DOI: 10.1002/asia.201500420
Communication
BODIPY Dyes
Towards meso-Ester BODIPYs with Aggregation-Induced Emission
Properties: The Effect of Substitution Positions**
Ming Hui Chua,[a, b] Yong Ni,[b] Monalisa Garai,[b] Bin Zheng,[c] Kuo-Wei Huang,[c] Qing-
Hua Xu,[b] Jianwei Xu,*[a] and Jishan Wu*[a, b]
tions of AIE luminogens a hot research topic for the past
Abstract: Three meso-ester boron dipyrromethene
decade.[3]
(BODIPY) dyes have been synthesized and functionalized
There has been intensive focus on the development of biop-
with aggregation-induced emission (AIE)-active tetraphe-
robes with far-red and near infrared (NIR) emission. Such fluo-
nylethene or triphenylethene moieties. It was found that
rescent probes are particularly preferred over visible-emitting
functionalizing at the different positions of the BODIPY
ones because they have low phototoxicity, low auto-fluores-
core resulted in the final dye having different emission
cent background, and the ability to penetrate deeper into
properties in response to aggregation: from aggregation-
tissue samples, thus making them especially useful for in vivo
induced quenching (ACQ) to being AIE active. X-ray crys-
experiments and procedures.[4] A few established classes of or-
tallographic analysis was thus performed to provide an ex-
ganic luminogens have been reported to achieve the highly
planation for these differences.
desired far-red and NIR emission. One of these is 4,4-difluoro-
4-borata-3a,4a-diaza-s-indacene (BODIPY) dyes.[5] BODIPY dyes
are well known for their chemical stability, high fluorescence
Many organic luminogens, owing to their planar structure,
suffer from an aggregation-induced quenching (ACQ) effect,
which can reduce their effectiveness in applications. In 2001,
Tang’s group first discovered a new class of organic lumino-
gens, which displayed the opposite effect of ACQ.[1] These lu-
minogens, such as hexaphenylsilane (HPS) and tetraphenyle-
thene (TPE), are non-emissive in dilute solutions but their emis-
sion intensifies on forming nano-aggregates in the presence of
poor solvents. This is mainly due to their propeller-like struc-
tures that suppress p–p interactions and cause restriction-to-
intramolecular rotation upon aggregation. Tang thus coined
the term “Aggregation-Induced Emission” (AIE) for the intrigu-
ing property that this group of luminogens possess.[2] AIE-
active luminogens outshine their ACQ-counterparts in many
applications and overcome problems previously associated
with ACQ luminogens. This has made the design and applica-
quantum yield, and versatile functionalization at various posi-
tions of the BODIPY core to tune its photophysical properties.
A number of fluorescent bioprobes based on the BODIPY
structure have been developed for bioimaging, but not many
have managed to reach far-red and NIR emission.[6]
Recently, our group reported the unique synthesis of meso-
ester-substituted BODIPY dyes that were able to push the
emission range beyond 600 nm (of normal BODIPY dyes) into
the far-red and NIR region.[7] Positive results were obtained for
bioimaging applications of these dyes as well. Encouraged by
this successful study, we envisaged to introduce the AIE prop-
erties to BODIPY dyes of such designs with the ultimate aim to
develop an AIE-active fluorescent probe with far-red and NIR
emission. To the best of our knowledge, the first example of
an AIE BODIPY was reported by Tang and co-workers, through
functionalizing the meso-position with an AIE-active triphenyla-
mine moiety, and several other AIE-active BODIPY dyes were
successively reported.[8] All these reported cases are based on
functionalizing the meso group with either AIE-active moieties
or sterically bulky groups, which hinders close p–p stacking.
By considering previous successful studies of introducing
AIE properties to conventionally ACQ luminophores by func-
tionalizing them with AIE-active moieties (e.g. HPS and
TPE),[3g,9] we attempted to do the same for our meso-ester
BODIPY. However, the introduction of AIE properties into our
meso-ester BODIPY system was not as straightforward as we
had anticipated. Herein, we wish to report our attempts and
findings, where we have successively synthesized three meso-
ester BODIPY dyes (1–3), each with AIE-active TPE or triphenyl-
ethene functionalized at different positions of the core
(Scheme 1), to produce derivatives that are either ACQ (1),
slightly ACQ (2), or AIE-active (3). X-ray crystallographic analysis
[a] M. H. Chua, Dr. J. Xu, Prof. J. Wu
Institute of Materials Research and Engineering
A*STAR
3 Research Link, 117602 Singapore (Singapore)
[b] M. H. Chua, Dr. Y. Ni, M. Garai, Prof. Q.-H. Xu, Prof. J. Wu
Department of Chemistry
National University of Singapore
3 Science Drive 3, 117543 Singapore (Singapore)
[c] Dr. B. Zheng, Prof. K.-W. Huang
KAUST Catalysis Center and Division of Physical Sciences&Engineering
King Abdullah University of Science and Technology
Thuwal 23955-6900 (Saudi Arabia)
[**] BODIPY=Boron dipyrromethene.
Supporting information for this article is available on the WWW under
Chem. Asian J. 2015, 10, 1631 – 1634
1631
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim