Dresden 2011 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 31: Organic Semiconductors IV: Excitations and Charges (jointly with HL, DS)
CPP 31.6: Talk
Wednesday, March 16, 2011, 15:45–16:00, ZEU 222
The effect of energetic disorder on the spectral diffusion of singlet and triplet states in phenylene-type polymers — •Anna Köhler1, Sebastian T Hoffmann1, Heinz Bässler1, Jan-Moritz Koenen2, and Ullrich Scherf2 — 1Experimental physics II, Universität Bayreuth — 2Macromolecular Chemistry, Bergische Universität Wuppertal
We have employed quasicontinuous temperature dependent fluorescence and phosphorescence spectroscopy to monitor the spectral diffusion of singlet and triplet excitons in a series of pi-conjugated polymers.(1) The experimental results are complemented by Monte-Carlo simulations. We investigated (i) how spectral diffusion is controlled by the degree of energetic disorder present in the amorphous film and (ii) how this process depends on the range of the electronic coupling by comparing singlet exciton diffusion via long-range Förster transfer against triplet exciton diffusion by short-range Dexter transfer. For singlets, we find that the fluorescence spectra bear out a bathochromic shift upon cooling the sample down to a critical temperature below which the shift saturates. This bathochromic shift is a signature of spectral relaxation. In contrast we observe a hypsochromic shift of the phosphorescence spectra below a characteristic temperature for triplets in systems with at least moderate energetic disorder. We show that Random-walk theory applied to excitation transport within a Gaussian density-of-states distribution is both necessary and sufficient to rationalize the experimental results in a quantitative fashion. (1) S.T. Hoffmann et al. PRB 81, 115103 (2010)