Singular Temperatures Connected to Charge Transport Mechanism Transitions in Perylene Bisimides from Steady-State Photocurrent Measurements

Perylene bisimides (PBIs) are n-type semiconducting and photogenerating materials widely used in a variety of optoelectronic devices. Particularly interesting are PBIs that are simultaneously water-soluble and liquid-crystalline (PBI-W+LC) and, thus, attractive for the development of high-performing easily processable applications in biology and “green” organic electronics. In this work, singular temperatures connected to charge transport mechanism transitions in a PBI-W+LC derivative are determined with high accuracy by means of temperature-dependent photocurrent studies. These singular temperatures include not only the ones observed at 60 and 110 °C, corresponding to phase transition temperatures from crystalline to liquid-crystalline (LC) and from LC to the isotropic phase, respectively, as confirmed by differential scanning calorimetry (DSC), but also a transition at 45 °C, not observed by DSC. By analyzing the photocurrent dependence simultaneously on temperature and on light intensity, this transition is interpreted as a change from monomolecular to bimolecular recombination. These results might be useful for other semiconducting photogenerating materials, not necessarily PBIs or even organic semiconductors, which also show transport behavior changes at singular temperatures not connected with structural or phase transitions.

¿Las plantas pueden revertir su sexo?

The sex determination is an event of great relevance in the life cycle of those plants that reproduce sexually. In recent years we have obtained substantial advances in elucidating the mechanisms involved, and in particular the role of epigenetic factors, in plant sex determination. Taking into account the relevance of this topic especially for dioecious species threatened as Cycads studies have been underwent to determine the basis of epigenetics of sex and to test whether compounds such as the de-metilating agent 5-azacytidine may be involved in sexual expression. This paper reviews the main progress made within this context obtained in Z. furfuraceae as well as cases of reversal of sex in cycads and different plant species.