Total absorption spectrum of benzene aggregates obtained from two different approaches

CONTEXT

The study of molecular aggregation effects on the electronic spectrum is essential for the development of optoelectronic devices. However, investigating the entire valence absorption spectrum of aggregates using quantum mechanical methods is a challenging task. In this work, we perform systematic simulations of the absorption spectrum of benzene molecular clusters up to 35 eV applying two approaches based on time-dependent density functional theory. The results show that depending on the dimer packing, different energy shifts occur for the symmetry allowed [Formula: see text] transition, in comparison to the monomer. The transition intensity increases for the band around 6 eV for larger aggregates from the monomer to dimers and tetramer, indicating the occurrence of the symmetry forbidden (in [Formula: see text] point group) [Formula: see text] [Formula: see text] transition. The benzene crystal exhibits a large redshift following the experimental spectrum. Also, the continuum regions of all spectra show a good agreement with the experiments both in gas and solid phases.

METHODS

Geometry optimization of the monomer was carried out with Gaussian 09 software using the PBE0/def2-TZVP level of theory. We used dimers and tetramer molecular geometries extracted from the experimental crystal structure. The absorption spectra were directly obtained by the Liouville-Lanczos TDDFT approach with plane waves basis set or indirectly by TDDFT pseudo-spectra calculated in a [Formula: see text] basis followed by analytic continuation procedure to obtain complex polarizability. The former is available at Quantum ESPRESSO, and the latter was calculated using Gaussian 09 with the post-processing performed with a code previously developed in our group.

On the Nature of Charge-Injecting Contacts in Organic Field-Effect Transistors

Organic field-effect transistors (OFETs) are key enabling devices for plastic electronics technology, which has a potentially disruptive impact on a variety of application fields, such as health, safety, and communication. Despite the tremendous advancements in understanding the OFET working mechanisms and device performance, further insights into the complex correlation between the nature of the charge-injecting contacts and the electrical characteristics of devices are still necessary. Here, an in-depth study of the metal-organic interfaces that provides a direct correlation to the performance of OFET devices is reported. The combination of synchrotron X-ray spectroscopy, atomic force microscopy, electron microscopy, and theoretical simulations on two selected electron transport organic semiconductors with tailored chemical structures allows us to gain insights into the nature of the injecting contacts. This multiple analysis repeated at the different stages of contact formation provides a clear picture on the synergy between organic/metal interactions, interfacial morphology, and structural organization of the electrode. The simultaneous synchrotron X-ray experiments and electrical measurements of OFETs in operando uncovers how the nature of the charge-injecting contacts has a direct impact on the injection potential of OFETs.

Nanoscale morphology and electronic coupling at the interface between indium tin oxide and organic molecular materials

The correlation between nanoscale morphology and charge injection rates at the interface between an organic semiconductor layer and a transparent metal oxide electrode was investigated by integrating molecular dynamics simulations with electronic structure calculations. The simulation approach proposed has been applied to the analysis of the hole injection mechanism at the interface between an amorphous layer of tris[(3-phenyl-1H-benzimidazol-1-yl-2(3H)-ylidene)-1,2-phenylene]Ir (DPBIC), a hole transport and emitter molecule, and the surface of indium tin oxide (ITO), a material commonly used as anode in OLEDs. The link between interface morphology and charge injection was investigated by implementing a two-step, top-down simulation approach. Namely, nanoscale molecular aggregation phenomena at the organic/electrode interface were first assessed by molecular dynamics simulations, mimicking different processing conditions, and followed by density functional theory calculations of the electronic coupling between molecular levels and the manifold of electrode states involved in the charge injection process. The correlation between structural parameters and electronic coupling suggests a significant role of specific molecule/electrode configurations on charge transport processes at the interface, resulting in a broad distribution of charge injection rates, and highlights the link between molecular structure, nanoscale aggregation and processing in the realization of heterointerfaces for efficient charge injection in organic electronic devices.

Spatial and orientational dependence of electron transfer parameters in aggregates of iridium-containing host materials for OLEDs: coupling constrained density functional theory with molecular dynamics

The integration between molecular dynamics and constrained density functional theory allows to evaluate charge transport parameters in bulk organic semiconductors.

Modeling electrochromic poly-dioxythiophene-containing materials through TDDFT

Here we report the first colormetric model using mPW1PBE/cc-PVDZ with CPCM to predict the chemical properties of three electrochromic polymers in which the largest UV-Vis absolute peak maximum difference when compared to experiment was 14 nm.