UV‐induced in‐plane anisotropy in layers of mixture of the azo‐dyes SD‐1/SDA‐2 characterized by spectroscopic ellipsometry

Abstract

The optical properties of the azo‐dyes SD‐1/SDA‐2, which are used for photoaligning of liquid crystals (LCs), are investigated with Variable Angle Spectroscopic Ellipsometry (VASE). Films of mixture of SD‐1/SDA‐2 are deposited by spin coating on silicon wafers. The estimated thickness is approximately 10 nm. To achieve photo‐induced anisotropy, one of the samples is illuminated during 15 minutes with linearly polarized UV light followed by thermal stabilization during 1 hour at 150 °C. VASE measurements are performed in the wavelength range 200–1350 nm at several angles of incidence and at different sample orientations. Dielectric functions of azo‐dye films without/with polarized UV light illumination were modelled using an ensemble of Lorentz oscillators. The results confirm the diffusion model proposed recently for explanation of the formation of the photo‐induced order in azo‐dye films under the action of polarized light. Refractive indices, their wavelength dispersion and thicknesses of films of SD‐1/SDA‐2 are reported here. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced and Polarization-Dependent Coupling for Photoaligned Liquid Crystalline Conjugated Polymer Microcavities

“…All spectra comprise either one or several inhomogeneously broadened distributions of chain-delocalized exciton transitions (E X PFO peaked at around 3.23 eV, E X F8BT 1 and E X F8BT 2 peaked at respectively 3.82 and 2.70 eV, and E X F6T2 at 2.79 eV), with higher lying features above 5 eV associated with ring-localized fluorene states. 60 Following photoalignment of an SD1 spin-coated film in the in-plane y direction, the optical components n x , n y , n z , k x , k y , and k z were extracted using a biaxial anisotropic model 61 and are shown in Figure 1(a). As expected, the alignment brings about intense n y , k y optical components compared to their perpendicular counterparts n x , k x .…”

Photoalignment of Liquid Crystals: Applications to Fast Response Ferroelectric Liquid Crystals and Rewritable Photonic Devices

“…27,40−42 Good homogeneous alignment was detected with polarized microscopy and FTIR spectroscopy methods. The alignment technique presented here is based on proper development of photoaligning azo-dye materials 43 and is a promising non-contact method for LC orientation in complex photonic crystal structures. The order parameter S of LC has been obtained from FTIR spectroscopy data and has demonstrated good alignment quality.…”

Exciton-Polaritons in Uniaxially Aligned Organic Microcavities

“…As the polymer chains tend to lie in the plane of the film, [53][54][55] the resulting optical constants are well fitted 27,56 with excitation states lying above 5 eV associated to ring-localized fluorene states. 57 Following photoalignment of an SD1 spincoated film in the in-plane y direction, the optical components n x , n y , n z , k x , k y , k z were extracted using a biaxial anisotropic model 58 and are shown in Figure 1 to the number of underlying contributing dipoles, we calculate the ratio R = 1 − fx fx+fy where f x,y is the oscillator strength in the corresponding direction and estimate the total percentage of dipoles aligned in the y direction. For all excitons, R exceeds 83% (calculated for E X F8BT 1 ) with a maximum value of 94% (for E X F6T2 ) underlining the remarkable alignment quality.…”