Study on Nonlinear and Charge Transport Properties of Multi-branched Molecules via Quantum Chemical Methods.

Abstract

This research project aims to find multi-branched organic molecules with promising nonlinear optical (NLO) and charge transport properties for technological applications, seeking in particular to understand and explore the effect of interbranch electronic coupling on these properties. The recent literature reports that multi-branched organic molecules represent a class of molecules with high potential for application in the photonics and organic electronics areas, which highlights the importance of investigating this class of molecules. The multi-branched molecules to be investigated in this project consist of a core with donor charge character to which are covalently linked two (quadrupolar structure) or three (octupolar structure) molecular branches with dipolar character. Although still little studied systematically, it is understood that in such molecules the electronic coupling between their molecular branches promotes an additive effect, or even a cooperative one, which explains their interesting NLO and charge transport (intramolecular transfer) properties. In this project, quantum chemistry methods based on the density functional theory will be employed to assess and predict the quality of the projected multi-branched molecules for photonics applications involving the two-photon absorption (2PA) and the second harmonic generation (SHG). The methods will also be employed for the determination of parameters that characterize the charge transport properties of these molecules, such as the electron affinity, the ionization potential and reorganization energies, which are crucial to predict the quality of the molecules for applications in organic electronics. In order to gain a deeper understanding on the NLO and charge transport properties of these molecules, these properties will still be modeled using essential state models and the Frenkel exciton model. The use of these physical models will allow to evaluate the importance of the electronic coupling to the NLO and charge transport properties of these molecules and, from the information obtained, multi-branched molecules in which the electronic coupling enhances the NLO and charge transport properties will be projected and also assessed. (AU)