Berlin 2014 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 5: Posters 1: Electronic Spectroscopy, Photochemistry, Femtosecond Spectroscopy

MO 5.5: Poster

Montag, 17. März 2014, 16:30–18:30, Spree-Palais

Single-Molecule Spectroscopy on π-Conjugated Oligomers and Polymers — •Sebastian Baderschneider¹, Ullrich Scherf², Jürgen Köhler¹, and Richard Hildner¹ — ¹Experimentalphysik IV and BIMF, Universität Bayreuth, Universitätsstrasse 30, 95447 Bayreuth — ²Fachbereich C - Mathematik und Naturwissenschaften & Institut für Polymertechnologie, Universität Wuppertal, Gauss-Strasse 20, 42097 Wuppertal

We employ low-temperature single-molecule fluorescence spectroscopy on a ladder-type oligo(para-phenylene) with two chemical repeat units, constituting a model system for a chromophore on a conjugated polymer. The oligomer spectra are compared to those of single chromophores of the corresponding ladder-type polymer with ≈ 80 repeat units. The profile of the electronic spectra of both single oligomers and polymers feature a narrow line with a width of 1 - 80 cm⁻¹ (FWHM) that we attribute to the purely electronic transition (zero-phonon line, ZPL). For the oligomer the ZPL is accompanied by a weaker line at lower energy (≈ 150 cm⁻¹) that is ascribed to an intra-molecular backbone stretch mode coupling to the electronic transition. For the polymer, in contrast, this vibration is not detectable. Instead we identified a shoulder in the low-energy tail of the ZPL that arises from phonon modes of the surrounding matrix (mean phonon energy: ≈ 20 cm⁻¹). For both systems the electron-phonon coupling strength to these low-energy (< 200 cm⁻¹) vibrational modes is weak with a Debye-Waller factor > 0.2.