Synthesis, dual fluorescence, and fluoroionophoric behavior of dipyridylaminomethylstilbenes

Article abstract of DOI:10.1021/jo0509049

The synthesis, dual fluorescence, and fluoroionophoric behavior of two donor-σ spacer-acceptor (D-s-A) compounds, trans-4-(N,N-bis(2-pyridyl) amino)methylstilbene (1H) and trans-4-(N,N-bis(2-pyridyl)amino)methyl-4′- cyanostilbene (1CN), are reported and compared to that of trans-4-(N,N-bis(2- pyridyl)amino)methyl-4′-(N,N-dimethylammo)stilbene (1DPA). To gain insights into the dual fluorescence properties for 1H and 1CN in polar but not in nonpolar solvents, model compounds resulting from a replacement of the stilbene group by alkyl (2R) or xylyl (2X) groups or from a replacement of the dipyridylamino (dpa) group by dianisoleamino (3AA), diethylamino (SEE), methylanilino (3MP), or diphenylamino (3PP) groups also have been investigated. In addition to 1H and 1CN, all four compounds of 3 display dual fluorescence. The locally excited (LE) fluorescence mainly results from the stilbene group and the ICT fluorescence from the through-bond interactions between the amino donor and the stilbene acceptors. In the presence of transition metal ions such as Zn(II), Ni(II), Cu(II), and Cd(II), the ICT processes are switched from dpa → stilbene (A) in 1H and 1CN to stilbene (D) → dpa/metal ion (A) in their complexes. Whereas the ICT states for the complexes are generally nonfluorescent, an exception was found for the case of 1H/Zn(II). As a result, substituent-dependent fluoroionophoric behavior has been demonstrated by 1H, 1CN, and 1DPA in response to Zn(II).

Full text of DOI:10.1021/jo0509049

Synthesis, Dual Fluorescence, and Fluoroionophoric Behavior of
Dipyridylaminomethylstilbenes
Jye-Shane Yang,*,† Yan-Duo Lin,† Ya-Ho Chang,† and Shin-Shin Wang‡
Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, and
Union Chemical Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan 30043
jsyang@cc.ncu.edu.tw
Received May 6, 2005
The synthesis, dual fluorescence, and fluoroionophoric behavior of two donor-σ spacer-acceptor
(D-s-A) compounds, trans-4-(N,N-bis(2-pyridyl)amino)methylstilbene (1H) and trans-4-(N,N-bis(2-
pyridyl)amino)methyl-4′-cyanostilbene (1CN), are reported and compared to that of trans-4-(N,N-
bis(2-pyridyl)amino)methyl-4′-(N,N-dimethylamino)stilbene (1DPA). To gain insights into the dual
fluorescence properties for 1H and 1CN in polar but not in nonpolar solvents, model compounds
resulting from a replacement of the stilbene group by alkyl (2R) or xylyl (2X) groups or from a
replacement of the dipyridylamino (dpa) group by dianisoleamino (3AA), diethylamino (3EE),
methylanilino (3MP), or diphenylamino (3PP) groups also have been investigated. In addition to
1H and 1CN, all four compounds of 3 display dual fluorescence. The locally excited (LE) fluorescence
mainly results from the stilbene group and the ICT fluorescence from the through-bond interactions
between the amino donor and the stilbene acceptors. In the presence of transition metal ions such
as Zn(II), Ni(II), Cu(II), and Cd(II), the ICT processes are switched from dpa (D) f stilbene (A) in
1H and 1CN to stilbene (D) f dpa/metal ion (A) in their complexes. Whereas the ICT states for
the complexes are generally nonfluorescent, an exception was found for the case of 1H/Zn(II). As
a result, substituent-dependent fluoroionophoric behavior has been demonstrated by 1H, 1CN,
and 1DPA in response to Zn(II).
Introduction
(ICT) states, respectively. The highly dipolar nature of
the ICT state is evidenced by a large positive solvato-
fluorochromism, where the fluorescence maximum shifts
toward the red upon increasing solvent polarity. For
donor-σ spacer-acceptor (D-s-A) systems, observations
of the ICT fluorescence strongly depend on the length
and flexibility of spacer and the polarity of solvent.1,2
When the spacer allows the formation of a sandwich
geometry between D and A, the ICT state could be formed
in both nonpolar and polar solvents, but it is generally
nonfluorescent in polar solvents such as acetonitrile,
presumably due to the fast generation of well-solvated
radical ion pairs (D+•-s-A-•).1,2 The net process of D-A
interactions in the latter case is thus a complete photo-
induced electron transfer (PET) from D to A, correspond-
ing to a fluorescence quenching of the LE state (D*-s-A
or D-s-A*). In contrast, dual fluorescence in polar solvents
has been observed for systems with short spacers such
as one or two CH2 groups.1 While this might be an avenue
toward the design of fluoroionophores with the LE-ICT
The phenomenon of dual fluorescence emission of
electron donor (D)-acceptor (A) integrated systems is
attractive, because the interplay of the two emissive
states with the enviroment is not only informative on
excited-state D-A interactions but also useful in fluo-
rescence sensory applications.1-3 In general, the short-
and long-wavelength fluorescence bands are ascribed to
locally excited (LE) and intramolecular charge transfer
† National Central University.
‡ Industrial Technology Research Institute.
(1) Kavarnos, G. J.; Turro, N. J. Chem. Rev. 1986, 86, 401-449.
(2) Brouwer, F. In Conformational Analysis of Molecules in Excited
States; Waluk, J., Ed.; Wiley-VCH: New York, 2000; Chapter 4, pp
177-235.
(3) (a) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.;
Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem.
Rev. 1997, 97, 1515-1566. (b) de Silva, A. P.; Fox, D. B.; Moody, T. S.;
Weir, S. M. In Molecular and Supramolecular Photochemistry; Vol. 7,
Optical Sensors and Switches; Marcel Deckker, Inc.; New York, 2001;
pp 93-151.
10.1021/jo0509049 CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/24/2005
6066
J. Org. Chem. 2005, 70, 6066-6073

Dipyridylaminomethylstilbenes
SCHEME 1
SCHEME 2
ratiometric fluorescence responses,4,5 the vast majority
of the hitherto reported ionophoric D-s-A systems, dis-
regarding the chain length of spacers, display only the
LE fluorescence and the PET-based “on-off” or “off-on”
fluoroionophoric behavior in polar solvents.3
The N,N-bis(2-pyridyl)amino (dpa) group is known to
possess a remarkable binding ability to transition metal
ions such as Zn(II) and Ni(II),6,7 which has been applied
in the formation of fluoroionophores.7,8 However, these
dpa-derived D-s-A systems with a C1 (e.g., 1DPA) or a
virtual C0 spacer all display the “on-off”-type fluores-
cence sensing mode. We report herein that the dpa
derivatives 1H and 1CN display dual fluorescence in
acetonitrile, based on which the ratiometric fluorescence
sensing behavior is demonstrated. In addition, the ICT
fluorescence of 1H undergoes a red shift that is selec-
tively induced by Zn(II). To understand the dual fluo-
rescence and fluoroionophoric properties of 1H and 1CN,
studies on model compounds 2 and 3 were also carried
out.
Results and Discussion
Synthesis and Crystal Structures. The synthetic
methodology for 1H is analogous to that previously
reported for 1DPA (Scheme 1),8 but a different route was
required for the synthesis of 1CN (Scheme 2) due to the
susceptibility of the cyano group to the LAH reduction.
The intermediates 4,9 5,10 6,11 and 712 in Scheme 1 are
known compounds and our melting points and/or 1H
NMR spectra conform to the literature values. The
starting material 8 in Scheme 2 is also a known com-
pound13 and was prepared in a way similar to that for 4
with 4-cyanobenzyl bromide and 4-(diethoxymethyl)-
benzaldehyde to form the stilbene backbone, followed by
acid-catalyzed hydrolysis to convert the acetal to alde-
hyde. The conversion of 8 to 9 was via a two-step reaction,
imine formation, and reduction, according to the litera-
ture procedures.14
(4) (a) Collins, G. E.; Choi, L.-S.; Callahan, J. H. J. Am. Chem. Soc.
1998, 120, 1474-1478. (b) Collado, D.; Perez-Inestrosa, E.; Suau, R.;
Desvergne, J.-P.; Bouas-Laurent, H. Org. Lett. 2002, 4, 855-858. (c)
Kawakami, J.; Kimura, H.; Nagaki, M.; Kitahara, H.; Ito, S. J.
Photochem. Photobiol. A: Chem. 2004, 161, 141-149.
Compounds 2X and 2R15 were prepared following the
methods in Scheme 1, starting with the Mitsunobu
(5) (a) Sankaran, N. B.; Banthia, S.; Das, A.; Samanta, A. New J.
Chem. 2002, 26, 1529-1531. (b) Boiocchi, M.; Colucci, G.; Licchelli,
M.; Monzani, E.; Sacchi, D. Chem. Commun. 2003, 2906-2907.
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Commun. 1998, 2101-2102. (b) Ho, K.-Y.; Yu, W.-Y.; Cheung, K.-K.;
Che, C.-M. J. Chem. Soc., Dalton Trans. 1999, 1581-1586. (c) Yang,
W.; Schmider, H.; Wu, Q.; Zhang, Y.-S.; Wang, S. Inorg. Chem. 2000,
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Pang, J.; Marcotte, E. J.-P.; Seward, C.; Brown, R. S.; Wang, S. Angew.
Chem., Int. Ed. 2001, 40, 4042-4045. (f) Seward, C.; Pang, J.; Wang,
S. Eur. J. Inorg. Chem. 2002, 1390-1399. (g) Jia, W.-L.; Song, D.;
Wang, S. J. Org. Chem. 2003, 68, 701-705. (h) Liu, Q.-D.; Jia, W.-L.;
Wu, G.; Wang, S. Organometallics 2003, 22, 3781-3791. (i) Seward,
C.; Jia, W.-L.; Wang, R.-Y.; Wang, S. Inorg. Chem. 2004, 43, 978-
985.
(9) Fuson, R. C.; Cooke, H. G., Jr. J. Am. Chem. Soc. 1940, 62, 1180-
1183.
(10) Kochi, J. K.; Hammond, G. S. J. Am. Chem. Soc. 1953, 75,
3452-3458.
(11) Hadrich, D.; Berthold, F.; Steckhan, E.; Bo¨nisch, H. J. Med.
Chem. 1999, 42, 3101-3108.
(12) Cavallito, C. J.; Yun, H. S.; Edwards, M. L.; Foldes, F. F. J.
Med. Chem. 1971, 14, 130-133.
(13) Erckel, R.; Fru¨hbeis, H. Z. Naturforsch. 1982, 37b, 1472-1480.
(14) O’Connor, S. J.; Barr, K. J.; Wang, L.; Sorensen, B. K.; Tasker,
A. S.; Sham, H.; Ng, S.-C.; Cohen, J.; Devine, E.; Cherian, S.; Saeed,
B.; Zhang, H.; Lee, J. Y.; Warner, R.; Tahir, S.; Kovar, P.; Ewing, P.;
Alder, J.; Mitten, M.; Leal, J.; Marsh, K.; Bauch, J.; Hoffman, D. J.;
Sebti, S. M.; Rosenberg, S. H. J. Med. Chem. 1999, 42, 3701-3710.
(15) The choice of a long alkyl chain instead of a methyl group for
2R is simply due to a more feasible preparation and purification.
(7) (a) Yang, J.-S.; Lin, Y.-H.; Yang, C.-S. Org. Lett. 2002, 4, 777-
780. (b) Kang, Y.; Seward, C.; Song, D.; Wang, S. Inorg. Chem. 2003,
42, 2789-2797.
(8) Yang, J.-S.; Lin, Y.-D.; Lin, Y.-H.; Liao, F.-L. J. Org. Chem. 2004,
69, 3517-3525.
J. Org. Chem, Vol. 70, No. 15, 2005 6067

Yang et al.
TABLE 1. Selected Structural Data, Including the Sum
of Bond Angles (θ) Around the Amino Nitrogen Atom,
Dihedral Angles (øph, øpy, and øph-py), and Csp2-N Bond
Lengths (dpy) for 1H, 1DPA, 2X, 2X/ZnCl2, and 3PP
SCHEME 3
compd
1H
θ (deg) øph (deg) øpy (deg)b øph-py (deg)b dpy (Å)b
360.0
359.9
359.9
79.2
85.2
88.2
82.6
72.1
6.2
42.4
25.1
37.9
29.7
30.0
48.2
60.9
12.5
56.3
83.5
86.1
82.7
84.4
76.1
84.8
37.7
71.7
78.9
80.4
1.390
1.411
1.394
1.409
1.398
1.413
1.414
1.410
1.389
1.424
1DPAa
2X
2X/ZnCl2 355.4
3PP 359.8
reaction16 for 4-methylbenzyl alcohol and the Pd-cata-
lyzed amination reaction17 for hexadecylamine, respec-
tively. The former was involved with known compounds
1018 and 1119 as the intermediates.
a Data from ref 8. b The subscript py corresponds to the pyridine
ring in 1H, 1DPA, 2X,and 2X/ZnCl2 and to the N-phenyl ring in
3PP.
the CNC plane (øph) or the pyridyl planes (øph-py). All
these values suggest that the dpa group would have a
negligible orbital overlap or through-space electronic
interaction with the stilbene group in 1H and 1CN as
well as in 1DPA.
An attempt to grow single crystals of the ZnCl2
complexes of compound 1H, 1CN, or 1DPA was unsuc-
cessful. However, we were able to obtain the X-ray crystal
structures of 2X and its complex with ZnCl2 (2X/ZnCl2)
(Figure 1), which could serve as model compounds for
compounds 1 to investigate the geometry of the dpa/ZnCl2
moiety and the change in spatial alignment between the
stilbene and the dpa groups upon coordination with
The strategies in Scheme 2 were adopted for the
synthesis of 3AA by replacing the 2-aminopyridine and
2-bromopyridine reagents with 4-methoxyaniline and
4-bromoanisole, respectively, through the intermediate
12. However, compounds 3EE, 3PP, and 3MP were pre-
pared by SN2 reactions between 4-chloromethylstilbene
(13) and sodium diethylamide, sodium diphenylamide,
and sodium N-methylanilide, respectively, where the
nucleophiles were prepared in situ from sodium hydride
and the corresponding amines. Compound 13 was in turn
prepared from 5 by reacting with thionyl chloride.20
The X-ray crystal structures of 1H and 3PP have been
determined and selected structural data are reported in
Table 1.21 For comparison, the data for 1DPA are also
included.8 As shown in Figure 1, the stilbene group is
essentially planar in both 1H and 3PP. Regarding the
dpa group, the geometry is similar to those in the
previously reported dpa derivatives in terms of the Cpy-N
bond lengths and the dihedral angles (øpy) be-
tween the pyridyl planes and the plane defined by the
C(sp2)-N(amino)-C(sp2) fragment.6-8 In addition, as
evaluated by the sum of bond angles (θ) about the amino
nitrogen, the amino nitrogen atom is coplanar with the
three carbon atoms to which it attaches in both cases (θ
∼ 360°), indicating an sp2-hybridized character of the
amino nitrogen atom. As is the case of 1DPA, the
adjacent phenyl ring of stilbene is nearly orthogonal to
(16) Mitsunobu, O. Synthesis 1981, 1-28.
(17) (a) Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805-818. (b) Hartwig, J. F. Angew. Chem., Int.
Ed. 1998, 37, 2046-2067.
(18) Sasaki, K.; Shibata, Y.; Hashimoto, Y.; Iwasaki, S. Biol. Pharm.
Bull. 1995, 18, 1228-1233.
(19) Hauser, C. R. J. Am. Chem. Soc. 1930, 52, 1108-1111.
(20) Chen, D.-W.; Beuscher, A. E., IV; Stevens, R. C.; Wirsching,
P.; Lerner, R. A.; Janda, K. D. J. Org. Chem. 2001, 66, 1725-1732.
(21) See the Supporting Information for details.
FIGURE 1. Crystal structures of (a) 1H, (b) 3PP, (c) 2X, and
(d) 2X/ZnCl2. The red lines highlight the planar vs pyramidal
geometries of the amino nitrogen in 1H, 3PP, and 2X vs
2X/ZnCl2.
6068 J. Org. Chem., Vol. 70, No. 15, 2005

Dipyridylaminomethylstilbenes
TABLE 2. Maxima of UV-Vis Absorption (λabs) and
Corrected Fluorescence (λfl), Stokes Shift (∆νst), 0,0
Transition (λ0,0), and Fluorescence Quantum Yields (Φf)
for Compounds 1-3 in Acetonitrile at Room
Temperature (ca. 298 K)
b
compd λabs (nm)a λfl (nm) ∆νst (cm-1
)
λ0,0 (nm)c
Φf
1H
300 (311) 359, 459 5478, 11546
322 385, 552 5081, 12939
332
355
415
338
335
329
332
332
332
0.013
0.027
0.68
0.045
0.035
0.002
0.021
0.013
0.003
1CN
1DPAd (299) 365 464
2R
2X
3AA
3MP
3PP
3EE
5846
6224
5829
306
303
378
368
298 (311) 358, 685 5624, 18958
300 (311) 356, 578 5243, 16032
298 (312) 359, 530 5701, 14689
299 (311) 359, 590 5590, 16496
a The second vibronic peak is given in parentheses. b ∆νst
)
νabs(maximum) - νfl(maximum of the LE or ICT band). c The value
of λ0,0 was obtained from the intersection of normalized absorption
and fluorescence spectra. d Data from ref 8.
FIGURE 2. Normalized fluorescence spectra of 1H and 1CN
in (a) hexane, (b) toluene, (c) ethyl acetate, (d) THF, (e)
CH2Cl2, (f) acetone, and (g) MeCN. The spectra of 1H in (b)
and (c) resemble those in (a) or (d) and are not shown for the
purpose of clarity.
transition metal ions. Indeed, the selected structural data
for 2X resemble those for 1H and 1DPA (Table 1). Thus,
it is reasonable to assume that the corresponding data
for their ZnCl2 complexes should be similar to one
another. According to the θ and øpy values for 2X/ZnCl2
vs 2X, the amino nitrogen becomes pyramidal and the
Cpy-N bond is more twisted, which indicates that the
conjugation interactions in the dpa moiety, particularly
between the amino lone-pair electrons and the pyridyl
groups, become weaker in the complexes vs free ligands.
Photophysical Properties. As shown in Figure 2,
both 1H and 1CN display dual fluorescence in acetoni-
trile (curve g). On the basis of the large solvatofluoro-
chromic shift for the long-wavelength but not for the
short-wavelength fluorescence band,22 the short- and the
long-wavelength bands can be attributed to the LE and
ICT states, respectively. The ICT fluorescence could not
be observed for 1H in solvents less polar than acetone
and for 1CN in solvents less polar than ethyl acetate.
Evidently, there is a larger driving force for the ICT
formation in 1CN vs 1H, but the ICT state is thermo-
dynamically unfavorable for both 1H and 1CN in non-
polar solvents. In conjunction with the larger Stokes shift
(∆νst) for the ICT fluorescence of 1CN vs 1H (Table 2),
the D and A should correspond to the dpa and the
stilbene groups, respectively. Since the crystal structures
in Figure 1 reveal that the short C1 methylene spacer in
1 cannot allow a significant orbital overlap between the
D and A groups, the D-A interactions should be mainly
through the σ bonds. This is also consistent with the
observation of ICT fluorescence in polar but not in
nonpolar solvents.1,2,23
FIGURE 3. The absorption and normalized fluorescence
spectra of 1H (10 µM, solid line) and 2R (dash line, 10 µM) in
acetonitrile.
As demonstrated by 2R, N-alkylated dpa compounds
are fluorescent with a fluorescence quantum yield (Φf )
0.045, Table 2) larger than that for trans-stilbene (Φf )
0.028) and that for trans-4-cyanostilbene (Φf ) 0.005)24
in acetonitrile. However, a combination of the dpa and
stilbene groups (i.e., 1H or 1CN) results in a weaker LE
fluorescence due to the formation of an ICT state. The
absorption spectrum of 2R also overlaps very well with
that of trans-stilbene, but the molar absorptivity (ꢀ) for
2R (ꢀ ) 1.43 × 104 L mol-1 cm-1) is only about one-half
of that for trans-stilbene (ꢀ ∼ 2.82 × 104 L mol-1 cm-1 25
)
(Figure 3). As a result, the absorption spectrum for 1H
is more like that for trans-stilbene than that for 2R. It
is interesting to note that the value of ꢀ (5.00 × 104 L
mol-1 cm-1) for 1H is somewhat larger than the sum of
the two components (4.25 × 104 L mol-1 cm-1). While the
(23) (a) Hoffmann, R. Acc. Chem. Res. 1971, 4, 1-9. (b) Migita, M.;
Okada, T.; Mataga, N.; Sakata, Y.; Misumi, S.; Nakashima, N.;
Yoshihara, K. Bull. Chem. Soc. Jpn. 1981, 54, 3304-3311. (c) Verho-
even, J. W.; Scherer, T.; Willemse, R. J. Pure Appl. Chem. 1993, 65,
1717-1722. (d) Lewis, F. D.; Cohen, B. E. J. Phys. Chem. 1994, 98,
10591-10597. (e) Oosterbaan, W. D.; van Gerven, P. C. M.; van Walree,
C. A.; Koeberg, M.; Piet, J. J.; Havenith, R. W. A.; Zwikker, J. W.;
Jenneskens, L. W.; Gleiter, R. Eur. J. Org. Chem. 2003, 3117-3130.
(24) Singh, A. K.; Kanvah, S. J. Chem. Soc., Perkin Trans. 2 2001,
395-401.
(22) The slope of the plot of ICT fluorescence maxima against the
solvent polarity parameter, ∆f ) (ꢀ - 1)/(2ꢀ + 1) - 0.5(n2 - 1)/(2n2
1), is ∼36 700 cm-1 for 1CN.
+
(25) Go¨rner, H.; Kuhn, H. J. Adv. Photochem. 1995, 19, 1-117.
J. Org. Chem, Vol. 70, No. 15, 2005 6069

Yang et al.
TABLE 3. Redox Potentials (ED and EAred),a Singlet
Excitation Energies (ES), and Free Energy of ICT (∆GICT
for Compounds 1-3, 1H/Zn(II), and 1CN/Zn(II) in
Acetonitrile
ox
)
compd
EDox(V)b
EAred (V)b
ES (eV)
∆GICT (eV)c
1H
1.30
1.30
1.30
0.65
0.85
0.93
0.96
1.41e
1.64f
0.80
-2.1d
3.73
3.51
2.99
3.73
3.73
3.73
3.73
3.73
3.51
2.99
-0.39
-0.47
> 0.35
-1.04
-0.84
-0.76
-0.73
-0.86
-0.41
-0.73
1CN
-1.8d
1DPA
< -2.1
-2.1d
3AA
3MP
-2.1d
3PP
-2.1d
3EE
-2.1d
1H/Zn(II)
1CN/Zn(II)
1DPA/Zn(II)
-1.52g
-1.52g
-1.52g
a Half-wave redox potentials vs SCE. b This work unless
otherwise noted. c Calculated by eq 1. d From ref 26. e From ref
29. f From ref 30 and data converted to half-wave potential with
respect to SCE. g Determined from 2R/Zn(II) in dichloromethane.
FIGURE 4. Fluorescence spectra of 3AA, 3EE, 3MP, and
3PP in acetonitrile (excitation at 310 nm). Peaks denoted with
an asterisk are due to the double wavelength of the scattered
light (600-620 nm) or the LE emission (660-800 nm).
by addition of 0.29 V27 or by using ferrocene (E1/2 ) 0.39
V vs SCE)28 as an external reference. Both methods
produce essentially the same results. These data along
with the calculated values of ∆GICT are summarized in
Table 3.
excitation of 1H should simultaneously generate two LE
states, namely, D*-s-A and D-s-A*, it appears that the
LE fluorescence mainly results from the stilbene fluoro-
phore. For one reason, the fluorescence spectrum of 2R
is red-shifted by 27 nm with respect to that of trans-
stilbene (λfl ) 351 nm), but the observed LE emission (λfl
) 359 nm) is stilbene-like instead of 2R-like. In addition,
compound 3EE, which has only the stilbene fluorophore,
possesses a LE band nearly the same as that of 1H (Table
2). This in turn indicates that both the D-s-A* and
D*-s-A LE states for 1H could lead to the ICT state with
the latter being more efficient. The contribution of the
dpa fluorescence to the LE fluorescence of 1CN in
acetonitrile should also be low in view of its extremely
weak LE band (Figure 2).
Further evidence for the dpa (D)-methylene (s)-stil-
bene (A) assignment in accounting for the dual fluores-
cence of 1H and 1CN is the red shift of the ICT
fluorescence when the electron-donating power of the
amino group is enhanced, as demonstrated by compounds
3AA, 3EE, 3MP, and 3PP (Figure 4). The driving force
for the ICT state formation (∆GICT) could be estimated
according to the Weller equation:2
It is interesting to note that for the compound series 3
the intensity ratio of the ICT/LE fluorescence maxima
increases with increasing the value of -∆GICT (i.e., 3AA
(3.37) > 3MP (3.16) > 3PP (0.86) > 3EE (0.66)). The
value of -∆GICT for 1CN is as expected to be larger than
that for 1H, but it is smaller than those for compounds
3. However, the ICT/LE fluorescence intensity ratio for
1CN (13.5) is the largest among the six compounds. In
contrast, the corresponding dpa-stilbene interactions in
1DPA are predicted to be thermodynamically unfavor-
able, which is consistent with the absence of ICT fluo-
rescence and nearly the same fluorescence properties of
1DPA and trans-N,N-diphenylaminostilbene.8 In con-
junction with their fluorescence quantum yields (Table
2), the ICT state for 1CN appears to fluoresce the most
efficiently. The correlations between the Stokes shift of
ICT fluorescence and -∆GICT are shown in Figure 5,
where the six compounds could be divided into two groups
with essentially the same slope. It is interesting to note
that 3EE correlates better with 1H and 1CN rather than
with the other three compounds of 3. In other words, with
the same driving force of ICT formation (i.e., ∆GICT), the
group of 1H, 1CN, and 3EE are predicted to have a larger
Stokes shift, corresponding to a better solvated ICT state.
This appears to suggest that, in addition to the redox
properties, the structural nature of the amino donor is
important in determining the ICT luminescence proper-
ties of D-s-A systems.
∆GICT ) EDox - EAred - ES - 0.06 eV
(1)
ox
red
where ED and EA are the oxidation and reduction
potentials of D and A, respectively, and ES is the singlet
excitation energy of D or A. The literature values26 of
EAred ) -2.1 and -1.8 V (vs SCE) for trans-stilbene and
trans-4-cyanostilbene, respectively, were adopted. The
corresponding values of ES were converted from the 0-0
transition energies (λ0,0) of 1H and 1CN (Table 2). It
should be noted that the values of λ0,0 are essentially the
same for 1H and compounds 3, indicating that the
common stilbene group is the primary light absorber and
Fluoroionophoric Behavior. Addition of Zn(II) to
the acetonitrile solution of 1H results in a shift of the
ICT fluorescence toward the red from 459 to 521 nm
(Figure 6a). Since the absence of a stilbene group in
2R/Zn(II) could only lead to an emission at 479 nm, the
521-nm emission band for 1H/Zn(II) can be ascribed to
the stilbene (D)-dpa/Zn(II) (A) ICT state. In other words,
a fluorescent ICT state is present in both 1H and
ox
LE-band emitter. The values of ED for the donors in
compound series 1 and 3 could be estimated from the
half-peak potentials of their cyclic voltamograms, which
were recorded with respect to a reference electrode of
Ag/AgNO3 in dichloromethane solutions. The values of
ox
ED vs Ag/AgNO3 were converted to the SCE electrode
(27) Suga, K.; Ohkubo, K.; Fukuzumi, S. J. Phys. Chem. A 2003,
107, 4339-4346.
(28) Zanello, P.; de Biani, F. F.; Glidewell, C.; Koenig, J.; Marsh, S.
J. Polyhedron 1998, 17, 1795-1801.
(26) Le´onel, E.; Paugam, J. P.; Ne´de´lec, J.-Y.; Pe´richon, J. J. Chem.
Res. (S) 1995, 278-279.
6070 J. Org. Chem., Vol. 70, No. 15, 2005

Dipyridylaminomethylstilbenes
metal ions such as Ni(II), Cd(II), and Cu(II) that are
fluorescence quenchers.31 In contrast, the LE band of 1H
does not undergo wavelength shift or monotonic intensity
change upon titration with Zn(II). The fluctuation of the
LE fluorescence intensity during the titration might be
associated with the change in D-A character for the
stilbene and dpa groups, but a more detailed mechanism
remains to be investigated.
It might be interesting to make a correlation between
the X-ray structures of the dpa and dpa/Zn(II) groups
(Figure 1) and their ICT interactions with the stilbene
group. In principle, the electron-rich amino nitrogen and
the π-deficient pyridine rings in dpa and dpa/Zn(II)
should dominate the electron-donating and electron-
accepting character, respectively. Whereas the inductive
effect of the N-pyridyl group would reduce the electron-
donating ability of the amino nitrogen, the planar and
sp2-hybridized geometry of the amino nitrogen in free
ligands in fact would facilitate the ionization process of
the amino nitrogen.32 Upon coordination with Zn(II), the
electron-accepting ability of the pyridine ring would be
enhanced and become sufficiently strong to interact with
arenes, as previously demonstrated by the metal-ion
induced fluorescence quenching or ICT formation in
arene/pyridine or arene/bipyridne systems.5,33 While the
electron-accepting ability of the Zn(II)-coordinated pyri-
dine rings in dpa/Zn(II) is expected to be reduced by the
conjugated electron-donating amino nitrogen, this amino
nitrogen effect appears to be largely diminished due to a
pyramidylization of the amino nitrogen and a twisting
of the Cpy-N bond (i.e., less π-conjugated).
FIGURE 5. Plots of the Stokes shift of the ICT fluorescence
(cm-1) against the free energy of ICT formation (-∆GICT) for
1H, 1CN, 3AA, 3EE, 3MP, and 3PP.
Unlike the Zn(II)-induced fluorescence quenching for
1DPA and red shift of the ICT fluorescence for 1H, the
complexation of 1CN with Zn(II) results in a small
increase in the LE fluorescence at the large expense of
the ICT fluorescence (Figure 7a). The corresponding plot
of the intensity change for the ICT fluorescence against
the concentration of Zn(II) is shown in Figure 7b along
with the cases of Cu(II), Ni(II), and Cd(II). Nonlinear
fittings of the data in Figure 7b lead to binding con-
stants, expressed as log K, of 5.4, 5.1, 5.0, and 5.0 for
Zn(II), Ni(II), Cu(II), and Cd(II), respectively.34 The
Weller equation (eq 1) also predicts an exogonic ICT
process between the stilbene and the dpa/Zn(II) group,
but the driving force is relatively smaller than that for
1H/Zn(II) and 1DPA/Zn(II) (Table 3). Thus, the absence
of a new ICT fluorescence indicates that the ICT interac-
tion in 1CN/Zn(II) is weak and/or the ICT state of 1CN/
Zn(II) is nonfluorescent. In addition, the small recovery
in the LE fluorescence is consistent with the inherently
low fluorescence quantum yield of trans-4-cyanostilbene
(Φf ) 0.005),24 which is known to undergo efficient trans
FIGURE 6. (a) Fluorescence titration spectra of 1H (10 µM)
with Zn(ClO4)2‚6H2O (0, 0.3, 0.4, 0.5, 0.6, 0.7, 1.0, 3.0, 5.0, 10.0
equiv) in acetonitrile (excitation at 300 nm), where the curved
arrow shows the fluctuation of the LE fluorescence intensity
and the arrow shows the red shift of the ICT fluorescence, and
(b) fluorescence spectra of 1H in its free form (solid line) and
in the presence of a mixture of Zn(II), Ni(II), and Cd(II) (dash
line, 1 equiv for each), a mixture of Zn(II), Ni(II), Cd(II), and
Cu(II) (dot line, 1 equiv for each), or a mixture of Ni(II),
Cd(II), and Cu(II) (dash dot line, 1 equiv for each).
1H/Zn(II), but the direction of charge transfer is reversed
on going form 1H to 1H/Zn(II). The presence of an ICT
state for 1H/Zn(II) agrees with the electron-accepting
character of dpa/Zn(II) that was previously indicated by
the “on-off” fluorescence response of 1DPA to Zn(II).8
It is also supported by a negative value of ∆GICT calcu-
lated based on eq 1 (Table 3). According to the X-ray
crystal structure of 2X/ZnCl2 (Figure 1), the stilbene-
dpa/Zn(II) ICT interactions should also occur through the
σ bonds. It is interesting to note that such a red-shifted
ICT fluorescence is only selectively induced by Zn(II), and
the other metal ions investigated in this work either
quench both the ICT and the LE fluorescence (i.e.,
Ni(II), Hg(II), Y(III), Co(II), Cd(II), Cu(II), and Ag(I)) or
have a negligible influence in the spectra (i.e., Li(I),
Na(I), K(I), Mg(II), Ca(II), and Ba(II)). As shown in Figure
6b, the 1H/Zn(II) ICT fluorescence is still observed even
when the acetonitrile solution contains other transition
(29) Majima, T.; Tojo, S.; Ishida, A.; Takamuku, S. J. Phys. Chem.
1996, 100, 13615-13623.
(30) Lewis, F. D.; Bedell, A. M.; Dykstra, R. E.; Elbert, J. E.; Gould,
I. R.; Farid, S. J. Am. Chem. Soc. 1990, 112, 8055-8064.
(31) Varnes, A. W.; Dodson, R. B.; Wehry, E. L. J. Am. Chem. Soc.
1972, 94, 946-950.
(32) Sakanoue, K.; Motoda, M.; Sugimoto, M.; Sakaki, S. J. Phys.
Chem. A 1999, 103, 5551-5556.
(33) (a) de Silva, A. P.; Dixon, I. M.; Gunaratne, H. Q. N.;
Gunnlaugsson, T.; Maxwell, P. R. S.; Rice, T. E. J. Am. Chem. Soc.
1999, 121, 1393-1394. (b) Wagner, B. D.; McManus, G. J.; Moulton,
B.; Zaworotko, M. J. Chem. Commun. 2002, 2176-2177.
(34) Connors, K. A. Binding Constants-The Measurement of Mo-
lecular Complex Stability; John Wiley & Sons: New York, 1987; p 152.
J. Org. Chem, Vol. 70, No. 15, 2005 6071

Yang et al.
second fluorophore36 or the participation of fluorophore
in the binding of Zn(II) (i.e., an intrinsic fluoroiono-
phore).37 It is noted that dpa is an arylamino donor, but
dpma is an alkylamino donor. Although D-C1 spacer-A
systems with alkylamino donors generally show no ICT
fluorescence, an arylamino donor is not necessary to
observe dual fluorescence for current stilbene systems,
as shown by 3EE.
Concluding Remarks
The LE-ICT dual fluorescent properties for 1H and
1CN in acetonitrile have been investigated in the absence
and presence of metal ions. The presence of ICT fluores-
cence in polar but not in nonpolar solvents is a charac-
teristic of a through-bond ICT state, consistent with their
short C1 spacer. The ICT process in free ligands occurs
from the dpa (D) to the stilbene (A) group. When the dpa
group in 1H is replaced by stronger amino donors, the
ICT fluorescence persists with a larger Stokes shift. Upon
binding with transition metal ions, the direction of ICT
processes is reversed, resulting in changes in both the
LE and ICT fluorescence bands. Whereas the LE/ICT
intensity ratio is increased in most cases, indicating that
the complexes do not produce noticeable ICT fluorescence,
dual fluorescence is observed for 1H/Zn(II). The formation
of a fluorecent ICT state for 1H/Zn(II) has provided new
evidence, complementary to the Zn(II)-induced fluores-
cence quenching for 1DPA, for the dpa/Zn(II) group being
an effective electron acceptor. The fluorescence spectra
for both the free ligands and complexes are very sensitive
to the redox properties of the stilbene group, as mani-
fested by the substituent-dependent fluoroionophoric
properties for 1H, 1CN, and 1DPA toward Zn(II). Our
results presented herein not only show that dpa-based
fluoroionophores could be selective and sensitive but also
indicate that stilbene fluorophore is useful in the design
of LE-ICT ratiometric D-s-A probes. Further exploration
of the photochemical behavior of these and the related
D-s-A systems is in progress.
FIGURE 7. (a) Fluorescence titration spectra of 1CN (10 µM)
with Zn(ClO4)2‚6H2O (0, 0.2, 0.4, 0.6, 0.8, 1.0, 3.0, 5.0, 10.0
equiv) in acetonitrile (excitation at 320 nm) and (b) the
corresponding plot of the change in the ICT fluorescence
intensity at 552 nm (∆I552) against the concentration of
Zn(II), Ni(II), Cu(II), and Cd(II).
FIGURE 8. Ratiometric fluorescence responses of the LE (385
nm) vs ICT (552 nm) for 1CN (10 µM) to 1 equiv of metal ions
(10 µM) in acetonitrile.
f cis photoisomerization.25 Spectral changes with a
decrease of the ICT band and an increase of the LE band
are also observed for other transition metal ions, but the
conversion yield of ICT f LE fluorescence depends on
the nature of metal ions. When compared with Zn(II),
the conversion yield is similar for Ni(II) but it is much
smaller for metal ions such as Cu(II), Co(II), and Ag(I).
Alkali and alkaline earth metal ions again show negli-
gible effects on the fluorescence of 1CN. These results
are illustrated in Figure 8 by comparing the LE (385 nm)/
ICT (552 nm) fluorescence intensity ratio (LE/ICT) at the
presence of 1 equiv of metal ion vs that of the free ligand
(i.e., (LE1/ICT1)/(LE0/ICT0)). The use of a different evalu-
ation parameter, LE1/(LE0 + ICT0), focusing on the
intensity of the LE band, leads to a similar result of ion
selectivity.
The fluorescent ICT formation in 1H, 1H/Zn(II), and
1CN is one thing particularly interesting when compared
to the D-s-A systems with the dpa analogue, bis(2-
pyridylmethyl)amine (dpma), as the ionophoric donor for
Zn(II). The dpma derivatives display only the LE fluo-
rescence in the absence and the presence of Zn(II)
and thus the “off-on” fluorescence sensing mode.35 For
ratiometric measurement, the dpma systems require a
Experimental Section
Materials. Solvents for organic synthesis were reagent
grade or HPLC grade but all were HPLC grade for spectra
and quantum yield measurements. Typical procedures for the
synthesis of compounds 1-3 have been previously reported,8
and the characterization data of new compounds 1H, 1CN,
2R, 2X, 3AA, 3MP, 3PP, 9, and 12 are as follows:
trans-4-N,N-Bis(2-pyridyl)aminomethylstilbene (1H).
1
Mp 118-119 °C; H NMR (500 MHz, CDCl3) δ 5.51 (s, 2H),
6.83 (dd, J ) 4.9 and 7.0 Hz, 2H), 7.02 (d, J ) 16.3 Hz, 1H),
7.07 (d, J ) 16.3 Hz, 1H), 7.18 (d, J ) 8.3 Hz, 2H), 7.24 (t, J
) 7.4 Hz, 1H), 7.32-7.35 (m, 4H), 7.41 (d, J ) 8.3 Hz, 2H),
7.47 (d, J ) 7.4 Hz, 2H), 7.55 (ddd, J ) 1.2 7.0, and 8.3 Hz,
2H), 8.31 (dd, J ) 1.2 and 4.9 Hz, 2H) ppm; 13C NMR (125
(35) (a) Walkup, G. K.; Burdette, S. C.; Lippard, S. J.; Tsien, R. Y.
J. Am. Chem. Soc. 2000, 122, 5644-5645. (b) Hirano, T.; Kikuchi, K.;
Urano, Y.; Higuchi, T.; Nagano, T. J. Am. Chem. Soc. 2000, 122,
12399-12400. (c) Burdette, S. C.; Walkup, G. K.; Spingler, B.; Tsien,
R. Y.; Lippard, S. J. J. Am. Chem. Soc. 2001, 123, 7831-7841. (d) Ojida,
A.; Mito-oka, Y.; Inoue, M.; Hamachi, I. J. Am. Chem. Soc. 2002, 124,
6256-6258. (e) Hirano, T.; Kikuchi, K.; Urano, Y.; Nagano, T. J. Am.
Chem. Soc. 2002, 124, 6555-6562.
(36) Woodroofe, C. C.; Lippard, S. J. J. Am. Chem. Soc. 2003, 125,
11458-11459.
(37) Maruyama, S.; Kikuchi, K.; Hirano, T.; Urano, Y.; Nagano, T.
J. Am. Chem. Soc. 2002, 124, 10650-10651.
6072 J. Org. Chem., Vol. 70, No. 15, 2005

Dipyridylaminomethylstilbenes
MHz, CDCl3) δ 51.2, 114.57, 114.60, 117.2, 126.4, 126.5, 127.5,
128.1, 128.6, 128.7, 135.8, 137.2, 137.5, 139.1, 148.3, 157.1
ppm; IR (KBr) 969, 1319, 1373, 1469 cm-1; FAB-HRMS calcd
for C25H21N3 (M+) 363.1735, found 363.1734.
126.4, 126.5, 126.7, 127.2, 127.6, 128.4, 128.7, 128.9, 129.2,
136.1, 137.4, 137.5, 138.6, 149.8, 157.8 ppm; IR (KBr) 690, 960,
1221, 1258, 1495, 1589, 3024 cm-1; FAB-HRMS calcd for
C22H21N 299.1674, found 299.1674.
trans-4-N,N-Bis(2-pyridyl)aminomethyl-4′-cyanostil-
trans-4-N,N-Diphenylaminomethylstilbene (3PP). Mp
1
1
bene (1CN). Mp 139-141 °C; H NMR (500 MHz, CDCl3) δ
133-134 °C; H NMR (500 MHz, CDCl3) δ 5.00 (s, 2H), 6.93
5.50 (s, 2H), 6.84 (dd, J ) 4.9 and 7.8 Hz, 2H), 6.98 (d, J )
16.3 Hz, 1H), 7.13 (d, J ) 16.3 Hz, 1H), 7.16 (d, J ) 8.4 Hz,
2H), 7.35 (d, J ) 8.2 Hz, 2H), 7.40 (d, J ) 8.2 Hz, 2H), 7.48-
7.52 (m, 4H), 7.58 (d, J ) 8.4 Hz, 2H), 8.31 (dd, J ) 1.4 and
4.9 Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 51.1, 110.4,
114.5, 117.3, 119.07, 126.1, 126.8, 127.0, 127.7, 132.3, 132.5,
134.7, 137.3, 140.4, 142.0, 148.3, 157.1 ppm; IR (KBr) 963,
1322, 1468, 2218 cm-1; FAB-HRMS calcd for C26H20N4 (M+)
388.1688, found 388.1690. Anal. Calcd for C26H20N4: C, 80.39,
H, 5.19, N, 14.42. Found: C, 80.10, H, 5.05, N, 14.43.
N,N-Bis(2-pyridyl)-N-hexadecylamine (2R). Mp 36-38
°C; 1H NMR (500 MHz, CDCl3) δ 0.85 (t, J ) 5.7 Hz, 3H), 1.20-
1.30 (m, 26H), 1.65 (quin, J ) 7.5 Hz, 2H), 4.13 (t, J ) 7.5 Hz,
2H), 6.82-6.84 (m, 2H), 7.06 (d, J ) 8.3 Hz, 2H), 7.48-7.51
(m, 2H), 8.33 (d, J ) 4.9 Hz, 2H) ppm; 13C NMR (125 MHz,
CDCl3) δ 14.1, 22.7, 27.1, 28.3, 29.4, 29.5, 29.6, 29.67, 29.71,
31.9, 48.4, 114.7, 116.8, 137.1, 148.3, 157.5 ppm; IR (KBr) 1321,
1376, 1468, 2847, 2917 cm-1; FAB-HRMS calcd for C30H41N3
(M+) 395.3300, found 395.3292.
(t, J ) 7.3 Hz, 2H), 7.07 (d, J ) 7.9 Hz, 6H), 7.24 (t, J ) 7.2
Hz, 5H), 7.3 (m, 2H), 7.44 (d, J ) 8.1 Hz, 2H), 7.49 (d, J ) 7.4
Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 56.2, 120.7, 121.4,
126.5, 126.8, 126.9, 127.6, 128.4, 128.7, 129.3, 136.0, 137.4,
138.8, 148.1 ppm; IR (KBr) 693, 962, 1221, 1258, 1495, 1589,
3024 cm-1; FAB-HRMS calcd for C27H23N 361.1830, found
361.1832.
trans-4-Cyano-4′-(N-(2-pyridyl)amino)methylstil-
bene (9). Mp 199-201 °C; 1H NMR (500 MHz, CDCl3) δ 4.57
(d, J ) 5.8 Hz, 2H), 5.31 (br s, 1H), 6.44 (d, J ) 8.4 Hz, 1H),
6.65 (dd, J ) 4.2 and 8.0 Hz, 1H), 7.10 (d, J ) 16.3 Hz, 1H),
7.23 (d, J ) 16.3 Hz, 1H), 7.41 (d, J ) 8.1 Hz, 2H), 7.47 (dd,
J ) 8.0 and 8.4 Hz, 1H), 7.53 (d, J ) 8.1 Hz, 2H), 7.60 (d, J )
8.3 Hz, 2H), 7.66 (d, J ) 8.3 Hz, 2H), 8.13 (d, J ) 4.2 Hz, 2H)
ppm; 13C NMR (125 MHz, CDCl3) δ 46.0, 107.2, 110.6, 113.2,
119.0, 126.7, 126.8, 127.2, 127.8, 131.9, 132.5, 135.4, 138.1,
139.6, 141.8, 147.1, 158.1 ppm; IR (KBr) 969, 1325, 1472, 2218,
3243 cm-1; FAB-HRMS calcd for C27H18N3 (M + H+) 312.1501,
found 312.1495.
N,N-Bis(2-pyridyl)-N-(4-methylbenzyl)amine (2X). Mp
98-100 °C; 1H NMR (500 MHz, CDCl3) δ 2.29 (s, 3H), 5.48 (s,
2H), 6.84 (dd, J ) 4.9 and 7.2 Hz, 2H), 7.07 (d, J ) 7.9 Hz,
2H), 7.18 (d, J ) 8.4 Hz, 2H), 7.24 (d, J ) 7.9 Hz, 2H), 7.51
(ddd, J ) 1.3, 7.2 and 8.4 Hz, 4H), 8.32 (dd, J ) 1.3 and 4.9
Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 21.0, 51.0, 114.5,
117.0, 126.9, 129.0, 136.0, 136.2, 137.1, 148.2, 157.1 ppm; IR
(KBr) 1227, 1375, 1426, 1470 cm-1; FAB-HRMS calcd for
C18H17N3 (M+) 275.1422, found 275.1422.
trans-4-N-(4-Methoxyphenyl)aminomethylstilbene (12).
1
Mp 153-154 °C; H NMR (500 MHz, CDCl3) δ 3.00 (s, 3H),
4.52 (s, 2H), 6.60 (d, J ) 6.9 Hz, 2H), 6.76 (d, J ) 6.9 Hz, 2H),
7.08 (s, 2H), 7.24 (m, 1H), 7.34 (m, 4H), 7.47 (d, J ) 8.2 Hz,
2H), 7.50 (d, J ) 8.0 Hz, 2H) ppm; 13C NMR (125 MHz, CDCl3)
δ 49.0, 55.8, 114.2, 114.9, 126.5, 126.7, 127.6, 127.9, 128.3,
128.5, 128.7, 136.3, 137.3, 139.1, 142.3, 152.2 ppm; IR (KBr)
691, 967, 1245, 1506 cm-1; FAB-HRMS calcd for C22H21NO
315.1623, found 315.1621.
trans-4-N,N-Bis(4-methoxyphenyl)aminomethylstil-
1
Acknowledgment. Financial support for this re-
search was provided by the National Science Council,
ROC, and by the NCU-ITRI Joint Research Center. We
greatly appreciate Professor S.-L. Wang and Miss F.-L.
Liao at the Instrumentation Center of National Tsing
Hua University for resolving the crystal structures of
1H, 2X, 3PP, and 2X/ZnCl2.
bene (3AA). Mp 128-129 °C; H NMR (500 MHz, CDCl3) δ
3.76 (s, 6H), 4.87 (s, 2H), 6.79 (d, J ) 8.9 Hz, 4H), 6.95 (d, J
) 8.9 Hz, 4H), 7.07 (s, 2H), 7.25 (m, 1H), 7.34 (m, 4H), 7.45
(d, J ) 8.1 Hz, 2H), 7.50 (d, J ) 7.5 Hz, 2H) ppm; 13C(125
MHz, CDCl3) δ 55.6, 56.9, 114.6, 121.8, 126.5, 126.7, 127.1,
127.5, 128.3, 128.4, 128.7, 136.0, 137.4, 142.5, 154.3 ppm; IR
(KBr) 694, 965, 1238, 1514, 3386 cm-1; FAB-HRMS calcd
for C29H27NO2 421.2042, found 421.2040. Anal. Calcd for
C29H27NO2: C, 82.63, H, 6.46, N, 3.32. Found: C, 82.48, H,
6.44, N, 3.09.
Supporting Information Available: Experimental meth-
ods, 1H and 13C NMR spectra for new compounds, and crystal
refinement data for 1H, 2X, 3PP, and 2X/ZnCl2, as well as
X-ray experimental details (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
trans-4-N-Methyl-N-phenylaminomethylstilbene (3MP).
1
Mp 100-101 °C; H NMR (500 MHz, CDCl3) δ 3.00 (s, 3H),
4.52 (s, 2H), 6.73 (m, 3H), 7.07 (s, 2H), 7.22 (m, 4H), 7.37 (t, J
) 7.5 Hz, 2H), 7.44 (d, J ) 8.1 Hz, 2H), 7.48 (d, J ) 7.6 Hz,
2H) ppm; 13C NMR (125 MHz, CDCl3) δ 38.5, 56.5, 112.5, 116.6,
JO0509049
J. Org. Chem, Vol. 70, No. 15, 2005 6073