6 research outputs found
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
Polymer-dispersed liquid crystals : from the nematic curvilinear aligned phase to ferroelectric films
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