3-Cyano thiophene-based π-conjugated mesogens: XRD and ¹³C NMR investigations

Abstract

Experimental SectionSynthesis of 4-bromo-4'-(octyloxy) biphenyl (1) The reaction is carried out in oven-dried glassware. In a 250 ml round bottom flask 10g 4'-bromobiphenyl-4-ol and 3.86g (moles) K2CO3 were taken and dissolved in 100 ml DMF. The mixture was stirred and heated to 90 °C followed by dropwise addition of 25 ml of 1-bromooctane. The temperature of the mixture was maintained at 90° C for 5h. Then the reaction mixture was poured into 1L distilled water and transferred to a separating funnel and extracted with chloroform. The chloroform layer was washed using 5% NaOH solution and distilled water, and the organic layer was dried over anhydrous sodium sulfate. Upon evaporation white solid is obtained and is further purified by recrystallization from acetonitrile. Yield:80%. synthesis of 2,5-bis(4'-(octyloxy)-[1,1'-biphenyl]-4-yl)thiophene-3-carbonitrile: (PCN8)To a degassed mixture of 4-bromo-4'-(octyloxy) biphenyl (4.14 g, 18 mmol ), 3cyanothiophene(1g, 3.08 mmol), K2CO3 (6 mmol, 0.81g), Pd(OAc)2 (6 mol %, 0.178 mmol, 40 mg), PCy3.HBF4 (12 mol %, 0.358 mmol, 132 mg), pivalic acid (30 mol %, 0.90 mmol, 92 mg), 8 ml of dry N,N-dimethyl acetamide was added via syringe. The reaction mixture was then vigorously stirred at 110 º C for 12 h under argon. The solution was then cooled to room temperature and diluted with CH2Cl2. The aqueous phase was extracted with CH2Cl2 (3 times). The organics layer was dried over MgSO4 and evaporated under reduced pressure and then eluted with hexane /ethyl acetate (9: 1). The solid obtained was recrystallization from 1propanol. [1,2] Yield: 76%, m.p.:91.1  C.

13C NMR investigations of molecular order of rod‐like, bent‐core, and thiophene mesogens

“…The usefulness of the 2D-SLF spectroscopy for providing information on the molecular order and thereby on the dynamics and the topology of mesogens has been demonstrated. The combination of 13 C chemical shifts and 13 C─ 1 H dipolar [51] MN-2 SmA Veeraprakash et al [83] MN-3 SmC, SmB Veeraprakash et al [83] MN-4 Nematic, SmA, SmC Veeraprakash et al [82] MN-5 SmA Pratap et al [64] MN-6 SmA Pratap et al [64] MN-7 Nematic Santhosh Kumar Reddy et al [60] MN-8 SmC, SmB Santhosh Kumar Reddy et al [60] Abbreviations: SmA, smectic A; SmB, smectic B; SmC, smectic C.…”

“…Thus, the scaling factor of the 2D SAMPI-4 and PELF sequences were estimated to be respectively 1.09 and 0.42. Accordingly, the F 1 dimension frequency scale was adjusted during the data processing [63] M-23 Nematic Santhosh Kumar Reddy et al [47] M-24 Nematic, SmA, SmC Pratap et al [64] Abbreviations: SmA, smectic A; SmC, smectic C. to take care of the scaling factor, so that the actual dipolar frequencies can be read out directly from the 2D plots and 1D cross sections. The extracted 13 C─ 1 H dipolar couplings from these experiments can be related to the order parameters of a particular ring by considering its local symmetry.…”

“…Significant effort has been made to investigate thiophenebased mesogens by our group using 13 C NMR measurements. [47,51,58,[60][61][62][63][64][82][83][84][85][86] It was well recognized that the replacement of phenyl ring with thiophene in mesogen results in decrease of melting point, increase of optical anisotropy, reduction in viscosity, promotion of negative dielectric anisotropy, and fast switching times. [87,88] Samulski et al showed that replacement of phenyl ring with thiophene would bring profound changes in molecular shape.…”

“…[47] FIGURE 16 Two-dimensional SAMPI-4 spectrum of M-23 mesogen at 100°C in nematic phase (Adapted with permission from Santhosh Kumar Reddy et al [47] Copyright 2016 American Chemical Society) FIGURE 17 Two-dimensional PELF spectrum of M-24 in smectic C at 195°C. (Adapted from Pratap et al [64] with permission of the publisher Taylor & Francis Ltd, http://www. tandfonline.com)…”

“…Following the work on 3-hexyl thiophene mesogens, another class of π-conjugated mesogens in which 3-cyano thiophene at the center of the core flanked by phenyl or biphenyl rings and terminal alkoxy chains were investigated (M-24). [64] Due to the bent-core nature of the shape, the lone CH vector of thiophene was easily identified in the 2D spectrum ( Figure 17) from the rest of the contours, and the order parameters of thiophene, as well as other rings, were determined from 13 C─ 1 H dipolar couplings (Table 9). Due to the presence of cyano group at the central thiophene ring, the molecular dipole has transverse component in addition to parallel component along the long axis of the molecule.…”