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-π-A push–pull molecules based on a methoxyphenyl or methoxynaphthyl donor unit and a diazine acceptor unit with different π-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

pH-Sensitive Fluorescence Lifetime Molecular Probes Based on Functionalized Tristyrylbenzene

The dependence of the fluorescence on pH for two 1,3,5-tristyrylbenzenes decorated with polyamine (compound <b>1</b>) and poly­(amidoamine) (compound <b>2</b>) chains at the periphery was investigated. The highest fluorescence intensities were observed under acidic conditions because electrostatic repulsions between positively charged molecules reduce the fluorescence quenching. The slopes observed in the fluorescence pH titration curves were associated with deprotonation of the different types of amine groups, which results in quenching by photoinduced electron transfer and aggregation processes. The linear dependence of fluorescence lifetime observed for different pH ranges is a valuable property for applications in the field of fluorescence lifetime sensors and imaging microscopy. The influence of the pH and the peripheral chains on the aggregation processes was also analyzed by absorption and emission spectroscopy, dynamic light scattering measurements, and transmission electron microscopy. For compound <b>1</b>, bands associated with the formation of aggregates were detected along with micrometric aggregates surrounded by fibers with lattice fringes typical of columnar mesophases. For compound <b>2</b>, which contains longer peripheral chains with a higher degree of branching, aggregates with lower internal order were observed. In this case, the peripheral chains hindered aggregation by π-stacking although the amine groups did allow hydrogen bonding

PPV–PAMAM Hybrid Dendrimers: Self-Assembly and Stabilization of Gold Nanoparticles

Different generations of PPV–PAMAM hybrid dendrimers have been prepared and characterized. Our initial studies showed the high tendency of these materials to aggregate and form nanoassemblies in different media. Nile Red experiments and DLS measurements allowed us to determine the critical aggregation concentration (CAC) and the size of the aggregates, which have also been used to stabilize small gold nanoparticles. The nanoparticles influence the assembly and optical properties of the dendrimer molecules and lead to strong quenching of their intrinsic fluorescence. Nevertheless, these gold particles will be very useful as biomarkers in living cells by means of electron microscopy because of their high electron contrast