Triphenylamine, carbazole or tetraphenylethylene-based gold(I) complexes: Tunable solid-state room-temperature phosphorescence and various mechanochromic luminescence characteristics

Article abstract of DOI:10.1016/j.dyepig.2018.07.016

Three novel gold(I) complexes based on triphenylamine, carbazole or tetraphenylethylene moiety have been successfully designed and synthesized. Meanwhile, their structures were characterized by nuclear magnetic resonance spectroscopy and elemental analysis. Their solid-state luminescence characteristics were surveyed by photoluminescence spectroscopy, and their distinct mechanical stimulus-responsive behaviors in the solid state were also investigated by photoluminescence spectroscopy. Interestingly, the solid-state phosphorescence and emission lifetimes of these mononuclear gold(I) complexes 1–3 could be tuned by introducing different fluorophores involving triphenylamine, carbazole or tetraphenylethylene. Furthermore, luminogen 1 exhibited switchable mechanochromic luminescence behavior with color change from yellow to colorless, and the solid-state luminescence on-off mechanochromism between yellow-green and colorless of luminogen 2 could also be observed. However, no mechanochromism phenomenon was observed for tetraphenylethene-containing luminogen 3. The powder X-ray diffraction results suggested that the unusual high-contrast mechanochromism characteristics of luminogens 1 and 2 could be attributed to a crystalline-to- amorphous morphology transition.

Full text of DOI:10.1016/j.dyepig.2018.07.016

Accepted Manuscript
Triphenylamine, carbazole or tetraphenylethylene-based gold(I) complexes: Tunable
solid-state room-temperature phosphorescence and various mechanochromic
luminescence characteristics
Zhao Chen, Gang Liu, Shouzhi Pu, Sheng Hua Liu
PII:
S0143-7208(18)31213-0
10.1016/j.dyepig.2018.07.016
DYPI 6870
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 30 May 2018
Revised Date: 26 June 2018
Accepted Date: 7 July 2018
Please cite this article as: Chen Z, Liu G, Pu S, Liu SH, Triphenylamine, carbazole or
tetraphenylethylene-based gold(I) complexes: Tunable solid-state room-temperature phosphorescence
and various mechanochromic luminescence characteristics, Dyes and Pigments (2018), doi: 10.1016/
j.dyepig.2018.07.016.
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ACCEPTED MANUSCRIPT
Triphenylamine, carbazole or tetraphenylethylene-based gold(I)
complexes: tunable solid-state room-temperature phosphorescence
and various mechanochromic luminescence characteristics
Zhao Chena,b, Gang Liua, Shouzhi Pua,**, Sheng Hua Liub,*
Synopsis
Three carbazole-based gold(Ι) complexes were successfully synthesized. These
complexes showed color-tunable solid-state room-temperature phosphorescence
characteristics. Furthermore, these luminogens exhibited various mechanical
stimulus-responsive luminescence behaviors.

ACCEPTED MANUSCRIPT
Triphenylamine, carbazole or tetraphenylethylene-based gold(I)
complexes: tunable solid-state room-temperature phosphorescence
and various mechanochromic luminescence characteristics
Zhao Chena,b, Gang Liua, Shouzhi Pua,**, Sheng Hua Liub,*
a Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology
Normal University, Nanchang 330013, PR China.
b Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College
of Chemistry, Central China Normal University, Wuhan 430079, PR China.
Tel: +86-791-83831996 Fax: +86-791-83831996
** Corresponding author E-mail: pushouzhi@tsinghua.org.cn
* Corresponding author E-mail: chshliu@mail.ccnu.edu.cn
ABSTRACT
Three novel gold(I) complexes based on triphenylamine, carbazole or
tetraphenylethylene moiety have been successfully designed and synthesized.
Meanwhile, their structures were characterized by nuclear magnetic resonance
spectroscopy and elemental analysis. Their solid-state luminescence characteristics
were surveyed by photoluminescence spectroscopy, and their distinct mechanical
stimulus-responsive behaviors in the solid state were also investigated by
photoluminescence spectroscopy. Interestingly, the solid-state phosphorescence and
emission lifetimes of these mononuclear gold(I) complexes 1-3 could be tuned by
introducing different fluorophores involving triphenylamine, carbazole or
1

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tetraphenylethylene.
Furthermore,
luminogen
1
exhibited
switchable
mechanochromic luminescence behavior with color change from yellow to colorless,
and the solid-state luminescence on-off mechanochromism between yellow-green
and colorless of luminogen 2 could also be observed. However, no
mechanochromism phenomenon was observed for tetraphenylethene-containing
luminogen 3. The powder X-ray diffraction results suggested that the unusual
high-contrast mechanochromism characteristics of luminogens 1 and 2 could be
attributed to a crystalline-to- amorphous morphology transition.
Keywords: Gold(I) complexes; Triphenylamine; Carbazole; Tetraphenylethylene;
Phosphorescence; High-contrast mechanochromism
1. Introduction
The design and construction of solid-state luminescence materials has attracted
great attention for their potential applications in photoelectronic devices and display
devices[1-7]. In particular, mechanical stimulus-responsive mechanochromic
luminescent materials have been a major focus in recent years due to their promise
for applications in force-sensitive devices, security ink and sensors[8-12]. In the
solid state, the changes of the emission color and intensity of mechanochromic
luminogens can be affected by not only chemical structure but also by the molecular
packing[13,14]. In general, chemical structural changes suffer from the destruction
and formation of covalent bonds, which usually involve irreversible reactions. In
contrast, the physical changes of molecular packing are often considered to be more
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promising in achieving the reversible solid emission of mechanochromic compounds.
Actually, the research of the effect of the various molecular packing modes on the
photophysical characteristics of luminescence molecules has become a hot spot in
the field of opto-electronic materials, such as organic light-emitting diodes (OLEDs)
[15,16], organic field-effect transistors (OFETs) [17] and optical sensors[18]. On the
other hand, in order to the high-efficiency applications of mechanochromic emissive
materials, high contrast before and after mechanical grinding is extremely important
[19,20]. To date, a lot of mechanochromic luminescent molecules with mechanical
force-responsive feature have been proven to be organic compounds[21-26].
However, examples of mechanochromic luminescence metal complexes are still
insufficient, which is because of the absence of the effective design strategies for
metal-containing mechanochromic complexes.
Over the last two decades, gold(I) chemistry has been attracting extensive
interest owing to the presence of significative aurophilic Au-Au interactions between
gold centers[27-35]. Although a few mechanochromic gold(I) complexes have been
discovered[36-41], gold(I)-bearing mechanochromic complexes involving
luminescence on-off switch are extremely rare. Indeed, it is helpful for the
acquisition of high-contrast mechanochromism materials to prepare the
mechanochromic emissive compounds exhibiting luminescence quenching behavior
after grinding. Therefore, it is an attractive research topic to synthesize gold(I)
complexes with novelty structure and interesting solid-state luminescence on-off
mechanochromic phenomenon. In addition, motivated by the fact that
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triphenylamine, carbazole or tetraphenylethylene unit has been widespread used in
the area of emissive materials[42-44], we have been attempting to design and
construct the triphenylamine, carbazole or tetraphenylethylene-based gold(I)
complexes with intriguing solid-state luminescence and mechanochromism
characteristics. In the present work, we described three novel mononuclear gold(I)
isocyanide complexes based on triphenylamine, carbazole or tetraphenylethylene
moiety (Chart 1). Solid-state luminescence, emission lifetimes and
mechanochromism characteristics of these luminogens were systematically surveyed.
These gold(I) complexes showed color-tunable room-temperature phosphorescence
and various mechanical stimulus-responsive luminescence characteristics.
Chart 1. The molecular structures of gold(I) complexes 1-3.
2. Materials and methods
2.1. Experimental
General: All manipulations were carried out under an argon atmosphere by using
standard Schlenk techniques, unless otherwise stated. The starting materials 1-a, 1-1
and 2-1 purchased from J&K Chemical were used as received. CH2Cl2 was dried
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with CaH2 then distilled. All other starting materials and reagents were obtained as
analytical-grade from commercial suppliers and used without further purification.
Compounds 1-b [45], 3-1 [46] and C6F5Au(tht) (tht = thiophane) [47] were prepared
1
by procedures described in the corresponding literatures. H NMR (400 MHz) and
13C NMR (100 MHz) spectra were collected on American Varian Mercury Plus 400
1
spectrometer (400 MHz). H NMR spectra are reported as followed: chemical shift
in ppm (δ) relative to the chemical shift of TMS at 0.00 ppm, integration,
multiplicities (s = singlet, d = doublet, t = triplet, m = multiplet), and coupling
13
constant (Hz). C NMR chemical shifts reported in ppm (δ) relative to the central
line of triplet for CDCl3 at 77 ppm, and 13C NMR chemical shifts reported in ppm (δ)
relative to the central line of quintet for CD2Cl2 at 54 ppm. 19F NMR chemical shifts
are relative to C6F6 (δ = -163.00). EI-MS was obtained using Thermo scientific DSQ
II. Elemental analyses (C, H, N) were carried out with a PE CHN 2400 analyzer.
Ultraviolet/Visible spectra were obtained on U-3310 UV Spectrophotometer.
Fluorescence spectra were recorded on
a
Hitachi-F-4600 fluorescence
spectrophotometer. Luminescent decay experiment was measured by Edinburgh
FLS980 spectrometer. XRD studies were recorded on a Shimadzu XRD-6000
diffractometer using Ni-filtered and graphite-monochromated Cu Kα radiation (λ =
1.54 Å, 40 kV, 30 mA). Column chromatographic separations were carried out on
silica gel (200-300 mesh). TLC was performed by using commercially prepared
100-400 mesh silica gel plates (GF254) and visualization was effected at 254 nm.
2.2. Synthesis
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2.2.1. Synthesis of monoisocyano ligands 1-3, 2-3 and 3-3. A mixture of compounds
1-b (3.50 g, 12.55 mmol), 1-1 or 2-1 or 3-1 (27.00 mmol), K2CO3 (100.40 mmol),
Pd(PPh3)4 (0.13 mmol) were stirred in toluene (80 ml), ethanol (80 ml) and H2O (8
ml) for 16 h under an argon atmosphere at 80℃. After completion of present reaction,
the mixture was extracted with dichloromethane (3×30 mL), the combined organic
layers were washed with brine, dried (Na2SO4), and concentrated in vacuo, affording
the white solid 1-2, 2-2 or 3-2. The corresponding NMR data of these compounds
were not obtained due to the poor solubility. Subsequently, a CH2Cl2 solution (15 ml)
of the corresponding white solid and triethylamine (5 ml) were cooled to 0 ℃. To
the mixture was added dropwise a CH2Cl2 solution (10 ml) of triphosgene (4.10 g,
13.81 mmol). The mixture was refluxed under an argon atmosphere for 3 h, then
10% aq. Na2CO3 (30 mL) was added dropwise at room temperature. Next, the
mixture was extracted with dichloromethane (3×20 mL), the combined organic
layers were washed with brine, dried (Na2SO4), and concentrated in vacuo. In the
end, the residues were purified by column chromatography, affording the expected
white solid product 1-3, 2-3 or 3-3 in a yield of 75%, 74% or 73%, respectively. 1-3:
1H NMR (400 MHz, CDCl3): δ (ppm) = 7.75 (s, 1H), 7.48-7.45 (m, 6H), 7.31-7.27
(m, 8H), 7.14 (t, J = 4 Hz, 12H), 7.07 (t, J = 6 Hz, 4H). 13C NMR (100.6 MHz,
CDCl3): δ (ppm) = 164.0, 148.2, 147.4, 142.7, 132.6, 129.4, 127.8, 125.8, 124.8,
123.4, 122.5. EI-MS: m/z = 589.27[M]+. Anal. Calcd for C43H31N3：C, 87.58; H,
5.30; N, 7.13. Found: C, 87.65; H, 5.39; N, 7.07. 2-3: 1H NMR (400 MHz, CDCl3): δ
(ppm) = 8.18 (d, J = 8 Hz, 4H), 8.02 (s, 1H), 7.90 (d, J = 8 Hz, 4H), 7.74 (t, J = 4 Hz,
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6H), 7.51-7.43 (m, 8H), 7.35-7.31 (m, 4H). 13C NMR (100.6 MHz, CDCl3): δ (ppm)
= 165.2, 142.7, 140.7, 138.2, 137.9, 128.7, 127.9, 127.6, 126.9, 126.1, 124.0, 123.6,
120.4, 120.3, 109.7. EI-MS: m/z = 585.23[M]+. Anal. Calcd for C43H27N3：C, 88.18;
1
H, 4.65; N, 7.17. Found: C, 88.11; H, 4.73; N, 7.12. 3-3: H NMR (400 MHz,
CDCl3): δ (ppm) = 7.70 (s, 1H), 7.46 (s, 2H), 7.32 (d, J = 8 Hz, 4H), 7.12-7.02 (m,
13
34H). C NMR (100.6 MHz, CDCl3): δ (ppm) = 164.1, 144.0, 143.5, 143.5, 142.7,
141.6, 140.1, 136.7, 132.0, 131.3, 131.3, 127.8, 127.8, 127.7, 126.7, 126.6, 126.6,
126.4, 126.3, 123.2. EI-MS: m/z = 763.22[M]+. Anal. Calcd for C59H41N：C, 92.76;
H, 5.41; N, 1.83. Found: C, 92.66; H, 5.35; N, 1.90.
2.2.2. Synthesis of gold(I) complexes 1, 2 and 3. The mixture of C6F5Au(tht) (tht =
thiophane, 0.16 g, 0.35 mmol) and 1-3, 2-3 or 3-3 (0.34 mmol) was stirred in CH2Cl2
(30 ml) for overnight at room temperature. After completion of present reaction, the
solvent was evaporated. Subsequently, a small amount of CH2Cl2 was added, and
then a lot of n-hexane was added. Collecting the white solid product 1, 2 or 3 by
suction filtration in a yield of 84%, 84% or 79%, respectively. 1: 1H NMR (400 MHz,
CDCl3): δ (ppm) = 7.91 (s, 1H), 7.61 (s, 2H), 7.46 (d, J = 8 Hz, 4H), 7.30 (t, J = 8
Hz, 8H), 7.15 (t, J = 4 Hz, 12H), 7.09 (t, J = 8 Hz, 4H). 13C NMR (100.6 MHz,
CD2Cl2): δ (ppm) = 149.2, 147.8, 143.9, 132.0, 130.7, 129.1, 127.6, 127.5, 126.3,
124.9, 124.7, 124.3, 124.3, 123.9, 123.4, 122.7, 122.3. 19F NMR (CDCl3): δ (ppm) =
-116.53, -157.88, -162.85. Anal. Calcd for C49H31AuF5N3：C, 61.71; H, 3.28; N, 4.41.
Found: C, 61.77; H, 3.19; N, 4.52. 2: 1H NMR (400 MHz, CDCl3): δ (ppm) = 8.18 (d,
J = 8 Hz, 5H), 7.91 (t, J = 6 Hz, 6H), 7.78 (d, J = 8 Hz, 4H), 7.52-7.44 (m, 8H), 7.34
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13
(t, J = 8 Hz, 4H). C NMR (100.6 MHz, CD2Cl2): δ (ppm) = 143.8, 141.2, 139.0,
137.7, 130.1, 130.1, 129.0, 129.0, 128.5, 128.5, 127.4, 127.4, 125.9, 125.8, 124.1,
121.7, 120.1, 111.1, 111.0, 109.5, 109.4. 19F NMR (CDCl3): δ (ppm) = -116.54,
-157.66, -162.74. Anal. Calcd for C49H27AuF5N3：C, 61.97; H, 2.87; N, 4.42. Found:
C, 61.88; H, 2.95; N, 4.47. 3: 1H NMR (400 MHz, CDCl3): δ (ppm) = 7.86 (s, 1H),
7.60 (s, 2H), 7.33 (d, J = 8 Hz, 4H), 7.16-7.05 (m, 34H). 13C NMR (100.6 MHz,
CDCl3): δ (ppm) = 157.2, 144.7, 144.6, 144.6, 143.5, 141.9, 139.9, 138.3, 135.8,
133.1, 133.0, 132.1, 131.4, 130.5, 129.3, 128.6, 127.5, 127.5, 127.0, 125.9, 125.9,
125.5, 125.5, 125.1, 124.1, 122.4. 19F NMR (CDCl3): δ (ppm) = -116.51, -157.86,
-162.84. Anal. Calcd for C65H41AuF5N：C, 69.21; H, 3.66; N, 1.24. Found: C, 69.29;
H, 3.75; N, 1.13.
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OH
OH
N
N
N
B
Triphosgene
1-1
NEt3, CH2Cl2
NHCHO
1-2
(Yield = 65%)
OH
N
N
N
B
OH
Br
Br
Br
Br
Pd(PPh3)4, K2CO3
HCOOH
Triphosgene
2-1
3-1
reflux
NEt3, CH2Cl2
toluene/ethanol/water
NHCHO
2-2
NH2
1-a
1N-bHCHO
(Yield = 61%)
OH
OH
(Yield = 87%)
B
Triphosgene
NEt3, CH2Cl2
NHCHO
3-2
(Yield = 59%)
N
N
F
F
F
N
N
S
Au
F
F
N
C
CH2Cl2
Au
F
N
C
F
F
1-3
F
(Yield = 75%)
F
1
(Yield = 84%)
N
N
F
F
F
N
N
S
Au
F
N
C
F
Au
CH2Cl2
F
F
F
F
N
C
2-3
F
2
(Yield = 74%)
(Yield = 84%)
F
F
S
Au
F
N
C
F
F
CH2Cl2
Au
N
F
F
F
F
C
3-3
(Yield = 73%)
F
3
(Yield = 79%)
Scheme 1. Synthesis routes of the gold(I) complexes 1-3.
3. Results and discussion
3.1. Synthesis
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As can be seen in Scheme 1, the triphenylamine, carbazole and
tetraphenylethylene-based gold(I) complexes were prepared in 84%, 84% or 79%
yield respectively according to the typical coordination reaction of intermediate
product 1-3, 2-3 or 3-3 and C6F5Au(tht) (tht = thiophane).
3.2. The solid-state luminescence characteristics of complexes 1-3
Solid-state luminescence behaviors of the gold(I) complexes 1-3 were initially
investigated in detail by solid-state photoluminescence (PL) spectroscopy. As shown
in Fig. 1, the emission spectrum of triphenylamine-based gold(I) complex 1 showed
two emission bands with λmax at 453 nm and 560 nm, corresponding to a yellow
emission under 365 nm UV light. However, the carbazole-based gold(I) complex 2
exhibited yellow-green emission with a λmax at 526 nm. In addition, unlike complex 1
and complex 2, the solid sample of tetraphenylethylene-based gold(I) complex 3
exhibited one emission band with a λmax at 512 nm, and the corresponding solid
sample emitted bright blue-green light upon UV illumination at 365 nm.
Subsequently, the related solid-state emission lifetimes of luminogens 1-3 were
tested. As can be seen in Fig. 2, the room-temperature solid-state luminescence
lifetimes of 1 and 2 were as high as 13.72 µs and 30.79 µs separately, suggesting that
the yellow emission and the yellow-green emission belonged to room-temperature
phosphorescence [48-50]. Furthermore, the solid sample of 1 or 2 at 77 K showed a
longer phosphorescence lifetime up to 4006.43 µs or 2766.45 µs separately (Fig. 3).
Similarly, luminogen 3 also showed the room-temperature phosphorescence feature
with the solid-state emission lifetime of 4.20 µs (Supporting Information: Fig. S1). It
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was possible that the corresponding luminescence was attributed to the two factors of
tetraphenylethylene fluorophore and intermolecular significant aurophilic
interactions, and thus it showed bi-exponential decay profile. The emission lifetime
of solid sample 3 at 77 K was 4.85 µs (Supporting Information: Fig. S2). Based on
the above research results, the solid-state phosphorescence and emission lifetimes of
1-3 could be adjusted by introducing various fluorophores involving triphenylamine,
carbazole or tetraphenylethylene.
Fig. 1. (a) Solid-state PL spectra of complexes 1-3. (b) The luminescence image
of triphenylamine-based gold(I) complex 1 under 365 nm UV light. (c) The
luminescence image of carbazole-based gold(I) complex 2 under 365 nm UV light. (d)
The luminescence image of tetraphenylethylene-based gold(I) complex 3 under
irradiation with UV light at 365 nm.
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Fig. 2. (a) Decay curve of complex 1 at the peak emission wavelength of 560 nm.
Excitation wavelength: 365 nm. (b) Decay curve of complex 2 at the peak emission
wavelength of 526 nm. Excitation wavelength: 365 nm.
Fig. 3. (a) Decay curve of complex 1 (temperature: 77 K) at the peak emission
wavelength of 560 nm. Excitation wavelength: 365 nm. (b) Decay curve of complex 2
(temperature: 77 K) at the peak emission wavelength of 526 nm. Excitation
wavelength: 365 nm.
3.3. The different mechanical stimulus-responsive behaviors of complexes 1-3
To determine whether the gold(I) complexes 1-3 had mechanochromic
luminescence properties, the solid-state emission behaviors of 1-3 in different
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conditions were studied. As presented in Fig. 4, complex 1 belonged to a yellow
emissive sample. Interestingly, it was found that the yellow-emitting solid powder
exhibited a turning off of luminescence after grinding, which is different from the
most of mechanochromic emissive compounds. Futhermore, when the ground
sample was treated with fuming dichloromethane vapor for 1 min, the original
yellow emission band was restored, and the corresponding yellow luminescence
re-appeared. It is no doubt that the unusual luminescence on-off mechanochromic
complex 1 may be an ideal candidate for the high-contrast mechanochromism
materials. Furthermore, the switchable mechanochromic conversion of 1 could be
repeated many times without fatigue by the grinding-exposure process (Fig. 5).
Complex 2 had a similar mechanochromic phenomenon to 1, and the
mechanochromic behavior of 2 was verified by measuring changes in its PL
spectrum. as shown in Fig. 6, upon grinding the powder sample of 2 using a spatula
or a pestle, the intensity of the yellow-green emission was significantly weakened,
and luminogen 2 emitted hardly any luminescence under a 365 nm UV lamp.
Moreover, the yellow-green luminescence could also be recovered by treatment with
dichloromethane. Thus, complex 2 also exhibited switchable luminescence on-off
mechanochromic behavior. The reversibility of the mechanochromic property of 2
was very similar to that of 1. As evident from Fig. S3, this reversible
mechanochromic luminescence transformation could also be repeated many times by
alternating grinding and dichloromethane treatments.
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Fig. 4. (a) PL spectra of luminogen 1 before grinding, after grinding, and after
treatment with dichloromethane solvent vapor. Excitation wavelength: 365 nm.
Photographic images of luminogen 1 at different conditions under 365 nm UV
illumination: (b) the as-synthesized powder sample. (c) the ground powder sample. (d)
the powder sample after treatment with dichloromethane.
fuming
grinding
0
2
4
6
8
Number of cycles
Fig. 5. Switchable grinding-fuming processes of the photoluminescence of
complex 1 at 560 nm.
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Fig. 6. (a) PL spectra of luminogen 2 before grinding, after grinding, and after
treatment with dichloromethane solvent vapor. Excitation wavelength: 365 nm.
Photographic images of luminogen 2 at different conditions under 365 nm UV
illumination: (b) the as-synthesized powder sample. (c) the ground powder sample. (d)
the powder sample after treatment with dichloromethane.
On the other hand, the luminescence images of the solid sample of complex 3 in
various conditions under 365 nm UV-light are shown in Fig. 7. Obviously, the
emission spectrum, luminescent color and luminous intensity of luminogen 3
displayed no variation when the freshly prepared powder sample was ground with a
mortar and pestle. Therefore, tetraphenylethylene-based gold(I) complex 3 did not
exhibit any mechanochromic emissive phenomenon. In order to gain insight into the
possible mechanism for the mechanochromic effect of luminogens 1 and 2, X-ray
diffraction (XRD) measurements for 1 and 2 in various situations were performed.
According to Fig. 8, the XRD pattern for the as-synthesized sample 1 revealed many
sharp and intense diffraction peaks, suggesting the crystalline state of the freshly
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prepared sample. In contrast, most reflection peaks remarkably weakened or
disappeared for the ground sample, which indicated the ground sample was an
amorphous structure. Following treatment of the ground powder using a
dichloromethane solvent, the XRD curve reflection peaks coinciding with those of
the pristine sample were obtained again, indicating the recovery of the crystalline
nature. Similar phenomena were also observed for solid sample 2 in the XRD
measurements (Supporting Information: Fig. S4). However, no obvious changes
were observed for solid sample 3 in the corresponding XRD measurements
(Supporting Information: Fig. S5). As a consequence, the XRD test results confirmed
that the luminescence on-off mechanochromic characteristics of 1 and 2 was due to
the reversible morphological transition between the ordered crystalline and
amorphous phases.
Fig. 7. (a) PL spectra of luminogen 3 before grinding and after grinding.
Excitation wavelength: 365 nm. Photographic images of luminogen 3 at different
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conditions under 365 nm UV light: (b) the as-synthesized powder sample. (c) the
ground powder sample.
Fig. 8. XRD patterns of triphenylamine-based gold(I) complex 1: unground,
ground and after treatment with dichloromethane.
4. Conclusions
In
summary,
three
novel
triphenylamine,
carbazole
or
tetraphenylethylene-based mononuclear gold(I) complexes were designed to
investigate their solid-state luminescence and mechanical stimulus-responsive
characteristics. Intriguingly, these gold(I) complexes 1-3 exhibited various solid-state
room-temperature phosphorescence with different emission colors and lifetimes.
Moreover, we found that the (donor) D-π-A (acceptor) luminogen 1 or 2 using the
triphenylamine or carbazole group as an electron donor and a pentafluorphenyl unit
as an electron acceptor showed switchable mechanochromic luminescence on-off
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behavior, which was beneficial to the realization of high-contrast mechanochromism
phenomenon. However, no mechanochromic luminescence behavior was observed
for the tetraphenylethylene-based gold(I) complex 3. Besides, as confirmed by the
powder XRD experiments, grinding and fuming of solid samples 1 and 2 resulted in
the reversible transformation between crystalline and amorphous states, and thus the
corresponding morphological transition before and after grinding was responsible for
the luminescence on-off mechanochromic effect of 1 or 2 with a D-π-A structure.
These results may not be only useful for the design of new gold(I) complexes with
mechanochromic phosphorescence feature, but also for developing high-contrast
stimuli-sensitive materials.
Acknowledgments
The authors are grateful for the financial support from the National Natural
Science Foundation of China (21702079 and 21472059), the “5511” Science and
Technology Innovation Talent Project of Jiangxi Province (20165BCB18015), the
key project of Natural Science Foundation of Jiangxi Province (20171ACB20025),
the youth project of Natural Science Foundation of Jiangxi Province
(20171BAB213004), the Young Talents Project of Jiangxi Science and Technology
Normal University (2017QNBJRC005).
Supporting Information Available
Decay curve of complex 3 (room temperature or 77 K) at the peak emission
wavelength of 512 nm (Excitation wavelength: 365 nm), switchable grinding-fuming
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processes of the photoluminescence of complex 2 at 526 nm, XRD patterns of
carbazole-based gold(I) complex 2 in different conditions, and Copies of NMR
spectra and Mass spectra.
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Mater Chem C 2014;2:2243-50.
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Highlights
© Three novel mononuclear gold(I) complexes were successfully synthesized.
© All these gold(Ι) complexes showed room-temperature phosphorescence feature.
© These gold(Ι) complexes showed tunable solid-state luminescence characteristics.
© These gold(Ι) complexes exhibited various mechanochromic luminescence
behaviors.
© 1 and 2 exhibited solid-state luminescence on-off mechanochromic phenomena.