An experimental and computational study of calamitic and bimesogenic liquid crystals incorporating an optically active [2,2]-paracyclophane

Figures & data

Figure 1. The DFT(B3LYP/6-311G(dp)) optimised geometry of both the S (left) and R (right) forms of 4-fluoro[2,2]paracyclophane.

short-legendScheme 1.

Figure 2. Plot of the reciprocal pitch (1/P, μm⁻¹) as a function of concentration (wt %) for binary mixtures of 1 in 5CB.

Figure 3. The molecular structures of compound 2 (Cr 138.3 Iso) and the related dimer CB6OCB (Cr 102 TB 110.5 N 154.2 Iso. Liq.) [15,17].

Table 1. Transition temperatures (°C) and pitch lengths (P_N*, μm) for mixtures A – I and extrapolated values (*) for compound 1. Measurements were performed at 20°C for all materials which correspond to the reduced temperatures (Tr, T_N-Iso/T) indicated.

Mix No. (wt% 1)	MP	N* – Iso	PN* (μm)	Tr (a.u.)
A (0.76)	22.9	34.8	82.8	0.63
B (1.00)	17.9	34.7	64.4	0.63
C (1.65)	16.0	34.5	41.4	0.64
D (2.35)	15.4	34.3	30.5	0.64
E (3.03)	15.4	34.1	24.5	0.65
F (4.14)	15.1	33.7	18.4	0.65
G (5.89)	15.5	33.1	14.7	0.66
H (7.50)	14.9	32.6	11.0	0.67
I (9.09)	14.9	32.4	9.2	0.68
1 (100)	41.8 [44.0]	5.0 [2.6]	0.88*	-

Table 2. Transition temperatures (°C), associated enthalpies of transition [kJ mol⁻¹] and pitch lengths (P_N*, μm) for mixtures A – F and extrapolated values (*) for compound 2. # The pitch of mixture A was too long (>100 μm) to be measured by the Cano Wedge method. Measurements were performed at 20°C for all materials which corresponds to the reduced temperatures (Tr, T_N-Iso/T) indicated.

Mix No. (wt% 2)	MP	N* – Iso	PN* (μm)	Tr (a.u.)
A (0.46)	22.2	34.9	#	0.63
B (1.10)	22.1	34.9	64.4	0.63
C (1.63)	15.5	34.7	41.4	0.63
D (2.26)	15.5	34.7	27.6	0.63
E (2.70)	15.2	34.5	23.0	0.64
F (3.83)	15.0	34.4	14.7	0.64
2 (100)	138.3 [38.3]	19.9*	0.52*	-

Figure 4. Plot of the reciprocal pitch (1/P, μm⁻¹) as a function of concentration (wt %) for binary mixtures of 2 in 5CB.

Figure 5. Plot of the energy relative to the lowest conformer (kJ mol⁻¹) as a function of the indicated torsional angle (τ, °) for p-terphenyl (a) and (R) 4-biphenyl-[2,2]-paracyclophane (b) as calculated at the wB97XD/6-31G(d,p) level of DFT. Spline fits (solid lines) are presented as a guide to the eye.

Figure 6. (A) The wB97XD/6-31G(d,p) minimised geometry of compound 2; (B) histogram plot of the probability of a given bend angle – defined as the angle between the long axis of each mesogenic unit – for CB6OCB and compound 2 determined using the AM1 semi empirical method as described in ref [15].

Figure 7. A hypothetical [2,2] paracyclophane in which both rings are incorporated into the mesogenic unit. When three of the four R groups are different the resulting material is chiral.

Archbold CT, Mandle RJ, Andrews JL, et al. Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases. Liq Cryst. 2017;1–10. DOI:10.1080/02678292.2017.1360954

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Paterson DA, Gao M, Kim YK, et al. Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB. Soft Matter. 2016;12:6827–6840.

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