Researchers improve highly fluorescent dyes
David Shenkenberg
Although the high fluorescent intensity of Bodipy dyes makes them
desirable for use in biochemical assays, their excitation and emission spectra are
so close that researchers cannot discriminate between them. Chemists have modified
these dyes to contain two chromophores, so that the rapid intramolecular transfer
of the chromophores artificially creates a larger Stokes shift. One group of chemists
recently synthesized two-chromophore Bodipy dyes that transfer intramolecular energy
more efficiently.
Researchers at the University of Newcastle in
the UK and at Centre National de la Recherche Scientifique in Strasbourg, France,
detail the production and properties of the dyes in the Aug. 10 ASAP edition of
the Journal of the American Chemical Society. As others have done, they added
an aromatic polycyclic compound that transfers energy to the Bodipy dye. However,
they replaced the fluorine atoms of the dye with the compounds, rather than attaching
them to the Bodipy framework with an ethylnylene linker. Whereas previous synthesis
necessitated the use of symmetrical polycyclic compounds, this method allowed the
scientists to attach two different compounds, enabling them to create unique spectral
properties.
The scientists created three dyes with
similar properties. The polycyclic compound did not affect the spectral profile
of the Bodipy dye, unlike the past method of synthesis. The dyes absorbed a broad
range of wavelengths, from 250 to 530 nm, and they had a quantum yield of 0.9 ±0.05
and a fluorescence lifetime of 6.5 ±0.1 ns. The fluorescence quantum yield
did not change greatly with polarity or temperature.
Using an excitation wavelength of 480
nm, the dyes emitted light at 550 nm. Using a computer simulation, the researchers
calculated the energy transfer rate constant to be 5 x 1010 for the third dye, which
has pyrene and perylene groups.
Although the dyes have similar properties,
the pyrene/perylene dye has a broader excitation spectrum and Stokes shift, so the
scientists believe that the dye is the most suitable for biochemical applications.
Their computer simulations suggested that they could generate an energy cascade
with that dye, but they did not have the facilities to test their hypothesis.
Published: September 2006