Unraveling the electrochemical and spectroscopic properties of neutral and negatively charged perylene tetraethylesters

A detailed investigation of the energy levels of perylene-3,4,9,10-tetracarboxylic tetraethylester as a representative compound for the whole family of perylene esters was performed. It was revealed via electrochemical measurements that one oxidation and two reductions take place. The bandgaps determined via the electrochemical approach are in good agreement with the optical bandgap obtained from the absorption spectra via a Tauc plot. In addition, absorption spectra in dependence of the electrochemical potential were the basis for extensive quantum-chemical calculations of the neutral, monoanionic, and dianionic molecules. For this purpose, calculations based on density functional theory were compared with post-Hartree–Fock methods and the CAM-B3LYP functional proved to be the most reliable choice for the calculation of absorption spectra. Furthermore, spectral features found experimentally could be reproduced with vibronic calculations and allowed to understand their origins. In particular, the two lowest energy absorption bands of the anion are not caused by absorption of two distinct electronic states, which might have been expected from vertical excitation calculations, but both states exhibit a strong vibronic progression resulting in contributions to both bands

Effects of Composition and Polymerization Conditions on the Electro-Optic Performance of Liquid Crystal–Polymer Composites Doped with Ferroelectric Nanoparticles

The presence of a polymer network and/or the addition of ferroelectric nanoparticles to a nematic liquid crystal are found to lower transition temperatures and birefringence, which indicates reduced orientational order. In addition, the electro-optic switching voltage is considerably increased when a polymer network is formed by in situ polymerization in the nematic state. However, the resulting polymer network liquid crystal switches at similar voltages as the neat liquid crystal when polymerization is performed at an elevated temperature in the isotropic state. When nanoparticle dispersions are polymerized at an applied DC voltage, the transition temperatures and switching voltages are reduced, yet they are larger than those observed for polymer network liquid crystals without nanoparticles polymerized in the isotropic phase

Curved polar dibenzocoronene esters and imides versus their planar centrosymmetric homologs: photophysical and optoelectronic analysis

Isomeric columnar liquid crystalline dibenzo­[a,j]­coronene-tetracarboxylic tetraesters and bisimides that differ only by having either a centrosymmetric bis-peri or a polar bis-ortho substitution pattern, exhibit striking differences in the makeup of their electronic ground and excited states as well as in their performance as emitters in electroluminescent diodes. Quantum chemical calculations show that the key molecular orbitals consist essentially of perylene-like ones responsible for the longest-wavelength absorptions and coronene-like ones responsible for the very intense shorter-wavelength absorptions with modifications, in particular for the ortho-imide due to its pronounced deviation from planarity. Additionally, the ortho-imide and ortho-ester, which tend to a slipped-stacked configuration within their columns due to their nonplanarity, strongly outperform their peri-counterparts as emitters in organic light emitting diodes