Solvent and pH effects on the fluorescence of 7-(Dimethylamino)-2- fluorenesulfonate

Kwanghee Koh Park, Joon Woo Park, Andrew D. Hamilton

Research output: Contribution to journalArticle

Abstract

A novel water-soluble solvatochromic molecule, 7-(dimethylamino)-2- fluorenesulfonate (2,7-DAFS), was prepared by a three-step reaction from 2-nitrofluorene in good overall yield. The pH and solvent effects on the UV-VIS absorption and fluorescence spectra of 2,7-DAFS have been studied. Protonation of the dimethylamino group switches the absorption from intramolecular charge-transfer (ICT) to π∈→∈π* transition. The ground state pKa value of 2,7-DAFS was determined as 4.51. The fluorescence spectrum of the excited basic form, *(DAFS), shows a structureless single band with a large Stokes shift, whereas that of the acidic form, *( +HDAFS), exhibits a structured band with a small Stokes shift. The emission intensities of the basic and acidic forms versus pH/Ho plots show stretched sigmoidal curves and indicate that (1) the rate of deprotonation of *( +HDAFS) is comparable to the fluorescence decay of the species, and (2) the efficient proton-induced quenching of *(DAFS) fluorescence occurs. The pKa *was estimated as -1.7 from the fluorescence titration curve. The fluorescence maximum of *(DAFS) is blue-shifted as the polarity of solvent decreases. However, no clear dependency of the emission intensity and spectral half width, and thus fluorescence quantum yield, on the solvent polarity was revealed. It appears that the fluorescence sensitivity of 2,7-DAFS is 15∈ ∈25 times greater than the sensitivity of a widely utilized fluorescent probe, 5-(dimethylamino)-1-naphthalenesulfonate. This higher sensitivity, together with the ease of derivatization, would provide the fluorene-based fluorescent molecules significant advantages for a variety of applications.

Original languageEnglish (US)
Pages (from-to)361-369
Number of pages9
JournalJournal of Fluorescence
Volume17
Issue number4
DOIs
StatePublished - Jul 2007

Keywords

  • Aminofluorene
  • Fluorescent probes
  • Intramolecular charge transfer
  • Proton-induced quenching
  • Prototropism
  • Solvatochromic shift

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Psychology
  • Social Sciences (miscellaneous)
  • Sociology and Political Science
  • Spectroscopy
  • Clinical Biochemistry
  • Law

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