Luminescence Behavior of Protonated Methoxy-Substituted Diazine Derivatives: Toward White Light Emission

White light-emitting diodes (WOLEDs) are an efficient alternative to conventional lighting sources. Nevertheless, approaches to obtain WOLEDs still require complex processes that lead to high costs. In this sense, the use of a single emitting material that can take two forms of complementary emitting colors has emerged as a new strategy for the fabrication of WOLEDs. In this paper we describe the luminescent behavior upon protonation of a series of D-pi-A push pull molecules based on a methoxyphenyl or methoxynaphthyl donor unit and a diazine acceptor unit with different pi-bridges. The effect of protonation on the emission properties depends on the nature of the diazine ring. The addition of trifluoroacetic acid (TFA) to pyrazine and quinoxaline derivatives led to quenching of the fluorescence whereas pyrimidine derivatives remained luminescent after protonation, which prompted a color change in the emission due to the appearance of a new red-shifted band in the spectra. These results were rationalized with the help of TD-TFT calculations. White photoluminescence could be obtained in solution by the controlled protonation of some pyrimidines, which resulted in the formation of an orange emissive acidified form. This phenomenon opens up the possibility of exploiting these materials for the fabrication of WOLEDs.