Linear free energy relationships. Part 10. Synthesis, thermal, spectral, electrochemical, and hole transport (conduction) properties of some novel carbazole derivatives

Abstract

A series of carbazole anils was prepared from 9-ethylcarbazole-3-carbaldehyde and 3-amino-9-ethylcarbazole. Thermal properties were examined by differential scanning calorimetry; most of the compounds form stable glasses and T_g/T_m values (average 0.75) are exceptionally high. The oxidation potentials of these compounds are not very sensitive to the substituent, except for the dimethylamino-case, where presumably oxidation of the amino-group itself occurs; the oxidations are generally irreversible. Hammett plots of the long-wavelength absorption energies have an inverted V shape with crossovers at σca. 0, as expected. Hole transport measurements reveal that in general the compounds derived from the carbazole carbaldehyde are superior to those derived from the aminocarbazole. This result is unexpected on the basis of the electrochemical results, in which the aminocarbazole derived compounds have lower oxidation potentials. This suggests that either the higher polarizability of the carbazolecarbaldehyde derived compounds, as reflected in their higher extinction coefficients, or less irreversible oxidation processes may be responsible for the better transport characteristics of the carbazolecarbaldehyde derived anils.