Synthesis and characterization of two new TiO₂-containing benzothiazole-based imine composites for organic device applications

Abstract

The effect of the presence of titanium dioxide in two new imines, (<i>E</i>,<i>E</i>)-(butane-1,4-diyl)bis(oxybutane-4,1-diyl) bis(4-{[(benzo[<i>d</i>][1,3]thiazol-2-yl)methylidene]amino}benzoate) (SP1) and (<i>E</i>)-<i>N</i>-[(benzo[<i>d</i>][1,3]thiazol-2-yl)methylidene]-4-dodecylaniline (SP2), on the properties and stability of imine:TiO₂ composites for organic device applications were examined. The investigated titanium dioxide (in anatase form, obtained via the sol-gel method) exhibited a surface area of 59.5 m²/g according to Brunauer-Emmett-Teller theory, and its structure is a combination of both meso- and microporous. The average pore diameter calculated by the Barrett-Joyner-Halenda method was 6.2 nm and the cumulative volume of pores was 0.117 m³/g. The imine SP1 exhibited columnar organization (Col), while SP2 revealed a hexagonal columnar crystalline phase (Col_hk). The imine:TiO₂ mixtures in various weight ratio (3:0, 3:1, 3:2, 3:3) showed a lower energy gap and HOMO-LUMO energy levels compared to pure TiO₂. This implies that TiO₂ provides not only a larger surface area for sensitizer adsorption and good electron collection, but also causes a shift of the imine energy levels resulting from intermolecular interaction. Also the temperature of the phase transition was slightly affected with the increase of TiO₂ concentration in imine-based composites. The changes observed in the Fourier transform middle-infrared absorption (FT-MIR) spectra confirmed the significant influence of TiO₂ on structural properties of both investigated imines. Similar interactions of oxygen vacancies existing on the TiO₂ surface with SP1 and SP2 were observed. The imine:TiO₂ mixtures showed good air stability and reusability, which demonstrates its potential for organic device applications.