Photo-stimulated electro-optic response of liquid-crystalline system with<i>trans-cis</i>photo-isomerizable agent

A rather strong photo-stimulated enhancement of photo-induced bend flexoelectric effect based on trans-cis photoisomerization of azo bond was found in a guest-host system formed from the nematic liquid crystal (LC) N-(4-methoxybenzylidene)-4-butylaniline (MBBA) as a host, and the azobenzene LC 4-hexyloxybenzoloxy-4'-cyanoazobenzene, as a guest photoactive agent at 1 wt.% concentration. Upon application of electric field, thin homeotropic layers of thickness 100 pm containing this photo-sensitized LC mixture were investigated as subjected to a relatively weak illumination with UV light (λ = 375 nm, from narrow-band light-emitting diode, LED). The stimulation of the photoactive electro-optic response of azobenzene-doped MBBA (owing to enhanced photo-induced bend flexoelectric effect driven by the photo-isomerizable dopants) was achieved by pre-resonant excitation of the photoactive agent. The degree of the effect measured is of potential interest for thin-film photoactive electro-optic applications. The UV light-induced effect in azobenzene-doped MBBA was reversible; the back (relaxation) process was stimulated by light in the blue from a LED with broadband spectrum centered at 455 nm.