent liquid crystalline compound containing a bulky dispiro[fluorene-9,11′-indeno[1,2-b]fluorene-12′,9′′-fluorene] has been designed and synthesized by di-substitution of a bromo derivative with N-(4-ethynylphenyl)-3,4,5-tris(hexadecyloxy)benzamide fragments. This di-substituted 3π-2spiro derivative forms stable and well-organized mesophases over large temperature ranges. Combination of DSC, POM and SAXS analyses has revealed the formation of a lamellar mesophase between 60 and 150 °C followed by another mesophase with a 2-dimensional lattice of rectangular symmetry that remains up to the isotropization point near 225 °C. In the original molecular packing model deduced from SAXS, the tert-butyl terminal groups fill the centre of hollow columns constituted by both the dihydro(1,2-b)indenofluorene and benzamide fragments and separated from each other by the surrounding aliphatic tails. The merging of the columns yielding the lamellar phase turned out to be governed by the dynamics of both, the micro-phase segregation process and the network of hydrogen bonds. In the various mesomorphic states and in solution, a strong luminescence was observed. The emission spectrum however depends on temperature and drastically changes between both mesophases and the isotropic liquid. In particular, a strong modulation of the emission wavelength occurs at the isotropic to 2D phase transition. This luminescence modulation results from an enhanced contribution of the vibronic peaks at higher energies in the emission profile. The compound was also found to be soluble in 5CB and was integrated in a guest-host LC cell, allowing efficient modulation of the photoluminescence polarization, in the presence or absence of an electrical field

Supramolecular aggregates of metallo–organic acids with stilbazoles. Formation of columnar mesophases and Langmuir films

Producción CientíficaSupramolecular metal complexes formed through hydrogen bonding between tris(3,4,5-decyloxy)stilbazole and several metallo–organic acids of the type [Au(R)(CNC6H4CO2H)] (R = C6F5, C6F4OC10H21), [cis-[MCl2(CNC6H4COOH)2] and [trans-[MI2(CNC6H4COOH)2] (M = Pd, Pt) have been synthesized. All the supramolecular palladium and platinum polycatenar aggregates display a hexagonal columnar mesophase at temperatures close to room temperature. Most of the supramolecular trisalkoxystilbazole complexes exhibit luminescent behaviour. Aggregates of [Au(C6F4OC10H21)(CNC6H4CO2H)] and [trans-[MI2(CNC6H4COOH)2] (M = Pd, Pt) form stable Langmuir films at the air–water interface.Ministerio de Ciencia e Innovación (Projects CTQ2011-2513)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA248A11-2

Room‐Temperature Columnar Mesophases in Triazine–Gold Thiolate Metal–Organic Supramolecular Aggregates

Producción CientíficaSupramolecular mono‐ and dinuclear liquid‐crystalline gold(I) aggregates have been synthesized by means of hydrogen bond interactions of 2,4,6‐triarylamino‐1,3,5‐triazine with thiolate moities of gold metalloacids [Au(PR3)(SC6H4COOH)] or [μ‐(binap){Au(SC6H4COOH)}2], in 1:1 and 2:1 molar ratio, respectively. All of the supramolecular aggregates display a stable columnar hexagonal mesophase (Colh) at room‐temperature. The supramolecular arrangement within the columns consists of the one‐dimensional stacking of triazine units, with the core of the attached metallic thioacid fragments acting as the fourth branch. The phosphine‐containing moieties of the metallic thioacid protrude out in the aliphatic continuum. These complexes do not show metallophilic interactions, but this strategy appears very promising for the future design of room‐temperature LC mesophases containing interacting metallic fragments.Ministerio de Ciencia e Innovación (Proyect CTQ2011–25137)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA248 A11‐2