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Article 13

C NMR studies, Molecular Order and Mesophase Properties of Thiophene Mesogens Bathini Veeraprakash, Nitin Prakash Lobo, and Tanneru Narasimhaswamy J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.5b09859 • Publication Date (Web): 09 Nov 2015 Downloaded from http://pubs.acs.org on November 9, 2015

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The Journal of Physical Chemistry

13

C NMR studies, Molecular Order and Mesophase Properties of Thiophene Mesogens B. Veeraprakash†, Nitin P. Lobo‡ and T. Narasimhaswamy*† † Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India.

ABSTRACT Three ring mesogens with a core comprising thiophene linked to one phenyl ring directly and to the other via flexible ester are synthesised with terminal alkoxy chains to probe the mesophase properties and find the molecular order. The phenyl thiophene link in the core offers to compare the mesophase features with the molecular shape of the mesogen. The synthesised mesogens display enantiotropic polymesomorphism and accordingly nematic, smectic A, smectic C and smectic B mesophases are perceived depending upon the terminal chain length. For some of the homologs, monotropic higher order smectic phases such as smectic F and crystal E are also witnessed. The existence of polymesomorphism are originally observed by HOPM, DSC further confirmed by powder X-ray diffraction studies. For C8 homolog, high resolution solid state

13

C NMR spectroscopy is employed to find the molecular

structure in liquid crystalline phase and using the 2D SLF technique, the

13

C-1H

dipolar couplings are extracted to calculate the order parameter. By comparing the ratio of local order of thiophene as well as phenyl rings, the bent-core shape of the mesogen is established. Importantly, for assigning the carbon chemical shifts of the core unit of aligned C8 mesogen, the

13

C NMR measured in mesophase of the

synthetic intermediate is employed. Thus the proposed approach addresses the key step in the spectral assignment of target mesogens with the use of mesomorphic intermediate.

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C NMR data of


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KEYWORDS: smectic B, smectic C, XRD, 2D SLF, 13C-1H dipolar couplings, order parameter, INTRODUCTION Thermotropic liquid crystals comprising of thiophene as a constituent of the core unit have emerged as important class of molecular mesogens.1-3 In contrast to wholly phenyl ring based mesogens, molecules consisting of thiophene contributes for pronounced change in properties like increase in optical anisotropy, decrease in melting point, encourages negative dielectric anisotropy and notably reduces the viscosity.4-6 Additionally, the recent work unambiguously demonstrated that the replacement of phenyl rings with thiophene moieties favour interesting optoelectronic and opto-photonic properties leading to plethora of applications in organic light emitting diodes, thin film transistors and organic photovoltaics etc.7-10 Among them, those based on thiophene as a part of the three ring core have attained significant importance due to their low melting transition as well as excellent polymesomorphism.11-13 In this class of mesogens, depending on the location of thiophene in a three ring core, either rod-like or bent core molecules are realized.14,15 For instance, if the thiophene is located at the end of the core, rod-like mesogens are obtained while its presence in the centre of the core yields bent-core molecules. Thus linking the 2-substituted thiophene with the rest of the core favour mostly nematic phase whereas thiophene at a central location with 2, 5-substitution promotes polymesomorphism.16,17 Further, the direct link between thiophene and phenyl ring i.e. phenyl thiophene based calamitic mesogens are found to be interesting molecules.18-20 Many studies on phenyl thiophene based mesogens revealed polymesomorphism exhibiting nematic as well as wide range of smectic mesophases. The direct link between phenyl ring and thiophene also favour π-conjugation leading 2 ACS Paragon Plus Environment

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to photoluminescence properties which are not generally observed if a linking unit such as ester is present.21,22 In a recent work, we explored the polymesomorphism in three ring mesogens in which thiophene is placed at the end of the core and reported the orientational order of phenyl as well as thiophene rings.23 In the present work, we examine yet another three ring series where thiophene is located at the centre of the core. In recent years, the combined approach of Density Functional Theory (DFT), powder X-ray diffraction (XRD) and solid state

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C NMR has become popular for

investigating the molecular packing and order in liquid crystalline molecules.24-26 Thus the DFT provides the energy optimised structure as well as 13C chemical shifts in isotropic phase and XRD offers information about molecular packing while

13

C

NMR provides site specific chemical shift information across the molecule in mesophase. This work also addresses one of the important issues related to chemical shift assignment of molecules in mesophase by making use of a synthetic intermediate that exhibits liquid crystalline phase. It is anticipated that the proposed method of chemical shift assignments of core unit carbons in liquid crystalline phase with the aid of structurally similar intermediate would be a viable approach. Thus the overall emphasis of the investigation is to characterize the synthesised mesogens by Hotstage optical polarising microscopy (HOPM), differential scanning calorimetry (DSC) and XRD and also find the local order of phenyl as well as thiophene rings by high resolution solid state 13C NMR spectroscopy. EXPERIMENTAL SECTION The experimental details of intermediates and final mesogens (4-alkoxyphenyl 5-(4(dodecyloxy) phenyl) thiophene-2-carboxylates) and spectral data of all the



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intermediates are furnished in Supporting Information (SI). The spectral data of final mesogens are furnished below. Materials Thiophene-2-carboxylic acid, 4-bromophenol, sodium hydroxide, palladium acetate, 1-bromo dodecane, pivalic acid, PCy3.HBF4, 10% Pd/C, ammonium formate, 4benzyloxy phenol were purchased from Aldrich, USA. Tetrahydrofuran (THF), nheptane, ethanol from (SD Fine, India) were used as received. Ethyl acetate, diethyl ether, n-hexane, isopropanol, anhydrous potassium carbonate, anhydrous sodium sulfate, Celite-540, and silica gel (100-200 mesh) were used as received from Merck, India. Ethyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylate (EDTC) Yield: 78.3%, m.p-60 °C, FT-IR (KBr, cm-1): 3112(aromatic C-Hstr), 3077, 2962, (CHstr), 1715(C=Ostrester carbonyl), 1623, 1446(C=Cstraromatic). 1H NMR (400 MHz, CDCl3); δ 7.73 (d, J = 3.9 Hz, 1H), 7.55 (d, J = 7.8 Hz, 2H), 7.17 (d, J = 3.9 Hz, 1H), 6.92 (d, J = 7.9 Hz, 2H), 4.35 (q, J = 6.9 Hz, 2H), 3.98 (t, J = 6.2 Hz, 2H), 1.87-1.72 (m, 2H), 1.45 (d, J = 6.6 Hz, 2H), 1.38 (t, 3H), 1.27-1.15 (m, 16H), 0.88 (t, J = 5.9 Hz, 3H).

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C NMR (100 MHz, CDCl3); δ 162.41, 159.79, 151.37, 134.32, 131.34,

127.49, 126.05, 122.43, 115.01, 68.20, 61.06, 31.93, 29.67, 29.65, 29.60, 29.58, 29.39, 29.36, 29.21, 26.02, 22.70, 14.39 and 14.13. MS (HRMS): m/z calculated for C25 H36 O3 S [M + H ]+ 417.2457; found, 417.2458. 4-ethoxyphenyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylate (EDPTC) Yield (72%), m.p-99.8 °C, FT-IR (KBr, cm-1): 3102(aromatic C-Hstr), 3073, 3038, 2965(C-Hstr), 1722(C=Ostr), 1605, 1508, 1420(C=Cstr aromatic), 1237(C-O-Cstr); 1H NMR (400 MHz, CDCl3); δ 7.81 (d, J = 3.9 Hz, 1H), 7.51 (d, J = 8.5 Hz, 2H), 7.16


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(d, J = 3.9 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H), 6.87-6.83 (t, J = 8.1 Hz, 4H), 3.98-3.89 (t, J = 6.7 Hz, 4H), 1.76-1.67 (m, 6H), 1.34 (m, 5H), 1.24 (m, 12H), 0.81 (t, J = 6.6 Hz, 3H).

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C NMR (100 MHz, CDCl3); δ 161.12, 159.98, 156.72, 152.65, 144.04,

135.67, 130.09, 127.60, 125.84, 122.69, 122.46, 115.06, 68.22, 63.85, 31.96, 29.71, 29.68, 29.64, 29.62, 29.43, 29.40, 29.22, 26.05, 22.74, 14.88 and 14.18. 4-butoxyphenyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylate (BDPTC) Yield (78.0%), m.p-91.4 °C, FT-IR (KBr, cm-1 ): 3032, 3028(C-Hstr aromatic), 2948(C-Hstr), 1728 (C=Ostrester), 1610, 1578(C=Cstraromatic), and 1268, 1077(C-OCasym&symstr); 1H NMR (400 MHz, CDCl3); δ 7.89 (d, J = 3.9 Hz, 1H), 7.6 (d, J = 8.7 Hz, 2H), 7.23 (d, J = 3.9 Hz, 1H), 7.12 (d, J = 9.0 Hz, 2H), 6.94-6.90 (t, J = 7.5 Hz, 4H), 4.01-3.94 (t, 6.5 Hz, 4H), 1.84-1.73 (m, 4H), 1.53-1.42 (m, 4H), 1.17 (m, 16H), 0.98 (t, J = 6.5 Hz, 3H), 0.88 (t, J = 6.6 Hz, 3H).

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C NMR (100 MHz, CDCl3); δ

161.06, 160.01, 156.95, 152.63, 144.06, 135.58, 130.19, 127.60, 125.89, 122.67, 122.38, 115.10, 68.24, 68.15, 31.92, 31.34, 29.64, 29.59, 29.38, 29.35, 29.21, 26.02, 22.68, 19.24, 14.10 and 13.83. MS (HRMS): m/z calculated for C33 H44 O4 S [M + H]+ 537.3032; found, 537.3033. 4-(hexyloxy)

phenyl

5-(4-(dodecyloxy)

phenyl)

thiophene-2-carboxylate

(HDPTC) Yield (78.0%), m.p-92.5 °C, FT-IR (KBr, cm-1 ): 3067, 3048(C-Hstr aromatic), 2953, 2870(C-Hstr), 1722(C=Ostr), 1605, 1508(C=Cstraromatic), and 1237, 1037(C-OCasym&symstr); 1H NMR (400 MHz, CDCl3) δ 7.88 (d, J = 3.9 Hz, 1H), 7.58 (d, J = 7.2 Hz, 2H), 7.23 (d, J = 3.9 Hz, 1H), 7.12 (d, J = 9.0 Hz, 2H), 6.94-6.90 (t, J = 6.5 Hz, 4H), 4.02-3.86 (t, J = 6.6 Hz, 4H), 1.87-1.70 (m, 4H), 1.53-1.40 (m, 4H), 1.38-1.32 (m, 6H), 1.27 (m, 14H), 0.93-0.86 (m, 6H); 13C NMR (100 MHz, CDCl3); δ 161.09, 159.99, 156.94, 152.63, 144.03, 135.62, 130.15, 127.59, 125.87, 122.67, 122.40,



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115.08, 68.45, 68.22, 31.94, 31.61, 29.68, 29.66, 29.62, 29.60, 29.41, 29.38, 29.26, 29.22, 26.04, 25.74, 22.71, 22.63, 14.14 and 14.06. MS (HRMS): m/z calculated for C35 H48 O4 S [M + H]+ 565.3345; found, 565.3346. 4-(octyloxy) phenyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylate (ODPTC) Yield (78.0%), m.p-90.6 °C, FT-IR (KBr, cm-1 ): 3070(C-Hstr aromatic), 2956, 2922(C-Hstr), 1727(C=Ostr), 1608, 1513(C=Cstraromatic);

1

H NMR (400 MHz,

CDCl3); δ 7.89 (d, J = 3.9 Hz, 1H), 7.59 (d, J = 8.5 Hz, 2H), 7.24 (d, J = 3.9 Hz, 1H), 7.12 (d, J = 8.9 Hz, 2H), 6.95-6.9 (t, J = 8.4 Hz, 4H), 4.01-3.94 (t, J = 6.5 Hz, 4H), 1.84-1.75 (m, 4H), 1.45 (m, 4H), 1.37-1.26 (m, 24H), 0.90-0.87 (t, J = 6.5 Hz, 6H); 13

C NMR (100 MHz, CDCl3); δ 161.13, 159.97, 156.93, 152.63, 143.99, 135.65,

130.11, 127.60, 125.86, 122.68, 122.41, 115.06, 68.44, 68.22, 31.94, 31.84, 29.68, 29.66, 29.62, 29.59, 29.40, 29.38, 29.27, 29.20, 26.06, 26.03, 22.72, 22.69, 14.15 and 14.14. MS (HRMS): m/z calculated for C37 H52 O4 S [M + H]+ 593.3658; found, 593.3659. 4-(decyloxy) phenyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylate (DDPTC) Yield (72.6%), m.p-97.9°C, FT-IR (KBr, cm-1 ): 3022(C-Hstraromatic), 2955, 2933, 2849(C-Hstr), 1721(C=Ostr), 1608, 1513, 1473(C=Cstraromatic); 1H NMR (400 MHz, CDCl3); δ 7.89 (d, J = 3.8 Hz, 1H), 7.59 (d, J = 8.5 Hz, 2H), 7.24 (d, J = 3.9 Hz, 1H), 7.12 (d, J = 8.8 Hz, 2H), 6.95-6.91 (t, J = 6.5 Hz, 4H), 4.01-3.94 (t, 6.5 Hz, 4H), 1.841.75 (m, 4H), 1.50-1.42 (m, 4H), 1.29 (m, 28H), 0.90-0.87 (t, J = 6.8 Hz, 6H);

13

C

NMR (100 MHz, CDCl3); δ 161.13, 159.97, 156.93, 152.63, 143.98, 135.65, 130.11, 127.60, 125.85, 122.68, 122.41, 115.06, 68.44, 68.22, 31.94, 31.92, 29.68, 29.66, 29.59, 29.42, 29.38, 29.35, 29.29, 29.20, 26.06, 26.03, 22.71 and 14.15. MS (HRMS): m/z calculated for C39 H56 O4 S [M + H]+ 621.3971; found, 621.4073.


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4-(dodecyloxy)

phenyl

5-(4-(dodecyloxy)

phenyl)

thiophene-2-carboxylate

(DDDPTC) Yield: (68.7%) m.p-97.9 °C, FT-IR (KBr, cm-1): 3097, 3112(CHstraromatic), 2953(C-Hstr) 1727(C=Ostr), 1606, 1449(C=Cstraromatic), 1064(C-OCasym&symstr ether); 1H NMR (400 MHz, CDCl3); δ 7.81 (d, J = 3.7 Hz, 1H), 7.51 (d, J = 8.3 Hz, 2H), 7.16 (d, J = 3.8 Hz, 1H), 7.05 (d, J = 8.6 Hz, 2H), 6.95-6.91 (t, J = 8.3 Hz, 4H), 4.01-3.94 (t, J = 6.5 Hz, 4H), 1.84-1.75 (m, 4H), 1.37-1.26 (m, 4H), 1.22 (m, 32H), 0.90-0.87 (t, J = 6.5 Hz, 6H); 13C NMR (100 MHz, CDCl3); δ 161.12, 159.98, 156.72, 152.65, 144.04, 135.67, 130.08, 127.60, 125.84, 122.69, 122.46, 115.06, 115.05, 68.21, 63.85, 31.96, 29.70, 29.68, 29.64, 29.61, 29.42, 29.40, 29.22, 26.05, 22.74, 14.88 and 14.1. MS (HRMS): m/z calculated for C41 H60 O4 S [M + H]+ 649.4284; found, 649.4285. Instrumental Details FT-IR spectra of samples were recorded on ABB BOMEM MB3000 spectrometer using KBr pellets. 1H and

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C NMR spectra of the samples were run on a 400 MHz

BrukerAvance-III spectrometer at room temperature using CDCl3 as a solvent and tetramethylsilane (TMS) as an internal reference. The resonance frequencies of 1H and

13

C nuclei were 400.23 and 100.64 MHz respectively. LCMS-ESI spectra were

recorded on a Bruker Impact-HD spectrometer. Optical polarizing microphotographs were taken using Carl Zeiss Axiocam MRC5 polarizing microscope equipped with Linkam THMS heating stage with TMS 94 temperature programmer. The photomicrographs were taken using Imager A2M digital camera. The samples were placed between 12 mm glass cover slips and transferred to heating stage and were heated with predetermined heating rate. Differential scanning calorimetry (DSC) traces were recorded using a DSC Q200 instrument with a heating rate of 10 °C/minute in nitrogen atmosphere. The samples were subjected to two heating and



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two cooling cycles and the data obtained from second cycle is considered for discussion. UV-Visible absorption spectra were recorded on Varian Cary 50 Bio UVVisible spectrophotometer in chloroform solution and the Photoluminescence (PL) spectra were measured in chloroform on Varian Cary eclipse fluorescence spectrophotometer. Variable temperature powder X-ray diffraction (VT-XRD) measurements were carried out on unoriented samples filled in Lindemann capillary of diameter of 1 mm (Hampton Research, Aliso Viejo, CA, USA) using Cu-Kα (λ=1.54 Å) radiation from PANalytical instrument (DY 1042-Empyrean) and a linear detector (PIXcel 3D). The sample temperature was controlled with a precision of 0.1°C using a heater and a temperature controller (Linkam).27 The gas phase molecular geometries of EDTC BDPTC and ODPTC mesogens were optimized by using DFT-based Becke’s three parameter hybrid exchange functional and Lee-Yang-Parr correlation functional (B3LYP) method employing 6-31G (d) basis set Gaussian 09W suite of programs.28-30 Solid-state 13C NMR experiments The solid state 13C NMR measurements were performed on a Bruker Avance III HD 400 WB NMR spectrometer operating at resonance frequencies of 400.07 and 100.61 MHz for 1H and 13C nuclei respectively. A double resonance 5 mm static probe with a horizontal solenoid coil was used to record the spectra in the liquid crystalline phases. The sample alignment was attained by heating the sample to the isotropic phase and then slowly cooling to the respective mesophases. The 1D

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C NMR spectra in

various mesophases were obtained by standard cross-polarization (CP) scheme with a 50 kHz radio frequency (RF) field strength on both 1H and

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C channels during the

contact time of 3 ms, number of scans 128 and recycle delay of 8 s. High resolution


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2D-SLF spectra were acquired by using the SAMPI-4 pulse sequence (Figure S1 of Supporting Information).31 The efficiency of SAMPI-4 for getting the 13C-1H dipolar couplings in liquid crystalline phase for wide variety of mesogens is reported in our earlier work.23-26,32-35 The SAMPI-4 experimental conditions for EDTC and ODPTC mesogens were as follows: CP contact time τ = 3 ms/ 3 ms, number of t1 increments= 128/148, number of scans= 20/22 and recycle delay= 16 s/16 s to reduce RF heating effects. The data were zero filled in both the t2 and t1 dimensions, yielding a 4096 × 256 real matrix. A shifted sine bell window function was applied to the time domain data and the spectrum was processed in the phase sensitive mode. For both 1D and 2D measurements, 1H 90˚ pulse length was 5µs and SPINAL-64 decoupling strength of 30 kHz was used during the carbon signal acquisition.36 The variable temperature measurements were performed by using a Bruker BVTB-3500 temperature control unit and

207

Pb NMR chemical shift of Lead Nitrate sample was used for temperature

calibration.37 The

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C chemical shift was externally referenced by considering the

solid adamantane methine resonance at 29.5 ppm. RESULTS AND DISCUSSION The synthetic route for the preparation of 4-alkoxyphenyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylates is sketched in (Scheme 1 of Supporting Information). Accordingly, 1-bromo-4-(dodecyloxy)benzene is synthesized by Williamson’s etherification from 4-bromo phenol while ethyl thiophene-2-carboxylate is made from thiophene-2-carboxylic acid and ethanol under reflux with an acid catalyst.38 The synthesis of ethyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylate is then achieved via direct arylation of 1-bromo-4-(dodecyloxy) benzene with ethyl thiophene-2-carboxylate using palladium acetate.39,40 The hydrolysis of the resultant ester with sodium hydroxide led to acid which is condensed with 4-alkoxy phenols41 9 ACS Paragon Plus Environment


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to get 4-alkoxyphenyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylates (Scheme 1 of Supporting Information). By keeping the dodecyloxy chain at one end constant, the alkoxy chain at the other side is varied from C2 to C12 with even carbons to get the homologs of target mesogens. Figure 1 shows the planar structure along with carbon numbers and the energy-optimized model of EDTC and ODPTC mesogens computed from the DFT method of quantum chemical calculations. Mesophase Transitions and Molecular Organization The synthesised mesogens are examined by HOPM, DSC and VT-XRD to establish the nature of the mesophases, transition temperatures as well as the molecular organization respectively. The HOPM and DSC studies revealed enantiotropic mesophases with polymesomorphism for entire range of mesogens (Table 1). Thus, the EDPTC homolog in HOPM (Figure S2 A-C of Supporting Information), on cooling the isotropic phase, showed birefringent droplets. These droplets on further cooling coalesced to give threaded texture characteristic of nematic phase (Figure S2 A of Supporting Information).42 At 144.4 °C, the texture changes to focal conic fan with homeotropic domains indicating the formation of smectic A phase phase (Figure S2 B of Supporting Information).43 The texture is retained till the sample temperature is lowered to 86.6 °C. Interestingly, the DSC (Figure S3 A of Supporting Information) cooling cycle of the EDPTC homolog shows a monotropic transition at 86.6 °C with an enthalpy of 0.67 k.cal/mole. In HOPM, however, at this temperature, no clear change in texture is noticed. Since the transition enthalpy associated with the change is high and homeotropic domains persisted in HOPM even at 86.6 °C, the phase is assigned to be smectic B phase (Figure S2 C of


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Supporting Information). The crystallization of the sample is noticed at 55.5 °C. Table 1 lists the transition temperatures and their enthalpy values. For BDPTC homolog, upon cooling the isotropic phase, formation of batonnets are observed which on further cooling transformed to focal conic fan texture characteristic of smecticA phase (Figure S2 D of Supporting Information).43 At 143.7 °C, a textural change is observed where in the focal conic fans convert to sanded broken-fan texture (Figure S2 E of Supporting Information) indicating the formation of smectic C phase. At 99.8 °C, yet another variation is observed where the sanded broken-fan texture showed arcs for a short duration followed by transformation to smooth fans signifying the phase change (Figure S2 F of Supporting Information).44 The sample at 58.3 °C showed concentric lines which persisted till 32.5 °C and the phase is recognized as crystal E phase (Figure S2 G of Supporting Information).45 The DSC (Figure S3 B of Supporting Information) cooling curve of BDPTC homolog supports the phase changes noted in HOPM examination (Figure S2 D-G of Supporting Information) indicating the existence of polymesomorphism. The ∆H values (Table 1) associated with the phase transitions from isotropic to smectic A and smectic C to smectic B are 1.71 and 0.75 k.cal/mole respectively while the smectic A to smectic C transition is found to be very low (0.012 k.cal/mole). These values are very much in agreement with the literature data of calamitic mesogens.46 Further, the occurrence of polymesomorphism in BDPTC homolog is confirmed by VT-XRD investigation (Figure S4 A-D of Supporting Information). In XRD, the existence of smectic A mesophase is established by observing a sharp reflection in small angle region and broad hump in wide angle region. The broad hump in the wide angle region indicates the absence of in plane order and liquid like nature of molecules within the layer.47 The XRD measurements at 150 °C and 147 °C showed a 11 ACS Paragon Plus Environment


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sharp peak at small angle region with a layer spacing (d) of 34.369 Å (Figure S4 A of Supporting Information). The molecular length of the BDPTC mesogen as calculated from energy optimised molecular structure by DFT is 37.28 Å. The layer spacing (d) measured in the range 142-120°C is 34.02 Å-33.68 Å (Table S1 of Supporting Information). Although variation in layer spacing is noticed in the range 142-120 °C, the broad hump observed in the wide angle region is unaltered. As the layer spacing decreased with lowering of temperature, the phase is assigned as smectic C in concurrence with the HOPM and DSC results. Further, the XRD profile in the temperature range 100-90 °C reveal increase in layer spacing (35.46 Å-35.83 Å) and also the broad hump seen at wide angle region for both smectic A and smectic C is replaced by a sharp peak indicating layer in plane order (Figure S4 B-C of Supporting Information).47,48 These features unambiguously support the presence of smectic B phase and confirm the DSC data. For C6-C12 homologs, on cooling the isotropic phase, either broken fan texture alone (Figure 2B) or broken fans with schlieren texture (Figure S2 H, K and M of Supporting Information) is noticed. The transition enthalpy of the phase change for these homologs is 1.84-2.48 k.cal/mole as per DSC (Table 1). Thus based on the high enthalpy values as well as the texture in HOPM, the phase is assigned as smectic C. On further cooling of HDPTC and ODTPC samples, phase change is noticed at 98.1°C and 98.8°C respectively (Figure S2 I of Supporting Information and Figure 2C-D). The corresponding enthalpies of the transitions (Figure S3 C of Supporting Information and Figure 3B) are found to be 0.69 and 0.75 k.cal/mole. Since the ∆H values are high for the transition, the XRD investigation is undertaken to confirm the nature of the mesophase. The XRD profile of HDPTC homolog (Figure S5 A-D of Supporting Information) in the temperature range 148-110 °C, shows sharp and 12 ACS Paragon Plus Environment

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intense reflection in the small angle region with a layer spacing of 34.36 Å and a broad hump in the wide angle region (Figure S5 A of Supporting Information). Interestingly, the d values remain constant in the temperature range 148-110°C despite the phase being smectic C. This kind of behaviour i.e. constant layer spacing with lowering of temperature is common feature for mesogens that exhibit isotropic to direct smectic C transition (Table S2 of Supporting Information).49 At 98 °C, for HDPTC homolog, the d value showed sudden increase (37.01 Å) and the wide angel broad hump is replaced by sharp reflection. Thus increase in layer spacing as well as layer in plane order establishes that the phase under observation is smectic B (Figure S5 B-C of Supporting Information). For ODPTC homolog also, similar XRD profile (Figure 4B) is noticed where the layer spacing (35.08 Å) is constant in the temperature range 145-110°C (Table S3 of Supporting Information). At 98 °C, similar to HDPTC homolog, the wide angle profile exhibited sharp peak confirming the presence of smectic B phase (Figure S6 A-B of Supporting Information). On further cooling, in HOPM, the HDPTC homolog exhibited a phase change at 47.7 °C for which the enthalpy values is 2.15 k.cal/mole (Table 1). The XRD pattern showed three orders of reflection in the small angle region which are assigned 001, 002, 003 and wide angle region showed multiple reflections with varying intensity (Figure S5 D of Supporting Information). The phase has been assigned as Crystal E (Figure S2 J of Supporting Information) by considering the wide angle pattern of XRD.45,50-52 In the case of ODPTC homolog, on cooling the smectic B phase, crystallisation is observed with an enthalpy value of 7.68 k.cal/mole (Table 1). Thus it is concluded based on the HOPM, DSC and XRD studies that the HDPTC and ODPTC homologs exhibits enantiotropic smectic C and smectic B phases.



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In the case of DDPTC and DDDPTC mesogens (Figure S2 K-N of Supporting Information), upon cooling the isotropic phase, broken fan or schlieren (Figure S2 K of Supporting Information) or schlieren-mosaic texture of smectic C phase is noticed (Figure S2 M of Supporting Information). On further cooling, smectic C to higher order smectic phase change is observed (Figure S2 L and N of Supporting Information) for DDPTC and DDDPTC respectively with transition enthalpies of 0.38 and 0.43 k.cal/mole (Figure S3 D-E of Supporting Information). In order to confirm the low temperature mesophases of DDDPTC homolog, the XRD investigation is undertaken (Figure S7 A-C of Supporting Information). The XRD profile of the mesogen in the temperature range 145-110°C shows sharp reflection in the small angle region and a broad hump in the wide angle region (Figure S7 A of Supporting Information). The layer spacing in the measured temperature range is 37.80 Å (Table S4 of Supporting Information). At 105°C, the layer spacing increases (38.23 Å) and the wide angle region shows sharpened reflection in contrast to smectic C phase (145120°C). Interestingly, for both DDPTC and DDDPTC mesogens, the smectic C to lower temperature mesophase is found to be monotropic from DSC studies. Based on the transition enthalpy value and XRD profile in the wide angle region (Figure S7 BC of Supporting Information), the phase is assigned as smectic F for DDDPTC. Since the transition enthalpy of low temperature smectic phase of DDPTC is comparable with that of DDDPTC, smectic F is also assigned for the later (Table 1).48 It is to be noted that for HDPTC and ODPTC homologs, the transition enthalpy values of smectic C to higher order phase (smectic B) is high and also the wide angle reflection is much sharper than the one observed for DDDPTC homolog. The EDTC (Figure 1A) which is the synthetic intermediate for the target mesogens is also subjected to HOPM, DSC and XRD investigation to find mesophase 14 ACS Paragon Plus Environment

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properties as well as molecular organization. The sample on cooling the isotropic phase (HOPM), shows focal conic fan texture with homeotropic domains (Figure 2A).43 The DSC measurement (Figure 3A) confirms enantiotropic nature of the mesophase and the transition temperatures from crystal to smectic A is 56.9°C and smectic A to isotropic temperature is 71.3°C. The transitions enthalpies for these pahse changes are 8.23 and 1.65 kcal/mole. The XRD profile of the mesogen measured at 70°C shows sharp reflection in small angle region and a broad hump at wide angle region (Figure 4A). These features are characteristic of layer ordering observed for smectic phases.47,52 In order to find the nature of the smectic phase, the d/L values are determined where L represents the molecular length calculated from energy optimised structure from DFT method. Table S5 of Supporting Information lists the d/L values in the temperature range 50-70 °C which is ~1 and is constant across the temperature range suggesting the monolayer smectic A phase (Table S5 of Supporting Information). 13

C NMR Investigations A detailed investigation of

13

C NMR of EDTC and ODPTC in liquid

crystalline phases are undertaken to find the orientational order of phenyl and thiophene rings. Additionally, the chemical shift assignment of aligned spectrum of ODPTC is carried out by making use of EDTC NMR data which exhibits smectic A phase. Prior to the the spectral assignment of aligned molecules, the solution

13

C

NMR spectra of EDTC and ODPTC is first recorded. The proton decoupled 13C NMR of EDTC is shown in Figure 5A. The assignments of the lines are carried out by utilizing the spectrum generated from Chemsketch (version 3.0) software. Table 2 lists the assigned carbons of core region of EDTC. The spectrum in the range 110-165



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ppm shows 9 sharp lines accounting for thiophene ring, phenyl ring, and ester carbonyl carbons. The identification of phenyl ring methine carbons is relatively easy owing to higher intensity in contrast to other carbons of the core. The thiophene carbons showed lower intensity than phenyl ring methine carbons while the quaternary carbons of both the rings and ester carbonyl carbon showed lowest intensity. For the terminal chain carbons, the lines appeared in the range 60-70 ppm are assigned to OCH2 carbons of alkoxy chains while the terminal two methyl carbons showed lines at 14 ppm. The other methylene carbons of the terminal chains are noticed in the range 20-35 ppm. Thus the well resolved spectral lines of EDTC are very much in agreement with the molecular structure (Figure 1A). Figure 5B shows the proton decoupled

13

C NMR of ODPTC. For clarity the spectrum of EDTC and

ODPTC are shown in Figure 5 with line assignment of core unit carbons. The ODPTC spectrum shows 13 lines in the range 110-165 ppm accounting for two phenyl rings, thiophene ring and ester carbonyl carbon of core unit. The terminal chains showed lines in the range 14-70 ppm. The OCH2 carbons show peaks at 65 ppm while methyl showed at 14 ppm. The rest of methylene carbons are seen in the range 20-35 ppm. Table 3 list the chemical shift values of core unit carbons. Further it is clear from Figure 5 that the carbon lines of core unit of EDTC and ODPTC are very much similar since they have structural resemblance (Figure 1A, 1C). The static 13C NMR spectra of EDTC and ODPTC in liquid crystalline phase are shown in Figure 6 and Figure S8 A of Supporting Information. For EDTC, the spectrum is recorded in smectic A phase at 66 °C while for ODPTC, the measurement is carried out in smectic C phase at 130 °C. The static aligned 13C NMR spectrum of EDTC (Figure 6A) shows very well resolved peaks both for the core unit as well as terminal chains. The core unit carbons exhibited peaks in the range 140-230 ppm 16 ACS Paragon Plus Environment

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while for terminal chain carbons the signals are noticed in the range 15-65 ppm. It is relatively easy to identify peaks arising from phenyl as well as thiophene methine carbons based on intensity. Thus two peaks with high intensity are attributed to phenyl ring methine carbons while the identification of thiophene methine carbons is attempted using 2D-SLF spectrum which is discussed in subsequent section. The rest of the quaternary carbons are identified by making use of structurally similar mesogens reported recently.23 Figure 6A shows the spectrum with line assignments of carbons of the core unit while Table 2 lists the chemical shifts as well as alignment induced chemical shifts (AIS). Figure 6B shows the static

13

C NMR spectrum of

ODPTC measured in smectic C phase at 130 °C. The spectrum shows resolved peaks in the range 140-230 ppm mainly from core unit carbons. The terminal chain carbons showed peaks in the range 10-60 ppm. Among the core unit carbons, four peaks are more intense and are attributed to phenyl rings while the intensity of other carbons is comparable. As a consequence, the identification of thiophene methine carbons is found to be difficult. Hence, the 2D SAMPI-4 spectrum is utilized for the location of thiophene carbons. Since EDTC is a synthetic intermediate of ODPTC, the static 13C NMR spectrum of EDTC is also used for the assignment of core unit carbons. It is unambiguous from Figure 6B that identification of core unit carbons can be easily achieved by comparing the EDTC spectrum (Figure 6A). It is to be noted that even though EDTC and ODPTC show different liquid crystalline phases with dissimilar transition temperatures, the static

13

C NMR data of EDTC is very useful for the

assignment of ODPTC carbons (Table 3). Despite variation in chemical shift values of core unit carbons of both the mesogens, the spectral assignment of ODPTC could be carried out since the sequence of appearance of peaks is similar for both the



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molecules (Figure 6). Further, the 2D data provided the additional source of confirmation for the core unit carbons of ODPTC. In addition to static 13C NMR experiments, the 2D SAMPI-4 is also used both for EDTC and ODPTC mesogens for determining the 13C-1H dipolar couplings which are used for confirmation of structural assignment attempted by 1D data and find the orientational order parameter. The 2D SAMPI-4 spectrum of EDTC is shown in Figure 7A. Similar to 1D static spectrum, 9 contours are seen in the range 145-230 ppm for the core unit carbons. The remarkable feature of the 2D spectrum is clear separation of thiophene methine carbons from rest of the core unit carbons. Accordingly, the 13C-1H dipolar couplings of methine carbons of thiophene are noted in the range ~4-5 kHz whereas the phenyl methine dipolar couplings are observed ~3 kHz. The dipolar couplings of quaternary carbons of the core unit are seen in the range ~0.75-2 kHz. The clear separation of thiophene methine carbons from rest of the carbons is mainly due to the high 13C-1H dipolar couplings which suggest that the phenyl as well as thiophene rings are not experiencing similar orientation with respect to long axis. For the terminal chain carbons also, better separation of contours is seen in contrast to 1D static spectrum due to variation in

13

C-1H dipolar couplings of

metheylene carbons across the chain. The 2D SAMPI-4 spectrum of ODPTC is shown in Figure 7B and Figure S8 B of Supporting Information. Similar to 1D static feature, the 2D spectrum also shows 13 contours for all the core unit carbons. Quite interestingly, the thiophene carbons are not showing large variation in contrast to phenyl rings as noted for EDTC. Nevertheless, the identification of thiophene methine carbons in contrast to 1D static 13C spectrum is easy since the 2D data for structurally similar mesogen is available in literature.23 Table 3 shows the

13

C-1H dipolar

couplings of all the resolved carbons which are used for computing the orientational 18 ACS Paragon Plus Environment

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order parameter. For phenyl rings, the extracted from the

13

C-1H dipolar oscillation frequencies can be

13

C-1H dipolar coupling obtained from 2D SAMPI-4 experiment

by following the established approach.23-26,32-35,53-55 A similar strategy extended for thiophene ring and the final dipolar frequencies for C6 and C7 carbons can be expressed

as[(DC6-H6)2+

(DC6-H7)2] 1/2and

[(DC7-H7)2+(DC7-H6)2] 1/2,

respectively.

Similarly, for C5 and C8 carbons the dipolar frequencies would be [(DC5-H6)2+2(DC52 1/2 H3) ] and

(DC8-H7), respectively. Now, these dipolar frequencies are used for

computing the orientational order parameter by using following equation 1,56-59 DCH =K [½ (3 cos2θz-1) Szz+ ½ (cos2θx - cos2θy) (Sxx-Syy)]

(1)

where K=-hγHγC/4π2r3CH, with γH and γC are the gyromagnetic ratios of 1H and

13

C

nuclei respectively, rCH is the inter-nuclear vector, θx, θy and θz are angles between rCH vector and the corresponding molecular axes. For the phenyl rings, the molecular frame is defined by considering para-axis (C2 axis) as the z-axis, the x-axis is in the plane of the ring while the y-axis is perpendicular to the plane. Standard bond distances, rCH= 1.1 Å for the C–H bond and rCC= 1.4 Å for the C–C bond, are taken. The two C–C–H bond angles are also slightly varied around 120˚ to get the best fit.60 In arriving at the order parameters of thiophene ring, a model suggested earlier is used (Figure S9 of Supporting Information).23,61 In view of irregular pentagonal geometry of thiophene moiety, three order parameters namely, Szz, (Sxx–Syy) and Sxz are required for an arbitrary choice of the axis system.62 Here the z-axis is chosen along the C4-C5 bond by which thiophene is directly connected to the phenyl ring I (Figure 1C).23 The bond angles and bond distances computed from the energy minimized structure of thiophene for EDTC and ODPTC mesogens are utilized (Figure 1B, 1D). Initially, only two order parameter namely, Szz and (Sxx–Syy) taken for fitting with an



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assumption that the other order parameter is likely to be small. The quality of the fit is improved by introducing an angle β between the z-axis and the C4-C5 bond. Moreover the efficiency of the fit is enhanced by varying the two CCH bond angles by ±2 degree. Further the addition of third order parameter namely Sxz did not improve the fit appreciably. Hence, the Szz and (Sxx-Syy) order parameters for thiophene as well as phenyl rings of EDTC and ODPTC are considered by employing the equation 1 and are listed in Tables 4-7. In both the cases i.e. EDTC and ODPTC, the order parameters of thiophene and phenyl rings are dissimilar. This feature indicates that with respect to the long axis, the phenyl and thiophene rings are experiencing different orientation. This is mainly due to the change in the geometry of phenyl and thiophene rings as already discussed in the earlier work.24 An examination of order parameters of phenyl ring II and thiophene provides information about the tilt angle between the long axis versus local axis of the side phenyl ring. Accordingly, the values are found to be 19.4°, 18.8° at 95 °C (smectic B) and 130 °C (smectic C) for ODPTC. It is well known that 2, 5substitution on thiophene will results in bent-core shape with typical bond angle of ~ 147° which is in close agreement with the tilt angles noticed for ODPTC.17 A plot of temperature versus AIS of EDTC is shown in Figure S10 A of Supporting Information. With increase in temperature, the AIS values showed decreasing trend. Since all the measurements are carried out in smectic A phase, a smooth decrease is noticed. The similar plot for ODPTC is also shown in Figure S10 B of Supporting Information, where like EDTC with increase in temperature decrease in AIS is observed. However, an abrupt change in AIS values is noticed at 98 °C for ODPTC indicating phase transition from smectic B to smectic C phase. The DSC data


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confirms the first order nature of the transition and accordingly clear change in AIS values in NMR data is also observed. The photophysical studies of all the mesogens in chloroform (2×10-6 M) are carried out to find the absorption and photoluminescence properties (Figure S11 of Supporting Information). Accordingly, the absorption band is noticed at 335 nm while the fluorescence emission band is observed at 405 nm. Thus the fluorescence emission of synthesised mesogens is an interesting feature which is mainly attributed to the π-conjugation of the phenyl thiophene link of the core unit. It is to be noted that the mesogens in which phenyl and thiophenes are separated by linking units; the fluorescence emission is not commonly noticed. Also thiophene molecular materials which are used for organic light emitting diodes are often constructed with phenyl and thiophene rings directly to facilitate π overlap to enable to have photoluminescence in solid state for the device fabrication.7 CONCLUSIONS Six

homologs

of

(4-alkoxyphenyl

5-(4-(dodecyloxy)

phenyl)

thiophene-2-

carboxylates) were synthesised from thiophene -2- carboxylic acid with direct arylation using palladium acetate followed by esterification with 4-alkoxy phenols. The HOPM and DSC measurements indicated enantiotropic mesophases consisting of nematic, smectic A, smectic C and smectic B phases depending on the terminal chain length. Additionally, for some homologs, smectic F as well as crystal E phases were noticed in monotropic fashion. The HOPM and DSC observations were confirmed by powder X-ray diffraction where layer ordering typical of smectic mesophases were clearly seen. For smectic A and C phases, the wide angle region showed broad hump whereas for smectic B and F, the broad hump was replaced by sharp reflection 21 ACS Paragon Plus Environment


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indicating in plane order within the layers. The high resolution solid state 13C NMR of ODPTC was carried out in smectic C phase and the

13

C-1H dipolar couplings

measured from 2D-SLF experiments were employed for determining the order parameter of phenyl and thiophene rings. The higher order for thiophene ring (0.85) over phenyl (0.71) was attributed to its location at the centre and using the order parameter ratios of phenyl and thiophene rings, the bent-core nature of the mesogen was established. Further, the

13

C chemical shift assignments of octyl homolog was

carried out by making use of the

13

C NMR data of synthetic intermediate (EDTC)

which exhibited smectic A phase. This approach facilitated the assignments of

13

C

NMR peaks of the core unit of ODPTC relatively easy. Thus the investigation demonstrates the utility of 13C NMR data of mesomorphic synthetic intermediate for the final assignment of target mesogens.


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AUTHOR INFORMATION Corresponding Author *E-mail:[email protected]

ACKNOWLEDGEMENTS The authors would like to thank Dr. A. B. Mandal, Outstanding Scientist, CLRI and Prof. K. V. Ramanathan, NMR Research Centre, Indian Institute of Science, Bangalore, India for their support and keen interest in this project. We are grateful to Prof. V. A. Raghunathan and Ms. K. N. Vasudha, Raman Research Institute, Bangalore, India for the powder X-ray measurements. We acknowledge the partial financial support from NWP-55 while B. Veeraprakash acknowledges the financial support from Council of Scientific and Industrial Research (CSIR), New Delhi in the form of Senior Research Fellowship. SUPPORTING INFORMATION It contains synthetic details, spectral data of intermediates, powder XRD data of EDTC, BDPTC, HDPTC, ODPTC, DDDPTC mesogens, Figure of SAMPI-4 pulse sequence, HOPM photographs, DSC plots, VT-XRD plots of BDPTC, HDPTC, ODPTC, DDDPTC mesogens, plot of AIS as a function of temperature for EDTC and ODPTC mesogens, 1D 13C NMR and 2D SAMPI-4 spectra of ODPTC mesogen at 95 °C in smectic B phase, thiophene model, UV-visible spectra and Fluorescence emission plots. This material is available free of charge via the Internet at http://pubs.acs.org 23 ACS Paragon Plus Environment


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Kovářová, A.; Kohout, M.; Svoboda, J., Novotná, V. New Liquid Crystal Based on 2-Phenylthiophene Central Core. Liq. Cryst. 2014, 41, 1703-1718.

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Synthesis

and

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Properties

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3,3′,5,5′-

Tetrakis(phenylethynyl)-2,2′-Bithiophene Derivatives. Liq. Cryst. 2014, 41, 1191-1211. (4)

Narasimhaswamy, T.; Lee, D. K.; Somanathan,N.; Ramamoorthy, A. SolidState NMR Characterization of a Novel Thiophene-Based Three Phenyl Ring Mesogen. Chem. Mater. 2005, 17, 4567-4569.

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O’Neill, M.; Kelly, S. M. Ordered Materials for Organic Electronics and Photonics. Adv. Mater. 2011, 23, 566-584.

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of

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Akagi, K., Ed. Perepichka, I. F.; Perepichka, D. F. Handbook of Thiophenebased Materials: Applications in Organic Electronics and Photonics; John Wiley & Sons: Chichester, UK, 2009.

(10) Ponomarenko, S. A.; Luponosov,Y. N.; Min, J.; Solodukhin, A. N.; Surin, N. M.; Shcherbina, M. A.; Chvalun, S. N.; Americ, T.;Brabec, C. Design of DonorAcceptor Star-Shaped Oligomers for Efficient Solution Processible Organic Photovoltaics. Faraday Discuss. 2014, 174, 313-339. (11) Bunning, J. D.; Butcher, J. L.; Byron, D. J.; Mathuru, A. S.; Wilson, R. C. Xray Diffraction Studies of the Liquid Crystal Phases of Certain 4-nAlkoxyphenyl 4-(5-n-alkyl-2-Thienyl) Benzoates. Liq. Cryst. 1995, 19, 693698. (12) Butcher, J. L.; Byron, D. J.; Matharu, A. S.; Wilson, R. C. Properties of the Liquid

Crystals

Formed

by

Certain

4′-n-Alkylbiphenyl-4-yl

5-n-

Alkylthiophene-2-Carboxylates. Liq. Cryst. 1995, 19, 387-396. (13) Byron, D. J.; Matharu, A. S.; Shirazi, S. N. R.; Tajbakhsh, A. R.; Wilson, R. C. A Study of Homologation and the Occurrence of an SA-SC-SA Sequence of Phases in the 4-n-Alkoxy-3-fluorophenyl 4-(5-n-alkyl-2-thienyl) benzoates. Liq. Cryst. 1993, 14, 645-652. (14) Brown, J. W.; Byron, D. J.; Harwood, D. J.; Wilson, R. C. Some Three-Ring Esters Containing a Five-Membered Heteroaromatic Ring. A Comparison of Liquid Crystal Properties. Mol. Cryst. Liq. Cryst. 1989, 173, 121-140. (15) Han, J.; Zhang, F.Y.; Wang, J.Y.; Wang, Y.M.; Pang, M.L.; Meng, J.B. Synthesis and Comparative Study of the Heterocyclic Rings on Liquid Crystalline Properties of 2,5-aryl-1,3,4-oxa(thia)diazole Derivatives Containing Furan and Thiophene Units. Liq. Cryst. 2009, 36, 825-833.



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Table 1: Transition temperatures for the 4-alkoxyphenyl 5-(4-(dodecyloxy) phenyl) thiophene-2-carboxylates in the second cooling cycle. Transition temperatures (ºC) and enthalpy values Code (∆H k.cal/mol) in parenthesis on cooling from isotropic phase EDTC I-SmA SmA-Cr 70.1 30.8 (2.00) (5.28) EDPTC I-N N-SmA SmA-SmB SmB-Cr 150.1 144.0 [86.6] 55.5 (0.32) (0.60) (0.67) (5.98) BDPTC I-SmA SmA-SmC SmC-SmB SmB-CrE 150.5 143.7 99.8 [58.3] (1.71) (0.012) (0.75) (1.58) HDPTC I-SmC SmC-SmB SmB-CrE 148.9 98.1 [47.7] (0.69) (2.15) (2.10) ODPTC I-SmC SmC-SmB SmB-Cr 146.8 98.8 48.7 (2.48) (0.75) (7.68) DDPTC I-SmC SmC-SmF SmF-Cr 145.5 [96.5] 72.0 (2.23) (0.38) (11.67) DDDPTC I-SmC SmC-SmF SmF-Cr 144.5 [99.1] 80.5 (1.84) (0.43) (14.23) [ ] indicates monotropic transition; Cr, crystal; CrE, crystal E; SmB, smectic B; SmC, smectic C; SmA, smectic A; SmF, smectic F; N, nematic; I, isotropic.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 2: 13C NMR chemical shifts (CS), alignment induced chemical shifts (AIS) and 13C-1H dipolar couplings (DC) of EDTC mesogen in smectic A liquid crystalline phase.

Solution C. No (ppm) 1 2 3 4 5 6 7 8 9

159.8 115.0 127.5 126.0 151.4 122.4 134.3 131.3 162.4

66 ºC CS AIS (ppm) (ppm) 228.7 68.9 144.8 29.8 154.0 26.5 201.0 75.0 207.4 56.0 157.1 34.7 191.0 56.7 184.5 53.2 212.2 49.8

DC (kHz) 1.54 2.97 3.11 1.51 1.25 4.69 4.09 1.11 1.08



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 3: 13C NMR chemical shifts (CS), alignment induced chemical shifts (AIS) and 13 1 C- H dipolar couplings (DC) of ODPTC mesogen in smectic C and smectic B liquid crystalline phases.

Solution C. No (ppm) 1 2 3 4 5 6 7 8 9 10 11 12 13

160.0 115.1 127.6 125.9 152.6 122.7 135.6 130.1 161.1 144.0 122.4 115.1 156.9

95 ºC

130 ºC

CS AIS DC CS AIS DC (ppm) (ppm) (kHz) (kHz) (ppm) (kHz) 235.8 75.8 1.60 226.8 66.8 1.50 145.6 30.5 3.44 141.9 26.8 2.98 155.8 28.2 3.20 151.1 23.5 2.75 208.7 82.8 1.60 199.3 73.4 1.53 216.5 63.9 1.38 210.5 57.9 1.23 165.1 42.4 4.35 161.0 38.3 3.30 198.1 62.5 3.02 189.7 54.1 2.27 188.6 58.5 1.33 183.1 53.0 1.17 233.7 72.6 0.71 217.5 56.4 0.49 224.6 80.6 1.63 214.5 70.5 1.51 156.5 34.1 3.60 153.5 31.1 3.06 147.4 32.3 3.41 144.3 29.2 2.89 228.4 71.5 1.61 218.9 62.0 1.50


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Table 4: Orientational order parameter for phenyl ring of EDTC mesogen in smectic A phase.a c d

Angles T Ring (°C) 66

I

a

θb

θc

SZZ (Sxx-Syy)

119.6 119.2 0.68

0.064

b a

Calculated dipolar oscillation frequencies (kHz) b c a d 2.99 3.11 1.55 1.54 (2.97±0.03) (3.11±0.02) (1.54±0.04) (1.51±0.04)

Values in parenthesis represents experimental dipolar oscillation frequencies (kHz)


RMSD (kHz) 0.02


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Table 5: Orientational order parameter for thiophene ring of EDTC mesogen in smectic A phase.a 6

7 8

5

S

Angles T βb (°C)

SZZ (Sxx-Syy) θ6

Calculated dipolar oscillation frequencies (kHz)

θ7 C-6

66

6 116.01 45.97 0.78

0.043

C-7

C-5

RMSD c θ (kHz)

C-8

4.73 4.08 1.18 1.09 0.03 17.0 (4.69±0.02) (4.09±0.02) (1.25±0.03) (1.11±0.03)

a


b

β is the angle between the local z-axis and C4-C5 bond.

c

θ is the angle between the local z- axes of thiophene and phenyl ring.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 6: Orientational order parameter for phenyl ring of ODPTC mesogen in smectic B and smectic C liquid crystalline phases.a b

c

a

d

Angels T Ring (°C) θb I

θc

SZZ (Sxx-Syy)

118.7 119.4 0.71 0.070

95 II 118.3 118.9 0.71 0.074 I

119.3 120.1 0.65 0.066

130 II 119.1 119.6 0.65 0.068

a

Calculated dipolar oscillation frequencies (kHz) b 3.44 (3.44±0.03) 3.60 (3.60±0.02) 2.98 (2.98±0.02) 3.06 (3.06±0.01)

c 3.21 (3.20±0.02) 3.40 (3.41±0.03) 2.74 (2.75±0.01) 2.90 (2.89±0.02)

a 1.60 (1.60±0.04) 1.59 (1.63±0.04) 1.48 (1.50±0.03) 1.48 (1.51±0.03)

d 1.62 (1.60±0.03) 1.61 (1.61±0.03) 1.50 (1.53±0.02) 1.49 (1.50±0.02)



RMSD (kHz)

0.01 0.02 0.02 0.02


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Table 7: Orientational order parameter for thiophene ring of ODPTC mesogen in smectic B and smectic C liquid crystalline phases.a 6

7 8

5

S

Angles T βb (°C)

SZZ (Sxx-Syy) θ6

θ7

C-6

95 8.5 118.60 48.65 0.85

0.074

130 10 120.10 50.05 0.77

0.060

a

Calculated dipolar oscillation frequencies (kHz) C-7

C-5

C-8

4.32 3.00 1.36 1.28 0.03 19.4 (4.35±0.03) (3.02±0.02) (1.38±0.03) (1.33±0.02) 3.29 2.24 1.23 1.18 0.02 18.8 (3.30±0.02) (2.27±0.02) (1.23±0.02) (1.17±0.02)

Values in parenthesis represents experimental dipolar oscillation frequencies (kHz) b c

RMSD c θ (kHz)

β is the angle between the local z-axis and C4-C5 bond. θ is the angle between the local z- axes of thiophene and phenyl ring.


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Figure Captions: Figure 1: (A) Planar and (B) energy optimized structures of EDTC mesogen. (C) Planar and (D) energy optimized structure of ODPTC mesogen. Figure 2: HOPM photographs of mesogens on cooling the isotropic phase (A) EDTC in smectic A phase at 70.0 °C. ODPTC in (B) smectic C phase 146.2 °C, (C) smectic B phase at 98.8 °C and (D) smectic B phase at 95.3 °C. Figure 3: DSC scans of (A) EDTC and (B) ODPTC mesogens. Figure 4: High-resolution powder X-ray diffraction patterns of mesogens (A) EDTC in smectic A phase at 70 °C and (B) ODPTC in smectic C at 145 °C (black line) and in smectic B phase at 95 °C (red line). Figure 5: Solution proton-decoupled 13C NMR spectra of (A) EDTC and (B) ODPTC mesogens. Figure 6: 13C NMR spectrum of the oriented samples of (A) EDTC mesogen at 66 °C in the smectic A phase and (B) ODPTC mesogen at 130 °C in smectic C phase. Figure 7: 2D SAMPI-4 spectrum of the mesogens (A) EDTC at 66 °C in smectic A phase and (B) ODPTC at 130 °C in smectic C phase.



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Page 40 of 47

Figure 1 (A)

(B)

L=29.48Å (C)

(D)

L=42.19Å


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Figure 2



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Figure 3

(A)

(B)


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Figure 4

(A)

(B)



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Figure 5


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Figure 6



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Figure 7


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