New star-shaped triarylamines: synthesis, mesomorphic behavior, and photophysical properties

A total of 18 compounds 1–6 derived from triphenylamine as core group were prepared and characterized, and their mesomorphic properties were also investigated. Compounds 1–4 and 5,6 were prepared from p,p′,p″-triformyltriphenylamine and p,p′-diformyltriphenylamine with appropriate alkoxyphenylamines. The phase behavior of these mesogenic compounds was characterized and studied by differential scanning calorimetry, polarized optical microscopy, and powder XRD diffraction. Compounds 1–3 exhibited columnar mesophase, however, compounds 4–6 were nonmesogenic. The mesophases observed in compounds 1–3 were found to be side dependent. Compounds 1a, 2a, and 3a appended with one, two, or three side chains exhibited lamellar columnar (ColL) phases, and compounds 2b and 3b with four or six side chains formed hexagonal columnar (Colh) phases. The formation of the mesophases, lamellar or columnar mesophases, was probably induced by H-bonding formed between –CH2NH groups. The oxidation process determined by cyclic voltammetry showed two redox waves, one appeared at 220–255 mV and the other one at 503–677 mV, which gave energy to HOMOs range of 5.02–5.36 eV. The fluorescent properties of the compounds were examined. All λmax peaks of the absorption and photoluminescence spectra of compounds occurred at ca. 307–392 nm and 368–456 nm, respectively. Compound 4a has a larger red shift due to a better conjugation linked by Cdouble bond; length as m-dashC double bonds instead of –CH2NH in other compounds.