Molecular dynamics of pyrene based discotic liquid crystals confined in nanopores probed by incoherent quasielastic neutron scattering Makha Ndao, ab Ronan Lefort, * a Carole V. Cerclier, ac R ´ emi Busselez, ad Denis Morineau, a Bernhard Frick, e Jacques Ollivier, e Andriy V. Kityk f and Patrick Huber g Semiconducting nanowires made of discotic columnar liquid crystals can be obtained by impregnation into solid nanoporous templates, and provide new opportunities to tailor devices for organic electronics with promising charge carriers transport properties. These properties are tightly related to the self-assembly and molecular dynamics of the discotic columns inside the nanowires. We recently studied and rationalized the formation of different nanostructures in the columnar phase of pyrene derivative discotics nanoconfined in anodic alumina and porous silicon templates ([Cerclier et al., J. Phys. Chem. C, 2012, 116, 18990–18998, Kityk et al., Soft Matter, 2014, 10, 4522–4534]). We now present the molecular dynamics of nano-confined pyrene derivative mesogenic phases as studied by incoherent quasielastic neutron scattering over a broad range of correlation times. The combination of backscattering and time- of-flight techniques has allowed to describe the nature of the molecular motions at play on the pico to nanosecond time scale. The dynamics of the columnar phase is dominated by fluctuations of the lateral chains, while the onset of larger amplitude motions like whole-body reorientations and slow center-of- mass translational diffusion occurs at high temperature in the isotropic phase. Interestingly, nano- confinement does not qualitatively alter the nature of the molecular dynamics, but essentially blocks the long range translational motions and induces broader distributions of correlation times of the fastest local relaxations. 1 Introduction Discotic columnar liquid crystals (DCLC) are organic materials able to self-arrange into mesogenic columnar orders in a dened temperature range. 1–4 This ability is due to the usually planar disc-like geometry of the molecule, ensured by a rigid polyaromatic core surrounded by so functional branches (usually simple alkyl tails). 5–10 These discotic molecules tend to form an isotropic liquid phase at high temperature, and stack on top of each other in columns at lower temperatures. The columns also self-assemble into a highly orientationally ordered hexagonal lattice, 11,12 that nevertheless does not exhibit trans- lational order along the column axis because of the liquid-like mobility of the exible branched chains that ll in the inter- columnar space. This liquid crystalline structural stacking is accompanied by a strong overlap of the aromatic p electronic orbitals, that propagates along the columns and gives rise to long-range transport of charge-carriers. This one dimensional charge transfer pathways confer to DCLC materials unique properties suitable for new organic electronic applications. In particular, their exceptional charge mobility and short lived excitonic response compared to conductive polymers has raised considerable interest on DCLC based devices such as molecular transistors or solar cells. 5,13–19 Up to now, the electronic and structural properties of bulk or thin lm materials have been extensively studied on typical discotics such as triphenylene and hexa-peri-hexabenzocor- onene (HBC) derivatives. 20–23 Recently, our group has also focused on a new generation of pyrene based DCLCs. 15,24–27 Clearly, applicability of DCLC in operational devices strongly relies on the control of their growth into large monodomains. Usually, columns exhibit planar (edge-on) alignment in open thin lms, while they align homeotropically when sandwiched a Institut de Physique de Rennes (IPR), UMR-CNRS 6251, Universit´ e de Rennes 1, Campus de Beaulieu, 35042 Rennes, France. E-mail: ronan.lefort@univ-rennes1.fr b Institut de Chimie de Clermont-Ferrand (ICCF) – UMR-CNRS 6296, Universit´ e Blaise Pascal, Campus des C´ ezeaux, 63171 Aubiere Cedex, France c Institut des Mat´ eriaux Jean Rouxel (IMN), Universit´ e de Nantes, CNRS, 2 rue de la Houssiniere, BP32229, 44322 Nantes Cedex 3, France d Institut des Mol´ ecules et Mat´ eriaux du Mans, UMR-CNRS 6283, Universit´ e du Maine, 72085 Le Mans Cedex 9, France e Institut Laue-Langevin (ILL), 71 avenue des Martyrs, 38000 Grenoble, France f Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland g Institute of Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany Cite this: RSC Adv. , 2014, 4, 59358 Received 29th September 2014 Accepted 4th November 2014 DOI: 10.1039/c4ra13032d www.rsc.org/advances 59358 | RSC Adv., 2014, 4, 59358–59369 This journal is © The Royal Society of Chemistry 2014 RSC Advances PAPER