Chirale Dotierstoffe mit außergewöhnlich hohem Verdrillungsvermögen

Abstract

Mesogenic Chiral Dopants With Unusual High Helical Twisting PowerMesogenic chiral esters of 1-phenyl-1,2-ethandiol, l-cyclohexyl-l,2-ethanediol, 1,2-diphenyl-1,2-ethanediol, l,l'-bi-2-naphthol, 1-phenylethanol, 1-phenyl-2,2,2-trifluorethanol and l-(9-anthryl)-2,2,2-trifluorethanol were synthesized. The temperature dependence of the molecular twisting power was determined in the nematic wide range mixture RO-TN 404. All compounds show good solubility and unusual high values of the Einleitung

TADDOLs, Their Derivatives, and TADDOL Analogues: Versatile Chiral Auxiliaries

“…The standard measure for this characteristic is called the helical twisting power (HTP, expressed in mm À1 , Figure 8). [117] Before the first TADDOLs were tested as doping agents, HTP values of 100 mm À1 were regarded as high, [119] but experiments based on our stock of TADDOLs quickly resulted in derivatives with HTP values of 300 ± 400 mm À1 . [83] A record of 534 mm À1 was achieved with a fluorenylidene derivative containing two tetrakis(2-naphthylmethanol) substituents [118,120] (Figure 8).…”

Design and Synthesis of Chiral Nematic Liquid Crystals

“…Type IIa use chiral flexible spacer units and can be typified by the use of systems such as (R)-3-methyladipic acid [164][165][166][167][168], derivatives of lactic acid [169][170][171], or optically active alcohol or diols [172][173][174][175][176][177][178] positioned between two liquid-crystalline cores.…”

“…Research on diesters derived from the optically active diols, (S)-1,2-propandiol and (R,R)-2,3-butandiol, has shown the diesters to have high helical twisting powers (β) when used as dopants in suitable nematic mixtures. However, only one of these materials is known to show a liquid-crystalline phase; this is a derivative of (R,R)-2,3-butandiol (125) [172]. The high thermal stability of the chiral nematic phase is not surprising, considering the size of the liquid-crystalline core (4 -(trans-4-pentylcyclohexyl)biphenyl-4-carboxylic acid); the chiral nematic phase occurs between 212 and 255 • C. [172] This compound has been demonstrated to give highly twisted chiral nematic phases when used as a dopant and shows a helix inversion at approximately 60 • C in a commercially available wide range nematic mixture.…”

“…The synthesis of the oxirane units is of interest as it is achieved by use of the Sharpless asymmetric epoxidation procedure by treatment of either cis-or trans-allylic alcohols with a stoichiometric mixture of l-(+)-diethyl tartrate, titanium isopropoxide, and t-butyl hydroperoxide at low temperature to give the appropriate epoxide [204,[206][207][208]. This process is demonstrated in the synthesis of (2R,3S)-(−)-4-heptoxyphenyl-3-[trans-4-(trans-4-pentylcyclohexyl)cyclohexyl]oxirane-2-carboxylate (172), as shown in Scheme 14.11 [206]. The use of a further mild oxidation and neutral esterification methods ensure that ring opening of the epoxide ring is minimized.…”

TADDOLe, ihre Derivate und Analoga – vielseitige chirale Hilfsstoffe

“…[116] Wie in der Katalyse ist es dabei wichtig, so wenig wie mˆglich Dotierstoff zu verwenden, um den gew¸nschten Grad an Helizit‰t (Ganghˆhe in mm der induzierten Helix) zu erreichen; die Ma˚zahl hei˚t Helical Twisting Power (HTP, Einheit mm À1 ; Abbildung 8). [117] Bevor die ersten TADDOLe als Dotierstoffe getestet wurden, galten HTP-Werte von 100 mm À1 als hoch, [119] beim Test unserer TADDOL-Sammlung fanden wir schnell Derivate mit Werten von 300 ± 400 mm À1 , [83] und den Rekord mit 534 mm À1 h‰lt ein Fluorenylidenderivat mit zwei Tetrakis(2-naphthylmethanol)-Substituenten [118,120] (Abbildung 8). Die Theorie des HTP-Effektes ist kompliziert, [121] und es ist bisher nicht sicher, ob nur die Konformation des TADDOLs wichtig ist oder ob auch die aenderung der Orientierung der Hauptachsen des Ordnungstensors zum Molek¸lger¸st im Fl¸ssigkristall eine Rolle spielt (siehe die starke Abnahme von 250 auf 150 mm À1 bei 24 8C, wenn das 2-Naphthyl-TADDOL 1 f als cyclisches OSi(Me 2 )O-Derivat πgesch¸tzt™ wird, Abbildung 8, rechts unten).…”