Effect of triphenylamine agents as screening moieties for electrostatic interaction in the nonlinear optical response of hybrid organic-inorganic films

A nonlinear optical (NLO) chromophore (2-(3-cyano-4-(4-((2-hydroxyethyl)(methyl)amino) styryl)-5,5-dimethylfuran-2(5H)-ylidene)malononitrile, abbr. FS) and a hole-transporting molecular ((4-(diphenylamino)phenyl)methanol, abbr. TPA) were synthesized and reacted with (3-isocyannatopropyl) triethoxysilane (ICTES) to form two functionalized silicon alkoxide precursors (named ICTES-FS and ICTES-TPA, respectively). Sol solutions were obtained after co-hydrolysis/condensation of tetraethoxysilane, ICTES-FS and ICTES-TPA. Transparent films were only fabricated with the sol containing ICTES-TPA. Thermal stabilities and aggregation behaviors of the NLO chromophores in hybrid films were studied by ultraviolet-visible spectra. ICTES-TPA units with triphenylamine groups at high concentration were found useful to abate dipolar chromophore interactions and consequent aggregation problems. Second-order NLO properties and temporal stabilities of sol-gel films were also investigated by virtue of in-situ second harmonic generation.