Novel luminescent phenothiazine-based Schiff bases with tuned morphology. Synthesis, structure, photophysical and thermotropic characterization

Abstract

New Schiff base dimers based on phenothiazine heterocycle have been obtained with high yield and purity by condensation of 3-formyl-10-methyl-phenothiazine with various amines. The structural characterization was performed by elemental analysis , FTIR, 1D and 2D NMR spectroscopy and single crystal and powder wide angle X-ray diffraction. The obtained compounds have high thermal stability and some of them self-assemble into cubic mesophase and form stable molecular glass. The thermotropic study performed by polarized optical microscopy and differential scanning calorimetry revealed the possibility to control the compound morphology by thermal annealing and blending miscible components. The photophysical characterization indicates green light emission, with good absolute fluorescence quantum yield , large Stokes shift and high purity and fully saturated color. The special thermal behavior and photophysical properties appear to be significantly dependent on the special supramolecular architecture generated by the hockey-stick shape of the imino-phenothiazine mesogenic core. Collectively, the properties of these azomethines provide a starting point for new compounds with great advantages for optoelectronic applications. ► New phenothiazine containing imine dimers were obtained with high yield and purity. ► The mesogenic core adopts a hockey-stick shape. ► Some dimers exhibit cubic mesophase or molecular glass forming. ► The films morphology has been controlled by thermal annealing and blending. ► The dimers emit green light with good quantum yield and large Stokes shift.