Crystal to Liquid-Crystal Transition Studied by Raman Scattering

Borer, W. J.; Mitra, S. S.; Brown, Chris W.

doi:10.1103/physrevlett.27.379

Cited by 39 publications

(6 citation statements)

References 9 publications

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“…[4 -7] In the heating cycle the transition is usually observed at a relatively higher temperature. [20] As pointed out by Shen et al, [21] a pronounced hysteresis which involves a new state has been observed during the crystal → N transition of P-(p-ethoxyphenylazo)-phenyl undecylenate (PPU) and the N → isotropic transitions also present hysteresis. Further, the transition temperature during heating is higher than that during the cooling cycle.…”

Section: Resultsmentioning

confidence: 93%

“…The 3CHBT is reported to undergo a crystal → N transition at 38.5 °C and a nematic to isotropic transition at 41.5 °C in the cooling cycle 4–7. In the heating cycle the transition is usually observed at a relatively higher temperature 20. As pointed out by Shen et al ,21 a pronounced hysteresis which involves a new state has been observed during the crystal → N transition of P‐(p‐ethoxyphenylazo)‐phenyl undecylenate (PPU) and the N → isotropic transitions also present hysteresis.…”

Section: Resultsmentioning

confidence: 99%

“…3), the vibrational modes 6b and 6a appear at 638 and 682 cm −1 in the Raman spectra and the calculated wavenumbers for these modes are at 645 and 665 cm −1 , respectively. The coupling of 6b with C-X C 1 -C 2 1.5410 C 1 -C 6 1.5467 C 1 -H 7 1.1018 C 1 -H 35 1.0969 C 2 -C 3 1.5516 C 2 -H 8 1.1002 C 2 -H 36 1.0975 C 3 -C 4 1.5514 C 3 -C 11 1.5211 C 3 -H 37 1.1011 C 4 -C 5 1.5402 C 4 -H 9 1.0999 C 4 -H 32 1.0975 C 5 -C 6 1.5464 C 5 -H 10 1.0984 C 5 -H 33 1.1016 C 6 -C 21 1.5452 C 6 -H 34 1.1041 C 11 -C 12 1.4060 C 11 -C 13 1.4083 C 12 -C 14 1.3949 C 12 -H 15 1.0859 C 13 -C 16 1.3936 C 13 -H 17 1.0850 C 14 -C 18 1.4058 C 14 -H 19 1.0840 C 16 -C 18 1.4071 C 16 -H 20 1.0840 C 18 -N 31 1.3793 C 21 -H 22 1.1018 C 21 -H 23 1.1009 C 21 -C 24 1.5407 C 24 -H 25 1.1002 C 24 -H 26 1.0982 C 24 -C 27 1.5376 C 27 -H 28 1.0973 C 27 -H 29 1.0973 C 27 -H 30 1.0961 N 31 -C 38 1.1888 C 38 -S 39 1.6426 stretching is negligible. PED (Table 1) shows that the mode 6b is a mixture of ring deformation (81%) and (-C-C-C-) bending (5%).…”

Section: Radial Skeletal Vibrations 6a and 6bmentioning

confidence: 99%

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Crystal → nematic phase transition in the liquid crystalline system 1‐isothiocyanato‐4‐(trans‐4‐propylcyclohexyl) benzene (3CHBT) probed by temperature‐dependent micro‐Raman study and DFT calculations

Vikram

Tarcea

Srivastava

et al. 2009

J Raman Spectroscopy

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Raman spectra of 3CHBT in unoriented form were recorded at 14 different temperature measurements in the range 25-55 • C, which covers the crystal → nematic (N) phase transition, and the Raman signatures of the phase transition were identified. The wavenumber shifts and linewidth changes of Raman marker bands with varying temperature were determined. The assignments of important vibrational modes of 3CHBT were also made using the experimentally observed Raman and infrared spectra, calculated wavenumbers, and potential energy distribution. The DFT calculations using the B3LYP method employing 6-31G functional were performed for geometry optimization and vibrational spectra of monomer and dimer of 3CHBT. The analysis of the vibrational bands, especially the variation of their peak position as a function of temperature in two different spectral regions, 1150-1275 cm −1 and 1950-2300 cm −1 , is discussed in detail. Both the linewidth and peak position of the (-C-H-) in-plane bending and ν(N C S) modes, which give Raman signatures of the crystal → N phase transition, are discussed in detail. The molecular dynamics of this transition has also been discussed. We propose the co-existence of two types of dimers, one in parallel and the other in antiparallel arrangement, while going to the nematic phase. The structure of the nematic phase in bulk has also been proposed in terms of these dimers. The red shift of the ν(N C S) band and blue shift of almost all other ring modes show increased intermolecular interaction between the aromatic rings and decreased intermolecular interaction between two -NCS groups in the nematic phase.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Radial Skeletal Vibrations 6a and 6bmentioning

confidence: 99%

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Crystal → nematic phase transition in the liquid crystalline system 1‐isothiocyanato‐4‐(trans‐4‐propylcyclohexyl) benzene (3CHBT) probed by temperature‐dependent micro‐Raman study and DFT calculations

Vikram

Tarcea

Srivastava

et al. 2009

J Raman Spectroscopy

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“…The former process in fact anticipates the transition, and the softening entails lattice vibrations with a translational component along the layer shifting direction. The latter displays instead the fingerprint of discontinuity in the abrupt spectral changes at the transition, with features typical of crystal to liquid crystal transitions. ,− …”

Section: Discussionmentioning

confidence: 99%

Interlayer Sliding Phonon Drives Phase Transition in the Ph-BTBT-10 Organic Semiconductor

et al. 2023

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In the field of organic electronics, the semiconductor 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) has become a benchmark due to its high charge mobility and chemical stability in thin film devices. Its phase diagram is characterized by a crystal phase with a bilayer structure that at high temperature transforms into a Smectic E liquid crystal with monolayer structure. As the charge transport properties appear to depend on the phase present in the thin film, the transition has been the subject of structural and computational studies. Here such a process has been investigated by polarized low frequency Raman spectroscopy, selectively probing the intermolecular dynamics of the two phases. The spectroscopic observations demonstrate the key role played by a displacive component of the transition, with the interpenetration of the crystal bilayers driven by lattice phonon mode softening followed by the intralayer rearrangement of the molecule rigid cores into the herringbone motif of the liquid crystal. The mechanism can be related to the effectiveness of thermal annealing to restore the crystal phase in films.

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“…This has been conÐrmed by the temperature dependence of the low-wavenumber spectrum of MBBA. 15 The pronounced structures in the crystalline phase, around 100 cm~1, remain in the nematic phase with the same energy but with lower intensities. However, in the isotropic liquid phase these modes were totally absent.…”

Section: Low-wavenumber Modesmentioning

confidence: 96%

Micro-Raman investigations of pressure-induced transformations in MBBA

Jin

Sinha

Dobal

et al. 1999

J. Raman Spectrosc.

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The pressure-induced changes in the Raman spectra of a nematic N-(p-methoxybenzylidene)-p-(n-butyl)aniline (MBBA) liquid crystal were investigated in the wavenumber range 5-1670 cm-1. With increasing pressure, the Raman spectrum undergoes qualitative changes in a systematic manner and three distinct phase transitions, from nematic to plastic crystal, from plastic to crystalline and from to are obtained around 0.39, 0.78 and C 6P C 6P C 5P , 3.12 GPa, respectively. The room temperature results obtained in this pressure study provide information on the structural modiÐcations and phase behavior of MBBA molecules. The appearance of a plastic-like state was veriÐed just below the nematic phase. The e †ects of pressure variation on MBBA phonon modes are discussed in detail.

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Crystal to Liquid-Crystal Transition Studied by Raman Scattering

Cited by 39 publications

References 9 publications

Crystal → nematic phase transition in the liquid crystalline system 1‐isothiocyanato‐4‐(trans‐4‐propylcyclohexyl) benzene (3CHBT) probed by temperature‐dependent micro‐Raman study and DFT calculations

Crystal → nematic phase transition in the liquid crystalline system 1‐isothiocyanato‐4‐(trans‐4‐propylcyclohexyl) benzene (3CHBT) probed by temperature‐dependent micro‐Raman study and DFT calculations

Interlayer Sliding Phonon Drives Phase Transition in the Ph-BTBT-10 Organic Semiconductor

Micro-Raman investigations of pressure-induced transformations in MBBA

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