A naked-eye colorimetric indicator to discriminate aromatic compounds by solid-state charge-transfer complexation

Article abstract of DOI:10.1246/cl.2008.550

A colorimetric indicating system has been developed using solid-state charge-transfer complexation to demonstrate color changes in response to various aromatic compounds and their isomers that provide no color changes under diluted solution conditions. Copyright

Full text of DOI:10.1246/cl.2008.550

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50
Chemistry Letters Vol.37, No.5 (2008)
A Naked-eye Colorimetric Indicator to Discriminate Aromatic Compounds
by Solid-state Charge-transfer Complexation
ꢀ
ꢀ
Darshak R. Trivedi, Yuzo Fujiki, Yuta Goto, Norifumi Fujita, Seiji Shinkai, and Kazuki Sada
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University,
44 Motooka, Nishi, Fukuoka 819-0395
7
(Received February 18, 2008; CL-080184; E-mail: sadatcm@mbox.nc.kyushu-u.ac.jp)
A colorimetric indicating system has been developed using
O
N
O
O
N
O
solid-state charge-transfer complexation to demonstrate color
changes in response to various aromatic compounds and their
isomers that provide no color changes under diluted solution
conditions.
N
N
1
2
3
NDI
2
6: R = N(CH3)2
7: R2 = OH
: R = OCH3
R2
2
8
9
2
: R = CH3
10:R = CHO
Color-change observable by the naked eye is the easiest
method to detect chemicals and chemical reactions, and has been
attracting many chemists to develop qualitative or quantitative
analyzing systems accompanied with color changes. Most of
the colorimetric indicators are reported to detect metal ions or
anions by changes of intermolecular charge-transfer bands
of chromogenic signalling units. However, research efforts
towards the establishment of qualitative colorimetric indicators
2
6
-14
4
5
2
11:R = Cl
n-C9H19
OH
2
OH
OH
OH
OH
12:R = COOH
3:R = SO3H
4:R = CN
2
1
1
2
1
5
OH
16
17
18
19
NH2
O
CCl3
CH
1
–3
for organic compounds are still in infancy. Moreover, most
of them are performed in solution states, and design of solid-
state indicators in the absence of any solvent is still in demand
Cl
Cl
NH2
20
21
22
4
from green-chemistry. Thus, here we wish to report a novel
colorimetric indicator for a wide range of aromatic compounds
Chart 1. Structures of NDI and analytes used in the present in-
dicator system.
3
by solid-state formation of charge-transfer (CT) complexes.
4
,5
Solvent-free co-grinding of analytes with the indicator provid-
ed more vivid color changes in comparison with those in the
solution states.
indicated that as ꢀ-electron conjugation increases, the ꢁmax of
the CT complexes also shifts towards higher value. Thus, poly-
aromatic hydrocarbons can easily be identified by visualization
of color changes in the presence of NDI. The identification limit
of the analytes by this method was about 1.0 mg (ꢁ0:00625
mmol) of analytes means it can be consider as a qualitative
analysis aspect.
6
CT complexes in solution have been utilized rarely as chro-
3
mophores due to their low binding constants, and in the solid
7
,8
state they have attracted growing interest in the recent years.
9
Thus, inspired by result of the color-sensing organogels, here
we developed a new indicator system based on CT complexation
in the solid state. We chose a naphthalenediimide (NDI) deriva-
tive as the acceptor molecule, because NDI easily forms inclu-
sion crystals with DMF by recrystallization, and does not form
one-dimensional columnar structures or ꢀ–ꢀ stacking structures
of naphthalenediimide groups in the crystalline state. In this re-
port, we demonstrate the appearance of colorful CT complexes
of NDI with a wide variety of aromatic compounds as summariz-
Formation of the CT complexes by the solid-state reaction
1
1
was monitored by X-ray diffractions. For example, the pow-
dered sample of NDI and 5 freshly prepared by mixing in the
solid state revealed that the solid-state reaction provides the
same crystal structure as that from the solution as shown in
Figure 2. After 30 min grinding of NDI and 5 in a 1:1 molar ratio
in the solid state, new crystalline morph was observed which is
different from the starting materials NDI and 5, and identical to
the simulated diffraction pattern of a single crystal obtained from
the solution. The similarity of the product is in contrast to the
1
0
4
,5
ed in Chart 1 by the solid-state co-grinding technique.
The naphthalenediimide (NDI) was synthesized by a report-
ed procedure (ESI).12 Without any electron-donors, it was slight-
ly yellow-colored powder after recrystallization from DMF
followed by drying in vacuo. In a typical experiment, NDI and
an aromatic molecule have been taken in a 1:1 molar ratio in
the solid state in molten pastern and ground. Within one minute,
colors originating from CT complexation were developed. Pro-
longed grinding for 30 min made the mixture much brighter.
The acceptor NDI forms the CT complexes (1NDI–5NDI) with
a series of polyaromatic hydrocarbons (Chart 1); orange-yellow
color for 1, yellow with 2, gray-green with 3, dark yellow with 4,
and orange with 5 as shown in Figure 1.
7
result reported recently in a similar CT complex formation. In
the crystal structure of 5NDI, the two ꢀ-electron planes of
NDI and 5 are in close proximity to form the charge-transfer
complex between the donor and the acceptor (distance between
˚
two ꢀ planes is 3.316–3.390 A). The stacking of the ꢀ-electron
planes with offset formed one-dimensional columnar assemblies
slightly tilting from the perpendicular axis of the ꢀ-electron
planes.
Since stronger electron donors are expected to form
CT complexes more red-shifted ꢁmax in the visible region, and
the electron-donating properties of the aromatic donors depend
upon the functional groups on the aromatic ring of the donors,
Solid-state visible absorption spectra of these complexes
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.5 (2008)
551
pollutants such as potent endocrine disruptors and some model
compounds of persistent organic pollutants. Bisphenol A (18),
a)
4-nonylphenol (19), 1,5-diaminonaphthalene (20), and dibenzo-
furan (21) can be identified by different color CT complex for-
12
mation with acceptor molecule NDI, as shown in Figure SI2.
It is important to mention that in the present studies, acceptor
NDI did not form a CT complex with well-known toxic chemical
DDT (22).
1NDI
2NDI
3NDI
4NDI
5NDI
b)
1
1
0
0
0
0
0
0
0
0
0
0
.1
.0
.9
.8
.7
.6
.5
.4
.3
.2
.1
.0
1NDI
2
3
NDI
NDI
4NDI
5NDI
NDI
In summary, the use of simple solid-state co-grinding com-
bined with CT complexation allows remarkable qualitative
colorimetric recognition of a vast range of aromatic molecules
5
by the naked eye. The solid-state co-grinding with aromatic liq-
-0.1
4
00
600
800
uids and solids easily provided solvent-free highly concentrated
conditions that promote the formation of the CT complexes
with brighter color changes than those in the solution and gel
state. Thus, for the first time, solid-state CT complexation ena-
bles us to demonstrate the color changes in response to various
aromatic compounds that provide no color changes under the
diluted solution conditions. Combinatorial approaches or two-
λ / nm
Figure 1. (a) CT complexes of NDI with a series of polyaro-
matic compounds and (b) their solid-state absorption spectra.
a)
5NDI simulated from single crystal X-ray
1
c,13
dimensional array
by changing acceptor molecules should
provide more accurate identifying tools for isomers of more
complicated aromatic compounds and other organic molecules
with an aromatic ring including highly toxic and environmental
pollutants and regulated narcotics are currently underway in
our laboratory.
5
NDI solid state synthesis
5
NDI
5
10
15
20
25
30
2
θ / deg
Financial support for this research was provided by the
Grand-in-Aid (S) from the Ministry of Education, Culture,
Sports, Science and Technology of Japan (MEXT) for K. S.
and S. S. DRT thankfully acknowledge JSPS for financial
support.
b)
References and Notes
1
a) J. S. Kim, S. J. Lee, J. H. Jung, I. Hwang, N. J. Singh, S. K. Kim, S. H.
Lee, H. J. Kim, C. S. Keum, J. W. Lee, K. S. Kim, Chem.—Eur. J. 2007,
13, 3082. b) J. H. Jung, S. J. Lee, J. S. Kim, W. S. Lee, Y. Sakata, T.
Kaneda, Org. Lett. 2006, 8, 3009. c) N. A. Rakow, A. Sen, M. C. Janzen,
J. B. Ponder, K. S. Suslick, Angew. Chem., Int. Ed. 2005, 44, 4528.
Y.-P. Tseng, G.-M. Tu, C.-H. Lin, C.-T. Chang, C.-Y. Lin, Y.-P. Yen,
Org. Biomol. Chem. 2007, 5, 3592.
F. L. Dickert, P. Lieberzeit, M. Tortschanoff, Sens. Actuators, B 2000,
65, 186.
F. Toda, Acc. Chem. Res. 1995, 28, 480.
A. V. Trask, W. Jones, Topics in Current Chemistry, 2005, Vol. 254,
p. 41, and references cited therein.
For example: a) D. E. Laskowski, W. C. McCrone, Anal. Chem. 1954,
26, 1497. b) J. O. Onah, Acta Pharm. 1999, 49, 217.
For examples see: a) Y. Imai, N. Tajima, T. Sato, R. Kuroda, Org. Lett.
2
3
Figure 2. (a) Comparison of XRPD patterns of complex 5NDI
in different crystallization condition, together with 5 and NDI,
(
b) crystal packing diagram for 5NDI.
4
5
we further investigated the solid-state complexation of NDI with
1
2
a series of 2-substituted naphthalene (Figure SI1).
6
7
It is quite interesting that some aromatic compounds had no
obvious color changes in the solution mixtures. The highly con-
centrated state in the solid-solid co-grinding mixtures should
promote the formation of CT complexes and develop vivid
colors. Moreover, the absorption maxima of the CT complexes
were red-shifted according to increase in the electron-donating
abilities, and the present system showed a good correlation of
the Hammett constant and ꢁmax of the CT complex in the solid
state (Figure SI1).12 Another important merit of the present indi-
cator system is visualization of the differences of the isomers.
For examples, co-grinding of NDI with stoichiometric amount
of o-, m-, and p-cresol present as a liquid at room temperature,
provided the CT complexes with the different colors which
can be easily visualized by the naked eye. Moreover, solid-state
grinding of molecule NDI to form CT complexes could be
applicable for liquid donors. Finally, the most important aspect
for this system is applicability to a wide range of toxic aromatic
2006, 8, 2941. b) Y. Imai, N. Tajima, T. Sato, R. Kuroda, Chirality 2002,
14, 604.
8
9
1
S. Shimomura, R. Matsuda, T. Tsujino, T. Kawamura, S. Kitagawa,
J. Am. Chem. Soc. 2006, 128, 16416.
P. Mukhopadhyay, Y. Iwashita, M. Shirakawa, S. Kawano, N. Fujita,
S. Shinkai, Angew. Chem., Int. Ed. 2006, 45, 1592.
J. Mizuguchi, T. Makino, Y. Imura, H. Takahashi, S. Suzuki, Acta
Crystallogr., Sect. E 2005, 61, o3044.
0
11 Crystal data for 5NDI (CCDC 662775) at 298 K: C40H22N4O4, Triclinic
ꢀ
˚
˚
ꢂ
˚
˚ 3
P1, a ¼ 7:9274ð16Þ A, b ¼ 9:1680ð19Þ A, c ¼ 10:337ð2Þ A, ꢂ ¼
ꢂ
ꢂ
8
9:515ð4Þ , ꢃ ¼ 88:543ð4Þ , ꢄ ¼ 72:661ð5Þ , V ¼ 716:9ð3Þ A , Z ¼ 2,
ꢃ3
dcalcd ¼ 1:442 g cm , 3269 reflections measured, 1459 unique reflec-
tions. Final R1 ¼ 0:0476 and wR2 ¼ 0:1267. This crystallographic data
have been deposited with CCDC as no. 662775. Copy of the data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html
or as ESI on the CSJ journal website.12
12
Supporting Information is available electronically on the CSJ-Journal
Web site, http://www.csj.jp/journals/chem-lett/.
13 N. A. Rakow, K. S. Suslick, Nature 2000, 406, 710.
Published on the web (Advance View) April 19, 2008; doi:10.1246/cl.2008.550