Web Release Date: March 11,
Tuning the Photoinduced Electron-Transfer Thermodynamics in 1,3,5-Triaryl-2-pyrazoline Fluorophores: X-ray Structures, Photophysical Characterization, Computational Analysis, and in Vivo Evaluation
Contribution from the School of Chemistry and Biochemistry, Georgia Institute of Technology, 770 State Street, Atlanta, Georgia 30332
Received August 23, 2002
Abstract:
A series of donor-substituted 1,3,5-triaryl-2-pyrazoline fluorophores were structurally characterized
by X-ray analysis, and their photophysical properties studied by steady-state absorption and emission
spectroscopy. The photoinduced electron-transfer thermodynamics of the derivatives was estimated on
the basis of the spectroscopic data and redox potentials of the fluorophores. The aryl substituents in the
1- and 3-position of the pyrazoline ring influence the photophysical properties of the fluorophores in distinctly
different ways. The excited-state equilibrium energy 
E00 is primarily influenced by changes of the substituent
in the 1-position, whereas the reduction potential of the fluorophore is essentially determined by the 3-aryl
group. Density functional calculations were used to probe the electronic structure and energy ordering of
the emissive and the electron-transfer state. The results from the computational analysis agree qualitatively
well with the experimental data. In addition, we have evaluated a water soluble pyrazoline derivative in
vivo as a potential intracellular pH probe. Membrane permeability, low toxicity, and high quantum yield
render the fluorophore attractive for biological applications.
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