Computational studies on photophysical properties of molecular aggregates

Resumen

The present project is devoted to analyze the electronic structure of the ground and excited electronic states and the associated optical properties of organic dyes and supramolecular assemblies of potential interest for optical applications. Following these points, the project has been classified in three interrelated research lines. First, we report a join experimental and computational investigation at the DFT level on monomers and covalently-linked dimers of borondifluoride complexes of curcuminoid derivatives, a prototype example of conjugated organic dyes. The nature of the electronic states was analyzed by employing an effective approach based on the development of the electronic wave functions in terms of diabatic basis states. A similar approach was used in a second study for rationalizing the absorption and fluorescence emission properties of conjugated dyes composed of dimethylamino flavylium heterocycles linked by a polymethine chain, which were recently reported to act as efficient shortwave infrared emitters. Finally, a third study focused on the development of a new theoretical approach allowing the precise characterization of electronic excited states resulting from the interaction between chromophoric units in model molecular aggregates. Theoretical descriptions of such systems are usually achieved by means of excitonic models, using effective Hamiltonians built on a basis of diabatic states that enable physical interpretations in terms of local excitations, charge transfer, or multiexcitonic configurations. The alternative approach that has been developed is based on a diabatization scheme, which allows the decomposition of the adiabatic excited state energies of molecular aggregates into contributions issued from intermolecular couplings, without requiring any a priori definition of diabatic states. This methodology constitutes a promising tool to extract accurate ab initio diabatic state energies and interstate couplings for eventual derivation of model excitonic Hamiltonians.