UV Stability of High Birefirngence Liquid Crystals

Lin, Pao Tai; Wu, Shin Tson; Chang, Chin Yen; Hsu, Chain‐Shu

doi:10.1080/15421400490435233

Cited by 53 publications

(18 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…All these features of 8CB/8OCB mixtures are characteristic of LC molecules, due to π→π * transition as found in single liquid crystals. Thus, these results in chloroform media seem to confirm the reported stability of mixtures to photodegradation [22]. One can choose the adequate wavelength and the corresponding molar ε for the LC mixture assays.…”

Section: Uv Spectroscopysupporting

confidence: 86%

Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Özğan

Okumuş

2011

Braz J Phys

View full text Add to dashboard Cite

The binary system of 4-octyl-4′-cyanobiphenyl (8CB) and 4-octyloxy-4′-cyanobiphenyl (8OCB) has been studied by means of differential scanning calorimetry (DSC) and ultraviolet absorption spectrophotometry (UV). The phase-transition temperatures, enthalpies, and entropies have been determined by using calorimetric methods on DSC. The results indicate clearly the existence of threephase regions across the crystalline-to-smectic A, smectic A-to-nematic, and nematic-to-isotropic transitions in the 8CB/8OCB mixtures. The obtained phase-transition temperatures of the 8CB/8OCB mixtures are between the data for 8CB and 8OCB. A few of the phase transitions cannot be observed at high heating rates. The phase-transition temperatures of the 8CB/8OCB mixtures rise with the heating rate between 2°C/min and 15°C/min. The activation energies were calculated by the Ozawa method for the phase transitions of 25% 8CB and 75% 8OCB liquid crystal mixtures. UV experiments were carried out to characterize the absorptivity constants of liquid crystal and their mixtures. The molar absorptivity and maximum absorption wavelengths were measured in chloroform solution by UV spectrophotometry. The maximum absorption wavelength of the 8CB/8OCB mixtures increases with decreasing percent weight of 8CB in 8OCB, a result associated with the different lengths of the alkyl chain.

show abstract

Section: Uv Spectroscopysupporting

confidence: 86%

Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Özğan

Okumuş

2011

Braz J Phys

View full text Add to dashboard Cite

show abstract

“…For example, the T c were decreased by 4.8 °C for 3-2 and 2.6 °C for 3F2, respectively, after 240 minutes UV illumination. Similar results were also observed by Wu et al [7]. They reported that there were several changes of physical properties after UV exposure, such as birefringence and viscosity.…”

Section: Uv Stabilitysupporting

confidence: 89%

“…Recently, Highbirefringence (Δn) LCs have attracted much attention because of their potential applications in liquid crystal photonics, such as beam steerers, tunable focus lens and electrically controlled phase shifter in GHz and THz region [3,4]. Generally, high-Δn LCs can be obtained by extending π-electron conjugation, and the previous studies revealed that the introduction of tolane unit into a liquid crystal compound is an effective way to obtain high-Δn LCs with good solubility and low viscosity [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Improving UV stability of tolane-liquid crystals in photonic applications by the ortho fluorine substitution

Chen

Wang

Chen

et al. 2015

Opt. Mater. Express

View full text Add to dashboard Cite

A series of ortho fluoro-tolane liquid crystals was prepared via multi-step reactions based on 4-alkylcyclohexanecarboxylic acids. Their synthetic routes, thermotropic mesophases and UV stability properties are discussed by comparision with the non-fluorinated analogs. All of the measurements from DSC, UV-vis absorption and fluorescence emission spectra demonstrate that the presence of ortho fluorine can significantly improve the UV stability of tolane-liquid crystals. Meanwhile, the ultimate failure mechanism of tolane-LCs during UV exposure is deduced by a photochemical reaction. DFT calculations of molecular polarizabilities, triple bond lengths, electrostatic potential maps and molecular orbitals are used to correlate the experimental findings. The interaction mechanism for stabilization of the tolane structures by the ortho fluoro substitution is also explained. This work may provide an effective solution for the obstacle existed in tolane-liquid crystals and pave a way for their applications in liquid crystal photonics. , "A highly selective synthesis of diarylethynes and their oligomers by a palladium-catalyzed Sonogashira coupling reaction under phase transfer conditions," J. Org.

show abstract

“…One of the most exciting developments in LC science and technology is the possibility of using light instead of electricity to control the behavior of a material [22,23]. Increasing the number of carbon atoms in the end chain is the widely used technique in order to alter the physical properties of LC molecules.…”

Section: B Electronic Absorption Spectrummentioning

confidence: 99%

Computational analysis of molecular properties and spectral characteristics of cyano-containing liquid crystals: Role of alkyl chains

Praveen¹,

Ojha²

2011

Phys. Rev. E

View full text Add to dashboard Cite

The electronic transitions in the uv-visible range of 4'-n-alkyl-4-cyanobiphenyl (nCB) with propyl, pentyl, and heptyl groups, which are of commercial and application interests, have been studied. The uv-visible and circular dichroism spectra of nCB (n = 3,5,7) molecules have been simulated using the time dependent density functional theory Becke3-Lee-Yang-Parr hybrid functional-6-31 + G (d) method. Mulliken atomic charges for each molecule have been compared with Loewdin atomic charges to analyze the molecular charge distribution and phase stability. The highest occupied molecular orbital and lowest unoccupied molecular orbital energies corresponding to the electronic transitions in the uv-visible range have been reported. Excited states have been calculated via the configuration interaction single level with a semiempirical Hamiltonian (intermediate neglect of differential overlap method, as parametrized by Zerner and co-workers). Further, two types of calculations have been performed for model systems containing single and double molecules of nCB. Furthermore, the dimer complexes during the different modes of molecular interactions have also been studied. The interaction energies of dimer complexes have been taken into consideration in order to investigate the most energetically stable configuration. These studies are helpful for understanding the role and flexibility of end chains, in particular, phase behavior and stability.

show abstract

UV Stability of High Birefirngence Liquid Crystals

Cited by 53 publications

References 8 publications

Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Improving UV stability of tolane-liquid crystals in photonic applications by the ortho fluorine substitution

Computational analysis of molecular properties and spectral characteristics of cyano-containing liquid crystals: Role of alkyl chains

Contact Info

Product

Resources

About