Films fabricated from commercially available poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) aqueous dispersions have been widely used in many electronic and optoelectronic applications. Previous attempts to utilize them as anodes in organic light-emitting diodes (OLEDs) were not satisfactory due to their low conductivity. In this letter we report on the fabrication and characterization of an OLED device made using a highly conductive form of PEDOT:PSS as anode and demonstrate its superior performance relative to that of a similar device using the commercial conducting polymer as an anode. An external electroluminescence quantum efficiency of ∼0.73% was measured at 100 A/m2.

Highly efficient exciplex emission is observed from molecular organic light-emitting diodes (MOLEDs) based on silole derivatives as emissive and electron transport materials, and a hole transporting amine derivative. A silole derivative, 2,5-di-(3-biphenyl)-1,1-dimethyl- 3,4-diphenylsilacyclopentadiene (PPSPP), which shows blue fluorescence (476 nm) with a high solid-state photoluminescence quantum yield of 85% was used as the emitter. Another silole derivative, 2,5-bis-(2′,2″-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene which exhibits high electron mobility, was used as the electron transport material. MOLEDs using these two siloles and N,N′-diphenyl-N,N′-(2-napthyl)-(1,1′-phenyl)-4,4′-diamine (NPB) as the hole transporter show electroluminescence (EL) emission centered at 495 nm. This red-shifted EL band relative to the blue fluorescence of PPSPP is assigned to a NPB:PPSPP exciplex. An operating voltage of 4.5 V was measured at 100 cd/m2 and an EL quantum efficiency of 3.4% was achieved at 100 A/m2.

The intrinsic properties of quantum dots (QDs) and the growing ability to interface them controllably with living cells has far-reaching potential applications in probing cellular processes such as membrane action potential. We demonstrate that an electric field typical of those found in neuronal membranes results in suppression of the QD photoluminescence (PL) and, for the first time, that QD PL is able to track the action potential profile of a firing neuron with millisecond time resolution. This effect is shown to be connected with electric-field-driven QD ionization and consequent QD PL quenching, in contradiction with conventional wisdom that suppression of the QD PL is attributable to the quantum confined Stark effect.