Influence of methoxy substitution on the properties of 9,9-fluorenylidene-linked triphenylamine derivatives

• Derivatives of triphenylamine derivatives with 9,9-fluorenylidene linking units.
• High thermal stability with the 5% weight loss temperatures up to 458 °C.
• High triplet energy levels of 2.88 eV.
• Hole mobilities in the solid amorphous films exceeding 10−3 cm2 V−1 s−1.

Triphenylamine derivatives, comprised of two methoxy-substituted triphenylamine moieties linked through 9,9-fluorenylidene unit, were synthesized via Ullmann-type coupling reaction from primary aromatic diamine, 9,9-bis(4-aminophenyl)fluorene, and respective aryl iodides. Thermal behaviour, photophysical, electrochemical and charge-transporting properties of the materials were investigated. Ortho- and meta-methoxy-substituted derivatives readily form molecular glasses which exhibit glass-transition temperatures of 114 °C and 86 °C, respectively. Solid state ionization potentials of methoxy-substituted derivatives are set in the range of 5.35–5.58 eV. The materials exhibit fluorescence in UV-violet light region with the maxima situated in the range of 360–389 nm. The phosphorescence spectra of all the compounds are almost identical and not influenced by methoxy-substitution. The materials exhibit high triplet-energy levels of 2.88 eV. Hole mobilities in solid amorphous films of the neat compounds exceed 10−3 cm2 V−1 s−1 at the electric field of 1 MV cm−1.