Synthesis, electrochemistry and optical properties with electroluminescence ability of new multisubstituted naphthalene derivatives with thiophene and carbazole motifs

A series of solution-processable tetrasubstituted naphthalene derivatives bearing thiophene or carbazole units were synthesized using the tandem cycloaddition [2+1+2+1] and Diels-Alder reaction[4+2]. Thermal, electrochemical, absorption, and emission properties of synthesized compounds were studied. They can be considered as molecular glasses with glass transition temperature ranging from 37 to 122 degrees C with high thermal stability up to 300 or 400 degrees C. The naphthalene derivatives were electrochemically active and showed low energy band gap between 1.64 and 1.85 eV. All derivatives were luminescent and emitted light with maximum emission band located at 379-436 nm with photoluminescence quantum yield in the range of 9.5-19.8% in solution. They photo-and electroluminescence ability in solid state as thin film and blends with poly(9-vinylcarbazole) (PVK) and mixture PVK with (2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole) (PBD) were tested. Together with increase of compound content from 2 to 15 wt% in binary matrix, the increase of electroluminescence intensity was observed. Diodes with guest-host configuration showed electroluminescence with maximum of emission band from 593 to 637 nm. The most intense emission of light under applied voltage characterized devices based on compound bearing carbazole derivatives and one methyl group.