Phenanthroimidazole-based chromophores for organic light-emitting diodes: synthesis, photophysical, and theoretical...

Organic light-emitting diodes (OLED) are gaining attention and making a significant contribution to the area of lighting and displays technology. The synthesis of new materials that can act as a host as well as emissive materials is crucial and efforts have been made in this direction in this research. Here, four star-shaped fluorophores, with a donor-acceptor (D-A) structure and with triphenylamine and phenanthroimidazole groups with different substitutions at the N₁ position of the imidazole moiety, were designed and synthesized. Synthesized fluorophores showed sufficient thermal stability (10% T_d in the range 230-280°C). Ultraviolet-visible (UV-vis) spectra of the fluorophores showed multiple absorption bands (bands in the UV region, due to π-π* transitions of the conjugated aromatic portion) and all fluorophores showed blue emission in dichloromethane solution. Electrochemical analysis indicated that all fluorophores had excellent oxidation and reduction characteristics. Theoretical calculations were also performed to better understand the structural and electronic properties of the synthesized fluorophores. All fluorophores had higher triplet (T₁ ) energy (ranging from 2.49-2.52 eV) than the widely used green (Ir(ppy)₃ -2.4 eV) and red (Ir (piq)₂ acac - 2.2 eV) dopant materials. These results indicated that these fluorophores would be useful as host materials for efficient green and red phosphorescent OLEDs.