A novel substitution reaction of perylene bisimides with Ph2PLi at the α-position

Article abstract of DOI:10.1039/b9nj00364a

A novel substitution reaction of perylene bisimides has been developed. The Ph₂PO group was attached to the PBI core at the α-position instead of the usual bay position. This substitution kept the high fluorescence of the PBI dyes and caused th

Full text of DOI:10.1039/b9nj00364a

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A novel substitution reaction of perylene bisimides with Ph2PLi
at the a-positionw
Xue Wu, Chuanwei Yin, Zhiqiang Shi,* Maoyou Xu, Jin Zhang and Juanjuan Sun
Received (in Montpellier, France) 1st June 2009, Accepted 27th July 2009
First published as an Advance Article on the web 23rd October 2009
DOI: 10.1039/b9nj00364a
A novel substitution reaction of perylene bisimides has been developed. The Ph2PO group was
attached to the PBI core at the a-position instead of the usual bay position. This substitution
kept the high fluorescence of the PBI dyes and caused the adjacent proton at the bay position
1
and a tertiary proton at the cyclohexyl group to be shifted significantly in the H-NMR spectra.
(1, 2 and 3) were synthesized from corresponding PBIs
Introduction
(1a, 2a and 3a) following the strategy outlined in Scheme 1.
N,N0-Dicyclohexylperylene-3,4:9,10-tetracarboxylic acid
bisimide 1a, N,N0-dicyclohexyl-1,7-dibromoperylene-3,4:9,10-
tetracarboxylic acid bisimide 2a and N,N0-dicyclohexyl-
1,6,7,12-tetrachloroperylene-3,4:9,10-tetracarboxylic acid bisimide
3a were synthesized and purified according to literature
procedures.16 A solution of lithium diphenylphosphide (DPPLi)
was prepared from triphenylphosphine in THF.17 1,7-Bibromo-
perylene bisimide 2a was used to carry out this reaction. Under
an argon gas stream, DPPLi in THF was added into the THF
solution of 2a. Originally we aimed to substitute the bromine
atoms of 2a. However, MALDI-TOF mass data suggested
that a proton on the perylene core was substituted by a Ph2PO
group instead of substitution of the halogen atom. The
suggestion was further confirmed by 1H-NMR, 13C-NMR
and 31P-NMR spectra. These data indicated that a novel type
of substitution reaction of PBIs was developed. This new
reaction was also verified by the reactions of DPPLi with 1a
(no halogen substituted) and 3a (all of the bay positions
halogen substituted).
In recent years, functionalized perylene bisimides (PBIs)
have received considerable attention for a wide range of
applications, for example, as fluorescent dyes for single
molecule spectroscopy1 and bio-imaging2 and as organic
semiconductors for organic and polymeric light-emitting
diodes (OLEDs and PLEDs),3 organic field-effect transistors
(OFETs),4 and solar cells.5 They also have been proven to be
good building blocks for constructing supramolecular or
giant-molecular systems.6 The molecular properties that
enable all these applications are the high fluorescent quantum
yield, fairly persistent radical anion state, easy accessibility,
and outstanding stability of these dyes against environmental
influences.7 Due to the intrinsic insolubility of perylene
bisimides, two different strategies have been developed to
modify the dyes. One is introducing solubilizing substitutes
at the imide nitrogen,8 which exhibits usually indistinguishable
absorption and emission properties.9 Another is introducing
substituents at the carbocyclic scaffold in the so-called bay-
area (b-position of imide groups). The latter strategy is more
elaborate.10 For example, aryloxy-, cyano-, pyrrolidino, alkoxy
and/or alkylthio-substituted PBIs as well as the Suzuki
coupling reaction have been investigated. Usually the readily
available halogenated PBIs, such as 1,7-dibromo or 1,6,7,12-
tetrachloro derivatives, were used as starting materials.11,12 As
far as we know, it has seldom been reported that the PBI dye
was directly modified at a-position of the aromatic core.13
Phosphines have been widely used for organic synthesis. For
example, organophosphide anions are considered to be powerful
nucleophiles. The diphenylphosphide anion (Ph2Pꢀ) readily
reacts with haloaromatic compounds involving SRN1 mecha-
nism of nucleophilic substitution with both thermal and
photochemical initiation steps.14 And phosphines reduce
hydroperoxides, peroxides, disulfides, sulfoxides, epoxides
and so on.15 However, the reaction of Ph2Pꢀ with PBI dye
has not been reported. Herein, a series of diphenylphosphinoyl
(Ph2PO) group substituted perylene bisimides at the a-position
The substitution of the aromatic core of perylene-3,4:9,10-
tetracarboxylic acid bisimides generally takes place at bay (b)
positions. For 1,6,7,12-tetrachloroperylene bisimide 3a, four
Department of Chemistry, Shandong Normal University, Jinan,
250014, P. R. China. E-mail: zshi@sdnu.edu.cn;
Fax: +86 531 82615258; Tel: +86 531 86182540
w Electronic supplementary information (ESI) available: The MS and
1H-, 13C-, 31P-NMR spectra of 1–3. See DOI: 10.1039/b9nj00364a
Scheme 1 The synthesis of compounds 1, 2 and 3.
ꢁc
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b-positions are occupied by chlorine atoms and no chlorine
atom is substituted according to the MS spectrum. Conse-
quently, the Ph2PO group is incorporated at an a-position of
the perylene core. All data from the 1H-NMR, 13C-NMR and
31P-NMR spectra are consistent with this result. Due to the
shielding effect of the Ph2PO group on compound 3, the
tertiary proton on a nearer cyclohexyl group (H1 proton,
Scheme 1) shifts upfield 0.99 ppm compared with the tertiary
proton on another cyclohexyl group (H2 proton, Table 1).
Similar effects are also observed for 1 and 2. Compared with
H2 proton, the H1 proton shifts upfield 0.41 and 0.30 ppm,
respectively, for 1 and 2. These values are less than that for 3.
Because the relatively bulky chlorine atom at the adjacent
position makes the Ph2PO group near the H1 proton, and as a
result, the shielding effect of the Ph2PO group is reinforced for
3 (Fig. 1). The remarkable chemical shifts of the tertiary
protons on cyclohexyl groups reveal that the substitutions
also take place at the a-positions of the perylene bisimides
1 and 2.
Table 1 The special chemical shift of the compounds at 25 1C.
(Because of the poor solubility of 1a, we do not have the NMR
chemical shift of 1a)
H1 (ppm)
H2 (ppm)
H3 (ppm), J/Hz
1
2
2a
3
3a
4.65
4.71
5.06
4.01
5.02
5.06
5.01
5.06
5.00
5.02
9.70, 12.6
9.91, 13.7
8.63, 8.1
—
—
until separation. After purification with column chromato-
graphy, the target compounds obtained were strongly
fluorescent. The Ph2P group can quench the fluorescence of
the fluorophore connected due to photo-induced electron
transfer (PET) processes. Whereas the PET processes are
stopped after the Ph2P group has been oxidized to a Ph2PO
group.19 Therefore, it was proposed that non-fluorescent Ph2P
incorporated PBIs were yielded firstly. After the Ph2P group
has been oxidized to the stable Ph2PO group in the purification
procedure,20 the fluorescence of PBIs was restored again due
to the hindrance of the PET process.
1
In addition, an unusual change in H-NMR spectrum of 1
was noted. The adjacent proton of the substituted group at
bay position shifts downfield to 9.70 ppm with a large coupling
constant of 12.6 Hz (300 M at 25 1C, Table 1). The remarkable
increase in chemical shift mainly results from the deshielding
effect of Ph2PO group because this proton locates at a strong
induced paramagnetic area of two phenyl groups. The large
coupling constant indicates that this proton is split by an
adjacent P atom. For compound 2, a doublet signal at low
field of 9.91 ppm with a large coupling constant of 13.7 Hz
(far more than the coupling constant of 8.1 Hz at 8.63 ppm for 2a)
Spectroscopic grade solvents were used in UV/vis measure-
ments. For the purpose of comparison, the starting materials
of perylene bisimides are also included in Fig. 2 and the optical
data are summarized in Table 2. Over 400 nm, compounds 1
and 2 show the PBI core absorption band with the same
maximum absorption at 534 nm in CHCl3, and compound 3
shows the maximum absorption at 528 nm. The absorption
maximum of the derivatives are red-shifted by about 8–9 nm
after substitution. In the emission spectra of compounds 1, 2
and 3, the maximum emission locate at 545 nm, 555 nm and
558 nm, which are red-shifted by 8 nm, 7 nm and 8 nm,
respectively, compared to their corresponding PBI starting
materials. These results mainly are attributed to the extension
of the aromatic system after the substitution. From Fig. 2, we
know that the modified PBI dyes have similar absorption and
emission profiles to their starting materials. Especially, the
absorption and emission bands are not broadened. Whereas
the substitution at the bay-area usually results in the
maximum absorption and emission bands being red-shifted
and broadening of the bands due to the electron-donating
effect of the substituted group and the steric twisting of the
perylene core.6,21
1
is also observed in the H-NMR spectrum, revealing that the
adjacent atom of Ph2PO group is also a proton instead of a
Br atom.
In the synthesis of the target compounds, lithium diphenyl-
phosphide was used to react with PBIs. However, it was found
that the group incorporated was not Ph2P but Ph2PO. In most
cases, reactions of alkali metal diphenylphosphide with simple
aryl halides produce aryldiphenylphosphines, which are stable
in air.18 But the incorporation of the large aromatic PBI
moiety caused the phosphines to be three-coordinate structures,
which are unstable and readily oxidize to penta-coordinate
compounds. The experimental phenomena observed in synthesis
were that the resulting solutions remained non-fluorescent
From Table 2, we know that the fluorescence quantum yield
of 1, 2 and 3 show little difference from the corresponding 1a,
2a and 3a. So the incorporation of the Ph2PO group to the
perylene core at a-position keeps the fluorescence property
well. These are in agreement with the calculation results. As
clearly shown in Fig. 1, the geometries of compound 1, 2 and 3
are kept well after the substitution. This is quite different to the
substitution at the bay-area, which usually results in a large
PDI core twist.22
In summary, a series of Ph2PO group substituted perylene
bisimides have been synthesized firstly by reaction of lithium
diphenylphosphide with corresponding PBI dyes. The substi-
tuted group is attached to the PBI core at the a-position
instead of the usual substitution of a halogen atom at the
bay-area. Owing to the shielding or deshielding effect of the
Ph2PO group, the adjacent proton on the perylene core and
Fig. 1 DFT (B3LYP/6-31G*) geometry-optimized structures of 1a,
2a, 3a and 1, 2, 3. The geometry calculations were performed with
Gaussian 03 installed on a Windows PC.
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optically dilute method with N,N0-dicyclohexylperylene-
3,4:9,10-tetracarboxylic acid bisimide in chloroform solution
as reference (using an excitation wavelength of 527 nm).
The solution of lithium diphenylphosphide (DPPLi) was
prepared from triphenylphosphine as follows. Triphenyl-
phosphine (5.24 g, 0.02 mol) and lithium (0.84 g, 0.12 mol)
which had been washed with hexane and dried carefully with a
paper towel were suspended in a three-neck flask containing a
magnetic stirring bar and fitted with an argon inlet, and the
flask was evacuated and backfilled with argon three times.
After the solvent of anhydrous THF (150 ml) had been added,
the mixture was stirred vigorously at room temperature for 3 h
under an argon gas stream. Then the residual lithium was
removed by passing the mixture through a glass tube which
was stuffed with glass wool loosely; an argon gas stream was
also needed in this step. The red solution of lithium diphenyl-
phosphide (DPPLi) was used directly in the next step of the
reaction.
A three-neck flask was charged with N,N0-dicyclohexyl-
perylene-3,4:9,10-tetracarboxylic acid bisimide 1a (280 mg,
0.5 mmol), and the flask was evacuated and backfilled with
argon three times. After the solvent of anhydrous THF had
been added, the mixture was stirred vigorously at room
temperature for 1 h. Subsequently, the solution of lithium
diphenylphosphide (DPPLi) was added by syringe with a
gentle flow of argon. TLC was used to monitor the reaction.
When the reaction was finished, the solvent was removed by
rotary evaporation at room temperature. The crude product
was purified by silica gel column chromatography with
CH2Cl2–THF (50 : 1) as eluent. The main second band was
collected, and removal of the solvent yielded 121 mg (32%) as
Fig. 2 UV/vis (left axis) and fluorescence (right axis) spectra of the
perylene bisimides (10ꢀ5 M) in chloroform at room temperature. a: 1
(dashed line) and 1a (solid line), b: 2 (dashed line) and 2a (solid line), c:
3 (dashed line) and 3a (solid line).
Table 2 UV/vis absorption and fluorescence emission properties of
substituted PBIs and their corresponding PBI starting materials
in chloroform
a
Ffl
l
abs/nm
e/Mꢀ1 cmꢀ1
lex/nm
lem/nm
1a
2a
3a
1
2
3
526
525
519
534
534
528
70 800
49 600
27 600
52 100
46 600
34 500
527
527
521
534
535
530
537
548
550
545
555
558
1.00
0.82
0.92
1.00
0.83
0.87
a red-brown solid. MS (MALDI-TOF): m/z 754.2 (M+).
3
1H-NMR (300 MHz, CDCl3, 25 1C): d = 9.70 (d, 1H, JPH
=
12.6), 8.66–8.71 (m, 6H), 7.81–7.89 (m, 4H),7.54–7.56 (m, 2H),
7.28 (m, 4H), 5.06 (m, 1H), 4.65 (m, 1H), 2.57–2.60 (m, 2H),
2.01–2.05 (m, 2H), 1.96–2.01 (m, 2H), 1.76 (m, 4H), 1.47–1.52
(m, 4H), 1.12–1.39 (m, 6H) ppm. 13C-NMR (75 MHz, CDCl3,
25 1C): d = 163.775, 163.685, 162.982, 162.169, 134.666,
133.983, 133.808, 132.137, 131.772, 131.659, 131.507,
131.406, 131.276, 128.261, 128.096, 124.282, 124.047,
123.990, 123.067, 54.171, 54.089, 52.986, 29.665, 29.336,
29.113, 28.593, 26.528, 26.246, 25.427, 25.159 ppm. 31P-NMR
(121 MHz, CDCl3, 25 1C): d = 34.5403 ppm.
a
Determined with N,N0-dicyclohexylperylene-3,4:9,10-tetracarboxylic
acid bisimide as reference (lex = 527 nm).
the tertiary proton at a nearer cyclohexyl group shift signifi-
1
cantly in the H-NMR spectra. The substitution results in a
slight red-shift both in absorption and emission spectra and
keeps the high fluorescence of the PBI dyes. This reaction
provides a new method to modify PBI dyes.
A three-neck flask was charged with N,N0-dicyclohexyl-1,7-
dibromoperylene-3,4:9,10-tetracarboxylic acid bisimide 2a
(360 mg, 0.5 mmol), and the flask was evacuated and back-
filled with argon three times. After the solvent of anhydrous
THF had been added, the mixture was stirred vigorously at
room temperature for 1 h. Subsequently, the solution of
lithium diphenylphosphide (DPPLi) was added by syringe
with a gentle flow of argon. TLC was used to monitor the
reaction. When the reaction was finished, the solvent was
removed by rotary evaporation at room temperature. The
crude product was purified by silica gel column chromato-
graphy with CH2Cl2–THF (50 : 1) as eluent. The main second
band was collected, removal of the solvent yielded 198 mg
(43%) as a red-brown solid, which was further purified by
silica gel column chromatography with toluene–THF (5 : 1) as
eluent. The first band was collected, and the solvent was
Experimental
1H NMR and 13C NMR were measured with Bruker 300 MHz
or 600 MHz spectrometers. Mass spectra were recorded on a
Bruker BIFLEXIII spectrometer for MALDI-TOF-MS.
Infrared spectra were determined with a Bruker Tensor-27
spectrometer. Electronic absorption spectra were measured on
a Beijing Purkinje General Instrument Co. Ltd. TU-190
spectrophotometer. The photoluminescence spectra were
recorded on
a HITACHI FL-4500 spectrofluorometer.
Triphenylphosphine, lithium, and THF were purchased from
Sinopharm Chemical Reagent Co. Ltd. The THF used was
anhydrous THF which was distilled over sodium and benzo-
phenone. Fluorescence quantum yields were measured by the
ꢁc
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New J. Chem., 2010, 34, 61–64 | 63

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removed by rotary evaporation to afford 97 mg (49%) of 2 as a
red solid. MS (MALDI-TOF): m/z 911.9 (M+). 1H-NMR
(300 MHz, CDCl3, 25 1C): d = 9.91 (d, 1H, 3JPH = 13.7), 9.50
(d, 1H, J = 8.2), 8.94 (s, 1H), 8.82 (s, 1H), 8.69 (d, 1H, J =
8.1), 7.74–7.80 (m, 4H), 7.53–7.57 (m, 2H), 7.46–7.48 (m, 4H),
5.01 (m, 1H), 4.71 (m, 1H), 2.51–2.55 (m, 2H), 2.11–2.16
(m, 2H), 1.90–1.93 (m, 2H), 1.73–1.77 (m, 4H), 1.19–1.60
(m, 10H) ppm. 13C-NMR (75 MHz, CDCl3, 25 1C): d =
163.201, 162.621, 161.930, 161.824, 138.730, 137.903, 134.188,
134.030, 133.862, 132.741, 132.361, 132.249, 132.167, 131.638,
131.512, 130.474, 129.910, 129.143, 128.600, 128.495, 128.325,
127.462, 126.901, 126.577, 124.014, 123.622, 123.468, 122.103,
121.454, 54.424, 54.275, 29.067, 28.624, 26.471, 26.217, 25.347,
25.126 ppm. 31P-NMR (121 MHz, CDCl3, 25 1C): d =
2.9746 ppm.
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A three-neck flask was charged with 1,6,7,12-tetrachloro-
perylene bisimide 3a (350 mg, 0.5 mmol), and the flask was
evacuated and backfilled with argon three times. After the
solvent of anhydrous THF has been added, the mixture was
stirred vigorously at room temperature for about 1 h. Sub-
sequently, the solution of lithium diphenylphosphide (DPPLi)
was added by syringe with a gentle flow of argon. TLC was
used to monitor the reaction. When the reaction was finished,
the solvent was removed by rotary evaporation at room
temperature. The crude product was purified by silica gel
column chromatography with CH2Cl2–THF (50 : 1) as eluent.
The main second band was collected, removal of the
solvent yielded 190 mg (42%) as a red-brown solid. MS
(MALDI-TOF): m/z 891.9 (M+). 1H-NMR (600 MHz,
CDCl3, 25 1C): d = 8.65 (s, 1H), 8.63 (s, 1H), 8.55 (s, 1H),
8.03–8.06 (m, 2H), 7.62–7.65 (m, 1H), 7.57–7.60 (m, 4H),
7.45–7.48 (m, 1H), 7.38–7.40 (m, 2H), 5.00 (m, 1H), 4.01
(m, 1H), 2.49–2.55 (m, 2H), 1.90–1.92 (m, 2H), 1.70–1.75
(m, 6H), 1.43–1.50 (m, 2H), 1.12–1.37 (m, 8H) ppm.
13C-NMR (75 MHz, CDCl3, 25 1C): d = 162.512, 161.669,
136.342, 135.842, 135.441, 133.317, 132.786, 132.650, 132.098,
131.904, 131.765, 130.933, 130.796, 128.760, 128.586, 128.476,
128.303, 123.987, 123.857, 123.680, 122.675, 55.359, 54.470,
29.068, 29.003, 28.780, 28.328, 26.454, 26.291, 26.062, 25.307,
25.174, 21.382 ppm. 31P-NMR (121 MHz, CDCl3, 25 1C):
d = 33.1312 ppm.
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This work was supported by the National Natural Science
Foundation of China (20771067 and 20531060) and Natural
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64 | New J. Chem., 2010, 34, 61–64