Berlin 2018 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 3: Organic Electronics and Photovoltaics - Layer Morphology and Molecular Aggregation
CPP 3.11: Vortrag
Montag, 12. März 2018, 12:30–12:45, C 243
Elucidating Aggregation Pathways And Structural properties Of Chromophores With The Help Of MD-Simulations — •Axel Bourdick1, Markus Reichenberger2, Anna Köhler2, and Stephan Gekle1 — 1Biofluid Simulation and Modeling, University of Bayreuth, 95440 Bayreuth (Germany) — 2Experimental Physics II, University of Bayreuth, 95440 Bayreuth (Germany)
We investigate the aggregation behaviour of the donor-acceptor molecules pDTS(FBTTh2)2 ("T1") and p-SIDT(FBTTh2)2 ("H1") in MTHF solutions. Using optical spectroscopy, we find that T1 forms aggregates in solution while H1 aggregates only when processed as a thin film, but not in solution. Free energy molecular dynamics (MD) simulations based on force-fields derived from quantum-mechanical density functional theory fully reproduce this difference. Interestingly, our simulations reveal that this difference is not due to the lengthy carbon side chains. Instead, it can be traced back to the different molecular symmetry which allows T1 to form an aggregated state in which the central donor units are spatially well separated while a similar configuration is sterically impossible for H1. As a consequence, any aggregation of H1 necessarily involves aggregation of the central donors which requires, as a first step, stripping the central donor of its protective MTHF solvation shell. This unfavorable process leads to a significant kinetic hindrance for aggregation and explain the strongly differing aggregation behavior of T1/H1 in MTHF despite their otherwise similar structure.