title: Time-dependent stokes shifts of fluorescent dyes in the hydrophobic backbone region of a phospholipid bilayer: combination of fluorescence spectroscopy and ab initio calculations.
abstract: We explored the time-dependent Stokes shifts of fluorescent dyes containing an anthroyloxy chromophore (2-AS, 9-AS, and 16-AP) in bilayers composed of palmitoyl-oleoyl-phosphatidylcholine. The obtained data revealed a nontrivial solvation response of these dyes, which are located in the backbone region of the bilayer with a gradually increasing depth. For comparison, steady-state emission spectra in the neat solvents of various polarities and viscosities were also recorded. The results indicate that on the short picosecond time scale the AS dyes undergo complex photophysics including formation of states with a charge-transfer character. This observation is supported by ab initio calculations of the excited states of 9-methylanthroate. The slower nanosecond part of the relaxation process can be attributed to the solvation response of the dyes. A slowdown in solvent relaxation is observed upon moving toward the center of the bilayer. A mechanism similar to preferential solvation present in the mixture of a polar and nonpolar solvent is considered to explain the obtained data.
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, Prague 8, Czech Republic. jan.sykora@jh-inst.cas.cz
authors.forename: Jan
authors.initials: J
authors.lastname: Sýkora
authors.forename: Petr
authors.initials: P
authors.lastname: Slavícek
authors.forename: Pavel
authors.initials: P
authors.lastname: Jungwirth
authors.forename: Justyna
authors.initials: J
authors.lastname: Barucha
authors.forename: Martin
authors.initials: M
authors.lastname: Hof
mesh_terms: D003198:Computer Simulation; D005456:Fluorescent Dyes / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D010743:Phospholipids / Q000737:chemistry*; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000379:methods; D013997:Time Factors
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D010743:Phospholipids