Synthesis and unexpected halochromism of carbazole-functionalized dithienophospholes

Article abstract of DOI:10.1039/c2nj40022g

A series of π-conjugated donor-acceptor (D/A) chromophores using dithieno[3,2-b:2′,3′-d]phosphole oxide as an acceptor and 3,6-carbazole as a donor component have been synthesized and characterized. The studies involved several molecular species with D-A, A-D-A, D-A-D architecture, as well as a polymeric species (D-A)_n. The different photophysical properties of the systems can be attributed to the carbazole unit de facto acting as aniline species for the π-conjugated system. Treatment of the donor-acceptor materials with acids resulted in the significant red shift of the absorption and emission wavelengths and the process was found to be reversible. Investigations via Density-Functional Theory (DFT) calculations revealed the nature of the unexpected red shift upon protonation. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012.

Full text of DOI:10.1039/c2nj40022g

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New Journal of Chemistry
A journal for new directions in chemistry
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Volume 36 | Number 5 | May 2012 | Pages 1123–1286
ISSN 1144-0546
COVER ARTICLE
Stolar and Baumgartner
Synthesis and unexpected halochromism of carbazole-functionalized
dithienophospholes

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PAPER
Synthesis and unexpected halochromism of carbazole-functionalized
dithienophospholes
Monika Stolar and Thomas Baumgartner*
Received (in Montpellier, France) 10th January 2012, Accepted 14th February 2012
DOI: 10.1039/c2nj40022g
A series of p-conjugated donor–acceptor (D/A) chromophores using dithieno[3,2-b:20,30-d]phosphole
oxide as an acceptor and 3,6-carbazole as a donor component have been synthesized and
characterized. The studies involved several molecular species with D–A, A–D–A, D–A–D
architecture, as well as a polymeric species (D–A)n. The different photophysical properties of the
systems can be attributed to the carbazole unit de facto acting as aniline species for the
p-conjugated system. Treatment of the donor–acceptor materials with acids resulted in the
significant red shift of the absorption and emission wavelengths and the process was found to be
reversible. Investigations via Density-Functional Theory (DFT) calculations revealed the nature of
the unexpected red shift upon protonation.
Reaction with either the donor or the acceptor component will
result in an increased energy gap, which can translate into
Introduction
Organic p-conjugated materials are increasingly gaining attention
due to their exceptional utility for practical applications in
organic electronics such as Organic Light-Emitting Diodes
altered photophysics or electronics for the system, and is thus
a desirable feature for the design of sensory materials. While
the sensing of anions (e.g., Fꢀ and CNꢀ) can be accomplished
with electron-deficient units such as organoboron species,3b
(OLEDs), Organic Field-Effect Transistors (OFETs), and
Organic Photovoltaics (OPVs), but also as highly sensitive
chromophores in the area of molecular sensing.1,2 A major
acids, H+) requires electron rich sites; nitrogen-based chromo-
the detection of cationic or electron deficient species (Lewis
strength of organic materials is their highly versatile tunability
that allows tailoring the materials’ properties using a simple
phores have a proven utility for such a purpose due to their
pronounced basicity.4
building block approach. Recent research has shown that the
incorporation of heteroelements—main group elements such
Our comprehensive studies, using the dithieno[3,2-b:20,30-d]-
phosphole system over the past eight years or so, have revealed
as B, Si, and P in particular—can also be used to efficiently
that this unit shows exceptionally strong photoluminescence
properties and is highly tunable through simple modification at
tailor the properties of p-conjugated materials.3 Remarkably,
the phosphorus center.5 More importantly, others and we could
this approach can lead to unique properties due to the intrinsic
electronics and chemistry of these elements, which are not
establish that the oxidation of the phosphorus center significantly
enhances the electron-acceptor character of phosphole-based
accessible using purely carbon-based building blocks.
systems.6 In combination with appropriate donor groups, we were
A particularly intriguing strategy toward highly desirable
photophysics involves the combination of donor- (D) and
acceptor- (A) building blocks within the same p-conjugated
able to access a variety of molecular dithienophosphole chromo-
phores with photoluminescence emissions that cover the full
scaffold.1,2 The electron-rich nature of the donor commonly
optical spectrum.5c Moreover, using the 2,6-bis(dimethylaniline)
increases the energy of the Highest Occupied Molecular
Orbital (HOMO), while the electron-poor nature of the acceptor
functionalized dithienophosphole I (Scheme 1), we could show
that protonation of the nitrogen centers significantly blue-shifts
the emission color of the system from orange (lem = 601 nm) to
green (lem = 524 nm), which we could then use for the
generation of white-light emission in combination with a
suitable blue dithienophosphole chromophore.7
concurrently lowers the Lowest Unoccupied Molecular Orbital
(LUMO). This leads to very narrow energy gaps for comparatively
small chromophores. Furthermore, the intrinsic electronics of the
donor/acceptor units provide an excellent opportunity for stimulus-
responsive behavior of the system, as these functional groups
Inspired by these initial results, we set out to further study
can easily react with electrophiles and nucleophiles, respectively.2
N-donor-functionalized dithienophospholes and their halochromic
behavior in more detail. In this contribution we now report our
systematic studies on such systems using 3(6)-carbazole as the
donor component8 for the dithienophosphole acceptor system.
The 3(6)-carbazole isomer was chosen because it provides
Department of Chemistry, University of Calgary, 2500 University
Drive NW, Calgary, AB T2N 1N4, Canada.
E-mail: Thomas.baumgartner@ucalgary.ca; Fax: +1 (403) 289-9488
c
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Scheme 1 A halochromic dithienophosphole.
optimal conjugation of the nitrogen center with the p-conjugated
scaffold, and access to larger extended oligomers/polymers that
allows for the investigation of the potential communication
between building block chromophores.
Results and discussion
Synthesis and properties of the neutral carbazole-functionalized
dithienophospholes
Scheme 3 Synthesis of the donor–acceptor chromophores.
To gain some deeper insight into the photophysics and halo-
chromism of this system, we have targeted molecular chromo-
phores with A–D, D–A–D and A–D–A architecture, as well as
a polymeric material (A–D)n. The synthetic strategy towards
these four different species followed established procedures
using either mono- or difunctionalized building blocks, with a
Suzuki–Miyaura cross-coupling as the central linking step.
The mono- and dibrominated dithienophosphole derivatives
19 and 25c were reported by us earlier. The 3-borylated carbazole
3 had also been reported in the literature before.10 The synthesis
of the 3,6-diborylated carbazole 4 was adapted from the
literature, involving N-alkylation of 3,6-dibromocarbazole
and subsequent borylation with isopropoxypinacolborane
after lithiation with n-BuLi at ꢀ78 1C in THF (Scheme 2).
With the necessary building blocks in hand, we then proceeded
with the synthesis of the four targeted chromophores 5–8 in a
standard Suzuki–Miyaura protocol in refluxing THF for 72 h using
Pd(PPh3)4 as catalyst and CsF as base (Scheme 3). After column
chromatography, or precipitation into methanol for the polymer,
the corresponding chromophores could be isolated as orange/red
solids in moderate yields, respectively. Multinuclear (1H, 13C, 31P)
NMR spectroscopy as well as high-resolution mass spectro-
metry confirmed the identity of the compounds.
The photophysics of the four chromophores exhibited some
interesting features that revealed the electronic communica-
tion within the different species. UV-vis absorption as well as
fluorescence emission showed two sets of spectra with similar
maxima, one for 5 (A–D) and 7 (A–D–A) with labs E 420 and
lem E 515 nm, and one for 6 (D–A–D) and polymer 8 with
labs E 455 and lem E 563 nm (Table 1 and Fig. 1).
From these data it is clear that the 3,6-carbazole unit does
not strongly promote extended conjugation throughout its
scaffold, as anticipated, and basically only functions as an
p-aniline component to the overall chromophore.11 In addition, the
incorporation of the nitrogen center in the aromatic framework
reduces its donor character for the dithienophosphole acceptor to
some extent, which is evident in the stronger red-shifted data for
the reported bis(dimethylaniline) species I (cf.: labs = 524 nm;
lem = 601 nm). However, the large Stokes shifts and low
photoluminescence quantum yields of 93 nm (fPL = 0.20) for
5, 85 nm (fPL = 0.21) for 7, 107 nm (fPL = 0.15) for 6 and
113 nm (fPL = 0.06) for 8 clearly support the presence of
charge-transfer processes involving non-radiative relaxation
pathways within the chromophores that are more pronounced
in the latter two species, in line with the contribution of two
donor units.2
Acid response of the chromophores
To investigate the halochromic behavior of the four new
chromophores, CHCl3 solutions of the compounds were treated
with p-toluenesulfonic acid (TsOH) to provide for a homo-
genous environment. Remarkably however, a very large excess
of acid (ca. 100 equiv.) is required to induce a shift in the
photophysics of the chromophores. This observation is in line
with our earlier studies and was first attributed to the reduced
Scheme 2 Synthesis of the diborylated carbazole 4.
c
1154 New J. Chem., 2012, 36, 1153–1160
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Table 1 Photophysical data and calculated frontier orbital energies for compounds 5–8 and their protonated congeners
emaxa/L molꢀ1 cmꢀ1
lexb/nm
lemb/nm
fPL
EHOMOd/eV
ELUMOd/eV
DEbgd/eV
c
Compound
labsa/nm
5
6
7
8
417
457
421
454
427
465
—
13 160
24 960
33 830
—
11 880
22 360
—
423
455
427
450
432
457
—
516
562
512
563
580
583
—
0.20
0.15
0.21
0.06
0.08
0.06
—
ꢀ5.12
ꢀ4.83
ꢀ5.13
—
ꢀ5.77
ꢀ5.59
ꢀ5.50
ꢀ6.50
—
ꢀ1.81
ꢀ1.77
ꢀ1.91
—
ꢀ3.33
ꢀ3.28
ꢀ3.35
ꢀ3.86
—
3.31
3.06
3.22
—
2.44
2.31
2.15
2.64
—
5(+)
6(+)
7(+)-mono
7(+)-di
8(+)
428
463
29 650
—
433
503
572
624
0.08
0.02
a
b
UV-Vis absorption in CHCl3. Fluorescence excitation and emission maxima in CHCl3. Photoluminescence quantum yield in CHCl3 solution,
c
relative to quinine sulfate (10ꢀ4 M in 0.1 M H2SO4). Calculated energies, B3LYP/6-31G(d); a PCM solvation model (CHCl3) used for cationic species.
d
Fig. 1 Photophysics of 5–8 in CHCl3. Top: normalized absorption;
bottom: normalized emission.
Fig. 2 Normalized emission spectra of 5, 7 (top), and 6, 8 (bottom);
neutral species: solid; protonated species: dashed; in CHCl3.
basicity of the nitrogen lone pair due to its incorporation within
the p-conjugated system.7 As mentioned in the introduction,
protonation of the nitrogen centers would result in a blue shift
due to the elimination of the donor-component. However, the
most striking observation with these studies is that the photo-
physical properties in fact experience a red shift (Fig. 2). The
effect of the protonation is furthermore stronger on the fluores-
cence emission values, compared to the corresponding absorption
values, which correlates with a more polar nature of the excited
state,2 again contradicting the anticipated results.
show fairly similar emission profiles upon protonation
(lem E 580 nm), while 6(+) and 8(+) exhibit distinctly different
profiles from each other. The polymer 8(+) shows the strongest
red shift upon protonation with an emission at lem = 624 nm
suggesting further extended conjugation within the scaffold.
Notably, the emission maximum of 6(+) at lem = 583 nm is
very similar to that of the other two molecular species 5(+)
and 7(+). However, the further reduced photoluminescence
quantum yields for the protonated species in the range of fPL
o 0.09 suggest the preservation of charge-transfer processes.
The necessity of a large amount of acid to trigger the
halochromic response implies that the binding of protons to
the chromophores is not very strong, suggesting the potential
reversibility of the process. To investigate whether the acid
In general, the absorption maxima of the four chromo-
phores experience a red shift of about Dlabs = 10 nm, while
the red shifts for the emission range from Dlem = 21 nm for
6(+) to Dlem = 64 nm for 5(+) (Table 1). Analogous to the
observations with their neutral congeners, 5(+) and 7(+)
c
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Fig. 3 Fluorescence for 5–8 changes upon treatment with TsOH.
response was indeed reversible, water was added to the CHCl3
solutions of the protonated species to create a biphasic mixture.
In our earlier studies we could show that water was a strong
enough base to deprotonate the reported bis(dimethylaniline)
species I by transferring the acid into the aqueous phase.7
A
similar behavior was also observed for the chromophores 5–8
that all reverted back to their original emission colors upon
treatment with water (Fig. 3). Remarkably, this process can be
repeated several times without compromising the integrity of
the chromophores.
The obtained data and observations strongly suggest that
protonation does actually not occur at the nitrogen donor units.
The only other possible option for the site of protonation is thus the
phosphoryl group. It is well known that PQO bonds are strongly
polar bonds and better described with the canonical structure
P+–Oꢀ, which inherently creates the possibility for the oxide
species to interact with electrophiles, such as protons, as confirmed
by Pietschnig and co-workers for Me3PO and HCl.12 In fact, we
have also recently reported the change in the photo-physics of
acylated dithienophosphole oxides in the presence of Lewis acids,
such as BF3, that are based on similar interactions.13 Our studies
could clearly show that the BF3 coordinates to the PQO group
rather than the CQO group that was also present in the molecules.
To lend the binding of protons to the PQO group in the
present case more credibly, we have obtained 31P NMR spectro-
scopic data for the protonated versions of 6 and 7 that both show
noticeably downfield-shifted resonances (6(+): Dd = 2.1 ppm;
7(+): Dd = 4.2 ppm). The stronger shift for the D–A–D species
can be explained with an increased polar (P+–Oꢀ) character in
7(+) due to the effect of the two donor units that can transfer
more electron density onto the cationic phosphorus center, thus
stabilizing the polar (P+–Oꢀ) form, as opposed to the one donor
in the A–D–A species 6(+) that has to share its electron pair
with two cationic phospholium centers.
Fig. 4 Effects of different acids on the emission (normalized) of 6
(top) and 7 (bottom).
The different emission values obtained with the two acids as
well as the necessity of large excess of acid are a strong
indication that full protonation of the PQO group does not
occur. Therefore, the halochromism of the four carbazole–
dithienophosphole species is very likely the result of the formation
of chromophore–acid complexes with R3P+–Oꢀ-Hꢁ ꢁ ꢁA
interactions.
Theoretical calculations
To gain a better understanding of the observed photophysics,
and to further solidify the ‘‘protonation’’ at the phosphoryl
group instead of the nitrogen centers, we have performed DFT
calculations on two representative chromophores at the
B3LYP/6-31G(d) level of theory that also include some repre-
sentative examples of their N- and PO-protonated forms.14
For simplicity we have assumed full protonation of the PO
group and truncated the dodecyl group with a N-methyl
substituent. To counterbalance the effects of the absence of
the corresponding anions, the calculations were performed
using a PCM solvation model that has provided satisfactory
results for cationic dithienophospholes in the past.6b,15 The
energy values for the corresponding HOMO and LUMO levels
are listed in Table 1. Fig. 5 shows the effects of N- and
PO-protonation on the energy levels of 50.
To investigate the effect of the acid strength on the halo-
chromism and to also confirm the generality of the acid–
chromophore interaction with the phosphoryl group, we then
representatively treated 6 and 7 with trifluoroacetic acid
(TFA). Again a large excess of acid is required, but a similar
red shift of the emission is observed. However, due to the
increased acidity of TFA compared to TsOH, the ‘‘protonated’’
versions of 6 and 7 show further red-shifted emission maxima at
lem = 612 nm and lem = 604 nm, respectively (Fig. 4).
The frontier orbitals for neutral 50 confirm that the HOMO
is delocalized over the whole conjugated scaffold, while the
LUMO is largely located at the dithienophosphole acceptor
end of the chromophore, as expected. Protonation of the
c
1156 New J. Chem., 2012, 36, 1153–1160
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Fig. 5 Frontier orbitals of 50: (A) neutral species; (B) protonated at
Fig. 6 Frontier orbitals of 70: (A) neutral species; (B) mono-PO
nitrogen; (C) protonated at PO.
protonated; (C) di-PO protonated.
nitrogen center has two major effects: (i) the energies of both
HOMO and LUMO are lowered, but the energy gap between
them remains fairly constant, and (ii) only one of the benzene
rings in carbazole is part of the main conjugated scaffold,
which consequently eliminates the possibility of N-protonation
being responsible for the altered photophysics. Protonation of
the phosphoryl group, on the other hand, results in a signifi-
cantly lowered energy gap between HOMO and LUMO
(DE = 0.87 eV), mostly due to a significantly lowered LUMO,
supporting the red shift of the photophysics. From the frontier
orbitals it is also clear that protonation of PO significantly
increases the acceptor character of the dithienophosphole unit,
as the HOMO is now largely located at the carbazole donor
end, while the LUMO has less contribution from this unit
compared to the neutral species.
results in an increase in the energy gap to E = 2.64 eV, which
is mainly the result of a significantly lowered HOMO level that
is somewhat shifted towards the carbazole unit. The LUMO
and LUMO + 1 represent the two dithienophosphole acceptor
groups, respectively.
The results from these calculations can also be used to
explain the observed red-shifted emission maximum for the
polymer 8, compared to its D–A–D relative 6. It is inherently
plausible that the interaction of the molecular species 6 with
TsOH leads to the interaction of both phosphoryl groups with
the acid, while the morphology of the polymer 8 very likely
does not allow for the complete interaction of all PO-groups
with acid. The latter de facto creates mono-protonated triads
(D–A–D+), with reduced energy gap, as supported by the
theoretical calculations.
To investigate the effects of the degree of protonation of the
phosphoryl groups as well as to confirm the increased acceptor
character of the protonated dithienophosphole vs. the neutral
variety, we have also considered the mono- and di-PO-protonated
70 (A–D–A) for the calculations. Fig. 6 shows the effects of the
stepwise protonation of the two PO-groups. In the neutral form,
the HOMO is again evenly delocalized across the whole scaffold,
while the LUMO is shifted toward both dithienophosphole
acceptor units. Protonation of one PO-group results in a
significant decrease in the energy gap from E = 3.22 eV
(neutral) to E = 2.15 eV. Notably the HOMO now comprises
of the carbazole and the non-protonated dithienophosphole,
while the LUMO is exclusively located at the protonated
acceptor end. This clearly confirms the enhanced acceptor
character of the latter. Surprisingly, the second protonation
Conclusions
In conclusion, we have synthesized a series of donor/acceptor
functionalized p-conjugated materials, in which the donor
component is a 3(6)-carbazole unit and the acceptor component
a 2(6)-dithienophosphole species. The carbazole was found to
only have limited conjugation throughout its scaffold, and its
effect on the photophysics is similar to that of an aniline
substituent. The new chromophores show altered photophysics
in the presence of large amounts of acids and the unexpected
red-shifted absorption and emission maxima could be explained
with the protonation of the PQO group of the dithieno-
phosphole acceptor end, instead of the nitrogen-donor end
c
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5
of the chromophores. The studies furthermore suggest that full
protonation of the phosphoryl group does not occur, as the
PQO is only a relatively weak nucleophile, but also that the
process is reversible so that significantly different emission
colors can be realized for the chromophores in the presence/
absence of acids. The latter clearly supports a desirable stimulus-
responsive behaviour for this new kind of chromophore.
3JH,H = 8.4 Hz, Ar), 8.68 (2H, dd, JH,H = 0.8 Hz,
4JH,H = 1.2 Hz, Ar); 13C{1H} NMR (100 MHz, CDCl3)
14.4 (s, CH3), 22.8 (s, CH2), 25.0 (s, CH2), 27.3 (s, CH2),
29.0 (s, CH2), 29.4 (s, CH2), 29.5 (s, CH2), 29.5 (s, CH2), 29.6
(s, CH2), 29.7 (s, CH2), 29.8 (s, CH2), 32.0 (s, CH2), 43.2 (s,
a-CH2), 83.5 (s, O–C), 108.2 (s, Ar), 118.9 (s, B–Ar), 122.9
(s, Ar), 128.1 (s, Ar), 132.1 (s, Ar), 142.7 (s, Ar).
Compound 5 (A–D). 2-Bromodithieno[3,2-b:20,30-d]phosphole
oxide (64 mg, 0.17 mmol), 3-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-9-dodecylcarbazole (318 mg, 0.69 mmol),
caesium fluoride (205 mg, 1.36 mmol), and [Pd(PPh3)4] (45 mg,
0.03 mmol) were dissolved in THF (20 mL) and refluxed at
70 1C for 72 h. After cooling, the mixture was extracted with
chloroform. The organic phase was washed with saturated
NH4Cl solution and water, dried over MgSO4 and solvent was
evaporated under reduced pressure to give a brown oil.
Compound 5 (35 mg, 33%) was isolated by column chromato-
graphy on silica using chloroform and ethyl acetate (1 : 1) as a
Experimental section
General
Reactions were carried out in dry glassware and under an inert
atmosphere of purified nitrogen using Schlenk techniques. Solvents
were dried using a MBraun solvent purification system. n-Butyl-
lithium,
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxa-borolane,
caesium fluoride, and tetrakis(triphenylphosphine)-palladium(0)
were used as purchased from Sigma Aldrich or Oakwood,
and liquids were distilled prior to use. 2-Bromodithieno-
[3,2-b:20,30-d]phosphole oxide 1,9 2,6-dibromodithieno-
[3,2-b:20,30-d]phosphole oxide 2,5c 3,6-dibromo-9-dodecyl-carbazole,
and 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9-dodecyl-
carbazole 310 were prepared according to literature methods.
1H NMR, 13C NMR, 31P NMR spectra were obtained on a
Bruker UGI-400 or RDQ-400 spectrometer. Chemical shifts are
reported in ppm, referenced to external 85% H3PO4 (31P) or
solvent signal (1H, 13C); 13C NMR was measured with proton
decoupling and the attached proton test (APT); 31P NMR
spectra were measured with proton decoupling. Elemental
analyses were performed in the Department of Chemistry at
the University of Calgary. MALDI-TOF mass spectra were run
on a Bruker Daltonics AutoFlex III system. Photophysical data
were obtained from chloroform solutions using a Jasco FP-6600
spectrometer and an UV-Vis-NIR Cary 5000 spectrometer. Gel
permeation chromatography (GPC) analyses were carried out
on a Waters Breeze instrument in THF solutions. Molecular
weights are reported against polystyrene standards.
yellow solid; 1H NMR (400 MHz; CDCl3) 0.88 (3H, t, 3JH,H
=
6.6 Hz, CH3), 1.24–1.38 (18H, br m, CH2), 1.84–1.91 (2H,
3
m, CH2), 4.29 (2H, t, JH,H = 7.2 Hz, a-CH2), 7.11 (1H, dd,
=
4JH,P = 2.4 Hz, 3JH,H = 4.8 Hz, S2PO), 7.19 (1H, td, 4JH,H
3
0.8 Hz, JH,H = 7.6 Hz, cbz), 7.23 (1H, dd, JH,P = 3.6 Hz,
4
4
3JH,H = 5.2 Hz, S2PO), 7.31 (1H, d, JH,P = 2.8 Hz, S2PO),
7.34 (2H, t, 3JH,H = 8.0 Hz, cbz), 7.37–7.42 (3H, m, m-Ph (2H)
and cbz (1H)), 7.47–7.51 (1H, m, p-Ph), 7.57 (1H, dd, 3JH,H
=
4
8.4 Hz, JH,H = 2.0 Hz, cbz), 7.74–7.90 (2H, m, o-Ph), 8.03
3
4
(1H, d, JH,H = 7.6 Hz, cbz), 8.19 (1H, d, JH,H = 2.0 Hz,
cbz); 31P{1H} NMR (121.5 MHz, CDCl3) 20.04; 13C{1H}
NMR (100 MHz, CDCl3) 14.2 (s, CH3), 22.7 (s, CH2), 27.3
(s, CH2), 29.0 (s, CH2), 29.3 (s, CH2), 29.4 (s, CH2), 29.5
(s, CH2), 29.6 (s, CH2), 29.6 (s, CH2), 31.9 (s, CH2), 43.3 (s,
a-CH2), 109.1 (s, cbz), 109.3 (s, cbz), 117.8 (s, cbz), 119.3
(s, cbz), 120.2 (d, JC,P = 14.3 Hz, Ar), 120.5 (s, cbz), 122.6
(s, cbz), 123.3 (s, cbz), 123.9 (s, cbz), 124.6 (s, cbz), 126.0 (d,
JC,P = 14.3 Hz, Ar), 126.3 (s, cbz), 127.9 (d, JC,P = 14.9 Hz,
Ar), 128.9 (d, JC,P = 13.0 Hz, Ar), 129.9 (d, 1JC,P = 107.1 Hz,
ipso-Ph), 131.0 (d, JC,P = 11.3 Hz, Ar), 132.4 (d, JC,P = 2.6 Hz,
Syntheses
1
3,6-Bis(4,4,5,5,-tetramethyl-1,3,2-dioxaborolan)-9-dodecyl-carba-
zole 4. 3,6-Dibromo-9-dodecyl-carbazole (3.541 g, 7.168 mmol)
was dissolved in THF (50 mL) and was added dropwise to a
solution of n-BuLi (6.6 mL, 15.77 mmol, 2.5 M in hexanes) in
THF (10 mL) at ꢀ78 1C with stirring. The mixture was left to
stir for 2 h, following the addition of 2-isopropoxy-4,4,5,5-tetra-
methyl-1,3,2-dixoaborolane (2.992 g, 16.09 mmol) dropwise at
ꢀ78 1C and then left to stir overnight to reach room temperature.
Upon reaction, water (25 mL) was added to the solution and
stirred for an additional 30 min, resulting in a pale brown
solution. This mixture was extracted with ether and the organic
layer was washed with water, dried over MgSO4 and solvent was
evaporated under reduced pressure. The clear yellow oil was
purified by column chromatography on silica using hexanes
and ethyl acetate. Purified 4 (652 mg, 15%) was obtained as
a colorless oil. 1H NMR (400 MHz; CDCl3) 0.88 (3H, t,
3JH,H = 6.8 Hz, CH3), 1.24–1.33 (18H, br m, CH2), 1.40
(24H, s, pin-CH3), 1.83–1.90 (2H, m, CH2), 4.32 (2H, t,
p-Ph), 138.5 (d, JC,P = 112.1 Hz, ipso-Ar), 139.8 (d,
1JC,P = 109.4 Hz, ipso-Ar), 140.4 (s, cbz), 141.0 (s, cbz), 142.9
(d, JC,P = 22.9 Hz, Ar), 146.6 (d, JC,P = 24.6 Hz, Ar), 150.2
(d, JC,P = 14.5 Hz, Ar); HR-MALDI/TOF-MS: m/z 621.2283
(M+. C62H71N2OPS2 requires 621.2289).
Compound 6 (D–A–D). 2,6-Dibromodithieno[3,2-b:20,30-d]-
phosphole oxide (220 mg, 0.49 mmol), 3-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-9-dodecylcarbazole (721 mg, 1.56 mmol),
caesium fluoride (558 mg, 3.70 mmol), and [Pd(PPh3)4] (60 mg,
0.04 mmol) were dissolved in THF (25 mL) and refluxed for 70 1C
for 72 h. After cooling, the mixture was extracted with chloroform.
The organic phase was washed with saturated NH4Cl solution and
water, dried over MgSO4 and solvent was evaporated under
reduced pressure to afford a dark brown solid. Compound 6
(60 mg, 13%) was isolated by column chromatography on
silica using chloroform and ethyl acetate (1 : 1) as a red solid
(found: C, 77.01; H, 7.41; N, 2.74. C62H71N2OPS2 requires C,
5
1
3JH,H = 7.2 Hz, a-CH2), 7.40 (2H, dd, JH,H = 0.8 Hz,
77.95; H, 7.49; N, 2.93%); H NMR (400 MHz; CDCl3) 0.90
3
(6H, t, JH,H = 7.0 Hz, CH3), 1.26–1.38 (36H, br m, CH2),
4
3JH,H = 8.4 Hz, Ar), 7.92 (2H, dd, JH,H = 1.2 Hz,
c
1158 New J. Chem., 2012, 36, 1153–1160
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1.86–1.93 (4H, m, CH2), 4.31 (4H, t, 3JH,H = 7.2 Hz, a-CH2),
7.29 (2H, td, 4JH,H = 0.8 Hz, 3JH,H = 7.4 Hz, cbz), 7.40–7.44
(6H, m, cbz (4H) and S2PO (2H)), 7.48–7.54 (4H, m, m-Ph
(2H) and cbz (2H)), 7.56–7.61 (1H, m, p-Ph), 7.90–7.96
(0.60 mg, 0.04 mmol) were dissolved in THF (20 mL),
degassed, and heated to 65 1C for 72 h. After cooling, the
solution was precipitated in methanol (1 L) and the precipi-
tated polymer was collected on a Buchner funnel. The
precipitated solids were washed with hot methanol, hexanes,
and then taken up in chloroform. The solution was evaporated
to dryness under reduced pressure to afford polymer 8 (40 mg,
8%) as a dark orange film; 1H NMR (400 MHz; CDCl3)
0.88–0.90 (br m, CH3), 1.25–1.28 (br m, CH2), 1.80–1.87 (br
m, CH2), 4.29–4.32 (br m, a-CH2), 7.50–7.54 (br m, S2PO),
7.55–7.59 (br m, Ph), 7.66–7.75 (br m, Ph), 7.81–7.86 (br m,
cbz), 7.92–7.97 (br m, Ph), 8.23–8.28 (br m, cbz), 8.64 (br s,
cbz); 31P{1H} NMR (121.5 MHz, CDCl3) 21.34 (br s);
13C{1H} NMR (100 MHz, CDCl3) 14.1 (br s, CH3), 22.7 (br
s, CH2), 27.3 (br s, CH2), 29.0 (br s, CH2), 29.3 (br s, CH2),
29.4 (br s, CH2), 29.5 (br s, CH2), 29.5 (br s, CH2), 31.9 (br s,
CH2), 43.3 (br s, a-CH2), 109.3 (br s, cbz), 109.6 (br s, cbz),
117.9 (br s, cbz), 120.2 (br s, cbz), 120.3 (br s, Ar), 120.5 (br s,
cbz), 122.4 (br s, cbz), 123.2 (br s, cbz), 123.7 (br s, cbz), 124.4
(br s, cbz), 125.1 (br d, JC,P = 12.8 Hz, Ar), 125.2 (br s, cbz),
128.5 (br d, JC,P = 14.5 Hz, Ar), 129.0 (br d, JC,P = 14.0 Hz,
3
(2H, m, o-Ph), 8.13 (2H, d, JH,H = 7.6 Hz, cbz), 8.28
4
(2H, d, JH,H = 1.6 Hz, cbz); 31P{1H} NMR (121.5 MHz,
CDCl3) 21.24; 13C{1H} NMR (100 MHz, CDCl3) 14.2
(s, CH3), 22.7 (s, CH2), 27.3 (s, CH2), 29.0 (s, CH2), 29.4
(s, CH2), 29.4 (s, CH2), 29.5 (s, CH2), 29.6 (s, CH2), 29.6 (s,
CH2), 31.9 (s, CH2), 43.3 (s, a-CH2), 109.0 (s, cbz), 109.2 (s,
cbz), 117.7 (s, cbz), 119.3 (s, cbz), 120.2 (d, JC,P = 14.4 Hz,
Ar), 120.6 (s, cbz), 122.6 (s, cbz), 123.4 (s, cbz), 123.9 (s, cbz),
124.6 (s, cbz), 126.2 (s, cbz), 129.0 (d, JC,P = 13.0 Hz, Ar),
130.2 (d, 1JC,P = 106.6 Hz, ipso-Ph), 131.1 (d, JC,P = 11.4 Hz,
Ar), 132.4 (d, JC,P = 2.8 Hz, p-Ph), 138.7 (d, 1JC,P = 111.4 Hz,
ipso-Ar), 140.4 (s, cbz), 141.0 (s, cbz), 143.6 (d, JC,P = 23.3 Hz,
Ar), 149.7 (d, JC,P = 14.6 Hz, Ar); HR-MALDI/TOF-MS:
m/z 954.4707 (M+. C62H71N2OPS2 requires 954.4745).
Compound
7
(A–D–A). 2-Bromodithieno[3,2-b:20,30-d]-
phosphole oxide (367 mg, 1.00 mmol), 3,6-bis(4,4,5,5,-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-9-dodecylcarbazole (245 mg,
0.42 mmol), caesium fluoride (434 mg, 2.86 mmol) and
[Pd(PPh3)4] (45 mg, 0.03 mmol) were dissolved in THF
(30 mL) and heated to 65 1C for 72 h. After cooling, water
was added and the mixture was extracted with chloroform.
The organic phase was washed with saturated NH4Cl solution
and water, dried over MgSO4 and solvent was evaporated
under reduced pressure to give a dark orange oil. Pure 7
(141 mg, 37%) was isolated by column chromatography on
silica using ethyl acetate and acetone (1 : 0 to 0 : 1) as a golden
yellow solid (found: C, 67.61; H, 5.29; N, 1.54. C52H47NO2P2S4
Ar), 130.9 (d, 1JC,P = 113.9 Hz, ipso-Ph), 131.9 (br d, JC,P
=
3.3 Hz, p-Ph), 132.6 (br d, JC,P = 12.0 Hz, Ar), 137.8 (br d,
1
1JC,P = 107.4 Hz, ipso-Ar), 138.7 (br d, JC,P = 111.3 Hz,
ipso-Ar), 140.5 (s, cbz), 140.8 (s, cbz), 143.1 (br d, JC,P = 20.3
Hz, Ar), 146.6 (br s, Ar), 149.7 (br s, Ar); GPC analysis (THF
solution): Mw = 2568 g molꢀ1; Mn = 1486 g molꢀ1; PDI = 1.7.
Acknowledgements
Financial support by NSERC of Canada and the Canada
Foundation for Innovation (CFI) is gratefully acknowledged.
M. S. thanks the University of Calgary for a PURE scholarship.
1
requires C, 68.77; H, 5.22; N, 1.54%); H NMR (400 MHz;
3
CDCl3) 0.89 (3H, t, JH,H = 7.0 Hz, CH3), 1.25 (18H, br m,
3
CH2), 1.85–1.92 (2H, m, CH2), 4.31 (2H, t, JH,H = 7.0 Hz,
a-CH2), 7.20 (2H, dd, 4JH,P = 2.4 Hz, 3JH,H = 4.8 Hz, 6,60-H,
Notes and references
3
3
S2PO), 7.31 (2H, dd, JH,P = 3.4 Hz, JH,H = 4.8 Hz, 5,50-H,
S2PO), 7.39 (2H, d, 4JH,P = 2.4 Hz, 3,30-H, S2PO), 7.41 (2H, d,
4JH,H = 8.4 Hz, cbz), 7.46–7.50 (4H, m, m-Ph), 7.56–7.60
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(2H, m, p-Ph), 7.68 (2H, dd, JH,H = 8.4 Hz, JH,H = 1.6 Hz,
4
cbz), 7.81–7.87 (4H, m, o-Ph), 8.27 (2H, d, JH,H = 1.6 Hz,
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29.0 (s, CH2), 29.3 (s, CH2), 29.4 (s, CH2), 29.5 (s, CH2), 29.5
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(s, cbz), 120.4 (d, JC,P = 14.6 Hz, Ar), 123.2 (s, cbz), 124.5
(s, cbz), 125.1 (s, cbz), 126.9 (d, JC,P = 14.5 Hz, Ar), 128.5 (d,
JC,P = 14.8 Hz, Ph), 129.9 (d, 1JC,P = 107.1 Hz, ipso-Ph), 131.5
(d, JC,P = 11.1 Hz, Ar), 132.5 (d, JC,P = 2.6 Hz, p-Ph), 137.8
(d, 1JC,P = 112.3 Hz, ipso-Ar), 140.0 (d, 1JC,P = 110.6 Hz, ipso-Ar),
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