Synthesis and characterisation of benzoxazole-based liquid crystals possessing 3,5-difluorophenyl unit

Series of fluorinated compounds, 2-(3′,5′-difluoro-4′-alkoxybiphenyl-4-yl)-benzoxazole derivatives (nFBx), were prepared and characterised. Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. In the case of carbon atoms in the alkoxy chain between 4 and 10, they exhibited enantiotropic mesophases with the mesophase ranges of 12–119°C and 23–152°C on heating and cooling for compounds bearing different substituents (H, CH₃, Cl, and NO₂). With the exception of nitro-substituted compounds, the nFBx series displayed intense photoluminescence emission at 380–385 nm in methylene chloride solution when they were excited at their absorption maxima. Compared to non-fluorinated analogues, fluorinated compounds nFBx (apart from nitro-substituted compounds) exhibited much lower melting points, but comparable or slightly narrower mesophase ranges during both heating and cooling, which were attributed to the disruption of the side-to-side intermolecular packing caused by the two lateral fluoro substituents.     

Synthesis and mesomorphic properties of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives

Three series of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives (nM-x), which possessed 5-nitrobenzimidazole (nM-N series), benzimidazole (nM-H series) or 5-methylbenzimidazole (nM-M series) units at the end of the molecule, were synthesised and characterised by infrared, ¹H- and ¹³C-nuclear magnetic resonance spectra, electrospray ionisation-mass spectrometry and elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. All the compounds exhibited enantiotropic smectic mesophases with wide temperature domains for a carbon number in the alkoxy chain from 6 to 16, where the mesophase ranges were 14–91°C and 17–99°C during heating and cooling processes for the nM-N compounds, 7–25°C and 8–49°C for the nM-H compounds and 48–81°C and 52–85°C for the nM-M compounds, respectively. The effect of the length of alkoxy chain on mesomorphic properties was discussed. The nM-N and nM-M exhibited a much wider mesophase range whether during heating or cooling process than the corresponding nM-H series, especially for the longer terminal chain (n > 8), which indicated that the substituent in the benzimidazole moiety was helpful in increasing the mesophase stability.     

Preparation and characterisation of laterally monofluorinated mesogenic benzimidazole-based compounds

Series of laterally monofluorinated compounds, 2-(4?-alkoxy-3-fluorobiphenyl-4-yl)-1H-benzimidazole derivatives (nPPF(3)Mx) bearing different substituents (H, CH₃, NO₂, coded as nPPF(3)MH, nPPF(3)MM and nPPF(3)MN, respectively) at 5-position, were prepared and their structures were characterised. According to the results from differential scanning calorimetry and polarising optical microscopy, the present compounds nPPF(3)Mx exhibit enantiotropic smectic mesophases, for which the mesophase ranges are 13–67 and 47–111°C on heating and cooling for nPPF(3)MH, 84–112 and 126–154°C for nPPF(3)MM, and 23–102 and 49–117°C for nPPF(3)MN, respectively. Compared to non-fluorinated analogues, monofluorinated nPPF(3)Mx have low melting/clearing points and display enhanced mesophase range both in heating and cooling, which are attributed to the disruption of the side-to-side intermolecular packing caused by the ortho lateral fluoro substituents and the increased dipole–dipole interaction between the polar fluoro-substituted molecules, respectively. It is noted that nPPF(3)MM and nPPF(3)MN show a much wider mesophase range than nPPF(3)MH, which suggest that the substituent at benzimidazole moiety can improve the mesophase stability.     

Synthesis and mesomorphic properties of benzoxazole derivatives with lateral multifluoro substituents

Fluorinated aromatics is generally chosen as mesogenic cores to design novel liquid crystal compounds. Here, a series of benzoxazole derivatives with laterally multifluorinated biphenyl units, 2-(3′,3-difluoro ?4′-alkoxy-1,1′-biphenyl-4-yl)-benzoxazole derivatives (coded as nPF(3)PF(3)Bx), are synthesized and characterized, where methyl and nitro moieties are selected as terminal groups to investigate the effects of different polar substituents on the liquid crystal properties. The compounds nPF(3)PF(3)Bx show enantiotropic mesophases with mesophase ranges of 0–40°C and 0–63°C on heating and cooling for hydrogen-terminated derivatives (nPF(3)PF(3)BH), 43–93°C and 54–123°C for methyl-terminated ones (nPF(3)PF(3)BM), 60–108°C and 74–152°C for nitro terminated ones (nPF(3)PF(3)BN), respectively. They exhibit photoluminescence emission peaks at 390–392 nm and UV–vis absorption bands with maxima at 327–330 nm, respectively. The results reveal that lateral multifluoro substituents lead to a decrease in melting/clearing points, while electron-withdrawing terminal nitro moiety results in increases in both melting point and mesophase range.     

Nematic mesophase enhanced via lateral monofluorine substitution on benzoxazole-liquid crystals

Fluorine is widely used as a lateral substituent to modify the physical properties of liquid crystals. Here, laterally monofluorinated compounds, 2-(4?-alkoxy-2-fluorobiphenyl-4-yl)-benzoxazole derivatives (nPPF(2)Bx) bearing different substituents (H, CH₃, NO₂, coded as nPPF(2)BH, nPPF(2)BM and nPPF(2)BN, respectively) at 5-position, were synthesised and characterised. It is interesting to note that these only display enantiotropic nematic mesophases with mesophase ranges of 12–28°C and 13–45°C on heating and cooling for nPPF(2)BH, 46–97°C and 62–120°C for nPPF(2)BM and 82–108°C and 87–113°C for nPPF(2)BN, which are very different from the corresponding monofluorine-substituted analogue (compounds I) with enantiotropic smectic or smectic/nematic mesophases. The enhanced nematic mesophase is attributed to the reduced π–π interaction/conjugation resulting from the twisted structure of the molecule caused by the introduction of a fluorine atom into the inter-ring of the biphenyl unit. These results suggest that modification of the monofluorine substituent position is an effective method to improve the nematic mesophase in benzoxazole-liquid crystals.     

Effect of lateral bromo substituent on the phase behavior of four-ring azo/ester/azo liquid crystalline materials

ABSTRACT

In order to study the influence of lateral Br substitution on mesophase behaviour, five homologous series of 4-substituted phenylazo phenyl 4?-(3?-bromo-4?-alkoxyphenylazo) benzoates (In_a–e) have been synthesised. Within each homologous series, the alkoxy group varies from 6 to 16 carbons, while other terminal group substituents, X, are CH₃O, CH₃, H, Br and NO₂ groups; the mesophase behaviour of these series is compared with previously prepared laterally neat analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (IIn_a–e) and laterally methyl analogues, 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIIn_a–e). Similar to lateral methyl analogues, the present series, lateral Br substitution showed that, independent of the polarity of the substituent X or the alkoxy-chain length, the nematic phase is predominant with relatively high stability and broad temperature ranges. The mesophase stability varies between 204.0°C and 335.0°C for the nematic phase and 169.6°C and 281.0°C for the SmA phase. Their total mesophase temperature ranges vary between 87.2°C and 201.4°C. All compounds were found to be thermally stable within the mesophase temperature range, except the lower homologue of the nitro and Br substituted derivatives. The obtained results are discussed in terms of molecular polarisability.     

Synthesis and Characterization of Fluorinated Polyimide Derived from 3,3′‐Diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane

A novel aromatic diamine monomer, 3,3′‐diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane (PAFM), was successfully synthesized by coupling of 2‐isopropylaniline and 3,4‐difluorobenzaldehyde. The aromatic diamine was adopted to synthesize a series of fluorinated polyimides by polycondensation with various dianhydrides: pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (ODPA) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) via the conventional one‐step method. These polyimides presented excellent solubility in common organic solvents, such as N,N‐dimethylformamide (DMF), N,N‐dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N‐methyl‐2‐pyrrolidone (NMP), chloroform (CHCl₃), tetrahydrofuran (THF) and so on. The glass transition temperatures (T_g) of fluorinated polyimides were in the range of 260–306°C and the temperature at 10% weight loss in the range of 474–502°C. Their films showed the cut‐off wavelengths of 330–361 nm and higher than 80% transparency in a wavelength range of 385–463 nm. Moreover, polymer films exhibited low dielectric properties in the range of 2.76–2.96 at 1 MHz, as well as prominent mechanical properties with tensile strengths of 66.7–97.4 MPa, a tensile modulus of 1.7–2.1 GPa and elongation at break of 7.2%–12.9%. The polymer films also showed outstanding hydrophobicity with the contact angle in the range of 91.2°–97.9°.     

The effect of terminal substituents on crystal structure,mesophase behaviour and optical property of azo-ester linked materials

A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH₃, –OC₂H₅ and –OC₃H₇) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R¹₂(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R²₂(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH₃, –OC₂H₅ and –OC₃H₇) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λ_max) of nearly 370 nm.     

Conformational effects on mesophase stability: numerical comparison of carborane diester homologous series with their bicyclo[2.2.2]octane,cyclohexane and benzene analogues

Three series of diesters of 4‐alkoxyphenols containing 12‐vertex p‐carborane (1A[n], n = 1–22), 10‐vertex p‐carborane (1B[n], n = 1–12) or bicyclo[2.2.2]octane (1C[n], n = 1–12) as the central structural element were prepared and investigated by optical and calorimetric methods. All carborane diesters exhibited exclusively nematic behaviour, whereas the carbocyclic analogues 1C[n] and also cyclohexane (1D[n]) and benzene (1E[n]) derivatives, showed early onset of SmA phase and complete disappearance of nematic behaviour. The isotropic transition temperatures, T _MI, for the five series of mesogens were analysed numerically using a three‐parameter exponential function. The resulting limiting values, T _MI(∞), provided a quantitative assessment of the central element ability to support the mesogenic state. They demonstrated that, whereas the T _MI(∞) values for the carbocycles, C, D, and E, are around 125°C, for carboranes A and B this value is 70±2°C and 49±19°C, respectively. Two types of comparative analysis of trends in T _MI relative to those of the terephthalate series 1E[n] demonstrated abnormal behaviour of both carborane series (1A[n] and 1B[n]) and also the cyclohexane series (1D[n]). The former showed progressive destabilisation of the mesophase, whereas the series 1D[n] exhibited increasing mesophase stability relative to 1E[n] with increasing chain length. Both of these effects were explained using conformational analysis of theoretical models and experimental molecular structures for 1A[3], 1B[4] and 1C[4]. The increasing relative destabilisation of the mesophase in the carborane derivatives was rationalised by the high order rotational axes in A and B and D _4d symmetry for B. The trend of the ΔT _MI values for series 1D[n] was explained with the existence of the equatorial‐axial conformational equilibrium for the cyclohexane derivatives. The clearing temperatures for the hypothetical pure diequatorial conformers 1D[n]‐ee were estimated.     

Synthesis and characterisation of chiral liquid crystalline elastomers containing four-arm crosslinking agent

A new series of side-chain chiral liquid crystalline elastomers derived from M₁ (cholest-5-3-ol(3β)-4-(2-propen-yloxy)]benzoate) and M_C(2,5-[3,5-bis(4-(3-(4-(allyloxy)phenyl)propanoyloxy)benzoyloxy)benzoic acid]isosorbide diester). The structures of monomers and elastomers measured by using Proton Nuclear Magnetic Resonance Spectra (¹H-NMR) and Fourier transform infrared spectroscopy (FTIR) separately are consistent with our design. IIP~VIP all appeared blue Grandjean (GJ) texture on the heating cycle or cooling cycle. The glass sheets of IIP~VIP were made under 150°C and measured its ultraviolet–visible spectrophotometry by PerkinElmer Lambda 950 instrument (Shelton, CT, USA). IIP~VIP all have absorptions at about 481~483 and 561~562 nm. The optical activities were measured at different temperatures on heating and cooling cycles. And the blue selective reflection of IIP~VIP on the round glass sheet can be seen. The elastomers containing less than 6 mol% of the crosslinking units displayed elasticity, reversible phase transition and high thermal stability. The glass transition temperatures reduced first and then increased, the isotropisation temperatures and the mesophase temperature ranges increased first and then decreased with increasing content of crosslinking unit. The thermogravimetric analysis (TGA) results showed that the temperatures at which 5% weight loss occurred (T_d) were greater than 310°C for all the polymers.     

X-ray diffraction study of the smectic mesophase of some azobenzene-containing polyacrylates

Abstract

An X-ray study is performed on powder specimens and on stretched oriented fibres of two liquid crystalline polyacrylates containing the azobenzene mesogenic unit with either a 4′-n-pentyloxy (sample 1–4) or 4′-n-hexyloxy (sample 1–5) substituent. The X-ray diffraction patterns of both samples showed the presence of a bilayer smectic C mesophase with the mesogneic groups tilted by an angle β ～ 45° (1–4) or β ～ 38° (1–5) with respect to the layer normal. The electron density profile p(z) along the direction normal to the smectic layers was calculated by Fourier inversion and possible structural models of the smectic mesophase are discussed. A partial interdigitation of the terminal alkyloxy substituents appears to occur.     

Synthesis and Characterization of Achiral Bent‐Core Liquid Crystalline Molecules Containing Salicylaldimine‐Based with a Wide Temperature Range of SmCP Phase

The design and synthesis of a series bent‐core materials base on a 3,4′‐biphenyldiol central core containing salicylaldimine‐based and two terminal tetradecyloxy tails are reported. In addition, the effects of lateral substituents (R = F and Cl) at the biphenyl core into 3′‐position are examined. These substituents have a strong influence in reducing the clearing temperatures and increasing temperature range of SmCP phase. Upon cooling process the isotropic liquid, compound SB‐Cl exhibits the lowest clearing transition temperature of 180°C and the widest SmCP phase range of 129°C. The mesophase behaviour were investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and electro‐optical (EO) measurements in the mesophase temperature range.     

Synthesis,liquid crystallinity,and mechanical properties of thermotropic polyquinolines

Thermotropic liquid-crystalline polyquinolines with high molecular weights, i.e., poly[2,2′-(α,ω-dioxyphenylene (or -dioxybiphenylene) alkane)-6,6′-(4,4′-dioxybiphenyl)-bis(4-phenylquinoline)]s (P-H-B1Mns or P-H-B2Mns), were synthesized by polycondensation of 4,4′-bis(4-amino-3-benzoylphenoxy)biphenyl and α,ω-bis(4-acetophenoxy (or -acetobiphenoxy))alkanes. For P-H-B1Mn series, the T_m and T_i were in the range of 129–230°C and 156–254°C, respectively, while for the P-H-B2Mn series, those were 182–275°C and 217–309°C, respectively. The introduction of both the dioxybiphenylene group and an alkylene spacer induced thermotropic liquid crystallinity in the polyquinoline, although the introduction of the alkylene spacer alone did not induce it. In addition, polyquinolines substituted with methyl, methoxy, and chloro groups exhibited larger mesophase temperature ranges as well as higher T_ms and T_is than the unsubstituted ones. Tensile strengths of these thermotropic polyquinolines were considerably high in the range of 770 to 1170 kgf/cm². © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 749–759, 1998     

Synthesis and characterization of side chain cholesteric liquid crystalline elastomers derived from chiral bisolefinic crosslinking units

In this work we prepared a nematic monomer (4′‐allyloxybiphenyl 4′‐ethoxybenzoate, M₁ ), a chiral crosslinking agent (isosorbide 4‐allyloxybenzoyl bisate, M₂ ) and a series of new side chain cholesteric liquid crystalline elastomers derived from M₁ and M₂ . The chemical structures of the monomers and polymers were confirmed by FTIR and ¹H NMR spectroscopy. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X‐ray diffraction. The effect of the content of the crosslinking unit on phase behaviour of the elastomers is discussed. Polymer P₁ showed a nematic phase, P₂ –P₇ showed a cholesteric phase; P₆ formed a blue Grandjean texture over a broad temperature range 145–209.6°C, with no changed on the cooling. Polymers P₄ –P₇ , with more than 6?mol?% of chiral crosslinking agent, gave rise to selective reflection. Elastomers containing less than 15?mol?% of the crosslinking units displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. Experimental results demonstrated that, with increasing content of crosslinking agent, the glass transition temperatures first fell and then increased; the isotropization temperatures and mesophase temperature ranges decreased.     

LIQUID CRYSTALLINE POLYMERS. 3. SYNTHESIS AND LIQUID CRYSTAL PROPERTIES OF THERMOTROPIC POLY(ARYLIDENE-ETHER)S AND COPOLYMERS CONTAINING CYCLOALKANONE MOIETY IN THE POLYMER BACKBONE

Two novel series of poly(arylidene-ether)s and copoly(aryl-idene-ether)s were synthesized by polycondensation of 4,4^′-diformyl-α,ω-diphenoxyalkane and 4,4′-diformyl-2,2′-dimeth-oxy-α,ω-diphenoxyalkane with cyclohexanone and/or cyclo-pentanone. The inherent viscosity of the polymers and copolymers thus prepared were in the range of 0.42–1.27 dL/g. The phase behavior of these polymers was studied by differential scanning calorimetry (DSC), optical polarizing microscopy using a heated stage, and thermogravimetric analyses. Almost all the polymers and copolymers exhibited thermotropic liquid crystalline properties. In most cases, the mesophase extends up to 310°C, where thermal decomposition prevents further observation. Methoxy substituents, on the benzene ring of these polymers, lower the transition temperature significantly. The morphology of polymer IX_f was examined by scanning electronic microscope.     

Synthesis and thermal behavior of Janus dendrimers,part 2

The thermal properties of twelve Janus-type dendrimers up to the second generation were evaluated by termogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-bis-dodecyloxybenzoic acid, 3,5-bis-dodecyloxybenzoic acid or 3,4,5-tris-dodecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The thermal stability of the compounds was evaluated by TGA, displaying onset decomposition temperatures (T_d) at around 250 °C. DSC measurements upon heating and cooling confirmed that OH terminated Janus dendrimers featuring large polarity difference in opposite sides display liquid crystalline phases with exception of 3,5-type G1 dendrimer; while acetonide terminated dendrimers displayed merely melting transitions. Dendrimers having terminal alkyl chains at positions 3,4 or 3,4,5 in aromatic moieties exhibited enantiotropic mesophases. However, the thermal behavior of the dendrimers with 3,5-substitution pattern was different: the 3,5-type G1 dendrimer exhibit a lack of mesomorphic transition, and in the case of the 3,5-type G2 dendrimer, the mesophase was absent in the first heating scan but was observed during the subsequent cooling and heating scans at the rate of 10 °C/min.     

Synthesis and mesomorphic behaviour of novel chiral nematic side chain liquid crystalline polysiloxanes

A series of novel thermotropic side chain liquid crystalline polymers was synthesized by grafting copolymerization of a mesogenic monomer, 4-allyloxybenzoyl-4′?-(4-n-alkylbenzoyl)–p-benzenediol bisate and a chiral monomer, menthyl undecylenate. The mesogenic monomers exhibited nematic threadlike textures during heating and cooling. The polymers showed thermotropic liquid crystalline properties with a broad mesomorphic region over a range of 100°C. The polymers exhibited a cholesteric mesophase with a colourful Grand-Jean texture when the content of chiral units was greater than 15?mol?%; the others exhibited nematic threadlike textures. All of the polymers were thermally stable over 300°C, and most were laevorotatory as the chiral monomer.     

Thermally stable and organosoluble poly(amide-imide)s based on the imide ring-preformed dicarboxylic acids derived from 3,4′-oxydianiline with trimellitic anhydride and 6FDA

A diimide-dicarboxylic acid (DIDA) (I) was prepared from the condensation reaction of trimellitic anhydride (TMA) and 3,4′-oxydianiline (3,4′-ODA) in a 2:1 molar ratio, and another new tetraimide-dicarboxylic acid (TIDA) (II) was synthesized by condensation from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), TMA, and 3,4′-ODA in a 1:2:2 molar ratio. Two series of aromatic poly(amide-imide)s (PAI) IVa-k and Va-k were synthesized by Yamazaki phosphorylation polyamidation reactions of DIDA I and TIDA II, respectively, with various aromatic diamines. Due to highly random segmental sequence for both series in the polymer chain and the incorporation of 6FDA moieties for the V series, all the polymers were readily soluble in many organic solvents and could be casted into transparent, flexible, and tough films with good mechanical properties. Glass-transition temperature (T_gs) of the IV series and V series were recorded in the range of 242–274°C and 264–295°C. In addition, almost all the polymers showed 10% weight loss temperatures higher than 500°C under a nitrogen or an air atmosphere.     

Synthesis and mesomorphic properties of the nematic mesophase benzoxazole derivatives with big twist angle of difluoro-biphenyl unit

Modifying the position and numbers of lateral fluorine substituent is a common method to design and adjust the mesophase of liquid crystal compounds. Here, a series of 2-(2,2?-difluoro-4?-alkoxy-1,1?-biphenyl-4-yl)-5-substituted benzoxazole with both non-polar (H, CH₃) and polar (NO₂) groups (coded as nPF(2)PF(2)Bx) is synthesised and characterised. All of the compounds show a conspicuous inter-ring twist angle of 38° compared with corresponding reference compounds I and II which are calculated by density functional theory method, and it is interesting to note that the final compounds nPF(2)PF(2)Bx show only nematic mesophase during heating or cooling. Meanwhile, the UV-vis absorption bands and photoluminescence emission peaks both display remarkable blue-shifted. The aforementioned results reveal that lateral difluoro substituents play a key role to stable the nematic mesophase by increasing the dihedral angle of biphenyl.     

Preparation and properties of lateral monofluoro-substituted benzoxazole-based mesogenic compounds

A series of 2-(3?-fluoro-4?-alkoxy-1,1?-biphenyl-4-yl)-benzoxazole liquid crystals (coded as nPF(3)PBx) were prepared, where a lateral fluorine substituent, as well as methyl, chlorine and nitro terminal groups, was introduced into the molecules to investigate the effects of different polar substituents on the liquid crystal properties. The mesomorphic and photophysical properties were investigated. The results show that compounds nPF(3)PBx have enantiotropic mesophases; meanwhile, they exhibit UV–vis absorption bands with maxima at 323–326 nm and photoluminescence emission peaks at 389–395 nm, respectively. It is noted that nPF(3)PBx with terminal polar groups or electron-withdrawing groups (NO₂, Cl) display higher clearing temperatures and wider mesophase range than those of the corresponding homologues with terminal non-polar groups or electron-donating groups (CH₃, H). Meanwhile, compared with two lateral fluorine-substituted analogues containing 3,5-difluorophenyl unit, lateral monofluoro-substituted nPF(3)PBx display enhanced mesophase range both in heating and cooling except for terminal methyl-substituted compounds, as well as show obvious red-shifted UV–vis absorption bands and photoluminescence emission, which are attributed to the enhanced dipole–dipole interaction caused by increased dipole moment.