title: Dark states in ionic oligothiophene bioprobes--evidence from fluorescence correlation spectroscopy and dynamic light scattering.
abstract: Luminescent conjugated polyelectrolytes (LCPs) can upon interaction with biological macromolecules change their luminescent properties, and thereby serve as conformation- and interaction-sensitive biomolecular probes. However, to exploit this in a more quantitative manner, there is a need to better understand the photophysical processes involved. We report studies of the conjugated pentameric oligothiophene derivative p-FTAA, which changes optical properties with different p-FTAA concentrations in aqueous buffers, and in a pH and oxygen saturation dependent manner. Using dynamic light scattering, luminescence spectroscopy and fluorescence correlation spectroscopy, we find evidence for a monomer-dimer equilibrium, for the formation of large clusters of p-FTAA in aqueous environment, and can couple aggregation to changed emission properties of oligothiophenes. In addition, we observe the presence of at least two dark transient states, one presumably being a triplet state. Oxygen was found to statically quench the p-FTAA fluorescence but also to promote molecular fluorescence by quenching dark transient states of the p-FTAA molecules. Taken together, this study provides knowledge of fluorescence and photophysical features essential for applying p-FTAA and other oligothiophene derivatives for diagnostic purposes, including detection and staining of amyloid aggregates.
authors.affiliation: Biomolecular and Organic Electronics, Department of Applied Physics, IFM, Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Heike
authors.initials: H
authors.lastname: Hevekerl
authors.forename: Jens
authors.initials: J
authors.lastname: Wigenius
authors.forename: Gustav
authors.initials: G
authors.lastname: Persson
authors.forename: Olle
authors.initials: O
authors.lastname: Inganäs
authors.forename: Jerker
authors.initials: J
authors.lastname: Widengren
mesh_terms: D000085:Acetates / Q000737:chemistry*; D015374:Biosensing Techniques; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D008027:Light; D049408:Luminescent Agents / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence; D013876:Thiophenes / Q000737:chemistry*
chemical_list: D000085:Acetates; D049408:Luminescent Agents; D013876:Thiophenes; C572917:pentamer formyl thiophene acetic acid; D010100:Oxygen