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.