Dalius Gudeika

Structure–property relationship of isomeric diphenylethenyl-disubstituted dimethoxycarbazoles

Isomeric 3,6-dimethoxy- and 2,7-dimethoxycarbazoles containing diphenylethenyl moieties were synthesized by condensation of the appropriate dimethoxycarbazoles with diphenylacetaldehyde. The solid-state structures and the molecular order of the compounds were proven by X-ray crystallography. Both compounds were found to be capable of glass formation with comparable glass transition temperatures (70–71 °C). They exhibited high thermal stabilities, with the 5% weight loss temperatures exceeding 375 °C. The isomer having diphenylethenyl groups at C-3 and C-6 positions and methoxy groups at C-2 and C-7 positions (3a) exhibited aggregation-induced emission (AIE), while its counterpart having diphenylethenyl groups at C-2 and C-7 positions and methoxy groups at C-3 and C-6 positions (3b) showed the opposite effect, i.e. aggregation-caused quenching (ACQ). The derivative 3b showed superior charge transporting properties. Time-of-flight hole drift mobilities in its layers approached 10−3 cm2 V−1 s−1 at high electric fields. A comparative theoretical analysis of the compounds was performed using density functional theory (DFT) and time-dependent DFT calculations. They proved more effective π-conjugation in the derivative of 3,6-dimethoxy carbazole (3b), which was also observed by UV and fluorescence spectroscopies. The theoretical study revealed relatively low ground state dipole moment of 0.69 D of the isomer 3b, while its counterpart (3a) showed much higher ground state dipole moment of 5.98 D. The difference in polarity was found to have the crucial effect on the molecular arrangement in the crystals and consequently, on the thermal transitions and charge-transporting properties.

Synthesis and properties of the derivatives of triphenylamine and 1,8-naphthalimide with the olefinic linkages between chromophores

Two donor–acceptor type molecules consisting of triphenylamine and 1,8-naphthalimide moieties with the olefinic linkages between chromophores were synthesized by Heck reaction. The compounds obtained are capable of forming molecular glasses with glass transition temperatures of 56 and 75 °C recorded for mono- and di-substituted derivatives of triphenylamine, respectively. They exhibit high thermal stabilities with 5% weight loss temperatures of 350 and 363 °C. Fluorescence quantum yields of the dilute solutions of the synthesized compounds range from 0.065 to 0.72 while those of the solid films are 0.028 and 0.034. The Stokes shifts increased with the increase of the solvent polarity. Cyclic voltammetry measurements revealed close values of the solid state ionization potentials (5.22 and 5.27 eV) and of electron affinities (−3.20 and −3.18 eV). For the layer of the monosubstituted derivative of triphenylamine core hole mobility was found to be 2.1 × 10−3 cm2 V−1 s−1. Good intrinsic hole transport parameters were theoretically estimated in the frame of Marcus theory, and the impact of polaron-type hole transport in these materials is discussed.

Synthesis and Properties of the Derivatives of 2,4,6-Tris(Phenoxy)-1,3,5-Triazine

Five derivatives of 2,4,6-tris(phenoxy)-1,3,5-triazine were synthesized and characterized by 1H NMR, IR and mass spectrometries. The optical and electrochemical properties of the synthesized compounds were studied. Dilute solutions of 1,3,5-triazines compounds in acetonitrile absorb electromagnetic radiation in the region of 200-400 nm with the band gaps of 3.96–4.58 eV. Cyclic voltammetry studies revealed that the electron affinities of the synthesized compound range from −3.24 eV to −3.58 eV, and solid state ionization potentials range from 7.20 eV to 8.16 eV.

Synthesis and Properties of 1,3-Indandione-Disubstituted Derivatives of Carbazole, Phenothiazine, and Phenoxazine

Donor-acceptor type 1,3-indandione derivatives were synthesized and their thermal, optical, photophysical, electrochemical, and photoelectrical properties were studied. They form glasses with the glass transition temperatures ranging from 164 to 249°C. 3,6-di(1,3-indandionyl)-10-methyl-phenothiazine showed the lowest energy emission bands in all the investigated solvents, as well as the largest Stokes shifts. Cyclic voltammograms of the synthesized compounds showed one reversible oxidation couple and quasi-reversible reduction waves. The ionization potentials of the solid samples of the synthesized materials were found to be in the range of 5.52–6.01 eV.

Synthesis and properties of glass-forming 2-substituted perimidines

ABSTRACT 2-Substituted perimidine derivatives were synthesized by condensation of 1,8-diaminonaphthalene and the different formyl derivatives. Alkylation of the intermediate compounds was performed using microwave irradiation using potassium and cesium carbonate as a base. The synthesized compounds were characterised by UV and luminescence spectroscopies, cyclic voltammetry, thermogravimetry, differential scanning calorimetry. They exhibit relatively high thermal stability with the temperatures of the onset of thermal degradation ranging from 230 to 392°C. Most of the synthesized perimidines are capabale to form glasses with glass transition temperatures up to 197°C. The alkyl group attached to the perimidinyl moiety influences the conformation of the molecules and consequently the absorption and emission spectra. The values of ionization potential of the layers of the synthesized derivatives range from 5.26 to 5.52 eV.

Synthesis, properties and self-polymerization of 1,8-naphthalimide-based vinyl monomer

ABSTRACT 1,8-Naphthalene imide with reactive vinyl group was synthesized by Suzuki reaction. Self-polymerization of the compound starts at 177°C as confirmed by differential scanning calorimetry. The electron affinity values of the monomer and the polymer were found to be −3.30 eV and −3.05 eV, respectively. The solid state ionization potential values of the monomer and the polymer were recorded to be 6.42 eV and 6.17 eV, respectively. The activation energy of the process was estimated using Ozawa method. It depends on the conversion degree and was found to be in the range of 136-195 kJ/mol. Pre-exponential factor values decrease during polymerization with decreasing chain mobility due to increasing molecular weight of the polymer.