Heliconal nematic twist bend (NTB) phases are usually not well oriented in planar commercial cells, even in thin (~1 µm) ones where a micron-sized periodic texture is usually observed [1,2,3] (see Fig.1-a). The origin of the stripe patterns is attributed to the rapid shrinking of the pseudo-layers below the N-NTB phase transition temperature, which yields an undulation instability. The observed periodicity is found to be twice the cell gap [1].
We have explored the effect of the strength of the anchorings of the substrates on the resulting patterns. We used polymer aligning layers of tunable azimuthal and zenithal strengths to design liquid crystal cells with surface anchorings ranging from ultraweak to strong. We then have studied the patterns formed by the NTB phase of 1,7-bis-4-(4-cyanobiphenyl) heptane (CB7CB). We will show how the period of the stripes can be varied in a large range in cells of the same thickness but with different anchoring preparations. With adequate anchoring conditions (see Fig.1-b-c), an excellent and spontaneous planar alignment of the NTB phase of CB7CB can be obtained much below the phase transition temperature.
[1] Panov V.P. et al; Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogenswith a Nematic-Nematic Transition and a Negative Elastic Constant; Phys. Rev. Lett. ; 105; 167801; 2010.
[2] Challa P. K. et al; Twist-bend nematic liquid crystals in high magnetic fields; Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys.; 89; 060501; 2014.
[3] Vaupotič N. et al.; Polarization Gratings Spontaneously Formed from a Helical Twist‐Bend Nematic Phase; Chem. Phys. Chem.; 19; 2566; 2018.

Heliconal nematic twist bend (NTB) phases are frequently found at high temperatures. In the last years the search of stable room-temperatures NTB phases has led to the synthesis of new compounds [1] and to the design of multicomponent systems. Mixtures of NTB compounds with nematogens ,such as 4-Cyano-4'-pentylbiphenyl (5CB) dimeric liquid crystal 1,7-bis(4-cyanobiphenyl-4-yl) heptane (CB7CB) decrease strongly the temperature range of the NTB phase and tune the optical, thermal and dielectric properties of NTB [2]. In this work we have explored the physical properties of mixtures of CB7CB with several smectogens with a particular focus on 4′-octyl-4-biphenylcarbonitrile (8CB). The 8CB/CB7CB phase diagram reveals striking features compared to the 5CB/CB7CB one. Despite their macroscopic resemblance, SmA and NTB domains appear incompatible and remain separated by a nematic phase that extends to very low temperature (-20°C) at a CB7CB fraction of ϕ_c≈20%. We have characterized the optical, thermal, dielectric and anchoring properties of the N and NTB phases of the mixtures. Compared to the pure CB7CB system, the N phase shows unusual behavior over a large range of composition and reveals strong pre-transitional effects when approaching ϕ_c. We also found that, for specific aligning substrates, adding 8CB to CB7CB drastically changes the anchoring properties (fig1) facilitating homeotropic alignment.
[1] Yuan Wang, Quan Li; Room temperature heliconical twist-bend nematic liquid crystal; Cryst. Eng. Comm; 17; 2778-2782; 2015.
[2] Nina Trbojevic and Mamatha Nagaraj; Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases; Phys. Rev. E ;96; 052703; 2017.

Dye encapsulation into host single-walled carbon nanotubes is an elegant way to create hybrid nano-systems with tunable opto-electronic properties. To this aim, different kinds of molecules (either electron donor or acceptor, absorbing either in the blue or the red visible range) are encapsulated into metallic or semiconducting nanotubes displaying different diameters. Up to now, we have mainly studied encapsulated quaterthiophene derivatives (4T), tetracyanoquinodimethane (TCNQ) and phthalocyanine (MPc) molecules. In this work, we discuss the supramolecular organization of dyes inside the nanotube, the optical properties and the charge transfer for some of our hybrid systems. For instance, using Raman spectroscopy, a significant electron transfer is reported with 4T, whose magnitude strongly depends on the nanotube diameter, and on the metallic or semiconducting character. Experiments also suggest a photo-activated electron transfer for small diameter (~9 Å) semiconducting and metallic tubes. Confinement of electron donor (4T) (respectively electron acceptor (TCNQ)) into small diameter tubes leads to a red shift (blue shift) of the optical absorption energy and an increase (decrease) of the photoluminescence intensities, evidenced by the photoluminescence excitation maps.

Dye confinement into carbon nanotube significantly affects the electronic charge density distribution of the final hybrid system. Using the electron-phonon coupling sensitivity of the Raman G-band, we quantify experimentally how charge transfer from thiophene oligomers to single walled carbon nanotube is modulated by the diameter of the nano-container and its metallic or semiconducting character. This charge transfer is shown to restore the electron-phonon coupling into defected metallic nanotubes. For sub-nanometer diameter tube, an electron transfer optically activated is observed when the excitation energy matches the HOMO-LUMO transition of the confined oligothiophene. This electron doping accounts for an important enhancement of the photoluminescence intensity up to a factor of nearly six for optimal confinement configuration. This electron transfer shifts the Fermi level, acting on the photoluminescence efficiency. Therefore, thiophene oligomer encapsulation allows modulating the electronic structure and then the optical properties of the hybrid system.

The monomeric chlorophyll, Chl(D1), which is located between the PD1PD2 chlorophyll pair and the pheophytin, Pheo(D1), is the longest wavelength chlorophyll in the heart of Photosystem II and is thought to be the primary electron donor. Its central Mg2+ is liganded to a water molecule that is H-bonded to D1/T179. Here, two site-directed mutants, D1/T179H and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus elongatus, and characterized by a range of biophysical techniques. The Mn4CaO5 cluster in the water-splitting site is fully active in both mutants. Changes in thermoluminescence indicate that i) radiative recombination occurs via the repopulation of *Chl(D1) itself; ii) non-radiative charge recombination reactions appeared to be faster in the T179H-PSII; and iii) the properties of PD1PD2 were unaffected by this mutation, and consequently iv) the immediate precursor state of the radiative excited state is the Chl(D1)(+)Pheo(D1)(-) radical pair. Chlorophyll bleaching due to high intensity illumination correlated with the amount of O-1(2) generated. Comparison of the bleaching spectra with the electrochromic shifts attributed to Chl(D1) upon Q(A)(-) formation, indicates that in the T179H-PSII and in the WT*3-PSII, the Chl(D1) itself is the chlorophyll that is first damaged by O-1(2), whereas in the T179V-PSII a more red chlorophyll is damaged, the identity of which is discussed. Thus, Chl(D1) appears to be one of the primary damage site in recombination-mediated photoinhibition. Finally, changes in the absorption of Chl(D1) very likely contribute to the well-known electrochromic shifts observed at similar to 430 nm during the S-state cycle.

The conformation of single-chain nanoparticles (SCNPs) in presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders. A model describing the scattering of aggregating polydisperse SCNPs has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Two different crowders – of low and high molecular weight, respectively – are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and shall contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects, and in particular the effect of crowding on biomacromolecules.