Hannover 2010 – scientific programme

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MO: Fachverband Molekülphysik

MO 14: Femtosecond Spectroscopy II

MO 14.6: Talk

Wednesday, March 10, 2010, 15:30–15:45, F 102

Energy Transport by Exciton Diffusion in Thin Organic Films — •Franziska Hellmuth and Stefan Lochbrunner — Universitätsplatz 3, 18055 Rostock

Thin organic films are central components of organic light emitting diodes, solar cells and plastic electronics. Energy transport via exciton migration is a crucial element for their functional capabilities. However, in most organic films trapping limits the transfer to short distances. To circumvent this limitation we incorporate in polymer films dye molecules as active sites. Perylene Red is used as dye due to its high quantum yield and little interaction with the environment. To characterize the energy transport properties an additional energy acceptor is added at low concentration to the film (0.1 M Perylene Red, 1.4 mM acceptor). We find that the excitation is transferred from the optically excited Perylene Red molecules to the acceptor with an efficiency of 90%. To model the energy transfer and calculate the exciton diffusion length a diffusion approach is applied. A diffusion length of about 30 nm is estimated for the studied system. The results are in good agreement with Förster theory. However, femtosecond pump probe measurements indicate a red shift of the transient spectra within the first picoseconds. The evaluation of the excitation induced anisotropy and its picosecond decay leads to distinctly shorter transfer times than predicted by Förster theory. Those two facts might be explained by dispersive energy transport, i.e. the primary transfer steps lead from more energetic donors to less energetic acceptor states.