Original Paper

Journal of Sol-Gel Science and Technology

, Volume 56, Issue 1, pp 7-18

Preparation and photophysical properties of monomeric liquid-crystalline azo-dyes embedded in bulk and film SiO2-sonogel glasses

  • V. Torres-ZúñigaAffiliated withNonlinear Optics Lab. Centro Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, CCADET-UNAM
  • , O. G. Morales-SaavedraAffiliated withNonlinear Optics Lab. Centro Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, CCADET-UNAM Email author 
  • , E. RiveraAffiliated withInstituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, IIM-UNAM
  • , R. Castañeda-GuzmánAffiliated withNonlinear Optics Lab. Centro Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, CCADET-UNAM
  • , J. G. BañuelosAffiliated withNonlinear Optics Lab. Centro Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, CCADET-UNAM
  • , R. Ortega-MartínezAffiliated withNonlinear Optics Lab. Centro Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, CCADET-UNAM

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Abstract

SiO2-based bulk and film sol–gel hybrid materials were prepared with a family of novel liquid crystalline (LC) amphiphilic azo-dyes bearing oligo(ethylene glycol) spacers (named here RED-PEG-n, n = 2, 3, 4, 6). The catalyst-free-sonogel route was implemented to produce optically active hybrid monoliths and spin-coated films with these materials. Comprehensive morphological, thermal, photo-acoustic and spectroscopic sample characterizations were performed in order to elucidate the physical properties of these novel compounds within the sonogel environment. Film samples were also studied via the nonlinear optical (NLO) second harmonic generation (SHG)-Maker fringes technique. Results show that the chromophores were homogeneously embedded within the highly pure SiO2-sonogel network, showing a clear thermotropic mesogenic behavior. The push–pull structure of the implemented azo-dyes allowed effective electrically-induced monomeric alignment within the sonogel confinement; thus, stable quadratic NLO-SHG-activity in the organic–inorganic film samples was achieved despite the lack of glass transition temperature (T g ) of the guest LC-compounds.

Keywords

Azo-dyes Liquid crystals Thin films Sol–gel Sonogel Hybrid materials Optical materials Nonlinear optics