H. Strzelecka

Mesogenic Dithiolates: New Disk Like π-Acceptors

Abstract Starting from p-hydroxyphenylacetic acid we have been able to synthesize mesogenic dithiolates of transition metals with long chain substituents. Introduction of n-alkoxy side chains reduces the electronic affinity of this system, nevertheless those compounds are weak acceptors and can form complexes with π-donors which have a low ionization potential (EA −IP < 0.1V).

Liquid Crystalline Organic Conductors: Studies in Crystalline and Mesomorphic Phase

Abstract The present results concern a liquid crystalline organic conductor: DIPSAr4–TCNQ. The ac conductivity was measured for the first time in the mesophase and indicates the actual possibility of obtaining organic conductors with mesomorphic behavior.

Synthese et Proprietes Redox des π-Donneurs Mesogenes

Abstract In the sequence of previous work on 2,2′,6.6′-titraaryl-4,4′-bipyrannylidbne and their sulfur analogs1,2 we report the synthesis (Scheme 1 and 2) and redox properties of heterocycles having long chain substituents. Introduction of four alkyl groups Cn H2n+1 in the para position of the phenyl groups leads to π-donors having mesomorphic (disco-like) properties (n > 9). In contrast, the presence of alkyloxy substituents leads only to mesomorphic species when the heteroatom is S but not O (n ≥ 12). All new donors give stable 1 :1 charge transfer complex with TCNQ, several of them having also mesomorphic properties.

Heteroaromatic Salts Exhibiting Thermotropic Liquid Crystalline Properties

Abstract We present a new class of thermotropic liquid crystals in which the rigid part of the molecules are constituted of heteroaromatic cations (1,2-dithiolium, pyrylium and thiopyrylium).

The Smectic a Phases of Some Long Chain Substituted Diaryl-2,6 Pyrylium and Thiopyrylium Salts

Abstract We report on the characterization of smectic A phases in pyrylium perchlorates. Different models of the layered structure are discussed.

Sels de pyrylium et de thiopyrylium mésomorphes

Abstract Recently we described the redox and liquid-crystal properties of 2,2′, 6,6′-tetraaryl-4,4′-bipyrannylidenes and their sulfur analogs, in which aryls are substituted with long alkyl or alkoxy chains. Some of the synthesis intermediate perchlorate salts of 2,6-λ diaryl pyrylium and thiopyrylium also show a mesomorphic behavior. So the introduction of long alkyl or alkoxy chain substituants in para position of the phenyls leads to liquid-crystals for both pyrylium and thiopyrylium perchlorates, but the mesomorphic phase is larger for the thiopyrylium ones. The systematic study of the position of the substituant in the phenyl cycle of pyrylium salts demonstrates that the meta-substituted compounds have a lower transition temperature (Cr-M) than the para. Finally the ortho ones do not exhibit a liquid-crystal behavior. Between the dialcoxy-substituted pyrylium salts, only the ortho, meta ones show mesomorphic phase, and the effect of the introduction of the second alcoxy-chain is the decrease of the t...

Synthese Efficace de Composes Aromatiques Polyalcoxyles

Abstract Obtaining liquid crystals like heteroaromatic salts and phasmids needs, as starting materials, substituted aromatic compounds. Rational synthesis of acetophenones, benzaldehydes, chalcones, benzoates … having alkoxy groups is presented. Alkylation of aromatic polyhydroxy derivatives is performed by two procedures : phase transfer without solvent : RBr/KOH (Brams method), or the action of RBr in DMF/Base: CS2CO3 or K2CO3). Typical examples of experimental conditions are given.

Raman Study at Low Temperature of Polyiodidesin the Series DIPSφ4

Abstract We report low temperature Raman scattering study of polyiodides in a series of DIPSφ4 (tetraphenyldithiapyranylidene). Iodine species consist of I− 3 or I− 3 and I− 5 ions and at low temperature, Raman spectra reveal new features. A splitting of the stretching vibration of the I− 3 ion is observed, which depends on the iodine concentration, in connection with the conductivity value. This phenomenon can be interpreted in terms of an interaction between two I− 3 ions located on the same iodine column.

The resistivity of a liquid crystalline organic conductor measured within the mesophase from 100 to 1000 MHz

Abstract The a.c. conductivity of a liquid crystalline organic conductor is measured for the first time within the mesophase. The charge transfer complex is still conducting above the transition temperature of 120[ddot]C; but each stay in the mesophase produces an irreversible degradation of the transport properties, the consequences of which can be observed in the crystalline phase too.

Synthesis and Properties of Mesogenic π-Donors Precursors of Mesomorphic Organic Conductors

Abstract In sequence with previous work on 4-(2,6 diphenyl 4-H pyran-4 ylidene-2,6 diphenyl) and their sulfur analogs, useful precursors of organic conductors, we now report on the synthesis and properties of parent heterocyclic compounds, 1, in which the phenyls have long chain substituents. Introduction of four alkyl or alkoxy side chains in the para position of phenyl leads to compounds, 2, which exhibit disk-like mesophases. All new donors 2 give stables 1: 1 charge transfer complexes, 3, with TCNQ. Disk-like donors lead to mesomorphic conducting complexes. For example the TCNQ complex of 2b, × = S, R = C12H25 exhibits a SA phase between 120-154°C. The electrical conductivity at room temperature of a single crystal is 0.7 (Ωcm)−1.