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RESEARCH PRODUCT

Flexibility of phenylene oligomers revealed by single molecule spectroscopy

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The rigidity of a p-phenylene oligomer (p-terphenyl) has been investigated by single molecule confocal fluorescence microscopy. Two different rylene diimide dyes attached to the terminal positions of the oligomer allowed for wavelength selective excitation of the two chromophores. In combination with polarization modulation the spatial orientation of the transition dipoles of both end groups could be determined independently. We have analyzed 597 single molecules in two different polymer hosts, polymethylmethacrylate and Zeonex. On average we find a 22 degrees deviation from the linear gas phase geometry (T = 0 K), indicating a rather high flexibility of the p-phenylene oligomer independent of the matrix. To substantiate our experimental results, we have performed quantum chemical calculations at the density functional theory level for the molecular geometry and the electronic excitations. Our findings are in agreement with former experiments on the persistence length of poly(p-phenylenes).