Structure–properties relationship of linear and star-shaped imines with triphenylamine moieties as hole-transporting materials

We have presented 17 solution-processable linear and star-shaped imines with triphenylamine moieties. Six different amines with electron-donating or electron-withdrawing substituents and three aldehydes varying in the number of carbonyl groups have been used to study structure–optical property correlations. The unsymmetrical and symmetrical imines have been examined as a hole-transporting material (p-type) for organic light-emitting diodes (OLED)s. Current–voltage measurements were performed on ITO/compound/Alq3/Al devices. The lowest optical band gap value was detected at 2.12 eV. The symmetry and shape of the compounds along with the structure of the amines influenced the photoluminescence (PL) properties. Most of the obtained imines emitted blue light. The excitation wavelength and concentration of the imines also affected PL. Relative PL intensity of the imines investigated in chloroform solution was found at the range of 0.15–61% in relation to 9,10-diphenylanthracene. Melting point and glass transition temperature detected via differential scanning calorimetry (DSC) increased in the following order: unsymmetrical imines, symmetrical linear imines and star-shaped ones.