Characterization of benzotriazole based molecules in thin films

Full text: Liquid Crystals (LCs) are an interesting class of soft materials which have been widely studied and applied in organic electronics due to their distinguished electrical and physical properties, which combines the fluidity of a liquid and the long-range order of a crystalline solid. As a result of the strong π–π interactions between the conducting cores, the rod-like (calamitic) molecules are able to align in layers, allowing a quasi-bidimensional charge transport [1]. Recently, a large range of benzotriazole derivatives have been applied in electronic devices due to high functionality and good electron-transporting and hole-blocking abilities [2]. The aim of this research is to study a serie of eight liquid crystalline rod-like compounds derived from benzotriazole heterocycle and evaluate their properties in thin films. The molecules differentiate from one another by varying the non-symmetric aromatic units linked to the benzotriazole core through a carbon-carbon triple bond, which produces a highly π-polarizable and conjugated moiety and is responsible for a large birefringence in the material [3]. The liquid crystalline behavior of the compounds was investigated by X-ray diffraction, differential scanning calorimetry and polarizing optical microscopy. The spin-coated thin films were characterized by atomic force microscopy, photoluminescence and UV-Vis spectroscopy and photoluminescence dependent on temperature. Preliminary results showed that all compounds present optical properties in the visible spectrum with intense photoluminescence and high quantum yield. On the other hand, the molecule containing an electron acceptor aromatic group showed total suppression of its photoluminescence. References: [1] M. Kumar and S. Kumar, Polymer Journal, 49, 85 (2017). [2] I. Torres, et al.,The Royal Society of Chemistry, 6, 36544 (2016). [3] A. Vieira, et al., Journal of Molecular Structure, 875, 364 (2007). (author)