Effects of the nature of donor substituents on the photophysical and electroluminescence properties of derivatives of perfluorobiphenyl: donor–acceptor versus donor–acceptor–donor type AIEE/TADF emitters

Abstract

The synthesis and properties of a group of organic electroactive compounds based on electron-deficient perfluorobiphenyl (PFBP) are described. The influence of electron-donating substituents on the properties of PFBF is analyzed. A comparative study of the derivatives with donor–acceptor versus donor–acceptor–donor molecular architectures is reported. The geometry and electronic characteristics of compounds in the ground and the excited states were studied within density functional theory. It is shown that for all the studied compounds S₀ → S₁ excitations are characterized by intramolecular charge transfer from electron-donating phenothiazine, phenoxazine and furoindole moieties to the electron-accepting PFBP moiety. The differences and similarities in the absorption and emission spectra of the compounds and aggregation-induced emission enhancement are explained in terms of their geometrical and electronic structures. The compounds are characterized by the relatively high values of temperature of 5% weight loss reaching 333 °C. The synthesized perfluorobiphenyl derivatives exhibit photoluminescence in the full visible spectrum covering from deep-blue to red colors. The compounds containing phenothiazine or phenoxazine fragments are characterised by the combination of thermally activated delayed fluorescence and aggregation-induced emission enhancement. The ionization potentials of the solid films of the compounds estimated by photoelectron emission spectroscopy range from 5.67 to 5.95 eV. Phenoxazine-based compounds exhibit a time-of-flight hole mobility of 8.78 × 10⁻⁵ cm² V⁻¹ s⁻¹ at an electric field of 7.22 × 10⁵ V cm⁻¹. A green organic light emitting diode based on the derivative with two phenoxazine donor units shows an external quantum efficiency of 11.5%.