2,3-Tetrakis[4-(N-2-naphthyl-N-phenylamino)phenoxy]-substituted metal-free and metal phthalocyanines as a novel class of amorphous molecular materials

Article abstract of DOI:10.1246/cl.2001.788

A novel family of metal-free and metal phthalocyanines containing triarylamine moieties are synthesized. These compounds are well soluble and readily form stable amorphous glasses with high glass transition temperatures, as evidenced by differential scanning calorimetry and X-ray diffraction, and constitute a new class of amorphous molecular materials.

Full text of DOI:10.1246/cl.2001.788

788
Chemistry Letters 2001
2,3-Tetrakis[4-(N-2-naphthyl-N-phenylamino)phenoxy]-substituted Metal-free and Metal
Phthalocyanines as a Novel Class of Amorphous Molecular Materials
Martin Ottmar, Toshiki Ichisaka, L. R. Subramanian,† Michael Hanack,† and Yasuhiko Shirota*
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamadaoka, Suita, Osaka 565-0871
†Institut für Organische Chemie, Fakultät für Chemie und Pharmazie, Universität Tübingen, D-72076 Tübingen, Germany
(Received May 11, 2001; CL-010436)
A novel family of metal-free and metal phthalocyanines con-
synthesis of 4, 7 was treated with ammonia in methanol to give
the isoindolenine 8, which was condensed to the corresponding
dichlorosilicon phthalocyanine with silicon tetrachloride in qui-
noline. After hydrolysis to its dihydroxy analogue, reaction with
triisopropylsilyl triflate in dichloromethane and pyridine gave 4.
1–4 were all obtained as mixtures of the four constitutional iso-
mers that normally form during synthesis of 2,3-tetrasubstituted
phthalocyanines due to statistical orientation of the 4-substituted
precursor nitrile in yields shown in Table 1. Scheme 1 shows
only the most symmetrical C4v isomer. The isomers’ existence
alone generally does not prevent the formation of crystalline
solids despite contributing to solid state disorder.2
taining triarylamine moieties are synthesized. These compounds
are well soluble and readily form stable amorphous glasses with
high glass transition temperatures, as evidenced by differential
scanning calorimetry and X-ray diffraction, and constitute a new
class of amorphous molecular materials.
Actual applications usually require materials as solids.
Hence, the solid state morphology of candidate materials and con-
trol over it is of great interest in materials science. The inevitable
presence of grain boundaries in polycrystalline materials can
affect the performance of electronic and optoelectronic devices
due to possible electric short circuits or light scattering. By con-
trast, amorphous molecular materials have recently demonstrated
their suitability and versatility in a number of roles in organic
optoelectronic devices.1 We report here the creation of a novel
class of amorphous molecular materials containing phthalocya-
nine cores. Phthalocyanines have seen more than sixty years of
active scientific pursuit and refinement from a class of simple pig-
ments into functional materials for a wide range of purposes.2
However, they are generally crystalline and many are also insolu-
ble in organic solvents. It is therefore of both fundamental and
technological interest to develop soluble and amorphous glass-
forming phthalocyanines with high glass transition temperatures
(Tgs). To our best knowledge, known examples of such phthalo-
cyanines are very scarce and have comparatively low Tgs. 3
In this study, four new, soluble phthalocyanines that readily
form stable amorphous glasses with high Tgs were synthesized,
comprising 2,3-tetrakis[4-(N-2-naphthyl-N-phenylamino)phen-
oxy]phthalocyanine 1, 2,3-tetrakis[4-(N-2-naphthyl-N-phenyl-
amino)phenoxy]phthalocyaninato copper 2, 2,3-tetrakis[4-(N-2-
naphthyl-N-phenylamino)phenoxy]phthalocyaninato titanium
oxide 3 and 2,3-tetrakis[4-(N-2-naphthyl-N-phenylamino)phen-
oxy]phthalocyaninato bis(triisopropylsiloxy)silicon 4. These
compounds constitute a new class of phthalocyanines whose
molecular architecture differs significantly from that of previ-
ously reported ones.
1–4 were synthesized as shown in Scheme 1. N-Phenyl-2-
naphthylamine was treated with 4-iodoanisole in the presence of
potassium carbonate, 18-crown-6 ether and copper powder to give
N-(4-methoxyphenyl)-N-phenyl-2-naphthylamine 5, which was
deprotected to the free phenol 6 with boron tribromide in dry
dichloromethane under nitrogen at –78 °C, and subsequently
reacted with 4-nitrophthalonitrile in DMSO in the presence of
potassium carbonate to give the phthalocyanine precursor 7. 1–3
were synthesized directly from 7 in 1-pentanol catalyzed by 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU). For 2 and 3, anhydrous
copper chloride and titanium tetra-n-butoxide served as metal
sources. 1 also forms as a by-product of 3 in low yield. For the
1–4 were purified by silica-gel column chromatography.
Precipitation from dichloromethane with excess methanol gave
turquoise (1, 2) or green powders (3), while solvent evaporation to
dryness afforded dark blue or dark green flakes. 4 could not be
precipitated with methanol and was obtained as blue flakes with a
violet sheen. 1–4 were identified by various spectroscopic meth-
ods, mass spectrometry and elemental analysis.4
The four synthesized new phthalocyanines were obtained as
amorphous solids despite attempted crystallization from solu-
tion. Their amorphous glassy state was evidenced by polarized
light microscopy, X-ray diffraction (XRD) and differential scan-
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
789
ning calorimetry (DSC). All samples showed only broad haloes
in their diffraction patterns, and exhibited defined, high Tgs in
their DSC thermograms (see Table 1). Upon further heating
above the Tgs, no crystallization was observed. They are well sol-
uble in organic solvents such as dichloromethane, chloroform,
toluene and THF, 4 also in acetone. Amorphous thin films were
obtained easily by spin coating onto glass substrates from solu-
tion. The morphological stability of 3 was found to be greatly
improved over its polymorphic parent compound PcTiO, whose
vacuum deposited amorphous film swiftly crystallizes to its α-
phase under exposure to ethanol or THF vapors.5 1–4 do not
show any morphological changes from exposure to solvent
vapors.
of 1–3, the amorphous state demonstrably prevails over crys-
tallinity despite the aggregation. It can therefore be safely
assumed that there is only a short-range ordering into very likely
irregularly spaced, short stacks that lack the long-range order
required for crystal formation. By contrast, bisaxially bulkily sub-
stituted 4 shows very clearly that it is not aggregated in the amor-
phous solid state, and retains the highly desirable optical proper-
ties of the isolated molecule as in solution.
In summary, we have synthesized a new class of well soluble
and amorphous phthalocyanines with high Tgs that readily form
stable, uniform amorphous thin films by spin coating and are of
high interest for their optical and electronic properties. They are
expected to find application in organic devices, into which
research is currently under way.
M. O. thanks the Japan Society for the Promotion of Science
(JSPS) for a post-doctoral grant.
References and Notes
1
2
Y. Shirota, J. Mater. Chem., 10, 1 (2000) and references cited therein.
a) “Phthalocyanines, Properties and Applications” ed. by C. C. Leznoff
and A. B. P. Lever, VCH, New York, (1989–1996), Vol. 1–4. b) M.
Hanack and M. Lang, Adv. Mater., 6(11), 819 (1994) and references
cited therein. c) D. Hohnholz, S. Steinbrecher, and M. Hanack, J. Mol.
Struct., 231, 521 (2000) and references cited therein.
3
4
a) R. D. George and A. W. Snow, Chem. Mater., 6(10), 1587 (1994). b)
N. B. McKeown, Adv. Mater., 11(1), 67 (1999). c) M. Brewis, G. J.
Clarkson, A. M. Holder, and N. B. McKeown, Chem. Commun., 1998,
969. d) M. Brewis, G. J. Clarkson, V. Goddard, M. Helliwell, A. M.
Holder, and N. B. McKeown, Angew. Chem. Int. Ed., 37(8), 1092
(1998).
(2-NDPAO)4PcM Series: 1: MS (FD, m/z): 1751.5, 875.8, 583.9. IR
(cm–1): 3053, 3035, 1591, 1499, 1399, 1331, 1269, 1228, 1119, 1072,
1
949, 748, 696. H NMR (CDCl3): Signals marked br are broad, unre-
solved bands. δ = 6.97–7.05 (4H, m), 7.18–7.40 (48H, m; CHCl3),
7.49–7.53 (4H, m), 7.55–7.62 (4H, m), 7.69–7.74 (8H, m), 7.81–8.25
(8H, br). Anal. Calcd for C120H78N12O4: C, 82.27; H, 4.49; N, 9.59%.
Found: C, 82.24; H, 4.77; N, 9.27%. 2: MS (FD, m/z): 1813.1, 906.6,
604.1. IR (cm–1): 3054, 3036, 1591, 1499, 1467, 1403, 1267, 1229,
1118, 1093, 1052, 951, 848, 815, 747, 695. Anal. Calcd for
C120H76N12O4Cu: C, 79.48; H, 4.22; N, 9.27%. Found: C, 79.36; H,
4.68; N, 8.62%. 3: MS (FD, m/z): 1813.4, 906.7, 604.5, 453.7. IR
(cm–1): 3053, 3035, 1591, 1499, 1 399, 1331, 1269, 1228, 1119, 1072,
949, 748, 696. 1H NMR (CDCl3): δ = 6.98–7.10 (4H, m), 7.11–7.45
(44H, m), 7.49–7.57 (4H, m), 7.58–7.67 (4H, m), 7.68–7.88 (12H, br),
8.36–9.15 (8H, br). Anal. Calcd for C120H76N12O5Ti C, 79.46; H, 4.22;
N, 9.27%. Found: C, 79.23; H, 4.52; N, 9.10%. 4: MS (FD, m/z):
2125.0, 1951.0, 1327.1 IR (cm–1): 3054, 3003, 2940, 2861, 1616, 1592,
1499, 1468, 1406, 1353, 1330, 1269, 1231, 1204, 1120, 1081, 1058,
All the synthesized compounds show electronic absorption
spectra composed of the characteristic Q (red region) and Soret
bands (blue region) of a phthalocyanine, the latter overlapping
with their quadruple arylamine chromophores’ absorption (see
also Table 1). Figure 1 shows a comparison of the electronic
absorption spectra of 2 and 4 in solution and as amorphous spin
coated thin films. While 1, 2 and 3 show aggregation in the solid
state, visible in 2’s spectrum (see Figure 1, Ib) as a broadening of
the Q band into the red region accompanied by a substantial
decrease in intensity, 4 is not aggregated and retains the absorp-
tion properties of the solution (see Figure 1, IId).
1
1022, 957, 881, 848, 814, 762, 746, 696, 476. H NMR (CDCl3): δ =
–2.07 to –1.96 (6H, m), –1.16 to –1.09 (36H, d), 7.03–7.13 (4H, m),
7.25–7.46 (48H, m), 7.52–7.84 (12H, m), 7.95–8.01 (4H, m), 9.10–9.14
(4H, m), 9.47–9.62 (4H, m). Anal. Calcd for C138H118N12O6Si3 C,
78.01; H, 5.60; N, 7.91%. Found: C, 78.18; H, 65.95; N, 7.54%.
a) T. Tsuzuki, Y. Kuwabara, N. Noma, Y. Shirota, and M. R. Willis,
Jpn. J. Appl. Phys., 35, L447 (1996). b) H. S. Nalwa, T. Saito, A.
Kakuta, and T. Iwayanaji, J. Phys. Chem., 97, 10515 (1993).
a) M. J. Stillman and T. Nyokong in “Phthalocyanines, Properties and
Applications” ed. by C. C. Leznoff and A. B. P. Lever, VCH, New
York, (1986), Vol. 1. b) W. J. Schutte, M. Sluyters-Rehbach, and J. H.
Sluyters, J. Phys. Chem., 97, 6069 (1993). c) M. Cook, Pure Appl.
Chem., 71(11), 2145 (1999).
5
6
Aggregation is a well-known phenomenon for phthalocyan-
ines whose cores are not kept apart by bulky peripheral or bis-
axial substituents, resulting from co-facial π–π interactions
between the macrocycle discs.6 It should be noted that in the case