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Volumn 22, Issue 9, 2010, Pages 2869-2884

Achiral bent-core molecules with a series of linear or branched carbosilane termini: Dark conglomerate phases, supramolecular chirality and macroscopic polar order

Author keywords

[No Author keywords available]

Indexed keywords

ACHIRAL COMPOUND; ANTIFERROELECTRICS; BENT-CORE MOLECULES; CARBOSILANES; CONJUGATED AROMATIC CORE; ELECTRO-OPTICAL; ENTROPIC CONTRIBUTIONS; EXPERIMENTAL OBSERVATION; EXTERNAL ELECTRIC FIELD; FREQUENCY-DEPENDENT; GLASSY STATE; LIQUID-CRYSTALLINE; MACROSCOPIC DOMAINS; MACROSCOPIC POLAR ORDER; ORGANIC-INORGANIC HYBRID MATERIALS; POLAR ORDER; POLARIZING MICROSCOPY; REVERSIBLE TRANSITIONS; SOFT MATTER; SPONTANEOUS SYMMETRY BREAKING; SUPRAMOLECULAR CHIRALITY; SWITCHING MODES; WAVE FORMS;

EID: 77951949370     PISSN: 08974756     EISSN: 15205002     Source Type: Journal    
DOI: 10.1021/cm100134f     Document Type: Article
Times cited : (52)

References (103)
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    • Herein ferroelectric (FE) switching is used to denote a polar single peak switching between the two field-induced polar states with opposite signs, where switching current curves show only one single peak upon the application of a triangular wave (TW) voltage and optical investigations confirm bistable switching. Proper FE switching is always related to the ferroelectricity of the ground-state structure. If the ferroelectric states are only metastable (due to surface stabilization or if there is not sufficient time (at 0 V) to allow the polar states to relax to the ground-state AF structure), the switching process is more precisely assigned as polar single peak switching. Thus ground-state AF materials always exhibit polar single peak switching upon the application of a square wave (SW) voltage. As we observed single-peak switching and optical bistability under TW fields also at very low frequencies, we use the more common term "FE switching", although we cannot fully exclude that the ferroelectric states might be field-induced or surface-stabilized long-lived metastable states.
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    • Melting points strongly depend on the history of the sample. To keep the consistency of phase transition temperatures, samples for DSC measurements were initially heated to the isotropic liquid and then stored in vials at room temperature for 3 days prior to DSC measurements, except as noted.
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    • [*], the C stands for a tilted organization of the molecules in the layers, P indicates polar order in the layers, the subscript "FE" denotes that ferroelectric switching is observed experimentally, and the superscripted symbol "[*]" denotes that, in the ground-state structure, a texture composed of a conglomerate of chiral domains with opposite handedness (see Figures 2 a and 2 b) can be observed (although the molecules themselves are achiral).
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    • S textures are retained in the glassy state when cells are cooled to room temperature and stored overnight at room temperature.
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    • S textures were stored overnight at room temperature and reheated to 80 °C, the threshold voltages at which FE switching occurs are 0.3-1.0 V/μm, which are much less than those that induce FE switching from the supercooled glassy state of DC phases.
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    • The molecular geometry was optimized by MOPAC calculations using the AM1 Hamiltonian. The molecular lengths are equal to the sum of the lengths of the molecular long axis from molecular modelling and twice the van der Waals radius (0.12 nm) of the H atom.
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    • 3 groups provides a larger distance between these units with a mean distance of 0.58 nm.
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    • F layer stacks would be entropically more favorable.
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    • Herein, all threshold voltages denote the peak voltages of switching current curves.
    • Herein, all threshold voltages denote the peak voltages of switching current curves.
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    • Examples of polar switching columnar phases of nonsilylated compounds
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    • Upon application of a TW voltage, the peak voltage is always higher than the threshold, because a certain period of time with the voltage above the threshold is required to achieve complete switching.
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    • note
    • Because the two threshold voltages are very close, synclinic and anticlinic circular domains coexist in different regions of the cell, because the field is <17 V/μm. However, as the field becomes >17 V/μm, only anticlinic circular domains were observed.
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    • The two slightly different polar nonmodulated states F1/F2 and the modulated states CF1/CF2 cannot be distinguished optically, but these are postulated to explain the distinct types of switching depending on the threshold voltage.
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    • note
    • F states via rotation of the molecules around the molecular long axis upon the application of a field.
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    • Examples for switching of chirality flipping by collective rotation around the long axis
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    • 4t B 5.
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    • F is 86 °C (onset) during cooling.
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    • note
    • A phase at 0 V.
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    • Note that all threshold voltages are temperature-dependent.
    • Note that all threshold voltages are temperature-dependent.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.