title: Chiral power change upon photoisomerization in twisted nematic liquid crystals.
abstract: In this work, we use the photoisomerization of azobenzenes, a phenanthrospirooxazine, and a fulgide in a twisted nematic liquid crystalline phase to change the chiral twisting power of the system. The changes are probed by the rotatory power of linearly polarized light. Time resolved and steady state experiments are carried out. The chiral change and the photoisomerization process have similar characteristic recovery times and activation energy, thus probing that the change is induced by the modification in the chemical composition of the photochromic dopant system. The amplitude of the light twisting power change correlates with the order change in the liquid crystal (LC) but not with the modification in the absorption characteristics of the system. This indicates that the driving force of the chiral change is the microscopic order modification in the LC phase that affects the helical pitch of the phase.
authors.affiliation: INQUIMAE and Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428 Ciudad de Buenos Aires, Argentina; CIBION, Centro de Investigaciones en Bionanociencias "Elizabeth Jares-Erijman", Godoy Cruz 2390, 1425 Ciudad de Buenos Aires, Argentina. Electronic address: sabrina.simoncelli@gmail.com.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Simoncelli
authors.affiliation: INQUIMAE and Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428 Ciudad de Buenos Aires, Argentina; CIBION, Centro de Investigaciones en Bionanociencias "Elizabeth Jares-Erijman", Godoy Cruz 2390, 1425 Ciudad de Buenos Aires, Argentina. Electronic address: pedro.aramendia@cibion.conicet.gov.ar.
authors.forename: Pedro F
authors.initials: PF
authors.lastname: Aramendía
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D007536:Isomerism; D008027:Light; D050866:Liquid Crystals / Q000737:chemistry*; D044367:Phase Transition; D055668:Photochemical Processes; D013816:Thermodynamics
chemical_list: D001391:Azo Compounds; C009850:azobenzene
keywords: Azobenzenes; Chiral power change; Liquid crystals; Photochromism; Photoisomerization; Spirooxazine