Synthesis, characterization and spectroscopic investigation of a novel phenylhydrazone Schiff base with solvatochromism

Article abstract of DOI:10.1016/j.saa.2009.11.050

A novel Schiff base of 4,5-diazafluorene-9-p-nitrophenylhydrazone (DAFND) has been synthesized and characterized. The crystal structures of DAFND and its analogue 4,5-diazafluorene-9-phenylhydrazone (DAFPD) were determined by single crystal X-ray diffraction method. X-ray analyses reveal that DAFPD comprise of a nonplanar molecule and all atoms of DAFND are essentially coplanar. The color of DAFND changes from brown to blue when heated, so called thermochromism and the spectroscopic properties of the two compounds are investigated by electronic absorption spectra, showing DAFND possess solvatochromism, while DAFPD does not have thermochromic and solvatochromic properties. The λ_max of DAFND within various pure solvents are different ranging from 370 nm in toluene to 614 nm in pyridine. The imaginable mechanisms of thermochromism and solvatochromism are proposed. Crown Copyright

Full text of DOI:10.1016/j.saa.2009.11.050

Spectrochimica Acta Part A 75 (2010) 753–759
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and spectroscopic investigation of a
novel phenylhydrazone Schiff base with solvatochromism
Mingtian Lia,∗, Jun Huangb, Xuan Zhoub, Hong Luoa
a Institute of Materials and Chemical Engineering, Sichuan University of Science and Engineering, Zigong 643000, China
b Key Laboratory of Fiber Optic Sensing Technology and Information Processing (Ministry of Education), Wuhan University of Technology, Wuhan 430070, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 August 2009
Accepted 20 November 2009
A novel Schiff base of 4,5-diazafluorene-9-p-nitrophenylhydrazone (DAFND) has been synthesized and
characterized. The crystal structures of DAFND and its analogue 4,5-diazafluorene-9-phenylhydrazone
(DAFPD) were determined by single crystal X-ray diffraction method. X-ray analyses reveal that DAFPD
comprise of a nonplanar molecule and all atoms of DAFND are essentially coplanar. The color of DAFND
changes from brown to blue when heated, so called thermochromism and the spectroscopic properties
of the two compounds are investigated by electronic absorption spectra, showing DAFND possess sol-
vatochromism, while DAFPD does not have thermochromic and solvatochromic properties. The ꢀmax of
DAFND within various pure solvents are different ranging from 370 nm in toluene to 614 nm in pyridine.
The imaginable mechanisms of thermochromism and solvatochromism are proposed.
Keywords:
Phenylhydrazone
Crystal structure
Thermochromism
Solvatochromism
Mechanism
Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.
1. Introduction
DAFPD was first reported by Mlochowski and Szulc in 1983
[17], however, its crystal structure has not yet been reported.
Hydrazones and their metal complexes are of current interest
for their physico-chemical properties and applications in many
fields such as sensors, non-linear optics, medicine, DNA probe and
others [1–8], which is determined by their structures influenced
largely by the type and position of the substituent group. As far
as we know, however, the derivatives of phenylhydrazone without
hydroxy hardly have thermochromism or solvatochromism. The
compounds exhibit the change of color reversibly or irreversibly
with temperature variation, so called thermochromism [9,10], and
the term “solvatochromism” describes a significant change in posi-
tion or intensity of an absorption or emission band of a compound
in solution, when the polarity of the medium is changed [11].
The thermochromic compounds are much interesting in various
applications such as smart dyes, temperature sensitive light filters,
fiber optic biosensors and imaging systems as well [9,12,13], while
solvatochromic dyes play a key role in the understanding of sol-
vent polarity effects and are increasingly important as probes of
complex biological systems [14–16]. As far as we are concerned,
the Schiff bases of phenylhydrazone without hydroxy hardly have
thermochromism and solvatochromism. In this study, we found
for the first time that 4,5-diazafluorene-9-p-nitrophenylhydrazone
(DAFND) hold thermochromic and solvatochromic properties,
demonstrating the notable originality of the research.
In order to interpret the property difference from structure, the
crystal structures of two Schiff bases are presented in this paper.
Their spectroscopic properties have been explored by electronic
absorption spectra and the mechanisms on thermochromism and
solvatochromism of DAFND are proposed based on the structural
difference of the two compounds.
2. Experimental
2.1. Materials
All solvents involving in spectral experiments were of UV
grade (Merck UVASOL). All other analytical reagents were
obtained from commercial sources and used without further
purification. Doubly distilled water was used. 4,5-diazafluorene-
9-one was prepared following the literature procedure
[18].
2.2. Syntheses of DAFPD and DAFND
DAFPD: was synthesized according to the literature [17], and
the yellow block crystals were obtained from recrystallization with
methanol. Yield: 0.261 g, 80%. mp: 225–227 ◦C. 1H NMR (600 MHz,
CDCl3, ı): 8.95 (s, 1H), 8.77 (d, J = 4.2 Hz, 1H), 8.70 (d, J = 4.2 Hz, 1H),
8.23 (t, J = 3.6 Hz, 2H), 7.34–7.42 (m, 6H), 7.08 (d, J = 6.0 Hz, 1H). Anal.
calcd. for C17H12N4: C, 74.98; H, 4.44; N, 20.58. Found: C, 74.73; H,
4.65; N, 20.87%.
∗
Corresponding author. Tel.: +86 813 5505837; fax: +86 813 5505837.
E-mail address: limt63646616@yahoo.com.cn (M. Li).
1386-1425/$ – see front matter. Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.11.050

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M. Li et al. / Spectrochimica Acta Part A 75 (2010) 753–759
monochromatized Mo K␣ radiation (ꢀ = 0.71073 Å) at 20(2) ◦C. An
Table 1
Crystallographic data for DAFPD and DAFND.
empirical absorption correction (SADABS) was applied to the raw
intensities [19]. The structures were solved by direct method and
refined on F2 by full-matrix least-squares, employing the SHELXTL
program [20]. Geometrical calculations and the molecular diagram
were obtained with the program PLATON [21]. All non-hydrogen
atoms were refined with anisotropic thermal parameters. The
H atoms from imine group were located in a different Fourier
map and refined with Uiso(H) = 1.5Uiso(N). H atoms on C atoms
were placed in geometrically idealized positions and refined as
riding with Uiso(H) = 1.2Uiso(C). Crystal parameters and details of
the data collection and refinement are given in Table 1. Selected
bond lengths and angles were listed in Table 2. CCDC: 697125,
685276
Crystal data
DAFPD
DAFND
Empirical formula
Formula weight
Crystal system
Space group
C17H12N4
272.31
Orthorhombic
P2(1)2(1)2(1)
C17H11N5O2
317.31
Monoclinic
P21/n
´
˚
a (A)
5.4372(10)
11.078(2)
9.063(2)
´
˚
b (A)
13.473(3)
´
˚
c (A)
22.589(4)
90.00
12.215(3)
104.691(4)
ˇ (◦)
´
3
˚
V (A )
1360.7(4)
4
0.083
568
1.80 to 27.49
1442.7(6)
4
0.101
656
2.29 to 28.00
Z
ꢁ (mm−1
F(0 0 0)
)
ꢂ Range (◦)
−6 ≤ h ≤ 6
−11 ≤ h ≤ 8
−17 ≤ k ≤ 17
−15 ≤ l ≤ 16
9237/3443
3443/19/214
1.044
R1 = 0.0608,
wR2 = 0.0853
R1 = 0.1298,
wR2 = 0.1927
3. Results and discussion
Index ranges
−12 ≤ k ≤ 14
−27 ≤ l ≤ 28
9589/1812
1812/0/194
1.115
3.1. Crystal structures
No. refln./unique
Data/restraints/parameters
S on F2
Perspective views of DAFPD and DAFND are shown in
Figs. 1 and 2. In spite of the different crystal systems, the asym-
metric units of the two compounds are the same and contain a
neutral molecule. The molecule of DAFPD is absent from nitro
group compared with DAFND molecule. X-ray analysis, within
DAFND, reveals that the diazafluoren plane forms an angle of
2.83(3)◦ with the C N–N plane and the dihedral angle between
4,5-diazafluorenylidene and phenyl planes is 2.58(10)◦, which
is different from that of the reported compound phenylamine
4,5-diazafluorene-9-one (104.3◦) [7], indicating all atoms are
R1, wR2 [I > 2ꢃ(I)]a,b
R1 = 0.0502,
wR2 = 0.1087
R1 = 0.0745,
wR2 = 0.1231
R1, wR2 (all data)a,b
´
3
˚
ꢄꢅmin and ꢄꢅmax (e/A )
0.214
and–0.194
0.598
and–0.191
ꢀ
ꢀ
a
R =
||Fo| − |Fc||/
|Fo|.
ꢀ
ꢀ
w(|Fo| − |Fc| )2]/
w|Fo| ]1/2
b
2
2
2
wR = [
DAFND: 4–5 drops of acetic acid were added to a methanol
´
˚
essentially coplanar with a r.m.s. deviation of 0.002 A, and the
solution of 4,5-diazafluorene-9-one (0.182 g, 1.0 mmol) and p-
nitrophenylhydrazine (0.183 g, 1.2 mmol,). A yellow solid formed
after refluxing for 3 h was isolated. Yield: 0.284 g, 90%. mp:
188–189 ◦C. 1H NMR (600 MHz, CDCl3, ı): 9.14 (s, 1H), 8.82 (d,
J = 4.8 Hz, 1H), 8.75 (d, J = 4.8 Hz, 1H), 8.31 (d, J = 8.4 Hz, 2H), 8.24
(s, 2H), 7.38–7.44 (m, 4H). Anal. calcd. for C17H11N5O2: C, 64.35; H,
3.53; N, 22.14. Found: C, 64.67; H, 3.04; N, 22.37%.
´
˚
largest departure is −0.088(3) A for C2. However, the equivalent
angles within DAFPD are 11.6(3)◦ and 29.15(12)◦, respectively,
which is obviously larger than those of DAFND, illustrating the
planarity of DAFPD is worse than DAFND. Bond lengths and
angles of two compounds are in accord with anticipated val-
ues [22,23]. The distances of N1–N2 from 4,5-diazafluorenylidene
are notably larger than that of the maternal compound 1,10-
phenanthroline (phen), and the N–N distances are 3.048(13),
2.3. Physical measurements
´
˚
3.0402(13) and 2.623(18) A for DAFPD, DAFND and phen [24],
respectively.
Melting point was measured on Netzsch STA 449 instruments.
The temperature ranged from 25 to 184 ◦C with a speed of 3 ◦C/min.
The electronic absorption spectra were recorded between 200
and 800 nm in a 10 mm path-length cell on a Shimadzu UV-2450
PC spectrophotometer. The UV–vis spectra of thermochromism
and solvatochromism were performed with a concentration of
5.0 × 10−4 M within various solvents.
Due to the characteristic conjugated structure, there is signifi-
cant intermolecular ꢆ–ꢆ stacking within the two compounds. As
for DAFPD, the centroid–centroid distance, Cg1· · ·Cg2ii, between
the pyridine rings in two symmetry-related diazafluoren plane is
´
˚
3.7867(16) A, [Cg1 and Cg2 are the centroids of the rings C1–C5/N1
and C6–C10/N2, (ii): −x + 1, y, z], and the dihedral angle ˛ (between
planes Cg1 and Cg2) and deviation angle ˇ (between the Cg1–Cg2
vector and the normal to centroid Cg1) are 2.03◦ and 24.46◦, respec-
tively, indicating there is a significant ꢆ–ꢆ stacking interaction [25].
Similarly, within DAFND, the centroid–centroid distance between
the C6–C10/N2 pyridine ring (centroid Cg1) and the C12–C17 ben-
2.4. X-ray crystallography
X-ray diffraction data for the compounds were collected on
a
Bruker APEX SMART CCD diffractometer with a graphite-
Table 2
´
˚
◦
Selected bond lengths (A) and angles ( ) for DAFPD and DAFND.
Bond
Dist
Angle
(◦)
Angle
(◦)
DAFPD
C(11)-N(3)
C(12)-N(4)
N(3)-N(4)
N(1)-N(2)
1.299(3)
1.407(3)
1.334(3)
3.048(13)
C(11)-N(3)-N(4)
N(3)-N(4)-C(12)
N(3)-C(11)-C(4)
C(13)-C(12)-N(4)
119.3(2)
120.0(2)
133.3(3)
117.9(3)
C(7)-C(11)-N(3)-N(4)
C(4)-C(11)-N(3)-N(4)
C(17)-C(12)-N(4)-N(3)
C(13)-C(12)-N(4)-N(3)
−179.3(2)
−10.4(4)
−3.2(4)
179.7(3)
DAFND
C(11)-N(3)
C(12)-N(4)
N(3)-N(4)
N(1)-N(2)
1.307(3)
1.397(3)
1.324(3)
3.0402(13)
C(11)-N(3)-N(4)
N(3)-N(4)-C(12)
N(3)-C(11)-C(4)
C(13)-C(12)-N(4)
120.1(2)
119.8(2)
134.9(2)
119.2(3)
C(7)-C(11)-N(3)-N(4)
C(4)-C(11)-N(3)-N(4)
C(17)-C(12)-N(4)-N(3)
C(13)-C(12)-N(4)-N(3)
178.3(2)
−2.1(5)
0.2(4)
179.9(2)

M. Li et al. / Spectrochimica Acta Part A 75 (2010) 753–759
755
Fig. 1. Ortep view of DAFPD.
Fig. 2. Ortep view of DAFND.
´
˚
ii
zene ring [Cg2 , (ii): −x, −y, −z + 1] is 3.6715(3) A, while ␣ and ˇ
are 1.25◦ and 22.47◦, respectively, which indicates that the stacking
interaction is stronger than that of DAFPD.
Hydrogen bonds play a key role in the formation of 1D chains
and 2D layers and in stabilization of the crystal structures for DAFPD
and DAFND, whereas the nitro group is vital to the type of hydrogen
bond and the crystal stacking mode. Within DAFPD, the H atom
of imine group is linked by a N atom from diazafluoren plane in
symmetry-related molecule via N· · ·H. N hydrogen bond, and the N
atom from a pyridine ring simultaneously links the other H atom
of imine group belonging to the third DAFPD molecule, thus 1D
zigzag chain along with (0 1 0) direction is formed, as shown in
Fig. 3. However, the hydrogen bonds formed by O2 of nitro group
and H of imine group within DAFND and the infinite 1D chains are
extended along with (0 1 0) direction shown in Fig. 4. The hydrogen
bonds as well as the previously discussed ꢆ–ꢆ stacking interactions
Fig. 3. View of packing diagram of DAFPD.

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M. Li et al. / Spectrochimica Acta Part A 75 (2010) 753–759
Fig. 5. UV–vis spectra of DAFND in DMF at various temperatures.
blue in the solid state when heated. The color change is irreversible
ranging from 95 to 96 ◦C. However, DAFPD melt at about 226 ◦C
and had no color change. Obviously, the nitro group is important
to thermochromism of DAFND. It is necessary to thermochromism
that the planarity and stacking interaction of organic compound
[26]. The planarity and stacking interaction of DAFND are better
than those of DAFPD (vide supra), on the other hand, there may be
two isomeric molecular species in DAFND when heated, shown in
Scheme 1. The thermochromism of organic compound occurs via an
equilibrium process between two isomeric molecular species [27].
The conjugated degree of the zwitterionic structure is obviously
larger than that of the neutral compound, which is favorable to the
electron transfer, so the color changes yellow to green and blue.
As a matter of fact, the tautomerism of DAFND can be proved by
the electronic absorption spectra in DMF at various temperatures
shown in Fig. 5. The intensities at 609 nm were gradually reduced
and had a 30% value of I0 (T = 25 ◦C) at 95 ◦C, indicating the con-
centration of DAFND was changed. The imaginable interpretation
is that the two isomers take place the structural transformation,
which can also be proved the intensities at 423 nm. The intensi-
ties were increased in the range of 25 and 75 ◦C and then obviously
decreased to a minimum at 95 ◦C with little hypochromatic shift
from 423 to 418 nm.
Fig. 4. View of packing diagram of DAFND.
take part in the formation of a 2D network and in the stabilization
of the crystal structure.
3.3. Solvatochromism
3.2. Thermochromism
Table 3 presents the thermal properties of DAFND and DAFPD.
The brown color of DAFND at about 95 ◦C changed to green and then
DAFND exhibits not only thermochromism but also solva-
tochromism because of the existence of the nitro group. The colors
Table 3
Thermal properties of DAFND and DAFPD.
mp (◦C)
Point of change color
Change color
Acuity
Reversibility
DAFND
DAFPD
188–189
225–227
95–96
–
Brown–green–blue
–
Obvious
–
Inreversible
–
Scheme 1. The tautomeric structures of DAFND.

M. Li et al. / Spectrochimica Acta Part A 75 (2010) 753–759
757
Fig. 6. UV–vis spectra of DAFND in various pure solvents.
of DAFND in various pure solvents range from yellow to green and
blue, while DAFPD is identical with yellow at the same concentra-
tion. The UV–vis spectra of DAFPD and DAFND in different pure
solvents were shown in Figs. 6 and 7. The ꢀmax of DAFPD in all pure
solvents are the same at 395 nm and the intensities are nearly equal.
However, the positions of the maximal absorption peak for DAFND
are different ranging from 370 nm in toluene to 614 nm in pyridine
(py) with the diverse intensities. It is interesting that the intensities
of DAFND at about 600 nm are smaller than those at about 423 nm in
strong polar solvents such as py, DMF, DMSO, acetonitrile and gly-
col, however, the intensities of the maximal peak at below 430 nm
are irregular (Table 4). In the mixed solvents of DMF and methanol,
the positions of the maximal peak are red-shift from at 398 nm in
methanol to at 609 nm in DMF as the increasing voluminal ratios
of DMF, with the intensities raised, as shown in Fig. 8.
Solvatochromic compounds can be described by two extreme
resonance contributing structures: one form is quinoidal, nonpolar-
ized, and formally nonaromatic; the other is zwitterionic, polarized,
and fully aromatic [11]. The change in the absorption band with
solvent arises from variation in the contribution of these canon-
ical forms to the overall resonance hybrid [28]. The nitro group
undoubtedly plays a key role in solvatochromism, and the tau-
tomerism is shown Scheme 1.
The solvatochromic behavior can be attributed to a number of
specific and nonspecific solute/solvent interactions as summarized
in the linear solvation energy relationship (LSER) of Eq. (1) [29]
E = E0 + sꢆ ∗ +a˛ + bˇ
(1)
where s, a, and b are coefficients and ꢆ*, ˛ and ˇ reflect, respectively,
the general solvent dipolarity/polarizability, its specific H-bond
donating ability, and its specific H-bond accepting ability, which
may or may not oppose one another in terms of solvatochromic
Fig. 7. UV–vis spectra of DAFPD in various pure solvents.

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M. Li et al. / Spectrochimica Acta Part A 75 (2010) 753–759
Fig. 8. UV–vis spectra of DAFND in mixed solvents and the positions of the maximal absorption peak.
Table 4
Solvatochromic data for DAFPD and DAFND in various liquid solvents.
Solvent
DAFPD
DAFND
ꢆ*
˛
ˇ
ꢀmax (nm)
ꢇmax ×103 (cm−1
)
ꢀmax (nm)
ꢇmax ×103 (cm−1
)
Py
DMSO
Glycol
DMF
395
396
395
395
394
395
394
393
395
395
394
396
396
395
395
–
25.32
25.25
25.32
25.32
25.38
25.32
25.38
25.44
25.32
25.32
25.38
25.25
25.25
25.32
25.32
–
614
613
610
609
597
430
429
428
425
423
423
418
417
414
413
392
370
16.27
16.31
16.40
16.42
16.75
23.26
23.31
23.36
23.53
23.64
23.64
23.92
23.98
24.15
24.21
25.51
27.03
87
00
64
76
52
69
40
75
55
43
66
86
84
45
37
10
10
47
11
100
92
88
75
54
58
71
60
40
48
55
55
58
82
109
54
00
90
00
19
86
00
08
98
84
76
00
00
20
13
117
00
CH3CN
C2H5OH
THF
(CH3)2CO
CH3OH
Isoamylol
Isopropanol
Ethyl acetate
Dioxane
CHCl3
CH2Cl2
H2O
C6H5CH3
395
25.32
DMF: N,Nꢀ-dimethylformamide, DMSO: dimethylsulfoxide, Py: pyridine, THF: tetrahydrofuran.
contributions. E0 is the transition energy for a solvent where
ꢆ* = ˛ = ˇ = 0 (e.g. cyclohexane).
The individual form of the LSER for DAFND is given by Eq. (2)
based on the data in Table 4, Eq. (1) and published values of ꢆ*, ˛
and ˇ [30]
4. Conclusions
novel
A
Schiff
base
of
4,5-diazafluorene-9-p-
nitrophenylhydrazone was synthesized. X-ray analyses reveal that
the planarity of DAFND is better than that of 4,5-diazafluorene-
9-phenylhydrazone in solid state and the nitro group affects the
planarity of the compound and crystal structures. The UV–vis
spectra investigation exhibits that DAFND has thermochromism
and solvatochromism determined by the nitro group. The color
of DAFND changes from brown to green and blue at about 95 ◦C
in solid state, furthermore, the colors of DAFND are diverse in
different pure solvents at the same conditions.
E = 35.03 − 19.66 ꢆ ∗ −0.1543 ˛ − 0.0008 ˇ
(2)
where energy units are 103 cm−1 (kK), and n = 16 (the data of H2O
are omitted), r = 0.965, SD = 513 cm−1. Points to be emphasized are
as follows:
Acknowledgments
(1) The value for E0 corresponds to a transition absorption maxi-
mum of 285 nm, which is well consistent with the polarity order
(cyclohexane 0.1 is lower than toluene 2.4).
This work is financially support by the National Natural Science
Foundation of China (60877048) and the Program for Changjiang
Scholars and Innovative Research Team in University (IRT0547),
Ministry of Education, China.
(2) The coefficient for ꢆ* and ˇ are much more larger and smaller
than those of the other compounds [29,31–33], indicating
DAFND hold unusual solvatochromism for example the obvious
difference of ꢀmax in various solvents. ꢀmax in polar solvent is
notably larger than that of nonpolar or low polar solvent shown
in Table 4, which is also demonstrated by the ꢀmax in the mixed
solvents of methanol and DMF with different ratios shown in
Fig. 8.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2009.11.050.

M. Li et al. / Spectrochimica Acta Part A 75 (2010) 753–759
759
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