Rational Design of Fluorophores for In Vivo Applications - Progress in Molecular Biology and Translational Science - page 78

SO 3 Na

COOH

N

N

F

O

N

B N

O

6 3

F

O

O

N

N

SO 3 Na

F

B
F

Excitation
l

N

= 501 nm

Emission
l = 599 nm

Energy transfer

O

3

O

Figure 3.4 BDP energy-transfer dyad. 158

electronic communication between the donor and the acceptor enables
through-bond energy transfer. 156,157 The linker-mediated through-bond
energy transfer does not require spectral overlap between the donor and
acceptor bands and hence offers a greater flexibility in choosing both
molecules. Several energy-transfer arrays containing two different BDP, or
aza-BDP subunits, have been reported, and many of them exhibit efficient
energy transfer and large difference between the absorption maximum of the
donor and the emission maximum of the acceptor (pseudo-Stokes
shift). 158-162 Most of the BDP dyads reported so far absorb and emit at
shorter wavelength than is required for in vivo imaging; however, in
principle, energy-transfer dyads can be also constructed from red and near-
IR absorbing/emitting derivatives.
Taken together, the excellent optical properties and the rich chemistry
that allows synthesis of diverse derivatives and fine-tuning of their chemical
and optical properties make BDP and aza-BDP likely candidates for broad in
vivo applications.

4.3. Related fluorophores
Besides BDP, there are classes of related boron complexes with excellent op-
tical properties suitable for in vivo applications. The boron complexes of pyr-
rolopyrrole cyanine dyes ( Chart 3.4 ) exhibit absorption/emission wavelengths
in the near-IR (up to 864 nm), a high extinction coefficient, narrow absorp-
tion and emission bands, and high fluorescence quantum yield. 163-165
Pyrrolopyrrole cyanines are more chemo- and photostable than classical
cyanine dyes. This class of compounds exhibits also relatively long