Intrinsic and extrinsic temperature-dependency of viscosity-sensitive fluorescent molecular rotors

Sarah Howell, Marianna Dakanali, Emmanuel A. Theodorakis, Mark A. Haidekker

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Molecular rotors are a group of environmentsensitive fluorescent probes whose quantum yield depends on the ability to form twisted intramolecular charge-transfer (TICT) states. TICT formation is dominantly governed by the solvent's microviscosity, but polarity and the ability of the solvent to form hydrogen bonds play an additional role. The relationship between quantum yield φ F and viscosity η is widely accepted as a power-law, φ F = C · η x. In this study, we isolated the direct influence of the temperature on the TICT formation rate by examining several molecular rotors in protic and aprotic solvents over a range of temperatures. Each solvent's viscosity was determined as a function of temperature and used in the above power-law to determine how the proportionality constant C varies with temperature. We found that the power-law relationship fully explains the variations of the measured steady-state intensity by temperatureinduced variations of the solvent viscosity, and C can be assumed to be temperature-independent. The exponent x, however, was found to be significantly higher in aprotic solvents than in protic solvents.We conclude that the ability of the solvent to form hydrogen bonds has a major influence on the relationship between viscosity and quantum yield. To use molecular rotors for the quantitative determination of viscosity or microviscosity, the exponent x needs to be determined for each dye-solvent combination.

Original languageEnglish (US)
Pages (from-to)457-465
Number of pages9
JournalJournal of Fluorescence
Issue number1
StatePublished - Jan 2012


  • Hydrogen bonds
  • Molecular rotors
  • Polarity
  • TICT
  • Twisted intramolecular charge transfer
  • Viscosity sensors

ASJC Scopus subject areas

  • Biochemistry
  • Spectroscopy
  • Clinical Biochemistry


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