Synthesis and optical properties of two cationic cyclopentadienyliron complexes of arene containing the triphenylbutene structure

Article abstract of DOI:10.1007/s11164-014-1591-z

Two novel cationic cyclopentadienyliron complexes of arene containing the triphenylbutene group (TPBE-Fc) were synthesized and characterized by IR, UV-visible, ¹H NMR, and ¹³C NMR spectroscopy, and by MS. The optical properties of th

Full text of DOI:10.1007/s11164-014-1591-z

Res Chem Intermed
DOI 10.1007/s11164-014-1591-z
Synthesis and optical properties of two cationic
cyclopentadienyliron complexes of arene containing
the triphenylbutene structure
•
•
•
•
Tao Wang Jiqiang Liu Junru Han Guanglei Li
Xiaoning Wang
Received: 13 December 2013 / Accepted: 11 March 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract Two novel cationic cyclopentadienyliron complexes of arene containing
the triphenylbutene group (TPBE-Fc) were synthesized and characterized by IR,
1
UV–visible, H NMR, and 13C NMR spectroscopy, and by MS. The optical prop-
erties of the compounds were studied by experimental and theoretical methods.
Positive solvatochromism of the UV–visible absorption of TPBE-Fc on increasing
the solvent polarity was observed experimentally. Quantum chemical calculations
of the orbital energy, geometric structure, absorption spectra, and first hyperpolar-
izability (b) values of the TPBE-Fc were performed by use of density functional
(DFT/B3LYP and TD-DFT) methods. The spectra observed experimentally were in
good agreement with the calculated values. The calculated HOMO and LUMO
energies revealed the presence in the compounds of charge transfer mediated by the
metal center.
Keywords Triphenyl conjugated butene ꢀ Synthesis ꢀ Cyclopentadienyliron ꢀ
Optical property ꢀ Quantum chemical calculation
T. Wang (&)
State Key Laboratory of Chemical Resource Engineering, College of Science, Beijing University of
Chemical Technology, Beijing 100029, People’s Republic of China
e-mail: wangtwj2000@163.com
J. Liu ꢀ J. Han
Department of Organic Chemistry, College of Science, Beijing University of Chemical Technology,
Beijing 100029, People’s Republic of China
G. Li
Beijing Schengenbiya Bioengineering Technology Company Limited, Beijing 100029,
People’s Republic of China
X. Wang
College of Material Engineering, Beijing Institute of Fashion Technology,
Beijing 100019, People’s Republic of China
123

T. Wang et al.
Introduction
The electron-donating and electron-accepting capabilities of organic–ligand–metal
species have been successfully used in push–pull substituted chromophores to
obtain special functional molecules. Recent studies have shown that this kind of
organic material has promising features for use in optical devices [1–8]. Stilbene-
containing and triphenylbutene-containing p-conjugated compounds are particularly
promising classes of organic nonlinear materials. Research has shown that these
kinds of organic material have large second-order optical nonlinearity and might be
good candidates for electro-optic modulators [9–11]. Stilbene-containing p-conju-
gated compounds containing a metallic atom in their structures have the combined
properties of the metal and the stilbene [12–16].
Stilbene-containing and triphenylbutene-containing p-conjugated compounds
containing ferrocenyl groups have been reported to have special biological and
medicinal activity [17–21].
In this paper we report the synthesis, characterization, and optical properties of
two novel D-p-A cyclopentadienyliron complexes of arene containing the trip-
henylbutene structure (TPBE-Fc). TPBE-Fc contain a push–pull system formed by
diphenyl ether or diphenyl sulfide as donor group and cationic cyclopentadienyliron
as acceptor group. Quantum chemical calculations of the orbital energy, geometric
structure, absorption spectra, and first hyperpolarizability (b) for TPBE-Fc were
performed by use of density functional (DFT/B3LYP and TD-DFT) methods.
Experimental
Materials and instruments
All chemicals used were of analytical reagent grade from commercial sources and
used without further purification. (g6-Chlorobenzene) (g5-cyclopentadienyl) iron
hexafluorophosphate (Fc-Cl) was prepared by ligand-exchange reaction of ferrocene
and chlorobenzene as described elsewhere [22, 23].
1H NMR and 13C NMR spectra were recorded on a Bruker 400 high resolution
console, using d6-acetone as deuterated solvent and TMS as internal standard. FT-IR
spectra were recorded on a Nicolet 5700 instrument (Thermo Electron Corporation,
Waltham, MA, USA). UV–visible absorption spectra were recorded on an Hitachi
U2500 spectrophotometer (Hitachi High-Technologies, Tokyo, Japan). Fluores-
cence spectra were obtained on an Hitachi F-4500 spectrophotometer at room
temperature. Elemental analysis was performed with Thermo–Finnigan Flash EA
1112 CHNS/O analyzer.
Computational details
In this work we used density functional theory (DFT) at the Becke 3-Lee–Yang–
Parr (B3LYP)/Genecp [24, 25] (Fe with Lanl2dz basis set [26] and C, H, N, and O
with 6-31G** basic set [27, 28]) basis set level for computation of the molecular
123

Synthesis and optical properties
structures and energies of the optimized structures in the ground state. All
calculations were performed by use of Gaussian09 software [29]. The absorption
spectra of TPBE-Fc were calculated by use of the time-dependent density functional
theory (TD-DFT) method from gas phase optimized geometries [30, 31].
The dipole moment (l), mean polarizability (a), and total first static hyperpo-
larizability (b) of TPBE-Fc were calculated in terms of x, y, z components, which
are given by the equations:
ꢀ
ꢁ
1=2
l ¼ l2x þ l2y þ l2z
ð1Þ
ð2Þ
ꢂ
ꢃꢄ
a ¼ axx þ ayy þ azz
3
ꢀ
ꢁ
1=2
b ¼ b2x þ b2y þ b2z
ð3Þ
.
X
ꢂ
ꢃ
bj ¼ bjjj þ
bjii þ 2bijj
3
ði ¼ j; i; j ¼ x; y; zÞ
The b components of the Gaussian output are reported as atomic units and,
therefore, the calculated b components have been converted into electrostatic units
btot (esu) (1 a.u. = 8.6393 9 10-33 esu) [32, 33].
General methods for preparation of hydroxy-substituted triphenylbutene (TPBE)
and TPBE-Fc
The experimental procedure used in this study was based on that used in our
previous study [21]. The synthetic route to TPBE-Fc is shown in Scheme 1. Ketones
were prepared by acylation of diphenyl ether and diphenyl sulfide. TPBE were then
prepared from the ketones by McMurry coupling with hydroxybenzophenone, with
Zn and TiCl4 as catalysts. The reaction was easy to perform and gave good yields of
mixtures of Z and E isomers. TPBE-Fc were then synthesized by SNAr reaction of
the TPBE with Fc-Cl in N,N0-dimethylformamide (DMF), in the presence of
potassium carbonate as base, at 80 °C. Completion of the SNAr reaction was
monitored by observing the disappearance of Fc-Cl by thin-layer chromatography
with acetone–methanol (1:1) as mobile phase and Silica gel as stationary phase.
Characterization data for 1-(4-Hydroxyphenyl)-1-phenyl-2-(4-
phenyloxyphenyl)butene (TPBE-1)
1
Yield: 68.2 %, Z/E isomers ratio of 4:3. m.p. = 87–90 °C. H NMR (400 MHz,
acetone-d6) dppm: 0.88–0.94 and 1.15–1.21 (2 9 t, 3H, –CH3), 2.40–2.46(q, 2H,
–CH2–), 8.16 and 8.37 (2 9 s, 1H, –OH), 6.43–7.28 (m, 18H, Ar). 13C NMR
(100 MHz, acetone-d6) dppm: ((157.85, 157.49) C–OH), ((155.51, 155.20, 154.60,
153.79) C–O–C), ((141.21, 140.43, 138.57, 137.58, 135.89, 135.51, 131.08, 130.89,
127.38, 127.02, 125.72, 122.98, 119.03, 118.54, 117.69, 117.27, 115.05, 114.41,
113.98,) Ph, C=C), ((29.21, 28.92) CH2CH3), ((13.92, 13.71) CH2CH3). FT-IR (KBr
cm-1): 3347.3 (m, O–H), 2974.7 (m, -CH3), 2873.4 (m, –CH2–), 1699.1 (w, –C=C–),
1222.1 (s, C–O). ESI–MS (m/z): 393 [M ? 1]?.
123

T. Wang et al.
Scheme 1 Synthesis of TPBE-Fc
Characterization data of 1-(4-Hydroxyphenyl)-1-phenyl-2-(4-
phenylthiophenyl)butene (TPBE-2)
1
Yield: 50.8 %, Z/E isomers ratio of 4:1. m.p. = 92–95 °C. H NMR (400 MHz,
acetone-d6) dppm: 0.84–0.90 and 1.12–1.19 (2 9 t, 3H, –CH3), 2.38–2.45(q, 2H,
–CH2–), 9.23 and 9.44 (2 9 s, 1H, –OH), 6.40–7.26 (m, 18H, Ar); 13C NMR
(100 MHz, acetone-d6) dppm: ((153.41, 152.66) C–OH), ((142.66, 142.45, 139.88,
139.58, 135.79, 135.52, 134.61, 134.38, 131.09, 130.19, 129.81, 129.63, 128.81,
128.04, 126.35, 125.91, 125.53, 124.83, 113.99, 113.36) Ph, C–S–C, C=C), ((28.02,
27.71) CH2CH3), ((12.91, 12.61) CH2CH3). FT-IR (KBr cm-1): 3383.1 (m, –OH),
2953.9 (m, –CH3), 2867.4 (m, –CH2–), 1696.1 (w, –C=C–), 1219.2 (s, C–O), 1168.5
(s, C–S). ESI–MS (m/z): 409 [M ? 1]?.
Characterization data of [(g5-Cyclopentadienyl)-Fe-(g6-(1-(4-phenoxyphenyl)-1-
phenyl-2- (4-phenoxyphenyl) butene] hexafluorophosphate (TPBE-Fc-1)
1
Yield: 59.1 %, Z/E isomers ratio of 3:2. m.p. = 106–108 °C. H NMR (400 MHz,
acetone-d6) dppm: 0.89–0.93 (2 9 t, 3H, –CH3–), 2.39–2.56 (q, 2H, –CH2–), 5.09
and 5.18 (2 9 s, 5H, Cp), 6.02–6.20 (m, 5H, Ar), 6.76–7.42 (m, 18H, Ar). 13C NMR
(100 MHz, acetone-d6) dppm: ((157.31, 157.08, 156.92, 155.68, 155.59, 155.48,
150.90, 150.55) C–O–C), ((142.77, 142.00, 137.01, 136.83, 133.52, 133.21, 130.98,
129.56, 126.12, 125.58, 123.30, 123.08, 119.99, 119.45, 118.74, 118.61, 118.55,
123

Synthesis and optical properties
118.49) Ph, C=C), ((87.71, 87.47, 86.09, 85.65) Ph(C, C)-Fe-Cp), ((77.84, 77.66)
Ph(C)-Fe-Cp), ((77.04, 76.73) Ph-Fe-Cp(C)), ((29.26, 28.99,) CH2CH3), ((13.73,
13.56) CH2CH3). FT-IR (KBr cm-1): 2942.3 (m, –CH3), 2864.5 (m, –CH2–), 1234.1
(s, C–O), 831.7 (s, P–F). ESI–MS (m/z): 589[M-145(PF6-)]?. Anal. Calc. for
C39H34F6FeO2P (590.5 g mol-1): C, 79.32; H, 5.80; O, 5.42. Found: C, 79.01; H,
5.78; O, 5.31.
Characterization data of [(g5-Cyclopentadienyl)-Fe-(g6-(1-(4-phenoxyphenyl)-1-
phenyl-2- (4-phenylthiophenyl) butene] hexafluorophosphate (TPBE-Fc-2)
1
Yield: 60.6 %, Z/E isomers ratio of 4:1. m.p. = 125–128 °C. H NMR (400 MHz,
acetone-d6) dppm: 0.90–0.96 (2 9 t, 3H, –CH3–), 2.41–2.58 (q, 2H, –CH2–), 5.10
and 5.19 (2 9 s, 5H, Cp), 6.14–6.35 (m, 5H, Ar), 6.92–7.47 (m, 18H, Ar); 13C NMR
(100 MHz, acetone-d6) dppm: ((151.89, 150.89, 142.14, 141.78, 140.90, 140.42,
137.95, 137.64, 135.32, 135.08, 133.58, 131.12, 130.86, 130.56, 130.22, 129.71,
129.44, 128.42, 126.53, 126.17, 120.42, 120.00, 119.01, 118.67, 117.45, 117.95) Ph,
C–O–C, C–S–C, C=C), ((86.80, 86.65, 84.87, 84.72) Ph (C, C)-Fe-Cp), ((77.02,
76.97) Ph(C)-Fe-Cp), ((76.83, 76.55) Ph-Fe-Cp(C)), ((28.22, 28.08), CH2CH3),
((13.34, 13.26) CH2CH3). FT-IR (KBr cm-1): 2974.5 (m, –CH3), 2874.4 (m, –CH2–),
1243.1(s, C–O), 1165.5 (s, C–S), 825.7 (s, P–F). ESI–MS (m/z): 605 [M-
145(PF6-)]?. Anal. Calc. for C39H34F6FeOSP (606.1 g mol-1): C, 77.22; H,
5.65; S, 5.29; O, 2.64. Found: C, 76.98; H, 5.56; S, 5.17; O, 2.51.
Results and discussion
Characterization and molecular geometry of TPBE-Fc
1
The chemical structure of TPBE-Fc was confirmed by IR, H NMR, and 13C NMR
spectroscopy, and by MS; results are given in the ‘‘Experimental’’ section. The most
useful diagnostic resonances in the NMR spectra of TPBE or TPBE-Fc were the
singlets from the phenolic hydroxyl groups of TPBE and the cyclopentadienyl
groups of TPBE-Fc. The 1H NMR spectra of TPBE-Fc-1 and TPBE-Fc-2 are shown
in Fig. 1. Obviously, the singlets for the phenolic hydroxyl and cyclopentadienyl
groups have split into two peaks because of the E/Z isomerization shown in Fig. 1.
For direct comparison we measured the chemical shifts and the integrals of the
singlets for TPBE (*9.30 ppm) and TPBE-Fc (*5.10 ppm) in the NMR spectra.
We tried to obtain the trans and cis isomers by column chromatography and
fractional crystallization but could not isolate the pure isomers. Assignments in
NMR spectra of cis–trans mixtures are tentative; peaks were, in part, identified by
analogy with the work of Collins et al. [34], who used NMR chemical shifts to
distinguish between cis and trans antiestrogenic and antifertility compounds. Their
work showed that for substitution of the aromatic ring trans to the alkyl group, the
E isomer peaks were approximately 0.1–0.2 ppm downfield of the corresponding
peaks for the Z isomers. E-to-Z isomer ratios were estimated from the peak heights
123

T. Wang et al.
Fig. 1 1H NMR spectra of TPBE-Fc-1 and TPBE-Fc-2
of the appropriate phenolic hydroxyl group and cyclopentadienyl group resonances;
the results are given in the ‘‘Experimental’’ section.
The geometric structure of (E)-TPBE-Fc, optimized at the DFT level by use of
the B3lyp/Genecp(6-31G**/Lanl2dz) basis set, is shown in Fig. 2. Optimized
structural data, including predicted bond lengths, valence angles, and dihedral
angles, are listed in Table 1, on the basis of the atomic numbering scheme given in
Fig. 2. Steric hindrance results in spatial dihedral angles among the three phenyl
rings bonded with double bonds. As shown in Table 1, bond lengths and valence
angles for TPBE-Fc agree with those of structures of closely related compounds
determined by X-ray crystallography [35]. The C=C bond length calculated for E-
˚
TPBE-Fc is 1.338 A; the reference values for cis-tamoxifen (E) and trans-tamoxifen
˚
˚
(Z) are 1.33 A and 1.34 A, respectively. 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 trans
tamoxifen (reference values). For (E)-TPBE-Fc-1 the bond angles are: C(30)–
C(33)–C(45) 123.0°, C(34)–C(33)–C(45) 123.3°, C(33)–C(45)–C(57) 123.4°, and
C(33)–C45)–C(47) 121.0°. For (E)-TPBE-Fc-2, the bond angles are: C(30)–C(33)–
C(45) 123.0°, C(34)–C(33)–C(45) 123.3°, C(33)–C(45)–C(57) 123.5°, and C(33)–
C45)–C(47) 121.1°. There is widening of the angle on the ethyl side and narrowing
on the side on which the diphenyl ether or diphenyl sulfide group is located. This is
probably attributable to the greater bulk of the cyclopentadienyl iron group, which is
located at the other side of the ethylene skeleton relative to the diphenyl ether or
diphenyl sulfide group. It is also apparent that the four substituents on the double
bond do not lie in the same plane, the C(47)–C(45)–C(33)–C(30) atoms forming a
123

Synthesis and optical properties
Fig. 2 The optimized geometric structure of E-TPBE-Fc at DFT level
dihedral angle of 8.13°–8.60° in E-TPBE-Fc. According to Top et al., this angle was
13° for E-ferrocenyltamoxifen [36].
UV–visible spectra
The UV–visible absorption of TPBE-Fc in CH3CN was investigated; the results are
shown in Fig. 3a. TPBE-Fc has a wide conjugated absorption band in the UV–
visible region from 220 nm to 350 nm; this is ascribed to an electron-transition
process along the entire conjugate system.
The electron absorption spectra of TPBE-Fc-1 and TPBE-Fc-2 were calculated to
rationalize the observed spectral properties; the results are shown in Fig. 3b. The
first 100 spin-allowed singlet–singlet excitations for TPBE-Fc were calculated by
use of the TD-DFT approach. TD-DFT calculations started from the optimized
123

T. Wang et al.
Table 1 Selected bond distances, bond angles, and torsional angles of optimized structures of TPBE-Fc-
1 and TPBE-Fc-2
Property
TPBE-Fc-1
TPBE-Fc-2
Experimental XRDa results of tamoxifen
˚
Bond lengths (A)
C(5)–O(46)
1.338
1.414
1.359
1.338
1.414
1.358
C(23)–O(46)
C(33)–C(45)
1.330
Bond angles (°)
C(5)–O(46)–C(23)
C(30)–C(33)–C(45)
C(34)–C(33)–C(45)
C(33)–C(45)–C(57)
C(33)–C(45)–C(47)
C(54)–O(64)–C(65)
C(54)–S(75)–C(64)
Dihedral angles (°)
C(30)–C(33)–C(45)–C(47)
C(34)–C(33)–C(45)–C(47)
120.5
123.0
123.3
123.4
121.0
120.8
120.6
123.0
123.3
123.5
121.1
122–124
122–124
122–124
122–124
121.1
8.16
8.57
8.13
8.60
13
a
From Ref. [36]
Fig. 3 Comparison of experimental (a) and calculated (b) UV–visible spectra
geometry, using the same level of theory, and were performed for the gas phase to
calculate excitation energies. The wavelength (k), oscillator strength (fos), and major
contributions of the calculated transitions are listed in Table 2. The calculated
results are indicative of a metal-to-ligand charge transfer (MLCT) transition for
TPBE-Fc and agree reasonably well with the experimentally measured spectral data
123

Synthesis and optical properties
Table 2 Main electronic transitions of TPBE-Fc-1 and TPBE-Fc-2 by the TD-DFT method
Molecule
E (eV)
k (nm)
fos
Main contribution
Transition
TPBE-Fc-1
3.5811
5.1363
346.22
241.39
0.1235
0.4291
HOMO - 1 ? LUMO ? 4
HOMO ? LUMO ? 4
MLCT
p–p*
HOMO - 6 ? LUMO ? 4
HOMO - 5 ? LUMO ? 8
HOMO - 3 ? LUMO ? 8
HOMO - 2 ? LUMO ? 8
HOMO - 1 ? LUMO ? 8
HOMO - 1 ? LUMO ? 13
HOMO ? LUMO ? 14
HOMO ? LUMO ? 15
TPBE-Fc-2
3.4103
5.0858
363.56
243.79
0.0733
0.4125
HOMO - 6 ? LUMO
MLCT
HOMO ? LUMO ? 4
p–p*
HOMO - 6 ? LUMO ? 4
HOMO - 5 ? LUMO ? 8
HOMO - 4 ? LUMO ? 8
HOMO - 2 ? LUMO ? 14
HOMO - 1 ? LUMO ? 16
HOMO - 1 ? LUMO ? 17
MLCT metal-to-ligand charge transfer
listed in Table 3. For example, the calculated gas-phase transitions for TPBE-Fc-1
and TPBE-Fc-2 appeared at 241.4 nm and 243.8 nm, in good agreement with the
experimental data obtained from the UV–visible result, viz. 240 nm and 242 nm in
acetonitrile solution. The value of calculated kmax for TPBE-Fc-1 was blue shifted
relative to that for TPBE-Fc-2, also in good agreement with the previous
experimental result. MLCT of the two compounds were observed at 346.2 nm
and 363.6 nm.
The UV–visible absorption spectra of TPBE-Fc in solvents of different polarity
were investigated; the results are summarized in Table 3 and Fig. 4. Positive
solvatochromism (bathochromic shift) of the absorption of TPBE-Fc-1 and TPBE-
Fc-2 was observed on increasing the polarity of the solvent. This is related to greater
stabilization of the excited state relative to the ground state with increasing solvent
polarity.
HOMO and LUMO analysis
The energies of the highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) of the target compounds were computed on
the basis of the optimized structures. Table 4 shows that the HOMO–LUMO energy
gaps, DE, are smaller for TPBE-Fc than for TPBE, and that DE for the E isomers are
lower than those for the Z isomers. Figure 5 shows the delocalization of the electron
123

T. Wang et al.
Table 3 UV–visible data for
TPBE-Fc in different solvents
Solvent
kmax (nm)
e 9 104 (L mol-1 cm-1
)
TPBE-Fc-1
DMF
266
250
243
240
240
0.96
1.40
1.85
1.71
2.01
THF
CHCl3
CH2Cl2
CH3CN
TPBE-Fc-2
DMF
265
251
244
243
242
0.99
1.38
1.54
1.92
1.97
THF
CHCl3
CH2Cl2
CH3CN
DMF
2.0
1.5
1.0
0.5
CHCl3
CH3CN
CH2Cl2
THF
TPBE-Fc-2
0.0
2.0
CH2Cl2
CH3CN
DMF
THF
CHCl3
TPBE-Fc-1
1.5
1.0
0.5
0.0
200
300
400
500
600
Wavelength(nm)
Fig. 4 UV–visible absorption spectra of TPBE-Fc in solvents of different polarity
123

Synthesis and optical properties
Table 4 Calculated values of HOMO and LUMO energies and electrostatic first hyperpolarizability
Compound
TPBE-1
EHOMO (eV)
ELUMO (eV)
DE (eV)a
b 9 10-30 esu
(Z)
(E)
(Z)
(E)
(Z)
(E)
(Z)
(E)
-3.327
-3.558
-3.177
-3.281
-7.913
-7.171
-7.790
-6.970
1.371
1.672
4.699
5.230
9.327
4.970
2.963
2.007
2.846
1.811
0.633
1.428
0.810
0.729
4.216
14.801
4.410
16.171
TPBE-2
TPBE-Fc-1
TPBE-Fc-2
a
1.379
1.690
-4.950
-5.164
-4.944
-5.159
DE = (ELUMO - EHOMO
)
densities of the frontier orbitals of the E-TPBE and E-TPBE-Fc molecules. In the
HOMO and LUMO of TPBE, the electron densities are all delocalized over the
–C=C– and aryl rings. From HOMO to LUMO, no electron transfer occurred in
TPBE. In the HOMO of TPBE-Fc, the electron densities delocalized over the
–C=C– bond and aryl rings, whereas in their LUMO orbitals the electron densities
delocalized over the cyclopentadienyl iron cation and the coordinated arene. This
result is clearly indicative of significant molecular charge delocalization, which
strengthened its nonlinear optical (NLO) response.
Enhancement of charge separation is known to favor large NLO responses. The
electrostatic first hyperpolarizability (b) was calculated by use of the Gaussian 09
package. On the basis of the calculated electronic properties and geometries, the
electrostatic first hyperpolarizability bl was calculated by use of the DFT/B3LYP
method. Values of bl for compounds TPBE-Fc-1 and TPBE-Fc-2 were reasonable
(Table 4), although slightly weaker than values reported for the extended p-
conjugated organic tolane derivative (1.02 9 10-28 esu) or the pyridoneimine
derivative (2.0 9 10-29 esu) terminated with a similar cationic sandwich acceptor
fragment [37]. However, the bl values are significantly greater than the 149, 154,
and 267 9 10-48 esu values previously determined for three dipolar organoiron
methylenepyran hydrazone complexes and pyranylideneacetaldehyde-hydrazone
complexes with similar acceptor end groups [38, 39]. Interestingly, it is worthy of
note that the second-order optical susceptibility of the target compounds followed
the order: bl (TPBE) \ bl (TPBE-Fc) and bl (Z) \ bl (E). This trend is
attributed to the intermolecular charge-transfer of the TPBE-Fc compounds. The
presence of the electron-rich diphenyl ether and diphenyl sulfide moiety as a
strong donor-group and the cationic cyclopentadienyliron fragment as a strong
acceptor-group led to a larger value of bl (TPBE-Fc) than in our previous study.
This switching of electron delocalization directly affected the NLO coefficient,
which could generate push–pull systems. Such systems favor the generation of
large NLO responses.
123

T. Wang et al.
(E)-TPBE-1 LUMO
(E)-TPBE-1 HOMO
(E)-TPBE-2 HOMO
(E)-TPBE-2 LUMO
(E)-TPBE-Fc-1 LUMO
(E)-TPBE-Fc-2 LUMO
(E)-TPBE-Fc-1 HOMO
(E)-TPBE-Fc-2 HOMO
Fig. 5 Molecular orbital surface and energies of the frontier molecular orbitals of E-TPBE and E-TPBE-
Fc
Conclusions
In this work, two cyclopentadienyliron complexes of arene containing the triphenyl
conjugated butane moiety (TPBE-Fc) were synthesized. UV–visible absorption
spectra were analyzed by experimental and theoretical methods. The double bond
configuration of the compounds was determined from 1H NMR data. The optimized
molecular structures and energy levels of frontier molecular orbitals were obtained
on the basis of DFT at the B3LYP/Genecp level. It was found that these two
molecules are second-order nonlinear optical materials with large first hyperpolar-
izability of 1.48 9 10-29 and 1.62 9 10-29 esu for E-TPBE-Fc-1 and E-TPBE-Fc-
2, respectively. The cyclopentadienyl iron unit was found to be a strong electron-
123

Synthesis and optical properties
withdrawing group and MLCT occurs in the molecule. This change in electron
distribution resulted in the high second-order optical susceptibility of TPBE-Fc.
Acknowledgments The authors wish to thank the National Natural Science Foundation of China for
financial support (project grant no. 21176016). We also thank Beijing University of Chemical Technology
Chem Density Computing Platform for supporting the calculations.
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