Evidence of a Photoinduced Electron-Transfer Mechanism in the Fluorescence Self-quenching of 2,5-Substituted Selenophenes Prepared through In Situ Reduction of Elemental Selenium in Superbasic Media.

A series of new 2,5-disubstituted selenophene derivatives are described from elemental selenium and 1,3-diynes in superbasic media. The activation of elemental selenium in a KOH/DMSO system allows cyclization with conjugated diynes at room temperature. The cyclization reaction is extended to a broad range of functional groups, for which photophysics were experimentally and theoretically investigated. The selenophene derivatives present absorption maxima in the UV-A region and fluorescence emission in the violet-to-blue region. Fluorescence decay profiles were obtained showing a monoexponential decay with fast fluorescence lifetimes (∼0.118 ns), as predicted by the Strickler-Berg relations. In general, in both investigations, no dependence on the solvent polarity on the absorption and emission maxima location was observed. On the other hand, solvents and substituents are shown to play a role in the fluorescence quantum yield values. In addition, a fluorescence self-quenching behavior could be observed, related to a photoinduced electron-transfer mechanism. Theoretical calculations performed at the MP2/ADC(2)/cc-pVDZ level of theory were performed in order to investigate the photophysical features of this series of selenophene derivatives.

White-light generation from all-solution-processed OLEDs using a benzothiazole-salophen derivative reactive to the ESIPT process.

A salicylidene derivative, N,N'-bis(salicylidene)-(2-(3',4'-diaminophenyl)benzothiazole) (BTS), reactive in the Excited State Intramolecular Proton Transfer (ESIPT) process, was synthesized and its photophysical properties were evaluated, presenting an emission covering the entire range of the visible spectrum. Due to its broad emission band, BTS was successfully tested as an active layer in solution-processed organic light-emitting diodes with white-light emission. These diodes were prepared using solution-based protocols with the dye solubilized in a poly(9-vinylcarbazole) matrix. Different guest : host (polymer : BTS) molar ratios were used to optimize the diode performance. The optimized architecture rendered the best so far all-solution-processed ESIPT OLED with a luminance of 34 cd m-2 at 13.5 V with CIE coordinates 0.31, 0.40.

Photoacidity as a tool to rationalize excited state intramolecular proton transfer reactivity in flavonols.

This work presents the determination of acidic strengths at the electronic ground and excited states (pKa and ) of three flavonol derivatives using electronic absorption and fluorescence emission spectroscopy. The differences of the pKa and values were successfully correlated with the molecular structures according to the substitution pattern at the flavonol structure (hydrogen, diethylamino or fluoro moieties). In order to obtain more information about the observed photoacidity of these superacids, geometry optimizations and excitation energy calculations were performed at the CAM-B3LYP/6-311++G(d,p) level for their neutral, protonated and deprotonated species.

A relativistic study of the electronic and magnetic properties of cerocene and thorocene and its anions.

In this study, we evaluated the importance of the relativistic effects on the optical and magnetic properties of cerocene and thorocene and its corresponding anions. The optimized molecular structures show D(8h) symmetry for all systems, in good agreement with the experimental data. Atomic charges were analyzed using different approaches (Mulliken, AIM, multipole, and NBO), and the results suggest that the net charge on the thorium is greater than on the cerium atom; however, none of the methodologies were able to predict the expected net charge Ce(III) and Th(IV) atoms. However, by an energy decomposition analysis, a significant electrostatic, ionic, interaction, ~58% and ~61%, was found between the metal and the COT(2-) rings, respectively. The calculated electronic excitations are underestimated in comparison with the experimental data, while the calculated EPR g-tensors are in agreement with previous theoretical and experimental data. Besides, the NICS analysis shows an increased ring electron delocalization due to the lanthanide and actinide metals.