Conjugated polymers for pure UV light emission: Poly(meta-phenylenes)

We report the synthesis of a 3-ethylhexyloxy substituted poly(meta-phenylene), EHO-PMP that shows absorption and solid state photoluminescence exclusively in the UV region of the electromagnetic spectrum with an emission maximum of 345 nm. Computational analysis of model oligomers by DFT methods indicates that EHO-PMP is a wide bandgap polymer with the HOMO being localized on a dimeric (biphenyl) unit and with the LUMO being more delocalized. The energy of the LUMO, however, suggests that inefficient electron injection would occur from currently available cathode materials in standard light-emitting device architectures, and this was observed experimentally. The computational results, coupled with experimental observation, lead us to believe that efficient electroluminescence from organic polymer UV emitters requires advances in electron transport layers and cathode materials.