Low temperature dual fluorescence of several derivatives of 4-aminodiphenylamine is investigated quantitatively. A strong thermochromic and solvatochromic redshift is indicative of the high dipole moment of the CT state emitting at long wavelength. The combination of steady state and time-resolved data allowed the calculation of the excited-state equilibrium. The absence of CT-risetimes in diethyl ether and their presence in butyronitrile points to the complication by additional ground state conformational equilibria. Both ground and excited state equilibria depend on solvent polarity and temperature. High solvent polarity favours one of the ground state conformers.

The photophysical properties of several derivatives of 4-aminodiphenylamine (ADPA), model compounds of aniline dimers and trimers are investigated. Several compounds show dual fluorescence with a charge transfer (CT) component with a significantly reduced fluorescence rate constant which can be suppressed by bridging and enhanced by sterically hindering substituents, in close similarity to the compounds showing twisted intramolecular charge transfer (TICT). The relation to polyaniline (PANI) conductivity is also discussed.

The photophysical properties of 4-aminodiphenylamine (1) and two derivates 4,4'-diaminodiphenylamine (2) and 4-cyanodiphenylamine (3) are studied by absorption- as well as steady-state- and time-resolved fluorescence spectroscopy. 1 can be considered as a model oligomer of polyaniline. It is a central problem which properties of this conducting polymer can already be explained on the basis of small oligomers Like 1 and derivates 2 and 3 with weakened and strengthened donor-acceptor properties. The investigations on I indicate dual fluorescence and charge separation in polar solvents, connected with an excited state equilibrium. The relative population of the charge transfer species correlates with the substituent-induced changes of donor-acceptor properties in 2 and 3.