Electrical transport and optical properties of tetraanilinobenzene Langmuir-Blodgett films

We report a study of the electrical and optical properties of Langmuir-Blodgett films of tetraanilinobenzene. The optical absorption, peaking at 4.1 eV, is blue shifted by 0.2 eV, and photoluminescence, peaking at 3.0 eV, is red shifted by 0.4 eV compared to the material in solutions, indicating H aggregates. p-type doping by iodine gas or protonation in acidic solutions results in two polaronic subgap absorption bands and leads to an increase in conductivity from 10-10 to about 10-4 S/cm. The optical properties and doping mechanisms have been discussed and compared to those of vacuum-evaporated films. The oxidized units as well as polaronic states were found to act as nonradiative recombination centers for excitons. The conductivity s of the protonation-doped samples has a temperature T dependence logσ ∝T-1/2 indicating variable-range hopping in a quasigap, probably due to the Coulomb interactions between localized carriers in polaronic states. The nonohmic region was studied for moderately high electric fields up to 105 V/cm