DOI: 10.1002/chem.201102402
Water-Soluble Distyrylbenzenes: One Core with Two Sensory Responses—
Turn-On and Ratiometric
Juan Tolosa,[a] Jonathan J. Bryant,[a] Kyril M. Solntsev,[b] Kerstin Brçdner,[a]
Laren M. Tolbert,[b] and Uwe H. F. Bunz*[a, b]
Abstract: The synthesis of four water-
soluble distyrylbenzenes (compounds
1–4) is reported. Their acidochromicity
in aqueous media was investigated.
Blue shifts and increases in the quan-
tum yields were observed as a general
response. The pH-dependent photo-
physics of 1b–3b in water reveal unex-
pected protonation sequences upon ti-
tration: compound 1b is green–yellow
fluorescent at high pH (10) but be-
comes very weakly fluorescent between
pH 5 and pH 3, whereas below pH 2
strong blue fluorescence is observed.
This behavior can be explained in
terms of the interplay in the protona-
tion of aniline and of the carboxylate
groups. In compound 4, a higher basici-
ty of the amino group is observed and
ratiometric fluorescence change takes
place upon protonation or on reaction
with zinc salts in water. Compound 4
can therefore act as a weak ratiometric
zinc ligand in water, even though it has
only a dimethylamino unit as a binding
motif.
Keywords: acidochromicity
·
amines · distyrylbenzene · fluores-
cence · photophysics
Introduction
effect.[12] However, dialkylamino-DSBs act in acetonitrile as
successful ratiometric ligands for divalent manganese and
calcium cations.[13]
Distyrylbenzenes (DSBs)[1] find widespread applications as
paper whiteners, as fluorophores for light-emitting diodes,[2]
as competent two-photon absorbers,[3] and as b-amyloid
binding ligands.[4] DSBs are oligomers of poly(para-phenyle-
nevinylene) (PPV)[5–7] but also styryl-stilbenes.[8] Their opti-
cal properties, though, are more PPV-like and do not resem-
ble those of the stilbenes, as evidenced by the 10 times
higher quantum yield of DSB relative to that of (E)-stil-
bene.[9] DSBs have not (yet) been found to be useful as sen-
sory cores for the detection of pH changes in aqueous solu-
tions or as metal sensors, even though one of the first calci-
um ion sensors, developed by Tsien et al., was stilbene
based.[10] Tsienꢀs apparent lack of success with this specific
molecule was attributed to excited-state decomplexation[11]
of the aminostyryl-coordinated metal cation. In the case of
similar azacrown-substituted DSBs, carefully investigated by
Perry et al.,[3] the lack of fluorescence response upon expo-
sure to metal cations is probably due to a conformational
New metal-coordinating and acid-sensing fluoroiono-
phores are potentially important for biological applications
(cell staining etc.), so it would be attractive to develop
DSBs to this end.[14,15] We have recently synthesized water-
soluble X-shaped[16] DSB derivatives incorporating amino-
bisacetic acid structures.[17] In aqueous solution these com-
pounds did not show the expected acidochromic properties,
that is, blue shifts in absorption and emission, but formed
excimers that were broken up by the addition of protons or
metal salts.[17] Their unexpected behavior was probably due
to the electronegative effects of the two attached CH2CO2R
(R=H, Na, Et) groups, which greatly reduce the basicity of
the aniline groups. To remove the inductive electronic influ-
ence of the carboxylate groups, we envisioned a second gen-
eration of DSBs, compounds 1–3 (Scheme 1), in which the
aniline nitrogen atoms each bear two CH2CH2CH2CO2-
AHCTUNGTREG(NNUN H,Na) units as auxiliary metal chelating appendages. These
insulate the electron-withdrawing carboxylate groups from
the aniline nitrogen much more strongly than the CH2CO2-
AHCTUNGTREG(NNNU H,Na) groups do. Here we describe the water-soluble DSBs
1–4, which display either turn-on or ratiometric behavior
upon protonation in water.
[a] Dr. J. Tolosa, J. J. Bryant, K. Brçdner, Prof. U. H. F. Bunz
Organisch-Chemisches Institut
Ruprecht-Karls-Universitꢁt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
[b] Dr. K. M. Solntsev, Prof. L. M. Tolbert, Prof. U. H. F. Bunz
School of Chemistry and Biochemistry
Results and Discussion
Georgia Institute of Technology
901 Atlantic Drive, Atlanta, GA 30332 (USA)
Synthesis and spectroscopic properties of the distyrylben-
zenes 1–4: Direct or consecutive Horner reactions of A
(Scheme 1) gave rise to the formation of the DSBs 1a, 3a,
and 4 in 24–56% yields (see the Supporting Information).
Supporting information for this article is available on the WWW
for the synthesis of DSBs 1–4 are provided, as well as the correspond-
ing photophysical experiments performed with these compounds.
13726
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 13726 – 13731