Effect of Methoxy Substituents on the Properties of the Derivatives of Carbazole and Diphenylamine

The synthesis and properties of carbazole and diphenylamine derivatives with different numbers and positions of methoxy groups in the diphenylamino moiety are reported. A comparative study on their thermal, optical, and photoelectrical properties is presented. All the synthesized compounds are found to form glasses with the glass transition temperatures in the range of 39−69 °C, as characterized by differential scanning calorimetry. The ionization potentials of the synthesized compounds were estimated both theoretically by quantum chemical calculations and experimentally by an electron photoemission in air technique. The trends observed by theoretical calculations are confirmed by experimental results. The experimental values of ionization potentials range from 5.10 to 5.56 eV. Compounds containing monomethoxy-substituted phenyl rings exhibited lower ionization potentials than compounds containing di- and trimethoxy-substituted phenyl moieties. The highest ionization potential was observed for the compound containing trimethoxy-substituted phenyl rings. The best charge transport properties were observed for the compounds containing one methoxy group in para and ortho positions of phenyl rings of the diphenylamino moiety. Room-temperature hole drift mobility in the amorphous film of 3-[ N, N -(bis-4-methoxyphenyl)]amino-9-ethylcarbazole established by a xerographic time-of-flight technique was found to be 1.2 × 10 −4 V/cm at an electric field of 6.4 × 10 5 V/cm.