Photophysics of a series of efficient fluorescent pH probes for dual-emission-wavelength measurements in aqueous solutions

Publication Type:

Journal Article

Source:

CHEMISTRY-A EUROPEAN JOURNAL, WILEY-V C H VERLAG GMBH, Volume 12, Number 4, PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY, p.1097-1113 (2006)

DOI:

10.1002/chem.200500619

Keywords:

CROSS-SECTIONS; DONOR; EQUILIBRIUM-CONSTANTS; FLUOROPHORES; MICROSCOPY; MULTIWAVELENGTH SPECTROSCOPIC DATA; PROTEIN TITRATION CURVES; PROTON-TRANSFER; SALTS; SPECTRAL PROPERTIES

Abstract:

This paper evaluates the 5-aryl-2-pyridyloxazole backbone to engineer donor-acceptor fluorescent pH probes after one- or two-photon absorption. Parent fluorophores, as well as derivatives that can be used to label biomolecules, can be easily obtained in good yields. These molecules exhibit a large one-photon absorption in the near-UV range, and a strong fluorescence emission that covers the whole visible domain. The 5-aryl-2-pyridyloxazole derivatives also possess significant cross sections for two-photon absorption. Upon pyridine protonation, large shifts were observed in the absorption spectra after one- and two-photon excitation, as well as in the emission spectra. This feature was used to measure the pK(a) of the investigated compounds that range between 2 and 8. In most of the investigated derivatives, the pK(a) increased upon light excitation and protonation exchanges took place during the lifetime of the excited state, as shown by phase-modulation fluorometry analysis. Several 5-aryl-2pyridyloxazole derivatives are suggested as efficient probes to reliably measure the pH of aqueous solutions by means of ratiometric methods that are dependent on fluorescence emission.