Synthesis and light absorption/emission properties of novel bis-squaraine dyes with extensively conjugated π-electron systems

Article abstract of DOI:10.1039/b203793a

Novel symmetrical bis-squaraine dyes have been synthesised, in which two squaryl moieties are conjugatively linked by a phenylene or biphenyl unit. Such linkages produce significant perturbation of the absorption and fluorescence spectra in comparison wit

Full text of DOI:10.1039/b203793a

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Synthesis and light absorption/emission properties of novel
bis-squaraine dyes with extensively conjugated ꢀ-electron systems
Shigeyuki Yagi,* Shin Murayama, Yutaka Hyodo, Yoshihiko Fujie, Msahiko Hirose and
Hiroyuki Nakazumi*
1
Department of Applied Materials Science, Graduate School of Engineering,
Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan
Received (in Cambridge, UK) 18th April 2002, Accepted 14th May 2002
First published as an Advance Article on the web 27th May 2002
Table 1 Selected bond lengths in the solid state structure of 1a with
Novel symmetrical bis-squaraine dyes have been synthe-
sised, in which two squaryl moieties are conjugatively
linked by a phenylene or biphenyl unit. Such link-
ages produce significant perturbation of the absorption
and fluorescence spectra in comparison with analogous
symmetrical mono-squaraine dyes.
their estimated standard deviations in parentheses
Bond
Length/Å
Bond
Length/Å
O1–C11
O2–C13
C10–C11
1.230(5)
1.236(5)
1.520(6)
C10–C13
C11–C12
C12–C13
1.485(6)
1.444(6)
1.445(6)
Introduction
1,3-Squaraines† (SQs), often called squaryliums, exhibit
unique optical properties such as large light absorption, intense
fluorescence emission, and photoconductivity, and they have
been applied in the optoelectronics fields such as optical
recording,1 solar energy conversion,2 electrophotography,3 and
emitting layers and emitting dopants in EL devices.4 Although
the limitation in synthetic methodology affording symmetrical
SQ dyes5 has suppressed the development of SQ dyes in
material fields, recent achievements in preparation of unsym-
metrical SQ dyes6 and new classes of SQ homologues7 should
lead to wider utility of SQ dyes and their related compounds.
Therefore, the investigation of new electronic structures of SQ
derivatives should prompt research into optical and electro-
chemical properties for material uses. In the present paper, we
report the synthesis of a series of novel bis-squaraine dyes in
which two squaryl units are bridged by a phenylene or biphenyl
spacer. Tuning the light absorption and fluorescence emission
properties of the dyes is allowed by varying the spacer as well as
the heterocyclic components at both ends of the dye skeleton.
Fig. 1 The structure of the bis-squaraine dye 1a with the atom
numbering labels. Hydrogen atoms are omitted for clarity.
conjugated π-electron system. The bond lengths of O1–C11,
O2–C13, C10–C13, C11–C12, and C12–C13 exhibit conjugated
C᎐O and C᎐C bond characters, respectively (Table 1), whereas
᎐
᎐
the C10–C11 bond is approximately a single bond. Thus, such a
difference in the bond order indicates that the π-electrons in the
cyclobutene rings are significantly localized.
In Fig. 2 are shown typical examples of the electronic absorp-
tion (Fig. 2a) and fluorescence emission (Fig. 2b) spectra of the
bis-squaraine dyes. Various combinations of the spacer with
heterocyclic moieties afforded a wide range of variation in the
electronic absorption and fluorescence emission properties of
the bis-squaraine dyes, as summarized in Table 2. The absorp-
tion maxima of the dyes presented here vary from green (2b; λabs
= 543 nm in CHCl3) to near-IR region (3a; λabs = 768 nm). The
dyes bearing p-phenylene spacers 1a–4a exhibited bathochromic
shifts of λabs, compared with the dyes 1b–3b and 1c–2c which
have m-phenylene and biphenyl spacers, respectively. As
expected from the absorption spectra, the fluorescence emission
Results and discussion
As shown in Scheme 1, the synthesis of bis-squaraine dyes
1–4 started from the corresponding bissquaric acids 7a–c. In a
similar manner to the Liebeskind’s method,8 the Pd-catalyzed
cross-coupling reaction of (tributylstannyl)cyclobutenedione 5
and aromatic diiodides afforded bissquarates 6a–c in 53–82%
yields, which were converted to bissquaric acids 7a–c by acid-
promoted hydrolysis in 53–79% yields. Condensation of 7a–c
with heterocyclic methyl quaternary salts was carried out
in butan-1-ol–benzene (4 : 1, v/v) in the presence of a small
amount of quinoline or triethylamine, affording the bis-
squaraine dyes 1–4 in 8–90% yields. The characterization by 1H
NMR, MALDI-TOF mass and IR spectra as well as elemental
analysis afforded satisfactory data for each bis-squaraine dye.
As shown in Fig. 1, the structure of one of the bis-squaraine
dyes 1a was confirmed by X-ray crystallographic analysis.9
A single crystal suitable for X-ray analysis was obtained by
solvent diffusion from a CHCl3–MeOH solution of 1a to
diethyl ether. The structure clearly shows that two indolinyl-
idenemethylcyclobutene moieties are introduced to the central
p-phenylene group, and the molecule of 1a adopts a highly
planar structure: the mean deviation of the atoms in the
π-conjugation (C1–C16, N1, O1, and O2) from the least-squares
plane is 0.0494 Å. Therefore, 1a possesses an extensively
maxima were observed in the region from green–red (3b; λem
=
571 nm) to near-IR (3a; λmax = 809 nm), although the emission
intensity of each dye was approximately an order of magnitude
smaller than that of the bisanilinosquaraine dye 8 as a typical
emissive squaraine derivative. The excitation maxima of the
dyes were almost the same as the λabs, and the Stokes shifts were
moderate or not so large.
DOI: 10.1039/b203793a
J. Chem. Soc., Perkin Trans. 1, 2002, 1417–1419
This journal is © The Royal Society of Chemistry 2002
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Scheme 1
Conclusions
In summary, the synthesis of novel bis-squaraine dyes has been
demonstrated by employing bissquaric acid intermediates 7a–c
and heterocyclic methyl quaternary salts as starting materials,
and their light absorption and fluorescence emission properties
have been described. Various combinations of the heterocyclic
components with the central aromatic ring led to tuning of
absorption and fluorescence emission maxima of the dyes.
Applications of the absorption and emission properties of these
dyes are under investigation.
Experimental
Typical procedure for synthesis of the bis-squaraine dyes
(synthesis of 1a)
To a mixture of 7a (50 mg, 0.19 mmol) and 1-butyl-2,3,3-
trimethylindolium iodide (127 mg, 0.37 mmol) in 10 mL of
butan-1-ol–benzene (4 : 1, v/v) was added 0.1 mL of quinoline,
and then, the mixture was heated at 100 ЊC for 5 h. After cool-
ing, the solvent was removed on a rotary evaporator, and the
residue was purified by silica gel column chromatography
(chloroform–methanol, 10 : 1, v/v, as eluent). Further purifi-
cation by recrystallization chloroform–methanol–diethyl ether
afforded a crystal of 1a (92 mg, 0.14 mmol).
1a: Yield 75%. Mp 280–281 ЊC (dec). IR 1567, 1606, 1731
1
cmϪ1. H NMR (270 MHz, CDCl3–CD3OD, 4 : 1, v/v, 25 ЊC)
δ (ppm) = 1.04 (t, J = 7.6 Hz, 6H), 1.26–1.64 (m, 8H), 1.86
(s, 12H), 4.39 (t, J = 7.6 Hz, 4H), 6.53 (s, 2H), 7.36–8.26 (m,
8H), 8.28 (s, 4H). TOF-MS (m/z) 664 (Mϩ). Anal. Calcd for
C44H44N2O4: C, 79.49; H, 6.67; N, 4.21%. Found: C, 79.29;
H, 6.90; N, 3.95%.
Fig. 2 (a) Electronic absorption and (b) fluorescence emission spectra
of 1a, 1b, and 1c in CHCl3 at 25 ЊC. Each emission spectrum was
1b: Yield, 22%. Mp 212–213 ЊC (dec). IR 1554, 1616, 1738
cmϪ1 1H NMR (270 MHz, CDCl3, 25 ЊC) δ (ppm) = 1.02
.
monitored by excitation at λmax
.
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Table 2 Electronic absorption maxima (λabs), fluorescence emission maxima (λem), and Stokes shifts (∆λ) of bis-squaraine dyes 1, 2, 3, and 4a
Dye
λabs/nm (log ε/molϪ1 cmϪ1 dm3)
λem/nm (relative intensity)
∆λb/nm
1a
1b
1c
2a
2b
2c
3a
3b
4a
8
699 (5.25), 635 (4.93)
572 (5.27), 535 (4.87)
618 (5.28)
685 (5.28), 623 (4.99)
543 (5.15), 479 (4.71)
609 (5.01)
768 (5.13), 692 (4.80)
570 (5.30)
704 (5.29), 641 (4.98)
640 (5.50)
714 (126)
587 (56)
656 (226)
706 (206)
586 (34)
651 (157)
809 (15)
571 (3.4)
736 (77)
667 (2000)
22
13
37
21
15
32
45
1
24
12
a In CHCl3 at 25 ЊC. [dye] = 1.0 × 10Ϫ6 M. b ∆λ = λem Ϫ λex, where λex is the wavelength of the maximum peak in the excitation spectrum.
(t, J = 7.3 Hz, 6H), 1.44–1.55 (m, 4H), 1.87 (m, 16H), 4.36 (t,
J = 7.3 Hz, 4H), 6.44 (s, 2H), 7.28–7.52 (m, 9H), 8.29 (m,
2H), 9.00 (s, 1H). TOF-MS (m/z) 664 (Mϩ). Anal. Calcd for
C44H44N2O4ؒH2O: C, 77.39; H, 6.79; N, 4.10%. Found: C, 77.19;
H, 6.85; N, 3.94%.
2H), 7.76–7.80 (m, 3H), 7.90 (d, J = 8.6 Hz, 2H), 8.24–8.32
(m, 6H), 8.61 (d, J = 8.6 Hz, 2H), 8.93 (s, 1H). TOF-MS
(m/z) 632 (Mϩ). Anal. Calcd for C42H36N2O4ؒH2O: C, 77.52;
H, 5.89; N, 4.30%. Found: C, 77.40; H, 5.74; N, 4.18%.
4a: Yield, 8%. Mp 227–228 ЊC (dec). IR 1562, 1602, 1726
1
1c: Yield, 45%. Mp 260–261 ЊC (dec). IR 1556, 1616, 1739
cmϪ1. H NMR (CDCl3–CD3OD, 2 : 1, v/v, 50 ЊC) δ (ppm) =
1
cmϪ1. H NMR (270 MHz, CDCl2CDCl2–CD3OD, 1 : 1, v/v,
1.13 (t, J = 7.9 Hz, 6H), 1.66–1.74 (m, 4H), 2.01–2.11 (m, 4H),
4.79 (t, J = 7.9 Hz, 4H), 6.65 (s, 2H), 7.73 (t, J = 7.9 Hz, 2H),
7.94–8.05 (m, 6H), 8.15 (s, 4H), 8.41 (d, J = 9.2 Hz, 2H), 9.55
(d, J = 9.2 Hz, 2H). TOF-MS (m/z) 632 (Mϩ). Anal. Calcd for
C42H36N2O4ؒH2O: C, 77.52; H, 5.89; N, 4.30%. Found: C, 77.34;
H, 5.76; N, 3.98%.
25 ЊC) δ (ppm) = 1.02 (t, J = 7.6 Hz, 6H), 1.47–1.55 (m, 4H),
1.84–1.94 (m, 16H), 4.40 (t, J = 7.6 Hz, 4H), 6.50 (s, 2H), 7.51–
7.58 (m, 8H), 7.79 (d, J = 8.2 Hz, 4H), 8.24 (d, J = 8.2 Hz, 4H).
TOF-MS (m/z) 740 (Mϩ). Anal. Calcd for C50H48N2O4: C,
81.05; H, 6.53; N, 3.78%. Found: C, 80.85; H, 6.22; N, 3.59%.
2a: Yield, 90%. Mp 284–285 ЊC (dec). IR 1567, 1606, 1731
1
cmϪ1. H NMR (270 MHz, CDCl3–CD3OD, 4 : 1, v/v, 25 ЊC)
References and notes
δ (ppm) = 1.05 (t, J = 7.6 Hz, 6H), 1.51–1.60 (m, 4H), 1.91–2.01
(m, 4H), 4.55 (t, J = 7.6 Hz, 4H), 6.68 (s, 2H), 7.38–8.08 (m,
8H), 8.15 (s, 4H). TOF-MS (m/z) 644 (Mϩ). Anal. Calcd for
C38H32N2O4S2ؒ1.5H2O: C, 67.94; H, 5.25; N, 4.17%. Found: C,
67.97; H, 5.32; N, 3.82%.
† The IUPAC name for squaric acid is dihydroxycyclobutenedione.
1 J. Fabian, H. Nakazumi and M. Matsuoka, Chem. Rev., 1992, 92,
1197 and references cited therein.
2b: Yield, 30%. Mp 279–280 ЊC (dec). IR 1560, 1592, 1733
1
cmϪ1. H NMR (270 MHz, CDCl3–CD3OD, 5 : 1, v/v, 25 ЊC)
2 (a) V. Y. Merritt and H. Hovel, Appl. Phys. Lett., 1976, 29, 414; (b)
D. L. Morel, K. Ghosh, T. Feng, E. L. Stogryn, P. E. Purwin,
R. F. Shaw and C. Fishman, Appl. Phys. Lett., 1978, 32, 495.
3 K.-Y. Law, Chem. Rev., 1993, 93, 449, and references cited therein.
4 T. Mori, K. Miyachi, T. Kichimi and T. Mizutani, Jpn. J. Appl. Phys.,
1994, 33, 6594.
5 (a) A. Trebs and K. Jacob, Angew. Chem., Int. Ed. Engl., 1965, 4, 694;
(b) G. Maahs and P. Hegenberg, Angew. Chem., Int. Ed. Engl., 1966,
5, 888.
6 (a) K.-Y. Law and F. C. Bailey, J. Org. Chem., 1992, 57, 3278;
(b) E. Terpetschnig and J. R. Lakowicz, Dyes Pigm., 1993, 21, 227;
(c) S. Yagi, Y. Hyodo, S. Matsumoto, N. Takahashi, H. Kono and
H. Nakazumi, J. Chem. Soc., Perkin Trans. 1, 2000, 599.
7 (a) H. Nakazumi, K. Natsukawa, K. Nakai and K. Isagawa, Angew.
Chem., Int. Ed. Engl., 1994, 33, 1001; (b) Y. Hyodo, H. Nakazumi,
S. Yagi and K. Nakai, J. Chem. Soc., Perkin Trans. 1, 2001, 2823;
(c) S. Yagi, K. Nakai, Y. Hyodo and H. Nakazumi, Synthesis, 2002,
413.
8 (a) L. S. Liebeskind and R. W. Fengl, J. Org. Chem., 1990, 55, 5359;
(b) L. S. Liebeskind, M. S. Yu, R. H. Yu, J. Wang and K. S. Hagen,
J. Am. Chem. Soc., 1993, 115, 9048.
9 Crystal data of 1a: Formula, C44H44N2O4; molecular weight, 664.84;
crystal system, monoclinic; space group, P21/c; cell constants,
a = 8.277(6) Å, b = 18.29(6) Å, c = 12.121(10) Å, β = 106.71(7)Њ;
volume, 1757(6) Å3; Z = 2; dcalcd = 1.256 g cmϪ3; reflections, 2549;
R = 0.0579, RW = 0.173. CCDC reference number(s) 184342.
See http://www.rsc.org/suppdata/p1/b2/b203793a/ for crystallographic
files in .cif or other electronic format.
δ (ppm) = 1.05 (t, J = 7.6 Hz, 6H), 1.51–1.63 (m, 4H), 1.91–2.04
(m, 4H), 4.55 (t, J = 7.6 Hz, 4H), 6.69 (s, 2H), 7.42–8.22
(m, 9H), 8.23 (d, J = 8.2 Hz, 2H), 8.72 (s, 1H). TOF-MS
(m/z) 644 (Mϩ). Anal. Calcd for C38H32N2O4S2ؒH2O: C, 68.86;
H, 5.17; N, 4.23%. Found: C, 68.56; H, 5.54; N, 3.96%.
2c: Yield, 60%. Mp > 300 ЊC (dec). IR 1572, 1606, 1732 cmϪ1
.
1H NMR (270 MHz, CDCl3, 25 ЊC) δ (ppm) = 1.05 (t, J =
7.3 Hz, 6H), 1.59–1.70 (m, 4H), 1.89–1.97 (m, 4H), 4.43 (t, J =
7.3 Hz, 4H), 6.49 (s, 2H), 7.50–7.64 (m, 4H), 7.68–7.74 (m, 6H),
7.85 (d, J = 7.3 Hz, 2H), 8.29 (d, J = 7.9 Hz, 4H). TOF-MS
(m/z) 720 (Mϩ). Anal. Calcd for C44H36N2O4S2: C, 73.31;
H, 5.03; N, 3.89%. Found: C, 73.07; H, 4.87; N, 3.76%.
3a: Yield, 8%. Mp 286–287 ЊC (dec). IR 1575, 1614, 1716
1
cmϪ1. H NMR (270 MHz, CDCl3–CD3OD, 2 : 1, v/v, 50 ЊC)
δ (ppm) = 1.04 (t, J = 7.6 Hz, 6H), 1.44–1.58 (m, 4H), 2.00–2.08
(m, 4H), 4.72 (t, J = 7.6 Hz, 4H), 7.08 (s, 2H), 7.86 (t, J = 7.3 Hz,
2H), 8.01–8.09 (m, 8H), 8.61 (d, J = 7.3 Hz, 2H), 8.66 (d, J =
8.9 Hz, 2H), 9.36 (d, J = 8.9 Hz, 2H). TOF-MS (m/z) 632 (Mϩ).
Anal. Calcd for C42H36N2O4ؒH2O: C, 77.52; H, 5.88; N, 4.30%.
Found: C, 77.30; H, 6.14; N, 4.07%.
3b: Yield, 12%. Mp > 300 ЊC (dec). IR 1554, 1579, 1695 cmϪ1
.
1H NMR (270 MHz, DMSO-d6, 25 ЊC) δ (ppm) = 0.94 (t, J =
7.3 Hz, 6H), 1.37 (sext, J = 7.3 Hz, 4H), 1.79 (quint, J = 7.3 Hz,
4H), 4.42 (t, J = 7.3 Hz, 4H), 6.86 (s, 2H), 7.46 (t, J = 7.3 Hz,
J. Chem. Soc., Perkin Trans. 1, 2002, 1417–1419
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