Molecular Shape, Electronic Factors, and the Ferroelectric Nematic Phase: Investigating the Impact of Structural Modifications

Abstract

The synthesis and characterisation of two series of low molar mass mesogens, the (4-nitrophenyl) 2-alkoxy-4-(4methoxybenzoyl)oxybenzoates (NT3.m) and the (3-fluoro-4nitrophenyl)2-alkoxy-4-(4-methoxybenzoyl)oxybenzoates (NT3F.m), are reported in order to investigate the effect of changing the position of a lateral alkoxy chain from the methoxy-substituted terminal ring to the central phenyl ring in these two series of materials based on RM734. All members of the NT3.m series exhibited a conventional nematic phase, N, which preceded the ferroelectric nematic phase, N F , whereas all the members of the NT3F.m series exhibited direct N F -I transitions except for NT3F.1 which also exhibited an N phase. These materials cannot be described as wedgeshaped, yet their values of the ferroelectric nematic-nematic transition temperature, T N F N , exceed those of the corresponding materials with the lateral alkoxy chain located on the methoxy-substituted terminal ring. In part, this may be attributed to the effect that changing the position of the lateral alkoxy chain has on the electronic properties of these materials, specifically on the electron density associated with the methoxy-substituted terminal aromatic ring. The value of T NI decreased with the addition of a fluorine atom ortho to the nitro group in NT3F.1, however, the opposite behaviour was found when the transition temperatures of the N F phase were compared which are higher for the NT3F.m series. This may reflect a change in the polarity and polarizability of the NT3F.m series compared to the NT3.m series. Therefore, it is suggested that, rather than simply promoting a tapered shape, the role of the lateral chain in inhibiting anti-parallel associations and its effect on the electronic properties of the molecules are the key factors in driving the formation of the N F phase.

To Be or Not To Be Polar: The Ferroelectric and Antiferroelectric Nematic Phases

“…In order to stabilize the ferroelectric nematic phase and promote the parallel alignment of the calamitic molecules, the amplitude of the charge density waves at either end of the molecule should be reduced. We have reported previously that this may be achieved using a fluorine atom at the ortho position to the terminal nitro group, rather than a hydrogen atom, in order to reduce the electron density associated with the nitro group. , In this case, however, we are instead changing the electron density associated with the ring to which the terminal alkyl or alkyloxy chain is attached. An alkyloxy chain is a stronger activating functional group compared to an alkyl chain due to its enhanced electron-donating character, which means that there is a greater electron density in the terminal ring of the n OEC3F series compared to that of the n EC6F series (Figure ).…”

“…The high fluidity of the N F phase combined with its polar properties immediately caught the attention of scientists around the world due to not only its huge application potential but also its fundamental significance as a spontaneously ferroelectric fluid. The N F phase became one of the hottest topics in liquid crystal research. − Owing to the fluid nature of the N F phase, a uniform polarization direction can be obtained in large areasa key to realizing its application potential . However, the question arises whether the competitive interactions that drive the formation of the N F phase can also lead to other complex structures as is the case with the improper ferroelectric liquid crystal phases.…”

Achieving enhanced second-harmonic generation in ferroelectric nematics by doping D–π–A chromophores

“…Structural modifications were indicated to also affect β , with those resulting in an increase in β also leading to enhanced NLO properties of the dye. Consistent with this design principle, for many fluorinated N F LC molecules, 18,30,34,42–44 the introduction of fluorine atoms has been shown to increase the dipolar interaction and broaden the temperature range of the N F phase.…”

Rapid, solvent-minimized and sustainable access to various types of ferroelectric-fluid molecules by harnessing mechano-chemical technology

“…In the final stage (Fig. 6f), aryl iodine (17) and deprotected ethynyl biphenyl parts (21) were linked by the modified MC-SHC protocol, in which the LAG method (DIOX, Z = 0.3) was used. The modified MC-SHC reaction was completed at 80 1C for 20 min to obtain target compound (22).…”

“…Moreover, notable physical phenomena [9][10][11][12] and structures 13,14 are observed owing to the coupling between the polarization and fluidity. Since these discoveries, research into molecular design and synthesis of N F LCs and SmA F LCs has been launched 7,[15][16][17][18][19][20][21][22] toward a clear understanding of the underlying mechanism, 23,24 and development of state-of-the-art materials based on them. 25,26 However, typical synthetic routes of LC materials are through a multistep pathway that entirely rely on the traditional solution chemical (SC) synthesis.…”