Synthesis, spectroscopic characterization, and molecular structure of triphenyl butene derivatives containing a cyclopentadienyl iron unit

Article abstract of DOI:10.1016/j.ica.2012.03.056

Three hydroxyl substituted triphenyl butene compounds (PHB) and their derivatives containing a cyclopentadienyl iron (PHB-Fc) unit were efficiently synthesized. The synthesis involved the McMurry cross-coupling reaction of appropriate ketones and the nucleophilic aromatic substitution (S_NAr) reaction of (η⁶-chlorobenzene) (η⁵- cyclopentadienyl) iron hexafluorophosphate (Fc-Cl). The target compounds were characterized by IR, ¹H NMR, ¹³C NMR, and MS. Their photophysical processes were investigated by UV-Vis absorption and fluorescence emission spectra in acetonitrile. The geometric structure was optimized based on the density functional theory at the B3LYP level. Theoretical results reveal that electron transfer occurred from the HOMO to the LUMO in PHB-Fc. The change in electron distribution subsequently led to the improved second-order optical susceptibility of PHB-Fc.

Full text of DOI:10.1016/j.ica.2012.03.056

Inorganica Chimica Acta 392 (2012) 374–379
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, spectroscopic characterization, and molecular structure of
triphenyl butene derivatives containing a cyclopentadienyl iron unit
Junru Han b, Guanglei Li b, Tao Wang a,b,
⇑
a State Key Laboratory of Chemical Resource Engineer, College of Science, Beijing University of Chemical Technology, Beijing 100029, PR China
b Department of Organic Chemistry, College of Science, Beijing University of Chemical Technology, Beijing 100029, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three hydroxyl substituted triphenyl butene compounds (PHB) and their derivatives containing a cyclo-
pentadienyl iron (PHB-Fc) unit were efficiently synthesized. The synthesis involved the McMurry cross-
coupling reaction of appropriate ketones and the nucleophilic aromatic substitution (SNAr) reaction of
Received 10 January 2012
Received in revised form 24 March 2012
Accepted 28 March 2012
Available online 4 April 2012
(g g
6-chlorobenzene) ( 5-cyclopentadienyl) iron hexafluorophosphate (Fc-Cl). The target compounds were
characterized by IR, 1H NMR, 13C NMR, and MS. Their photophysical processes were investigated by UV–
Vis absorption and fluorescence emission spectra in acetonitrile. The geometric structure was optimized
based on the density functional theory at the B3LYP level. Theoretical results reveal that electron transfer
occurred from the HOMO to the LUMO in PHB-Fc. The change in electron distribution subsequently led to
the improved second-order optical susceptibility of PHB-Fc.
Keywords:
Phenyl conjugated alkene
Electron transfer
UV–Vis absorption
Fluorescence
Ó 2012 Elsevier B.V. All rights reserved.
Geometric structure
1. Introduction
the calculated electronic properties and geometries, the nonlinear
second-order optical susceptibility was also calculated.
Phenyl conjugated alkene derivatives, such as stilbene and
triphenyl butene, have drawn considerable attention in several
fundamental studies and applications, including photochemical,
biological, and medical activity studies, as well as light and witness
applications, photoresponsive materials, and organic electrolumi-
nescent materials [1–5]. Phenyl conjugated alkene compounds,
which contain a metallic atom in their structures, possess the com-
bined properties of metal and stilbene groups. These compounds
produce materials that can be processed with interesting magnetic,
electronic, optic, and anisotropic properties [6,7]. Phenyl conjugated
alkene derivatives containing the ferrocenyl group has been re-
ported to possess special biological and medical activities. However,
reports on the photochemical properties and geometric structure of
phenyl conjugated alkene containing cationic cyclopentadienyliron
group remain limited [8,9].
Consequently, three hydroxyl substituted triphenyl butene
compounds (PHB) and their derivatives containing a cyclopentadi-
enyl iron (PHB-Fc) unit were synthesized in the current study. The
relationship between the photochemical properties and structure
was investigated. The geometric structures of the triphenylbuten-
e-complexes were optimized, and energy calculations were
performed based on the density functional theory (DFT). Given
2. Experimental
2.1. Materials and instruments
All the reagents and solvents in this experiment were of re-
agent-grade quality, which were obtained from commercial
sources and used without further purification. (
g
6-Chlorobenzene)
(g
5-cyclopentadienyl) iron hexafluorophosphate (Fc-Cl) was pre-
pared through the ligand exchange reaction of ferrocene and chlo-
robenzene according to the reference procedure [10].
The melting points of the compounds were determined using an
XT-4 microscopic melting point apparatus. The 1H NMR and 13C
NMR spectra were recorded on a Bruker AV500 unity spectrometer
operated at 500 MHz using acetone-d6 as deuterated solvent. FTIR
spectra were recorded on a Nicolet 5700 instrument (Thermo Elec-
tron Corporation, Waltham, MA). UV–Vis absorption spectra were
recorded on a Hitachi U2500 UV–Vis spectrophotometer (Hitachi
High-Technologies Corporation, Tokyo, Japan). Mass spectrometry
was performed with a Nermag R 10-10C spectrometer. Fluores-
cence spectra were obtained on a Hitachi F-4500 spectrophotome-
ter at room temperature.
A Pentium IV personal computer (CPU at 3.20 GHz) with the
Windows XP operating system was used to calculate quantum
chemistry. The molecular structures of PHB-FC in the ground state
were optimized on the basis of density function theory at the Becke
⇑
Corresponding author at: Beijing University of Chemical Technology, 144#
Beijing 100029, PR China. Tel.: +86 013691179175; fax: +86 010 64445350.
E-mail address: wangtwj2000@163.com (T. Wang).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.03.056

J. Han et al. / Inorganica Chimica Acta 392 (2012) 374–379
375
3-Lee–Yang–Parr (B3LYP) (Fe with 6-31G⁄⁄ basis set and C, H, and
O with Lanl2dz basic set) and by means of visual inspection using
the GAUSSVIEW program (Version 5.0). All the calculations were per-
formed using the GAUSSIAN 09 software package.
(2C, C6H4), 127.55 (2C, C6H5), 128.71 (1C, C), 129.04 (2C, C6H4),
130.02 (2C, C6H4), 131.24 and 131.43 (2C, C6H5), 132.11 (2C,
C6H4), 132.30 (1C, C), 132.60 (1C, C6H4), 140.43 and 140.53 (1C,
C6H4), 142.29 (1C, C6H4), 144.55 (1C, C6H4), 156.58 (1C, C6H4);
FT-IR spectra
1509.6, 1438.7, 1236.8; MS(m/z): 334.5.
m
(cmꢀ1): 3377.1, 2965.5, 1699.7, 1607.3, 1588.9,
2.2. Synthesis of triphenyl conjugated butene derivatives
2.2.4. [(g g
5-Cyclopentadienyl)-Fe-( 6-1-(4-phenoxy)-1-phenyl-2-(4-
methylphenyl)butylene] hexafluorophosphate (PHB-Fc-1)
2.2.1. 1-(4-Hydroxyphenyl)-1-phenyl-2-(4-methylphenyl) butylenes
(PHB-1)
Propionyl chloride (13.3 g, 0.143 mol) was added dropwise to a
stirred solution of AlCl3 (37 g, 0.28 mol) in dry toluene (60 ml) at –
5 °C to 0 °C. The mixture was then warmed to room temperature
for 1 h and heated to 82 °C for 2 h. The resultant mixture was
poured into ice water. The organic layer was washed with 10%
Na2CO3 as well as saturated NaCl, and then dried over MgSO4.
4-Methyl propiophenone was obtained at 105–110 °C by vacuum
distillation (12.6 g, 60.12%).
TiCl4 (3 ml, 0.028 mol) was added dropwise to a stirred suspen-
sion of zinc powder (4 g, 0.035 mol) in dry tetrahydrofuran (THF;
40 ml) under N2 at ꢀ10 °C. The reaction mixture was then warmed
to room temperature and refluxed for 2 h. A solution of 4-hydroxy-
benzophenone (1.5 g, 0.0075 mol) and 4-methyl propiophenone
(2.2 g, 0.0148 mol) in dry THF (40 ml) was added to the cooled sus-
pension of the titanium reagent at 0 °C. The mixture was refluxed
in the dark for 2 h. After being cooled to room temperature, the
reaction mixture was quenched with 10% aqueous potassium car-
bonate (30 ml) and extracted with EtOAc. The organic layer was
dried over MgSO4 and concentrated. Flash chromatography affor-
ded PHB-1 (1.53 g, 68%) as a white solid. 4:3 mixture of E/Z iso-
mers, mp: 132–135 °C.
The compounds Fc-Cl (0.6 g, 0.0016 mol), PHB-1 (0.5 g,
0.0016 mol), and K2CO3 (0.5 g, 0.0.36 mol) were stirred in 40 ml of
N,N-dimethylformamide (DMF) in a 100 ml round bottom flask un-
der a nitrogen atmosphere at 80 °C. Reactions were monitored by
thin layer chromatography (TLC) using 0.25 mm aluminum-backed
silica gel plates. After Fc-Cl was reacted thoroughly, the reaction
mixture was transferred into a 15% (v/v) HCl solution, and a granular
precipitate was formed. The obtained filtrate was washed by ace-
tone resulting in the dissolution of the product. This solution was
then concentrated by evaporating acetone and treated with suffi-
cient KPF6 in water to allow for the complete precipitation of PHB-
Fcs as a granular solid. The crude product (PHB-Fc-1) was purified
by column chromatography and further recrystallized. 4:3 mixture
of E/Z isomers, yield: 65.7%, m.p. 172–175 °C.
3
4
6
1
13
12
10 11
5
7
2
8
9
14
15
1H NMR(400 MHz, CH3COCH3-d6) dppm: 0.89–0.93 (t, 3H,
J = 7.464 Hz, –CH2CH3), 2.23 and 2.25 (2 ꢁ s, 1H, Ar–CH3), 2.39–
2.45 and 2.46–2.52 (2 ꢁ q, 2H, J = 7.45 Hz, –CH2CH3), 8.08 and
8.32 (2 ꢁ s, 1H, –OH), 6.49–7.37 (m, 13H, 2 ꢁ Ar–H); 13C NMR
(400 MHz, acetone-d6): dppm: 8.04 and 8.15 (1C, CH3), 13.86 and
14.50 (1C, CH3), 21.01 and 21.11 (1C, CH2), 115.15 and 115.83
(2C, C6H4), 126.39 (2C, C6H4), 127.32 (2C, C6H5), 128.14 (1C, C),
128.98 (2C, C6H4), 130.12 (1C, C6H5), 131.29 and 132.58 (2C,
C6H5), 135.34 (2C, C6H4), 136.20 (1C, CH), 139.38 (1C, C6H4),
140.33 (1C, C6H4), 141.54 (1C, C6H4), 144.72 and 145.03 (1C,
22
Fe PF6
16
17
-
19
O
18
21
20
1H NMR(400 MHz, DMSO-d6) dppm: 0.85–0.91(t, 3H,
J = 7.451 Hz, –CH2CH3), 2.22 and 2.23(2 ꢁ s, 3H, Ar–CH3), 2.39–
2.45(q, 2H, J = 7.455 Hz, –CH2CH3), 5.09 and 5.18(2 ꢁ s, 5H,
arene-Fe-Cp), 6.13–6.34(t, 5H, arene-Fe-Cp), 6.91–7.44(m, 13H,
2 ꢁ Ar–H); 13C NMR (400 MHz, DMSO-d6): dppm: 13.25 and
13.30 (C1), 20.65 and 20.69 (C3), 28.44 (C2), 76.84 (5C22), 84.84
(C21), 86.86 (2C19), 120.39 (2C20), 125.94 (2C16), 126.90 (2C15),
127.68 (2C6), 128.50 (2C11), 128.95 (C8), 130.13 (C13), 131.15
(2C12), 132.44 (2C5), 135.49 (C9), 137.02 (C14), 138.22 (C7), 140.90
(C4), 142.68 (C10), 150.71 (C17), 151.74 (C18); FT-IR spectra
C6H5), 156.30 and 157.12 (1C, C6H4); FT-IR spectra
m
(cmꢀ1):
3370.1, 3023.3, 2971.1, 2871.9, 1700.3, 1608.51, 1508.8, 1441.7,
1258.5, 1235.9, MS (m/z): 314.
2.2.2. 1-(4-Hydroxyphenyl)-1-phenyl-2-(4-phenyl) butylenes (PHB-2)
Yield: 57.9%, 4:1 mixture of E/Z isomers, mp: 121–124 °C. 1H
NMR(400 MHz, CH3COCH3-d6) dppm: 0.89–0.92 and 1.18–1.22
(2 ꢁ t, 3H, J = 7.43 Hz, –CH2CH3), 2.41–2.47 (q, 2H, J = 7.43 Hz, –
CH2CH3), 8.18 and 8.38 (2 ꢁ s, 1H, –OH), 6.52–7.40 (m, 14H,
2 ꢁ Ar–H); 13C NMR (400 MHz, acetone-d6): dppm: 8.07 and 8.15
(C, CH3), 13.81 (1C, CH2), 115.14 and 115.85 (2C, C6H4), 126.77
and 126.87 (2C, C6H5), 127.40 and 127.54 (2C, C6H4), 128.13 (1C,
C6H4), 128.62 (2C, C), 130.55 (1C, C6H4), 131.30 and 131.41 (1C,
C6H4), 135.14 and 135.58 (1C, C6H5), 143.37 and 143.42 (1C,
m
(cmꢀ1): 1525.4, 1499.2, 1457.6, 1244.3, 829.6; MS(m/z): 511
[M-145(PF6ꢀ)].
2.2.5. [(
phenyl)butylene] hexafluorophosphate (PHB-Fc-2)
g g
5-Cyclopentadienyl)-Fe-( 6-1-(4-phenoxy)-1-phenyl-2-(4-
8
6
1
8
6
7
7
C6H5), 156.35 and 157.18 (1C, C6H4); FT-IR spectra
m
(cmꢀ1):
5
2
9
3362.2, 2966.9, 1699.1, 1609.6, 1508.4, 1441.3, 1215.54, 1169.9;
MS(m/z): 300.
3
4
10
11
18
2.2.3. 1-(4-Hydroxyphenyl)-1-phenyl-2-(4-chlorophenyl) butylenes
(PHB-3)
12
13
-
PF6
Fe
15
Yield: 62.5%, 7:1 mixture of E/Z isomers, mp: 90–93 °C. 1H
NMR(400 MHz, CH3COCH3-d6) dppm: 0.89–0.92 and 1.18–1.22 (t,
3H, J = 7.45 Hz, –CH2CH3), 2.42–2.47 and 2.49–2.54 (2 ꢁ q, 2H,
J = 7.443 Hz, –CH2CH3), 8.16 and 8.37 (2 ꢁ s, 1H, –OH), 6.52–7.40
(m, 13H, 2 ꢁ Ar–H); 13C NMR (400 MHz, acetone-d6): dppm:
13.75 and 14.50 (1C, CH3), 20.80 (1C, CH2), 115.31 and 115.88
14
17
O
16
Yield: 63.7%, 1:2 mixture of E/Z isomers, m.p. 170–174 °C. 1H
NMR(400 MHz, DMSO-d6) dppm: 0.87–0.92 (t, 3H, J = 7.166 Hz, –
CH2CH3), 2.40–2.45(q, 2H, J = 7.249 Hz, –CH2CH3), 6.12–6.34(t,

376
J. Han et al. / Inorganica Chimica Acta 392 (2012) 374–379
5H, arene-Fe-Cp), 5.09 and 5.18(2 ꢁ s, 5H, arene-Fe-Cp),
6.91–7.46(m, 14H, 2 ꢁ Ar–H); 13C NMR (400 MHz, DMSO-d6):
dppm: 13.20 (C1), 28.32 (C2), 76.83 (5C18), 84.68 (2C15), 86.86
(C17), 86.80 (2C16), 119.89 (2C12), 120.40 (2C11), 126.42 (4C6),
127.64 (C3), 127.93 (2C8), 128.93 (4C7), 129.41 (C4), 137.37 (C10),
140.80 (C5), 141.30 (C9), 142.33 (C13), 150.73 (C14); FT-IR spectra
3. Results and discussion
3.1. Synthesis and characterization
The synthetic pathway and structures of the target compounds
are shown in Fig. 1. PHBs were synthesized by the McMurry cou-
pling reaction (Zn and TiCl4), and PHB-Fcs were synthesized by a
SNAr reaction in the presence of potassium carbonate as a base in
N,N0-dimethylformamide at 80 °C. The termination of the SNAr
reaction was monitored by observing the disappearance of Fc-Cl
via thin-layer chromatography [11,12]. The products were mix-
tures of Z and E isomers.
The chemical structures of the derivatives were confirmed by
1H NMR, 13C NMR, IR, and MS, which are detailed in the Experi-
mental section. The optical properties of these target compounds
were studied, and isomerization was found to have a minor effect.
Consequently, no attempt was made to separate the structures of Z
and E isomers. The mixture of target compounds was synthesized
and the ratio of Z/E isomers was confirmed by 1H NMR. The 1H
NMR spectrum reveals a single peak at about 8.0 ppm (–OH) or
about 5.09 ppm (Cp-Fe). However, the mono peak was divided into
two peaks because of the isomerization. The proportion of peaks
stands for the ratio of Z and E isomers.
m
(cmꢀ1): 1523.5, 1498.7, 1455.3, 1235.5, 823.6; MS (m/z):
497[M-145(PF6ꢀ)].
2.2.6. 6[(g g
5-Cyclopentadienyl)-Fe-( 6-1-(4-phenoxy)-1-phenyl-2-(4-
chlorophenyl)butylene] hexafluorophosphate(PHB-Fc-3)
Cl
8
6
1
12
11
10
7
5
2
9
3
4
13
14
21
15
16
The IR spectra of PHB-Fcs displayed a strong peak at about
-
Fe PF6
18
820 cmꢀ1 because of the P–F stretching vibration, indicating the
existence of PF6ꢀ. In the IR spectra, the
v (O–H) vibration of
17
20
O
PHB-Fcs did not exist from 3600 to 3200 cmꢀ1, indicating the
disappearance of –OH. The mass spectra showed that the cation
was correctly identified.
19
Yield: 62.1%, 4:1 mixture of E/Z isomers, m.p. 209–213 °C. 1H
NMR(400 MHz, DMSO) dppm: 0.88(s, 3H, –CH2CH3), 2.42(s, 2H, –
CH2CH3), 6.31 and 6.14(2 ꢁ s, 5H, arene-Fe-Cp), 7.03–7.44(m,
13H, 2 ꢁ Ar–H); 13C NMR (400 MHz, DMSO-d6): dppm: 13.13
(C1), 28.11 (C2), 76.82 (5C21), 84.75 (2C18), 86.68 (C20), 87.35
(2C19), 120.03 (2C15), 127.09 (2C14), 127.96 (2C10), 128.52 (C3),
128.87 (2C6), 131.00 (C12), 131.33 (2C11), 132.23 (2C7), 132.50
(C4), 138.09 (C13), 140.22 (C8), 140.51 (C5), 141.39 (C9), 142.07
3.2. Optical properties
Fig. 2 shows the UV–Vis absorption spectra of the compounds in
acetonitrile solution. Table 1 summarizes the optical properties of
all target compounds. PHB and PHB-Fc had strong and wide
absorptions between 200 and 350 nm, which arose from an elec-
tron transition process along the entire conjugate system. The
(C16), 150.92 (C17); FT-IR spectra m
(cmꢀ1): 1522.7, 1497.4, 1455.3,
1233.0, 822.7; MS(m/z): 531[M-145(PF6ꢀ)].
O
R
AlCl3
R
+
Cl
O
O
R
-
Fe PF6
R
Cl
OH
Fc-Cl
reflux
TiCl4,
Zn,
THF,
K2CO3
-
Fe PF6
OH
O
(Z/E)
PHB
(Z/E)
PHB-Fc
R= -CH3
PHB-1
PHB-Fc-1
PHB-Fc-2
PHB-Fc-3
R= -CH3
PHB-2 R= -H
R= -Cl
R= -H
R= -Cl
PHB-3
Fig. 1. Synthesis pathway of hydroxyl substituted triphenyl butene compounds (PHB) and their derivatives containing a cyclopentadienyl iron (PHB-Fc) unit.

J. Han et al. / Inorganica Chimica Acta 392 (2012) 374–379
377
4
3
2
1
0
1.0
0.8
0.6
0.4
0.2
0.0
a
-4
1x10
-3
M
PHB-Fc-1
PHB-Fc-2
PHB-Fc-3
1x10
M
200
300
400
500
600
Fig. 3. Fluorescence spectra of PHB and PHB-Fc in CH3CN.
Wavelength (nm)
4
1.0
b
-3
-4
1x10
M
PHB-1
1x10
M
groups had little effect on the UV–Vis absorption of PHB. PHB-1,
PHB-2, and PHB-3 had quite similar absorption characteristics,
but PHB-3 had the strongest one because of chloride substitution.
The fluorescence spectra of PHB and PHB-Fc in acetonitrile are
shown in Fig. 3. PHB compounds exhibit extremely strong fluores-
PHB-2
PHB-3
0.8
0.6
0.4
0.2
0.0
3
2
1
0
cence. The efficient p-conjugation in PHB constituted by a double
bond and three phenyl rings, as well as the rigid structure were
responsible for the strong fluorescence. The substituted groups
had little effect on the location of the excited and emission peaks
of PHB. The emission peak was at 337 nm and the Stokes shift
was above 60 nm.
The PHB-Fc compounds exhibited relatively weak fluorescence,
a wide fluorescent emission from 330 to 400 nm, and a red-shift at
about 40–60 nm compared with PHBs. These characteristics can be
attributed to the existence of the electron-withdrawing [Cp-Fe]+
200
300
400
500
fragment in PHB-Fc, which could polarize p-electron systems and
excite the electron pair on the cyclopentadienyl ring.
Wavelength (nm)
Fig. 2. UV–Vis absorption spectra of PHB-Fc (a) and PHB (a) in acetonitrile.
3.3. Quantum chemical calculations
Quantum chemical calculations were used to gain insight into
the electronic properties and geometries of PHB and PHB-Fc. The
optimized geometries of E-PHB-Fcs in the electronic ground state
were obtained (Fig. 4). The predicted bond lengths, bond angles
and selected dihedral angles for most stable conformer of E-PHB-
Fc are tabulated in Table 2. As shown in Table 2, bond lengths
and valence angles for these new triphenyl conjugated butanes
agree with the X-ray crystallographically determined structures
that are known for closely related compounds [9b,13,14]. The bond
lengths calculated for C@C in E-PHB-Fcs are 1.358 Å, while that in
cis-tamoxifen (E) is 1.33 Å and that in trans-tamoxifen (Z) is 1.34 Å
at references. The angle formed by the double bond and one of the
four substituents is of the order of 122–124° for both the cis- and
the trans-tamoxifens at references. In the case of (E)-PHB-Fcs, the
bond angles have the following values: C30–C23–C45: 122.9–
123.0, C34–C33–C45:113.6–123.5, C33–C45–C57: 121.0–121.2,
and C33–C45–C57: 123.6–123.8. It can also be seen that the four
substituents on the double bond do not lie in the same plane, the
C47–C45–C33–C30 atoms forming a dihedral angle of 3.8–7.9° in
the case of E-PHB-Fcs. This angle has been found to be 13° for E-fer-
recenyl tamoxifen which was reported by Siden Top [9b].
Table 1
UV–Vis, fluorescent and quantum chemical calculations of the target compounds.
Compound kmax
(nm)a
ꢁ10 Eꢀ4 emax
kex
(nm)a
kem
(nm)a
Stokes shifts
(nm)b
a
(L molꢀ1 cmꢀ1
)
PHB-1
PHB-2
PHB-3
212
1.61
1.69
1.55
1.21
2.15
2.16
2.03
2.02
2.24
2.71
277
278
275
337
337
337
60
59
62
210
210
235
213
242
213
242
214
240
PHB-Fc-1
PHB-Fc-2
PHB-Fc-3
302
305
293
373
366
373
71
61
80
a
Solution in 10ꢀ4 mol Lꢀ1 CH3CN.
b
Stokes shifts = kem ꢀ kex
.
absorption of PHB-Fc was stronger than that of PHB, and red-
shifted to about 50 nm. In contrast, PHB-Fc possesses weak absorp-
tion between 400 and 500 nm owing to the d–d transition of the
cyclopentadienyl iron unit. Absorption above 400 nm conferred
PHB-Fc with photoactivity under visible light. The substituted
Figs. 5 and 6 show the electron cloud delocalization of the fron-
tier orbitals of the molecules of E-PHB and E-PHB-Fc, respectively.
In the highest occupied molecular orbital (HOMO) and lowest

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J. Han et al. / Inorganica Chimica Acta 392 (2012) 374–379
Table 2
Optimized geometrical parameters of PHB-Fc based on B3LYP.
Parameters
PHB-Fc-1
PHB-Fc-2
PHB-Fc-3
Bond lengths (Å)
C30–C33
C33–C34
C45–C57
C45–C47
1.498
1.499
1.523
1.500
1.358
1.498
1.499
1.522
1.501
1.358
1.498
1.499
1.523
1.501
1.358
C33–C45
Bond angles (°)
C30–C23–C45
C34–C33–C45
C33–C45–C47
C33–C45–C57
122.96
123.47
121.19
123.65
122.96
113.57
121.17
123.75
123.01
113.63
121.00
123.78
Dihedral angles (°)
C47–C45–C33–C30
C47–C45–C33–C34
3.894
7.945
3.700
7.587
3.928
7.974
Fig. 4. Optimized geometry of E-PHB-Fc on the electronic ground state.
unoccupied molecular orbital (LUMO) of the PHB-Fc compounds,
the electron cloud all delocalized over the –C@C– and aryl rings.
From HOMO to LUMO, no electron transfer occurred in PHB. In
the HOMO of PHB-Fc, the electron cloud delocalized over the –
C@C– and aryl rings, whereas in their LUMO orbitals, the electron
cloud delocalized over the cyclopentadienyliron cation and coordi-
nated arena. This finding suggested that electron transfer occurred
from the HOMO to the LUMO in PHB-Fc.
Fig. 5. Molecular orbital surface and energies of target compounds frontier
molecular orbitals of PHB.
3.4. Static second-order nonlinear optical (NLO) properties
Generally, the energy values of LUMO and HOMO, as well as
their energy gaps reflect the chemical activity of a molecule.
HOMO as an electron donor represents the ability to donate an
electron, and LUMO as an electron acceptor represents the ability
to obtain an electron. Smaller LUMO and HOMO energy gaps cor-
respond to an easier excitability the HOMO electrons. The HOMO
and LUMO energies of the target compounds based on the opti-
Organometallic and coordination complexes with enhanced
NLO properties continue to be in the limelight over the past two
decades [15–21]. They exhibit large and fast nonlinearities by
introducing new NLO active charge-transfer transitions between
the metal and the ligand, such as metal-to-ligand charge transfer
and ligand-to-metal charge transfer [22,23]. These advantages of
metal complexes are conducive to the efficient switching of sec-
ond-order NLO responses at the molecular level, which could pro-
vide the basis for a range of molecular-scale devices.
mized structure were computed. Table
HOMO–LUMO energy gaps E of PHB-Fc were smaller than those
of PHB compounds, and E of E-isomers were lower than those of
3 shows that the
D
D
Theoretical investigations play an important role in under-
standing structure–property relationships, which can assist in
designing novel NLO materials. In the PHB-Fc compounds, the
Z-isomers. These findings were consistent with those of the UV–
Vis absorption.

J. Han et al. / Inorganica Chimica Acta 392 (2012) 374–379
379
compounds. The electron-rich triphenylethylene group became
the donor, and the [Cp-Fe]+ fragment became the acceptor. This
switching of electron distribution directly affected the NLO coeffi-
cient, which could generate push–pull systems. Such systems favor
the generation of large NLO responses.
4. Conclusion
Three stilbene compounds (PHB) and their derivatives contain-
ing a cyclopentadienyl iron (PHB-Fc) unit were successfully syn-
thesized and characterized. UV–Vis absorption and fluorescence
emission spectrum analyses showed that introducing the cyclo-
pentadienyl iron unit strengthened the UV–Vis absorption of
PHB-Fc and weakened the fluorescence emission compared with
those of PHB. The optimized molecular structures and energy lev-
els of frontier molecular orbitals were obtained on the basis of DFT
at the B3PW91/Lanl2dz level. The cyclopentadienyl iron unit was
found to be a strong electron-withdrawing group. Electron transfer
occurred from the HOMO to the LUMO in PHB-Fc. The change in
electron distribution subsequently led to the improved second-
order optical susceptibility of PHB-Fc.
Acknowledgements
The authors wish to thank for financial support of National Nat-
ural Science Foundation of China (Project Grant No. 21176016).
Fig. 6. Molecular orbital surface and energies of target compounds frontier
molecular orbitals of E-PHB-Fc.
References
[1] S. Jashovam, G. Anviv, B. Shoshana, J. Med. Chem. 28 (1985) 1504.
[2] R. Olaf, L.R. Sophie, T. Alain, M.B. Kathleen, A. Isabelle, Inorg. Chim. Acta 357
(2004) 2211.
[3] G. Sylvain, M. Josee, L. Fernand, J. Org. Chem. 61 (1996) 3890.
[4] S. He, Y. Lu, L. Jiang, B. Wu, F.Y. Zhang, Y.J. Pan, J. Sep. Sci. 32 (2009) 2339.
[5] T.C. He, C.S. Wang, X. Pan, H. Yang, G.Y. Lu, Dyes Pigm. 82 (2009) 47.
[6] J. Bao, P.M. Weber, J. Am. Chem. Soc. 133 (2011) 4164.
[7] P.M.F. Karina, K.I. Melina, Y.M.I. Neyde, Inorg. Chim. Acta 363 (2010) 294.
[8] M. Marcaccio, J.A. McCleverty, W. Akemann, J.M. Nunzi, J. Photochem.
Photobiol., A 163 (2004) 413.
Table 3
Caculated values of the electrostatic first hyperpolarizability.
Compound
EHomo (eV)
ELumo (eV)
D
E (eV)a
b ꢁ 10ꢀ30 esu
PHB-1
PHB-2
PHB-3
PHB-Fc-1
PHB-Fc-2
PHB-Fc-3
(E) ꢀ 13.417
(E) ꢀ 12.126
(E)ꢀ11.677
(E) ꢀ 7.705
(E) ꢀ 7.726
(E) ꢀ 7.788
ꢀ2.542
ꢀ2.566
ꢀ2.500
ꢀ5.577
ꢀ5.174
ꢀ5.220
9.564
9.560
9.177
2.128
2.552
2.568
0.885
0.937
2.122
7.561
6.997
11.282
[9] (a) D. Plazuk, S. Top, A. Vessiéres, M.A. Plamont, M. Huche, J. Zakrzewski, A.
Makal, K. Wozniakc, G. Jaouen, Dalton Trans. 39 (2010) 7444;
(b) S. Top, A. Vessieres, G. Leclercq, J. Quivy, J. Tang, J. Vaissermann, M. Huche,
G. Jaouen, Chem. Eur. J. 9 (2003) 5223;
(c) K. Nikitin, Y. Ortin, H. Müller-Bunz, M.A. Plamont, G. Jaouen, A. Vessières,
M.J. McGlinchey, J. Organomet. Chem. 695 (2010) 595;
(d) S. Top, A. Vessiéres, C. Cabestaing, I. Laios, G. Leclercq, C. Provot, G. Jaouen, J.
Organomet. Chem. 637 (2001) 500;
(e) A. Nguyen, S. Top, A. Vessiéres, P. Pigeon, M. Huche, E.A. Hillard, G. Jaouen, J.
Organomet. Chem. 692 (2007) 1219;
(f) E.A. Hillard, A. Vessiéres, S. Top, P. Pigeon, K. Kowalski, M. Huche, G. Jaouen,
J. Organomet. Chem. 692 (2007) 1315;
(g) A. Vessiéres, S. Top, W. Beck, E. Hillarda, G. Jaouen, Dalton Trans. 35 (2006)
529.
a
D
E = (ELumo ꢀ EHomo).
coordination of ligand groups to metal centers could generate
push–pull systems. The enhancement of charge separation is
known to favor large NLO responses [24]. Consequently, the elec-
trostatic first hyperpolarizability (b) was calculated using the
GAUSSIAN 09 package.
Based on the calculated electronic properties and geometries,
[10] I.U. Khand, P.L. Pauson, W.F. Watts, J. Chem. Soc. 17 (1968) 2261.
[11] C.R. Denus, L.M. Hoffa, E.K. Todd, A.S. Abdelaziz, J. Inorg. Organomet. Polym. 10
(2000) 189.
[12] A.S. Abdelaziz, D.C. Schriemer, C.R. Denus, J. Organomet. Chem. 13 (1994)
374.
[13] B.T. Kilbourn, P.G. Owston, J. Chem. Soc. B26 (1970) 1.
[14] G. Precigoux, C. Courseille, S. Geoffre, M. Hospital, Acta Crystallogr. B 35 (1979)
3070.
[15] S.D. Bella, M. Dragoneetti, D. Pizzotti, J. Organomet. Chem. 28 (2010) 18.
[16] X.S. Xiu, Ch.Y. Guo, J. Organomet. Chem. 696 (2011) 3384.
[17] B. Azza, P. Benjamin, I. Fatima, J. Phys. Chem. A 114 (2010) 5429.
[18] G. Wei, Ch.Y. Guo, G.L. Chun, S. Ping, Inorg. Chem. 47 (2008) 5245.
[19] B. Karel, M.T. Tierney, F. Alain, Inorg. Chem. 38 (1999) 287.
[20] G.L. Chun, W. Guan, S. Ping, Inorg. Chem. 48 (2009) 6548.
[21] A. Inge, C. Koen, P. Andre, J. Mater. Chem. 14 (2004) 2831.
[22] B.J. Coe, S.P. Foxon, E.C. Harper, M. Helliwell, J. Am. Chem. Soc. 132 (2010)
1706.
the electrostatic first hyperpolarizability bijk and b were calcu-
l
lated using the DFT/B3LYP method. The components of b are de-
fined as the coefficients in the Taylor series expansion of the
external electric field energy. Using x, y, and z components, the
electrostatic first hyperpolarizability b is defined as:
l
1=2
b
¼ ðb2 þ b2 þ b2Þ
l
x
y
z
and
X
1
3
bj ¼ bjjj
þ
ðbjii þ 2bijjÞ
ði–j; i; j ¼ x; y; zÞ
i–j
The b of the title compounds are shown in Table 3. The second-
l
[23] H.L. Qiao, J.S. Rong, Q.W. Yong, W. Kechen, J. Phys. Chem. A 112 (2008)
4965.
[24] F. Meyers, S.R. Marder, J.L. Bredas, J. Am. Chem. Soc. 116 (1994) 10703.
order optical susceptibility of the target compounds followed the
order: b (PHB) < b (PHB-Fc) and b (Z) < b (E). This trend is
attributed to the intermolecular charge-transfer of the PHB-Fc
l
l
l
l