Synthesis and electronic properties of nanometer-size symmetrical tetrakis(poly-p-phenylene)ethylenes

A simple synthesis of soluble tetrakis(poly-p-phenylene)ethylenes (TPEs), where poly-p-phenylene units contain up to 4 phenylene moieties, is accomplished using an easily available tetrakis(4-bromophenyl)ethylene and phenyl, biphenyl, and p-terphenylboronic acids, containing solubilizing iso-alkyl groups as the end-capping substituents. Electrochemical oxidation of TPEs (i.e., T1-T4) showed that they undergo reversible electrochemical oxidations and form stable cation-radical salts in solution. The evaluation of absorption and emissions characteristics of T1-T4 in solution indicated that unlike parent tetratolylethylene (T1), the higher homologues (i.e., T2-T4) show emission centered at 520 nm and the quantum efficiency of emission increases with the increasing number of phenylene moieties in poly-p-phenylene units in various TPEs.