Synthesis, crystal structures and two-photon absorption properties of triphenylamine cyanoacetic acid derivative and its organooxotin complexes

Article abstract of DOI:10.1039/c4dt02251c

Three novel organooxotin complexes (Z1, Z2 and Z3) were synthesized by reaction of L1 (2-cyano-3-(4-(diphenylamino)phenyl) acrylic acid) with n-Bu₂SnO, Ph₃Sn(OH) and nBu₆Sn₂O. The structures of the three complex

Full text of DOI:10.1039/c4dt02251c

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Synthesis, crystal structures and two-photon
absorption properties of triphenylamine
cyanoacetic acid derivative and its organooxotin
complexes†
Cite this: DOI: 10.1039/c4dt02251c
Xuesong Zhao,a Jie Liu,a Hui Wang,a Yan Zou,a Shengli Li,a Shengyi Zhang,a
Hongping Zhou,a Jieying Wu*a and Yupeng Tian*a,b
Three novel organooxotin complexes (Z1, Z2 and Z3) were synthesized by reaction of L1 (2-cyano-3-(4-
(diphenylamino)phenyl) acrylic acid) with n-Bu2SnO, Ph3Sn(OH) and nBu6Sn2O. The structures of the
three complexes have been confirmed by single-crystal X-ray diffraction analysis. The metal complex Z1
features a ladder framework while Z2 and Z3 show discrete structures. The UV-vis absorption, single-
photon excited fluorescence (SPEF) and two-photon excited fluorescence (2PEF) of the complexes have
been systematically studied, suggesting that the three metal complexes have strong two-photon absorp-
tion (2PA) and large 2PA cross-sections. It is noteworthy that Z2 possesses an enhanced two-photon
absorption, and Z3 exhibits larger 2PA cross-section per molecular weight compared to L1. Finally, high
anti-tumor activity of these three metal complexes has also been identified.
Received 24th July 2014,
Accepted 29th October 2014
DOI: 10.1039/c4dt02251c
www.rsc.org/dalton
Numerous investigations of materials with large two-
photon absorptions (2PA) have progressed owing to their
Introduction
Research on organometallic compounds has aroused great attractive applications. These include three-dimensional
interest. Their intimate connection with the synthesis and optical data storage, up-converted lasing, two-photon dynamic
assembly of new materials, excellent optical properties, cataly- and bioimaging, and lower excitation energy NIR consequently
sis reactions and exploitation of many anti-cancer drugs resulting in lower photon damage.18–24 Lots of studies have
etc.,1–4 wherein the organotin compounds, especially ubiqui- been devoted to the design and synthesis of materials that
tous organotin carboxylates, exhibit a range of effects for possess large 2PA cross-sections, especially, metal complexes
chemotherapy,
biological,
catalytic
and
industrial have caused widespread attention because of their excellent
applications.5–11 Although their properties including diversity properties.25–29 However, organotin carboxylate complexes
of structures for constructing novel compounds, assembly/self- with 2PA properties still lack comprehensive coverage. Herein,
assembly for polymers, and anti-tumor/anti-bacterial have a series of organotin carboxylate complexes were designed and
been systematically investigated,12–16 only a few studies regard- investigated based on the following considerations. Firstly,
ing the two-photon absorption properties of the organotin car- organotin carboxylate complexes have a large structural diver-
boxylate derivatives have been reported.17
sity by relatively simple synthetic variations of organotin com-
pounds.30,31 Secondly, triphenylamine was used to construct
the ligand owing to its strong electron-donating ability and
good solubility. Therefore, its derivatives have good optical
properties, such as strong two-photon fluorescence, this might
promote their biological and clinical related applications.32–34
Here, four compounds including one triphenylamine car-
boxylic acid ligand (L1) and its three organotin complexes (Z1,
Z2, Z3) were synthesized and fully characterized accordingly.
The crystal structures of the three metal complexes have been
presented. The optical properties of all four compounds
including UV-vis absorption, single-photon excited fluo-
rescence (SPEF) and two-photon excited fluorescence (2PEF)
aDepartment of Chemistry, Key Laboratory of Functional Inorganic Materials
Chemistry of Anhui Province, Anhui University, Hefei 230039, P. R. China.
E-mail: yptian@ahu.edu.cn, jywu1957@163.com
bState Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing
210093, P. R. China
†Electronic supplementary information (ESI) available: Synthetic procedures
and detailed experimental information; X-ray crystallographic data (CIF); compu-
tation studies; optical measurements; two-photon excited fluorescence (2PEF)
spectroscopy and two-photon absorption (2PA) cross-section. CCDC 1015658,
871125 and 871126. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4dt02251c
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80 MHz, 140 fs) as the light source. The concentration of the
sample solution was 1.0 × 10−3 mol L−1. Thus, the σ values of
samples were determined by the following eqn (1):
δs ¼ δr ꢀFs ꢀΦr ꢀCr ꢀnr=Fr ꢀΦs ꢀCs ꢀns;
ð1Þ
here, the subscript ref stands for the reference molecule. σ is
the 2PA cross-section value. C is the concentration of the solu-
tion. n is the refractive index of the solution. F is the integrated
area of the detected two-photon-induced fluorescence signal,
and Φ is the fluorescence quantum yield. The σref value of
reference is taken from the literature.36
X-ray crystallography
The X-ray diffraction measurements were performed on a
Bruker SMART CCD area detector using graphite monochro-
mated Mo-Kα radiation (λ = 0.71069 Å) at 298(2) K. Intensity
data were collected in the variable ω-scan mode. The structures
were solved by direct methods and difference Fourier synth-
eses. The non-hydrogen atoms were refined anisotropically
and hydrogen atoms were introduced geometrically. Calcu-
lations were performed with SHELXTL-97 program package.37
Scheme 1 Synthetic routes for L1 and complexes Z1, Z2, and Z3.
TD-DFT studies
have been investigated in detail. Significantly, compared to
previous work by our group,17 TPA cross sections of the four
compounds have greatly improved and were located at the
near-IR region.
The synthetic route for ligand L1 and complexes Z1, Z2,
and Z3 are shown in Scheme 1.
Optimizations were carried out with B3LYP LANL2DZ without
any symmetry restraints, and the TD-DFT {B3LYP LANL2DZ}
calculations were performed on the optimized structure. All
calculations, including optimizations and TD-DFT, were per-
formed with the G03 software.38 Geometry optimization of the
singlet ground state and the TD-DFT calculation of the lowest
25 singlet–singlet excitation energies were calculated with a
basis set composed of 6-31G for C, H, N, and O atoms and the
Lanl2dz basis set for the Sn atom was downloaded from the
EMSL basis set library. The lowest 25-spin allowed singlet–
Experimental section
Materials and apparatus
All chemicals and solvents were dried and purified by standard singlet transitions, up to an energy of about 5 eV, were taken
methods. Elemental analyses were performed with a Perkin- into account for the calculation of the absorption spectra.
Elmer 240B instrument. IR spectra were recorded on a NEXUS
870 (Nicolet) spectrophotometer in the 4000–400 cm−1 region
Synthesis
with samples prepared as KBr pellets. MALDI-TOF mass
Synthesis of 2-cyano-3-(4-(diphenylamino)phenyl) acrylic
acid (L1). A mixture of 4-(diphenylamino) benzaldehyde
spectra were recorded using a Bruker Autoflex III Smartbeam.
1H- and 13C-NMR spectra were obtained on a Bruker Avance
(1 mmol, 0.28 g) and cyanoacetic acid (2 mmol, 0.17 g) were
400 MHz spectrometer (TMS as internal standard in NMR).
dissolved in acetonitrile (40 mL), then 2 drops of piperidine
119Sn-NMR spectra (proton-decoupled) were recorded on a
were added, heated at reflux for 2 h. Then, the mixture was
Bruker AV 400 spectrometer operating at 150 MHz; resonances
recrystallized from ethanol to afford yellow crystals. Yield:
are referenced to tetramethyltin (external standard, 119Sn).
0.26 g (75%). 1H-NMR (400 MHz, d6-DMSO, ppm), δ: 7.87 (s,
Melting points were measured on a FP62 instrument.
1H), 7.77 (d, 2H, J = 7.6 Hz), 7.37 (t, 4H, J = 7.6 Hz), 7.14 (q,
6H), 6.89 (d, 2H, J = 8.0 Hz). IR (KBr, cm−1) ν: 3446 (s), 2211
Optical measurements
(m), 1719 (m), 1618 (w), 1579 (w), 1505–1488 (m), 1175 (m),
UV-vis absorption spectra were recorded on a UV-265 spectro- 1076 (w), 957–757 (w), 724 (w). Maldi-Tof: 339.95.
photometer. Fluorescence measurements were performed
Synthesis of complex Z1. nBu2SnO (0.25 g, 1 mmol) and L1
using a Hitachi F-7000 fluorescence spectrophotometer. The (0.34 g, 1 mmol) were heated at reflux in benzene (30 mL) for
fluorescence quantum yields (Φ) were determined by using flu- 6 h. Yellow oil was obtained by distillation under reduced
orescein as the reference according to the literature method.35 pressure, then dispersed by methanol in chloroform (5 mL).
2PA cross-sections (σ) of the samples were obtained by the two- Pale yellow solid (Z1) was obtained after filtration and vacuum
photon excited fluorescence (2PEF) method with a femto- dried. Yield: 0.44 g (66%). m.p. >300 °C. Anal. Calcd for
second laser pulse and a Ti:sapphire system (680–1080 nm,
C120H132N8O10Sn4: C 62.96, H 5.81, N 4.89; Found: C 62.95, H
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5.80, N 4.85 (%). 119Sn-NMR (CDCl3): −206.55, −212.02 ppm.
1H-NMR (400 MHz, CDCl3): δ = 8.11 (s, 1H), 7.86 (d, 2H, J =
8.0 Hz), 7.32–7.30 (m, 4H), 7.16 (d, 6H, J = 7.2 Hz), 6.98 (d, 2H,
J = 8.0 Hz), 1.78–1.65 (m, 4H), 1.65–1.55 (m, 4H), 1.41–1.33 (m,
4H), 0.92 (q, 6H). 13C-NMR (CDCl3): δ = 13.71 (CH3), 26.86,
27.34, 27.87, 28.52, 30.48 (CH2), 118.04 (–CHvC), 119.84
(–CuN), 124.40, 125.03, 126.16, 129.69, 132.79, 146.10 (Phen),
151.76, 153.51 (–CHvC), 168.70 (–COOH). IR (KBr, cm−1):
2956 (s), 2926 (s), 2868 (s), 2210 (s), 1713 (s), 1582 (s), 1506 (s),
1490 (m), 1191 (s), 1179 (s), 758 (m), 701 (s), 636 (s), 512 (m).
Synthesis of complex Z2. Synthetic procedure of Z2 was
similar to Z1, afforded using Ph3SnOH (0.368 g, 1 mmol) and
L1 (0.341 g, 1 mmol). Yield: 77%. m.p. >300 °C. Anal. Calcd
for C42H33N3O2Sn: C 69.06, H 4.55, N 5.75; Found: C 69.05, H
4.57, N 5.73 (%). 119Sn-NMR(CDCl3): δ = −107.47 ppm.
1H-NMR (400 MHz, CDCl3): δ = 8.12 (s, 1H), 8.01 (s, 1H), 7.87
(m, 7H), 7.48 (m, 8H), 7.34 (t, 4H, 8.0 Hz), 7.18 (m, 6H), 6.96
(d, 2H, 8.8 Hz), 2.95 (s, 3H), 2.88 (s, 3H). 13C-NMR (CDCl3): δ =
117.50 (–CHvC), 119.31 (–CuN), 123.79, 125.32, 126.38,
129.03, 129.77, 130.33, 132.88, 136.68, 136.92, 137.26, 137.97,
145.85 (Phen), 152.09, 154.11 (–CHvC), 162.64, 168.62
(–COOH). IR (KBr, cm−1): 2219 (s), 1712 (s), 1582 (s), 1552 (m),
1505 (m), 1489 (m), 1391 (m), 1333 (m), 1191 (m), 757 (m),
700 (s), 618 (w), 577 (w), 517 (s).
Table 1 Crystal structure data refinement of Z1, Z2 and Z3
Compound
Z1
Z2
Z3
Empirical
formula
Formula weight 2320
C120H132N8O10Sn4 C43H37N3O3Sn C136H168N8O8Sn4
762
2517
T/K
293(2)
Monoclinic
P21/c
293(2)
296(2)
Crystal system
Space group
Orthorhombic Monoclinic
Pca21
P21/c
Crystal size/mm 0.30 × 0.20
× 0.20
0.30 × 0.20
× 0.20
0.30 × 0.20
× 0.20
a/Å
b/Å
c/Å
10.700
22.813
24.357
98.046
5887(3)
4
11.388(5)
18.873(5)
17.688(5)
90.000(5)
3802(2)
4
1.332
0.714
1560
18.958
32.449
22.172
100.510
134 072(3)
4
3.203
7.365
5216
β/°
V/Å3
Z
Dc/Mg m−3
μ/mm−1
F(000)
3.193
7.342
5040
Final R indices R1 = 0.0726,
I > 2σ(I) wR2 = 0.1868
R1 = 0.0378,
wR2 = 0.1111 wR2 = 0.1702
0.975 1.030
R1 = 0.0685,
Goodness-of-fit 1.333
on F2
trum of Z1 showed two peaks at −206.55 and −212.02 ppm,
which revealed that the tin atoms of the tetrameric structure of
Z1 have two different configurations in solution.
Synthesis of complex Z3. The same synthetic route as that
of Z2 was employed with the exception that the crude product
Crystal structures
was recrystallized by ethanol and dichloromethane to afford Crystallographic data for the complexes Z1, Z2 and Z3 are sum-
yellow needle-like crystals. Yield: 72%. m.p. >300 °C. Anal. marized in Table 1, with selected bond lengths and angles for
Calcd for C34H42N2O2Sn: C 64.85, H 6.74, N 4.41; Found: C Z1, Z2 and Z3 presented in Tables S1–S3,† respectively.
64.88, H 6.73, N 4.45 (%). 119Sn-NMR (CDCl3): δ = 132.50 ppm.
Crystal structure of C120H32N8O10Sn4 (Z1). Complex Z1 crys-
1H-NMR (400 MHz, CDCl3): δ = 8.03 (s, 1H), 7.83 (d, 2H, J = 8.8 tallizes in the monoclinic with P21/c space group. Fig. 1 shows
Hz), 7.34 (t, 4H, J = 8.0 Hz), 7.16 (t, 6H, J = 7.6 Hz), 6.98 (d, 2H, the molecular structure with the central atom numbering
J = 8.8 Hz), 1.68–1.62 (m, 6H), 1.9–1.32 (m, 12H), 0.92 (t, 9H, scheme, which consists of a tetranuclear dimeric ladder frame-
J = 7.2 Hz). 13C-NMR (CDCl3): δ = 13.64 (CH3), 26.70, 27.02, work. In the crystal structure of this centrosymmetric cluster
27.34, 27.65, 27.75, 27.85 (CH2), 100.18 (–CHvC), 117.66 compound, the central Bu4Sn2O2 core consists of two tin
(–CuN), 132.60, 129.70, 129.61, 126.25, 126.09, 125.11, 124.11 atoms and two oxygen atoms (O1, O1′). In addition, two
(Phen), 152.97 (–CHvC), 167.57 (–COOH). IR (KBr, cm−1): oxygen atoms were three coordinated with two central tin
2955 (s), 2922 (s), 2854 (s), 2218 (s), 1655 (s), 1577 (s), 1506 (s), atoms and another tin atom of the outer ring. Selection bond
1491 (m), 1455–1374 (w), 1315 (s), 1297 (m), 1223 (w), 1191 (s), lengths (Å) and angles (°) of Z1 are shown in Table S1.† The
1178 (m), 1076–700 (w), 759 (s), 701 (s), 675–537 (w), 518 (s).
main bond lengths Sn(1)–O(4) 2.669(5), Sn(2)–O(4) 2.195,
Sn(2)–O(3) 2.219, Sn(1′)–O(2) 2.262 Å fall in the typical Sn–O
bond length range.39 Two tin atoms of this central ring consti-
tute six-coordinated distorted octahedral while the external
two tin atoms are five-coordinated trigonal bipyramidal con-
figurations, thus two coordination modes were consistent with
Results and discussion
Synthesis and characterization
The synthetic routes for all the compounds are shown in the two chemical shifts of 119Sn-NMR. As shown in Fig. S1,†
1
Scheme 1. The H-NMR spectrum of L1 in d6-DMSO showed a intermolecular weak interactions C35–H⋯O2 (2.692 Å) form a
singlet at δ = 7.87 ppm for the vinyl proton, similar to Z1, Z2 one-dimensional chain structure, and through the weak inter-
and Z3 at 8.11, 8.12, 8.03 ppm in CDCl3, respectively. As shown action of C50–H50⋯O5 could build a two-dimensional structure
in the IR spectra, νCuN bands appeared at 2210, 2210, 2218 as shown in Fig. S2.†
and 2219 cm−1 for L1, Z1, Z2 and Z3, respectively. The reaction
Crystal structure of C43H37N3O3Sn (Z2). Complex Z2 crystal-
of L1 with Ph3SnOH and n(Bu3Sn)2O to afford Z2 and Z3 were lizes in the orthorhombic with Pca21 space group. Fig. 2(a)
mononuclear, compared to the tetranuclear product of Z1. The shows the molecular structure with the main atom numbering
119Sn-NMR spectrum of Z2 and Z3 exhibited single peaks at δ = scheme. The geometry around the central tin atom could be
−107.47 and 132.50 ppm, respectively, which was consistent described as trigonal bipyramidal, which is coordinated by
with a monomeric structure in solution. The 119Sn-NMR spec- three benzene rings and the oxygen atom of the carboxylic
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Fig. 1 Molecular structure of Z1; H atoms are omitted for clarity.
Fig. 2 Molecular structure of Z2 (a) and Z3 (b); H atoms are omitted for clarity.
acid, a solvent molecule (DMF) is also involved. A selection of 102(4)°, C(9C)–Sn(3)–C(1C) 109(6)°, and C(5C)–Sn(3)–C(9C)
bond lengths (Å) and angles (°) of Z2 are shown in Table S2.† 118 (5)°. In addition, due to the weak interaction between the
Bond length Sn(1)–O(1) 3.223 Å was much longer than Sn(1)– N atom of the cyano group and the Sn atom, the one-dimen-
O(2) 2.131(3), Sn(1)–O(3) 2.432(4) Å, which indicates that the sional and two-dimensional structures of the molecule have
O(2) atom did not participate in the coordination. In addition, the stacked assembly as shown in Fig. S5 and S6,† and the
the crystal structure also coordinated by a solvent molecule Sn–N bond length was between 2.600–2.950 Å. The weak inter-
(DMF), can be confirmed by NMR spectra and elemental analy- molecular forces in stabilizing the crystal structure play an
sis. Adjacent molecules interact with each other through H important role in the molecular assembly.
bonds (C–H⋯O) and (C–H⋯N) to form a 1D chain structure
and 2D chain structure as shown in Fig. S3 and S4,†
Optical properties
respectively.
UV-vis absorption spectra and TD-DFT studies. The linear
absorption spectra in five different solvents (c = 1.0 × 10−5 mol
L−1) of the chromophores (L1, Z1) are shown in Fig. 3, Z2 and
Z3 are shown in Fig. S7† because of the similar properties
compared to Z1. The spectra of all compounds feature a weak
absorption band in 280–300 nm and a moderately intense
absorption in the range 369–425 nm in all five solvents. Weak
solvatochromism was observed in the shorter absorption
bands, which indicates that weak dipole–dipole interactions
occurred within the four complex molecules in solution. Mean-
while, an obvious blue shift appeared at longer wavelength
bands with the increase of polarity, which is attributed to the
fact that the ground state in polar solvent has higher stabili-
zation than the excited state, leading to an elevated energy gap
(ΔEp) in polar solvents, and λmax shifts to shorter wave-
Crystal structure of C136H168N8O8Sn4 (Z3). Complex Z3 crys-
tallizes in the monoclinic with P21/c space group. Fig. 2(b)
shows the molecular structure with the main atom numbering
scheme. A selection of bond lengths (Å) and angles (°) of Z3
are shown in Table S3.† This organic tin complex contains
four molecules in the unit cell, each molecule had the same
weak force and the same configuration, so only one molecule
structure has been described as shown in Fig. 2(b). The bond
length Sn(3)–O(8) 2.11 Å falls in the typical Sn–O bond length
range, which reveals that between the central tin atom and car-
bonyl oxygen atom exists a weak bond and it was a monoden-
tate coordinated form between organic tin and the ligand. The
molecular geometry is a distorted tetrahedral structure due to
the bond angles O(8)–Sn(3)–C(1C) 102(6)°, O(8)–Sn(3)–C(9C)
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Fig. 3 UV-vis absorption spectra of L1 and Z1 (inset: normalized absorption).
length.40,41 In addition, polar solvent molecules associated
The lowest-energy excitation band of the ligand L1 (calcu-
with molecular hydrogen also caused the absorption peak to lated at 418 nm) is assigned to a whole intramolecular charge
move to a shorter wavelength.42 TD-DFT computational studies transfer (ICT) transition due to the HOMO → LUMO tran-
were performed to elucidate the electronic structures of the sition, the high-energy excitation band at λ = 295 nm is mainly
ground state of L1 and Z1–Z3. The schematic representation of due to the HOMO → LUMO+2 assigned to ICT transition
the molecular orbitals of L1 and Z1–Z3 are exhibited in Fig. 4, π→π*triphenylamine. Moreover, all of the three complexes are pre-
the energies and compositions of some frontier orbitals are sented with similar transition features, the low-energy exci-
listed in Table 2.
tation bands of complexes (λ = 433 for Z1, 411 for Z2 and
Fig. 4 Molecular orbital energy diagram for L1, Z1, Z2 and Z3.
Table 2 Calculated linear absorption properties (nm), excitation energy (eV), oscillator strengths and major contribution for L1, Z1, Z2 and Z3 (in
ethanol)
Compound
ΔE1a (eV)
λb (nm)
Oscillator strengths
Nature of the transition
Character
L1
Z1
Z2
Z3
2.9655
4.2067
2.8586
4.1148
3.0154
4.4349
2.8561
4.3660
418
295
433
301
411
280
434
284
0.7307
0.1245
0.0009
0.1454
1.0132
0.0139
0.9610
0.0008
89(HOMO) → 90(LUMO)
ICT
89(HOMO) → 92(LUMO+2)
500(HOMO−2) → 503(LUMO)
494(HOMO−8) → 503(LUMO)
172(HOMO) → 173(LUMO)
166(HOMO−6) → 173(LUMO)
140(HOMO) → 141(LUMO)
138(HOMO−2) → 141(LUMO)
π→π*(triphenylamine)
ICT
MLCT
ICT
MLCT
ICT
MLLCT
a The energy gap of the single-photon absorption band. b Peak position of the linear absorption band.
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Fig. 5 Single-photon excited fluorescence spectra (SPEF) of L1, Z1 (inset: normalized intensity).
434 nm for Z3) originating from HOMO−8 → LUMO, HOMO
Table 3 Single-photon-related photophysical properties of L1, Z1, Z2
and Z3 in five different solvents
−6 → LUMO, HOMO → LUMO are all being dominated by ICT
transitions, while high-energy bands (λ = 301 for Z1, 280 for Z2
and 295 nm for Z3) are assigned as the MLCT transition due to
the H−2 → L for Z1, H−5 → L for Z2 and H−2 → L for Z3 tran-
sitions, respectively. However, the charge distribution of
HOMO−2 for Z3 is located on the metal ions and the ligand,
so the excitation band for Z3 (at 295 nm) which is due to the H
−2 → L could be assigned to a MLLCT transition. Basically, it
can be concluded that the results from the experiments and
theoretical calculations are consistent, and the calculated tran-
sitions are in reasonable agreement with the extended electron
delocalization drawn from the structural determinations
above.
Single-photon exited fluorescence (SPEF). The single-
photon exited fluorescence (SPEF) spectra in five different sol-
vents of the chromophores are shown in Fig. 5 (L1, Z1) and
Fig. S8† (Z2, Z3) which were measured at the same concen-
tration as that of the linear absorption spectra. Single-photon-
related photophysical properties of L1 and Z1–Z3 are presented
in Table 3. As can be seen, the fluorescence emission peaks of
the three complexes (Z1, Z2, Z3) have an obvious blue shift
trend with increasing polarity. Moreover, the ligand (L1) and
complexes (Z1, Z2, Z3) exhibit almost the same emission wave-
lengths in all solvents, and the emission intensity of these
complexes is weaker when compared to the ligand (L1) as
shown in Fig. S9,† which is due to the involvement in Sn
atoms making the fluorescent molecules spin–orbit coupling
increase, causing the closer energy between the singlet excited
and triplet states, resulting in decreased probability of fluo-
rescence.41 And the fluorescence quantum yields of the com-
plexes (Z1, Z2, Z3) increase along with the increasing polarity
of the solvents, which are consistent with the blue-shift of
their spectra. Besides, the lifetime of four compounds are also
shown in Table 3, they all exhibit the longest lifetime in THF
solution, wherein Z1 (3.96 ns) is somewhat longer than that of
L1 (3.80 ns), Z2 (3.87 ns) and Z3 (2.78 ns), which can be attri-
buted to a larger delocalization within the whole molecule of
Z1 and more molecular stabilization effects for the excited
state of Z1 than the other three compounds.43
τd
(ns)
Φc
a
b
Compound Solvents
λmax
λmax
ε
L1
Z1
Z2
Z3
CH2Cl2
THF
CH3CH2OH 290, 395 521
CH3CN
DMF
CH2Cl2
THF
CH3CH2OH 288, 400 519
CH3CN
DMF
CH2Cl2
THF
CH3CH2OH 288, 404 519
CH3CN
DMF
CH2Cl2
THF
CH3CH2OH 288, 399 520
CH3CN
DMF
289, 419 522
290, 413 537
17737, 49925 0.015 3.56
19346, 45657 0.019 3.80
15903, 32360 0.051 2.68
19110, 35540 0.088 1.66
19550, 35206 0.073 2.84
14907, 39609 0.004 3.39
15520, 33040 0.036 3.96
15705, 35080 0.010 2.84
14505, 33190 0.015 3.62
15480, 31530 0.020 2.77
12206, 34110 0.003 3.61
13440, 32410 0.013 3.87
13510, 30879 0.011 2.75
12920, 30754 0.016 1.66
16013, 28817 0.020 2.91
17038, 41630 0.008 2.57
16981, 41672 0.023 2.78
15492, 36552 0.012 0.83
15936, 37368 0.011 1.87
17016, 33751 0.019 2.08
288, 404 522
292, 375 500
289, 426 553
290, 403 520
291, 403 511
293, 371 505
289, 414 565
290, 406 529
288, 400 515
293, 371 504
291, 419 556
291, 400 530
286, 400 512
295, 373 503
a Peak position of the largest absorption band. b Peak position of SPEF,
exited at the absorption maximum. c Quantum yields determined
using fluorescein as standard. d Fluorescence lifetime (ns).
L1 and Z1–Z3 in THF with c = 1.0 × 10−3 mol L−1 were
measured from 710 nm to 900 nm with an interval of 10 nm
with a pulse duration of 140 fs under 200 mW, as shown in
Fig. S10.† The emission intensity of compounds L1 and Z1–Z3
were investigated at 830, 820, 830 and 820 nm, respectively. As
shown in Fig. S11,† the linear dependence on the square of
input laser power suggests that it is a two-photon excitation
mechanism. 2PEF spectra of the four complexes in different
solvents have been measured as shown in Fig. 6 and S12.† It
can be seen that all the two-photon excited fluorescence
(2PEF) spectra of the compounds exhibited a broad emission
band, and the bands show an obvious red shift when com-
pared to the SPEF spectra of them. What’s more, all the four
compounds have presented strong intensity in THF solution,
however, fluorescence quenching occurred in higher polarity
solvent (DMF).
Two-photon excited fluorescence (2PEF) and 2PA cross-sec-
tions. The two-photon fluorescence spectra of the compounds
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Fig. 6 Two-photon exited fluorescence (2PEF) of L1 and Z1 in different solutions.
Two-photon absorption cross-section processing based on units), which form an extended π-conjugated system and are
fluorescein as a reference sample were calculated in CH2Cl2, more conducive of electron distribution in the complex mole-
THF, DMF solution (1 GM = 10−50 cm−4 s photon−1) as shown cules. Compared to previous work of our group,17 two-photon
in Fig. 7 and S13.† Generally, the maxima 2PA cross section absorption cross sections have largely improved several times,
values were observed in the solvent with intermediate which is attributed to the introduction of triphenylamine and
polarity,44 so larger 2PA cross sections were exhibited in the cyano groups of the ligand have changed the process of
CH2Cl2 and THF compared to extremely small in DMF solu- electron distribution. Importantly, the metal ion has increased
tion. From Fig. 8(a), the maximum two-photon absorption intramolecular charge transfer, thus resulting in enhanced
cross sections are 810GM for L1, 2500GM for Z1, 780GM for two-photon absorption and two-photon absorption cross sec-
Z2, 1600GM for Z3 in CH2Cl2 solution, the much stronger and tions for Z1 and Z3 in the near-IR range (about 850 nm),
intense two-photon absorption and larger σ values of Z1 may which is useful for applications such as biological imaging
be due to the increase of the number of ligands (LCOO− due to the lower optical damaging.
Fig. 7 2PA cross-sections of L1 and Z1 in different solutions.
Fig. 8 2PA cross-sections (a) and 2PA cross-sections per molecular weight (b) of L1 and Z1–Z3 in CH2Cl2 solution.
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Table 4 Inhibitory concentration IC50 (µM) of Z1–Z3 against tumor cell
lines
Acknowledgements
This work was supported by a grant for the National Natural
Science Foundation of China (21271004, 51372003, 51432001,
21271003, 21275006), the Ministry of Education Funded Pro-
jects Focus on returned overseas scholar, the Program for New
Century Excellent Talents in University (China), and the Doc-
toral Program Foundation of Ministry of Education of China
(20113401110004).
IC50 (µM)
Compounds
A549
MDA-MB-231
Z1
Z2
Z3
2.731
0.101
0.235
0.0017
2.6
0.195
0.057
0.067
0.0027
50
Paclitaxela
Cisplatina
a Used as a positive control.
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