| Abstract [eng] |
Four electroactive compounds containing pyrido[2,3-b]pyrazine acceptor fragments were synthesised. Their properties-structure dependence, and potential applications were investigated. Due to their favourable properties for optoelectronic applications, carbazole and phenothiazine were chosen as electron–donating fragments. The compounds were synthesised using the Buchwald–Hartwig cross–coupling reaction. The structures of the final compounds were confirmed by 13C and 1H nuclear magnetic resonance and FTIR, while molecular weights were determined by MS. Thermogravimetric analysis showed that all compounds are thermally stable, and their decomposition temperatures were determined. The 5 % weight loss temperatures of the compounds with one carbazole or phenothiazine fragment are 345 and 329 °C, respectively, and 434 °C for the compounds with two donor fragments. All compounds were found to be morphologically stable by differential scanning calorimetry. The compound containing two phenothiazine fragments and both compounds containing one carbazole or one phenothiazine fragment exhibited only glass transition (at 134, 89, and 82 °C, respectively). The product containing two carbazole fragments showed glass (155 °C), melting (310 °C), and crystallisation (249 °C) transitions. By analysis via an optical profilometer, it was confirmed that all compounds were capable of forming amorphous layers with a low surface roughness. The ionisation potentials of the compounds, determined by cyclic voltammetry and photoemission yield spectroscopy in air (5,31–5,54 eV and 5,25–5,55 eV, respectively), are compatible with the typical values of other OLED layers. All compounds are electrochemically stable. Monosubstituted compounds exhibit reversible oxidation, while disubstituted ones show quasi–reversible oxidation. UV–Vis spectroscopy showed that the toluene solutions of compounds absorb light up to 500 nm and thin films up to 650 nm. The emission maxima of the toluene solutions (468–652 nm) and thin films (505–663 nm) of compounds were determined via fluorescence spectroscopy. The toluene solutions emit blue to red light, while the films emit green to red light. Temperature-dependent emission analysis and the calculated singlet–triplet energy gaps (0,16–0,38 eV) confirmed that the compounds exhibit thermally activated delayed fluorescence. Based on the evaluated properties, it was concluded that all compounds are suitable for use in the emissive layer of OLEDs. Upon constructing OLEDs, a high external quantum efficiency (18 %) was achieved. A technological scheme was also developed for 10,10'-(pyrido[2,3-b]pyrazine-2,3-diylbis(4,1-phenylene))bis(10Hphenothiazine). |
