Benzo[c,d]indole-Containing Aza-BODIPY Dyes: Asymmetrization-Induced Solid-State Emission and Aggregation-Induced Emission Enhancement as New Properties of a Well-Known Chromophore

Article abstract of DOI:10.1002/chem.201501464

A series of symmetric and asymmetric benzo[c,d]indole-containing aza boron dipyrromethene (aza-BODIPY) compounds was synthesized by a titanium tetrachloride-mediated Schiff-base formation reaction of commercially available benzo[c,d]indole-2(1H)-one and heteroaromatic amines. These aza-BODIPY analogues show different electronic structures from those of regular aza-BODIPYs, with hypsochromic shifts of the main absorption compared to their BODIPY counterparts. In addition to the intense fluorescence in solution, asymmetric compounds exhibited solid-state fluorescence due to significant contribution of the vibronic bands to both absorption and fluorescence as well as reduced fluorescence quenching in the aggregates. Finally, aggregation-induced emission enhancement, which is rare in BODIPY chromophores, was achieved by introducing a nonconjugated moiety into the core structure.

Full text of DOI:10.1002/chem.201501464

DOI: 10.1002/chem.201501464
Full Paper
&
Dyes/Pigments
Benzo[c,d]indole-Containing Aza-BODIPY Dyes: Asymmetrization-
Induced Solid-State Emission and Aggregation-Induced Emission
Enhancement as New Properties of a Well-Known Chromophore
Soji Shimizu,*[a, b] Ai Murayama,[c] Takuya Haruyama,[c] Taku Iino,[c] Shigeki Mori,[d]
Hiroyuki Furuta,[a, b] and Nagao Kobayashi*[c, e]
Abstract: A series of symmetric and asymmetric benzo[c,d]-
indole-containing aza boron dipyrromethene (aza-BODIPY)
compounds was synthesized by a titanium tetrachloride-
mediated Schiff-base formation reaction of commercially
available benzo[c,d]indole-2(1H)-one and heteroaromatic
amines. These aza-BODIPY analogues show different elec-
tronic structures from those of regular aza-BODIPYs, with
hypsochromic shifts of the main absorption compared to
their BODIPY counterparts. In addition to the intense fluores-
cence in solution, asymmetric compounds exhibited solid-
state fluorescence due to significant contribution of the vi-
bronic bands to both absorption and fluorescence as well as
reduced fluorescence quenching in the aggregates. Finally,
aggregation-induced emission enhancement, which is rare
in BODIPY chromophores, was achieved by introducing
a nonconjugated moiety into the core structure.
Introduction
trogen atom, is known to exhibit bathochromic shifts of the
absorption and emission compared to the corresponding
BODIPY. Because of the absorption and emission of regular
aza-BODIPYs above 650 nm in the visible region, intensive re-
search has recently focused on their potential applications, in
particular in the field of bioimaging.[13] The bathochromic shift
can be explained by the effective stabilization of the LUMO
energy level by the higher electronegativity of nitrogen than
carbon at the meso position, on which MO coefficients were
found for the LUMO but not for the HOMO in DFT calcula-
tions.[14] In contrast to BODIPYs, the synthetic availability of
aza-BODIPYs still remains limited, which hinders the derivatiza-
tion or functionalization required for applications. Recently, we
reported a facile synthesis of dimeric aza-BODIPY analogues
from heteroaromatic amines and diketopyrrolopyrrole.[15] In
this reaction, lactam moieties of the diketopyrrolopyrrole were
successfully converted to an aza-BODIPY structure by a Schiff-
base formation reaction in the presence of titanium tetrachlor-
ide and triethylamine. It was therefore inferred that these reac-
tion conditions could be applied to other lactams to synthesize
novel aza-BODIPY analogues. As a synthetic target for this
method, benzo[c,d]indole-containing aza-BODIPY 1[16] was se-
lected because of its hypsochromic shift of the absorption
4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY), a boron
difluoride complex of dipyrrin,[1–4] is one of the most widely in-
vestigated functional chromophores and is frequently utilized
in a variety of fields, such as bioimaging,[5] chemosensors,[6]
laser dyes,[7] photodynamic therapy,[8] optoelectronic materials
including light-emitting diodes[9] and photovoltaics,[10] and
multichromophore systems for artificial photosynthetic
models,[11] due to its intense absorption in the visible region
and environmentally insensitive fluorescent properties. Aza-
BODIPY,[12] in which a carbon atom at the pyrrole-bridging po-
sition in BODIPY denoted meso position is replaced with a ni-
[a] Prof. Dr. S. Shimizu, Prof. Dr. H. Furuta
Department of Chemistry and Biochemistry
Graduate School of Engineering
Kyushu University, Fukuoka 819-0395 (Japan)
E-mail: ssoji@cstf.kyushu-u.ac.jp
[b] Prof. Dr. S. Shimizu, Prof. Dr. H. Furuta
Center for Molecular Systems (CMS)
Kyushu University, Fukuoka 819-0395 (Japan)
E-mail: ssoji@cstf.kyushu-u.ac.jp
[c] A. Murayama, T. Haruyama, T. Iino, Prof. Dr. N. Kobayashi
Department of Chemistry, Graduate School of Science
Tohoku University, Sendai 980-8578 (Japan)
E-mail: nagaok@m.tohoku.ac.jp
spectrum compared to its meso-carbon counterpart
2
(Figure 1),[17] which is a rare exception to the above-mentioned
general trend in the absorption and fluorescence spectra of
BODIPYs and aza-BODIPYs. Although this compound was once
reported, it was neither thoroughly investigated in the original
papers nor substantially addressed in the previous literature.
Moreover, optical properties other than absorption, such as
fluorescence, have not yet been elucidated. Herein, we report
the synthesis of a series of benzo[c,d]indole-containing aza-
[d] Dr. S. Mori
Division of Material Science, Advanced Research Support Center
Ehime University, Matsuyama 790-8577 (Japan)
[e] Prof. Dr. N. Kobayashi
Faculty of Textile Science and Technology, Shinshu University
Ueda 386-8567 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501464.
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Figure 1. Structures of benzo[c,d]indole-containing aza-BODIPY 1 and its
meso-carbon counterpart 2.
BODIPYs using our synthetic method.[18] In addition to address-
ing the hypsochromic shift of 1 from 2, novel aspects of the
aza-BODIPY chromophore, such as enhanced solid-state emis-
sion by asymmetrization of the structure and aggregation-in-
duced enhancement of emission by incorporating a nonconju-
gated moiety into the core structure, were achieved.
Results and Discussion
Synthesis and crystal structures of benzo[c,d]indole-contain-
ing aza-BODIPYs
Benzo[c,d]indole-containing aza-BODIPY 1 was synthesized in
41% yield by a Schiff-base formation reaction of commercially
available benzo[c,d]indole-2(1H)-one (lactam-1) and benzo[c,-
d]indole-2-amine (amine-1), which was derived in four steps
from lactam-1,[16,19] in the presence of TiCl4 and triethylamine
(TEA)[20] followed by in situ coordination of boron difluoride by
addition of BF3·OEt2 to the reaction mixture (Scheme 1a).[15]
The substituents on the boron atom can be changed from
fluoride to phenyl by using triphenylborane instead of BF3·OEt2
(3 in Scheme 1a). A dipyrrin ligand structure of 1, which can
also be synthesized without addition of boron reagent in the
last step, facilely formed zinc complex 4. In addition to these
symmetric aza-BODIPYs, asymmetric types 5–9 were also syn-
thesized (Scheme 1b and c) from lactam-1 and heteroaromatic
amines (amine-2–5) or from amine-1 and 2H-1,4-benzoxazine-
3(4H)-one (lactam-2). Compounds 5 and 7a can also be syn-
thesized from the opposite combination of an amine and lac-
tams, namely, amine-1 with 2(3H)-benzothiazolone and 2(3H)-
benzoxazolone, but the yields were lower than those of the re-
actions of lactam-1 with amine-2 and amine-4a.
Scheme 1. Synthesis of symmetric (a) and asymmetric (b, c) benzo[c,d]in-
dole-containing aza-BODIPY analogues.
Optical properties
All of these aza-BODIPYs were characterized by high-resolu-
tion MALDI-TOF Fourier transform ion cyclotron resonance (FT-
ICR) mass spectrometry and 1H NMR spectroscopy (see the
Supporting Information). All of the structures, except those of
1 and 4, were further unambiguously elucidated by X-ray crys-
tallography (Figure 2 and Figure S1 in the Supporting Informa-
tion). In the molecular packing diagram, both H- and J-type ar-
rangements or intermediate arrangements were observed for
the nearest neighbors with interplanar separations of the
mean planes of molecules ranging from 3.3 to 3.7 Š, apart
from 7b, 8, and 9, in which only J-type packing was found
(Figure 3 and Figure S1 in the Supporting Information). In addi-
tion, due to its slightly deformed structure, 9 is not arranged
in a parallel manner, but in a rather zigzag manner.
The absorption spectra of the aza-BODIPYs in the visible
region were characterized by either two intense bands or
a broad band with a lower-energy shoulder (Figure 4a and
Table 1). Compared with the main absorption of asymmetric
compounds 5–9 at 400–500 nm, symmetric compounds 1, 3,
and 4 exhibited bathochromic shifts due to the larger conju-
gated system of the benzo[c,d]indole moiety than those of the
other heteroaromatic moieties in 5–9. Among the symmetric
compounds, 3 and 4 exhibited a further bathochromic shift rel-
ative to 1. On the basis of time-dependent (TD) DFT calcula-
tions at the B3LYP/6-31G(d) level (Table S1 and Figure S2 in the
Supporting Information), which assigned these main absorp-
tions as a HOMO–LUMO transition, the observed higher-energy
absorption, such as the band of 1 at 503 nm, can be ascribed
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Figure 4. a) UV/Vis absorption and b) fluorescence spectra of benzo[c,d]in-
dole-containing aza-BODIPY analogues in CHCl3.
meso position in the LUMO (Figure S3 in the Supporting Infor-
mation). Therefore, replacement of a carbon atom at the meso
position of 2 with a more electronegative nitrogen atom
causes stabilization of the HOMO, which results in the ob-
served hypsochromic shift of 1 due to the increase of the
HOMO–LUMO gap (Table S1 in the Supporting Information).
All of the benzo[c,d]indole-containing aza-BODIPYs exhibited
intense fluorescence with Stokes shifts ranging from 69 to
1244 cmÀ1 and intense vibronic 0–1 bands (Figure 4b and
Table 1). Despite the small Stokes shifts, except for 9, overlap
of the absorption and fluorescence spectra is considerably re-
duced for the asymmetric compounds due to the contribution
of the vibronic bands to the absorption and emission (Figure 5
and Figure S4 in the Supporting Information). The absolute
fluorescence quantum yields FF were high and ranged from
0.83 to 0.60, except for 3, 4, 7b, and 9, among which the fluo-
Figure 2. Crystal structures of a) 3, b) 5, c) 6, d) 7a, e) 8, and f) 9. The ther-
mal ellipsoids were scaled to the 50% probability level.
to the vibronic 0–1 band. In the case of the asymmetric com-
pounds, this vibronic 0–1 band is more intense, and is ob-
served as a broad, main band, so that the 0–0 band can be de-
tected as a less-intense lower-energy band or a kind of should-
er absorption. This significant contribution of the vibronic
bands infers a structural change of these rigid chromophores
in the excited state.
The DFT and TDDFT calculations also gave an explanation of
the reported hypsochromic shift of 1 (lmax =539 nm) versus 2
(lmax =622 nm).[16,17] Large MO coefficients of the HOMO were
found on the meso position, whereas a node was found at the
Figure 3. Molecular packing diagrams of a) 3, b) 5, c) 6, d) 7a, e) 8, and f) 9. Interplanar distances between the mean planes of molecules excluding the two
fluorine atoms are shown in a)–e). Distances of the mean planes of over- and underlying molecules excluding the two fluorine atoms from the center of the
benzene ring of the benzoxazine moiety, represented by a gray dot, are shown in f).
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the Supporting Information). Aggregation-caused
quenching (ACQ) is a normal behavior for fluoro-
phores with small Stokes shifts. In contrast, in the
case of the asymmetric compounds with a fully
conjugated structure (5–8), moderately intense
emission with FF =0.13–0.27 was observed, de-
spite the small Stokes shifts. In general, solid-state
fluorescent compounds including BODIPYs either
exhibit large Stokes shifts in solution[21,22] or have
bulky substituents[23] that minimize interchromo-
phore interactions in the solid state. Neither is the
case for asymmetric compounds 5–8. Instead, the
solid-state fluorescence in this case can be ex-
plained in terms of the contribution of the vibronic
bands to both the absorption and emission, as de-
scribed above, and the molecular packing in the
solid state. The small overlap of the absorption
and emission caused by intensification of the 0–
1 band reduces self-absorption in the solid state.
Table 1. Summary of optical properties of aza-BODIPY analogues in CHCl3 and in the
solid state.
abs
00
em
00
[a]
[b]
FPMMA Fsol tF
[c]
Compound
l
lge00
l
Stokes FCHCl
kr
knr
[108 sÀ1
3
[d]
[e]
[nm]
[nm] shift
[cmÀ1
[ns] [108 sÀ1
]
]
]
1
3
4
5
539 4.68 541 69
602 4.30 626 637
563 4.72 572 279
468 4.20 481 534
468[f] 3.94 478 447
480 4.20 489 383
491 4.38 506 603
488 4.38 496 331
484 4.11 515[f] 1244
0.60
0.13
0.26
0.83
0.70
0.81
0.38
0.84
0.05
0.30
0.15
0.15
0.82
0.71
0.81
0.43
0.82
0.13
0.08 5.0 1.2
0.8
1.3
3.2
0.2
0.5
0.3
2.5
0.3
32
0.04 6.5 0.2
0.02 2.3 1.1
0.20 7.0 1.2
0.24 5.9 1.2
0.27 6.0 1.4
0.22 2.5 1.5
0.13 5.8 1.4
0.14 0.30 1.7
6
7a
7b
8
9
[a] Absolute fluorescence quantum yield in CHCl3. [b] Absolute fluorescence quantum
yield in PMMA film. [c] Absolute fluorescence quantum yield of amorphous drop-cast
film. [d] Rate constant for radiative decay in CHCl3: kr =FF/tF. [e] Rate constant for nonra-
diative decay in CHCl3: knr =(1ÀFF)/tF. [f] Shoulder bands were assigned as a 0–0 band.
rescence of 9 was nearly quenched (FF =0.05). Structurally
flexible moieties of these less-fluorescent compounds, such as
phenyl groups on the boron atom, long alkoxyl chains, and
a nonconjugated moiety, may enhance nonradiative decay pro-
cesses, which can be evidenced by short fluorescence lifetimes
and large nonradiative rate constants.
The fluorescence spectra of the poly(methyl methacrylate)
(PMMA) films, which exhibited similar absorption spectra to
those in solution, showed decrease or disappearance of the 0–
0 emission band due to self-absorption. The larger spectral
overlaps of symmetric compounds 1, 3, and 4 compared to
the asymmetric species results in significant quenching of the
emission with a decrease of FF, whereas FF of the asymmetric
compounds is almost entirely retained (Figure 5, Table 1, and
Figures S4 and S6 in the Supporting Information). The amor-
phous films prepared by a drop-casting method exhibited
broadening and a bathochromic shift of the emission. The
emission of the symmetric compounds was further significantly
In the solid state, the benzo[c,d]indole-containing aza-BODI-
PYs showed three types of emission behaviors, reflecting their
structural features (Figure 5, Table 1, and Figure S4 in the Sup-
porting Information). The emission of symmetric compounds
1, 3, and 4 was nearly quenched in the solid state of a drop-
cast film, which exhibited FF values of 0.02–0.08 (Figure S5 in
Figure 5. UV/Vis absorption in CHCl3 (black solid line) and fluorescence spectra of a) 1, b) 5, and c) 9 in CHCl3 solution (blue dashed line), a PMMA film (green
dashed line), and a drop-cast film (violet dashed line). d) Photographs of solutions (top) and drop-cast films (bottom) under irradiation by 365 nm light.
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quenched, whereas that of the asymmetric compounds was
rather moderately quenched (Figure 5, Table 1, and Figures S4
and S6 in the Supporting Information). Despite ACQ, the asym-
metric compounds were still fluorescent, which can be ex-
plained by the manner of aggregation of these compounds in
the amorphous films. Considering that H-type and J-type ar-
rangements or intermediate arrangements were present in the
molecular packing diagrams, both H- and J-type dimer forma-
tion can be expected for aggregates in the amorphous films.
According to the Kasha exciton theory,[24] H-type aggregates
are nonfluorescent because the lowest excited state becomes
forbidden.[25] As a rare exception, Würthner et al. reported
emission from H-type aggregates of merocyanine dyes and
concluded that small deviations of the direction of the transi-
tion dipole moments between nearest neighbors may reduce
the forbidden nature.[26] A similar mechanism may be possible
in the current case. Due to the asymmetric structures, the tran-
sition dipole moments would not be cancelled out, even if
molecules form H-type aggregates, so that the emission is not
completely quenched.
Conclusion
The titanium tetrachloride-mediated Schiff-base formation re-
action of lactam compounds was applied to benzo[c,d]indole-
2(1H)-one with the initial aim of elucidating the optical proper-
ties of benzo[c,d]indole-containing aza-BODIPY 1, but resulted
in an encounter with rather unexpected aspects of the proper-
ties of aza-BODIPY chromophores. The hypsochromic shifts of
these aza-BODIPYs, which were caused by their different elec-
tronic structures compared to regular aza-BODIPYs, imply that
there is a room for tuning the absorption and emission proper-
ties of aza-BODIPYs by incorporating heteroaromatic moieties
in place of pyrrole or isoindole rings. The significant contribu-
tion of the vibronic bands to both absorption and emission is
a novel strategy towards solid-state emission. Finally the incor-
poration of a nonconjugated moiety in the core structure of
the chromophores enables AIEE responses. With this knowl-
edge as a base, novel chromophore systems applicable in a va-
riety of fields can be developed.
In a stark contrast to the almost complete and partial ACQ
behaviors of the symmetric (1, 3, and 4) and asymmetric (5–8)
aza-BODIPYs, respectively, the emission of 9, which has a non-
conjugated moiety in the core structure, was enhanced on
going from solution to a PMMA film and an amorphous film
with an increase in FF from 0.05 to 0.14 (Figure 5, Table 1, and
Figures S4 and S6 in the Supporting Information). This behav-
ior can be recognized as a kind of aggregation-induced emis-
sion enhancement (AIEE).[27] To confirm the AIEE behavior of 9,
changes in the fluorescence spectra and development of FF
were investigated on increasing the water fraction in a THF so-
lution of 9 (Figure 6). The fluorescence spectra, which are simi-
Experimental Section
General procedures
Electronic absorption spectra were recorded on a JASCO V-570
spectrophotometer. Fluorescence spectra of CHCl3 solutions and
drop-cast films were measured on a Hitachi F-4500 spectrofluorim-
eter and on a Horiba Fluorolog-3 spectrofluorimeter, respectively.
Absolute fluorescence quantum yields and fluorescence spectra of
PMMA films were measured on a Hamamatsu Photonics C9920-
03G calibrated integrating-sphere system. The fluorescence lifetime
was measured with a picosecond light pulser (Hamamatsu Photon-
ics C4725: 408 nm, 59 ps FWHM) and a streak scope (Hamamatsu
Photonics C4334-02). 1H NMR spectra were recorded on a Bruker
1
AVANCE III 500 spectrometer (operating at 500.133 MHz for H) by
using residual proton signals of solvents as internal references for
1H (d=7.26 ppm for CDCl3, d=5.32 ppm for CD2Cl2, and d=
2.50 ppm for [D6]DMSO). High-resolution mass spectra were record-
ed on a Bruker Daltonics solariX 9.4T spectrometer. Preparative sep-
arations were performed by column chromatography on silica gel
(Wako). Toluene that was used for the synthesis of benzo[c,d]in-
dole-containing aza-BODIPYs was distilled over CaH2 prior to use.
All other reagents and solvents were of commercial reagent grade
and were used without further purification, except where noted.
Figure 6. a) Changes of fluorescence spectra of 9 depending on water frac-
tion of THF/water mixtures. The fluorescence spectrum of a drop-cast film of
9 is shown as a reference (gray dashed line). b) Dependence of the quantum
yield of 9 on water fraction.
Crystallographic data collection and structure refinement
Suitable crystals of 3, 5, 6, 7a, 7b, 8, and 9 for X-ray analysis were
obtained by slow diffusion of methanol or hexane into CHCl3 solu-
tions. Data were collected on a Bruker APEXII CCD diffractometer
with MoKa radiation (l=0.71073 Š) at À173(2)8C and on a Rigaku
R-AXIS RAPID diffractometer with CuKa radiation (l=1.54187 Š).
The structures were solved by a direct method (SHLEXS-97[28] and
Sir 2011[29]) and refined by using a full-matrix least-squares tech-
nique [SHELXL64 (SHELXL-2013)].[28] Yadokari-XG[30] software was
used as a GUI for SHELXL-2013. CCDC 1050935 (3), 1050936 (5),
1050937 (6), 1050938 (7a), 1050939 (7b), 1050940 (8) and 1050941
(9) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
lar to that observed for the amorphous film, gradually devel-
oped at high water fraction, while FF increased from 0.02 at
0% to 0.23 at 96% water fraction. These results clearly indicate
that aggregation in the solid state reduces the molecular dy-
namics caused by the nonconjugated sp3 carbon moiety. To
the best of our knowledge, 9 is the first aza-BODIPY system ex-
hibiting AIEE behavior.
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recrystallization from chloroform and hexane provided 4 as a red
powder in 8.6% yield (41 mg, 0.058 mmol). HR-MALDI-FT-ICR-MS:
m/z 701.1428 (calcd for C44H25N6Zn: 701.1427 [M++H]); 1H NMR
(CDCl3, 500 MHz, 298 K): d=8.53 (d, J=7.0 Hz, 4H), 8.03 (d, J=
8.0 Hz, 4H), 7.83 (dd, J1 =7.0, J2 =7.0 Hz, 4H), 7.51 (d, J=8.0 Hz,
4H), 7.22 (dd, J1 =8.0, J2 =8.0 Hz, 4H), 7.02 ppm (d, J=7.0 Hz, 4H);
UV/Vis (CHCl3): lmax [nm] (e [molÀ1 dm3 cmÀ1])=563 (53000), 525
(55000).
Computational methods
The Gaussian 09[31] software package was used to carry out DFT
and TDDFT calculations with the B3LYP functional and 6-31G(d)
basis set. Structural optimization was performed on model struc-
tures.
Sample preparation for solid-state fluorescence measure-
ments
Synthesis of 5: Benzo[c,d]indole-2(1H)-one (lactam-1, 170 mg,
1.0 mmol) and 2-aminopyridine (amine-2, 94 mg, 1.0 mmol) were
dissolved in toluene (5.3 mL), and then TEA (2 mL) and TiCl4
(0.2 mL) were added to the solution under reflux. After stirring for
15 min, BF3·OEt2 (2.5 mL) was added, and the resulting mixture was
further heated to reflux for 2 h. The reaction mixture was filtered,
and the filtrate was added to water. The organic phase was extract-
ed with chloroform and dried over Na2SO4. Finally the product was
purified by silica gel column chromatography with chloroform as
eluent and recrystallized from chloroform and hexane to afford 5
as a yellow powder in 5.2% yield (15 mg, 0.051 mmol). HR-MALDI-
FT-ICR-MS: m/z 294.1009 (calcd for C16H11BF2N3: 294.1009 [M++H]);
1H NMR (CD2Cl2, 500 MHz, 298 K): d=8.43 (m, 1H), 8.26 (d, J=
7.0 Hz, 1H), 8.14 (d, J=8.0 Hz, 1H), 8.00 (dd, J1 =8.0, J2 =8.0 Hz,
1H), 7.81 (dd, J1 =7.5, J2 =7.0 Hz, 1H), 7.70 (d, J=8.0 Hz, 1H), 7.61
(dd, J1 =8.0, J2 =7.5 Hz, 1H), 7.55 (d, J=8.0 Hz, 1H), 7.48 (d, J=
7.0 Hz, 1H), 7.28 ppm (dd, J1 =7.5, J2 =7.0 Hz, 1H); UV/Vis (CHCl3):
lmax [nm] (e [molÀ1 dm3 cmÀ1])=468 (16000), 441 (24000).
PMMA films for fluorescence measurements were prepared from
a chloroform solution of PMMA (100 mgmLÀ1) containing 0.2 wt%
sample by using a drop-casting method. Amorphous film samples
for fluorescence measurements were prepared by drop casting.
Synthesis of benzo[c,d]indole-containing aza-BODIPYs
Synthesis of 1: Benzo[c,d]indole-2-amine hydroiodide (amine-1,
100 mg, 0.34 mmol) and benzo[c,d]indole-2(1H)-one (lactam-1,
60 mg, 0.34 mmol) were dissolved in toluene (2 mL), and then TEA
(1 mL) and TiCl4 (0.05 mL) were added to the solution under reflux.
After stirring for 15 min, BF3·OEt2 (0.75 mL) was added, and the re-
sulting mixture was further heated to reflux for 2 h. The reaction
mixture was filtered, and the filtrate was added to water. The or-
ganic phase was extracted with chloroform and dried over Na2SO4.
Finally, the product was purified by silica-gel column chromatogra-
phy with chloroform as eluent and recrystallized from chloroform
and methanol to afford 1 as an orange powder in 41% yield
(51 mg, 0.14 mmol). HR-MALDI-FT-ICR-MS: m/z 368.1165 (calcd for
C22H13BF2N3: 368.1165 [M++H]); 1H NMR (CD2Cl2, 500 MHz, 298 K):
d=8.53 (d, J=7.0 Hz, 2H), 8.28 (d, J=7.5 Hz, 2H), 7.90 (m, 4H),
7.84 (d, J=7.0 Hz, 2H), 7.73 ppm (dd, J1 =7.5, J2 =7.0 Hz, 2H); UV/
Vis (CHCl3): lmax [nm] (e [molÀ1 dm3 cmÀ1])=539 (48000), 503
(43000).
Synthesis of 6: Benzo[c,d]indole-2(1H)-one (lactam-1, 0.34 g,
2.0 mmol) and 2-aminobenzooxazole (amine-3, 0.27 g, 2.0 mmol)
were dissolved in toluene (10 mL), and then TEA (5 mL) and TiCl4
(0.3 mL) were added to the solution under reflux. After stirring for
15 min, BF3·OEt2 (4.4 mL) was added, and the resulting mixture was
further heated to reflux for 2 h. The reaction mixture was filtered,
and the filtrate was added to water. The organic phase was extract-
ed with chloroform and dried over Na2SO4. Finally the product was
purified by silica-gel column chromatography with chloroform as
eluent and recrystallized from chloroform and methanol to afford
6 as a yellow powder in 4.3% yield (29 mg, 0.087 mmol). HR-
MALDI-FT-ICR-MS: m/z 334.0958 (calcd for C18H11BF2N3O: 334.0958
[M++H]); 1H NMR (CDCl3, 500 MHz, 298 K): d=8.41 (d, J=7.0 Hz,
1H), 8.22 (d, J=8.0 Hz, 1H), 7.82 (m, 4H), 7.68 (dd, J1 =7.5, J2 =
7.0 Hz, 1H), 7.58 (d, J=8.0 Hz, 1H), 7.49 ppm (m, 2H); UV/Vis
(CHCl3): lmax [nm] (e [molÀ1 dm3 cmÀ1])=468 (8800), 436 (19000).
Synthesis of 3: Benzo[c,d]indole-2-amine hydroiodide (amine-1,
0.51 g, 1.7 mmol) and benzo[c,d]indole-2(1H)-one (lactam-1, 0.30 g,
1.8 mmol) were dissolved in toluene (9 mL), and then TEA (5 mL)
and TiCl4 (0.25 mL) were added to the solution under reflux. After
stirring for 30 min, triphenylborane (0.41 g, 1.7 mmol) was added,
and the resulting mixture was further heated to reflux for 1.5 h.
The reaction mixture was filtered, and the filtrate was added to
water. The organic phase was extracted with chloroform and dried
over Na2SO4. Finally the product was purified by silica gel column
chromatography with chloroform as eluent and recrystallized from
chloroform and methanol to afford 3 as an orange powder in 5.1%
yield (42 mg, 0.086 mmol). HR-MALDI-FT-ICR-MS: m/z 484.1980
Synthesis of 7a: Benzo[c,d]indole-2(1H)-one (lactam-1, 85 mg,
0.50 mmol) and 2-aminobenzothiazole (amine-4a, 75 mg,
0.50 mmol) were dissolved in toluene (2 mL), and then TEA
(1.4 mL) and TiCl4 (0.08 mL) were added to the solution under
reflux. After stirring for 15 min, BF3·OEt2 (1.2 mL) was added, and
the resulting mixture was further heated to reflux for 2 h. The reac-
tion mixture was filtered, and the filtrate was added to water. The
organic phase was extracted with chloroform and dried over
Na2SO4. Finally the product was purified by silica-gel column chro-
matography with chloroform as eluent and recrystallized from
chloroform and methanol to afford 7a as a yellow powder in 16%
yield (28 mg, 0.081 mmol). HR-MALDI-FT-ICR-MS: m/z 350.0729
(calcd for C18H11BF2N3S: 350.0729 [M++H]); 1H NMR (CDCl3,
500 MHz, 298 K): d=8.35 (d, J=7.0 Hz, 1H), 8.19 (d, J=8.0 Hz, 1H),
8.17 (d, J=8.0 Hz, 1H), 7.78 (m, 4H), 7.67 (dd, J1 =8.0, J2 =7.5 Hz,
1H), 7.59 (dd, J1 =8.0, J2 =7.0 Hz, 1H), 7.44 ppm (dd, J1 =8.0, J2 =
7.5 Hz, 1H); UV/Vis (CHCl3): lmax [nm] (e [molÀ1 dm3 cmÀ1])=480
(16000), 450 (25000).
(calcd for C34H23BN3: 484.1980 [M++H]); H NMR (CDCl3, 500 MHz,
1
298 K): d=8.49 (d, J=7.0 Hz, 2H), 8.13 (d, J=8.0 Hz, 2H), 7.83 (dd,
J1 =8.0, J2 =7.0 Hz 2H), 7.63 (m, 6H), 7.32 (m, 4H), 7.21 (m, 4H),
6.85
(d,
J=7.5 Hz,
2H);
UV/Vis
(CHCl3):
lmax [nm]
(e [molÀ1 dm3 cmÀ1])=602 (20000), 561 (23000).
Synthesis of 4: Benzo[c,d]indole-2-amine (amine-1, 0.20 g,
1.2 mmol) and benzo[c,d]indole-2(1H)-one (lactam-1, 0.12 g,
0.68 mmol) were dissolved in toluene (4 mL), and then TEA (2 mL)
and TiCl4 (0.1 mL) were added to the solution under reflux. After
stirring for 2.5 h, the reaction mixture was filtered, and the filtrate
was added to water. The organic phase was extracted with chloro-
form and dried over Na2SO4. After removal of solvent, the residue
was dissolved in CHCl3/MeOH (50 mL, 2/1). Zn(OAc)2 (1.3 g,
6.8 mmol) and NaOAc (56 mg, 6.8 mmol) were then added, and
the resulting mixture was heated to reflux overnight. The reaction
mixture was washed with water, and the organic layer was extract-
ed with chloroform. The extract was purified by silica-gel column
chromatography with CHCl3/MeOH as eluent and GPC-HPLC. Finally
Synthesis of 7b: Benzo[c,d]indole-2(1H)-one (lactam-1, 61 mg,
0.36 mmol) and 2-amino-6-octyloxybenzothiazole (amine-4b,
100 mg, 0.36 mmol) were dissolved in toluene (1.3 mL), and then
Chem. Eur. J. 2015, 21, 12996 – 13003
www.chemeurj.org
13001
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
TEA (0.75 mL) and TiCl4 (0.04 mL) were added to the solution
under reflux. After stirring for 15 min, BF3·OEt2 (0.55 mL) was
added, and the resulting mixture was further heated to reflux for
2 h. The reaction mixture was filtered, and the filtrate was added
to water. The organic phase was extracted with chloroform and
dried over Na2SO4. Finally the product was purified by silica-gel
column chromatography with chloroform as eluent and recrystal-
lized from chloroform and methanol to afford 7b as a yellow
powder in 5.9% yield (6.6 mg, 0.014 mmol). HR-MALDI-FT-ICR-MS:
Shintaro Ishida, and Dr. Taniyuki Furuyama of Tohoku University
for the X-ray measurements.
Keywords: aggregation
· dyes/pigments · fluorescence ·
nitrogen heterocycles · solid-state emission
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1
m/z 478.1931 (calcd for C26H27BF2N3OS: 478.1931 [M++H]); H NMR
(CDCl3, 500 MHz, 298 K): d=8.31 (d, J=7.0 Hz, 1H), 8.16 (d, J=
8.0 Hz, 1H), 8.04 (d, J=8.0 Hz, 1H), 7.81 (dd, J1 =8.0, J2 =7.0 Hz,
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8.0, J2 =7.0 Hz, 1H), 7.22 (m, 2H), 4.03 (dd, J1 =6.5, J2 =6.5 Hz, 2H),
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491 (24000), 461 (35000).
Synthesis of 8: Benzo[c,d]indole-2(1H)-one (lactam-1, 0.17 g,
1.0 mmol) and 2-aminoquinoline (amine-5, 0.14 g, 1.0 mmol) were
dissolved in toluene (5.3 mL), and then TEA (2 mL) and TiCl4
(0.2 mL) were added to the solution under reflux. After stirring for
30 min, BF3·OEt2 (2.5 mL) was added, and the resulting mixture was
further heated to reflux for 2 h. The reaction mixture was filtered,
and the filtrate was added to water. The organic phase was extract-
ed with chloroform and dried over Na2SO4. Finally the product was
purified by silica-gel column chromatography with chloroform/
MeOH (60/1) as eluent and recrystallized from chloroform and
methanol to afford 8 as a yellow powder in 6.2% yield (16 mg,
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C20H13BF2N3: 344.1165 [M++H]); 1H NMR (CDCl3, 500 MHz, 298 K):
d=8.83 (d, J=8.5 Hz, 1H), 8.37 (d, J=7.0 Hz, 1H), 8.22 (d, J=
8.5 Hz, 1H), 8.15 (d, J=8.0 Hz, 1H), 7.82 (m, 3H), 7.73 (m, 2H), 7.65
(dd, J1 =7.0, J2 =7.0 Hz, 1H), 7.54 ppm (m, 2H); UV/Vis (CHCl3):
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Synthesis of 9: Benzo[c,d]indole-2-amine (amine-1, 0.20 g,
1.2 mmol) and 2H-1,4-benzoxazin-3(4H)-one (lactam-2, 0.15 g,
1.0 mmol) were dissolved in toluene (10 mL), and then TEA (2 mL)
and TiCl4 (0.2 mL) were added to the solution under reflux. After
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C19H13BF2N3O: 348.1114 [M++H]); 1H NMR ([D6]DMSO, 500 MHz,
298 K): d=8.51 (d, J=8.0 Hz, 2H), 8.08 (d, J=8.0 Hz, 1H), 8.02 (dd,
J1 =7.5, J2 =7.5 Hz, 1H), 7.90 (d, J=7.0 Hz, 1H), 7.80 (m, 2H), 7.20
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(e [molÀ1 dm3 cmÀ1])=484 (13000), 456 (21000).
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Acknowledgements
This work was partly supported by Grants-in-Aid for Scientific
Research on Innovative Area, “New Polymeric Materials Based
on Element-Blocks (No. 25102503), from the Ministry of Educa-
tion, Culture, Sports, Science and Technology (MEXT), Young
Scientists A (No. 26708003) from Japan Society for the Promo-
tion of Science (JSPS), and Bilateral Joint Research Program
promoted by JSPS and National Research Foundation (NRF) of
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Received: April 15, 2015
Published online on July 17, 2015
Chem. Eur. J. 2015, 21, 12996 – 13003
www.chemeurj.org
13003
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim