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In the field of supramolecular chemistry, anion recognition was explored at a later stage. However, nowadays, it has become a mature research area [1]. The formation of the host-guest receptor-anion complex is very often controlled by subtle interplay of several factors, including the structural and electronic complementarity between the two interacting partners. Receptor can form with guest hydrogen-bonding interaction, especially if it possesses strong hydrogen-bonded donor, such as NH group present in urea derivatives. Receptor-binding affinity could be additionally increased if more than one urea group is combined with several anions. We reported previously [2] anion binding properties of bis-urea derivative featuring a biphenyl spacer, 1, 1'-(4, 4'-biphenylene)bis(3-phenylurea) (1) (Fig. 1), through five receptor-anion complexes obtained using tetrabutylammonium salts, TBAX (X = AcO, H2PO4, Br, I and NO3). Herein we present influence of terminal substituents of 1 on binding properties of TBA anions, electron-deficient one due to the electron withdrawing effect of NO2 group (2), and electron-rich in which phenyl rings are replaced with naphthyl groups (3) (Fig. 1). X-ray structures of five receptor–anion complexes of 2 and 3 showed different solid-state architectures compared to that of 1. Solution studies and DFT calculations of anion-binding abilities of 2 and 3 will be also presented. References: [1] P.A. Gale, W. Dehaen, Anion Recognition in Supramolecular Chemistry, Springer, Berlin, 2010. [2] T. Grgurić, M. Petroselli, C. Bacchiocchi, M. Cametti, Z. Džolić, M. Cetina, Anion-templated assembly of biphenyl-bis-urea receptor, 27th Meeting of Chemists and Chemical Engineers, Veli Lošinj, October 5–8, 2021.

Liquid crystal (LC) dimers have attracted much interest as model compounds for liquid crystalline polymers [1,2], as well as building blocks in the development of new materials, for example, in the search for biaxial nematics. One example is provided by the class of symmetric dimers nBCB consisting of two cyanobiphenyl mesogens connected by a flexible (CH2)n alkyl chain spacer [3]. These dimeric LCs show pronounced odd-even effect in the nematic-isotropic transition temperatures and entropy. Moreover the possibility that a biaxial nematic phase could occur has been suggested [3]. Here we study the highly flexible odd-spacer dimer α,ω-bis(4'-cyanobiphenyl-4-yl)undecane (11BCB) by means of the Electron Spin Resonance (ESR) spin probe technique, already successfully employed in similar [4] and other complex systems [5] for its high sensitivity. We present results of different ESR experiments performed on 11BCB (here a cholestane-type nitroxide spin probe, 3β-doxyl-5α-cholestane (CSL) is used), with the aim of elucidating its behaviour, both from the point of view of the order and the molecular organization, as well as in terms of dynamics, issues about which very little is known as yet. The possibility that this system, which in view of its odd alkyl spacer should contain a high concentration of bent conformers, exhibits a biaxial phase has also been investigated. The experimental results show the clear presence of more than one contribution to the overall spectrum, which is typical of complex LC systems, that is of materials which display a coexistence of the spin probe close to different sites of the molecules, each one characterized by different degrees of alignment and dynamics [5]. Thus, the spectra can be well reproduced resorting to a model which takes into the account two fractions of the LC molecules, one ordered along a common director and the other mainly randomly oriented. Rotation experiments point out to the possible presence of a smectic (Sm) phase, as the mesogens do not reorient upon changing the magnetic field position. Coupling these findings to those of atomistic Molecular Dynamics simulations performed on the same system, we can deduce the CSL preferred location with respect to the LC dimers and their possible conformations, and therefore suggest a model for the dimer organization. Acknowledgments: This work was supported by the EU-STREP project “Biaxial Nematic Devices” (BIND)FP7-216025. References [1] A. C. Griffin and T. R. Britt, J. Am. Chem. Soc. 103, 4957 (1981). [2] C. T. Imrie and P. A. Henderson, Chem. Soc. Rev. 36, 209 (2007); I. Miglioli, L. Muccioli, S. Orlandi, M. Ricci, R. Berardi, C. Zannoni, Theor. Chem. Acc. 118, 203 (2007) [3] P. J. Barnes, A. G. Douglass, S. K. Heeks and G. R. Luckhurst, Liq. Cryst. 13, 603 (1993). [4] C. J. Dunn, P. J. Le Masurier and G. R. Luckhurst, Phys. Chem. Chem. Phys. 1, 3757 (1999) [5] C. Bacchiocchi, I. Miglioli, A. Arcioni, I. Vecchi, K. Rai, A. Fontecchio and C. Zannoni, J. Phys. Chem. B 113, 5391 (2009)

Electron Spin Resonance (ESR) spin probe spectroscopy technique is used to investigate the two phase Holographic Polymer Dispersed Liquid Crystal (HPDLC) system made of liquid crystal (LC) confined periodically in a polymer matrix. HPDLCs are prepared using two beam laser interference set up at 532 nm wavelength on the prepolymer mix [1] consisting of LC, a monomer and a light sensitive photoinitiation dye. Polymerization at the bright regions of the interference pattern causes the diffusion of the liquid crystal to the dark regions forming a regular array of nanosized droplets embedded in a polymer matrix. A beam of light shone across the HPDLC reflects specific wavelengths of light, depending on the periodicity of the grating structure. These systems have extensive application in the fields of telecom and spectroscopy [2], and in reflective displays [3]. Several microscopic and spectroscopic techniques were used to understand both droplets morphology and behaviour, ranging from SEM and AFM microscopy [2] to Nuclear Magnetic Resonance using deuterated 5CB LC [4] and protonated LC; however a better understanding of the director configuration inside the droplets is fundamental to improve the diffraction properties and the switching performance of HPDLCs. To this purpose the study was further extended by conducting ESR spectroscopy [5] on HPDLCs based on commercially viable LC BL038 by doping with a stable nitroxide free radical spin probe. The analysis was conducted for various temperatures ranging from the nematic to the isotropic phase of the LC to evaluate the effect of confinement on HPDLC local order and dynamics compared to bulk characteristics. At 283 K, below the LC nematic-isotropic transition temperature (TNI), the sample shows a peculiar equilibrium between a rigid-limit-like and an isotropic phase in approximately a 50:50 proportion. Increasing the temperature, the rigid-limit fraction decreases rapidly to about 5% while an ordered contribution, in the form of a relatively narrow distribution of nematic domains (quasi-monodomain) aligned along the magnetic field, begins to appear and can still be observed by a signature lineshape up to 373.2 K (the bulk BL038 TNI). The fractional contribution of this phase increases by field cooling the sample and decreases upon a zero field cooling treatment, with good reproducibility, and it occurs only along a direction parallel to the HPDLC droplet planes. The results are in agreement with the assumption of droplets stretched along the grating vector with homeotropic LC alignment at the polymer interface which induces a cylindrical (2D) distribution of local LC domain directors. Only when the uniform magnetic field is normal to the cylinder axis a fraction of this 2D distribution can be aligned to form the observed quasi-monodomain. References: [1] M. L. Ermold, K. Rai, A. K Fontecchio, J. Appl. Phys., 97, 104905 (2005). [2] T. J. Bunning et al., Annu. Rev. Mater. Sci., 30, 83 (2000). [3] J. Qi and G. P. Crawford, Displays, 25, 177 (2004). [4] M. Vilfan, B. Zalar et al., Phys. Rev. E, 66, 021710 (2002). [5] A. Arcioni, C. Bacchiocchi, I. Vecchi, G. Venditti, C. Zannoni, Chem. Phys. Lett., 396, 433 (2004).

We employ spin probe Electron Spin Resonance (ESR) spectroscopy to investigate the two phase Holographic Polymer Dispersed Liquid Crystal (HPDLC) system made of liquid crystal (LC) confined periodically in a polymer matrix. The spectroscopic analysis is conducted for various temperatures from the nematic to the isotropic phase of the LC to understand the orientation and behavior of the HPDLC. HPDLC are prepared using two beam laser interference set up at 532nm wavelength on the prepolymer mix [1] consisting of LC doped with a spin label, a monomer and a light sensitive photoinitiation dye. Polymerization at the bright regions of the interference pattern causes the diffusion of the liquid crystal to the dark regions forming a nanosize droplet structure. A beam of light shone across the HPDLC reflects specific wavelengths of light, depending on the periodicity of the grating structure. These systems have extensive application in the fields of telecom and spectroscopy, e.g. they can be used as switches to filter particular wavelengths of light in optical telecommunication applications [2]. The morphology and droplet behavior of HPDLC have been studied earlier employing Nuclear Magnetic Resonance using deuterated 5CB LC [3] and protonated LC by Crawford et al. Here we further extend the study by conducting ESR spectroscopy [4] on HPDLC based on commercially viable LC BL038 by doping with a stable nitroxide free radical spin probe and comparing it to its bulk state. We have determined the orientational order and the dynamics of the spin probe dissolved in the LC droplets, finding more order in the confined state with order reduction as the temperature is increased. Analysis of the droplet size, which varies from a range of 200nm to 300nm, and the interaction of the LC with the polymer matrix is also conducted. With this method we hope to further our understanding of the LC polymer interaction and improve its efficiency. References: [1] M. L. Ermold, K. Rai, A. K Fontecchio, J. Appl. Phys., 97, 104905 (2005). [2] T. J. Bunning et al., Annu. Rev. Mater. Sci., 30, 83 (2000). [3] M. Vilfan, B. Zalar et al., Phys. Rev. E, 66, 021710 (2002). [4] A. Arcioni, C. Bacchiocchi, I. Vecchi, G. Venditti, C. Zannoni, Chem. Phys. Lett., 396, 433 (2004).

We employ spin probe Electron Spin Resonance (ESR) spectroscopy to investigate the two phase Holographic Polymer Dispersed Liquid Crystal (HPDLC) system made of liquid crystal (LC) confined periodically in a polymer matrix. The spectroscopic analysis is conducted for various temperatures from the nematic to the isotropic phase of the LC to understand the orientation and behavior of the HPDLC. HPDLC are prepared using two beam laser interference set up of 532nm wavelength on the prepolymer mix [1] consisting of LC doped with a spin label,a monomer and a light sensitive photoinitiation dye. Polymerization at the bright regions of the interference pattern causes the diffusion of the liquid crystal to the dark regions forming a nanosize droplet structure. A beam of light shone across the HPDLC reflects specific wavelengths of light, depending on the periodicity of the grating structure. These systems have extensive application in the fields of telecom and spectroscopy, e.g. they can be used as switches to filter particular wavelengths of light in optical telecommunication applications [2]. The morphology and droplet behavior of HPDLC have been studied earlier employing Nuclear Magnetic Resonance using deuterated 5CB LC [3] and protonated LC by Crawford et al. Here we further extend the study by conducting ESR spectroscopy [4] on HPDLC based on commercially viable LC BL038 by doping with a stable nitroxide free radical spin probe and comparing it to its bulk state. We have determined the orientational order and the dynamics of the spin probe dissolved in the LC droplets, finding more order in the confined state with order reduction as the temperature is increased as seen in figure 1. Analysis of the droplet size, which varies from a range of 200nm to 300nm, and the interaction of the LC with the polymer matrix is also conducted. With this method we hope to further our understanding of the LC polymer interaction and improve its efficiency. References: [1] M. L. Ermold, K. Rai, A. K Fontecchio, J. Appl. Phys., 97, 104905 (2005) [2] T. J. Bunning et al., Annu. Rev. Mater. Sci., 30, 83 (2000) [3] M. Vilfan, B. Zalar et al., Phys. Rev. E, 66, 021710 (2002) [4] A. Arcioni, C. Bacchiocchi, I. Vecchi, G. Venditti, C. Zannoni, Chem. Phys. Lett., 396, 433 (2004).

Photoresponsive liquid crystal systems, formed by a nematic liquid crystal (LC) doped with azobenzene derivatives, are of great interest in view of their application as optical-switching and image-storing materials [1] and as model systems for more complex photoresponsive polymers [2]. The azo-derivative trans-cis reversible photo-isomerization can produce two types of photomodulation of the LC mesophase [3]: changes in the LC director orientation (“order-order” change) and shift of the phase transitions (“order-disorder” change). Qualitatively, the working principle of the photochemical phase transition is based on the change of molecular shape of the photochromic guest molecule: the trans form of the azobenzene derivative has a rodlike shape similar to that of the host LC, while the cis isomer destabilizes the LC phase because of its bent molecular shape. However, a detailed investigation of the relation between the azo-derivative molecular features and the changes in trans-host and respectively cis-host solute-solvent system is, to our knowledge, still lacking. Here we present the results of an ESR spin-probe study of the effects produced by both the trans and the cis forms of different p-azobenzene derivatives dissolved in 5CB on the order and dynamics of a nitroxide probe. In particular, we study the shift of the N-I phase transition temperature (TNI) and the changes in the temperature dependence of the order and their relationship with the composition of the mixture. Eight closely related non-mesogenic p-azobenzene derivatives with molecular formula 4-X-azobenzene (X= H, Br, F, CH3, CF3, OCH3, O-nBu, O-tBu) were used (at a mole fraction of 0.01 and 0.08). Even at the lower mole fraction studied the presence of the azo-compound caused, in all the cases, a depression of the TNI. The cis isomer slightly reduced the order of the 5CB nematic phase and, as expected, induced a larger TNI shift with respect to the trans isomer. At the higher molar fraction, we observed an analogous behavior with enhanced effects. In this case, we also detected with microscope investigations a biphasic region, near the TNI. The dynamics was essentially unaffected by the presence of the azo-compound in all the cases studied. These findings are currently examined to relate them to molecular properties, in particular changes of dipole moments or steric effects, but it seems that more refined theoretical interpretations and atomistic simulations will be required for a satisfactory rationalization. [1] K. Ichimura, Chem. Rev., 100, 1847 (2000). [2] H. Finkelmann, E. Nishikawa, G.G. Pereira and M. Warner, Phys. Rev. Lett., 87, 015501 (2001). [3] O. Tsutsumi, T. Shiono, T. Ikeda and G. Galli, J. Phys. Chem. B, 101, 1332 (1997); T. Ikeda, J. Mater. Chem., 13, 2037 (2003).

Electron Spin Resonance (ESR) technique has proven to be a powerful mean for investigating liquid crystals and model membranes from a molecular point of view [1]. Liquid crystals containing a suspension of silica particles of nanometric size (aerosil) present fascinating fundamental and applicative aspects. From the fundamental point of view, the interest in these “filled nematic” systems stems from the intricacies of the effect of a random perturbation on ordered phases. These complex systems also present technological interest in view of scattering displays exhibiting the so-called “memory effect” [2]. In this study we report on a comparison between the random disorder effects of an hydrophobic (R812) or an hydrophilic (A380) aerosil on the order and dynamics of the 3b-DOXYL-5a-cholestane spin probe in the liquid crystal 4-n-pentyl-40-cyanobiphenyl (5CB) using the ESR technique. Increasing the aerosil concentration up to 10 wt% the probe order parameter is depressed with a larger effect for the hydrophilic aerosil. The dynamics in the isotropic phase is of Arrhenius type and essentially concentration and aerosil-type independent. Deviations from this behavior are observed in the nematic even at 1 wt% of hydrophilic aerosil and are well represented by a Vogel–Fulcher–Tammann type law, suggesting that a glass-like state can be induced by a very small amount of random disorder. [1] L.J. Berliner (Ed.), Spin Labeling, Theory and Applications, Academic Press, New York, 1976. [2] Kreuzer M., Eidenschink R., in Liquid Crystals in Complex Geometries Formed by Polymer and Porous Networks, edited by Crawford G.P., Zumer S., chap. 3, 307-324, Taylor & Francis, London, 1996.

Liquid crystals containing a suspension of silica particles of nanometric size (aerosil) present fascinating fundamental and applicative aspects. From the fundamental point of view, the interest in these “filled nematic” systems stems from the intricacies of the effect of a random perturbation on ordered phases. According to the “Imry-Ma argument” an arbitrarily low amount of static disorder should suppress long range order in a large enough continuous symmetry system in three dimensions [1]. These systems also present technological interest in view of scattering displays exhibiting the so-called “memory effect” [2]. We have studied a system composed of either the hydrophobic (R812) [3] or the hydrophilic (A380) aerosils (Degussa) in the liquid crystal pentylcyanobiphenyl (5CB) using the ESR spin probe technique. The order parameter and the rotational diffusion coefficients of a cholestane spin probe have been determined as a function of temperature for different aerosil concentrations, near and above the gelation threshold. We find that an increasing concentration of aerosil destroys the local order instead of stabilising it, as it was suggested [4], and that the effect is stronger for the hydrophilic aerosil. The local dynamics has a smaller and more subtle dependence from the aerosil-type and concentration. In the isotropic phase, it is of Arrhenius type and essentially concentration and aerosil-type independent. This is quite surprising, in particular at 10 wt % of aerosil, when the sample is clearly a gel and does not flow. In the nematic phase, only the reorientation of the main molecular axis (tumbling rate) depends from the aerosil-type and concentration while the reorientation around this axis is unaffected. Moreover, deviations of the tumbling rate from the Arrhenius behaviour are clearly observed in the nematic phase even at 1 wt % of aerosil and are well represented by a Vogel-Fulcher-Tammann type law, suggesting that a glass-like state could be induced by an arbitrarily weak quenched disorder. The permanence of local fluidity can help rationalizing the fast switching response time of a filled nematic. On the other hand, the slowing of the dynamics, employed in the memory effect, appears to be essentially macroscopic. Information on the origin of the macroscopic viscosity can be obtained by studying the dependence of the degree of alignment of the local nematic domains from the annealing conditions of the sample (aerosil type, sonication, thermal history, field intensity, aging…). We observe that 1 wt % of hydrophilic aerosil is capable to prevent almost completely the reconstitution of a monodomain in a zero field cooled sample, whereas a monodomain can be easily formed even at 3 wt % of hydrophobic aerosil. This result suggests that the reconstitution of a monodomain requires the reorganization of an H-bond based aerosil network, which appears to be more impaired in the hydrophilic case. [1] Imry, Y.; Ma, S.K., Phys. Rev. Lett. 1975, 35, 199. [2] Kreuzer, M.; Eidenschink, R., in Liquid Crystals in Complex Geometries Formed by Polymer and Porous Networks, edited by Crawford, G.P.; Zumer, S., chap.3, 307-324, Taylor & Francis, London, 1996. [3] Arcioni, A.; Bacchiocchi, C.; Grossi, L.; Nicolini, A.; Zannoni, C., J. Phys. Chem. B 2002, 106, 9245. [4] Glushchenko, A.; Kresse, H.; Reshetnyak, V.; Reznikov, Y.; Yaroshchuk, O., Liq. Cryst. 1997, 23, 241.

EPR spin probe spectra of the liquid crystal phases exhibited, in the bulk, by the 1″,9″-bis(4-cyanobiphenyl-4’-yl)nonane (CB9CB) bent-shape dimer showed that, on cooling from the isotropic phase, this material forms a uniaxial nematic phase with a uniform director macroscopically aligned along the spectrometer field. Upon further cooling, a transition into the twist-bend nematic phase is observed after a biphasic region of approximately 4K. In this lower temperature nematic phase, the director does not appear to be macroscopically aligned. The non-uniform director distribution is modelled as a collection of monodomains tilted with respect to the magnetic field and orientationally distributed around the tilt direction.

The director configuration, the local order and the molecular-level reorientational dynamics (microviscosity) of the 5CB liquid crystal (LC) inside a polymer-stabilized LC (PSLC) cell prepared with the 4,4-bis(6-(acryloyloxy)hexyloxy)biphenyl (BAB6) diacrylic monomer have been studied with the EPR spin probe technique across the nematic and the isotropic phase of the LC. The cells made from glass slides, either clean or coated with an aligning layer, were filled with pure 5CB or with 0.5, 1.0 or 2.0wt% of BAB6, either in the monomeric state or polymerized. Local orientational order parameter () in the non treated cells was always slightly lower than in the coated ones and both were lower than in the bulk LC. Order appeared to be independent of polymerization state or BAB6 concentration up to 1.0wt%. Reorientational dynamics was essentially bulk-like in all cases, indicating that in our PSLC cells a full molecular mobility is retained. At the concentration of 2.0wt%, in the coated cell with polymerized BAB6, the monodomain did not reform after a 90 degrees rotation of the cell in the magnetic field, suggesting that the polymer network is, as expected, stabilizing the preexisting director configuration.