Abstract
A series of symmetric carbazole derivatives (CzP-H, CzP-CN, CzP-Me, and CzP-OMe), which comprise electron-donating and electron-drawing groups appending on a phenyl core, was synthesized and characterized in detail. These compounds exhibit excellent thermal stabilities, with thermal decomposition temperatures exceeding 400 °C. From the fluorescent spectra in film, CzP-H, CzP-Me, and CzP-OMe showed UV to blue-violet emission, with peaks at 396 nm, 402 nm, and 392 nm, respectively. The E00 energies of CzP-H, CzP-CN, CzP-Me, and CzP-OMe were 3.39 eV, 2.83 eV, 3.50 eV, and 3.35 eV, respectively. From the electrochemical measurements, the highest occupied molecular orbital (HOMOs) energy levels were −5.30 eV, −5.64 eV, −5.46 eV, and −5.24 eV for CzP-H, CzP-CN, CzP-Me, and CzP-OMe, respectively. Through calculations from HOMO energy levels and E00 energies, the lowest unoccupied molecular orbital (LUMOs) energy levels of CzP-H, CzP-CN, CzP-Me, and CzP-OMe were −1.91 eV, −2.81 eV, −1.96 eV, and −1.89 eV, respectively. Therefore, the introduction of different substitutes in phenyl cores would distinctly affect the photophysical properties. These results indicate that the prepared carbazole derivatives could be potential candidates for realizing ultraviolet or blue-violet emission.
Highlights
Organic electronics (OEs) are becoming more attractive due to their unique merits in low cost, lightweight, large-scale fabrication and flexibility
To promote the reaction yields and simplify the procedures of obtaining target compounds, the previous reaction systems of tetrabutylammonium bromide (TBAB), PdCl2, and the solvent of acetone were replaced by Pd(pph3 )4 and toluene, respectively [29,30]
The distinction of the electron density of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbital (LUMO) implies that the different substitutes in the phenyl cores can successfully change the twist angle of molecular structure, even though the π-bridge effect or intermolecular interactions could be influenced
Summary
Organic electronics (OEs) are becoming more attractive due to their unique merits in low cost, lightweight, large-scale fabrication and flexibility. Carbazole-based small molecules exhibit excellent performance in ultraviolet/deep-blue OLEDs; for example, they demonstrate large conjugation stability, high hole mobility and high thermal properties. They suffer from some defects that lead to the limited application in OLEDs. intense investigations have been carried out to improve the performance of carbazole-based ultraviolet molecules [34,35,36,37]. Through modifying different substitutes in phenyl cores, such as cyan as an electron-withdrawing group, and methyl and methoxy as electron donors, four small molecules were synthesized Their photophysical properties were investigated in detail with the aim of understanding structure–property relationships and providing distinct information for further developing novel carbazole-based ultraviolet molecules
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