Experimental LEDs were fabricated in the following manner. Indium tin oxide (ITO) sub-strates were cleaned by ultrasonication in detergent, acetone, and isopropanol. Cleaning was followed by a 5 min oxygen plasma etch at 100 W at 300 Torr of oxygen. After etching, poly(3,4-ethylenedioxythiophene) (PEDOT, Baytron P8000 from Bayer) was spin-cast at 3800 RPM in air. The substrates were baked at 110 C in a nitrogen atmosphere to remove the water. The organic blends were spin-cast to get 100 nm thick films. The substrates were baked at 80 C for 2 h after spin-casting the organic layer. Metalization of the cathodes was carried out at 7 10 ±7 Torr to deposit 80 nm of calcium and 130 nm of silver. All LED testing was done under nitrogen atmosphere. LIV (LIV = lumi-nance, current, voltage) data were acquired by inserting the substrate into a barium sulfate-coated integrating sphere with a radiometricaly calibrated detector and sweeping the voltage while the current and radiant flux was measured. The exitance was calculated by dividing the radiant flux by the emitting area. The electroluminescence spectra were acquired using an Ocean Optics S2000 fiber optic spectrometer. Cyclic voltammetric measurements were performed on an EG&G Princeton Applied Research model 273A potentiostat/galvanostat system using a standard three-electrode cell configuration. Electrolyte solutions utilized n-Bu 4 NPF 6 (0.10 M) in acetonitrile. The polymer or porphyrin films were coated on Pt or glassy carbon disk working electrodes by dipping the electrode into the corresponding solution and then drying in air. Pt wire and saturated calomel electrodes (SCE) were used respectively as counter and reference electrodes, while the ferrocene/ferricinium redox couple was utilized as an internal potentio-metric standard. Scan rates in these experiments were 100 mV s ±1. Assuming the energy level of the ferrocene/ferrocinium redox couple is 4.8 eV below the vacuum level, the potentiometrically derived HOMO and LUMO energy levels of the guests and hosts used in these experiments were plotted relative to vacuum. For polymers for which only reduction or oxidation potentials were obtained, their HOMO or LUMO levels were estimated from the combination of the cyclic voltammetric data and the optical bandgap (onset energy of the absorption spectrum); this method for estimating the valence and conduction band energies of conducting polymers has been discussed previously [21]. The absolute emission energy of DD and DDD in the solid state vary as a function of the host matrix and …