Theoretical Investigation of the Absorption Properties of 3,6-Bis(thiophen-2-yl)diketopyrrolopyrrole Derivatives in the Solid State

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The aim of this research project is the theoretical investigation of the absorption properties of 3,6-bis(thiophen-2-yl)diketopyrrolopyrrole (TDPP) chromophores in thin films. It has been recently shown that the absorption spectra of TDPP dyes in the solid state are significantly influenced by the different substituents at the lactam units of the chromophores, whereas no changes are observed for the respective monomeric dyes in solution. Thus, the different absorption properties in thin films can be attributed to the different packing in the solid state which, however, cannot be explained based on simple exciton theory. Therefore, the goal of this project is to elucidate the interchromophoric interactions leading to the different optical properties of TDPP dyes in the solid state using an extension of the exciton theory including exciton-vibrational and short-range coupling. In addition, the solid state absorption spectra will be also simulated based on the essential states model to account for polarization effects as well as interchromophoric charge transfer interactions. The gained insights will contribute to establish packing-structure-properties relationships for the class of diketopyrrolopyrrole (DPP) dyes, which exhibit high potential for application in organic electronics and photovoltaics.