precursors, 4 and 9, through the reaction of commercially
available phthalonitrile or 2,3-naphthalene-dicarbonitrile with
lithium methoxide. Bent conformations of 4 and 9 due to the
presence of the internal sp3 carbons are responsible for the
increased solubilities of these complexes in common organic
solvents. Thermal and photochemical conversions of the
precursors into CuPc or CuNc were examined by thermo-
gravimetric and photometric analyses, as well as by visual
demonstration of the color changes. In addition, we could
even perform calligraphic painting using ‘insoluble’ CuPc,
which implies that our compounds can also be applied to
novel functional colorants (see Fig. S3, ESIw). Our method is
superior in terms of cost and ease of preparation, compared to
the previous Pc precursors.
Fig. 2 Weight loss of 4 (dashed line) and 9 (solid line) during the
course of thermal elevation under nitrogen. Scan rate = 5.0 K minÀ1
.
occurs in the radical or anion form, it is conceivable that the
generated CuPc or CuNc skeleton received missing electrons
from the air. Results of the elemental analyses of the products
(found C, 66.51; H, 2.83; N, 19.22%, calcd for C32H16N8Cu
(CuPc): 66.72; H, 2.80; N, 19.45%; found C, 72.79; H, 3.02; N,
14.10%, calcd for C48H24N8Cu (CuNc): C, 74.26; H, 3.12; N,
14.43%) are also consistent with the thermal formation of
CuPc and CuNc. Comparison of the X-ray powder diffraction
pattern of the generated CuPc with that provided in the
literature suggests that the generated crystalline powder can
be characterized as the so-called a-phase CuPc (Fig. S1, ESIw).15,16
In order to observe spectral changes associated with the
transformations, the thermal conversions were attempted in
solution. As shown in Fig. S2a and b (ESIw), compounds 4 and
9 have practically no absorption bands above 500 nm in 1,2,4-
trichlorobenzene (TCB). Upon heating at 180 1C, prominent
Q absorption bands appeared at 676 and 775 nm for 4 and 9,
respectively. The spectral shapes and energies are strongly
indicative of the formation of CuPc and CuNc in TCB.17–19
Fig. 3 shows the color appearance observed before and after
the thermal conversion processes. In the solution phase, an
almost colorless dilute solution of 4 in TCB turned into the
sky-blue of CuPc as a result of heating the solution at 180 1C
for 20 min (Fig. 3a). A colorless coating on an ITO glass
electrode by using 4 dissolved in acetone can be converted
thermally into an insoluble, blue CuPc thin-film by heating at
as low as 85 1C for ca. 1 min (Fig. 3b), indicating that the
conversion temperature depends on the morphologies of 4.
Conversion of 4 into CuPc can also be achieved photo-
chemically. Fig. S2c (ESIw) displays the spectral changes in
the course of photo-irradiation of 4 dissolved in TCB. Upon
photo-irradiation by a deuterium lamp at room temperature,
the Q band at 676 nm gained intensity, clearly indicating the
formation of CuPc. A similar experiment was also performed
for 9, which, however, resulted in the severe decomposition of
the compound.
This work was partially supported by a Grant-in-Aid for
Scientific Research (C), No. 22550052 (TF), and by a
Grant-in-Aid for Scientific Research on Innovative Areas
(No. 20108007, ‘‘p-Space’’) from the MEXT (NK). TF is
also grateful to Kinki Regional Invention Foundation and
Mitsubishi Chemical Corporation Fund for their financial
support. We acknowledge Prof. Fumitoshi Kaneko for his
help in X-ray powder diffraction data collection.
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c
8520 Chem. Commun., 2011, 47, 8518–8520
This journal is The Royal Society of Chemistry 2011