Highly photostable "super"-photoacids for ultrasensitive fluorescence spectroscopy.
The photoacid 8-hydroxypyren-1,3,6-trisulfonic acid (HPTS, pyranine) is a widely used model compound for the examination of excited state proton transfer (ESPT). We synthesized five "super"-photoacids with varying hydrophilicity and acidity on the basis of HPTS. By chemical modification of the three sulfonic acid substituents, the photoacidity is enhanced by up to more than five logarithmic units from pK*≈ 1.4 to ∼-3.9 for the most acidic compound. As a result, nearly quantitative ESPT in DMSO can be observed. The novel photoacids were characterized by steady-state and time-resolved fluorescence techniques showing distinctively red shifted spectra compared to HPTS while maintaining a high quantum yield near 90%. Photostability of the compounds was checked by fluorescence correlation spectroscopy (FCS) and was found to be adequately high for ultrasensitive fluorescence spectroscopy. The described photoacids present a valuable palette for a wide range of applications, especially when the properties of HPTS, i.e. highly charged, low photostability and only moderate excited state acidity, are limiting.
Biophysical Chemistry, Saarland University, Campus B2 2, 66123 Saarbrücken, Germany. g.jung@mx.uni-saarland.de.
Björn
B
Finkler
Christian
C
Spies
Michael
M
Vester
Frederick
F
Walte
Kathrin
K
Omlor
Iris
I
Riemann
Manuel
M
Zimmer
Frank
F
Stracke
Markus
M
Gerhards
Gregor
G
Jung
D000042:Absorption; D002463:Cell Membrane Permeability; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics; D056945:Hep G2 Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D015394:Molecular Structure; D012997:Solvents / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013057:Spectrum Analysis; D013449:Sulfonamides / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics; D013451:Sulfonic Acids / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics; D014867:Water / Q000737:chemistry
D005456:Fluorescent Dyes; D012997:Solvents; D013449:Sulfonamides; D013451:Sulfonic Acids; D014867:Water