| Abstract [eng] |
Using four-step synthesis pathway five new organic compounds containing electrondonating 3,6-ditert-butyl-2,7-dimethoxycarbazole and 3-tert-butyl-2,7-dimethoxycarbazole chromophores connected with electronaccepting triazine, quinoxaline, quinoline moieties were syntesized. The structures of the compounds are identified using NMR and mass spectrometry technique. After analyzing the thermal properties of the synthesized compounds by differential scanning calorimetry and thermogravimetric analysis methods, it was found that all compounds have high melting point values (222-316°C) and relatively high thermal stability (336-390°C). Compound possessing quinoline and spatially restrained triazine fragments are capable to form stable molecular glasses (113-154°C). Cyclic voltamperometry has shown that compounds having electrondonating part as 3,6-di-tert-butyl-2,7-dimethoxycarbazole are characterized by reversible oxidation-reduction processes, i.e. after three repeated scans the shape of the voltamperograms did not change. The Ip values calculated from CV results vary in the range of 5,25–5,98 eV and they are comparable with the values obtained using electron photoemission in air technique (5,57–6,12 eV). The potential of computational chemistry was used to calculate final compounds excited state singlet (S1) and triplet (T1) energy values, HOMO/LUMO values and distribution of orbitals. Achieved DFT (B3LYP/631G (d,p) basic set) results – low ΔEST (0,01-0,27 eV) values and minimal overlap of HOMO/LUMO orbitals – complemented experimental data supporting thermally activated delayed fluorescence phenomena. The charge transporting properties were measured using the time of flight (TOF) technique. The results confirmed bipolar nature of the compounds, which means that in the neat films, these compounds are capable efficiently transfer electrons and holes. The holes and electrons mobility values in high electric fields reaches 10-4 cm2/Vs. UV/Vis absorption and fluorescence spectra of target compounds solutions and films were recorded at room temperature. The absorption bands of dilute THF solutions of the compounds vary in the range of 200-430 nm. The lowest-energy absorption band was observed of the solutions of spatially non-constricted triazine compound (~ 430 nm). Meanwhile, final compounds showed emission in green, yellow and orange visible spectrums zones (514–626 nm). Searching for thermally activated delayed fluorescence phenomenon additional properties were measured: spectra of fluorescence and phosphorescence at 77 K, fluorescence in different polarity solvents, fluorescence intensity in the air and argon atmosphere. The experimental ∆EST values of targeted compounds range from 0,12 to 0,7 eV and correlate with theoretical ones. Solvatochromism phenomenon was proved for all synthesized structures, i.e. compared to the fluorescence peaks of the compounds dissolved in the THF flurescence peaks of the compounds dissolved in the lower polarity solvent (toluene) were blue-shifted by 80-100 nm. Moreover, emission intensities of deoxygenated toluene solutions was found to be higher by a factor of 2,0–4,0. The results of the experimental and theoretical observation proved that compounds possess TADF 8 phenomenon. Therefore, materials with triazine moiety were employed as emitters and host in OLED stucture, which demonstrated following characteristics external quantum efficience reaching 3,02 %. |
