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

• Published in: Journal of sol-gel science and technology 2010-10, Vol.56 (1), p.7-18
• Main Authors: Torres-Zúñiga, V., Morales-Saavedra, O. G., Rivera, E., Castañeda-Guzmán, R., Bañuelos, J. G., Ortega-Martínez, R.
• Format: Article
• Language: English
• Subjects: Azo dyes; Catalysis; Ceramics; Chemistry; Chemistry and Materials Science; Chromophores; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Composites; Crystal structure; Crystallinity; Dyes; Ethylene glycol; Exact sciences and technology; General and physical chemistry; Glass; Glass transition temperature; Inorganic Chemistry; Liquid crystals; Materials Science; Nanotechnology; Natural Materials; Optical activity; Optical and Electronic Materials; Original Paper; Physical properties; Second harmonic generation; Silicon dioxide; Sol-gel processes; Spin coating; Temperature; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-010-2265-y

SiO 2 -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 SiO 2 -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.