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Photo-induced relaxation processes leading to excimer formations or other traps are in the focus of many investigations of optoelectronic materials because they severely affect the efficiencies of corresponding devices. Such relaxation effects comprise inter-monomer distortions in which the orientations of the monomer change with respect to each other, whereas intra-monomer distortions are variations in the geometry of single monomers. Such distortions are generally neglected in quantum chemical investigations of organic dye aggregates due to the accompanied high computational costs. In the present study, we investigate their relevance using perylene-bisimide dimers and diindenoperylene tetramers as model systems. Our calculations underline the importance of intra-monomer distortions on the shape of the potential energy surfaces as a function of the coupling between the monomers. The latter is shown to depend strongly on the electronic state under consideration. In particular, it differs between the first and second excited state of the aggregate. Additionally, the magnitude of the geometrical relaxation decreases if the exciton is delocalized over an increasing number of monomers. For the interpretation of the vibronic coupling model, pseudo-Jahn–Teller or Marcus theory can be employed. In the first part of this paper, we establish the accuracy of density functional theory-based approaches for the prediction of vibrationally resolved absorption spectra of organic semiconductors. These investigations underline the accuracy of those approaches although shortcomings become obvious as well. These calculations also indicate the strength of intra-monomer relaxation effects. [ABSTRACT FROM AUTHOR]

A study on phosphorchalcogenides conducted a detailed analysis of its vibrational spectrum to investigate the strength of its chemical bonds. Ab initio methods were used to compute the infrared and Raman vibrational frequencies to assign the experimental spectra of the P4O6Sm (m = 0-4) series. The differences between the P4O6Sm (m = 0-4) series and the oxygen series P4On (n= 6-10) were also analyzed to determine if oxygen influences the P4O6 cage bonds more strongly than sulfur substituents. Results are presented.

Large scale MR-CI calculations were used to study the reaction mechanism and energetics of the C(super2)-C(super7) and C(super2)-C(super6) cyclization of (Z)-1,2,4-heptatriene-6-yne. The influence of vibrational motion and temperature corrections on the barrier height of the reactions is also estimated. The first excited states were computed to give estimates of possible switches from diradical to zwitterionic reactions.

The bonding properties of the P4On (n = 6-10) series has been investigated using a combination of theoretical and experimental spectroscopy. The correlation between the spectra of the components and the shifts of the vibrational frequencies within the series were analyzed. The results showed that as the number of oxygens in the phosphorus centers increased, the frequencies of most modes involving the cage motions also increased. This indicates the increase in the strength of the P-O cage bonds along the P4On series.

The theoretical vibration spectra of P4O6X (X = S and Se) molecules are determined by employing the Hartree-Frock method in combination with a DZP basis set. A comparison of the three spectra and analysis of the shifts of the vibrational frequencies in the spectra indicated the significant influence of the mass effect on the different bond strengths of the compounds. Furthermore, compounds exhibited similar magnitudes of geometrica distortion.