Synthesis, characterization and photo physical properties of two novel n-type semiconductor materials with trifluoromethyl and cyano groups

Two π-conjugated materials (3a, 3b) possessing –CF3 and -CN were prepared by Knoevenagel condensation by reacting benzene 1,3,5-tricarboxaldehyde and 4-(trifluoromethyl) phenyl acetonitrile, 3,5-bis(trifluoromethyl) phenyl acetonitrile in the presence of sodium ethoxide. The proposed structures of 3a, 3b were elucidated by 1H NMR and Elemental analysis. To study the structure-property relationship, molecular structures of 3a and 3b were determined by X-ray diffraction analysis. In the crystal, molecules are linked by C_H⋯F, C⋯C and F⋯F short contacts, forming a layer like three dimensional networks. From X-ray diffraction analysis it was observed that molecule 3a has better planarity than molecule 3b suggested by angles between the planes of molecules. The molecules 3a and 3b displayed strong absorption maximum at 319 nm corresponding to the π→π* transitions within the whole conjugated molecules and emissions in the visible region at 373–475 nm. The shape and intensity of absorption and emission spectra of 3a, 3b almost identical. Further, we found that molecule 3b (M.p. 251–252 °C) has relatively higher melting point than molecule 3a (M.p. 231–232 °C). Molecules 3a and 3b have emissions close to blue light, may serve as model materials for new OLED applications.