Synthesis, spectroscopic, and electrochemical properties of three tetrathiafulvalenes attached to perylene

Article abstract of DOI:10.1007/s00706-008-0863-y

Three donor-acceptor dyads 1-3 comprising of a tetrathiafulvalene (TTF) unit linked with perylene by a simple σ-bond were synthesized and characterized. Spectroscopy and cyclic voltammetry provided an indication that intramolecular charge-transfer interactions in their ground states between TTF and perylene for dyads 1-3 are negligible. Compared with the compound perylene, dyads 1-3 exhibited large fluorescence quenching, which might be ascribed to photo-induced electron transfer interaction between TTF and perylene units in the excited state.

Full text of DOI:10.1007/s00706-008-0863-y

Monatsh Chem 139, 1357–1362 (2008)
DOI 10.1007/s00706-008-0863-y
Printed in The Netherlands
Synthesis, spectroscopic, and electrochemical properties of three
tetrathiafulvalenes attached to perylene
Haixiao Qiu1, Chengyun Wang1, Jinfeng Xu1, Guoqiao Lai2, Yongjia Shen1
1
Laboratory of Advanced Materials, Institute of Fine Chemicals, East China University of Science and Technology,
Shanghai, P.R. China
2
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education,
Hangzhou Normal University, Hangzhou, China
Received 18 September 2007; Accepted 6 November 2007; Published online 26 August 2008
# Springer-Verlag 2008
Abstract Three donor–acceptor dyads 1–3 com-
prising of a tetrathiafulvalene (TTF) unit linked with
perylene by a simple ꢀ-bond were synthesized and
characterized. Spectroscopy and cyclic voltammetry
provided an indication that intramolecular charge-
transfer interactions in their ground states between
TTF and perylene for dyads 1–3 are negligible. Com-
pared with the compound perylene, dyads 1–3 ex-
hibited large fluorescence quenching, which might
be ascribed to photo-induced electron transfer inter-
action between TTF and perylene units in the excited
state.
for the development of building blocks in electrical
conductors and superconductors [2]. These molecu-
lar systems perform distinctively in their photophys-
ical and electrochemical properties, which allow
them to be widely studied on intramolecular charge-
transfer interactions and photo-inducing electron-
transfer processes. Ongoing research leaves potential
applications open in materials science, including
chemical sensors, molecular switches, molecular
shuttles, organic ferromagnets, molecular rectifiers,
molecular transistors, nonlinear optical materials,
and photovoltaic materials [3–8].
One of the most interesting properties of TTF is
that it can be oxidized successively and reversibly to
the radical cation and dication species within a very
accessible potential window. Consequently, the pos-
sibility of exploiting these multistage redox states
Keywords Donor–acceptor effects; Fluorescence spectrosco-
py; UV=Vis spectroscopy; Cyclic voltammetry; Tetrathiaful-
valene.
þ
0
(TTF , TTFꢀ , TTF2þ) was investigated to construct
Introduction
supramolecular systems that can be controlled by ex-
ternal stimuli [9]. The peculiar electronic properties
of TTF were also opportunely applied to architecture
molecular systems, especially TTF-based fluores-
cence-redox switches attaching different acceptors
including phthalocyanine [10], porphyrin [11], an-
thrancene [12], or C60 [13], even highly fluorescent
acceptor perylene-3,4,9,10-bis(dicarboximide) (PDI)
[14]. While PDI involving fluorescence redox switch
has been demonstrated in a PDI-TTF-PDI triad or
Since the discovery of donor and acceptor systems
based on TTF–TCNQ [1] was first reported, tetra-
thiafulvalene (TTF) and its derivatives have been
extensively investigated as excellent electron donors
Correspondence: Yongjia Shen, Laboratory of Advanced
Materials, Institute of Fine Chemicals, East China University
of Science and Technology, Shanghai 200237, P.R. China.
E-mail: yjshen@ecust.edu.cn

1358
H. Qiu et al.
Scheme 1
PDI-TTF dyads, it still has the problems in low sol-
ubility in most of organic solvents. Considering the
difficulty to manipulate such insoluble materials, al-
kyl perylenes offer alternatives for exhibiting rela-
tively high electron affinity as well. Perylene, which
also possesses favorable photochemical properties,
such as high fluorescent quantum yield and stability,
was widely used in various fields, even including
application as a probe by hybridization with a target
DNA or RNA in biochemistry [15]. Considerable in-
terest in perylene applications is now focused on
organometallic materials but there are no reports on
the TTF-perylene system.
Results and discussion
Synthesis
The strategy to synthesize dyads 1–3 was through a
deprotection=realkylation process: selective removal
of 2-cyanoethyl protecting groups in 4 or 5 with
the aid of CsOH ꢀ H2O and subsequent reaction with
3-(bromomethyl)perylene 9 as crucial alkylating
agents (Scheme 2).
Cross-coupling reaction of 6 and 8 in the pres-
ence of P(OEt)3 led to the precursor 2,3-bis(2-cya-
noethylthio)-TTF 5 in 50% yield, and afterward it
was deprotected by CsOH ꢀ H2O in anhydrate DMF
and further reacted with MeI affording 2-(2-cya-
noethylthio)-3-methylthio-TTF 4 in 80% yield. The
key intermediate compounds 6–8 were synthesized
according to reported procedures [16–18].
In this work, we report the synthesis and elec-
trochemical and spectroscopic properties of dyads
1–3 (Scheme 1), which present potential ability of
being a new fluorescent redox dependent molecu-
lar system.
Reagents: (a) Br(CH2)6Br, MeCN; (b) BrCH2CH2CN, MeCN; (c) Hg(OAc)2, CHCl3=HOAc; (d) P(OEt)3, toluene; (e)
CsOH ꢀ H2O=MeOH, DMF, MeI
Scheme 2

Properties of three tetrathiafulvalene attached to perylene
1359
Reagents: (f) POCl3, DMF, o-dichlorobenzene; (g) NaBH4=MeOH, THF; (h) PBr3, CCl4
Scheme 3
On the other hand, new bromomethylperylene 9
was synthesized in a modified procedure (Scheme 3).
Formylation of perylene with POCl3=DMF gave
compound 11 [19], which was reduced by sodium
borohydride in methanol to afford hydroxymethyl-
perylene 10. After being treated with PBr3 and subse-
quent simple purification, compound 9 was isolated.
Because of the instability of 9 [20], it was used imme-
diately to carry out the deprotection=realkylation pro-
cedure mentioned above to obtain target dyads 1–3.
file offered by summation of the spectra of donor 4
and acceptor 9, and no new intramolecular charge-
transfer absorption bands or unique shoulders were
observed in the whole wavelength range. The results
also indicated that no significant interactions be-
tween TTF and perylene units in the 300–550 nm
range were arrested in the ground state.
Steady-state fluorescene
The fluorescence spectra were compared with the
perylene, which is more suitable as reference than
9 due to its higher stability and higher fluorescence
quantum yield. A mass quantitative quenching (ca.
80%) of the perylene moiety fluorescence emission
was observed in dyad 1 (Fig. 2 and Table 1).
Moreover, on comparison with dyad 1, dyads 2 and
3 showed much weaker fluorescence intensities, but
slight discrepancy in the shape. The fluorescence
UV=Vis absorption
The absorption spectra of dyads 1–3 showed com-
pared to compounds 9 and 4 in CH2Cl2 a wide ab-
sorption between 300–550 nm with the absorption
maximum at lmax ¼ 421, 447, 397, 333 nm (Fig. 1).
The TTF moiety absorbed strongly around 330 nm,
and the perylene moiety showed strong absorption
bands at 420 and 450 nm with a shoulder at 390 nm.
These UV=Vis absorption spectra matched the pro-
Fig. 2 Fluorescene spectra of dyads 1–3 (c ¼ 3ꢁ10ꢂ6 M),
compounds 4, 9, and reference compound perylene
(c ¼ 3ꢁ10ꢂ6 M) in CH2Cl2 excited at lexc ¼ 400 nm
Fig. 1 UV=Vis absorption spectra of dyads 1–3, reference
compounds 4, 9, and perylene (c ¼ 1ꢁ10ꢂ5 M) in CH2Cl2

1360
H. Qiu et al.
Table 1 Fluorescence quantum yield of 1–3, compound 9,
and the reference compound perylene (c ¼ 1.0ꢁ10ꢂ6 M) in
CH2Cl2 at rt
Compound
Reference
Quantum yield
Dyad 1
Dyad 2
Dyad 3
9
perylene
perylene
perylene
perylene
perylene
0.21 ꢃ 0.02
0.33 ꢃ 0.02
0.22 ꢃ 0.03
0.28 ꢃ 0.01
1
Perylene
spectra of the three dyads with two bands around
lmax ¼ 450 and 477 nm were indeed the mirror
images of UV=Vis absorption spectrum of com-
pound 9. No band was observed in the fluorescence
spectrum of compound 4. These phenomena implied
that the fluorescence spectra of dyads 1–3 were as-
cribed to their perylene unit. The reduction of fluo-
rescence intensities of dyads 1–3 was the result of an
intramolecular process because of slight change in
either shape or intensity in the fluorescence spectrum
of 9 by inducing a mixture of 4 and 9 (in 1:1 stoi-
chiometry). In addition, a photo-induced electron
transfer (PET) reaction between TTF and perylene
moieties in dyads 1–3 might be one reason for fluo-
rescence waning. And from Fig. 2, the low fluores-
cence intensity and low quantum yield of compound
9 were due to the bromine atom quenching effect.
Fig. 3 Cyclic voltammogram of dyads 1–3 (c ¼ 1ꢁ10ꢂ3 M)
using n-Bu4NPF6 in CH2Cl2 as a supporting electrolyte, plat-
inum wires as working and counter electrodes Ag=AgCl wire
as a reference electrode, and a scan rate of 100 mV=sec
tion around 1.32 V, two reductions around ꢂ1.89 and
ꢂ1.50 V) were detected. Comparing with compounds
4 and 9, the oxidation peaks maintained at 0.63
and 1.01 V pertain to the TTF unit oxidized to the
þ
radical cation TTFꢀ -perylene and dication TTF2þ-
perylene, while the irreversible oxidation peak was
attributed to the oxidation of the perylene unit. More-
over, the irreversible reduction waves (ꢂ1.89 and
ꢂ1.50 V) in dyad 1 were due to the reduction of
the perylene unit. Dyads 2 and 3 have a similar
electrochemistry character. The reversible reduction
waves were ambiguous as some might occur above
ꢂ2.0 V, which is the limit potential in our experi-
mental condition.
Cyclic voltametry
The cyclic voltammograms of dyads 1–3 are shown
in Fig. 3. The redox potentials of dyads 1–3, TTF
4–5, compound 9 are listed in Table 1.
TTF is well-known in respect of electrochemistry.
Cyclic voltametry of dyad 1 showed two manifest
and reversible one-electron TTF oxidation waves
(E1=2 ¼ 0.63 and 1.01 V). Three irreversible one-
electron waves from the perylene core (one oxida-
TTF is an outstanding electron donor, which gen-
erates radical cation or dication species by removing
one or two electrons. Its oxidation potentials lie low-
er than that of perylene, hence it should be possible
to selectively oxidize the TTF preventing it (when it
comes to oxidation) from acting as an electron donor
and quenching perylene emission.
Table 2 Redox potentials of 1–3, TTF 4–5, and compound 9
Compound
E1=2 red1=V
E1=2 red2=V
E1=2 ox1=V
E1=2 ox2=V
E1=2 ox3=V
Dyad 1
Dyad 2
Dyad 3
4
5
9
ꢂ1.89
ꢂ1.79
ꢂ1.76
–
ꢂ1.50
ꢂ1.35
ꢂ1.58
–
0.63
0.57
0.61
0.64
0.60
–
1.01
0.94
1.00
1.02
0.99
–
1.32
1.34
1.49
–
–
–
–
–
ꢂ2.43
ꢂ1.96
Condition: Potentials vs. Ag=AgCl, scan rate of 100mV=s, working electrode Pt, supporting electrolyte n-Bu4NPF6 in CH2Cl2

Properties of three tetrathiafulvalene attached to perylene
1361
H), 7.74 (d, 2H, J ¼ 8.0 Hz, Ar-H), 7.64 (t, 1H, J ¼ 7.9 Hz,
Ar-H), 7.56 (d, 1H, J ¼ 7.6 Hz, Ar-H), 7.51 (m, 2H, Ar-H),
4.95 (s, 2H, alkyl–H) ppm.
Experiment
1H NMR spectra were obtained with a Bruker AM 500 spec-
trometer with tetramethylsilane as internal standard. Elemental
analyses were performed on a Vario EL III (Elemental) instru-
ment; their results agreed favourably with the calculated values.
Mass spectra were obtained with an MA1212 instrument,
MALDI-TOF spectra were recorded on a 4700-Propeotics
analyzer, and UV=Vis spectra on a Varian Cary 500 spectro-
photometer (1cm quartz cell) at 25ꢄC. Fluorescence emission
spectra were recorded on a Varian Cary Eclipse fluorescence
spectrophotometer (1 cm quartz cell) at 25ꢄC. Melting
points were determined with a Fisher-Johns melting point
apparatus. Cyclic voltammetry experiments were carried
out with a computer-controlled BAS CV50W potentiostat at
a scan rate of 100 mV=s in CH2Cl2 using BuNPF6 as electro-
lyte, platinum as counter and work electrodes, and Ag=AgCl
as reference electrode.
2,3-Bis(2-cyanoethylthio)-6,7-bis(hexylthio)tetrathiafulvalene
(5, C24H34N2S8)
Synthetic procedure in analogy to Ref. [16]. MS(EI): m=z ¼
606; 1H NMR (500MHz, CDCl3): ꢁ ¼ 3.04 (t, 4H, J ¼ 7.8 Hz,
S–CH2–CH2–CN), 2.81 (t, 4H, J ¼ 7.3 Hz, S–CH2–), 2.74
(2H, t, J ¼ 7.4 Hz, S–CH2–CH2–CN), 1.72–1.58 (m, 4H,
alkyl–H), 1.46–1.42 (m, 4H, alkyl–H), 1.30–1.25 (m, 8H,
alkyl–H), 0.88 (t, 6H, J ¼ 6.8 Hz, alkyl–CH3) ppm.
2-(2-Cyanoethylthio)-3-methylthio-6,7-bis(hexylthio)-
tetrathiafulvalene (4, C22H33NS8)
Synthetic procedure in analogy to Ref. [15]. MS(EI): m=z ¼
567; 1H NMR (500MHz, CDCl3): ꢁ ¼ 3.03 (2H, t, J ¼ 7.5 Hz,
S–CH2–CH2–CN), 2.82 (4H, t, J ¼ 7.3 Hz, S–CH2–), 2.71
(2H, t, J ¼ 7.1 Hz, S–CH2–CH2–CN), 2.46 (s, 3H, S–CH3),
1.72–1.58 (m, 4H, alkyl-H), 1.46–1.42 (m, 4H, alkyl–H),
1.30–1.25 (m, 8H, alkyl–H), 0.88 (6H, t, J ¼ 6.7 Hz, alkyl–
CH3) ppm.
All solvents and chemicals were purchased from Shanghai
reagent company and distilled over appropriate drying agents
prior to use.
3-Formylperylene (11)
Perylene (2.52 g, 10 mmol) was added to a stirred mixture of
5 cm3 anhydrous o-dichlorobenzene and 4.75g anhydrous
DMF (65 mmol), the reaction mixture was heated to 100ꢄC,
3.07g POCl3 (20 mmol) were steadily added through a drop-
ping funnel over a period of 30 min, and then stirred for an
additional 2 h at the same temperature. The reaction mixture
was cooled, and neutralized to Congo red by pouring into
dilute aqueous sodium acetate and standing at 0ꢄC for 3 h.
The precipitate was filtered off, washed with 3ꢁ30cm3
H2O, and purified by column chromatography on silica gel
with CHCl3 as eluent. Compound 11 was obtained as orange-
crystals (1.76 g, 62.8%), mp 233–235ꢄC (Ref. [19] 236ꢄC).
6,7-Bis(hexylthio)-3-methylthio-2-(3-perylenylmethylthio)-
tetrathiafulvalene (1, C40H42S8)
To a solution of 0.567 g 4 (1mmol) in 50cm3 anhydrous
degassed DMF was added a solution of 0.168g CsOHꢀ H2O
(1mmol) in 5 cm3 absolute degassed MeOH over a period of
30min. The mixture was stirred for an additional 30 min,
whereupon 0.345g 3-bromomethylperylene (9) (1mmol) in
20cm3 anhydrous DMF were introduced and orange solid
started to precipitate. The mixture was stirred for an additional
6 h, stood for 4 h, and precipitate was filtered off, washed with
3ꢁ10cm3 MeOH, and dried. Purification by column chroma-
tography on silica gel with CH2Cl2=petroleum ether (60–90ꢄC)
(1=1, v=v) as eluent, provided 0.23g orange powder (29.6%),
mp 107–110ꢄC. MS(EI): m=z ¼ 778; 1H NMR (500 MHz,
CDCl3): ꢁ ¼ 8.28–8.13 (m, 4H, Ar-H), 7.96 (d, 1H,
J ¼ 7.8 Hz, Ar-H), 7.71 (d, 2H, J ¼ 8.2 Hz, Ar-H), 7.64 (t,
1H, J ¼ 7.9 Hz, Ar-H), 7.56 (d, 1H, J ¼ 7.6 Hz, Ar-H), 7.51
(m, 2H, Ar-H), 4.95 (s, 2H, alkyl–H), 2.82 (4H, t, J ¼ 7.3 Hz,
S–CH2–), 2.46 (s, 3H, S–CH3), 1.72–1.58 (m, 4H, alkyl–H),
1.46–1.42 (m, 4H, alkyl–H), 1.30–1.25 (m, 8H, alkyl–H),
0.88 (6H, t, J ¼ 6.2 Hz, alkyl–CH3) ppm.
3-Hydroxymethylperylene (10)
A solution of sodium 0.074 g borohydride (2mmol) in 5 cm3
absolute methanol was added dropwise to a stirred solution
of 0.52 g 3-formylperylene 11 (1.86 mmol) in 100 cm3 anhy-
drous degassed THF at room temperature over a period of
2 h, then stirred for an additional 4 h. The solvent was evapo-
rated under reduced pressure. The residue was dissolved in
100 cm3 CHCl3 and washed with 3ꢁ50 cm3 H2O. After
drying (MgSO4), the solvent was evaporated under reduced
pressure, and the residue was subjected to silica column chro-
matography (CH2Cl2 as eluent) to afford yellow powder 10
(0.28 g, 53.5%), mp 204–207ꢄC (Ref. [20] 208–210ꢄC).
6,7-Bis(hexylthio)-2,3-bis(3-perylenylmethylthio)-
tetrathiafulvalene (2, C60H52S8)
To a solution of 0.303 g 5 (1mmol) in 30cm3 anhydrous
degassed DMF was added a solution of 0.235g CsOHꢀ H2O
(1.4mmol) in 5 cm3 absolute degassed MeOH over a period of
30min. The mixture was stirred for an additional 30 min,
whereupon 0.690 g 3-bromomethylperylene (9) (2 mmol) in
20 cm3 anhydrous DMF were introduced and an orange
solid started to precipitate. After standing for 10 h, the pre-
cipitate was filtered off, washed with 3ꢁ10 cm3 MeOH, and
dried. Purification by column chromatography on silica gel
with CH2Cl2=petroleum ether (60–90ꢄC) (1=1, v=v) as elu-
3-Bromomethylperylene (9, C21H13Br)
To a suspension of 0.42 g 10 (1.5 mmol) in 50 cm3 CCl4 were
added 0.49 g PBr3 (1.8 mmol) at room temperature. The re-
action mixture was heated to reflux for 2 h, the solution was
evaporated under reduced pressured at room temperature, the
residue was stirred with 40cm3 absolute MeOH, whereupon
the bromide precipitated. The mixture was filtered, and
washed with 3ꢁ10 cm3 MeOH to obtain 0.37 g orange crystals
1
(72.5%). MS(EI): m=z ¼ 345; H NMR (500MHz, CDCl3):
ꢁ ¼ 8.28–8.13 (m, 4H, Ar-H), 7.90 (d, 1H, J ¼ 7.9 Hz, Ar-

1362
H. Qiu et al.
ent, gave 0.078 g orange powder (15.2%), mp 134–138ꢄC.
MS(EI): m=z ¼ 1028; 1H NMR (500 MHz, CDCl3):
ꢁ ¼ 8.28–8.13 (m, 4H, Ar-H), 7.96 (d, 1H, J ¼ 7.8 Hz, Ar-
H), 7.71 (d, 2H, J ¼ 8.2 Hz, Ar-H), 7.64 (t, 1H, J ¼ 7.9 Hz,
Ar-H), 7.56 (d, 1H, J ¼ 7.6 Hz, Ar-H), 7.51 (m, 2H, Ar-H),
4.95 (s, 2H, alkyl–H), 2.82 (4H, t, J ¼ 7.3 Hz, S–CH2–),
1.72–1.58 (m, 4H, alkyl–H), 1.46–1.42 (m, 4H, alkyl–H),
1.30–1.25 (m, 8H, alkyl–H), 0.88 (6H, t, J ¼ 6.2 Hz, alkyl–
CH3) ppm.
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3-(2-Cyanoethylthio)-6,7-bis(hexylthio)-2-(3-perylenyl-
methylthio)tetrathiafulvalene (3, C42H43NS8)
The synthesis procedure was the same as that of 2
described above, just the molar ratio of 5 and 9 was 1:1.
The product is an orange powder, yield: 17.1%, mp 162–
1
164ꢄC. MS(EI): m=z ¼ 817; H NMR (500 MHz, CDCl3):
ꢁ ¼ 8.28–8.13 (m, 4H, Ar-H), 7.96 (d, 1H, J ¼ 7.8 Hz, Ar-
H), 7.71 (d, 2H, J ¼ 8.2 Hz, Ar-H), 7.64 (t, 1H, J ¼ 7.9 Hz,
Ar-H), 7.56 (d, 1H, J ¼ 7.6 Hz, Ar-H), 7.51 (m, 2H, Ar-H),
4.95 (s, 2H, alkyl–H), 2.81 (4H, t, J ¼ 7.3 Hz, S–CH2–),
2.74 (2H, t, J ¼ 7.4 Hz, S–CH2–CH2–CN), 1.72–1.58 (m,
4H, alkyl–H), 1.46–1.42 (m, 4H, alkyl–H), 1.30–1.25 (m,
8H, alkyl–H), 0.88 (6H, t, J ¼ 6.2 Hz, alkyl–CH3) ppm.
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Acknowledgements
This work was supported by National Science Foundation of
China (No. 20676036), the Key Project of Chinese Ministry of
Education (No. 03053), and the foundation of East China
University of Science and Technology.
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