Inorganic Chemistry
Article
source (operated at 40 kV and 100 mA). Simulations of the powder
diffractograms were calculated with CrystalDiffract (2015 Crystal-
Maker Software Ltd.) using the single crystal cif files. Fluorescence
spectra were recorded on an Edinburgh FS5 instrument. The slit
width was fixed at 1 nm for both excitation and emission light.
Emission and excitation spectra were corrected for the spectral
response of the monochromator and the detector, using typical
correction spectra provided by the manufacturer.
Crystal Structure Determination. The diffraction intensity data
of azo-Zn2Eu2 (1) and azo-Zn2Er2 (3) at 173 K were collected on a
Bruker APEX-2 CCD with graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). Data collection, data reduction, and cell
refinement were performed by using the Bruker Instrument Service
v4.2.2 and SAINT V8.34A software.20,21 Structure was solved using
direct methods with the SHELXS program. Refinement was
performed using SHELXL based on F2 through the full-matrix least-
squares routine.22 Absorption corrections were applied using the
multiscan program SADABS.23 Hydrogen atoms of organic ligands
were generated geometrically by the riding mode, and all the non-
hydrogen atoms were refined anisotropically through full-matrix least-
squares technique on F2 with the SHELXTL program package.24,25 A
summary of the crystallographic data and refinement parameters is
given in Table 1.
temperature. The energy transfer cannot occur from the
chromophore to the visible-emitting lanthanide centers, such
as Eu3+ and Tb3+; that is an obvious shortcoming in the fields
of basic research and practical application. The emission
optimization needs maximizing energy transfer from the
sensitizing moiety to the lanthanoid by adjusting the energies
of the lanthanide-center excited state. As a continuous work,
here we report a photoswitchable 3d/4f metallorhomboid by
integrating an azobenzene-label ligand (azo-H2L, Scheme 1)
Scheme 1. Synthetic Procedure for the Preparation of Azo-
H2L
Calculation of Photoisomerization Quantum Yields and
Isomerization Rate Constants. The commercial UV light with
wavelength at 254 and 365 nm was used in the experiment. A 1 cm
path length quartz cell was used for the photoisomerization
measurements. The sample concentration was approximately 2.0 ×
10−5 M for all complexes.
We introduced the first-order kinetic eq 1 to study the
photoisomerization dynamics as follows26
A∞ − A0
A∞ − At
ln
= kisot
(1)
wherein A∞, A0, and At represent the saturated absorbance, the
absorbance before and after illumination, respectively. By plotting the
value on the left side of the above equation with respect to time (t), a
linear function was obtained. From the data, the isomerization
reaction conforms to the first-order reaction dynamics equation and
the slope was its rate constant kiso. The data rate constants (kiso) for all
complexes were the average of the three independent replicates
performed for each concentration.
The photoisomerization quantum yield was evaluated based on the
following eq 227
and the NIR-emitting lanthanoids (such as Yb3+, Er3+, etc.),
owing to their lower excited energy compared to the visible-
emitting lanthanoids. The modified ligand is grafted with an
azo moiety, and the character of simultaneously chelating 3d
and 4f metal ions is persistent to allow the formation of azo-
Zn2Ln2 metallorhomboid (Figure 1). This work represents a
promising case of an azo-label multimetallic molecular crystal
capable of generating a synergistic effect between efficient NIR
photoluminescence and photochromism.
1
1
Φ = k
0 I
0 1 − 10−εcl
(2)
where k0 is a zero-order rate constant for the initial isomer
concentration in mol L−1 s−1, I0 is the intensity of incident irradiation
light in einstein L−1 s−1, ε is the extinction coefficient in L mol−1 cm−1
at the irradiation wavelength of the solution, c is the concentration of
solution in mol L−1, and l is the path length of light through the
sample in cm. The k0 is given by eq 3
A0 − At = k0t
(3)
EXPERIMENTAL SECTION
■
Materials and General Procedures. All the reagents employed
were commercially available and used without further purification.
Methanol and dichloromethane were dried using standard procedures.
1-(Hydrazineylidenemethyl)-naphthalen-2-ol and 5-(2-phenyldiazen-
yl)-2-hydroxy-3-methoxybenzaldehyde were synthesized according to
a literature method,18,19 respectively.
Elemental analyses (C, H, and N) were conducted with a
PerkinElmer 2400 analyzer. The IR spectra of polycrystalline solids
were performed on a Nicolet Magna-IR 750 spectrophotometer in the
4000−400 cm−1 region (w, weak; b, broad; m, medium; s, strong) by
KBr discs. UV−visible studies were performed in a PerkinElmer
Lambda 950 UV−vis instrument. Powder X-ray diffraction (PXRD)
was recorded on a RINT2000 vertical goniometer with a Cu Kα X-ray
Synthesis of Ligand azo-H2L. The mixture of 1-(hydrazineyli-
denemethyl)-naphthalen-2-ol (0.43 g, 2.31 mmol) and 5-(2-phenyl-
diazenyl)-2-hydroxy-3-methoxybenzaldehyde (0.58 g, 2.26 mmol) in
60 mL of ethanol was heated at 80 °C in the presence of 0.5 mL of
glacial acetic acid for 6 h. The orange solid was filtered and
recrystallized from ethanol to obtain azo-H2L. Yield: ca. 85%.
Elemental analysis (%) calculated for C25H20N4O3: C, 70.74; H, 4.75;
N, 13.20; Found: C, 71.02; H, 4.73; N, 13.14; IR (KBr, cm−1):
3520(w), 1609(s), 1549(w), 1462(s), 1395(w), 1318(s), 1270(s),
1189(m), 1149(w), 1122(s), 1086(w), 974(m), 868(m), 808(s),
1
768(m), 743(s), 686(s), 429(m). H NMR (400 MHz, CDCl3) δ
12.94 (s, 1H), 12.24 (s, 1H), 9.68 (s, 1H), 8.92 (s, 1H), 8.18 (d, J =
8.6 Hz, 1H), 7.95 (dd, J = 8.3, 3.9 Hz, 3H), 7.85 (d, J = 8.0 Hz, 1H),
B
Inorg. Chem. XXXX, XXX, XXX−XXX