In the last few years, white-light emission from organic compounds has been the subject of increasing interest due to its potential impact on the lighting industry and backlight applications. In order to obtain white light from organic lightemitting devices (OLEDs), the simultaneous excitation of different molecular species emitting at different primary colors is required.[1, 2] So far, the most exploited approach has been the fabrication of multilayer devices by consecutive evaporations or co-evaporation of different emitting compounds.[1±6] However, this technique requires complex technological processes and a large amount of wasted organic materials, resulting in relatively high fabrication costs. Spin-coating of a blend of different soluble emitters in a single layer seems to be a more cost-effective technique.[7, 8] Though cheaper, this approach has the drawback that customized color combinations are not always possible due to Förster transfer from the highenergy emitting material (donor) to the low-energy one (acceptor), which induces emission only from the lower-gap compound.[9, 10] An alternative approach which overcomes such a problem is to blend two blue-light-emitting organic molecules of different electron affinities, whose interaction gives rise to exciplex states.[11, 12] The combination of the exciplex emission with the blue-light emission of the individual donor molecule results in the generation of white light. However, in both of these approaches the purity of the color emission is strongly dependent on the relative concentration of the different molecular species and, generally, on the applied voltage. This is a problem for lighting applications in which the source intensity (but not the color) has to be varied by changing the applied electrical power.[13]

In this frame, the synthesis of a soluble compound showing white-light emission in the solid state is strongly desirable because it would enable the fabrication of a new class of devices which combine the simplicity and low cost of the single-layer spin-coated structures without the problems connected with the material concentration and bias. In this work, we demonstrate a bright single-layer white OLED realized by spin-coating a single emitting molecular material, namely 3, 5-dimethyl-2, 6-bis (dimesitylboryl)-dithieno [3, 2-b: 2′, 3′-d] thiophene (compound 1 in Fig. 1). In 1, white electroluminescence is achieved by the superposition of the intrinsic blue±green-light emission (BGE) of the single molecule with a red-shifted emission (RSE) that occurs only in the solid state. The origin of the RSE peak is due to the formation of cross-like dimers between the molecules. This has been demonstrated by optical measurements and theoretical calculations, and also performed on similar compounds functionalized with different substitution patterns (2, 3, and 4 in Fig. 1) in order to control the self-assembling of the molecules. By virtue of the excellent properties of compound 1, namely the good electron-acceptor characteristics of the dimesitylboryl moieties, and the peculiar morphology of the spin-coated films, it was possible to obtain white-light electroluminescence (EL) with a maximum luminance of 3800 cdm±2 at 18 V and an external quantum efficiency (QE) of 0.35%, paving the way to the fabrication of low-cost single-active-material white-light-emitting devices. In Figure 2 we show the photoluminescence (PL) and absorption spectra of 1 in solution (Fig. 2a) and in the solid state (Fig. 2b). The absorption spectrum in the solid state does not show significant differences with respect to that in solution. Instead, strong changes are observed in the emission spectra. In solution, only the BGE is observed, whereas in solid …