Dithiazolo[5,4-b:4′,5′-d]phosphole: A highly luminescent electron-accepting building block

Article abstract of DOI:10.1002/chem.201204375

A family of highly emissive dithiazolo[5,4-b:4′,5′-d]phospholes has been designed and synthesized. The structures of two trivalent P species, as well as their corresponding P oxides, have been confirmed by X-ray crystallography. The parent dithiazolo[5,4-b:4′,5′-d]phosphole oxide exhibits strong blue photoluminescence at λ_em=442 nm, with an excellent quantum yield efficiency of φ_PL=0.81. The photophysical properties of these compounds can be easily tuned by extension of the conjugation and modification of the phosphorus center. Compared with the established dithieno[3,2-b:2′,3′-d]phosphole system, the incorporation of electronegative nitrogen atoms leads to significantly lowered frontier orbital energy levels, as validated by both electrochemistry and theoretical calculations, thus suggesting that the dithiazolo[5,4-b:4′, 5′-d]phospholes are valuable, air-stable, n-type conjugated materials. These new building blocks have been further applied to the construction of an extended oligomer with fluorene. Extension of the dithiazolophosphole core with triazole units through click reactions also provides a suitable N,N-chelating moiety for metal binding and a representative molecular species was successfully used as a selective colorimetric and fluorescent sensor for Cu^II ions. Sliding down with a glow: Incorporation of nitrogen atoms into the dithienophosphole scaffold generates a new building block, dithiazolo[5,4-b: 4′,5′-d]phosphole (see scheme), that combines intense luminescence with high electron affinity. A family of conjugated small molecules and a polymer based on this building block have been synthesized by a click reaction that also serves as a selective colorimetric and fluorescent sensor for Cu ^II. Copyright

Full text of DOI:10.1002/chem.201204375

FULL PAPER
DOI: 10.1002/chem.201204375
Dithiazolo[5,4-b:4’,5’-d]phosphole: A Highly Luminescent Electron-
Accepting Building Block
Xiaoming He, Alva Y. Y. Woo, Javier Borau-Garcia, and Thomas Baumgartner*[a]
Abstract: A family of highly emissive
dithiazolo[5,4-b:4’,5’-d]phospholes has
been designed and synthesized. The
structures of two trivalent P species, as
well as their corresponding P oxides,
have been confirmed by X-ray crystal-
lography. The parent dithiazolo[5,4-
tion of the phosphorus center. Com-
pared with the established dithieno[3,2-
b:2’,3’-d]phosphole system, the incor-
poration of electronegative nitrogen
atoms leads to significantly lowered
frontier orbital energy levels, as vali-
dated by both electrochemistry and
theoretical calculations, thus suggesting
that the dithiazolo[5,4-b:4’,5’-d]phosp-
holes are valuable, air-stable, n-type
conjugated materials. These new build-
ing blocks have been further applied to
the construction of an extended
oligomer with fluorene. Extension of
the dithiazolophosphole core with tria-
zole units through click reactions also
b:4’,5’-d]phosphole
oxide
exhibits
provides
a
suitable N,N-chelating
strong blue photoluminescence at lem
=
moiety for metal binding and a repre-
sentative molecular species was suc-
cessfully used as a selective colorimet-
ric and fluorescent sensor for CuII ions.
442 nm, with an excellent quantum
yield efficiency of fPL =0.81. The pho-
tophysical properties of these com-
pounds can be easily tuned by exten-
sion of the conjugation and modifica-
Keywords: conjugation · copper ·
heterocycles · luminescence · sen-
sors
Introduction
A crucial issue facing molecular design in the field of or-
ganic electronic materials is the balance of charge mobilities
(hole and electron), which can significantly affect the per-
formance of a device.[5] Over the past few decades, much of
the focus has been on the development of p-type materials
for hole transport,[6] whilst the number of n-type materials is
still strongly limited.[7] The most-popular approach for the
design of n-type materials is the introduction of electron-ac-
cepting moieties, such as carbonyl,[8] cyano,[9] fluoro,[10] and
imide groups,[11] which have been found to lower the LUMO
energy level of these species. Moreover, the replacement of
carbon atoms in conjugated scaffolds by more electronega-
tive nitrogen atoms (e.g., in nitrogen-containing heteroa-
cenes) tends to lower the HOMO and LUMO energies, thus
making it a promising way to generate air-stable n-type ma-
terials.[12] For example, (triisopropylsilyl)ethynylated “TIPS”
pentacene I (Figure 1a), is a stable and solution-processable
p-type organic semiconductor with high hole mobilities of
over 1.8 cm2 Vꢀ1 sꢀ1.[13] Following the incorporation of nitro-
gen atoms into the scaffold of compound I, tetraazapenta-
cene II exhibits excellent n-type properties, with high elec-
tron mobilities of up to 3.3 cm2 Vꢀ1 sꢀ1.[14] One of the reasons
for the high electron mobility of compound II is its lower
energy levels (EHOMO =ꢀ5.75 eV, ELUMO =ꢀ4.01 eV) relative
The exploration of highly emissive materials has drawn
much attention owing to their utility in practical applica-
tions, such as organic lasers, organic light-emitting diodes,
and sensors.[1–3] Along these lines, in recent years, we have
established the dithieno[3,2-b:2’,3’-d]phosphole system,
which displays superior photophysical properties with re-
spect to emission wavelength, intensity, and tunability.[4] The
parent dithienophosphole is a very strong blue-light emitter,
with photoluminescence efficiencies of up to 90%.[4a] Impor-
tantly, the photophysical and electrochemical properties of
this system can be easily tuned by installing different conju-
gated aromatic groups on its scaffold or by simple modifica-
tion of the phosphorus center (e.g., through its lone pair
with O, S, Me+, or BH3 groups or metal complexes).[4] To
date, we have successfully applied this intriguing building
block in a variety of different functional materials, such as
white-light-emitting materials, sensors, liquid crystals, and
organogels.[4]
[a] Dr. X. He, A. Y. Y. Woo, Dr. J. Borau-Garcia,
Prof. Dr. T. Baumgartner
to those in compound
I
(EHOMO =ꢀ5.17 eV, ELUMO
=
Department of Chemistry and Centre for Advanced Solar Materials
University of Calgary
2500 University Drive NW
Calgary, Alberta T2N 1N4 (Canada)
Fax : (+1)403-289-9488
E-mail: Thomas.baumgartner@ucalgary.ca
ꢀ3.30 eV). In this context, very recent research by our
group has shown that the incorporation of one or two nitro-
gen atoms into the scaffold of the dibenzophosphole system
also renders it a stronger electron acceptor (Figure 1b).[15]
However, this class of azadibenzophospholes is not emissive,
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201204375.
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Figure 1. Examples of N-containing pentacene derivatives (a) and dibenzophosphole (b), as well as the effect of nitrogen incorporation on the energy
levels.
very likely owing to the intrinsic weakly emissive character
of the parent dibenzophosphole (fPL =0.042).[16]
Thiazole, as a close analogue of thiophene, is also widely
used in high-performance n-type materials.[17] Several fused
tricyclic bithiazole systems that are bridged by N, C, CO, or
COCO groups (Figure 2a) have recently been designed for
tions, which have been demonstrated to stabilize the LUMO
energy level of phosphole derivatives, thus making this class
of phosphole-based materials very promising candidates for
n-type organic electronics.[19]
Results and Discussion
Synthesis and characterization of trivalent dithiazolophosp-
holes 1–4: The synthetic routes to the new dithiazolophosp-
holes are summarized in Scheme 1. The general synthetic
procedure involves the dilithiation of the 4,4’-dibromobithia-
zole precursors (S1 or S2), followed by the cyclization of the
phosphole ring through reaction with PhPCl2, according to
our established procedures for dithienophospholes and relat-
ed systems.[4,15] The formation of the phosphole ring is ac-
companied by the occurrence of strong fluorescence. Com-
pounds 1 and 2 have a basic dithiazolophosphole frame-
work, with R=TIPS, H (Scheme 1), whilst compounds 3
and 4 are the 2,5-dialkynyl-functionalized analogues of the
Figure 2. a) Examples of fused tricyclic dithiazole frameworks; b) struc-
tures of dithieno[3,2-b:2’,3’-d]phosphole and the target dithiazolo[5,4-
b:4’,5’-d]phosphole. lp=lone pair.
applications in organic photo-
voltaics (OPVs) and in organic
field-effect
transistors
(OFETs).[18] Therefore, the re-
placement of the thiophene
moieties in the dithienophosp-
hole scaffold by thiazole units
would lead to a new class of
Scheme 1. Synthesis of trivalent dithiazolo[5,4-b:4’,5’-d]phospholes.
building block that should com-
bine the intriguing photophysi-
cal properties of dithienophosphole with the intrinsically
high electron affinity of thiazole-based optoelectronic mate-
rials (Figure 2b).
Herein, we report the design and synthesis of the new di-
thiazolo[5,4-b:4’,5’-d]phosphole system, as well as an investi-
gation of its photophysical and electrochemical properties.
As a new member of the fused tricyclic bithiazole family,
the introduction of a phosphorus atom is expected to facili-
two former compounds, respectively. The incorporation of
two alkynyl groups into these latter compounds through
well-established Huisgen alkynyl–azide click reactions was
employed for the purpose of further tuning their molecular
and material properties.[20] It is worth noting that the reac-
tion temperature plays an important role in the deprotection
of the TIPS group in compounds 1 and 3 during their reac-
tions with tetrabutylammonium fluoride (TBAF) to afford
compounds 2 and 4. Unlike compound 2, which can be ac-
ꢀ
tate the typical phosphole s* p* orbital coupling interac-
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Dithiazolo[5,4-b:4’,5’-d]phosphole as a Luminescent Building Block
FULL PAPER
cessed at room temperature, low temperatures (ꢀ788C) are
very important for the successful synthesis of compound 4:
Performing the reaction at room temperature or 08C led to
the decomposition of compound 4. All of these compounds
1
were fully characterized by H, 13C, and 31P NMR spectro-
scopy, mass spectrometry, and elemental analysis. Moreover,
the structures of compounds 1 and 2 were confirmed by X-
ray crystallography, as shown in Figure 3a and Figures S1, S3
in the Supporting Information. A more-detailed discussion
of the molecular structures in the solid state will follow in a
subsequent section. The 31P NMR spectroscopic signals of
dithiazolophospholes 1–4 are within the range d=
ꢀ30(ꢁ3) ppm, very close to that of related dithienophosp-
hole species, thus confirming the trivalent nature of the P
center.[4]
Scheme 3. Modification of the phosphorus center.
For the preparation of the two necessary 4,4’-dibromobi-
thiazole precursors, the synthesis of compound S2 was
adapted from the known synthetic procedure for compound
S1,[18b] as shown in Scheme 2. Alkynylation of 2-bromothia-
opening. The oxidation of the phosphorus center is support-
ed by 31P NMR spectroscopic resonances at d=8.5-
(ꢁ0.3) ppm, which constitutes a significant downfield shift
compared to their trivalent counterparts. The structures of
compounds 1-O and 2-O were also confirmed by X-ray crys-
tallography, as shown in Figure 3b and Figure S2 in the Sup-
Scheme 2. Synthesis of precursor S2.
ꢂ
zole with HC CTIPS in the presence of [PdCl
N
CuI, and PPh3 in iPr2NH gave compound S4, followed by
lithiation with nBuLi at the 5-position and subsequent elec-
trophilic bromination to afford compound S3. The choice of
TIPS as a protecting group was based on its stability under
basic conditions in the subsequent steps. Further deprotona-
tion with lithium diisopropylamide (LDA) at the 4-position
of compound S3, followed by a halogen “dance” reaction
and oxidative dimerization upon treatment with CuCl2, af-
forded the desired precursor (S2).
Figure 3. Molecular structures of compounds 2 (a) and 2-O (b), as well as
their intermolecular interactions in the solid state (bottom); ellipsoids
are set at 50% probability and hydrogen atoms are omitted for clarity
(for the color version of this figure, see Figure S3 in the Supporting Infor-
mation).
Modification of the P center: To verify the reactivity of the
phosphorus center, several typical modifications (i.e.,
through its lone pairs with O, S, AuCl, or Me+ groups) were
targeted with the dithiazolophosphole system (Scheme 3).
The oxidation of compounds 1–4 into their corresponding
pentavalent P–oxo species (1-O to 4-O) proceeded in mod-
erate-to-high yields (50–80%) by reaction with about
2 equivalents of H2O2 at room temperature, through slight
modification of our reported procedure for related sys-
tems.[4,15] The presence of a large excess of H2O2 was found
to decrease the reaction yield, probably owing to further ox-
idation of the nitrogen atoms, which led to undesired ring
porting Information; these data will be discussed systemati-
cally with trivalent derivatives 1 and 2 below.
Further modification of the P center was carried out with
basic dithiazolophosphole 2 as a representative example.
For the sulfuration reaction, the established procedure for
the dithienophosphole system, by reaction with elemental
sulfur at room temperature, was found not to be suitable.[4]
High temperatures (reflux in toluene) are necessary for this
new system, which may be attributed to a decreased Lewis
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T. Baumgartner et al.
basicity of the P center as a result of the stronger electron-
accepting character of the dithiazolophosphole scaffold.
Compound 2-S exhibits a more-downfield-shifted 31P NMR
spectroscopic signal at d=19.8 ppm compared to compound
X-ray crystallography: Single crystals of compounds 1, 1-O,
2, and 2-O that were suitable for X-ray crystallography were
obtained from the slow evaporation of their concentrated
solutions in acetone at room temperature. As representative
examples, the solid-state molecular structures of compounds
2 and 2-O are shown in Figure 3. Selected bond lengths [ꢁ]
and angles [8] are summarized in Table 1. The crystal data
ꢀ
2-O (d=8.2 ppm), probably owing to the stronger p p
back-donation from the oxygen to phosphorus atoms in
compound 2-O, which results in increased shielding.[21] The
synthesis of gold(I) complex 2-Au is easily achieved by
using the reported procedures through reaction with [AuCl-
Table 1. Selected bond lengths [ꢁ] and angles [8] in compounds 1, 1-O, 2,
and 2-O.
ACHTUNGTRENNUNG
(tht)] (tht=tetrahydrothiophene) at room temperature.[4c] In
terms of methylation, the conversion of compound 2 can
only be observed upon the addition of a large amount of
MeOTf (Tf=4-methylphenylsulfonyl), but the reaction
occurs on the nitrogen atoms instead of at the phosphorus
center; moreover, monomethylation provides the dominant
1
1-O
2
2-O
ꢀ
P Cexo
1.828(4)
1.831(4)
1.823(4)
1.369(5)
1.371(5)
1.436(5)
NA
1.312(5)
1.317(5)
1.360(5)
1.366(5)
87.30(17)
1.8001(14)
1.817(6)
1.815(3)
1.815(3)
1.371(4)
1.371(4)
1.442(4)
NA
1.784(4)
ꢀ
P Cendo
1.8222(14)
1.8108(14)
1.3777(19)
1.3753(19)
1.4633(19)
1.4815(10)
1.3211(18)
1.3212(18)
1.3645(18)
1.3634(18)
89.97(6)
1.814(4)
1.800(4)
1.366(5)
1.369(5)
1.458(5)
1.478(3)
1.296(5)
1.310(5)
1.365(5)
1.373(5)
89.55(17)
108.08(17)
110.20(18)
307.8
AHCTUNGERTG(NNUN C=C)P
1
product, as observed in the H and 31P NMR titration ex-
ꢀ
AHCTUNGTRENNUNG
periments (see Figure S4 in the Supporting Information).
Overall, however, a family of dithiazolophosphole deriva-
tives can be prepared (Scheme 3) that demonstrate the par-
ticular advantage of organophosphorus materials, thus al-
lowing for further efficient tuning of their photophysical and
electrochemical properties.
G
1.297(4)
1.302(4)
1.366(4)
1.370(4)
87.21(13)
103.4 (2)
102.7(2)
293.3
ꢀ
AHCTUNGTRENNUNG
qACHTUNGTRENNUNG
100.02(17)
101.60(18)
288.9
111.46(6)
105.47(6)
306.9
qsumACTHNUTRGNE(UNG C-P-C)
Framework extension through Huisgen alkynyl–azide click
reactions: For the purpose of tuning the photophysical and
electrochemical properties of these compounds through ex-
tending their conjugation, our initial plan was to prepare a
2,5-dibromo-dithiazolophosphole species for subsequent
cross-coupling reactions (e.g., Suzuki–Miyaura, Stille); this
strategy is widely used for conjugated oligomers and poly-
mers and it works well for dithienophospholes. Unfortunate-
ly, several attempts with N-bromosuccinimide (NBS) in dif-
ferent solvent systems (e.g., CHCl3/AcOH, H2SO4/trifluoro-
acetic acid (TFA), DMF), CBr4/K3PO4, or nBuLi/Br2 met
with failure. As an alternative pathway, the Huisgen alkyn-
yl–azide click reaction was successfully applied to prepare
compound 5 in high yield (87%) under mild conditions by
using CuI as a catalyst and diisopropylethylamine (DIPEA)
as a base (Scheme 4).
and structure refinement are summarized in Table S1 in the
Supporting Information. In each compound, a highly planar
conjugated tricyclic core, which is comprised of two flanking
thiazole moieties around a central phosphole moiety, is ob-
served and the phosphorus center adopts a typical pyramidal
geometry. The phosphole ring has two short (1.37–1.38 ꢁ)
ꢀ
and one long C C bond (1.44–1.46 ꢁ) in a typical cis-dienic
phosphole fashion. The lengths of the endocyclic (1.80–
ꢀ
1.83 ꢁ) and exocyclic P C bonds (1.78–1.82 ꢁ) are compa-
rable to those in the dithienophosphole system.[4] In addi-
tion, on moving from the trivalent species to the P–oxo spe-
ꢀ
ꢀ
cies, significantly shortened P Cexo bonds (relative to the P
Cendo bonds) were observed. The sum of the angles around
the phosphorus center in the
two trivalent
P
derivatives
(qsum(P-C-P): 1=288.9, 2=
AHCTUNGTRENNUNG
293.38) is smaller than that in
their corresponding P–oxo spe-
cies (1-O=306.9, 2-O=307.88),
likely as a result of the sterical-
ly active phosphorus lone pair
in the trivalent derivatives.
In terms of molecular pack-
ing in the solid state, compara-
ble intermolecular p–p interac-
tions between neighboring tri-
cyclic cores (at about 3.6 ꢁ) are
observed for compounds 2 and
2-O. However, no such packing
is observed for compounds 1
and 1-O, owing to the bulky
Scheme 4. Synthesis of compounds 5 and 6 by using Huisgen alkynyl–azide click reactions.
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Dithiazolo[5,4-b:4’,5’-d]phosphole as a Luminescent Building Block
FULL PAPER
TIPS groups (see the Supporting Information).
band gap, owing to the introduction of electronegative N
atoms, which leads to a more significantly lowered HOMO
relative to the also-lowered LUMO (see below). A low
HOMO level is important for the design of n-type materials,
because it indicates a resistance towards oxidation with
oxygen and, consequently, in-
Photophysical properties: The photophysical data of the
new compounds are summarized in Table 2. The UV/Vis ab-
sorption spectra of the trivalent P derivatives show a p!p*
creased stability in air; more-
Table 2. Photophysical, electrochemical, and calculation data for compounds 1–3, 5, 1-O–4-O, 2-S, and 2-Au.
over, a low HOMO is equally
desirable for organic photovol-
taics because it increases the
open-circuit voltage (Voc).[7] As
expected, increasing the p-con-
jugation results in redshifted
[a]
[b]
[c]
Compd labs [nm] (e [dm3 molꢀ1 cmꢀ1]) lem[a] [nm] fPL
Ered [V]
Calculations[e]
LUMO [eV] HOMO [eV] Eg [eV]
1
344 (16040)
367 (7497)
322 (7230)
350 (3770)
309 (5990), 350 (3600)
337 (4880)
387 (13120)
317 (16040), 405 (20710)
307 (9500), 389 (12256)
313 (14510), 406 (15240)
410
453
396
442
442
420
444
491
474
500
0.34
–
ꢀ1.72
ꢀ2.14
ꢀ1.69
ꢀ2.21
--
ꢀ5.89
ꢀ6.11
ꢀ6.04
ꢀ6.35
–
4.17
3.97
4.35
4.14
–
1-O
2
0.60 ꢀ2.07
0.22
–
2-O
2-S
2-Au
3
0.81 ꢀ1.90
0.01
0.74
–
–
emission properties (lem):
(500)>3-O (491)>4-O (474)>
1-O (453)>2-O (442 nm),
5
–
–
–
0.12 ꢀ2.36[d]
0.37 ꢀ1.73
0.38 ꢀ1.68
0.64 ꢀ1.83
ꢀ2.30
ꢀ2.64
ꢀ2.74
ꢀ2.52
ꢀ5.58
ꢀ5.84
ꢀ6.09
ꢀ5.84
3.28
3.20
3.35
3.32
3-O
4-O
5
which are consistent with the
trend in the absorption spectra
[a] In CH2Cl2 at 298 K. [b] Fluorescence quantum yield, relative to quinine sulfate (0.1m in H2SO4); excitation (Figure 4b). The gold(I) com-
at 365 nm. [c] Half-potentials versus Fc/Fc+, nBu4NPF6 as a supporting electrolyte, in CH2Cl2. [d] Irreversible,
Epc value given. [e] Calculated by using Gaussian 03, Revision E.01, at the B3LYP/6-31G(d) level of theory.
plex, 2-Au, is also highly emis-
sive (lem =420 nm, fPL =0.74),
but has
a shorter emission
wavelength than compound 2-
O. However, modification of the P center with the heavier S
atom (2-S) leads to an almost-quenched emission that can
be attributed to strong spin-orbit coupling and to a photoin-
transition at lmax =322–387 nm, which was found to be large-
ly affected by the 2,5-substituents. From the trend
3
(387 nm)>1 (344 nm)>2 (322 nm), we can draw the conclu-
sion that increasing p-conjugation leads to a redshift of the
absorption band. A similar trend in the UV/Vis absorption
spectra is also observed for the P–oxo species, as shown in
Figure 4a: 5 (406)>3-O (405)>4-O (389)>1-O (367)>2-O
(350 nm). Owing to the s-donating nature of the silyl group,
the incorporation of the TIPS group increases the HOMO
and LUMO energies. An increased LUMO energy (versus
the non-TIPS species) is further supported by a higher elec-
trochemical reduction potential. However, a more pro-
nounced destabilization of the HOMO ultimately leads to
narrower band gaps, consistent with their optical spectra
and the theoretical calculations (see below). Compared to
their trivalent counterparts, the P–oxo species generally
show a redshift of 18–28 nm for the p!p* transition, owing
to the enhanced capability of phosphole oxide in decreasing
the LUMO energy and narrowing the HOMO–LUMO
gap.[4]
Similar to the dithienophosphole system, the dithiazolo-
phospholes are strongly emitting species and their emission
wavelength and intensity are highly dependent on the sub-
stituents at the 2,5-position on the framework, as well as, in
particular, on the modification of the phosphorus center.
The new phosphole-oxide compounds exhibit stronger pho-
toluminescence, with redshifted bands, than their trivalent
congeners, as is typically observed for many luminescent
phosphole systems.[4,19d] The parent dithiazolophosphole
oxide (2-O) exhibits a strong blue-emitting property (lem
442 nm), with a quantum yield of fPL =0.81. Compared to
the parent dithienophosphole oxide (lem =453 nm, fPL
=
=
0.90), a slight blueshift (Dlem =ꢀ11 nm) in the emission of
Figure 4. Normalized UV/Vis (a) and emission spectra (b) of compounds
1-O to 4-O and 5 in CH2Cl2.
compound 2-O indicates a larger HOMO–LUMO energy
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T. Baumgartner et al.
duced electron transfer (PET) from the lone pair on the S
atom to the emitting phosphole core.
which showed no obvious reduction process above ꢀ2 V,
one quasi-reversible reduction peak could be found in all of
the cyclic voltammograms for the dithiazolophosphole
oxides, thus confirming the electron-accepting character of
this new system. Among the P–oxo derivatives that were
tested, their half-wave reduction peaks (Ered,1/2) were deter-
mined to increase in the order: 4-O (ꢀ1.68)>3-O (ꢀ1.73)>
5 (ꢀ1.83)>2-O (ꢀ1.90)>1-O (ꢀ2.07 V), which was consis-
tent with the electron-accepting ability of the framework. P–
oxo derivative 3-O shows a much more positive reduction
potential than trivalent species 3, thus indicating a consider-
able increase in its electron-accepting ability upon simple
oxidation of the P center. In addition, the reduction poten-
tial of compound 1-O shows a slightly stronger electron-ac-
cepting ability (DEꢃ0.1 V) than a related monocarbonyl-
bridged dithiazole (Ered,1/2 =ꢀ2.14 V) reported by Marder
and co-workers.[18b]
Electrochemical properties: The electrochemical properties
of this new family of compounds were investigated by using
cyclic voltammetry in CH2Cl2 with 0.1m tetrabutylammoni-
um hexafluorophosphate (nBu4NPF6) and the ferrocene/fer-
rocenium couple as an internal reference. The electrochemi-
cal data are summarized in Table 2 and representative cyclic
voltammograms of compounds, 1-O, 3, and 3-O are shown
in Figure 5. In contrast to the dithienophosphole system,
DFT calculations: To gain deeper insight into the photo-
physical and electronic structures of these compounds, we
carried out DFT calculations by using the Gaussian 03 suite
of programs at the B3LYP level of theory and the 6-31G(d)
basis set, which had previously provided satisfactory results
for the dithienophosphole system.[22] The coordinates of the
optimized geometries for these compounds are included in
the Supporting Information. Representative HOMO and
LUMO diagrams of phosphole oxides S2PO, 2-O, 4-O, and
5, as well as of trivalent species 2, are shown in Figure 6.
Similar to the parent dithienophosphole system, the HOMO
Figure 5. Cyclic voltammograms of compounds 1-O, 3-O, and 3 in CH2Cl2
with 0.1m tetrabutylammonium hexafluorophosphate as a supporting
electrolyte. Scan rate: 100 mVsꢀ1. Ferrocene was added as internal stand-
ard and referenced to 0 V.
Figure 6. HOMO (bottom) and LUMO orbital diagrams (top) of structures S2PO, 2-O, 4-O, 5-Me, and 2, as well as their energies that were calculated at
the B3LYP/6-31G(d) level.
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Dithiazolo[5,4-b:4’,5’-d]phosphole as a Luminescent Building Block
FULL PAPER
Table 3. TD-DFT calculated transition data for compounds 1, 1-O, 2, and
2-O.[a,b]
and LUMO of the basic dithiazolophosphole mainly consti-
tute the p and p* orbitals of the tricyclic core, respectively.
The unique, phosphole-typical s*–p* hyperconjugation
1
1-O
2
2-O
4-O
ꢀ
between the s* orbital of the exocyclic P C bond and the
l [nm]
334
365
320
349
378
f
0.4724
H!L
(87%)
0.2926
H!L
(98%)
0.2042
H!L
(83%)
0.1194
H!L
(98%)
0.3816
H!L
(98%)
p* orbitals of the conjugated framework, which leads to the
desirable lowering of the LUMO level, is clearly observed.
However, in contrast to the P–oxo derivatives, the phospho-
rus lone pair in the trivalent species shows a large contribu-
tion to the LUMO. It is worth noting that, relative to the
transition[c]
[a] TD-DFT calculations by using Gaussian 03, revision E.1, at the
B3LYP/6-31G(d) level of theory; l=wavelength, f=oscillator strength,
H=HOMO, L=LUMO. [b] X-ray data were used as an input for the cal-
culations. [c] Coefficient percentage of orbitals that are involved in the
transition.
parent dithienophosphole oxide (EHOMO =ꢀ5.77, ELUMO
=
ꢀ1.86 eV),[23] the incorporation of nitrogen atoms into com-
pound 2-O significantly lowers both HOMO (DEHOMO
=
ꢀ0.58 eV) and LUMO levels (DELUMO =ꢀ0.35 eV), thus
providing theoretical evidence for the dithiazolophosphole
being a better electron-accepting building block for the
design of n-type organic conjugated materials. Installation of
the alkynyl group (2-O!4-O) leads to a pronounced stabili-
zation of the LUMO (DELUMO =ꢀ0.53 eV) and destabiliza-
tion of the HOMO (DEHOMO =0.26 eV) and, consequently, a
smaller energy gap (DEg =ꢀ0.78 eV), which is consistent
with the strong electron-accepting properties and the red-
shifted UV/Vis and emission spectra. Upon going from
alkyne to triazole groups (i.e., 4-O!5), the HOMO and
LUMO levels are both raised, thus indicating that the tria-
zole moiety is less electron-accepting than the alkyne group.
Similar to the dithienophosphole system, the presence of the
TIPS group (2!1, 2-O!1-O, 4-O!3-O) leads to a smaller
overall energy gap, which is in agreement with the experi-
mental redshifts in the UV/Vis and emission spectra.
To better understand the optical absorption properties of
these compounds, time-dependent DFT (TD-DFT) calcula-
tions were also carried out on four representative com-
pounds (1, 1-O, 2, and 2-O) by using the X-ray crystallo-
graphic data as an input. The assignment of the transitions is
summarized in Table 3. The contributions of the molecular
orbitals that were involved in the UV/Vis transitions were
determined based on their oscillator strengths (f). The calcu-
lated UV/Vis spectra agree very well with the experimental
data (see Figure S5 in the Supporting Information). In addi-
tion, the relative oscillator strengths of the predicted spectra
matched well with the molar extinction coefficients that
were derived from the experimental measurements, which
followed a similar trend, with the trivalent derivatives (1
and 2) showing larger values than their corresponding P–
oxo counterparts (1-O and 2-O). The UV/Vis absorptions
mainly come from p!p* HOMO–LUMO transitions, with
significant contributions of 83–98%.
noted that the reaction conditions that were used to access
molecular “click product” 5 (CuI, DIPEA, THF) were not
suitable for this further-extended species, owing to the ex-
tremely poor solubility of compound 6 in THF; in addition,
compound 6 was found to only have moderate solubility in
chlorinated solvents (e.g., CHCl3 and CH2Cl2). Nevertheless,
1H and 31P NMR spectroscopy confirmed the chainlike
nature of the product, which showed broad sets of signals in
1
the expected regions. The diagnostic H NMR spectroscopic
resonance signals of the triazole units were the most down-
field shifted, at d=8.59–8.70 ppm. However, MS (MALDI-
TOF) only showed one dominant peak at m/z: 1424.7 and a
modest peak at m/z: 1915.8, which were assigned to oligo-
meric FTPTF (F=fluorene, T=triazole, P=dithiazolo-
phosphole) and TPTFTPTFT species (for the structures, see
Scheme S1 in the Supporting Information,), respectively,
thus indicating that compound 6 was mainly an oligomeric
species. This result can be attributed to the limited solubility
of the growing, rigid p-conjugated chain, which inhibits fur-
ther propagation. Despite these limitations, the oligomer
was to be deemed suitable for further studies, which could
provide insight into the photophysics of such extended di-
thiazolophosphole species.
As shown in Figure 7, compound 6 shows two intense ab-
sorption bands at 340 and 405 nm in CH2Cl2, with a low-
energy tail up to 650 nm. The absorption band at 405 nm,
which is also observed in molecular species 5, is attributed
Probing studies toward a p-conjugated dithiazolophosphole-
based copolymer: To verify the suitability of this new build-
ing block as a monomer for the synthesis of extended mate-
rials through CuI-catalyzed Huisgen click reactions, we tar-
geted the synthesis of a dithiazolophosphole–fluorene co-
polymer. Compound 6 was synthesized from the reaction of
compound 4-O with 2,7-diazido-9,9-didodecyl-fluorene in
the presence of [Cu
ACHTUNGTRENNUNG(PPh3)3]Br as a catalyst and DIPEA as a
Figure 7. UV/Vis (dashed line) and emission spectra (solid line) of
oligomer 6 in CH2Cl2.
base in DMF at 608C for 8 h (Scheme 4).[24] It should be
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T. Baumgartner et al.
to originate from the triazole–phosphole–triazole moiety,
whilst the more intense band at 340 nm, which is not ob-
served in compound 5, is attributed to the fluorene unit.
The experimental UV/Vis data agree well with the TD-
DFT-predicted transitions. Figure 8 shows the predicted
oxide acts as an electron acceptor and the fluorene moiety
serves as an electron donor.
To ultimately overcome the solubility problems that limit
the practical value of polymer 6, a change in the co-mono-
mer or modification of the dithiazolophosphole itself
(through the introduction of solubilizing groups) appear
necessary to develop soluble polymers with higher molecu-
lar weight, as indicated by our previous research.[25] Studies
to this end are currently underway in our laboratory.
Selective CuII sensing: Because the emission of oligomer 6
was found to be surprisingly weak, we were interested in po-
tential scenarios that could trigger the observed features. In
particular, the triazole-extended dithiazolophospholes pro-
vide a suitable N,N-chelating moiety for metal-ion binding.
Similar chelating triazole systems for metal-ion sensing have
recently been reported by Bunz and co-workers.[26]
To verify this function, the metal-binding properties of
compound 5 were investigated by using several metal ions
(LiI, KI, ZnII, and CuII) in a CH2Cl2/MeOH mixture (1:1 v/
v). To our satisfaction, compound 5 was found to be a selec-
tive colorimetric and fluorescent sensor for CuII ions.
Figure 9 shows the UV/Vis and emission responses towards
CuII ions. The addition of CuII ions to a solution of com-
pound 5 in CH2Cl2/MeOH (1:1 v/v) produced large UV/Vis
spectroscopic changes, thus leading to a gradual decrease in
Figure 8. TD-DFT predicted electron transitions and frontier molecular
orbital diagrams for the model compound (FTPTF) of oligomer 6.
electronic transitions and the frontier molecular orbital dia-
grams for one of the model compounds (FTPTF) of polymer
6. Indeed, the TD-DFT calculations for FTPTF predict low-
and high-energy absorption bands at 302 and 440 nm, re-
spectively. The low-energy absorption is mainly comprised
of the HOMO!LUMO transition (p!p* of the dithiazolo-
phosphole moiety), whilst the high-energy absorption is
comprised of the HOMOꢀ1!LUMO+1 transition (p!p*
of the fluorene moiety). The emission of compound 6 (lem
=
560 nm) shows a modest redshift (Dl=60 nm) relative to
that of compound 5, thus supporting the assignment of ex-
tended conjugation throughout the material. The DFT cal-
culations show that the HOMO is delocalized over the ex-
tended conjugated system, whilst the LUMO is mainly local-
ized at the dithiazolophosphole oxide core, thus suggesting a
charge-transfer process in which the dithiazolophosphole
Figure 9. Changes in the a) UV/Vis and b) emission spectra of compound
5 (2.0ꢂ10ꢀ5 m) in CH2Cl2/MeOH (1:1 v/v) upon the addition of Cu-
AHCTUNTGREN(NGNU ClO4)2; excitation at the isosbestic point of 375 nm.
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Dithiazolo[5,4-b:4’,5’-d]phosphole as a Luminescent Building Block
FULL PAPER
the intensity of the low-energy absorption band at 406 nm
and a concomitant increase in the intensity of a new high-
energy band at 332 nm.
Conclusion
To explore highly emissive electron-accepting materials for
potential applications in molecular optoelectronics and sen-
sors, a new family of dithiazolo[5,4-b:4’,5’-d]phospholes has
been developed. The alkynyl-functionalized building block
4-O was purposely designed for further modification
through Huisgen click reactions. Similar to our established
dithieno[3,2-b:2’,3’-d]phosphole system, the photophysical
properties of these dithiazolo[5,4-b:4’,5’-d]phospholes can be
easily modified in terms of their wavelength and intensity by
placing substituents with different electronic properties at
the 2,5-positions of the rigid core or by facile modification
of the central phosphorus atom. In general, substituents
with stronger electron-donating ability at the 2,5-positions
lead to a redshift of both the UV/Vis absorption and emis-
sion bands, thus indicating an enhanced electron-accepting
character of the dithiazolo[5,4-b:4’,5’-d]phosphole core. In
addition, this building block has been successfully applied to
the design of oligomer 6, which exhibits red-shifted emission
features compared to those of its molecular relative (5),
thus suggesting the presence of an extended p-conjugated
system. Theoretical calculations predict that dithiazolo[5,4-
b:4’,5’-d]phospholes have much lower HOMO and LUMO
energy levels than the dithienophosphole system, thus dem-
onstrating that this new building block is a stronger electron
acceptor. Cyclic voltammetry studies revealed one quasire-
versible reduction process for these new phosphole oxides,
thus supporting their promising electron-accepting proper-
ties. Moreover, compound 5, which contains two triazole
units at the 2,5-positions, was found to be a selective colori-
metric and fluorescent sensor for CuII ions by interaction of
the metal ion with chelating thiazole–triazole N,N units.
A clean isosbestic point at 375 nm was observed, thus in-
dicating a clean transformation into the CuII-complexed spe-
cies. At the same time, an obvious color change of the solu-
tion from yellow into colorless was observed (see Figure S6
in the Supporting Information), which allowed compound 5
to be easily handled as a naked-eye sensor for CuII ions. The
gradual disappearance of the low-energy absorption band at
406 nm was assigned to the occurrence of new charge-trans-
fer transitions upon CuII binding, as a result of the redistrib-
ution of the molecular orbitals (see below). On the other
hand, significant quenching of the original emission at
500 nm, along with the appearance of a new weak emission
band at about 425 nm, as well as an isoemissive point at
450 nm, were observed. The pronounced emission color
change from green to almost nonemissive is shown in Fig-
ure S6 in the Supporting Information. Such emission
quenching has also been observed in other CuII-sensing sys-
tems,[27] owing to energy or electron transfer because of its
d9 electronic configuration.
The binding constant (logK) for CuII ions was determined
to be about 4.0 by using nonlinear least-squares fitting of
both the UV/Vis and emission titration data (see Figure S7
in the Supporting Information).[28] Several other biologically
relevant metal ions, such as LiI, KI, and ZnII ions, have also
been tested, but no obvious UV/Vis or emission changes
were observed. Consequently, the observed quenched lumi-
nescence for oligomer 6 can be attributed to the presence of
CuII ions that coordinate to the polymer backbone.
To further confirm the observed photophysical properties,
the molecular orbitals and their corresponding energies of
the CuII complex were calculated by using DFT (B3LYP/
LANL2DZ; see Figure S8 in the Supporting Information).
The HOMO to HOMOꢀ3 levels are mainly dominated by
the Cu d orbitals and the P–phenyl p orbital, whilst the p
and p* orbitals of the tricyclic framework contribute to the
LUMO and the LUMO+1 to LUMO+3 orbitals, respective-
ly. Such an orbital redistribution supports a possible elec-
tron-transfer process, which would lead to the quenching of
the emission. Whilst the calculated absorption wavelength
ultimately doesn’t match the experimental data very well
(presumably owing to the truncated and metal-based nature
of the molecule that is used in the calculations), neverthe-
less, TD-DFT (B3LYP/LANL2DZ) calculations show that
the major transitions in the CuII complex are from the
HOMO to the LUMO+1 levels, that is, a charge transfer
from the p orbital of the P–phenyl group (with some minor
contribution from the conjugated scaffold) to the p* orbital
of the tricyclic framework, which is clearly different from
Experimental Section
Materials and methods: All chemical reagents were purchased from com-
mercial sources (Aldrich, Alfa Aesar, Strem) and were used without fur-
ther purification, unless otherwise noted. Solvents were dried by using a
MBraun solvent purification system prior to use. Compound S1,[18b]
benzyl
AHCTUNGTRENNUNG
azide,[29]
2,7-diazido-9,9-didodecyl-fluorene,[30]
and
[Cu-
reactions and manipulations were carried out under a dry nitrogen at-
mosphere by employing standard Schlenk techniques. 31P{1H}, 1H, and
13C{1H} NMR spectroscopy were performed on Bruker DRX400 and
Avance (II, III) 400 MHz spectrometers. Chemical shifts were referenced
to external 85% H3PO4 (31P) or to residual undeuterated solvent peaks
(1H, 13C). Elemental analysis was performed at the Department of Chem-
istry, the University of Calgary. Mass spectroscopy was performed on Fin-
nigan SSQ 7000 or Bruker Daltonics AutoFlex III spectrometers. All
photophysical experiments were performed in CH2Cl2 on a Jasco FP-6600
spectrofluorometer and a UV/Vis/NIR Cary 5000 spectrophotometer.
Cyclic voltammetry analysis was performed on an Autolab PGSTAT302
instrument, with a polished glassy carbon electrode as the working elec-
trode, a Pt wire as the counter electrode, and a Ag/AgCl/KCl3M reference
electrode, by using the ferrocene/ferrocenium couple as an internal stand-
ard. Unless otherwise noted, cyclic voltammetry experiments were per-
formed in CH2Cl2 with tetrabutylammonium hexafluorophosphate (0.1m)
as a supporting electrolyte. Theoretical calculations were performed at
the B3LYP/6-31G(d) or B3LYP/LANL2DZ level of theory by using the
ꢀ
the p p* transition in the uncomplexed compound (see Fig-
ure S9 in the Supporting Information).
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T. Baumgartner et al.
Gaussian 03 suite of programs.[24] Crystal data and details of the data-col-
lection procedure are provided in Table S1 in the Supporting Informa-
tion. Diffraction data were collected on a Nonius Kappa CCD diffrac-
tometer by using graphite-monochromated MoKa radiation (l=
0.71073 ꢁ). The structures were solved by using direct methods
(SHELXTL) and refined on F2 by using full-matrix least-squares techni-
ques. CCDC-913316 (1), CCDC-913317 (1-O), CCDC-913318 (2), and
CCDC-913319 (2-O), contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
129.0 (d, JACTHNGUTERNNUG
(C,P)=7.6 Hz), 84.5 ppm (s); 31P NMR (CDCl3, 162 MHz): d=
ꢀ27.0 ppm.
Synthesis of compound 5: Benzyl azide (2.2 equiv), DIPEA (31 mg,
0.24 mmol, 4 equiv), and CuI (2.3 mg, 20%, 0.2 equiv) were added to a
solution of compound 4-O (20 mg, 0.06 mmol, 1 equiv) in THF (0.1m)
and the mixture was stirred overnight at RT. After removal of the vola-
tile compounds, the residue was purified by column chromatography on
silica gel (CH2Cl2/MeOH, 100:5). Yield: 31 mg, 87%; 31P NMR (CDCl3,
162 MHz): d=9.3 ppm; 1H NMR (CDCl3, 400 MHz): d=7.99 (s, 2H; tria-
zole), 7.85–7.79 (m, 2H; Ph), 7.54 (td, J
1H; Ph), 7.45–7.37 (m, 8H; Ph), 7.33–7.30 (m, 4H; Ph), 5.58 ppm (q,
4H; CH2Ph); 13C NMR (CDCl3, 100.6 MHz): d=162.5 (d,
(C,P)=
23.1 Hz), 155.3 (s), 153.9 (s), 142.7 (s), 138.1 (d, J(C,P)=29.8 Hz), 133.7
(s), 133.2 (d, J(C,P)=2.9 Hz), 131.5 (d, J(C,P)=11.5 Hz), 129.3 (d, J-
(C,P)=10.2 Hz), 129.1 (d, J(C,P)=13.5 Hz), 128.4 (s), 126.7 (d, J(C,P)=
ACHTUNGTNER(NUNG H,H)=7.6 Hz, J (H,P)=1.6 Hz,
JACHTUNGTRENNUNG
Synthesis of compound 1: 4,4’-Dibromo-2,2’-bis(triisopropylsilyl)-5,5’-bi-
thiazole (S1, 4 g, 6.27 mmol) was dissolved in Et2O (150 mL) and nBuLi
(5.3 mL, 13.2 mmol, 2.1 equiv, 2.5m in hexanes) was added to the solution
at ꢀ788C, after which the solution was kept stirring for 30 min before
warming to RT. The solution was cooled to ꢀ788C again and PhPCl2
(0.85 mL, 6.27 mmol, 1 equiv) was added. After the addition, the solution
was quickly warmed to RT and stirred for 1 h, before concentrating it
under vacuum and filtering the mixture through an alumina plug (pen-
tane). The residues were recrystallized from acetone to afford a pale-
yellow solid (1.92 g, 52%). 1H NMR (CD2Cl2, 400 MHz): d=7.68–7.63
(m, 2H; Ph), 7.35–7.29 (m, 3H; Ph), 1.61–1.49 (septet, 6H; TIPS), 1.25–
1.21 ppm (m, 36H; TIPS); 13C NMR (CD2Cl2, 100.6 MHz): d=172.8 (d,
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
109.5 Hz), 121.8 (s), 54.7 ppm (s); HRMS (MALDI-TOF): m/z calcd for
C30H21N9OPS2: 605.1096 [M+H]+; found: 605.1108; m/z calcd for
C30H21N8NaOPS2: 627.0915 [M+Na]+; found: 627.0878.
Synthesis of polymer 6: A Schlenk flask was charged with compound 4-O
(40 mg, 0.12 mmol, 1 equiv), 2,7-diazido-9,9-didodecyl-fluorene (70 mg,
0.12 mmol, 1 equiv), [CuACHTNUGTRNEUGN(PPh3)3]Br (11 mg, 20%), DIPEA (62 mg,
0.48 mmol, 4 equiv), and DMF (3 mL) and the reaction mixture was stir-
red at 608C for 8 h under a N2 atmosphere. After dilution with CHCl3
(2 mL), the polymer was precipitated into MeOH (about 50 mL) and
washed twice with MeOH to afford compound 6 as a black solid (20 mg,
18%); 1H NMR (CDCl3, 400 MHz): d=8.70–8.59 (2H; triazole), 8.04–
7.49 (m, 11H; Ar), 1.28–0.85 ppm (m, 50H; C12H25); 31P NMR (CDCl3,
162 MHz): d=9.3 and 5.7 ppm. The low solubility of compound 6 did not
allow us to obtain meaningful 13C NMR spectroscopic data.
J
N
N
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
3.7 Hz), 128.5 (s), 18.3 (s), 11.8 ppm (s); 31P NMR (CD2Cl2, 162 MHz):
d=ꢀ31.6 ppm; HRMS (EI, 70 eV): m/z calcd for C30H47N2PS2Si2:
586.2457 [M]+; found: 586.2472; elemental analysis calcd (%) for
C30H47N2PS2Si2: C 61.39, H 8.07, N 4.77; found: C 61.23, H 7.99, N 4.66.
Synthesis of compound 2: TBAF (6.8 mL, 1m in THF, 6.8 mmol) was
added to a solution of compound 1 (1 g, 1.7 mmol) in dry THF (30 mL)
at 08C. The reaction mixture was allowed to warm to RT and stirred for
5 h. After that, water was added to the reaction and the reaction mixture
was extracted with Et2O. The combined organic layer was washed with
brine, dried over anhydrous MgSO4, and concentrated under reduced
pressure. The residue was recrystallized from acetone to afford the de-
Acknowledgements
Financial support by the NSERC of Canada, the Canada School of
Energy and Environment, as well as the Canada Foundation for Innova-
tion (CFI) is gratefully acknowledged. We thank Prof. T. Sutherland for
the generous use of his UV/Vis spectrometer and electrochemistry equip-
ment.
sired product as
400 MHz): d=8.93 (d, J
Ph), 7.38–7.31 ppm (m, 3H; Ph); 13C NMR (CD2Cl2, 100.6 MHz): d=
164.4 (d, J(C,P)=3.1 Hz), 154.1 (d, J(C,P)=9.8 Hz), 133.3 (d, J(C,P)=
4.4 Hz), 132.3 (d, J(C,P)=19.0 Hz), 130.7 (d, J(C,P)=14.7 Hz), 129.6 (s),
128.9 ppm (d,
(C,P)=7.4 Hz); 31P NMR (CD2Cl2, 162 MHz): d=
a
yellow solid (0.44 g, 95%). 1H NMR (CD2Cl2,
(H,P)=1.6 Hz, 2H; thiazole), 7.52–7.47 (m, 2H;
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
JACHTUNGTRENNUNG
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Nyulꢅszi, Chem. Eur. J. 2005, 11, 4687–4699; c) Y. Dienes, S.
Durben, T. Kꢅrpꢅti, T. Neumann, U. Englert, L. Nyulꢅszi, T. Baum-
gartner, Chem. Eur. J. 2007, 13, 7487–7500; d) C. Romero-Nieto, S.
Durben, I. M. Kormos, T. Baumgartner, Adv. Funct. Mater. 2009, 19,
ꢀ29.5 ppm; HRMS (EI, 70 eV): m/z calcd for C12H7N2PS2: 273.9788
[M]+; found: 273.9799; elemental analysis calcd (%) for C12H7N2PS2:
C 52.54, H 2.57, N 10.21; found: C 52.63, H 2.72, N 9.96.
Synthesis of compound 3: This compound was prepared according to a
similar procedure to that of compound 1, except that compound S2
(4.3 g, 6.27 mmol) was used instead of compound S1. Yield: 2.5 g (63%);
1H NMR (CD2Cl2, 400 MHz): d=7.49–7.44 (m, 2H; Ph), 7.41–7.34 (m,
3H; Ph), 1.23–1.17 ppm (m, 42H; TIPS); 13C NMR (CD2Cl2, 100.6 MHz):
d=165.4 (d, J
(C,P)=3.7 Hz), 132.7 (d, J
14.7 Hz), 129.0 (d, JACHTUNGTRENNUNG(C,P)=7.9 Hz), 100.8 (s), 98.6 (s), 18.3 (s), 11.2 ppm
A
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
(s); 31P NMR (CD2Cl2, 162 MHz): d=ꢀ28.5 ppm; HRMS (MALDI-
TOF): m/z calcd for C34H48N2PS2Si2: 635.2535 [M+H]+; found: 635.2549.
Synthesis of compound 4: TBAF (1.0m in THF, 5 mL, 5 mmol) was
added to a solution of compound 3 (1.0 g, 1.6 mmol) in THF (30 mL) at
ꢀ788C and the mixture was stirred for 1 h at the same temperature.
After adding water (20 mL) to the resulting mixture, the aqueous phase
was extracted with EtOAc and the combined organic extracts were
washed with brine and dried with MgSO4. After removal of the volatile
compounds, the product was obtained without further purification (note:
the reaction temperature is very important; reaction at RT or 08C will
lead to decomposition of the product, thus affording a black precipitate).
Yield: 0.48 g (95%); 1H NMR (CDCl3, 400 MHz): d=7.49–7.44 (m, 2H;
Ph), 7.33–7.27 (m, 3H; Ph), 3.66 ppm (s, 2H; C CH); 13C NMR (CDCl3,
ꢂ
100.6 MHz): d=165.5 (s), 148.5 (d, J
3.5 Hz), 132.4 (d, J
A
H
T
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Dithiazolo[5,4-b:4’,5’-d]phosphole as a Luminescent Building Block
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Received: December 8, 2012
Revised: March 8, 2013
Published online: && &&, 0000
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!

T. Baumgartner et al.
Sliding down with a glow: Incorpora-
tion of nitrogen atoms into the dithie-
nophosphole scaffold generates a new
building block, dithiazolo[5,4-b:4’,5’-
d]phosphole (see scheme), that com-
bines intense luminescence with high
electron affinity. A family of conju-
gated small molecules and a polymer
based on this building block have been
synthesized by a click reaction that
also serves as selective colorimetric
and fluorescent sensor for CuII.
Luminescence
X. He, A. Y. Y. Woo, J. Borau-Garcia,
T. Baumgartner* ............. &&&& — &&&&
Dithiazolo[5,4-b:4’,5’-d]phosphole: A
Highly Luminescent Electron-
Accepting Building Block
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Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!