Unsymmetric leuco-TAM dyes, (2E, 2′E)-2,2′-{(E)-4-phenylpent-2- ene-1,5-diylidene}bis(1,3,3-trimethylindoline) derivatives. Part II: X-ray crystal structure

Article abstract of DOI:10.1016/j.dyepig.2012.02.007

The unequivocal solid-state structure and stereochemistry of the unsymmetric leuco-triarylmethane (Un-LTAM) dye 2,2′-{(E)-4-(phenyl)pent-2- ene-1,5-diylidene}bis(1,3,3-trimethylindoline) derivatives were established using X-ray single-crystal analysis. Th

Full text of DOI:10.1016/j.dyepig.2012.02.007

Dyes and Pigments 94 (2012) 490e495
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Unsymmetric leuco-TAM dyes, (2E, 20E)-2,20-{(E)-4-phenylpent-2-ene-1,5-
diylidene}bis(1,3,3-trimethylindoline) derivatives. Part II: X-ray crystal structureq
*
Sam-Rok Keum , So-Young Ma, Do-Kyung Kim, Hyun-Woo Lim, Se-Jung Roh
Department of Advanced Materials Chemistry, Korea University, Se-Jong Campus, Jochiwon, ChoongNam 339-700, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The unequivocal solid-state structure and stereochemistry of the unsymmetric leuco-triarylmethane
(Un-LTAM) dye 2,20-{(E)-4-(phenyl)pent-2-ene-1,5-diylidene}bis(1,3,3-trimethylindoline) derivatives
were established using X-ray single-crystal analysis. The X-ray analysis showed that the EEE isomers
were formed stereoselectively with an unsymmetric three-bladed propeller conformation from the
reaction of a Fischer’s base and cinnamaldehyde derivatives. The 5,50-dichloro-400-nitro-triarylmethane
dye displayed a triclinic crystal structure with the space group P-1. The molecules stack alternately to
form a dimer, adopting intermolecular distances of 8.53 and 9.40 Å for rings B and C, respectively.
Unsymmetric triarylmethane cations, the oxidized form of these dyes, have UV absorptions over 680 nm
and selected examples absorb close to the near-IR region.
Received 23 November 2011
Received in revised form
17 January 2012
Accepted 10 February 2012
Available online 16 February 2012
Keywords:
Unsymmetrical leuco-TAM
Unsymmetric three-bladed propeller
conformation
Ó 2012 Elsevier Ltd. All rights reserved.
EEE isomers
Stereoselective formation
Near-IR dyes
Cy5 TAMþ dye
1. Introduction
against the fungus Saprolegnia, which infects fish eggs in
commercial aquaculture, and is also known to be a good treatment
Triarylmethane (TAM) compounds, sometimes referred to as
“Leuco-TAM (LTAM) molecules,” are precursors of the TAMþ dyes
[1e4]. A number of TAMþ dyes such as malachite green (MG),
crystal violet, and pararosaniline are well known. These dyes have
potential in numerous applications in the chemical and life-
sciences industries, such as ink dyes, thermal imaging, carbonless
copying materials, and drugs [5,6]. They are also widely used in
pharmaceutical and medicinal applications, such as photo-
chemotherapy agents and particularly in eye-protection devices
[7,8]. In addition, triarylmethyl (trityl) cations are stabilized by the
resonance effect of the phenyl rings, and they have become useful
as protective groups, especially in nucleoside chemistry [9]. Trityl
groups generating cations of different colors have thus been used to
protect different nucleotides in oligonucleotide synthesis [10,11].
Among the abovementioned TAMþ dyes, MG is one of the most
commonly used chemicals in dye chemistry. Significant quantities
of MG and related triarylmethane dyes are produced annually for
this purpose [12]. MG is known to be absorbed by the human body
in other forms such as carbinol and leuco forms. MG is very active
against ichthyophthirius in freshwater aquaria. However, the
principal metabolite, leuco-MG (LMG), is found in fish treated with
MG, and this finding has been the subject of controversy and
government regulation. The use of this substance has thus been
restricted in many countries [13,14].
A number of research groups [15e17], including us [18e20],
have thus investigated structural modifications of LTAM molecules.
Significant progress has thus been made toward the synthesis of
novel LTAM/TAMþ dyes. Very recently, we reported [21] the
synthesis of unsymmetrical LTAM (2E,20E)-2,20-{(E)-4-phenylpent-
2-ene-1,5-diylidene}bis(1,3,3-trimethylindoline)
derivatives
obtained from the reaction of an excess Fischer’s base (FB) and
substituted cinnamaldehydes. The chemical structures of these
molecules in solution, determined tentatively by 1H and 13C NMR
spectroscopy using 1D and 2D techniques, were found to be
precursors of a Cy5 TAMþ dye [22]. The Cy5 TAMþ dye is a potent
near-IR heptamethine cyanine dye, which is a promising imaging
agent for human cancers, and can be further exploited to improve
cancer detection, prognosis, and treatment [23].
The unsymmetrical LTAM molecules (Un-LTAM) in the solid
state can be characterized by unambiguous structural and stereo-
chemical elucidation. The Un-LTAM molecules consist of a methane
molecule with three aromatic groups such as 2-allyidene-1,3,3-
q
Part I. Ref. 21.
* Corresponding author. Tel.: þ82 41 860 1332; fax: þ82 41 867 5369.
E-mail address: keum@korea.ac.kr (S.-R. Keum).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2012.02.007

S.-R. Keum et al. / Dyes and Pigments 94 (2012) 490e495
491
ꢀ
radiation source (
l
¼ 0.71073 A) and a CCD detector. All multi-
frames of the two-dimensional diffraction images were collected.
The frame data were processed to determine the structural factors
using the program SAINT [24]. The structure was found using direct
methods and refined with full-matrix least-squares on F2 for all of
the data using the SHELXTL software [25]. The hydrogen atom
positions were initially determined geometrically and refined using
a Dreiding model. The non-hydrogen atoms were refined using
anisotropic displacement parameters.
Scheme 1. Chemical structures of Un-LTAM molecules.
trimethylindolinyl (A), 1,3,3-trimethyl-2-methyleneindolinyl (B),
and a phenyl (C) ring, as shown in Scheme 1.
To the best of our knowledge, the X-ray crystal analysis of Un-
LTAM bearing two different types of 2-methyleneindoline (FB)
moieties has not yet been described in the literature. This work
describes the solid-state structure of the Un-LTAM molecule.
2.4. UVevis spectroscopy
UVevis absorption spectra were recorded using a Varian Cary 1E
UVevisible spectrometer, and IR spectra were recorded using an
Analet Instrument FT-IR (MAP-60) using KBr pellets.
Stock solutions (2.05 ꢂ10ꢁ5 M) of Un-LTAM 1e4 in DMF were
made in 5 mL volumetric flasks in an inert atmosphere. The flasks
were then capped with a rubber septum, wrapped in aluminum
foil, and stored at 0 ꢀC. Reproducible results of the acid-catalyzed
transformation of LTAM dye to cyanine dye were obtained using
a protocol that maximized the formation of the colored form.
Briefly, 3 mL of the selected organic solvent was injected into a 1-
cm-path-length quartz cuvette. The cuvette was then placed in
the thermostated (25 ꢀC) cell compartment of a UVevis spectro-
photometer. The absorption maxima in the UVevis spectra were
obtained from the final absorption scans of the colored cyanine
forms of the Un-LTAM molecules.
2. Materials and methods
2.1. General procedures
The melting points were determined on a FischereJohns block
and were not corrected for. The 1H NMR spectra were acquired
using a Bruker CXP-300 FT-NMR spectrophotometer. The electron-
impact mass spectra were recorded on a VG Quattro mass spec-
trometer at Queen’s University, Kingston Canada.
2.2. Materials
The required 2-methylene-1,3,3-trimethylindoline (FB), 5-
chloro-2-methylene-1,3,3-trimethylindoline, trans-cinnamaldehyde,
and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) were
purchased from Aldrich Chemical Co. and were used without
further purification.
3. Results and discussion
Un-LTAM dyes 1e4 were prepared by the reaction of the FB, 2-
methylene-1,3,3-trimethylindoline, with substituted cinnamalde-
hydes in a 2.5:1 ratio in ethanol, in a modification of the known
method [18].
The stereochemistry of the diastereomer of the prepared LTAM
molecules in organic solvents was tentatively determined using 1H
NMR and 2D NMR techniques. The EEE isomer was obtained as the
major product in all of the cases examined. For no apparent reason,
the other diastereomers could not be isolated in the solid state. This
An excess of FB was added dropwise to an ethanolic solution of
cinnamaldehyde. The reaction mixture was stirred in an ice bath for
5e6 h. The precipitate was filtered, washed thoroughly with cold
ethanol, and purified by precipitation from acetone/hexane.
Detailed synthetic procedures for the Un-LTAM molecules are
described elsewhere [18]. The TAMþ was obtained from a reaction
of Un-LTAM molecule with DDQ in the presence of HCl, followed by
separation of deep blue colored form from the product mixtures by
column chromatograph in MC/MeOH (7:1). TAMþ was then
converted into the carbinol in base (NaOH). Decomposed product
{5-chloro-1,3,3-trimethyl-2-((1E,3E)-4-(4-nitrophenyl)buta-1,3-
dienyl)indolium perchlorate} was isolated from the reaction of Un-
LTAM 4 with HClO4.
Table 1
Crystal data and structural refinement for Un-LTAM 4.
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Un-LTAM 4
33H33Cl2N3O2
574.52
C
5-chloro-1,3,3-trimethyl-2-((1E,3E)-4-(4-nitrophenyl)buta-
293(2) K
ꢀ
1,3-dienyl)indolium
perchlorate,
brown,
Yield
57%,
0.71073 A
M.p. ¼ 257e258 ꢀC, ir (KBr) 3072, 2984, 2934, 1707, 1596, 1340 and
Crystal system, space group
Unit cell dimensions
Triclinic, P-1, R ¼ 0.0558
¼ 114.033(3)ꢀ
¼ 93.314(3)ꢀ
ꢀ
a ¼ 11.1280(17) A,
a
b
1086 cmꢁ1, 1H NMR (DMSO-d6)
d 1.76 (6H, s), 4.03 (3H, s), 7.37 (1H,
ꢀ
b ¼ 11.7321(18) A,
d, J ¼ 15.3 Hz), 7.66 (1H, dd, J ¼ 10.2,15.3 Hz), 7.73 (1H, d, J ¼ 9.0 Hz),
7.79 (1H, d, J ¼ 15.3 Hz), 7.92 (2H, d, J ¼ 6.9 Hz), 7.95 (1H, d,
J ¼ 9.0 Hz), 8.09 (1H, s), 8.33(1H, dd, J ¼ 10.2, 15.3 Hz), 8.33(2H, d,
J ¼ 6.9 Hz).
ꢀ
c ¼ 13.808(2) A,
g
¼ 109.293(3)ꢀ
3
ꢀ
Volume
1514.7(4) A
2, 1.260 Mg/m3
0.248 mmꢁ1
604
Z, Calculated density
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Limiting indices
0.30 ꢂ 0.20 ꢂ 0.20 mm
1.66e28.30ꢀ
2.3. X-ray crystallography
ꢁ14 ꢃ h ꢃ 14, ꢁ15 ꢃ k ꢃ 15, ꢁ18 ꢃ l ꢃ 18
20,744/7485 [R(int) ¼ 0.0297]
99.4%
Reflections collected/unique
Completeness to theta ¼ 28.30
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Crystal data for Un-LTAM
triclinic, b ¼ 11.7321(18),
a ¼ 11.1280(17),
U ¼ 1514.7(4) Å, T ¼ 293(2) K, space group P-1, Z ¼ 2,
4
[C33H33N3Cl2O2], M ¼ 574.52,
c ¼ 13.808(2) Å,
(Mo-K
) ¼
0.9520 and 0.9293
m
a
Full-matrix least-squares on F2
7485/0/367
0.248 mmꢁ1
, 20,744 reflections measured, and 7485 unique
(R(int) ¼ 0.0297) were used in all calculations. The final wR(F2) was
0.1504. The intensity data for Un-LTAM 4 were collected using
a Siemens SMART CCD area detector mounted on a Siemens P4
1.043
R1 ¼ 0.0558, wR2 ¼ 0.1504
R1 ¼ 0.0912, wR2 ¼ 0.1738
ꢀꢁ3
Largest diff. peak and hole
0.338 and ꢁ0.389 e A
diffractometer equipped with a graphite-monochromated Mo-K
a

492
S.-R. Keum et al. / Dyes and Pigments 94 (2012) 490e495
Table 2
ꢀ
ꢀ
Selected bond distances (A), and bond angles ( ) for 4.
Ringa
Bond distances
Bond
Bond angles
Distances Bond
Angles (ꢀ)
ꢀ
(A)
A
N(1)eC(2)
N(1)eC(10)
C(2)eC(700)
1.397
1.439
1.345
C(2)eN(1)eC(7a)
111.66
123.9
117.1
123.8
128.67
C(2)eN(1)eC(10)
C(2)eC(700)eH(700)
C(700)eC(2)eN(1)
C(700)eC(2)eC(3)
Fig. 2. Propeller shape of Un-LTAM 4, showing the interplanar angles.
B
N(2)eC(20)
N(2)eC(100)
C(20)eC(1100)
1.408
1.445
1.324
C(20)eN(2)eC(7a0)
C(7a0)eN(2)eC(100)
C(20)eN(2)eC(100)
111.32
124.45
123.11
atomic coordinates (ꢂ104), and equivalent isotropic displacement
parameters (Å2 ꢂ103) for 4. The selected bond lengths and bond
angles are listed in Table 2.
Connecting C(100)eC(1000)
group
C(900)eC(1000)
1.516
1.516
C(900)eC(1000)eC(1100)
C(100)eC(1000)eC(1100)
C(900)eC(1000)eC(1100)
C(800)eC(900)eC(1000)
C(1100)eC(20)eN(2)
C(1100)eC(20)eC(30)
C(20)eC(1100)eH(1100)
C(800)eC(900)eH(900)
C(1000)eC(900)eH(900)
C(900)eC(800)eC(700)
C(900)eC(800)eH(800)
C(700)eC(800)eH(800)
C(2)eC(700)eC(800)
110.92
110.01
110.92
127.29
122.42
130.02
115.6
116.4
116.4
125.0
117.5
C(1000)eC(1100) 1.509
X-ray crystal structures of the Un-LTAM dye 4 showed a triclinic
crystal system with the space group P-1. An ORTEP diagram of 4,
including the atom-numbering scheme, is shown in Fig. 1.
The C(900)-C(1000) and C(1000)-C(1100) distances are 1.516 and
1.509 Å, respectively, which are typical CeC single bond lengths.
The single bond C(700)eC(800) distance, however, was 1.443 Å, which
is shorter than typical CeC single bond lengths and longer than
those typical for CeC double bonds, and is perhaps due to conju-
gation. It is known that the length (1.47 Å) of the central single
bond of 1,3-butadiene is approximately 6 Å shorter than that of the
analogous single bond (1.53 Å) in butane. The two enamine C(2)e
C(700) and C(20)eC(1100) bond lengths, and the C(800)eC(900) double
bond length were 1.354, 1.324 and 1.328 Å, respectively, which are
typical C]C bond lengths.
C(800)eC(900)
C(700)eC(800)
1.328
1.443
117.5
125.8
117.1
128.78
C(800)eC(700)eH(700)
C(20)eC(1100)eC(1000)
C(1000)eC(1100)eH(1100) 115.6
a
Symbols (rings A and B) are denoted as indicated in Scheme 1.
In the crystals, the three aromatic rings of 4 were linked to three
different layers, viz. a vinyl FB (ring A), a FB (ring B), and a phenyl
group. The unsymmetrical molecule is a distorted version of the
well-known three-bladed propeller conformation [18,19]. The
interplanar angles of the aromatic rings AeB, AeC, and BeC are
87.4ꢀ, 67.5ꢀ and 61.5ꢀ for 4, as shown in Fig. 2.
is somewhat surprising because the ZE-isomers are formed ster-
eoselectively for the FB-analogs of LTAM molecules in both solid
and solution states, as reported previously [18,19].
The Un-LTAM 4 compound was the only compound that gave
crystals (from acetone) suitable for X-ray analysis. Unfortunately,
crystal growth was unsuccessful for the remainder of the Un-LTAM
molecules. Table 1 shows the crystal data, structural refinement,
The dihedral angle (
4, in the solid state. For a representative comparison, the value was
q
) of H1000eC1000eC1100eH1100 was 170.9ꢀ for
Fig. 1. ORTEP diagram of Un-LTAM 4, showing the atom-numbering scheme.

S.-R. Keum et al. / Dyes and Pigments 94 (2012) 490e495
493
Table 3
Table 4
Interplanar angles and dihedral angles (ꢀ) for Un-LTAM 1e4.
UVevis spectral data of various forms of Un-LTAM 1e4.
Names
Compoundsa
Interplanar
anglesb (ꢀ)
Dihedral Noted
anglec
Compoundsa
Various structural formsb
Leuco- Carbinol- TAMþ- (c)c
(
lmax
)
Solid color
Conjugated
dye (d)
ArylA
ArylB
ArylC Ring Ring Ring
q
(ꢀ)
(a)
(b)
x-Band y-Band
AeB BeC CeA
Crystal violetd
265
266
265
343
327
381
383
368
374
585
620
609
578
693
686
686
704
e
e
Blue violet
Green
Blue
Bis-(FB)PPe
H
H
H
H
H
4-NO2
79.8 74.9 84.8 164.1
60.1 75.7 83.2 178.9
Exp
Exp
Calc
Calc
Calc
Malachite greene 265
430
426
370
412
414
353
417
e
Bis-(5-ClFB)PPe 5-Cl
5-Cl
5-Cl
H
Bis-(FB)PPf
284
296
322
326
324
326
385
391
420
415
435
425
Un-LTAM 1
Un-LTAM 2
Un-LTAM 3
5-Cl
H
e
e
e
162.0
163.0
166.0
Bis-(5-ClFB)PPf
Un-LTAM 1
Un-LTAM 2
Un-LTAM 3
Un-LTAM 4
Blue
e
e
e
Green
Green
Green
Green
5-Cl-7- 5-Cl-7- 4-NO2
NO2
5-Cl
5-Cl
NO2
5-Cl
5-Cl
Un-LTAM 4
Un-LTAM 4
4-NO2
e
e
e
162.0
Calc
Exp
4-NO2 87.4 61.5 67.5 170.9
a
Names of compounds are the same as in Table 3.
Symbols (a)e(d) are as indicated in Fig. 6.
Symbols (x-, y-band) are adopted from ref. 22.
Data for acetonitrile from ref. 26.
Data for acetonitrile from ref. 29.
Data in chloroform from refs. 18,19.
a
Symbols (ArylA, B & C) are in the order of Z-FB ring, E-FB ring and phenyl rings for
b
c
d
e
f
the LTAM, and vinylated FB, FB & phenyl rings for Un-LTAM, respectively.
b
Symbols (AeB) and numbering systems are denoted as indicated in Scheme 1.
c
Symbol (q
) is denoted a dihedral angle of H1000eC1000eC1100eH1100.
d
e
Exp and calc denote experimental and calculated values, respectively.
SymbolsareabbreviationsforthesymmetricLTAM(FB-analogsofMG)asinref. 18.
the ZEE and ZEZ isomers (Fig. 3). The central carbonecarbon double
bonds of these LTAM dyes are generally expected to have an E
configuration.
calculated using the modified Karplus relationship between
coupling constants and dihedral angles [26,27]. The calculated
value (162ꢀ for ) is compared with the experimental one (170.9ꢀ);
q
Although the presence of the ZEE and ZEZ diastereomers was
generally expected to be found in organic solvents, none of these
isomers were detected, unlike for the LTAM molecules examined
previously [20]. Diastereomeric isomerization between EEE and EEZ
forms of these Un-LTAM molecules are not detected in organic
solvents. Either the geminal dimethyl or N-methyl groups of ring B
locates in a proximity of the phenyl group, depending on the
configuration of the ring B. Thus, diastereomeric discrimination is
now possible only from the 1H NMR resonances of the geminal
dimethyl or N-methyl groups of ring B. Selected 1H NMR data for the
Un-LTAM molecules 1e4 are collected and listed in Table 4. The
stereoselective formation of the EEE isomer of these dyes from the
reaction of an excess FB and cinnamaldehydes requires further study.
these values are in reasonable agreement. This indicates that the
modified Karplus equation is acceptable for the values of the Un-
q
LTAM molecules, as is the case for the symmetric LTAM dyes [19].
The dihedral angles of the other three molecules 1e3 in the solu-
tion state were calculated using the modified Karplus equation
from the 1H NMR vicinal coupling-constant values. The calculated
and experimental values of interplanar and dihedral angles for 1e4
are given in Table 3.
The double bonds C(2)]C(700), C(800)]C(900), and C(20)]C(1100)
of Un-LTAM 4 have EEE configurations. The EEE isomers of these
LTAM dyes are formed as the sole product in all cases, even though
there are three possible isomers, the two other diastereomers being
Fig. 3. Structures of ZEE and ZEZ diastereomers.

494
S.-R. Keum et al. / Dyes and Pigments 94 (2012) 490e495
Fig. 4. Molecular packing diagram of Un-LTAM 4 showing dimer formation.
The distance between the ortho-proton, H200/H600, in the phenyl
UVevis spectral data in EtOH shows various structural forms of
the Un-LTAM 4, such as (a) leuco, (b) colored TAMþ, (c) carbinol and
(d) decomposed forms, similar to the TAM dyes. These spectra are
shown in Fig. 5.
From the reaction of Un-LTAM 4 with HClO4, a decomposed
product d was isolated, whose chemical structure is shown in
Scheme 2.
ring and gem-methyl protons, H80/H90, of the FB (B) ring is 5.221 Å,
whereas it is 4.840 Å for the gem-methyl protons, H8/H9, of the FB
(A) ring. This is the reason why a local diamagnetic anisotropy could
be detected only for the former by 1H NMR spectroscopy [18],
although both FB rings have the E configuration. This situation
would further explain the collapse of the N-methyl peaks at
3.00 ppm of the A and B rings. However, local diamagnetic
anisotropy was not detected because Un-LTAM has no FB unit
having a Z-configuration.
The chemical structure of the decomposed dye structure d has
been determined by 1H NMR and 2D COSY experiment. 1He1H
COSY was used to identify protons belonging to the central
protons, H11eH14, linking the two aromatic rings. The COSY in the
range of 7.0e8.5 ppm showed three correlation [H11eH12,
H12eH13, H13eH14] for the central protons of the decomposed
product.
A measure of the electronic effect of the FB group was obtained
from the spectrum of the FB analog of MG. A hypsochromic shift
(w20 nm) of the x-band of the FB analog dyes was observed relative
to MG itself, whereas, a pronounced bathochromic shift (w100 nm)
of the x-band was observed relative to MG. It is assumed that the
pronounced bathochromic shift is associated with the extended
conjugation [28] in the chain branch that includes ring A. All of the
prepared Un-TAMþ dyes 1e4 showed absorption maxima at longer
wavelengths, namely the x-band of the Un-TAM molecules, than
those of the well-known MG dyes. UVevis spectral data for various
forms of Un-LTAM 1e4, compared to those of the well-known
TAMþ dyes, are summarized in Table 4.
Compound 4 is stacked in an alternating fashion to form a dimer
in the unit cell of the crystal. Fig. 4 shows the molecular packing
diagram of Un-LTAM 4, showing the formation of the dimer. The
intermolecular distances in the dimer are 8.53 and 9.40 Å, for the
rings B and C, respectively.
The colored forms (c) were obtained from the reaction of the
Un-LTAM materials with DDQ/HCl. The colored forms, TAMþ, of the
prepared LTAM molecules have absorption maxima at 412e419 and
679e704 nm in ethanol, and the carbinol form (b) was detected at
360e380 nm in basic media. The leuco form of these molecules
decomposed in HCl-saturated EtOH to form conjugated molecules
(d) observed at 415e420 nm.
In the UVevis measurements, MG exhibits absorption maxima
at 620 and 430 nm for the x- and y-bands, respectively. On the
other hand, the absorption maxima of the vinylog of MG are red-
shifted for both x- and y-bands, viz. at 651 and 488 nm, respec-
tively. This observation suggests that the vinyl effects of a vinyl unit
may be like those due to extended conjugation for both x- and y-
bands, to a large extent. Chemical structures for various TAMþ dyes
are shown in Fig. 6 for the N w Nþ and C(phenyl) w Nþ responsible
for the x- and y-bands, respectively.
Fig. 5. UVevis spectral data for Un-LTAM 4 in EtOH showing the various forms such as
the leuco (a, solid), TAMþ (b, dash-dot-dot), carbinol (c, dash-dot), and decomposed
forms (d, dash).
Scheme 2. Chemical structure of the decomposed product d.

S.-R. Keum et al. / Dyes and Pigments 94 (2012) 490e495
495
Fig. 6. Chemical structures for the N w Nþ and C(phenyl) w Nþ responsible for the x- and y-bands, respectively, in the UVevis measurements.
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4. Conclusions
The unequivocal solid-state structure and stereochemistry of
novel
Un-LTAM,
(2E,20E)-2,20-{(E)-4-phenylpent-2-ene-1,5-
diylidene}bis(1,3,3-trimethylindoline) derivatives were established
using X-ray single-crystal analysis. The X-ray crystal analysis showed
that the EEE isomers formed stereoselectively, unlike the previously
reported symmetric ZE-LTAM FB-analogs of MG. UV data for these
Un-TAMþ dyes showed absorption in the near-IR region (w700 nm).
The pronounced bathochromic shift is presumably associated with
the extended conjugation effect of ring A in the Un-TAMþ dyes.
Acknowledgments
This work was supported by the Korea Research Foundation
grant funded by the Korea government (MEST) (No. 2009-0071425)
and partly by the Brain Korea 21 project.
[17] Liu C-R, Li M-B, Yang C-F, Tian S-K. Catalytic selective bis-arylation of imines
with anisole, phenol, thioanisole and analogues. Chem Commun;
2008:1249e51.
[18] Keum SR, Roh SJ, Lee MH, Saurial F, Buncel E. 1H and 13C NMR assignments for
new heterocyclic TAM leuco dyes, (2Z,20E)-2,20-(2-phenyl propane-1,3-
diylidene)bis(1,3,3-trimethylindoline) derivatives. Part II. Magn Reson Chem
2008;46:872e7.
Supplementary material
The crystallographic data for the structural analysis was provided
to the Cambridge Crystallographic Data Center as a supplementary
publication number CCDC 851595 for 4. A copy of this information
may be obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: þ44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
[19] Keum SR, Roh SJ, Kim YN, Im DH, Ma SY. X-ray crystal structure of hetaryl
leuco-TAM dyes, (2Z,20E)-2,20-(2-phenylpropane-1,3-diylidene) bis(1,3,3-
trimethyl indoline) derivatives. Bull Korean Chem Soc 2009;30:2608e12.
[20] Keum SR, Roh SJ, Ma SY, Kim DK, Cho AE. Diastereomeric isomerization of
hetaryl leuco-TAM dyes, (2Z, 20E)-2,20-(2-phenyl propane-1,3-diylidene)
bis(1,3,3-trimethylindoline) derivatives in various organic solvents. Tetrahe-
dron 2010;66:8101e7.
[21] Keum SR, Lee MH, Ma SY, Kim DK, Roh SJ. Novel unsymmetrical leuco-TAM,
(2E, 20E)-2,20-{(E)-4-phenylpent-2-ene-1,5-diylidene}bis(1,3,3-trimethylindo-
line) derivatives: synthesis and structural elucidation. Dyes Pigm 2011;90:
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