A host-guest approach, using 1% wt of DiKTa-DPA-OBuIm in DiKTa-OBuIm was also used, the latter acting as a host matrix for the former. The electroluminescence (EL) of the three device stacks is shown in Figure . Similar to the PL, the EL spectra are broad and unstructured. The EL of DiKTa-OBuIm and DiKTa-DPA-OBuIm occurs at lEL of 534 and 656 nm, respectively. Both neat-film EL spectra are red-shifted from the solution-state and the 1% wt in mCP film PL spectra. The origin of this red shift could be ascribed to the presence of emissive aggregates in the emissive layer. Interestingly, in the host-guest system the energy transfer is not complete and both molecules are responsible for the electroluminescence, with a lEL at 586 nm, between the emission of the neat films. JVL characterization