Syntheses and fluorescence of salicylaldimine Schiff base derivatives of 1,1′-Di(aminoethylaminocarbonylalkyl)-2,2′-biimidazole

Article abstract of DOI:10.1002/jhet.5570450645

(Chemical Equation Presented) The amide-amine, 1,1′- di(aminoethylaminocarbonylethyl)-2,2′-biimidazole (DAEPB) (1), and subsequent Schiff base imine product, 1,1′- di(salicylaldiminoethylaminocarbonylethyl)-2,2′-biimidazole (DSEB) (2a), have been synthesized from the ester, 1,1′-di(ethoxycarbonylethyl)-2, 2′-biimidazole (DEPB). Additionally, 1,1′- di(salicylaldiminoethylaminocarbonylmethyl)-2,2′-biimidazole (DSMB) (2b), was prepared from its corresponding amide-amine. All compounds were characterized with FTIR, NMR and elemental analyses. The salicylaldimines, compounds (2a) and (2b), exhibit fluorescence at 540 and 520 nm, respectively, over a broad range of excitation wavelengths.

Full text of DOI:10.1002/jhet.5570450645

Nov-Dec 2008
1843
Syntheses and Fluorescence of Salicylaldimine Schiff Base
Derivatives of 1,1'-Di(aminoethylaminocarbonylalkyl)-
2,2'-biimidazole
William M. Barnett, Peris J. Carr, Joseph A. Counsil and Harvest L. Collier*
Chemistry Department, University of Missouri University of Science and Technology,
Rolla, MO 65401
Email: hcollier@mst.edu
Received September 3, 2007
R
O
H
C
O
HN
C
N
HN
C
NH2
O
C
O
O
H
HO
(
)
(
(
)
(
(
)
(
CH2
CH2
CH2
n
n
n
HO
H2N
NH2
N
N
N
N
N
N
N
N
N
N
N
N
EtOH
)
)
)
H2C
n
H2C
H2C
OH
n
n
C
O
C
O
C O
R
O
H2N
NH
C
H
N
NH
n = 1, R = CH3
n = 2, R = CH2CH3
The amide-amine, 1,1'-di(aminoethylaminocarbonylethyl)-2,2'-biimidazole (DAEPB) (1), and
subsequent Schiff base imine product, 1,1'-di(salicylaldiminoethylaminocarbonylethyl)-2,2'-biimidazole
(DSEB) (2a), have been synthesized from the ester, 1,1'-di(ethoxycarbonylethyl)-2,2'-biimidazole (DEPB).
Additionally, 1,1'-di(salicylaldiminoethylaminocarbonylmethyl)-2,2'-biimidazole (DSMB) (2b), was
prepared from its corresponding amide-amine. All compounds were characterized with FTIR, NMR and
elemental analyses. The salicylaldimines, compounds (2a) and (2b), exhibit fluorescence at 540 and 520
nm, respectively, over a broad range of excitation wavelengths.
J. Heterocyclic Chem., 45, 1843 (2008).
INTRODUCTION
compounds assume a trans orientation in the crystalline
state that may preclude single metal binding by both
substituents.
Schiff base imines have been the focus of several
investigations recently with facile preparation of a variety
of acyclic and cyclic macromolecules and their transition
metal ion complexes [1,2]. Imine macrocycles, possessing
multidentate and polynuclear metal coordination sites, are
of particular interest for their antifungal and antibacterial
activity [1]. The macrocycles have been synthesized by
reacting rigid aromatic dicarboxaldehydes and aliphatic
diamines under high dilution conditions. Metal complexes
of salicylaldimine derivatives having liquid crystalline
properties have been prepared by reacting equimolar
quantities of amine and aldehyde, yielding compounds
The present study involves the synthesis of a pair of
disalicylaldimines for use as macromolecular precursors
for selective metal ion binding and macrocycle formation.
During the course of the investigation, the compounds
were observed to fluoresce brightly over a broad range of
excitation wavelengths. Fluorescent compounds are of
interest for their potential applications as light emitting
diodes, photovoltaic devices, biological probes and
sensors [17-19]. While fluorescence has been observed
for 2,2'-biimidazole and a few of its derivatives [20-22],
fluorescence of the biimidazole amide-amine precursors
for the title compounds was not observed to an
appreciable degree. However, fluorescence of salicyl-
aldehyde is well known and occurs in the yellow-green
region of the spectrum [25], precisely the region over
which the title compounds fluoresce.
exhibiting
high
birefringence,
polarizability,
paramagnetism and color [2].
Similarly, macromolecules containing 2,2'-biimidazole,
including polymers [3-8] and macrocycles [9,10] have
been described in efforts to explore relationships between
structure, selective binding of metal ions, and thermal
stability. Acyclic derivatives of 2,2'-biimidazole have
been shown to exhibit cardiotonic [11] and antiprotozoal
properties [12]. Over the past few years, new 1,1'-
disubstituted-2,2'-biimidazole ester, amide-amine, and
hydrazide macromolecules have been reported [13-16].
X-ray diffraction crystallography revealed these
RESULTS AND DISCUSSION
The disalicylaldimines were prepared by reacting
aliphatic amines with the aromatic aldehyde,
salicylaldehyde. The rigidity afforded by the aldehyde is
important for the chemical stabilization of the resulting

1844
W. M. Barnett, P. J. Carr, J. A. Counsil and H. L. Collier
Vol 45
imine functional group [1].
Acid catalyst was
Scheme I
unnecessary, as the relatively acidic proton of
salicylaldehyde was sufficient for the reaction to proceed
rapidly.
O
C
HC
N
O
Solid-state fluorescence was observed for both
compounds in their crystalline form. Both compounds
exhibited fluorescence in the green-yellow visible region
of the spectrum over a broad range of excitation
wavelengths. DSEB (2a) and DSMB (2b) had emission
maxima at 540 and 520 nm respectively (Figures 1 and 2).
UV-visible absorption also occurred over a broad range,
encompassing the excitation and remaining visible region.
When melted into an amorphous mass, fluorescence was
lost; however, after recrystallization, fluorescence was
restored. The compounds exhibited fluorescence in
suspension, but in solution, fluorescence was quenched.
These observations suggest solid-state morphology is an
important contributing factor for fluorescence.
NH
(
CH2
)
N
N
N
N
n
H
H
N
(
)
n
H2C
HN
O
CH
C
O
nitrogen and phenolic proton in Scheme I, have been
reported to involve excited state intramolecular proton
transfer [23,24], in which the nitrogen atom (oxygen atom
in the case of salicylaldehyde) serves as a proton acceptor
during the fluorescing process. As neither of the amide-
amine precursors was noted to fluoresce, the fluorescence
exhibited by the title compounds is likely due entirely to
the salicylaldimine moiety. Disruption of the hydrogen
bonding of this specific morphological state accounts for
the disappearance and quenching of visible fluorescence
in the melt and solution.
NMR studies indicate intramolecular hydrogen bonding
of the phenol proton as evidenced by the characteristic
downfield location of its chemical shift.
Several
intramolecular hydrogen bonding interactions are possible
for the disalicylaldimines (Scheme I.) Fluorescence of
salicylaldehyde [25] and 2-(2-hydroxyphenyl)imidazo-
[1,2-a]pyridine analogues [23,24] exhibiting hydrogen
bonding similar to that shown between the salicylaldimino
EXPERIMENTAL
Melting points were determined using an Electro-thermal
Capillary Melting Point Apparatus and are uncorrected. Infrared
spectra were obtained from a Nicolet Nexus 470 Fourier
Transform Infrared Spectrometer using pressed potassium
bromide pellets. 1H NMR spectra were obtained using a Varian
Unity Inova High Resolution 400 MHz Fourier Transform
Pulsed Nuclear Magnetic Resonance spectrometer. In the case
of D2O, sodium trimethylsilylpropionate was used as
a
reference. Elemental analyses were conducted using a Perkin
Elmer 2400 CHN Elemental Analyzer. Fluorescence specta
were obtained with
a Perkin Elmer LS-5 Fluorescence
Spectrophotometer. Absorbance spectra were obtained with a
Cary 100 Bio UV-Visible Spectrophotometer with solids
attachment. 1,1'-Di(aminoethylacetamido)-2,2'-biimidazole [13]
(DAEAB) and 1,1'-di(ethoxypropionato)-2,2'-biimidazole [15]
(DEPB) were prepared according to published procedures. All
other reagents were obtained from Aldrich Chemical Co., and
used as received.
Figure 1. Fluorescence spectrum of DSEB with emission maxima
at 540 nm.
1,1'-Di(aminoethylaminocarbonylethyl)-2,2'-biimidazole
(1). To 0.25 g (0.75 mmol) 1,1'-di(ethoxycarbonylethyl)-2,2'-
biimidazole (DEPB) was added 3.0 mL anhydrous 1,2-
diaminoethane. The mixture was stirred at room temperature
and dissolved rapidly to form a pale yellow solution. Over a
period of 24 hours, the product evolved as a white suspension.
The reaction contents were poured into 20 mL acetonitrile, the
white solid collected via gravity filtration, recrystallized from
acetonitrile and dried in vacuo to yield white powdery product,
0.17 g (63%), mp 154-155°C; ir: v 3132, 3117, 3045 (Ar-H),
1
1654, 1561 (CON) cm-1; H nmr (D2O): ꢀ 2.6 (m, 8H, CH2), 3.2
(t, 4H, CH2), 4.5 (t, 4H, CH2), 7.2 (s, 2H, H5, H5'), 7.3 (s, 2H, H4,
H4'). Anal. Calcd. for C16H26N8O2: C, 53.01; H, 7.24; N, 30.92;
O, 8.83. Found: C, 52.90; H, 7.21; N, 30.64.
Figure 2. Fluorescence spectrum of DSMB with emission maxima
at 520 nm.

Nov-Dec 2008
Schiff Base Derivatives of 1,1'-Di(aminoethylaminocarbonylalkyl)-2,2'-biimidazole
1845
[1] Ugras, H.I.; Basaran, I.; Kilic, T.; Cakir, U. J. Heterocyclic
Chem. 2006, 43, 1679.
[2] Paschke, R.; Liebsch, S.; Tschierske, C.; Oakley, M.; Sinn, E.
General Procedure for the Preparation of Salicylaldimine
Schiff Base Derivatives of 1,1'-Di(aminoethylamino-
carbonylalkyl)-2,2'-biimidazole. To 0.25 g (0.75 mmol) of
either 1,1'-di(aminoethyl-aminocarbonylmethyl)- or 1,1'-di-
Inorg. Chem. 2003, 42, 8230.
[3] Chi, W.; Collier, H. J. Macromol. Sci. Chem. 1988, A25,
1543.
(aminoethylamino-carbonylethyl)-2,2'-biimidazole
(1)
was
added 5.0 mL salicylaldehyde. The mixtures were stirred at
room temperature and the amines dissolved over the course of
two minutes to form yellow solutions. After several minutes,
the solutions became opaque as pale yellow precipitate formed.
To each of these stirred mixtures was added 5 mL ethanol and
heating applied via heating mantle to effect solution. Once the
transparent yellow solutions formed, heating was discontinued
and the reaction contents were allowed to cool with stirring.
Upon cooling, yellow suspensions were observed. The yellow
solids were collected by gravity filtration, recrystallized twice
from ethanol (0.2 g product to 15 mL ethanol) with chilling, and
dried in vacuo.
[4] Liu, F.J.; Kokorudz, J.S.; Collier H.L. J. Polym. Sci. Part A:
Polym. Chem. 1988, 26, 3015.
[5] Elmer, R.A.; Collier, H.L. Macromol. Rep. 1993, A30, 1.
[6] Lister, R.L.; Collier, H.L. Polym. Prep. 1993, 34, 360.
[7] Barnett, W.M. Ph.D. thesis, University of Missouri-Rolla,
Rolla, MO, 1997.
[8] Collier, H.L.; Cho, I.Y. Korea Polym. J. 1997, 5, 179.
[9] Sargent, A.L.; Hawkins, I.C.; Allen, W.E.; Liu, H.; Sessler,
J.L.; Fowler, C.J. Chem. Eur. J. 2003, 9, 3065.
[10] Lehn, J.; Regnouf de Vains, J. Tetrahedron Lett. 1989, 30,
2209.
[11] Matthews, D.P.; McCarthy, J.R.; Whitten, J.P.; Kastner, P.R.;
Barney, C.L.; Marshall, F.N.; Ertel, M.A.; Burkhard, T.; Shea, P.J.;
Kariya, T. J. Med. Chem. 1990, 33, 317.
[12] Melloni, P.; Metilli, R.; Bassini, D.F.; Confalonieri, C.;
Logemann, W.; deCarneri, I.; Trane, F. Arzneim. Forsch. 1975, 25, 9.
[13] Barnett, M.; Secondo, P.; Collier, H. J. Heterocyclic Chem.
1996, 33, 1363.
[14] Barnett, W.M.; Lin, G.; Collier, H.L.; Baughman, R.G. J.
Chem. Crystallogr. 1997, 27, 423.
[15] Barnett, W.M.; Baughman, R.G.; Collier, H.L.; Vizuete,
1,1'-Di(salicylaldiminoethylaminocarbonylethyl)-2,2'-bi-
imidazole (2a). Bright yellow needles, 0.23 g (58%), mp 170-
171°C; ir: v 3431 (O-H), 3336 (N-H), 3066 (Ar-H), 2974, 2927
1
(C-H), 1639 (C=O), 1614 (C=N), 1541 (II, N-H) cm-1; H nmr
(d7-DMF): ꢀ 2.7 (t, 4H, CH2-C=O), 3.4-3.6 (m, 4H, CON-CH2),
3.6-3.7 (t, 4H, CH2-N=C), 4.7 (t, 4H, Im-CH2), 6.9 (m, 4H, Ar-
H), 7.0 (s, 2H, Im-H5,5'), 7.2-7.3 (s, 2H, Im-H4,4'), 7.3-7.4 (t, 2H,
Ar-H), 7.4-7.5 (d, 2H, Ar-H), 8.2 (t, 2H, HN-C=O), 8.4-8.5 (s,
2H, N=CH), 13.3 (s, 2H, OH). Anal. Calcd. for C30H34N8O4: C,
63.13; H, 6.02; N, 19.64; O, 11.21. Found: C, 62.83; H, 5.78; N,
19.28.
W.G. J. Chem. Crystallogr. 1999, 29, 765.
[16] Barnett, W.M.; Baughman, R.G.; Secondo, P.M.; Hermansen,
C.J. Acta. Cryst. 2002, C58, 565.
[17] Arachchige, I.U.; Brock, S.L. J. Am. Chem. Soc. 2007, 129,
1840.
1,1'-Di(salicylaldiminoethylaminocarbonylmethyl)-2,2'-bi-
imidazole (2b). Fine pale yellow needles, 0.25 g (62%), mp
206-207°C; ir: v 3429 (O-H), 3302 (N-H), 3080 (Ar-H), 2933,
[18] Nakayama-Ratchford, N.; Bangsaruntip, S.; Sun, X.;
Welsher, K.; Dai, H. J. Am. Chem. Soc. 2007, 129, 2448.
[19] Behanna, H.A.; Rajangam, K.; Stupp, S.I. J. Am. Chem. Soc.
2007, 129, 321.
[20] Fu, Y.; Zhao, Y.; Lan, Y.; Wang, Y.; Qiu, Y.; Shao, K.; Su,
Z. Inorg. Chem. Comm. 2007, 10, 720.
[21] Sang, R.; Xu, L. Inorg. Chem. 2005, 44, 3731.
[22] Causey, C.P.; Allen, W.E. J. Org. Chem. 2002, 67, 5963.
[23] Tanaka, K.; Kurushima, T.; Iwata, S.; Shimada, S. J.
Heterocyclic Chem. 2007, 44, 303.
[24] Douhal, A.; Amat-Guerri, F.; Acuña, A.U. J. Phys. Chem.
1995, 99, 76.
1
2873 (C-H), 1660 (C=O), 1632 (C=N), 1560 (II, N-H) cm-1; H
nmr (d7-DMF): ꢀ 3.4-3.6 (m, 4H, CON-CH2), 3.6-3.7 (t, 4H,
CH2-N=C), 5.3 (s, 4H, Im-CH2), 6.9 (m, 4H, Ar-H), 6.9-7.0 (s,
2H, Im-H5,5'), 7.2-7.3 (s, 2H, Im-H4,4'), 7.3-7.4 (t, 2H, Ar-H), 7.4-
7.5 (d, 2H, Ar-H), 8.4 (t, 2H, HN-C=O), 8.5 (s, 2H, N=CH),
13.3 (s, 2H, OH). Anal. Calcd. for C28H30N8O4: C, 61.97; H,
5.58; N, 20.65; O, 11.79. Found: C, 61.68; H, 5.34; N, 20.32.
REFERENCES AND NOTES
*
Corresponding author: Tel: 573-341-4420; Fax 573-341-
[25] Stock, K.; Bizjak, T.; Lochbrunner, S. Chem. Phys. Lett.
2002, 354, 409.
6033; Email address: hcollier@mst.edu