Donor-Acceptor Interactions in Red-Emitting Thienylbenzene-Branched Dendrimers with Benzothiadiazole Core

Synthesis and characterization of dendrimers containing thienylbenzene repeating units, red-emitting benzothiadiazole core, and triarylamine peripheries that bear naphthyl units are reported. The relevant dendrimers of different generations are classified as G(nb) (n = 1-3), while the tert-butyl dendrimers G(na) with the acceptor alone were also synthesized to serve as control chromophores that avoid donor-acceptor interactions. The resulting dendrimers are capable of harvesting photon energy through efficient energy transfer among donor-acceptor moieties, so that highly luminescent red fluorophores result. Transient fluorescence studies suggest that the energy transfer and its efficiency are approximately unity in all G(n) dendrimers, whereas the rate of energy transfer for the G(b) dendrimers is suppressed, that is, charge transfer from the core to the periphery is a significant quenching pathway. These dendrimers are amorphous in nature with high glass transition temperatures (176-201 degrees C). Electroluminescent devices were fabricated by using the dendrimers as hole-transporting emitters, and the devices exhibit promising red emission parameters.