Karl Franzens University Graz
Graz University of Technology
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Karl Franzens University Graz | Graz University of Technology | |
Spotlight on (Chiral) Molecular Excitons in Squaraine Thin Films Video: https://tugraz.webex.com/meet/markus.koch Here, the material system of choice to study structure-correlated excitonic properties are anilino squaraine dyes. Their donor-acceptor-donor type pi-conjugated backbone allows for intense interactions with visible light and carries the transition dipole moment. Terminal groups attached to the backbone act as structure directors for the molecular aggregation and crystallization. The excitonic transitions arise from the linear combination of the molecular transition dipole moments for two or more molecules within a crystallographic unit cell. In case of homo-chiral groups another property arises as a result of the homo-chiral arrangement, which is circular dichroism, the differential absorption of left and right circular polarized light. Depending on the nature and extend of the (supra-)molecular interactions, this excitonic circular dichroism can be greatly enhanced gaining technological relevance.[1] All excitonic couplings show characteristic polarization patterns in micro-crystalline-textured thin film samples, and they can be spotted by polarized spectro-microscopy or imaging ellipsometry and polarimetry in a quantitative fashion.[2,3] By this the local texture and polymorphic structures are associated with the circular and linear optical anisotropies to get a complete picture of molecular alignment and excitonic transitions. |