Optical Studies of the Anisotropic Solute-Solvent Interaction in Liquid Crystals

Sackmann, E.; Krebs, Patrick; Rega, H.‐U.; Voss, J.; Möhwald, Helmuth

doi:10.1080/15421407308084238

Cited by 50 publications

(10 citation statements)

References 19 publications

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“…In liquid crystals of rod-like molecules, rod-like solutes tend to assume the same average orientation as that defined by the solvent matrix (29). However, it does not follow that flexible solutes will necessarily adopt all-trans conformations; rather, they will prefer whatever conformations are stabilized the most by the liquid crystalline matrix.…”

Section: Discussionmentioning

confidence: 99%

Photochemical probes of conformational mobility in liquid crystals. The photochemistry of β-phenyl-4-methoxypropiophenone in the nematic and smectic B phases of CCH-n and OS-nm liquid crystals

Workentin¹,

Fahie²,

Leigh³

1991

Can. J. Chem.

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. Can. J. Chem. 69, 1435 (1991).The photochemistry of P-phenyl-4-methoxypropiophenone (1) in the isotropic and liquid crystalline (nematic and smectic B) phases of trans,trans-4'-alkyl-(l,l'-bicyclohexyl)-4-carbonitrile (CCH-n) and trans-4-alkylcyclohexyl-trans-4'-alkylcyclohexylcarboxylate (0s-nm) mesogens has been investigated using nanosecond laser flash photolysis techniques. Solubility limits of 1 as a function of temperature in the smectic phases have been rigorously determined by 'H NMR spectroscopy, using a-, methoxy-, and P-phenyl-deuterated analogs of the ketone. Triplet decay of 1 in the smectic (Crystal B) phase of CCH-4 is multiexponential, suggesting that the ketone is solubilized in a distribution of conformations in the highly-ordered liquid crystalline lattice. The average triplet lifetime of 1 at various temperatures throughout the smectic phase is about a factor of three longer than that in homologous nematic and isotropic phases at the same temperature. The differences in the Arrhenius parameters for triplet decay in the smectic and nematiclisotropic phases are very small, however. The present results for 1 in the smectic phase of the CCH-n mesogens correct the interpretation of previously reported data obtained with higher concentration mixtures, and afford an accurate indication of the true effects of smectic B liquid crystalline order on the conformation-dependent triplet state behavior of this molecule. In 0s-nm liquid crystals, triplet decay follows clean first order kinetics in all phases, but the variations in Arrhenius dependence with solvent phase are similar to those observed in the CCH-n liquid crystals.Key words: smectic, liquid crystals, 'H NMR, nanosecond laser flash photolysis, intramolecular triplet quenching, photochemistry. On a CtudiC la photochimie de la P-phknyl-4-mCthoxypropiophCnone (1) dans les phases isotropes et cristalline liquide (nkmatique et smectique) des mCsogbnes trans,trans-4'-alkyl-(1,1-bicyclohexyl)-4-carbonitrile (CCH-n) et trans-4-alkylcyclohexyl-trans-4'-alkyl-cyclohexanecarboxylate (0s-nm) en utilisant la technique de photolyse Cclair avec un laser ?i nanoseconde. On a dCterminC rigoureusement par la rmn du 'H, la limite de solubilitC du composC 1 en fonction de la tempkrature dans la phase smectique, en utilisant les analogues a-mCthoxy et P-phCnyl deutCriCs de la cCtone. La dtcroissance du triplet du compost 1 dans la phase smectique (cristal B) du CCH-4 est multiexponentielle, suggkrant ainsi que la cCtone est solubiliske avec une distribution de conformations dans le rCseau cristallin liquide fortement ordond. La durCe de vie moyenne du triplet du compost 1 ?i diffkrentes temptratures ?i travers la phase smectique est environ trois fois plus longue que celle du triplet dans les phases homologues ntmatique et isotrope i la m&me temptrature. Cependant la diffkrence dans les parambtres d'ArrhCnius pour la dCcroissance du triplet dans les phases smectique et nCmatiquelisotrope, est trks faible. Les rksultats actuels relatifs au compost 1 dans la phase s...

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Section: Discussionmentioning

confidence: 99%

Photochemical probes of conformational mobility in liquid crystals. The photochemistry of β-phenyl-4-methoxypropiophenone in the nematic and smectic B phases of CCH-n and OS-nm liquid crystals

Workentin¹,

Fahie²,

Leigh³

1991

Can. J. Chem.

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“…[4] and [51 are replaced by the components of the polarizability tensor (38), or by molecular dimensions (based on van der Waals radii (39) and length model (18)), then the parameters B[poll and B [vdW], given also in Table 3, can be derived and compared with the experimental values. There is no agreement for either solvent, but if the experimental values of Bo are plotted against the calculated values, as in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…4 against the values of Ao[vdW] calculated using eq. [4] with the appropriate molecular dimensions and van der Waals radii. The earlier results on benzene, trichlorobenzene, and tribromobenzene (18) are included.…”

Section: Resultsmentioning

confidence: 99%

“…[4] and [5] with the a [ i ] terms replaced by the van der Waals dimensions, and the long-range terms, A OLR and (AOBO)LR, by where Qii are the components of the molecular quadrupole moment tensor, and F,, is the average electric field gradient along the liquid crystal director, the z-axis. The electric field gradient is temperature dependent, and it seems reasonable to assume that it is proportional to the solvent order parameter, Can.…”

Section: Resultsmentioning

confidence: 99%

“…Early attempts by Saupe and Nehring (1,2) to derive such expressions used a bond additive model for various fluoro-and chloro-benzene derivatives, which gave approximate agreement with the experimental results, but, due to the lack of experimental data at that time, this approach did not examine the effects of temperature, concentration, and solvent. Subsequent studies (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) have shown that the behaviour is more complicated, and the mean field approach, with a dependence on dispersion forces alone, is probably an oversimplification.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The orientational behaviour of dichlorobenzenes in nematic liquid crystal solvents

Yim¹,

Gilson²

1989

Can. J. Chem.

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. Can. J. Chem. 67, 54 (1989). The orientational order parameters of ortho-, meta-, and para-dichlorobenzene, dissolved in the nematic solvents EBBA and 1132, have been measured as functions of temperature and concentration, and used to determine the values of the potential energy parameters for each solute-solvent pair. These potentials have been interpreted in terms of a short-range contribution, which depends upon the shape and size of the solute molecule, plus a long-range term due to the interaction between the average electric field gradient from the solvent and the molecular quadmpole moment of the solute.

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Nematische Mesophasen als Orientierungsmatrizen in der optischen Absorptionsspektroskopie

Wedel

Haase

1976

Ber Bunsenges Phys Chem

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Nematische Mesophasen sind als anisotrope Lösungsmittel zur Messung des Lineardichroismus im sichtbaren Bereich und im nahen UV gut geeignet. Sie bieten den Vorteil relativ einfacher Experimentiertechnik und geringen Zeitaufwandes. An homogen orientierten Proben können die Messungen mit linear polarisiertem Licht, an homöotrop orientierten Schichten mit natürlichem Licht durchgeführt werden. Anthracen diente als Testsubstanz zur Überprüfung der experimentellen Anordnung. Weitere Beispiele sind Pyren, p‐Azoxyanisol (PAA) und β‐Carotin. Bei Banden geringer Intensität war eine Orientierung bis 500 μm Schichtdicke erforderlich. In Verbindung mit einem für die Spektroskopie an gereckten Polymerfolien entwickelten Reduktionsverfahren konnten die Polarisationsrichtungen der schwachen Banden von Pyren (372 nm) und β‐Carotin (350 nm) angegeben werden. Infolge der optischen Anisotropie der Flüssigkristallschichten müssen die relativen Extinktionen um den Beitrag der Doppelbrechung korrigiert werden. Die hier angewandte Methodik wird insbesondere den Messungen in kompensierten nematischen flüssigen Kristallen und gereckten Polymerfolien gegenübergestellt.

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Optical Studies of the Anisotropic Solute-Solvent Interaction in Liquid Crystals

Cited by 50 publications

References 19 publications

Photochemical probes of conformational mobility in liquid crystals. The photochemistry of β-phenyl-4-methoxypropiophenone in the nematic and smectic B phases of CCH-n and OS-nm liquid crystals

Photochemical probes of conformational mobility in liquid crystals. The photochemistry of β-phenyl-4-methoxypropiophenone in the nematic and smectic B phases of CCH-n and OS-nm liquid crystals

The orientational behaviour of dichlorobenzenes in nematic liquid crystal solvents

Nematische Mesophasen als Orientierungsmatrizen in der optischen Absorptionsspektroskopie

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