Investigation of conformational mobility of 4-pentyl-4'-cyanobiphenyl by IR spectroscopy methods

Babkov, L. M.; Vedyaeva, E. S.; Gnatyuk, I. I.; Puchkovska, Galina A.; Truhachev, S. V.; Kukielski, J.

doi:10.1117/12.486660

Cited by 3 publications

(7 citation statements)

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“…5c) do not practically change with the temperature growth. This proves the small changes of the alkyl chain conformation at heating, but according to Babkov et al [34] and Tanaka et al [35], at low temperatures the 5CB liquid crystal is already a mix of different conformers, where relative quantities do not change up to the nematic liquid-crystal state. Obviously, the simultaneous co-existence of the different conformers of the 5CB molecules in the low-temperature states explains the formation of different types of monomer and dimer structures, revealed by us during the analysis of the 5CB photoluminescence spectral properties.…”

Section: Ir-spectroscopy Datamentioning

confidence: 77%

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Low-temperature photoluminescence of 5CB liquid crystal

Bezrodna

Melnyk

Vorobjev

et al. 2010

Journal of Luminescence

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Section: Ir-spectroscopy Datamentioning

confidence: 77%

“…The molecular vibrational analysis is well-known as a useful tool for directly detecting molecular conformations [34,35].…”

Section: Ir-spectroscopy Datamentioning

confidence: 99%

Low-temperature photoluminescence of 5CB liquid crystal

Bezrodna

Melnyk

Vorobjev

et al. 2010

Journal of Luminescence

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“…In the present study, 5CB in the isotropic phase was examined up to 40 °C above the transition temperature. The nitrile stretch of 5CB is a sharp peak at 2230 cm –1 . Previous work has shown that using the CN stretch of 5CB as a vibrational probe resulted in significant experimental problems .…”

Section: Introductionmentioning

confidence: 99%

“…The nitrile stretch of 5CB is a sharp peak at 2230 cm −1 . 20 Previous work has shown that using the CN stretch of 5CB as a vibrational probe resulted in significant experimental problems. 21 The lifetime of the CN stretch is short, ∼4 ps, and because the sample is a pure liquid, it needed to be exceedingly thin, a few micrometers, to keep the absorbance sufficiently low to perform the experiments.…”

Section: Introductionmentioning

confidence: 99%

Length Scales and Structural Dynamics in Nematogen Pseudonematic Domains Measured with 2D IR Vibrational Echoes and Optical Kerr Effect Experiments

2014

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Nematogen liquids in the isotropic phase are macroscopically homogeneous but on multinanometer length scales have pseudonematic domains with correlation lengths that grow as the isotropic to nematic phase transition temperature (TNI) is approached from above. Orientational relaxation of nematogens in the isotropic phase manifests as two fast power laws and a slow exponential decay when measured by optical heterodyne detected optical Kerr effect (OHD-OKE) experiments. The long time exponential relaxation is associated with complete randomization of pseudonematic domains. We examine the effect of local orientational correlation on spectral diffusion (structural evolution) experienced by a vibrational probe molecule within the pseudonematic domains of 4-cyano-4'-pentylbiphenyl (5CB) using two-dimensional infrared (2D IR) vibrational echo spectroscopy. The addition of low concentration 4-pentyl-4'-thiocyanobiphenyl (5SCB) as a long-lived vibrational probe to 5CB is shown to lower TNI of the sample slightly, but the fast power law dynamics and exponential decays observed by OHD-OKE spectroscopy are unchanged. We compare the complete orientational relaxation and spectral diffusion for samples of 5SCB in 5CB to 5SCB in 4-pentylbiphenyl (5B) at four temperatures above TNI. 5B has a molecular structure similar to 5CB but is not a nematogen. At all but the lowest temperature, the spectral diffusion in 5CB and 5B is described well as a triexponential decay with very similar time constants. The results demonstrate that the presence of local orientational order at temperatures well above TNI does not affect the spectral diffusion (structural evolution) within pseudonematic domains when the correlation lengths are short. However, when the temperature of the sample is held very close to TNI, the spectral diffusion in 5CB slows dramatically while that in 5B does not. It is only as the correlation length becomes very long that its presence impacts the spectral diffusion (structural fluctuations) sensed by the vibrational probes located in pseudonematic domains. The orientational relaxation is modeled with schematic mode coupling theory (MCT). Fitting with MCT provides density and orientational correlation functions. The density correlation decays are similar for 5B and 5CB, but the orientational correlation decays are much slower for 5CB. Additionally, the time dependence of the spectral diffusion in 5CB is strikingly similar to that of the density correlation function decay, while the orientational correlation function decay is far too slow to contribute to the spectral diffusion. Therefore, density fluctuations are likely the source of spectral diffusion at temperatures at least 5 K above TNI.

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“…The orientational relaxation dynamics of nematic liquid crystals in the isotropic phase differ greatly from that of traditional liquids. These relatively long time scale dynamics have been studied by a wide variety of time- − and frequency-domain − experiments, including optical Kerr effect spectroscopy in our lab. − At temperatures above the nematic–isotropic phase transition, the orientational relaxation dynamics are dominated by the randomization of pseudonematic domains characterized by a correlation length, ξ . As the nematic–isotropic transition temperature is approached from above, ξ grows as described by Landau–de Gennes theory until it becomes infinite in the nematic phase.…”

Section: Introductionmentioning

confidence: 99%

Dynamics in the Isotropic Phase of Nematogens Using 2D IR Vibrational Echo Measurements on Natural-Abundance ¹³CN and Extended Lifetime Probes

Sokolowsky

Fayer

2013

J. Phys. Chem. B

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The long time scale orientational relaxation of nematogens in the isotropic phase is associated with the randomization of pseudonematic domains, which have a correlation length that grows as the isotropic-to-nematic phase transition temperature is approached from above. Here we begin to address the fast dynamics of the nematogen molecules within the domains using two-dimensional infrared (2D IR) vibrational echo experiments. The problems of performing ultrafast IR experiments in pure liquids are discussed, and solutions are presented. In addition, the issue of short vibrational lifetimes, which limit the ability of 2D IR experiments to examine dynamics over a wide range of times, is addressed. The experiments were performed on the nematogen 4-cyano-4'-pentylbiphenyl (5CB), with the CN stretch initially used as the vibrational probe. Although the CN stretch has a small transition dipole, because the sample is a pure liquid it is necessary to use an exceedingly thin sample to perform the experiments. The small sample volume leads to massive heating effects that distort the results. In addition, the high concentration in the pure liquid can result in vibrational excitation transfer that interferes with the measurements of structural dynamics, and the CN vibrational lifetime is very short (3.6 ps). These problems were overcome by performing the experiments on the natural-abundance (13)CN stretch (5(13)CB), which greatly reduced the absorbance, eliminating the heating problems; also, this stretch has a longer lifetime (7.9 ps). Experiments were also performed on benzonitrile, which showed that the heating problems associated with pure liquids are not unique to 5CB. Again, the problems were eliminated by conducting measurements on the (13)CN stretch, which has an even longer lifetime (20.2 ps) compared with the (12)CN stretch (5.6 ps). Finally, to extend the range of the dynamical measurements, 4-pentyl-4'-thiocyanobiphenyl (5SCB) was synthesized and studied as a dilute solute in 5CB. The CN stretch of 5SCB has a vibrational lifetime of 103 ps, which permits dynamical measurements to 200 ps, revealing the full range of fast structural dynamics in the isotropic phase of 5CB. It is shown that the 5SCB probe reports essentially the same dynamics as 5(13)CB on the short time scale that is observable with the 5(13)CB vibrational probe.

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Investigation of conformational mobility of 4-pentyl-4'-cyanobiphenyl by IR spectroscopy methods

Cited by 3 publications

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Low-temperature photoluminescence of 5CB liquid crystal

Low-temperature photoluminescence of 5CB liquid crystal

Length Scales and Structural Dynamics in Nematogen Pseudonematic Domains Measured with 2D IR Vibrational Echoes and Optical Kerr Effect Experiments

Dynamics in the Isotropic Phase of Nematogens Using 2D IR Vibrational Echo Measurements on Natural-Abundance ¹³CN and Extended Lifetime Probes

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Investigation of conformational mobility of 4-pentyl-4'-cyanobiphenyl by IR spectroscopy methods

Cited by 3 publications

References 0 publications

Low-temperature photoluminescence of 5CB liquid crystal

Low-temperature photoluminescence of 5CB liquid crystal

Length Scales and Structural Dynamics in Nematogen Pseudonematic Domains Measured with 2D IR Vibrational Echoes and Optical Kerr Effect Experiments

Dynamics in the Isotropic Phase of Nematogens Using 2D IR Vibrational Echo Measurements on Natural-Abundance 13CN and Extended Lifetime Probes

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Dynamics in the Isotropic Phase of Nematogens Using 2D IR Vibrational Echo Measurements on Natural-Abundance ¹³CN and Extended Lifetime Probes