Experimental Section
Materials and physical measurements: Commercially available chemicals
were used without further purification. Infrared spectra were obtained in
KBr disks using a Nicolet Avatar 360 FTIR spectrometer in the range of
4000–400 cmꢀ1 1H NMR spectroscopy was performed using a Bruker
.
DPX 400 spectrometer with tetramethylsilane as internal standard. All d
values are given in ppm. Elemental analyses of C, H, and N were deter-
mined using an Elementar Vario EL cube CHNS analyzer. Thermogravi-
metric (TG) analyses were performed using a TA Instruments Q50 ther-
mogravimetric analyzer under nitrogen flow (40 mLminꢀ1) at a typical
heating rate of 108Cminꢀ1. X-ray power diffraction (XRPD) experiments
were performed using a D8 Advance X-ray diffractometer.
Scheme 1. Dimer of trimers of the [Cu3Pz3]2 cluster with energetically fa-
vored staggered stacking mode,[14b,15e] in which the ligand-unsupported in-
tertrimeric Cu–Cu contacts are highlighted by dashed lines.
Steady-state photoluminescence spectra and lifetime measurements were
measured by a single-photon counting spectrometer using an Edinburgh
FLS920 spectrometer equipped with a continuous Xe900 xenon lamp, a
mF900 microsecond flash lamp, a red-sensitive Peltier-cooled Hamamatsu
R928P photomultiplier tube (PMT), and a closed cycle cryostat (Ad-
vanced Research Systems). The corrections of excitation and emission
for the detector response were performed ranging from 200 to 900 nm.
The data were analyzed by iterative convolution of the luminescence
decay profile with the instrument response function using the software
package provided by Edinburgh Instruments. Lifetime data were fitted
with triple-exponential-decay functions. The goodness of the nonlinear
least-squares fit was judged by the reduced c2 value (<1.3 in most of the
cases), the randomness of the residuals, and the autocorrelation function
(Table S4 and Figures S14–S16 in the Supporting Information). In all
cases, the crystalline samples were selected under microscope with 40ꢃ
amplification after being washed by ethanol and acetonitrile and then
dried. The purity of the samples was assured by elemental analysis and
X-ray powder diffraction measurement (Figure S19 in the Supporting In-
formation).
with halide-to-ligand charge-transfer excited state,
3XLCT),[13a,b] the bright phosphorescence of the [Cu3Pz3]2
cluster (Scheme 1) is attributed to the excimer formation of
the dimer of trimers.[14] This excimer regulated by means of
intertrimeric Cu–Cu contacts (which vary from approxi-
mately 2.9 to 4.6 ꢂ[15a,e]) are subject to the influences of sub-
stituent effects[15c] and supramolecular microenvironments
(e.g., stacking effects in the crystalline state) in both dis-
crete[15] and polymeric[10,16] forms, thus triggering several in-
teresting photophysical types of behavior, especially lumi-
nescence thermochromism.[10,15b]
A merit of this supramolecular system that incorporates
both Cu4I4 and [Cu3Pz3]2 is their well-resolved emissions that
can be excited under different wavelengths (Cu4I4: lex =350–
400, lem =540–580 nm; [Cu3Pz3]2: lex =270–320, lem =630–
720 nm).[10] This provides the possibility that 1·NH3 can be
populated to its two stable excited states under different ir-
radiations, and then give two distinguishable emission
maxima (i.e., dual emissions) through electron/energy trans-
fer in the thermal equilibrium process. In an attempt to ac-
quire more sophisticated manipulation of the luminescent
and thermochromic behaviors, one can consider tuning the
relative functioning efficacy of the two coordination lumino-
phores, which can contribute cooperatively to the visual
color of the phosphorescent MOF material. This strategy is
termed the “chemopalette” effect, and it can be achieved by
means of adjusting the supramolecular microenvironment
while maintaining the overall host framework (by taking ad-
vantage of the predictable structures of MOFs[7b]).
In this regard, relative to the configurationally more rigid
Cu4I4 cluster, the ligand-unsupported excimeric [Cu3Pz3]2
cluster (Scheme 1) is more sensitive (reflected by its various
packing modes and varying Cu–Cu distances[15e]) to the var-
iation in the supramolecular microenvironment that involves
host–host and host–guest interactions, and crystal-stacking
effects.[15,16] Interestingly, 1·NH3 exhibits a double-layer
stacking pattern,[10] in which every two adjacent layers are
connected by multiple interlayer Cu–Cu interactions in the
[Cu3Pz3]2 cluster. Herein, the “chemopalette” strategy is re-
alized by modifying two chemically inactive sites (see
below) in the host framework to adjust the supramolecular
microenvironment, and to fine-tune the interlayer Cu–Cu
distances in the [Cu3Pz3]2 luminophore, thus manipulating
the thermochromic behavior of the dual emissive MOF ma-
terials.
Synthesis: Two ligands, 3-(4-pyridyl)-5-p-tolyl-1H-pyrazole (HL1) and 3-
(4-pyridyl)-5-(2,4-dimethylphenyl)-1H-pyrazole (HL2), were used in this
work. HL1 was reported in our previous work,[10] and HL2 was prepared
by using a similar procedure as described previously by our group with
modifications.[16f,17]
1-(4-Pyridyl)-3-(2,4-dimethylphenyl)-1,3-propanedione: Methyl isonicoti-
nate (3.5 mL, 3.5 g, 0.025 mol) was added to a suspension of newly pre-
pared C2H5ONa (3.4 g, 0.05 mol) in anhydrous THF (100 mL). The mix-
ture was stirred at room temperature for 10 min and then 2,4-dimethyla-
cetophenone (3.7 mL, 3.7 g, 0.025 mol) was slowly added to the mixture.
After completing the addition, the mixture was kept with stirring for
about 10 h while equipped with a drying tube. Then the solvent was
evaporated completely under reduced pressure. The residual was dis-
solved in diluted acetic acid solution (100 mL, 3 molLꢀ1), left in a refrig-
erator at 0–48C for about 5 h, then filtered. Yellow solids were obtained
and dried under vacuum to give the product (3.50 g, 55.3%). M.p. 122–
1258C; 1H NMR (400 MHz, CDCl3, 298 K): d=8.78 (dd, J=4.5, 1.7 Hz,
2H; CHpy), 7.74 (dd, J=4.5, 1.7 Hz, 2H; CHpy), 7.55 (d, J=11.6 Hz,
1H; CHph), 7.17–7.01 (m, 2H; CHph), 6.60 (s, 1H; CHC=CH), 2.55 (s,
3H; CH3), 2.38 ppm (s, 3H; CH3) (see Figure S1 in the Supporting Infor-
mation).
Ligand
HL2:
1-(4-Pyridyl)-3-(2,4-dimethylphenyl)-1,3-propanedione
(2.53 g, 0.01 mol) was added to ethanol (50 mL). Then the mixture was
treated with an excess amount of hydrazine (80%, 3 mL) and heated to
reflux for 10 h. The solution was kept standing in air to allow the ethanol
solvent to evaporate. After several days, nearly colorless crystalline solids
were obtained and dried under vacuum (1.62 g, 65.0%). M.p. 206–2088C;
1H NMR (400 MHz, CD3OD): d=8.54 (d, J=5.3 Hz, 2H; CHpy), 7.88 (t,
J=5.4 Hz, 2H; CHpy), 7.32 (d, J=7.7 Hz, 1H; CHph), 7.16 (s, 1H;
CHph), 7.10 (d, J=7.7 Hz, 1H; CHph), 6.91 (s, 1H; CHpz), 2.39 (s, 3H;
CH3), 2.35 ppm (s, 3H; CH3) (see Figure S2 in the Supporting Informa-
tion; see also Figures S3–S5 in the Supporting Information for the crystal
structure descriptions of HL2); IR (KBr): n˜ =3405 (w), 3193 (m), 3139
(m), 3123 (m), 2982 (m), 2911 (m), 1605 (vs), 1557 (m), 1494 (s), 1428
(vs), 1216 (s), 1130 (m), 1083 (m), 966 (vs), 836 (s), 817 (vs), 788 (s), 697
(vs), 570 (s), 532 cmꢀ1 (s).
10218
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 10217 – 10225
Zhan, Shun-Ze
