Incorporating BODIPY fluorophores into tetrakis(arylethynyl)benzenes

Article abstract of DOI:10.1021/jo200491m

Six structural isomers of a tetrakis(arylethynyl)benzene (TAEB) chromophore functionalized with dibutylamine and BODIPY moieties as the corresponding donor and acceptor units were prepared. To evaluate the effectiveness of the donor group, two TAEB molecules and three structurally related bis(arylethynyl)benzene (BAEB) isomers containing only acceptors were also synthesized. The electronic absorption and emission spectra of each series were examined. Additionally, computational studies were employed to corroborate the relative energy levels and gaps present in each series.

Full text of DOI:10.1021/jo200491m

ARTICLE
pubs.acs.org/joc
Incorporating BODIPY Fluorophores into
Tetrakis(arylethynyl)benzenes
Daniel T. Chase, Brian S. Young, and Michael M. Haley*
Department of Chemistry and Materials Science Institute, University of Oregon, Eugene, Oregon 97403-1253, United States
S Supporting Information
b
ABSTRACT: Six structural isomers of a tetrakis(arylethynyl)-
benzene (TAEB) chromophore functionalized with dibutyl-
amine and BODIPY moieties as the corresponding donor and
acceptor units were prepared. To evaluate the effectiveness of
the donor group, two TAEB molecules and three structurally
related bis(arylethynyl)benzene (BAEB) isomers containing
only acceptors were also synthesized. The electronic absorption
and emission spectra of each series were examined. Addition-
ally, computational studies were employed to corroborate the
relative energy levels and gaps present in each series.
’ INTRODUCTION
Highly conjugated, carbon rich molecules are of great interest
due to their unique optoelectronic properties.1 These molecules
are now recognized as suitable materials for advanced applica-
tions such as light-emitting diodes, photovoltaics, and thin film
transistors.2 Over the last several years, we have described
detailed structureꢀproperty relationship studies on donor/ac-
ceptor-functionalized tetrakis(arylethynyl)benzenes (TAEBs).3
These cruciform-shaped molecules possess multiple pathways
for electronic and photonic transfer and are amenable to a host of
substitution patterns (Figure 1). We and others4 have shown that
the band gap of these molecules can be tuned with a high degree
of sensitivity with judicious choice of the nature and substitution
motif of the donor and acceptor units, thereby enhancing their
optical and nonlinear optical (NLO) properties. Additionally,
these molecules have aptly demonstrated their ability to act as
ionic sensors through dynamic shifting of their emission spectra
through stepwise intramolecular charge-transfer, as evidence of
fine control over their HOMO and LUMO energy levels.5
To further explore the potential of the TAEB system, we sought
out a stronger acceptor in an effort to increase charge transfer, as
seen by a stronger net dipole, and therefore to exhibit a larger
bathochromic shift into the red region. To meet these criteria, we
employed the 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene core,
better known as BODIPY, as our acceptor unit. The BODIPY
moiety has garnered a significant amount of attention due to its
strong UV-absorbing and emitting capabilities, high quantum
yields, and general insensitivity to various chemical environments
such as solution pH and solvent polarity.6 Not surprisingly,
BODIPYs are also pursued for a myriad of optoelectronic
applications7 in their own right, as well as molecular and ionic
sensors and as stains for biological markers or dyes.8 Very recently,
ethynylated BODIPYs were successfully fused together to form
dimeric and trimeric annulenes9 that were determined to possess
Figure 1. Conjugated pathways present in TAEB compounds. Path-
ways a and c represent linear and bent conjugation pathways, respec-
tively, whereas path b represents cross conjugation.
antiaromatic properties (24 and 36 π-electrons, respectively),
which represents another intriguing area of research to us.10 Here,
we report the synthesis of six structurally isomeric donor/acceptor-
functionalized TAEBs (1ꢀ6, Figure 2). For control purposes, two
additional TAEBs (7ꢀ8) and three structurally related bis-
(arylethynyl)benzene (BAEBs, 9ꢀ11) containing only acceptors
were also prepared. The electronic absorption and emission
spectra as well as computational studies of each series were also
examined for structureꢀproperty relationships.
’ RESULTS AND DISCUSSION
Synthesis. The general synthetic strategy for TAEBs 1ꢀ8 and
BAEBs 9ꢀ11 relies heavily on successive Sonogashira cross-
coupling reactions. Donor and acceptor fragments are attached
to a central tetrahalobenzene ring in a stepwise fashion that takes
advantage of the reactivity differences toward aryl bromides and
Received: March 5, 2011
Published: April 15, 2011
r
2011 American Chemical Society
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Figure 2. Target donor/acceptor-functionalized TAEBs 1ꢀ6, all-acceptor TAEBs 7ꢀ8, and BAEBs 9ꢀ11.
Scheme 1. Synthesis of TAEBs 1ꢀ3
Scheme 2. Synthesis of BODIPY Precursor 16
To investigate isomeric TAEBs 4ꢀ8, iodination of known
precursor 1312b furnished iodoBODIPY 14 (Scheme 2). Cross-
coupling with (trimethylsilyl)acetylene (TMSA) provided
silyl-protected 15 in high yield and subsequent desilylation afforded
ethynylBODIPY 16. The deprotection step should proceed no
longer than 15 min as the BꢀF bonds undergo metathesis with
iodides in the catalytic cycle.11 Specifically, cross-coupling of known
iodide 1212 to the terminal alkynes of our previously reported
bis(donor)-substituted precursors3c afforded TAEBs 1ꢀ3 as bright
orange/red solids in low to moderate yield (Scheme 1).
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Scheme 3. Synthesis of TAEBs 4ꢀ6
Scheme 4. Synthesis of TAEBs 7ꢀ8 and BAEBs 9ꢀ11
Figure 3. Electronic absorption spectra of (top) 1ꢀ6 and (bottom)
7ꢀ11, 16 in toluene (PhMe); all spectra recorded at 10 μM concentration.
transfer band. For example, 1ꢀ3 display high-energy absorptions
of 404, 423, and 443 nm, respectively, which are on par with
TAEBs containing ꢀNO2 and ꢀCF3 groups. Isomers 4ꢀ6,
however, exhibit absorptions of 400, 402, and 412 nm, respec-
tively, which are a considerably narrower range; similar absorp-
tions are seen for 9ꢀ11 (398, 399, and 408 nm, respectively).
Such behavior can be explained as a function of their attachment
to the BODIPY core: while 1ꢀ3 are bound to the phenyl group
on the meso position, 4ꢀ6 and 9ꢀ11 are bound directly to the
electron-rich pyrrole. All-acceptors 7ꢀ8 and ethynylBODIPY 16
exhibit muted absorptions in this region due to either the lack of
donor functionality (7ꢀ8) or conjugation altogether (16).
However, 1ꢀ6 and 9ꢀ11 also possess an intense low-energy
absorption, a trait not seen before in the TAEB scaffold. This low-
energy absorption, attributable to the BODIPY acceptor unit,
appears at ∼505 nm for 1ꢀ3, regardless of substitution pattern,
presumably due to the fact that the acceptor unit is orthogonal to
the π-system. A similar ortho < meta < para trend for the longest
λmax in the low-energy region with the para isomers exhibiting
the most red-shifted absorption is observed for 4ꢀ6 and 9ꢀ11.
Isomers 4ꢀ6, where the donor-functionalized phenylacetylene is
directly linked to the BODIPY core, exhibit broad absorptions
between 530 and 570 nm. Attachment of the acetylene to the
acceptor unit does not induce the aforementioned rotational
restrictions; therefore, full conjugation throughout the TAEB is
permitted.7h Hence, placement of the phenylacetylene scaffold
can have profound effects on the optical band gap as the lowest
energy transition of 6 is 64 nm bathochromically shifted from 3 in
the excess methoxide to produce undesirable MeO-functiona-
lized BODIPYs.13 Despite this potential pitfall, 16 can be cleanly
and efficiently synthesized in excellent overall yield.
Cross-coupling of 16 to the appropriate bis(donor)-substi-
tuted precursors3c afforded TAEBs 4ꢀ6 as bright red solids in
low to modest yield (Scheme 3). We explored alternate routes
(e.g., cross-coupling 16 with the appropriate bis(donor)
dibromoarenes)3c and methods (e.g., Negishi-modified Sonoga-
shira reaction),14 but these variations worked no better.
Fortunately, no such problems for the synthesis of 7ꢀ8 were
encountered. Specifically, cross-coupling ethynylBODIPY 16
with tetraiodobenzene or tetrabromopyrazine afforded all-accep-
tor TAEBs 7ꢀ8, respectively (Scheme 4). Similarly, 16 was cross-
coupled with 1,2-, 1,3- and 1,4-diiodobenzene to form related BAEBs
9ꢀ11, respectively.
Electronic Absorption Spectra. The absorption spectra of
1ꢀ11 and 16 in toluene are shown in Figure 3; the data for both
toluene and CHCl3 are given in Table 1. All illustrate the
characteristic pattern of two broad absorptions between 300
and 500 nm with extinction coefficients between 15 000 and
60 000 Mꢀ1 cmꢀ1, typical for intramolecular charge transfer
bands in phenylacetylene scaffolds.3 As seen with our previous
systems,3c,d 1ꢀ11 follow the established trend for the longest
λmax in the high-energy region where the trend is ortho < meta <
para with the para isomers exhibiting the most red-shifted charge
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Table 1. Absorption and Emission Data for TAEBs 1ꢀ8, BAEBs 9ꢀ11, and EthynylBODIPY 16
λabs (nm)
Stokes shiftc
(nm)
entry
solvent
high-energy
low-energy
log(ε)a
λem (nm)
Φf (%)b
(nm)
(cmꢀ1
)
(cmꢀ1
)
1
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
CHCl3
PhMe
404
407
423
418
443
438
400
398
402
403
412
407
502
505
503
505
503
505
533
533
553
553
564
569
540
542
541
541
525
526
542
544
551
551
520
522
5.07
5.30
4.92
5.06
5.19
5.06
4.91
4.96
4.96
4.92
4.77
4.22
5.33
4.66
5.40
5.25
4.99
4.87
5.04
5.08
5.06
4.96
4.85
4.89
520
524
518
520
520
520
606
603
608
606
602
601
590
591
579
579
575
578
569
567
586
586
537
539
4
20
4
116
117
95
5500
500
18
19
15
15
17
15
73
70
55
53
38
32
50
49
38
38
50
52
27
23
35
35
17
17
690
720
2
4300
4700
3300
3600
8500
8500
8400
8300
7700
7900
580
15
8
102
77
570
3
640
15
<0.1
44
<0.1
19
<0.1
19
54
74
38
42
62
81
78
78
60
60
74
72
82
570
4
206
205
206
203
190
194
2260
2180
1640
1580
1120
940
5
6
d
d
d
7
ꢀ
ꢀ
ꢀ
1570
1530
1210
1210
1660
1710
880
d
d
d
ꢀ
ꢀ
ꢀ
d
d
d
8
ꢀ
ꢀ
ꢀ
d
d
d
ꢀ
ꢀ
ꢀ
9
398
398
399
403
408
414
177
180
170
164
178
172
7700
7800
7500
7200
7400
7100
10
11
16
750
1080
1080
610
d
d
d
ꢀ
ꢀ
ꢀ
d
d
d
ꢀ
ꢀ
ꢀ
600
a Determined from the low-energy absorption. b Quantum yields measured against an internal integrating sphere.15 c Shifts determined as the difference
between λem and high-energy λabs. d Not applicable.
toluene. All-acceptor 7 exhibits an absorption at 540 nm, which
can be explained through similar means as 4ꢀ6. Structurally
related pyrazine 8 exhibits a similar shift at 541 nm, suggesting
that variation of the central arene plays a minimal role in charge
transfer. BAEBs 9ꢀ11 exhibit absorptions between 525 and
550 nm, which are hypsochromically shifted by 5ꢀ20 nm from
4ꢀ6, rationalized from the lack of donor groups on the central
arene. An approximate ratio exists between the extinction
coefficients of the high and low-energy regions: for 1ꢀ6, the
ratio is 1:2 while for 9ꢀ11, the ratio is 1:4. This can be
rationalized by the simple comparison that 1ꢀ6 have twice the
number of phenylacetylene groups bound to the central core
than 9ꢀ11. Also, the extinction coefficient for the low-energy
absorption appears to be directly proportional to the number of
acceptor groups present. For example, 1ꢀ6 and 9ꢀ11, which
have two acceptor groups, have low-energy extinction coefficients
between 80 000 and 130 000 Mꢀ1cmꢀ1, while 7 and 8 have approx-
TAEB/BAEB architecture, it is completely absent in 1ꢀ11, as is
well-known for BODIPY molecules.6 Positioning of the acceptor
groups around the central arene also has little effect on the
emission wavelengths: 1ꢀ3 all exhibit transitions near 520 nm
regardless of substitution motif. Although this lack of differentia-
tion is not unusual, typically seen by an 8ꢀ20 nm range between
isomers where the difference increases in nonpolar solvents, 1ꢀ3
exhibit remarkably narrow difference of 2 nm. This trend is also
observed with 4ꢀ6, which exhibit emissions near 605 nm with a
slightly larger deviation of 6 nm between isomers. The attach-
ment point of the acceptor group, however, has a significant
effect. As can be seen between 1ꢀ3 and 4ꢀ6, the largest
difference is observed between 2 and 5, which possess emissions
at 518 and 608 nm, respectively, where 5 demonstrates a 90 nm
bathochromic shift from 2. This behavior correlates well with
anthracene/BODIPY systems developed by Burgess et al. where
similar shifts were observed between like-systems.7h The emis-
sion for all-acceptors 7ꢀ8 were found at 590 and 579 nm,
respectively, demonstrating that direct substitution of the two
donors with an additional two acceptors results in a modest
hypsochromic shift; however, 7ꢀ8 show a significant bathochro-
mic shift compared to previously synthesized parent and tetra-
donor TAEBs 17ꢀ18,3b which suggests that an all-acceptor
system may well outperform an all-donor one. Interestingly
though, 9ꢀ11 emit between 570 and 590 nm, despite the lack
of additional conjugation that 7ꢀ8 possess. Despite this, 9ꢀ11
follow the trend of meta < ortho < para with the para isomer
imate extinction coefficients of 210 000 and 250 000 Mꢀ1 cmꢀ1
,
respectively. No significant solvatochromic effects were observed
for 1ꢀ11, as the absorption spectra differed within 5 nm when
compared to CH2Cl2 and toluene solutions.
Electronic Emission Spectra. The emission spectra for 1ꢀ11
and 16 in toluene are shown in Figure 4; the data for both toluene
and CHCl3 are given in Table 1. Perhaps the most striking feature
is the lack of fluorescence solvatochromism: the largest deviation
in emission λmax is 4 nm in the entire series. While this phenom-
enon is regularly observed (with shifts as large as 65 nm) in the
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Molecular Orbital Plots. Representative molecular orbital
plots of the ortho-substituted systems 10, 40, and 9 along with
all-acceptor 7 are shown in Figure 5, with the corresponding plots
for 20ꢀ30, 50ꢀ60, 8, and 10ꢀ11 in the Supporting Information.
Structures 10ꢀ60 are simplified by the replacement of NBu2
groups with NMe2 and all calculations are done on the B3LYP/6-
31G* level of theory.16 As seen with our previously synthesized
TAEBs,3c the FMO plots of 10 and 40 indicate that the majority of
density of the highest occupied molecular orbital (HOMO)
resides on the donor end of the molecule, while the majority of
density of the lowest unoccupied molecular orbital (LUMO)
resides on the acceptor, indicative of charge-transfer processes.
However, the majority of LUMO density resides on the acceptor
moiety itself, leaving very little on the neighboring acetylenes and
central arene; hence, the acceptor group is expected to be the
dominant factor in any electronic transitions. This is chiefly
observed with 10ꢀ30 as all the LUMO density is found on the
acceptor unit, which is situated orthogonally from the remainder
of the phenylacetylene scaffold, thereby eliminating any possible
overlap. Such behavior justifies the nearly identical emission
profiles of 1ꢀ3 in Figure 4, which closely resemble 12.12a The
remaining compounds avoid this orthogonality issue. By attach-
ing the acetylenes directly to one of the pyrrole units of the
acceptor core, this leads essentially to coplanarity of the aromatic
groups within TAEBs/BAEBs 4ꢀ11 as illustrated in the calcula-
tions as well as an X-ray structure for 8 (see Supporting
Information). Therefore, 4ꢀ6 exhibit significantly red-shifted
emission wavelengths with respect to 1ꢀ3, that is, 4ꢀ6 maintain
good intramolecular charge transfer while in full-conjugation
with the phenylacetylene scaffold. Like 10ꢀ60, the majority of
LUMO density for 7ꢀ11 resides on the acceptor unit; however,
the HOMO density for 7 and 9 extends throughout the entire
molecule. As such, there is considerable overlap between their
respective HOMO and LUMOs which give rise to πꢀπ*
transitions, similarly observed with 17ꢀ18.3b The emission
wavelengths of 7ꢀ11 confirm this assessment as their transitions
are hypsochromically shifted as much as 40 nm with respect to 4ꢀ6.
Figure 4. Emission spectra of (top) 1ꢀ6 and (bottom) 7ꢀ11, 16 in
toluene (PhMe); all spectra recorded at 10 μM concentration.
having the longest emission λmax. Due to the fact that the
emissions of 1ꢀ3 and 4ꢀ6 are within a narrow region, it is
difficult to discern whether each series follows this trend;
however, in terms of Stokes shifts, both 1ꢀ6 and 9ꢀ11 follow
the previously established trend of para < meta < ortho, where
the ortho isomer possess the largest dipole moment and hence
the largest shift.
’ CONCLUSIONS
Donor/acceptor-functionalized TAEBs 1ꢀ6 as well as TAEBs
7ꢀ8 and structurally related BAEBs 9ꢀ11 containing only
acceptors were synthesized and characterized. As such, these
molecules displayed an array of intriguing optical properties that
can be fine-tuned via small isomeric and structural variations.
This especially holds true through comparison of 1ꢀ3 and 4ꢀ6.
All-acceptors 7ꢀ8 and related 9ꢀ11 also demonstrate the
necessity for strong donors to ensure efficient charge transfer
pathways. Despite the duality-imposed nature of 1ꢀ6 and 9ꢀ11,
all were shown to follow the previously established trends with
respect to absorption and emission. However, the BODIPY
acceptor was found to have a remarkable impact on the overall
phenylacetylene scaffold such as its inability to exhibit any form
of solvatochromism, a trend most often found in these systems.
Furthermore, in some instances, despite the tendency to quench
in polar solvents, the BODIPY unit was able to enhance the
quantum yields to levels not yet seen with the TAEB molecules.
The fluorescence quantum yields were measured against an
internal integrating sphere and the values reported in both
CHCl3 and toluene in Table 1.15 In each instance, the Φf values
were lower in CHCl3 than in toluene. This holds specifically true
for 4ꢀ6 where Φf values were nearly nonexistent in CHCl3 while
in toluene, Φf values were as high as 0.81 for 9. In toluene, the
general isomer trend was para < meta < ortho, the exact opposite
found for pyridyl-functionalized systems. Furthermore, the CF3-
functionalized species afforded yet another order, suggesting that
no broad generalizations for fluorescence quantum yields can be
made for TAEBs/BAEBs.
’ EXPERIMENTAL SECTION
General Comments. 1H and 13C NMR spectra were recorded in
CDCl3 or CD2Cl2 using either a 300 (1H 299.93 MHz, 13C 75.42 MHz)
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Figure 5. Representative molecular orbital plots (B3LYP/6-31G*) of simplified 10, 40, 7, and 9.16 The lower plots represent the HOMOs while the
upper plots represent the LUMOs.
or 500 MHz (1H 500.11 MHz, 13C 125.75 MHz) NMR spectrom-
eter. Chemical shifts (δ) are expressed in ppm relative to the residual
chloroform (1H 7.27 ppm, 13C 77.2 ppm) or dichloromethane
(1H 5.32 ppm, 13C 54.0 ppm) reference. Coupling constants are
expressed in hertz. IR spectra were recorded using a FTIR 550 spectrom-
eter. UVꢀvis spectra were recorded on an UVꢀvis spectrometer.
Fluorescence spectra and quantum yields were recorded on a spectro-
fluorimeter. High resolution mass spectra were recorded on a MALDI
mass spectrometer. THF and CH2Cl2 were distilled from their appro-
priate drying agents under N2. Unless otherwise stated, all reagents were
purchased and used as received. Donor-functionalized phenylacetylenes
as well as BODIPYs 12ꢀ13 were prepared by the respective previously
reported methods.3c,12
(Trimethylsilylethynyl)BODIPY 15. IodoBODIPY 14 (0.358 g,
0.795 mmol), Pd(PPh3)2Cl2 (0.017 g, 0.024 mmol), and CuI (0.009 g,
0.048 mmol) were dissolved in THF (30 mL) and Et3N (30 mL). The
mixture was degassed with Ar for 45 min. TMSA (0.44 mL, 3.18 mmol)
was added to the solution and the resulting mixture was stirred overnight
at 50 °C. Upon completion, the mixture was evaporated to dryness and
the crude product was dissolved in CH2Cl2 and then passed through a
pad of silica to remove insoluble material. The filtrate was evaporated to
dryness and the crude product was chromatographed on silica (1:1
hexanes/CH2Cl2) to give 15 (0.325 g, 98%) as a red crystalline solid.
1H NMR (CD2Cl2): δ 7.52ꢀ7.50 (m, 3H), 7.28ꢀ7.26 (m, 2H), 6.06 (s,
1H), 2.62 (s, 3H), 2.54 (s, 3H), 1.47 (s, 3H), 1.40 (s, 3H), 0.23 (s, 9H).
13C NMR (CDCl3): δ 158.5, 156.9, 145.7, 143.8, 143.1, 135.2, 133.2,
130.6, 129.9, 129.8, 128.5, 122.8, 115.8, 101.5, 98.2, 15.1, 14.9, 13. 8,
13.5, 0.5. IR (NaCl, CH2Cl2) ν: 3054, 2987, 2305, 2149, 1541, 1422,
1313 cmꢀ1. UVꢀvis (CHCl3) λmax (log ε): 529 (4.74) nm. Em.
(CHCl3) λmax: 547. HRMS (MALDI) for C24H27BF2N2Si [Mþ]: calcd
420.2005, found 420.1991.
IodoBODIPY 14. TetramethylBODIPY 13 (0.400 g, 1.23 mmol)
and CaCO3 (0.185 g, 1.85 mmol) were added to CH2Cl2 (100 mL), and
MeOH (20 mL). BTEA ICl2 (0.480 g, 1.23 mmol) was then added and
3
the mixture was stirred at rt for 1 h. After completion, the solution was
evaporated to dryness. The crude material was chromatographed over
silica gel (7:3 hexanes/CH2Cl2) to give 14 (0.460 g, 83%) as a red
crystalline solid. 1H NMR (CD2Cl2): δ 7.53ꢀ7.51 (m, 3H), 7.29ꢀ7.27,
(m, 2H), 6.09 (s, 1H), 2.60 (s, 3H), 2.54 (s, 3H), 1.40 (s, 6H). 13C NMR
(CD2Cl2): δ 158.5, 154.7, 146.1, 143.8, 142.4, 135.3, 132.5, 131.4, 129.9,
129.8, 128.5, 123.9, 122.9, 84.5, 17.0, 16.1, 15.1, 14.9. IR (NaCl,
CH2Cl2) ν: 3054, 2987, 2306, 1540, 1421, 1305 cm. UVꢀvis
(CHCl3) λmax (log ε): 518 (4.93) nm. Em. (CHCl3) λmax: 537 nm.
HRMS (MALDI) for C19H18BF2IN2 [Mþ]: calcd 450.0576, found
450.0559.
EthynylBODIPY 16. (Trimethylsilylethynyl)BODIPY 15 (0.460 g,
1.09 mmol) and K2CO3 (1.51 g, 10.9 mmol) were dissolved in THF
(30 mL) and MeOH (30 mL) and then stirred for 15 min. The product
mixture was evaporated to dryness, and the crude product was dissolved
in CH2Cl2 and then passed through a pad of silica to remove excess
K2CO3. The filtrate was evaporated to dryness and the crude product
was chromatographed on silica (1:1 hexanes/CH2Cl2) to give 16 (0.292
1
g, 84%) as a red crystalline solid. H NMR (CD2Cl2): δ 7.53ꢀ7.50
(m, 3H), 7.28ꢀ7.26 (m, 2H), 6.08 (s, 1H), 3.37 (s, 1H), 2.62 (s, 3H),
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2.55 (s, 3H), 1.47 (s, 3H), 1.41 (s, 3H). 13C NMR (CD2Cl2): δ 158.9,
156.6, 146.0, 144.0, 143.1, 135.0, 133.2, 130.3, 129.9, 129.8, 128.4, 122.9,
114.3, 84.0, 76.8, 15.1, 14.9, 13.6, 13.3. IR (NaCl, CH2Cl2) ν: 3052,
2987, 2152, 2062, 1485, 1464, 1382 cmꢀ1. UVꢀvis (toluene) λmax (log
ε): 522 (4.89) nm. Em. (toluene) λmax: 539 nm. HRMS (MALDI) for
C21H19BF2N2 [Mþ]: calcd 348.1609, found 348.1623.
General Procedure for TAEB/BAEB Synthesis. BODIPY 12 or
14 was dissolved in THF (20 mL) and degassed with Ar for 45 min. In a
separate flask, the appropriate diethynylarene, Pd(PPh3)4, and CuI were
dissolved in THF (25 mL) and Et3N (25 mL) and also degassed with Ar
for 45 min. The solution containing 12 or 14 was then transferred by
cannula into the second flask and the mixture was heated at 60 °C for
18ꢀ48 h. After cooling, the mixture was evaporated to dryness and the
crude product was dissolved in CH2Cl2 and then passed through a pad of
silica to remove insoluble material. The filtrate was evaporated to
dryness and subsequently chromatographed on silica (1:1 CH2Cl2/
hexanes) to afford the appropriate TAEB/BAEB derivative.
ortho-D/A-TAEB 1. Following the general procedure, 12
(0.101 g, 0.224 mmol), 1,2-diethynyl-4,5-bis[(40-N,N-dibutylamino-
phenyl)ethynyl]benzene3c (0.060 g, 0.102 mmol), Pd(PPh3)4 (0.007 g,
0.006 mmol), and CuI (0.007 g, 0.012 mmol) were reacted for 48 h.
Chromatography on silica (1:1 CH2Cl2/hexanes) gave 1 (0.030 g, 23%)
as a red/orange solid. 1H NMR (CDCl3): δ 7.74 (s, 2H), 7.70 (d, J = 8.7
Hz, 4H), 7.44 (d, J = 8.7 Hz, 4H), 7.30 (d, J = 8.7 Hz, 4H), 6.61 (d, J = 8.7
Hz, 4H), 6.00 (s, 4H), 3.32 (t, J = 7.2 Hz, 8H), 2.56 (s, 12H), 1.62ꢀ1.56
(m, 8H), 1.44 (s, 12H), 1.42ꢀ1.36 (m, 8H), 0.98 (t, J = 7.2 Hz). 13C
NMR (CDCl3): δ 156.0, 148.5, 143.1, 140.8, 135.5, 134.7, 133.4, 132.5,
131.4, 128.5, 126.6, 124.2, 123.7, 121.7, 111.4, 108.6, 98.1, 94.0, 89.6,
86.2, 50.9, 29.6, 20.5, 14.8, 14.2. IR (NaCl, CH2Cl2) ν: 3054, 2987, 2305,
2194, 1605, 1547, 1523, 1513, 1471, 1307, 1270 cmꢀ1. UVꢀvis
(toluene) λmax (log ε): 505 (5.30) nm. Em. (toluene) λmax: 524 nm.
HRMS (MALDI) for C80H82B2F4N6 [Mþ]: calcd 1224.6723, found
1224.6744.
meta-D/A-TAEB 2. Following the general procedure, 12 (0.101 g,
0.224 mmol), 1,5-diethynyl-2,4-bis[(40-N,N-dibutylaminophenyl)-
ethynyl]benzene3c (0.060 g, 0.102 mmol), Pd(PPh3)4 (0.007 g, 0.006
mmol), and CuI (0.007 g, 0.012 mmol) were reacted for 48 h.
Chromatography on silica (1:1 CH2Cl2/hexanes) gave 2 (0.030 g,
23%) as a red/orange solid. 1H NMR (CDCl3): δ 7.75ꢀ7.72
(m, 6H), 7.40 (d, J = 8.7 Hz, 4H), 7.32 (d, J = 8.7 Hz, 4H), 6.57 (d,
J = 8.7 Hz, 4H), 6.01 (s, 4H), 3.30 (t, J = 7.2 Hz, 8H), 2.58 (s, 12H),
1.62ꢀ1.56 (m, 8H), 1.48 (s, 12H), 1.42ꢀ1.34 (m, 8H), 0.96 (t, J =
7.2 Hz, 12H). 13C NMR (CDCl3): δ 156.0, 148.7, 143.3, 141.1, 135.4,
135.0, 134.3, 133.4, 132.7, 131.5, 128.5, 127.3, 124.5, 123.2, 121.6, 111.4,
108.4, 98.3, 94.1, 89.9, 86.1, 51.0, 29.6, 20.6, 14.9, 14.2. IR (NaCl,
CH2Cl2) ν: 3054, 2987, 2194, 1606, 1547, 1523, 1469, 1404, 1370, 1307,
1270 cmꢀ1. UVꢀvis (toluene) λmax (log ε): 505 (5.06) nm. Em.
(toluene) λmax: 520 nm. HRMS (MALDI) for C80H82B2F4N6 [Mþ]:
calcd 1224.6723, found 1224.6741.
ortho-D/A-TAEB 4. Following the general procedure, 14 (0.050 g,
0.145 mmol), 1,2-diethynyl-4,5-bis[(40-N,N-dibutylaminophenyl)-
ethynyl]benzene3c (0.050 g, 0.072 mmol), Pd(PPh3)4 (0.006 g, 0.004
mmol), and CuI (0.002 g, 0.008 mmol) were reacted for 48 h.
Chromatography on silica (4:1 toluene/cyclohexane) gave 4 (0.031 g,
34%) as a red solid. 1H NMR (CDCl3): δ 7.58 (s, 2H), 7.50ꢀ7.48 (m,
6H), 7.40 (d, J = 8.7 Hz, 4H), 7.29 (m, 4H), 6.57 (d, J = 8.7 Hz, 4H), 6.05
(s, 2H), 3.29 (t, J = 7.2 Hz, 8H), 2.63 (s, 6H), 2.61 (s, 6H), 1.60ꢀ1.56
(m, 8H), 1.42 (s, 6H), 1.40 (s, 6H), 1.40ꢀ1.36 (m, 8H), 1.04 (t, J = 7.2
Hz, 12 H). 13C NMR (CD2Cl2): δ 158.9, 156.9, 149.1, 145.8, 143.3,
143.0, 135.1, 134.8, 133.6, 129.9, 129.8, 129.8, 129.7, 128.5, 125.9, 124.5,
122.8, 111.8, 111.7, 108.6, 97.8, 94.9, 88.0, 86.5, 30.28, 29.9, 20.7, 15.1,
14.9, 14.5, 14.3, 13.9, 13.5. IR (NaCl, CH2Cl2) ν: 3054, 2987, 2360,
2149, 1539, 1521, 1313, 1193 cmꢀ1. UVꢀvis (toluene) λmax (log ε): 533
(4.91) nm. Em. (toluene) λmax: 603 nm. HRMS (MALDI) for
C80H82B2F4N6 [Mþ]: calcd 1224.6723, found 1224.6704.
meta-D/A-TEAB 5. Following the general procedure, 14 (0.050 g,
0.145 mmol), 1,5-diethynyl-2,4-bis[(40-N,N-dibutylaminophenyl)-
ethynyl]benzene3c (0.050 g, 0.072 mmol), Pd(PPh3)4 (0.006 g, 0.004
mmol), and CuI (0.002 g, 0.008 mmol) were reacted for 48 h.
Chromatography on silica (4:1 toluene/cyclohexane) gave 5 (0.013 g,
15%) as a red solid. 1H NMR (CD2Cl2): δ 7.61 (s, 1H), 7.54 (s, 1H),
7.52ꢀ7.50 (m, 6H), 7.36ꢀ7.32 (m, 4H), 7.26 (d, J = 8.7 Hz, 4H), 6.55
(d, J = 8.7 Hz, 4H), 6.09 (s, 2H), 3.31 (t, J = 7.2 Hz, 8H), 2.68 (s, 6H),
2.55 (s, 6H), 1.63ꢀ1.56 (m, 8H), 1.53 (s, 6H), 1.42 (s, 6H), 1.39 (q, J =
6.5 Hz, 8H), 0.98 (t, J = 7.2 Hz, 12H). 13C NMR (CD2Cl2): δ 158.5,
156.9, 148.9, 145.7, 143.5, 142.9, 135.3, 135.1, 134.8, 133.6, 129.8, 129.7,
128.5, 125.6, 124.1, 122.7, 111.6, 108.3, 97.6, 95.1, 88.0, 86.3, 51.2, 29.8,
20.9, 15.1, 14.9, 14.3, 14.0, 13.7. IR (NaCl, CH2Cl2) ν: 3054, 2960, 2198,
1539, 1520, 1264 cmꢀ1. UVꢀvis (toluene) λmax (log ε): 553 (4.92) nm.
Em. (toluene) λmax: 606 nm. HRMS (MALDI) for C80H82B2F4N6
[Mþ]: calcd 1224.6723, found 1224.6696.
para-D/A-TAEB 6. Following the general procedure, 14 (0.050 g,
0.145 mmol), 1,4-diethynyl-2,5-bis[(40-N,N-dibutylaminophenyl)-
ethynyl]benzene3c (0.050 g, 0.072 mmol), Pd(PPh3)4 (0.006 g, 0.004
mmol), and CuI (0.002 g, 0.008 mmol) were reacted for 48 h.
Chromatography on silica (4:1 toluene/cyclohexane) gave 6 (0.009 g,
10%) as a red solid. 1H NMR (CD2Cl2): δ 7.59 (s, 2H), 7.53ꢀ7.50 (m,
6H), 7.36ꢀ7.32 (m, 4H), 7.26 (d, J = 8.7 Hz, 4H), 6.56 (d, J = 8.7 Hz,
4H), 6.09 (s, 2H), 3.31 (t, J = 7.5 Hz), 2.69 (s, 6H), 2.55
(s, 6H), 1.63ꢀ1.56 (m, 8H), 1.54 (s, 6H), 1.42 (s, 6H), 1.39 (q, J =
6.5 Hz, 8H), 0.99 (t, J = 7.2 Hz). 13C NMR (CD2Cl2) δ 158.5, 156.8,
149.0, 145.8, 142.9, 135.1, 133.6, 129.8, 129.7, 129.5, 128.5, 127.3, 126.5,
124.8, 122.8, 114.3, 111.7, 110.5, 110.57, 110.55, 108.3, 97.4, 95.2, 88.2,
86.2, 51.2, 30.3, 29.5, 20.9, 4.9, 14.5, 14.4, 14.3, 13.7. IR (NaCl, CH2Cl2)
ν: 3054, 2987, 2929, 2359, 1270 cmꢀ1. UVꢀvis (toluene) λmax (log ε):
569 (4.77) nm. Em. (toluene) λmax: 601 nm. HRMS (MALDI) for
C80H82B2F4N6 [Mþ]: calcd 1224.6723, found 1224.6743.
tetra-A-TAEB 7. Following the general procedure, 16 (0.177 g,
0.508 mmol), 1,2,4,5-tetraiodobenzene (0.074 g, 0.127 mmol), Pd-
(PPh3)4 (0.017 g, 0.015 mmol), and CuI (0.006 g, 0.030 mmol) were
reacted for 18 h. Chromatography on silica (4:1 CHCl3/toluene) gave 7
(0.066 g, 61%) as a red solid. 1H NMR (CDCl3): δ 7.53ꢀ7.49 (m, 14H),
7.29ꢀ7.27 (m, 8H), 6.07 (s, 4H), 2.62 (s, 24H), 1.43 (s, 12H), 1.39
(s, 12H). 13C NMR (CDCl3): δ 158.1, 156.7, 145.1, 143.1, 142.4, 135.0,
134.8, 132.8, 130.5, 129.5, 129.4, 128.0, 124.9, 122.4, 115.0, 94.3, 88.2,
15.0, 14.8, 13.8, 13.4. IR (NaCl, CH2Cl2) ν: 3054, 2987, 2305, 2203,
1541, 1421, 1270 cmꢀ1. UVꢀvis (toluene) λmax (log ε): 542 (5.33) nm.
Em. (toluene) λmax: 591 nm. HRMS (MALDI) for C90H74B4F8N8
[Mþ]: calcd 1462.6281, found 1462.6247.
para-D/A-TEAB 3. Following the general procedure, 12
(0.101 g, 0.224 mmol), 1,4-diethynyl-2,5-bis[(40-N,N-dibutylaminophenyl)-
ethynyl]benzene3c (0.060 g, 0.102 mmol), Pd(PPh3)4 (0.007 g, 0.006
mmol), and CuI (0.007 g, 0.012 mmol) were reacted for 48 h. Chroma-
tography on silica (1:1 CH2Cl2/hexanes) gave 3 (0.030 g, 23%) as a red/
orange solid. 1H NMR (CDCl3): δ 7.74 (d, J = 8.7 Hz, 4H), 7.73 (s, 2H),
7.40 (d, J = 8.7 Hz, 4H), 7.32 (d, J = 8.7 Hz, 4H), 6.57 (d, J = 8.7 Hz, 4H),
6.01 (s, 4H), 3.30 (t, J = 7.2 Hz, 8H), 2.58 (s, 12H), 1.62ꢀ1.56 (m, 8H),
1.48 (s, 12H), 1.42ꢀ1.34 (m, 8H), 0.96 (t, J = 7.2 Hz, 12H). 13C NMR
(CDCl3): δ 155.9, 148.6, 143.3, 141.1, 135.4, 134.6, 133.3, 132.7, 131.4,
128.5, 125.8, 124.6, 124.4, 121.6, 111.4, 108.4, 97.8, 94.3, 89.8, 86.0, 50.9,
29.6, 20.5, 14.9, 14.2. IR (NaCl, CH2Cl2) ν: 3055, 2958, 2305, 2196,
1604, 1547, 1523, 1471, 1422, 1370, 1307 cmꢀ1. UVꢀvis (toluene) λmax
(log ε): 505 (5.06) nm. Em. (toluene) λmax: 520 nm. HRMS (MALDI)
for C80H82B2F4N6 [Mþ]: calcd 1224.6723, found 1224.6767.
Pyrazine TAEB 8. Following the general procedure, 16 (0.133 g,
0.382 mmol), 1,2,4,5-tetrabromopyrazine (0.038 g, 0.096 mmol), Pd-
(PPh3)4 (0.013 g, 0.011 mmol), and CuI (0.005 g, 0.023 mmol) were
reacted for 18 h. Chromatography on silica (4:1 CHCl3/toluene) gave 8
4049
dx.doi.org/10.1021/jo200491m |J. Org. Chem. 2011, 76, 4043–4051

The Journal of Organic Chemistry
ARTICLE
(0.131 g, 93%) as a red solid. 1H NMR (CDCl3): δ 7.49ꢀ7.45 (m, 12H),
7.29ꢀ7.25 (m, 8H), 6.09 (s, 4H), 2.62 (s, 24H), 1.43 (s, 12H), 1.39
(s, 12H). 13C NMR (CDCl3): δ 159.1, 157.0, 145.7, 143.6, 142.6, 138.7,
134.6, 133.2, 130.3, 129.5, 128.0, 122.9, 113.7, 93.0, 91.1, 15.1, 14.8, 13.9,
13.4. IR (NaCl, CH2Cl2) ν: 3055, 2927, 2195, 1557, 1547, 1536, 1404,
1309, 1270 cmꢀ1. UVꢀvis (toluene) λmax (log ε): 541 (5.40) nm. Em.
(toluene) λmax: 579 nm. HRMS (MALDI) for C88H72B4F8N10 [Mþ]:
calcd 1464.6186, found 1464.6172.
ortho-BAEB 9. Following the general procedure, 16 (0.090 g,
0.259 mmol), 1,2-diiodobenzene (0.043 g, 0.129 mmol), Pd(PPh3)4
(0.007 g, 0.008 mmol), and CuI (0.002 g, 0.016 mmol) were reacted for
18 h. Chromatography on silica (7:3 CH2Cl2/hexanes) gave 9 (0.044 g,
44%) as a violet solid. 1H NMR (CD2Cl2): δ 7.53ꢀ7.47 (m, 8H), 7.31ꢀ
7.26 (m, 6H), 6.09 (s, 2H), 2.56 (s, 12H), 1.43 (s, 6H), 1.39 (s, 6H). 13C
NMR (CD2Cl2): δ 158.4, 156.6, 145.7, 143.2, 142.9, 135.0, 133.1, 132.2,
130.7, 129.8, 129.7, 128.4, 128.3, 126.0, 122.7, 115.3, 95.1, 86.6, 15.1,
14.9, 13.8, 13.4. IR (NaCl, CH2Cl2) ν: 3054, 2987, 2305, 2203, 1541,
1421, 1270 cmꢀ1. UVꢀvis (toluene) λmax (log ε): 526 (4.87) nm. Em.
(toluene) λmax: 578 nm. HRMS (MALDI) for C48H40B2F4N4 [Mþ]:
calcd 770.3375, found 770.3397.
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meta-BAEB 10. Following the general procedure, 16 (0.090 g,
0.259 mmol), 1,3-diiodobenzene (0.043 g, 0.129 mmol), Pd(PPh3)4
(0.009 g, 0.008 mmol), and CuI (0.003 g, 0.016 mmol) were reacted for
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1
68%) as a violet solid. H NMR (CD2Cl2): δ 7.55ꢀ7.52 (m, 7H),
7.40ꢀ7.37 (m, 2H), 7.32ꢀ7.30 (m, 4H), 7.29ꢀ7.26 (m, 1H), 6.08 (s,
2H), 2.66 (s, 6H), 2.55 (s, 6H), 1.51 (s, 6H), 1.42 (s, 6H). 13C NMR
(CD2Cl2): δ 158.6, 156.6, 145.9, 143.3, 143.0, 135.1, 133.2, 131.1, 130.7,
129.9, 129.8, 129.1, 128.5, 128.4, 124.5, 122.8, 115.2, 94.6, 83.2, 15.1.
14.9. 13.8. 13.5. IR (NaCl, CH2Cl2) ν: 3054, 2987, 2305, 2203, 1541,
1421, 1270 cmꢀ1. UVꢀvis (toluene) λmax (log ε): 544 (5.08) nm. Em.
(toluene) λmax: 567 nm. HRMS (MALDI) for C48H40B2F4N4 [Mþ]:
calcd 770.3375, found 770.3347.
para-TEAB 11. Following the general procedure, 16 (0.070 g, 0.201
mmol), 1,4-diiodobenzene (0.033 g, 0.100 mmol), Pd(PPh3)4 (0.007 g,
0.006 mmol), and CuI (0.002 g, 0.012 mmol) were reacted for 18 h.
Chromatography on silica (1:1 CH2Cl2/hexanes) gave 11 (0.068 g,
88%) as a violet solid. 1H NMR (CD2Cl2): δ 7.53ꢀ7.49 (m, 6H), 7.41
(s, 4H), 7.32ꢀ7.30 (m, 4H), 6.09 (s, 2H), 2.65 (s, 6H), 2.55 (s, 6H),
1.51 (s, 6H), 1.42 (s, 6H). 13C NMR (CD2Cl2): δ 158.6, 156.6, 145.9,
143.2, 143.0, 135.1, 133.2, 131.6, 130.9, 129.9, 129.8, 128.5, 123.6, 122.8,
115.3, 96.2, 84.5, 15.1, 14.9, 13.8, 13.5. IR (NaCl, CH2Cl2) ν: 3054,
2987, 2305, 2203, 1541, 1421, 1270 cmꢀ1. UVꢀvis (toluene) λmax (log
ε): 554 (4.96) nm. Em. (toluene) λmax: 586 nm. HRMS (MALDI) for
C48H40B2F4N4 [Mþ]: calcd 770.3375, found 770.3336.
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’ ASSOCIATED CONTENT
Supporting Information. Copies of H and 13C NMR
1
S
b
spectra for 1ꢀ11 and 14ꢀ16; molecular orbital plots for 10ꢀ60 and
7ꢀ11; computational details for 10ꢀ60 and 7ꢀ11; X-ray ORTEP
plot and cif file for 8. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: haley@uoregon.edu.
’ ACKNOWLEDGMENT
We thank the National Science Foundation (CHE-1013032)
for support of this research, as well as for support in the form of
instrumentation grants (CHE-0639170 and CHE-0923589). We
thank Dr. Lev Zakharov for obtaining the X-ray structure of 8.
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