Reduction of 2-(BMes2)pyrene (B1) and 2,7-bis(BMes2)pyrene (B2) gives rise to anions with extensive delocalization over the pyrenylene bridge and between the boron centers at the 2- and 2,7-positions, the typically unconjugated sites in the pyrene framework. One-electron reduction of B2 gives a radical anion with a centrosymmetric semiquinoidal structure, while two-electron reduction produces a quinoidal singlet dianion with biradicaloid character and a relatively large S0-T1 gap. These results have been confirmed by cyclic voltammetry, X-ray crystallography, DFT/CASSCF calculations, NMR, EPR, and UV-vis-NIR spectroscopy.

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Interface structures of a variety of molecular p-type semiconductors in heterojunction with fullerene C60 were generated in molecular dynamic simulations. Using the dimer method (i.e., dimers were used as the quantum-mechanical system) along with a continuum solvation approach and macroscopic electric fields, energetic profiles of the interfaces of organic solar cells (OSCs) were calculated. Several important loss mechanisms, such as exciton trapping, charge trapping, and interfacial charge-transfer traps, were observed. Structure–property relationships were established. They reveal that apart from the molecular orientation and dipolarity, molecular size is an important parameter that influences potential loss mechanisms.

We present an analysis of the optoelectronic properties of merocyanine dyes by means of VBSCF, TDDFT and high-level ab initio calculations. The electronic structure of merocyanines can be described as a superposition of two resonance structures, a neutral and zwitterionic one. Calculated VB weights for these resonance structures demonstrate the importance of strong accepting groups in increasing the weight of the zwitterionic structures of different merocyanines. The dependence of exciton and charge reorganization energies on the VB weights' composition is analyzed, demonstrating that the special case of equal contributions of both structures, the so-called cyanine limit, goes along with minimal exciton and charge reorganization energies. For the latter, it is shown that the external (outer-sphere) reorganization energy plays a crucial role. Furthermore, a careful investigation of the excited-state behavior of merocyanines indicates that a possible excited-state torsion might be another important parameter for merocyanine-based optoelectronic devices, while internal (innersphere) charge reorganization energies of a variety of merocyanines are in a typical range for molecular semiconductors.

Charge transport properties of materials composed of small organic molecules are important for numerous optoelectronic applications. A material's ability to transport charges is considerably influenced by the charge reorganization energies of the composing molecules. Hence, predictions about charge-transport properties of organic materials deserve reliable statements about these charge reorganization energies. However, using density functional theory which is mostly used for the predictions, the computed reorganization energies depend strongly on the chosen functional. To gain insight, a benchmark of various density functionals for the accurate calculation of charge reorganization energies is presented. A correlation between the charge reorganization energies and the ionization potentials is found which suggests applying IP-tuning to obtain reliable values for charge reorganization energies. According to benchmark investigations with IP-EOM-CCSD single-point calculations, the tuned functionals provide indeed more reliable charge reorganization energies. Among the standard functionals, ωB97X-D and SOGGA11X yield accurate charge reorganization energies in comparison with IP-EOM-CCSD values. © 2016 Wiley Periodicals, Inc.