Vapor-, thermo-, and mechanical-grinding-triggered tri-stimuli-responsive luminescence switching of cycloplatinated(II) complex bearing 8-quinolinol derivatives

Article abstract of DOI:10.1016/j.dyepig.2020.108451

Four novel cycloplatinated(II) complexes, Pt(ppy)(L1) (1), Pt(ppy)(L2) (2), Pt(ppy)(L3) (3) and Pt(ppy)(L4) (4) based on 5-[2-(4-substituent-phenyl)ethynyl]-8-quinolinol ligands {substituent = H (L1), Me(L2), Et(L3), ^t-Bu(L4)} were synthesized

Full text of DOI:10.1016/j.dyepig.2020.108451

Dyes and Pigments 180 (2020) 108451
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Vapor-, thermo-, and mechanical-grinding-triggered tri-stimuli-responsive
luminescence switching of cycloplatinated(II) complex bearing
8-quinolinol derivatives
Jun Ni*, Gao Liu, Mengmeng Su, Wei Zheng, Jianjun Zhang
College of Chemistry, Dalian University of Technology, Linggong Road No. 2, Dalian, 116024, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Four novel cycloplatinated(II) complexes, Pt(ppy)(L1) (1), Pt(ppy)(L2) (2), Pt(ppy)(L3) (3) and Pt(ppy)(L4) (4)
based on 5-[2-(4-substituent-phenyl)ethynyl]-8-quinolinol ligands {substituent ¼ H (L1), Me(L2), Et(L3), t-Bu
(L4)} were synthesized and characterized. Complex 4 has three main pseudopolymorphs, including orange
4⋅CH3CH2OH, red 4R, and dark-brown 4⋅½(CCl4). Complex 4 exhibits interesting tri-stimuli-responsive lumi-
nescence switching properties. Upon exposure to different VOC vapors, three pseudopolymorphs display unusual
irreversible vapoluminescence that 4R and 4⋅½ (CCl4) can be exchanged with each other and be irreversibly
converted to 4⋅CH3CH2OH. Furthermore, 4⋅½(CCl4) shows reversible thermochromic luminescence behaviour
and can be reversibly converted to 4R upon heating. No detectable change in color and luminescence of
4⋅CH3CH2OH and 4R can be found during the heating process, although 4⋅CH3CH2OH lost its solvent and
changed to desolvated 4O. In addition, 4⋅CH3CH2OH, and 4⋅½ (CCl4) also show the mechanoluminescent
property that both of them will be converted to the same red amorphous 4G peaked at 742 nm after grinding.
Systematic studies revealed that the tri-stimuli-responsive luminescence switching property of 4 is due to the
structural conversion and resultant changes of the lowest-energy excited states. In contrast, complexes 1–3 have
not any luminescent switching property. The reason is most likely due to the compact stacking structures of them
which prevent their structural conversion triggered by external stimuli.
Cycloplatinated(II) complex
Near-infrared
Vapoluminescence
Thermochromic luminescence
Mechanoluminescence
Tri-stimuli-responsive
1. Introduction
and data security storage [29–37].
Cycloplatinated(II) complexes are a very important part of square-
Square-planar Pt(II) complexes have attracted great attention due to
their various applications, such as organic light-emitting diodes(OLEDs)
[1–5], light-harvesting devices [6–8], display devices [9–12], and
bio-imaging probes [13–16]. The unique square-planar geometry and a
vacant coordination site of Pt(II) center allow the axial substrate-binding
interactions of Pt(II) complexes, which make them conducive to the
formation of different aggregates through intermolecular Pt-Pt in-
teractions, resulting in decrease of the energy gaps between HOMO and
LUMO and increase of emission wavelength [17–20]. In addition, their
rich excited state energy levels are very sensitive to the conversion of
stacking structures and resultant changes of intermolecular interactions
planar Pt(II) complex. They exhibit high-efficiency phosphorescence
caused by strong ligand-field effects and spin-orbit coupling and show a
wide application prospects in the fields of high efficiency light-emitting
or electroluminescence devices [38–43], photo-catalysis [44–46] and
photooxidation systems [47–49]. As one of the most famous ligands,
2-phenylpyridine (ppy) derivatives have been successfully used to pre-
pare different kinds of cycloplatinated(II) complexes by combining with
other bidentate auxiliary ligands such as β-diketonate, 8-quinolinol, and
2-carboxypyridine [50–58]. However, compared with diimine platinum
(II) complexes, the research on cycloplatinated(II) complex is still not
deep enough neither in the number of complex nor in the theory and
application. For example, no more than 30 platinum(II) complexes
based on both 2-phenylpyridine and 8-quinolinol derivatives have been
reported up until now [55–65]. Furthermore, although cycloplatinated
(II) complexes also have the square-planar structure, the luminescence
such as Pt-Pt contact, hydrogen bonding, or aromatic π-π stacking caused
by external stimulus [21–28]. These characteristics make square-planar
Pt(II) complexes have versatile luminescence switching behaviour and
exhibit important application value in phosphorescence sensors devices
* Corresponding author.
E-mail address: nijun@dlut.edu.cn (J. Ni).
https://doi.org/10.1016/j.dyepig.2020.108451
Received 13 March 2020; Received in revised form 14 April 2020; Accepted 14 April 2020
Available online 20 April 2020
0143-7208/© 2020 Elsevier Ltd. All rights reserved.

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
2.2. Synthetic procedures
2.2.1. General method for the preparation of L1-L4
A solution of 5-Bromo-8-tert-butoxycarbonyloxyquinoline (1.0 g,
3.09 mmol), the phenylacetylene derivatives (3.09 mmol), and diiso-
propylamine (30 mL) in THF (30 mL) was purged with argon for 15 min
at room temperature. Then a solid mixture of Pd(PPh3)2Cl2 (140 mg, 0.2
mmol) and CuI (38 mg, 0.2 mmol) was added under argon atmosphere
and the mixture was stirred at 60 �C overnight. The reaction mixture was
filtered and washed with THF (30 mL). The filtrate was concentrated
under vacuum and the pure Boc derivatives were obtained by silica gel
chromatography using petroleum ether and ethyl acetate (V/V ¼ 10:1)
as the eluent.
To a 30 mL dry CH2Cl2 solution of above obtained Boc derivatives,
piperidine (about 3 equiv) was added and the reaction mixture was
stirred for 2 h at room temperature. Then, the solvent was removed
under vacuum and the pure products were obtained by silica gel chro-
matography using CH2Cl2 as the eluent.
Scheme 1. Synthetic routes of ligands L1-L4 and complexes 1–4.
2.2.1.1. 5-(2-phenylethynyl)-8-quinolinol (L1). Phenylacetylene was
used as the starting acetylene derivative. Yield: 409 mg (54%) of a
yellowish powder. M.p. 139–142 �C. ESI-MS m/z calculated for [Mþ]
245.2, found 245.1. 1H NMR (400 MHz, CDCl3, ppm): δ 8.840 (d, J ¼ 4.0
Hz, 1H), 8.716 (d, J ¼ 8.0 Hz, 1H), 7.750 (d, J ¼ 8.0 Hz, 1H),
7.571–7.622 (m, 3H), 7.365–7.408 (m, 3H), 7.196 (d, J ¼ 8.0 Hz, 1H).
13C NMR (100 MHz, CDCl3, ppm): δ 155.76, 152.72, 148.34, 138.12,
135.20, 132.97, 131.99, 128.92, 122.68, 115.86, 114.37, 111.94,
109.98, 92.65, 85.33. Elem. Anal.: C17H11NO (%) Calcd for: C, 83.25; H,
4.52; N, 5.71. Found (%): C, 83.24; H, 4.54; N, 5.73.
switching property of them was seldom studied. Thus, the preparation of
new cycloplatinated(II) complexes and in-depth studied of their prop-
erties are very important and necessary for better understanding and
practical application of such materials.
Our research interests focus on the luminescence switching property
and application of Pt(II) complexes [20,23,36,66–68]. Recently, we re-
ported a series of cycloplatinated(II) complexes with ppy and β-diketo-
nate derivatives [68]. These complexes exhibited mechanoluminescence
and concentration-dependent luminescence switching properties caused
by the molecular aggregation. As a continuation of our research work,
we report here the syntheses, structures and luminescence switching
properties of four new cycloplatinated(II) complexes, Pt(ppy)(L) (1–4)
{where L ¼ 5-[2-(4-substituent-phenyl)ethynyl]-8-quinolinol; substitu-
ent ¼ H(L1), Me(L2), Et(L3), and t-Bu(L4)}, bearing 2-phenylpyridine
ligand and 8-quinolinol derivatives (Scheme 1). Among them, complex
4 has three main pseudopolymorphs, including orange 4⋅CH3CH2OH,
red 4R, and dark-brown 4⋅½(CCl4), which exhibit vapor-, thermo-, and
mechanical-grinding-triggered tri-stimulus-responsive color and lumi-
nescence switching properties. In contrast, 1–3 have not any lumines-
cence switching property. Systematic studies on the crystal structure,
luminescence spectra, TGA, and PXRD revealed that the
tri-stimulus-responsive luminescence switching properties of 4 is due to
the structural conversion and resultant changes of the lowest-energy
excited states. In contrast, 1–3 have not any luminescence switching
property which is most likely due to their compact stacking structure
that prevents the structural conversion triggered by external stimuli.
Interestingly, the dark-brown 4⋅½(CCl4) exhibits a near-infrared (NIR)
luminescence peaked at 808 nm. As far as we know, it is first Pt(II)
complex based on 8-quinolinol derivatives that emits more than 800 nm
in solid state.
2.2.1.2. 5-[2-(4-methylphenyl)ethynyl]-8-quinolinol
(L2). 4-Methyl-
phenylacetylene was used as the starting acetylene derivative. Yield:
464 mg (58%) of a yellowish powder. M.p. 147–150 �C. ESI-MS m/z
calculated for [Mþ] 259.3, found 259.5. 1H NMR (400 MHz, DMSO‑d6,
ppm): δ 8.939 (d, J ¼ 4.0 Hz, 1H), 8.658 (d, J ¼ 7.2 Hz, 1H),
7.701–7.740 (m, 2H), 7.547 (d, J ¼ 7.2 Hz, 2H), 7.263 (d, J ¼ 7.2 Hz,
2H), 7.109 (d, J ¼ 7.2 Hz, 1H), 2.359 (s, 3H). 13C NMR (100 MHz, CDCl3,
ppm): δ 159.69, 152.60, 148.24, 138.04, 135.17, 132.99, 131.98,
128.84, 122.40, 115.46, 114.12, 111.77, 109.93, 92.76, 85.00, 29.71.
Elem. Anal.: C18H13NO (%) Calcd for: C, 83.37; H, 5.05; N, 5.40. Found
(%): C, 83.34; H, 5.06; N, 5.38.
2.2.1.3. 5-[2-(4-ethylphenyl)ethynyl]-8-quinolinol (L3). 4-Ethyl-phenyl-
acetylene was used as the starting acetylene derivative. Yield: 472 mg
(56%) of a yellowish powder. M.p. 178–181 �C. ESI-MS m/z calculated
for [M]þ 273.3, found 273.2. 1H NMR (400 MHz, DMSO‑d6, ppm): δ
8.942 (d, J ¼ 3.2 Hz, 1H), 8.666 (d, J ¼ 3.2 Hz, 1H), 7.732 (d, J ¼ 6.4 Hz,
1H), 7.708 (t, J ¼ 3.2 Hz, 1H), 7.573 (d, J ¼ 6.4 Hz, 2H), 7.292 (d, J ¼
6.4 Hz, 2H), 7.112 (d, J ¼ 6.4 Hz, 1H), 2.634 (q, J ¼ 6.0 Hz, 2H), 1.192
(t, J ¼ 6.0 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm): δ 154.98, 152.77,
148.27, 138.04, 135.12, 132.13, 131.51, 128.03, 122.91, 122.42,
120.51, 111.63, 109.95, 93.01, 85.69, 31.94, 15.39. Elem. Anal.:
2. Experimental section
C
19H15NO (%) Calcd for: C, 83.49; H, 5.53; N, 5.12. Found (%): C, 83.47;
2.1. Regent and materials
H, 5.56; N, 5.55.
All reactions were protected by a dry argon. Intermediate di-
2.2.1.4. 5-[2-(4-tert-butylphenyl)ethynyl]-8-quinolinol (L4). 4-tert-butyl-
phenylacetylene was used as the starting acetylene derivative. Yield:
472 mg (56%) of a yellowish powder. M.p. 176–178 �C. ESI-MS m/z
calculated for [Mþ] 301.4, found 301.3. 1H NMR (400 MHz, DMSO‑d6,
ppm): δ 8.939 (d, J ¼ 4.0 Hz, 1H), 8.655 (d, J ¼ 8.0 Hz, 1H),
7.708–7.749 (m, 2H), 7.584 (d, J ¼ 6.8 Hz, 2H), 7.467 (d, J ¼ 6.8 Hz,
2H), 7.107 (d, J ¼ 6.8 Hz, 1H), 1.234 (s, 9H). 13C NMR (100 MHz, CDCl3,
ppm): δ 152.72, 151.66, 148.23, 138.01, 135.18, 132.17, 131.27,
128.90, 125.47, 122.44, 120.30, 111.65, 109.94, 92.95, 85.68, 34.84,
31.90. Elem. Anal.: C21H19NO (%) Calcd for: C, 83.69; H, 6.35; N, 4.65.
μ
-chlorobis[2-(2-pyridinyl-κN)-phenyl-κC]di-platinum
[Pt2(ppy)2(μ-
Cl)2] was prepared by the literature method [69]. The ligands,
5-(2-Phenylethynyl)-8-quinolinol (L1), 5-[2-(4-Methylphenyl)ethy-
nyl]-8-quinolinol (L2), 5-[2-(4-Ethylphenyl)ethynyl]-8-quinolinol (L3),
and 5-[2-(4-Ethylphenyl)ethynyl]-8-quinolinol (L4) were prepared by
similar method according to the reported procedure [70]. All other re-
agents were purchased from commercial sources and used as received.
2

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
Found (%): C, 83.70; H, 6.51; N, 4.65.
2.2.2.4. [5-(2-(4-tert-butylphenyl)ethynyl)-8-quinolinolato-κN1,κO8][2-
(2-pyridinyl-κN)phenyl-κC] platinum(II) (4). Yield: 585 mg (90%) of a
red powder. M.p.: >250 �C. IR (neat, cmÀ 1): 3064 (w), 2961(s), 2924(s),
2855(s), 2200(m), 1605(s), 1578(s), 1559(s), 1501(s), 1481(m), 1463
(s), 1404(s), 1334(s), 1295(m), 1265(m), 1234(m), 1165(w), 1116(w),
1100(s), 989(m), 827(s), 775(s), 748(s), 706(s). HRMS (m/z): calcd for
2.2.2. General method for the preparation of complex 1-4
Pt2(ppy)2(μ-Cl)2 (385 mg, 0.50 mmol), 8-quinolinol ligands (1
mmol), and Na2CO3 (530 mg, 5 mmol) were added to CH3CN (30 mL)
and the reaction mixture was stirred for 18 h at room temperature. Then,
the solvent was removed under vacuum and the pure products were
obtained by silica gel chromatography using CH2Cl2 as the eluent.
C
29H20N2OPt: 607.1224, found: 607.1234 [M]þ. 1H NMR (400 MHz,
DMSO‑d6, ppm): δ 9.428 (d, J ¼ 5.2 Hz, 1H), 9.275 (d, J ¼ 5.2 Hz, 1H),
8.942 (d, J ¼ 6.8 Hz, 1H), 8.124 (dd, J ¼ 12.0, 6.0 Hz, 2H), 7.900 (dd, J
¼ 6.8, 4.0 Hz, 1H), 7.800–7.825 (m, 2H), 7.692 (d, J ¼ 6.8 Hz, 1H),
7.600 (d, J ¼ 6.0 Hz, 2H), 7.484–7.527 (m, 3H), 7.288 (t, J ¼ 6.0 Hz,
1H), 7.190 (t, J ¼ 6.0 Hz, 1H), 6.966 (d, J ¼ 6.0 Hz, 1H), 1.337 (s, 9H).
13C NMR (100 MHz, CDCl3, ppm): δ 168.19, 167.09, 151.14, 149.45,
147.69, 146.66, 146.26, 138.99, 138.77, 137.69, 134.97, 131.91,
131.76, 131.10, 129.51, 125.42, 123.96, 123.56, 121.61, 121.50,
120.82, 118.16, 115.95, 104.87, 92.40, 86.19, 34.81, 31.25. Elem.
Anal.: C32H26N2OPt (%) Calcd for: C, 59.16; H, 4.03; N, 4.31. Found (%):
2.2.2.1. [5-(2-phenylethynyl)-8-quinolinolato-κN1,κO8][2-(2-pyridinyl-
κN)phenyl-κC]platinum(II) (1). Yield: 552 mg (93%) of a red powder. M.
p.: >250 �C. IR (neat, cmÀ 1): 3066 (w), 2961(s), 2915(s), 2851(s), 2200
(m), 1610(w), 1578(s), 1552(m), 1506(m), 1485(s), 1464(s), 1382(m),
1336(s), 1258(s), 1196(w), 1096(s), 1007(s), 911(w), 868(w), 795(s),
756(s), 728(s), 686(s). HRMS (m/z): calcd for C28H18N2OPt: 593.1067,
found: 593.1058 [M]þ. 1H NMR (400 MHz, DMSO‑d6, ppm): δ 9.413 (d,
J ¼ 4.4 Hz, 1H), 9.255 (d, J ¼ 4.4 Hz, 1H), 8.946 (d, J ¼ 6.0 Hz, 1H),
8.104 (dd, J ¼ 12.0, 6.0 Hz, 2H), 7.883 (dd, J ¼ 6.0, 4.4 Hz, 1H), 7.789
(dd, J ¼ 6.0, 4.0 Hz, 2H), 7.659–7.686 (m, 3H), 7.410–7.506 (m, 4H),
7.271 (t, J ¼ 4.0 Hz, 1H), 7.172 (t, J ¼ 4.0 Hz, 1H), 6.983 (d, J ¼ 6.0 Hz,
1H). 13C NMR (100 MHz, CDCl3, ppm): δ 168.20, 167.12, 149.52,
147.80, 146.72, 146.34, 138.95, 138.83, 137.83, 137.56, 135.21,
131.98, 131.81, 131.35, 129.61, 128.41, 127.87, 124.03, 123.70,
121.70, 121.61, 118.28, 116.06, 104.70, 92.36, 86.85. Elem. Anal.:
C, 59.14; H, 4.01; N, 4.30. UV/Vis (CH2Cl2) λmax nm (log ε): 503 (3.890),
359 (3.927), 321 (4.348), 272 (4.466), 229 (4.703).
2.3. Measurements
Infrared (IR) spectra were measured on Nicolet 6700 FT-IR spec-
trophotometer, while Bruker Advance II (400 MHz) spectrometer pro-
vided the 1H NMR and 13C NMR spectra. Thermogravimetric analysis
(TGA) was performed under the N2 atmosphere using a TA-Q50 ther-
mogravimetric analyzer with a heating rate of 10 �C/min. Differential
scanning calorimetry (DSC) was performed under the N2 atmosphere at
a heating rate of 5 �C/min in a TA Instrument Q20 Differential Scanning
Calorimeter. Electrospray ionization mass spectra (ESI-MS) was per-
formed on A Finnigan LCQ mass spectrometer. UV–vis absorption
spectra was acquired from PerkinElmer Lambda 25 UV–vis spectrom-
eter. Powder X-ray diffraction (PXRD) were measured on a D/MAX-2400
with the scan rate of 4�/min. Elemental analysis of C, H and N were
performed on a PerkinElmer model 240 C elemental analyzer. Lumi-
nescent properties were measured on the PerkinElmer LS55 lumines-
cence spectrometer with a red-sensitive photomultiplier type R928 and
Edinburgh analytical instrument (F920 fluorescence spectrometer).
Emission lifetimes in solid states and degassed solutions were deter-
mined using an Edinburgh analytical instrument (F920 fluorescence
C
28H18N2OPt (%) Calcd for: C, 56.66; H, 3.06; N, 4.72. Found (%): C,
56.67; H, 3.06; N, 4.71. UV/Vis (CH2Cl2) λmax nm (log ε): 480 (3.676),
358 (3.802), 316 (4.216), 265 (4.487), 227 (4.762).
2.2.2.2. [5-(2-(4-methylphenyl)ethynyl)-8-quinolinolato-κN1,κO8][2-(2-
pyridinyl-κN)phenyl-κC] platinum(II) (2). Yield: 559 mg (92%) of a red
powder. M.p.: >250 �C. IR (neat, cmÀ 1): 3064 (w), 2961(s), 2924(s),
2855(s), 2200(m), 1609(s), 1585(s), 1559(m), 1501(m), 1481(m), 1463
(s), 1404(m), 1334(s), 1295(m), 1265(m), 1234(m), 1165(w), 1116(w),
1100(s), 1016(w), 989(m), 827(s), 775(s), 748(s), 706(s). HRMS (m/z):
calcd for C29H20N2OPt: 607.1224, found: 607.1234 [M]þ. 1H NMR (400
MHz, DMSO‑d6, ppm): δ 9.046 (d, J ¼ 4.8 Hz, 1H), 9.253 (d, J ¼ 4.8 Hz,
1H), 8.926 (d, J ¼ 6.0 Hz, 1H), 8.100 (dd, J ¼ 12.0, 6.0 Hz, 2H), 7.874
(dd, J ¼ 6.0, 4.0 Hz, 1H), 7.770 (t, J ¼ 6.0 Hz, 2H), 7.670 (d, J ¼ 6.0 Hz,
1H), 7.543 (d, J ¼ 6.0 Hz, 2H), 7.480 (t, J ¼ 4.0 Hz, 1H), 7.258–7.293
(m, 3H), 7.168 (t, J ¼ 6.0 Hz, 1H), 6.973 (d, J ¼ 6.0 Hz, 1H), 2.361 (s,
3H). 13C NMR (100 MHz, CDCl3, ppm): δ 168.19, 167.10, 149.46,
147.70, 146.65, 146.27, 138.98, 138.78, 137.94, 137.70, 134.96,
131.88, 131.76, 131.24, 129.52, 129.18, 123.96, 123.57, 121.62,
121.50, 120.76, 118.17, 115.98, 104.86, 92.45, 86.17, 21.54. Elem.
Anal.: C29H20N2OPt (%) Calcd for: C, 57.33; H, 3.32; N, 4.61. Found (%):
spectrometer). The emission quantum yield (Φ
) in degassed
dichloromethane solution at room temperature was ceamlculated by Φs ¼
Φ (Br/Bs)(ns/nr)2(Ds/Dr) using [Ru(bpy)3](PF6)2 in degassed acetonitrile
r
as the standard (Φem ¼ 0.062), where the subscripts ‘r’ and ‘s’ denote
reference standard and the sample solution, respectively, and n, D, and Φ
are the refractive index of the solvents, the integrated intensity, and the
luminescence quantum yield, respectively. The quantity B is calculated
by B ¼ 1–10À AL, where A is the absorbance at the excitation wavelength
and L is the optical path length. Absolute quantum yields of complexes in
solid state were determined in air by an integrating sphere (142 mm in
diameter) using an Edinburgh FLS920 spectrofuorophotometer.
C, 57.34; H, 3.31; N, 4.60. UV/Vis (CH2Cl2) λmax nm (log ε): 498 (3.750),
358 (3.818), 316 (4.277), 271 (4.503), 229 (4.831).
2.2.2.3. [5-(2-(4-ethylphenyl)ethynyl)-8-quinolinolato-κN1,κO8][2-(2-
pyridinyl-κN)phenyl-κC] platinum(II) (3). Yield: 566 mg (91%) of a red
powder. M.p.: >250 �C. IR (neat, cmÀ 1): 3071 (w), 2955(s), 2917(s),
2850(s), 2206(m), 1606(s), 1585(s), 1562(m), 1496(m), 1463(s), 1384
(m), 1324(s), 1285(m), 1265(m), 1242(s), 1167(m), 1131(m), 1104(m),
1084(s), 1024(m), 943(w), 821(s), 766(s), 731(s). HRMS (m/z): calcd
for C30H22N2OPt: 621.1380, found: 621.1361 [M]þ. 1H NMR (400 MHz,
DMSO‑d6, ppm): δ 9.393 (d, J ¼ 2.8 Hz, 1H), 9.241 (d, J ¼ 5.2 Hz, 1H),
8.913 (d, J ¼ 6.8 Hz, 1H), 8.088 (dd, J ¼ 13.2, 6.0 Hz, 2H), 7.860 (t, J ¼
5.2 Hz, 1H), 7.766–7.787 (m, 2H), 7.662 (d, J ¼ 6.0 Hz, 1H), 7.563 (d, J
¼ 6.4 Hz, 2H), 7.467 (t, J ¼ 4.8 Hz, 1H), 7.285 (d, J ¼ 6.4 Hz, 2H), 7.260
(d, J ¼ 6.4 Hz, 1H), 7.164 (t, J ¼ 6.0 Hz, 1H), 6.965 (d, J ¼ 6.4 Hz, 1H),
2.636 (q, J ¼ 6.0 Hz, 2H), 2.361 (t, J ¼ 6.0 Hz, 3H). 13C NMR was not
measured due to low solubility of this complex in common NMR sol-
vents. Elem. Anal.: C30H22N2OPt (%) Calcd for: C, 57.97; H, 3.57; N,
4.51. Found (%): C, 57.94; H, 3.56; N, 4.50. UV/Vis (CH2Cl2) λmax nm
2.4. X-ray crystallography
Crystal of 1 was obtained by diffusing petroleum ether onto its
dichloromethane solution. The data of crystal was collected on a Bruker
SMART APEX II CCD area detector system. Structure was solved using
direct methods and refined by a full-matrix least-squares methods pro-
cedure on F2 with anisotropic thermal parameters for all non-hydrogen
atoms using the SHELXTL–97 program package [71,72]. Table S1 of the
Supporting Information gives the detailed crystallographic data and
structure refinement parameters.
(log ε): 500 (3.773), 359 (3.815), 316 (4.318), 271 (4.476), 229 (4.752).
3

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
Fig. 1. The molecular structure (a), 1-D scalene cylinder structure (b), and interactions between adjacent molecules along b axis (c) of complex 1.
3. Results and discussion
square-planar geometry with four cis-angles around the platinum center
in the range 80.38–106.0� (Table S2). Two coordinated N atoms from
ppy and 8-quinolinol ligands are in the opposite position. The molecule
of 1 displays good planarity with the dihedral angle between ppy and 8-
quinolinol ligands being 9.15�. Along a axis, adjacent molecules are
paralleled in the same direction and connected with each other through
3.1. Preparation and structures
Complexes 1–4 were prepared in high yields by the reaction of the
precursor Pt2(ppy)2(μ-Cl)2 with 5-[2-(4-substituent-phenyl)ethynyl]-8-
quinolinol ligands in the presence of Na2CO3 (Scheme 1). All com-
plexes were fully characterized by elemental analyses, HRMS, 1H(13C)
NMR and IR spectroscopy. The crystal structure of 1 was determined by
X-ray crystallography. Interestingly, when 4 was recrystallized from
different organic solvents, three kinds of pseudopolymorphs with
different color, luminescence and stacking structures, including five
orange solvated samples {4⋅½(Toluene), 4⋅CH3CH2OH, 4⋅½(Et2O),
4⋅½(CH3OH), and 4⋅½(Hexane)}, a red solvent-free sample 4R, and a
dark-brown sample 4⋅½(CCl4), were isolated (Figs. S1–S5). This phe-
nomenon indicates that complex 4 may have luminescence switching
property. Five orange solvated samples have almost the same PXRD
pattern, revealing that they have the same and very stable molecular
framework constructed by Pt(II) moieties (Fig. S1). In contrast, only red
solvent-free species could be obtained when 1–3 were recrystallized
from these solvents (Figs. S6–S9).
π-π stacking interactions to form the one-dimensional scalene cylinder
structure (Fig. 1b and Table S3). Because of the large slip between
adjacent molecules, the shortest Pt⋅⋅⋅Pt distance is 6.600 Å, indicating no
intermolecular Pt-Pt contact exists in the stacking structure (Table S2).
The molecules in neighboring scalene cylinder structures along b axis are
arranged in the opposite directions and connected by strong hydrogen
bonds (Fig. 1c and Table S3). The dihedral angles between molecules in
adjacent scalene cylinder structures are 26.31�. The molecules in adja-
cent scalene cylinder structures along c axis exhibit a head-to-head
structure with larger dihedral angles (64.35�) (Fig. S10). This kind of
arrangement allows the compact stacking of molecules through strong
C-H⋅⋅⋅π hydrogen bonding network (Fig. S1 and Table S3). Complexes 2
and 3 may also have the compact stacking structure, whereas 4 most
likely stacks in a relatively loose stacking structure considering the steric
hindrance of their substituents.
Fig. 1a shows the molecular structure of complex 1 and its selected
bond lengths and angles are given in Table S2 as the supporting infor-
mation. The Pt center of 1 is coordinated by C1N2O atoms and adopted a
Fig. 2. The UV–Vis absorption (a) and emission spectra (b) of complex 1–4 in CH2Cl2 solution: 1, 0.017 mM; 2, 0.024 mM; 3, 0.021 mM; 4, 0.018 mM.
4

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
Fig. 3. The UV–Vis absorption (a) and emission spectra (b) of complexes 1–3, 4⋅CH3CH2OH, 4R and 4⋅½(CCl4) in solid state.
500 nm for 3, and 503 nm for 4 can be assigned to π(5-substituted-8-
Table 1
quinolinol) →
π
*(ppy) ligand-to-ligand charge transfer (1LLCT) and d
π
Luminescence data of 1–4 in different states at ambient temperature.
(Pt) →
π
*(ppy) metal-to-ligand charge transfer (1MLCT) transitions ac-
Sample
medium
λem (nm)
τem
(μs)
Φem (%)
cording to the literatures [56,59,64]. All complexes display an
orange-red luminescence in dilute CH2Cl2 solution with maximum
emission band centered at 572 nm for 1, 582 nm for 2, 586 nm for 3, and
592 nm for 4, resulting from the admixture of 3LLCT and 3MLCT triplet
states. The red-shift of low-energy absorption and emission bands from 1
to 4 are result from the electronic effect of substituents on 8-quinolinol
ligand.
1
CH2Cl2 solution
solid state
572
4.65
0.19a
0.24
0.15a
0.05
0.16a
0.04
0.20a
0.29
0.35
<0.01
0.27
0.24
600, 693
582
4.97, 0.074
2.71
2
3
CH2Cl2 solution
solid state
621
2.80
CH2Cl2 solution
solid state
586
6.13
627
2.94
4
CH2Cl2 solution
solid state
592
2.42
4⋅CH3CH2OH
586
3.60
In solid state, the red forms of 1-3 exhibit similar UV–Vis absorption
spectra with low-energy absorption bands at about 450–555 nm
(Fig. 3a). The low-energy bands of orange sample 4⋅CH3CH2OH display
a slight blue-shift compared with those of 1-3 and occurred at 440–540
nm (Fig. 3a). All of them can be attributed to 1LLCT and 1MLCT tran-
sitions. Their difference in low-energy absorption bands are mostly
4R
solid state
735
1.87
4⋅½(CCl4)
4O
solid state
808
0.84
heated
586
3.45
4G
ground
742
1.56
a
The quantum yield was estimated relative to [Ru(bpy)3](PF6)2 in CH3CN as
the standard (Φem ¼ 6.2%).
likely due to the existence of intermolecular aromatic π-π stacking in-
teractions in red samples. Compared to those of 1-3 and 4⋅CH3CH2OH,
the low-energy absorption of red 4R in the range of 580–800 nm dis-
plays a noticeable red shift most likely due to the 1MMLCT (metal-metal
to ligand charge transfer) transition based on existence of Pt-Pt in-
teractions in the stacking structure (Fig. 3a). In comparison, the dark-
brown 4⋅½(CCl4) displays a distinct new low-energy absorption band
at 701 nm extending to 900 nm, indicating that it originates from the
different attribution (Fig. 3a). As this new absorption band is one of the
3.2. Photophysical properties
The absorption properties of all complexes 1–4 were measured in
dichloromethane at room temperature (Fig. 2a). The spectra all reveal
strong absorption bands between 225 and 360 nm mainly corresponding
to intraligand 1IL (ppy and 8-quinolinol ligands) charge transitions. The
low-energy absorption bands centered at 480 nm for 1, 498 nm for 2,
Fig. 4. Vapoluminescence of complex 4. (a) Photographic images under ambient light and UV light irradiation (λex ¼ 365 nm) and (b) emission spectra of 4R after
exposure to different VOC vapors.
5

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
Fig. 5. The vapor-triggered irreversible structural conversion
of 4. (a) The conversion routes of 4⋅CH3CH2OH, 4R and
4⋅½(CCl4) upon exposure to corresponding VOC vapors. (b)
The emission spectra and (c) PXRD patterns of 4⋅CH3CH2OH
after absorbing THF (black) and CCl4 (blue) vapor; 4R after
absorbing ethanol (magenta) and CCl4 (wine) vapor; and
4⋅½(CCl4) after absorbing ethanol (olive) and THF (red) vapor.
(For interpretation of the references to color in this figure
legend, the reader is referred to the Web version of this
article.)
characteristics of Pt(II) complex with 1-D “platinum wire” stacking
structure, there is no doubt it derives from the 1MMLCT transition [20,
36].
and stable stacking structures that prevents the structural conversion of
them once exposure to VOC vapor.
In contrast, 4 exhibits unusual irreversible vapoluminescent prop-
erty. As shown in Fig. 4, once exposure to toluene, hexane, ethanol,
diethyl ether, or methanol vapors, both the color and luminescence of
red 4R were changed from red to orange accompanied with the blue
shift of emission spectra from 735 nm to ca. 586 nm. Meanwhile, the
sample exposure to CCl4 vapor changed to the dark-brown color and the
original red luminescence was quenched. The luminescence spectrum,
TGA and PXRD measurements confirmed that this dark-brown sample is
4⋅½(CCl4) (Figs. S14 and S15). In contrast, there is no any change in
color and luminescence of the sample exposed to THF, acetone, CH2Cl2,
CH3CN, CHCl3, or ethyl acetate vapors (Fig. 4). These results are in good
agreement with the fact that 4 recrystallized from different solvents. The
interconversions between orange sample (4⋅CH3CH2OH is selected as
the representative), 4R and 4⋅½(CCl4) were also studied (Fig. 5). We
have known that 4R can be converted to 4⋅CH3CH2OH or 4⋅½(CCl4) once
absorbing ethanol or CCl4 vapors, respectively. When 4⋅½(CCl4) was
exposed to ethanol or THF vapor, 4⋅CH3CH2OH and 4R can also con-
verted as confirmed by luminescence spectra and PXRD measurements
(Fig. 5b–c). To our surprise, 4⋅CH3CH2OH can not be changed to 4R or
4⋅½(CCl4) by vapor absorption. The results indicate that the vapolumi-
nescent property of 4 is not fully reversible. As vapoluminescence of
square-planar Pt(II) complexes are usually caused by the structural
conversion and consequent changes in weak intermolecular in-
teractions, most vapoluminescent behaviours of Pt(II) complexes are
reversible, and only a few examples about irreversible vapoluminescent
behaviours have been reported up until now [36,68,77–80]. The results
demonstrate that the molecular framework of 4⋅CH3CH2OH may have a
better stability than that of 4R and 4⋅½(CCl4). Thus, 4R and 4⋅½(CCl4)
can be changed to other forms triggered by vapor absorption, while
4⋅CH3CH2OH could not. Furthermore, the vapoluminescence behaviour
of 4 can be attributed to the changes of the lowest-excited states between
LLCT/MLCT and MMLCT transitions caused by structural conversions
triggered by vapor absorption. Meanwhile, the experimental results
Under irradiation at 460 nm, 1 shows a distinct emission profile with
two components peaked at 600 and 693 nm, respectively (Fig. 3b and
Table 1). The high-energy emission band at 600 nm has a little red-shift
compared with its emission band in solution, revealing the same emis-
sion origin of them. As no Pt-Pt interaction exists in 1, the lower-energy
transition at 693 nm can not be 3MMLCT, so we suggest that it is the
exciplex emission generated by intermolecular aromatic π-π interactions
according to the literatures [58,73–76]. The red solid sample 2 and 3
exhibit the similar red luminescence with a broad emission band peaked
at 621 nm and 627 nm, respectively (Fig. 3b and Table 1). Both of them
arise from the 3LLCT and 3MLCT transitions. The yellow 4⋅CH3CH2OH
displays the yellow-orange luminescence peaked at 586 nm which is
similar with its emission in CH2Cl2 solution (Fig. 3b and Table 1).
Whereas, 4R emits a red luminescence with broad emission band
centered at 735 nm (Fig. 3b and Table 1). The significant large red-shift
of emission compared with that of 4⋅CH3CH2OH demonstrates that the
emission of 4R most likely originates from 3MMLCT transition. More
interestingly, under visible light (460 nm) irradiation, dark-brown
4⋅½(CCl4) emits an unusual NIR luminescence peaked at 808 nm
(Fig. 3b and Table 1) possibly mainly because of the formation of 1-D
“platinum wire” stacking structure with strong Pt-Pt interactions and
thus further reduced energy level of 3MMLCT excited state. To the best
of our knowledge, it is the first Pt(II) complex bearing 8-quinolinol de-
rivatives that exhibits NIR luminescence beyond 800 nm in the solid
state.
3.3. Vapoluminescence
The vapoluminescent properties of 1-4 were explored. Upon expo-
sure to different VOC vapors, there is no change in the color and lumi-
nescence of complexes 1–3, indicating they haven’t vapoluminescent
property (Figs. S11–S13). The reason is most likely due to their compact
6

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
molecular framework with that of 4⋅CH3CH2OH.
In contrast, once 4⋅½(CCl4) is heated at 155 �C, the color of the
sample changes to red (Fig. 7). This red sample does not contain any
solvent molecules and emits a red luminescence peaked at 735 nm
(Fig. 7b and Table 1). The PXRD measurement confirms that this red
sample is 4R (Fig. 7c). It’s well known that 1-D “platinum wire” stacking
structures have weak intermolecular interactions and large spaces be-
tween neighboring columns, they are usually broken and transformed to
dimeric with Pt-Pt interaction under external stimuli. The thermochro-
mic luminescence of 4⋅½(CCl4) is fully reversible as 4R can easily be
converted to 4⋅½(CCl4) upon exposure to CCl4 vapor. So, the mechanism
of thermochromic luminescence of 4⋅½(CCl4) is the conversion of the 1-
D “platinum wire” stacking structure to dimeric structure with inter-
molecular Pt-Pt interaction upon heating and the resultant changes of
the lowest-excited state energy levels.
3.5. Mechanoluminescence
Fig. 6. DSC curves of complexes 1–4 under the N2 atmosphere at a heating rate
of 5 �C/min.
Upon mechanical grinding, the color and luminescence of complexes
1–3 have no visibly discernible change although PXRD measurement
indicate that they have changed from crystalline state to amorphous
phase (Figs. S17–S20). The result demonstrates that grinding force could
not change their energy level of lowest excited states. Therefore, com-
plexes 1–3 have not mechanoluminescent property and the most likely
reason is their compact stacking structures.
suggest that Pt(II) complex with stable and compact stacking structure
may be not conductive to generation of vapoluminescent property.
3.4. Thermochromic luminescence
We also explored the responses of complexes 1–4 to heat. As shown
in Fig. 6, complexes 1–3 and 4R haven’t any change before decompo-
sition during the heating process, revealing they don’t have thermo-
chromic luminescence property.
In contrast, the color and luminescence of 4⋅CH3CH2OH and
4⋅½(CCl4) changed to red after ground, whereas those of 4R have no
visibly discernible change, revealing both 4⋅CH3CH2OH and 4⋅½(CCl4)
have the mechanoluminescence behaviour (Fig. 8, Fig. 9 and Fig. S21).
The ground samples of them are all in an amorphous phase and display
the same luminescence spectra with maximum emission wavelength
peaked at 742 nm (Fig. 8 and Table 1), indicating they are the same
product (namely 4G). The corresponding luminescence response shifts
of them to the mechanical grinding are ca. 156 nm for 4⋅CH3CH2OH, 7
nm for 4R, and À 66 nm for 4⋅½(CCl4). The large red-shift of
4⋅CH3CH2OH indicates the change of its excited state from original
3LLCT/3MLCT to the 3MMLCT transitions. Interestingly, the response of
Upon heating to 300 �C, 4⋅CH3CH2OH experience a phase transition
at 93.2 �C, corresponding to the transformation from 4⋅CH3CH2OH to
4O caused by the loss of CH3CH2OH solvent (Figs. 6 and 7 and Fig. S16).
The new polymorphs 4O has the same color, luminescence and PXRD
pattern with those of 4⋅CH3CH2OH and can be easily restored to original
4⋅CH3CH2OH by absorbing CH3CH2OH vapor (Fig. 7). Although sol-
vated CH3CH2OH was lost during the heating, 4⋅CH3CH2OH has not
thermochromic luminescence because 4O has the same stabled
Fig. 7. Thermochromic luminescence of 4. (a) The conversion
routes and photographic images of 4⋅CH3CH2OH and
4⋅½(CCl4) under ambient light and UV light (365 nm) irradi-
ation during
a reversible process of heating and vapor
absorbing. (b) The luminescence spectra of 4⋅CH3CH2OH and
4⋅½(CCl4) in different states: crystalline state (black color),
heated state (red color) and the restored state by exposure
heated samples to CH3CH2OH or CCl4 vapor (blue color). (c)
PXRD patterns of 4⋅CH3CH2OH and 4⋅½(CCl4) during
a
heating-vapor absorbing process. (For interpretation of the
references to color in this figure legend, the reader is referred
to the Web version of this article.)
7

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
Fig. 8. Mechanoluminescence of 4. (a) The reversible conversion routes of 4⋅CH3CH2OH, 4R, and 4⋅½(CCl4) in response to mechanical grinding and restored by
vapor absorbing. (b) The luminescence spectra and (c) PXRD patterns of 4⋅CH3CH2OH (black line), 4R (red line), and 4⋅½(CCl4) (blue line) after ground. (For
interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Fig. 9. The reversible mechanoluminescence of 4⋅CH3CH2OH. (a) Photographic images of samples under ambient light and UV light (365 nm) irradiation during the
reversible process. (b) Emission spectra and (c) PXRD patterns of unground sample (black line), ground sample (red line), and ground sample with a drop of ethanol
added (blue line). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
4R to mechanical grinding only has 7 nm. The results show that the
luminescence of 4R and 4G originates from the same excited state, and
the existence of Pt-Pt contact in 4G is also confirmed. For 4⋅½(CCl4),
mechanical grinding lead to a 66 nm blue shift in the emission spectrum.
The blue shift in emission is caused by the breaking of 1-D “platinum
wire” structure into the amorphous phase (existence of Pt-Pt contact)
and resultant increasing of energy gap between HOMO and LUMO.
Once either exposed to CH3CH2OH or CCl4 vapor or a drop of
8

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
CH3CH2OH or CCl4 was added, the color, luminescence and PXRD pat-
terns of 4G could be converted back to the original crystalline states of
4⋅CH3CH2OH or 4⋅½(CCl4), respectively (Fig. 9 and Fig. S21). In fact, 4G
could also be restored to 4R after exposure to THF vapor (Fig. S22).
Therefore, the mechanoluminescence property of 4⋅CH3CH2OH and
4⋅½(CCl4) are fully reversible. The emission wavelength and intensity of
both 4⋅CH3CH2OH and its ground sample have no evident changes even
after 20-cycles of grinding/solvent-adding process (Fig. S23). It is well
known that the mechanical grinding can result the desorption of the
solvent molecule from a solvated complex which may also lead to the
changes in color and luminescence. However, the mechanolumi-
nescence of 4⋅CH3CH2OH and 4⋅½(CCl4) are not due to the desorption of
the solvent molecules because their ground sample are quite different
with their heated samples.
References
[1] Fleetham T, Li GJ, Li J. Phosphorescent Pt(II) and Pd(II) complexes for efficient,
high-color-quality, and stable OLEDs. Adv Mater 2017;29:1601861.
[2] Tseng CH, Fox MA, Liao JL, Ku CH, Sie ZT, Chang CH, Wang JY, Chen ZN, Lee GH,
Chi Y. Luminescent Pt(II) complexes featuring imidazolylidene-pyridylidene and
dianionic bipyrazolate: from fundamentals to OLED fabrications. J Mater Chem C
2017;5:1420–35.
[3] Wang X, Wang SN. Phosphorescent Pt(II) emitters for OLEDs: from triarylboron-
functionalized bidentate complexes to compounds with macrocyclic chelating
ligands. Chem Rec 2019;19:1693–709.
[4] Strassner T. Phosphorescent platinum(II) complexes with C^C* cyclometalated
NHC ligands. Accounts Chem Res 2016;49:2680–9.
[5] Li GJ, Zhao XD, Fleetham T, Chen QD, Zhan F, Zheng JB, Yang YF, Lou WW,
Yang YN, Fang K, Shao ZZ, Zhang QS, She YB. Tetradentate platinum(II) complexes
for highly efficient phosphorescent emitters and sky blue OLEDs. Chem Mater
2020;32:537–48.
[6] Samiee S, Hossienpour P. A comparative theoretical study on the optoelectronic
and nonlinear optical properties of [Pt(bpy)(qdt)] derivatives with electron-
donating and -withdrawing anchors. New J Chem 2019;43:12865–73.
[7] Zhong FF, Zhao JZ. An platinum(II) bis(acetylide) complex with naphthalimide and
pyrene ligands: synthesis, photophysical properties, and application in triplet-
triplet annihilation upconversion. Eur J Inorg Chem 2017:5196–204.
[8] Wang PL, Koo YH, Kim W, Yang WB, Cui XN, Ji W, Zhao JZ, Kim D. Broadband
visible light harvesting N^N Pt(II) bisacetylide complex with bodipy and
4. Conclusions
In summary, four square-planar cycloplatinated(II) complexes based
on 5-substituted-8-quinolinol derivatives and 2-phenylpyridine ligand
have been designed and synthesized. Complexes 1–3 were isolated as
red desolvated samples. Whereas, three main types of 4 were obtained,
namely, orange 4⋅CH3CH2OH, red 4R and dark-brown 4⋅½(CCl4).
Among them the dark-brown 4⋅½(CCl4) exhibits a NIR luminescence
peaked at 808 nm, which is the longest luminescent wavelength of re-
ported Pt(II) complex based on 8-quinolinol derivatives to the best of our
knowledge. Complexes 1–3 show no detectable response to VOC vapors,
heating, or mechanical grinding, indicating they have not vapolumi-
nescent, thermochromic luminescent and mechanoluminescent proper-
€
naphthalene diimide ligands: forster resonance energy transfer and intersystem
crossing. J Phys Chem C 2017;121:11117–28.
[9] Cai WL, Zhao AC, Ren K, He RX, Li M, Shen W. Understanding the mechanisms of
white light emission of a tetradentate Pt complex in various surrounding
environments. J Phys Chem C 2019;123:17968–75.
[10] Yan ZP, Luo XF, Liu WQ, Wu ZG, Liang X, Liao K, Wang Y, Zheng YX, Zhou L,
Zuo JL, Pan Y, Zhang HJ. Configurationally stable platinahelicene enantiomers for
efficient circularly polarized phosphorescent organic light-emitting diodes. Chem
Eur J 2019;25:5672–6.
[11] Bachmann M, Suter D, Blacque O, Venkatesan K. Tunable and efficient white light
phosphorescent emission based on single component N-heterocyclic carbene
platinum(II) complexes. Inorg Chem 2016;55:4733–45.
ties. In contrast,
4 exhibits tri-stimuli-responsive luminescence
[12] Chi Y, Chou PT. Transition-metal phosphors with cyclometalating ligands:
fundamentals and applications. Chem Soc Rev 2010;39:638–55.
[13] Li K, Tong GSM, Wang QY, Cheng G, Tong WY, Ang WH, Kwong WL, Che CM.
Highly phosphorescent platinum(II) emitters: photophysics, materials and
biological applications. Chem Sci 2016;7:1653–73.
switching property caused by structural conversion and resultant
changes of the lowest-energy excited states. Upon exposure to VOC va-
pors, 4 exhibited unusual irreversible vapoluminescent property which
is mainly due to the compact stacking structure of 4⋅CH3CH2OH.
Furthermore, both orange 4⋅CH3CH2OH and dark-brown 4⋅½(CCl4) also
displayed reversible responses to heating and mechanical grinding.
Considering that the only difference of 1-4 is their substituents, the
different response of 4 to external stimuli compared with that of 1-3 is
mainly due to the large steric hindrance of tert-butyl group which results
the loose stacking structure and possibility of structural conversion.
[14] Zhang KY, Yu Q, Wei HJ, Liu SJ, Zhao Q, Huang W. Long-lived emissive probes for
time-resolved photoluminescence bioimaging and biosensing. Chem Rev 2018;118:
1770–839.
[15] Mauro M, Aliprandi A, Septiadi D, Kehr NS, De Cola L. When self-assembly meets
biology: luminescent platinum complexes for imaging applications. Chem Soc Rev
2014;43:4144–66.
[16] Law ASY, Lee LCC, Yeung MCL, Lo KKW, Yam VWW. Amyloid Protein-induced
supramolecular self-assembly of water-soluble platinum(II) complexes: a
luminescence assay for amyloid fibrillation detection and inhibitor screening. J Am
Chem Soc 2019;141:18570–7.
[17] Wong KMC, Yam VWW. Self-assembly of luminescent alkynylplatinum(II)
terpyridyl complexes: modulation of photophysical properties through aggregation
behavior. Acc Chem Res 2011;44:424–34.
Notes
The authors declare no competing financial interest.
Declaration of competing interest
[18] Yam VWW, Au VKM, Leung SYL. Light-emitting self-assembled materials based on
d8 and d10 transition metal complexes. Chem Rev 2015;115:7589–728.
[19] Law ASY, Yeung MCL, Yam VWW. Arginine-rich peptide-induced supramolecular
self-assembly of water-soluble anionic alkynylplatinum(II) complexes: a
continuous and label-free luminescence assay for trypsin and inhibitor screening.
ACS Appl Mater Interfaces 2017;9:41143–50.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[20] Kang JJ, Zhang XX, Zhou HJ, Gai XQ, Jia T, Xu L, Zhang JJ, Li YQ, Ni J. 1-D
“platinum wire” stacking structure built of platinum(II) diimine bis(σ-acetylide)
units with luminescence in the NIR region. Inorg Chem 2016;55:10208–17.
[21] Kobayashi A, Kato M. Vapochromic platinum(II) complexes: crystal engineering
toward intelligent sensing devices. Eur J Inorg Chem 2014:4469–83.
CRediT authorship contribution statement
[22] Zhang X, Wang JY, Ni J, Zhang LY, Chen ZN. Vapochromic and mechanochromic
phosphorescence materials based on a platinum(II) complex with 4-
Jun Ni: Project administration, Writing - original draft, Formal
analysis, Funding acquisition. Gao Liu: Data curation, Investigation,
Formal analysis. Mengmeng Su: Formal analysis. Wei Zheng: Formal
analysis. Jianjun Zhang: Formal analysis, Funding acquisition.
trifluoromethylphenylacetylide. Inorg Chem 2012;51:5569–79.
[23] Ni J, Zhang X, Wu YH, Zhang LY, Chen ZN. Vapor- and mechanical-grinding-
triggered color and luminescence switches for bis(σ-fluorophenylacetylide)
platinum(II) complexes. Chem Eur J 2011;17:1171–83.
[24] Yam WVV, Hu YC, Chan KHY, Chung CYS. Reversible pH- and solvent-responsive
micelle-mediated self-assembly of platinum(II) terpyridyl-based metallo-
supramolecular diblock copolymers. Chem Commun 2009:6216–8.
[25] Krikorian M, Liu S, Swager TM. Columnar liquid crystallinity and
mechanochromism in cationic platinum(II) complexes. J Am Chem Soc 2014;136:
2952–5.
Acknowledgements
This work is financially supported by the National Natural Science
Foundation of China (21471024, 21871038).
[26] Krikorian M, Voll CCA, Yoon M, Venkatesan K, Kouwer PH, Swager TM. Smectic A
mesophases from luminescent sandic platinum(II) mesogens. Liq Cryst 2016;43:
1709–13.
[27] Venkatesan K, Kouwer PHJ, Yagi S, Müller P, Swager YM. Columnar mesophases
from half-discoid platinum cyclometalated metallomesogens. J Mater Chem 2008;
18:400–7.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2020.108451.
[28] Cuerva C, Campo JA, Ovejero P, Torres MR, Oliveira E, Santos SM, Lodeiro C,
Cano M. Columnar discotic Pt(ii) metallomesogens as luminescence
9

J. Ni et al.
Dyes and Pigments 180 (2020) 108451
multifunctional materials with chemo and thermosensor abilities. J Mater Chem C
[55] Stacey OJ, Platts JA, Coles SJ, Horton PN, Pope SJA. Phosphorescent,
2014;2:9167–81.
cyclometalated cinchophen-derived platinum complexes: syntheses, structures, and
electronic properties. Inorg Chem 2015;54:6528–36.
[29] Thomas SW, Venkatesan K, Müller P, Swager TM. Dark-field oxidative addition-
based chemosensing: new bis-cyclometalated Pt(II) complexes and phosphorescent
detection of cyanogen halides. J Am Chem Soc 2006;128:16641–8.
[30] Cuerva C, Campo JA, Cano M, Lodeiro C. Multi-stimuli-responsive properties of
aggregation-enhanced emission-active unsymmetrical PtII metallomesogens
through self-assembly. Chem Eur J 2019;25:12046–51.
[56] Yang CJ, Yi C, Xu M, Wang JH, Liu YZ, Gao XC, Fu JW. Red to near-infrared
electrophosphorescence from a platinum complex coordinated with 8-
hydroxyquinoline. Appl Phys Lett 2006;89:233506.
[57] Shavaleev NM, Adams H, Best J, Edge R, Navaratnam S, Weinstein JA. Deep-red
luminescence and efficient singlet oxygen generation by cyclometalated platinum
(II) complexes with 8-hydroxyquinolines and quinoline-8-thiol. Inorg Chem 2006;
45:9410–5.
[31] Cuerva C, Campo JA, Cano M, Lodeiro C. Platinum(II) metallornesogens: new
external-stimuli-responsive photoluminescence materials. Chem Eur J 2016;22:
10168–78.
[58] Niedermair F, Trattnig R, Mereiter K, Schmuck M, Sax S, List EJW, Slugovc C. Red
electrophosphorescent platinum(II) quinolinolate complexes. Monatsh Chem 2010;
141:847–58.
[32] Cheng S, Liu SJ, Zhou LX, Xu WJ, Zhao Q, Huang W. Phosphorescent chemosensors
for metal cations based on heavy-metal complexes. Prog Chem 2011;23:679–86.
[33] Wong KMC, Yam VWW. Luminescence platinum(II) terpyridyl complexes - from
fundamental studies to sensory functions. Coord Chem Rev 2007;251:2477–88.
[34] Kato M, Omura A, Toshikawa A, Kishi S, Sugimoto Y. Vapor-induced luminescence
switching in crystals of the syn isomer of a dinuclear (bipyridine)platinum(II)
complex bridged with pyridine-2-thiolate ions. Angew Chem Int Ed 2002;41:
3183–98.
[59] Zhou CH, Zhao X. Theoretical investigation on quinoline-based platinum (II)
complexes as efficient singlet oxygen photosensitizers in photodynamic therapy.
J Organomet Chem 2011;696:3322–7.
[60] Lowe JA, Stacey OJ, Horton PN, Coles SJ, Pope SJA. Alkyl chain functionalised,
cyclometalated platinum(II) complexes: syntheses, luminescence properties and X-
ray crystal structure. J Organomet Chem 2016;805:87–93.
[35] Qiu DF, Li MM, Zhao Q, Wang HW, Yang CX. Cyclometalated platinum(II)
terpyridylacetylide with a bis(arylamine) donor as a proton-triggered
luminescence chemosensor for Zn2þ. Inorg Chem 2015;54:7774–82.
[36] Kang JJ, Ni J, Su MM, Li YQ, Zhang JJ, Zhou HJ, Chen ZN. Facile and equipment-
free data encryption and decryption by self-encrypting Pt(II) complex. ACS Appl
Mater Interfaces 2019;11:13350–8.
[61] Li XN, Feng JK, Ren AM, Li LJ. Theoretical studies of spectra properties of
cyclometalated platinum(II) complexes with 8-hydroxyquinolines and quinolino-8-
thiol ligand. Synthetic Met 2007;157:1046–53.
[62] Niedermair F, Kwon O, Zojer K, Kappaun S, Trimmel G, Mereiter K, Slugove C.
Heteroleptic platinum(II) complexes of 8-quinolinolates bearing electron
withdrawing groups in 5-position. Dalton Trans 2008:4006–14.
[63] Wu Y, Shan GG, Li HB, Wu SX, Ren XY, Geng Y, Su ZM. Theoretical study and
design of multifunctional phosphorescent platinum(II) complexes containing
triarylboron moieties for efficient OLED emitters. Phys Chem Chem Phys 2015;17:
2438–46.
[37] Zhang XQ, Chi ZG, Zhang Y, Liu SW, Xu JR. Recent advances in mechanochromic
luminescent metal complexes. J Mater Chem C 2013;1:3376–90.
[38] Cuerva C, Campo JA, Cano M, Arredondo B, Romero B, Oton E, Oton JM. Bis
(pyridylpyrazolate)platinum(II): a mechanochromic complex useful as a dopant for
colour-tunable polymer OLEDs. New J Chem 2015;39:8467–73.
[64] Li ZM, Yuan JS, Ye YT, He YB, Huang B, Gao XC. 8-Hydroxy quinoline derivatives
as auxiliary ligands for red-emitting cyclic-platinum phosphorescent complexes:
synthesis and properties. Helv Chim Acta 2017;100:e1600308.
[39] Haque A, Xu LL, Al-Balushi RA, Al-Suti MK, IIMi R, Guo ZL, Khan MS, Wong WY,
Raithby PR. Cyclometallated tridentate platinum(II) arylacetylide complexes: old
wine in new bottles. Chem Soc Rev 2019;48:5547–63.
[65] Niedermair F, Sandholzer M, Kremser G, Slugovc C. Solution self-assembly and
photophysics of platinum complexes containing amphiphilic triblock random
copolymers prepared by ROMP. Organometallics 2009;28:2888–96.
[66] Ni J, Kang JJ, Wang HH, Gai XQ, Zhang XX, Jia T, Xu L, Pan YZ, Zhang JJ.
~
[40] Sicilia V, Arnal L, Chueca AJ, Fuertes S, Babaei A, Munoz AMI, Sessolo M,
Bolink HJ. Highly photoluminescent blue ionic platinum-based emitters. Inorg
Chem 2020;59:1145–52.
[41] Cheng G, Wan QY, Ang WH, Kwong CL, To WP, Chow PK, Kwok CC, Che CM. High-
performance deep-red/near-infrared OLEDs with tetradentate [Pt(O^N^C^N)]
emitters. Adv Optical Mater 2019;7:1801452.
A colorimetric/luminescent benzene compound sensor based on a bis(σ-acetylide)
platinum(II) complex: enhancing selectivity and reversibility through dual-
recognition sites strategy. RSC Adv 2015;5:65613–7.
[42] Zhang YM, Chen Z, Wang X, He JJ, Wu JT, Liu HY, Song J, Qu JL, Chan WTK,
Wong WY. Achieving NIR emission for donor–acceptor type platinum(II)
complexes by adjusting coordination position with isomeric ligands. Inorg Chem
2018;57:14208–17.
[67] Ni J, Wang YG, Wang HH, Xu L, Zhao YQ, Pan YZ, Zhang JJ. Thermo- and
mechanical-grinding-triggered color and luminescence switches of diimine-
platinum(II) complex with 4-bromo-2,2’-bipyridine. Dalton Trans 2014;43:352–60.
[68] Gao LR, Ni J, Su MM, Kang JJ, Zhang JJ. Luminescence switching property of
cycloplatinated(II) complexes bearing 2-phenylpyridine derivatives and the
application for data security storage. Dyes Pigments 2019;165:231–8.
[69] Ghedini M, Pugliese T, La Deda M, Godbert N, Aiello I, Amati M, Belviso S, Lelj F,
Accorsi G, Barigelletti F. Spectroscopy and electrochemical properties of a
homologous series of acetylacetonato and hexafluoroacetylacetonato
cyclopalladated and cycloplatinated complexes. Dalton Trans 2008:4303–18.
[70] Montes VA, Pohl R, Shinar J, Anzenbacher P. Effective manipulation of the
electronic effects and its influence on the emission of 5-substituted tris(8-
quinolinolate) aluminum(III) complexes. Chem Eur J 2006;12:4523–35.
[71] Sheldrick GM. SHELXS-97, Program for X-ray crystal structure determination.
Germany: University of Gottingen; 1997.
[43] Wilde S, Ma DX, Koch T, Bakker A, Gonzalez-Abradelo D, Stegemann L,
Daniliuc CG, Fuchs H, Gao HY, Doltsinis NL, Duan L, Strassert CA. Toward tunable
electroluminescent devices by correlating function and submolecular structure in
3D crystals, 2D-confined monolayers, and dimers. ACS Appl Mater Interfaces 2018;
10:22460–73.
[44] Zhong JJ, Yang C, Chang XY, Zou C, Lu W, Che CM. Platinum(ii) photo-catalysis for
highly selective difluoroalkylation reactions. Chem Commun 2017;53:8948–51.
[45] Choi WJ, Choi SK, Ohkubo K, Fukuzumi S, Cho EJ, You YM. Mechanisms and
applications of cyclometalated Pt(II) complexes in photoredox catalytic
trifluoromethylation. Chem Sci 2015;6:1454–64.
[46] Shelar DP, Li TT, Chen Y, Fu WF. Platinum(II) schiff base complexes as
photocatalysts for visible-light-induced cross- dehydrogenative coupling reactions.
ChemPlusChem 2015;80:1541–6.
[72] Sheldrick GM. SHELXL-97, Program for X-ray crystal structure refinement.
Germany: University of Gottingen; 1997.
�
�
~
�
�
[47] Gonzalez-Munoz D, Casado-Sanchez A, del Hierro I, Gomez-Ruiz S, Cabrera S,
[73] Kalinowski J, Fattori V, Cocchi M, Williams JAG. Light-emitting devices based on
organometallic platinum complexes as emitters. Coord Chem Rev 2011;255:
2401–25.
Aleman J. Size-selective mesoporous silica-based Pt(II) complex as efficient and
reusable photocatalytic material. J Catal 2019;373:374–83.
[48] Vezzu DAK, Ravindranathan D, Garner AW, Bartolotti L, Smith ME, Boyle PD,
Hou SQ. Highly luminescent tridentate N^C*N platinum(II) complexes featured in
fused five-six-membered metallacycle and diminishing concentration quenching.
Inorg Chem 2011;50:8261–73.
[74] Ko SB, Park HJ, Gong SL, Wang X, Lu ZH, Wang SN. Blue phosphorescent N-
heterocyclic carbene chelated Pt(ii) complexes with an α-duryl-β-diketonato
ancillary ligand. Dalton Trans 2015;44:8433–43.
[75] Zhao JN, Kang H, Zhou SM, Sun HM, Yin SW, Zhao N, Tang BZ. Organic solid
fluorophores regulated by subtle structure modification: color-tunable and
aggregation-induced emission. Chem Sci 2017;8:577–82.
�
�
[49] Casado-Sanchez A, Gomez-Ballesteros R, Tato F, Soriano FJ, Pascual-Coca G,
�
Cabrera S, Aleman J. Pt(II) coordination complexes as visible light photocatalysts
for the oxidation of sulfides using batch and flow processes. Chem Commun 2016;
52:9137–40.
[76] Cui RR, Lv YC, Zhao YS, Zhao N, Li N. Solid-state fluorescent materials based on
coumarin derivatives: polymorphism, stimuli-responsive emission, self-assembly
and optical waveguides. Mater Chem Front 2018;2:910–6.
[50] Zhou GJ, Wong WY, Yang XL. New design tactics in OLEDs using functionalized 2-
phenylpyridine-type cyclometalates of iridium(III) and platinum(II). Chem Asian J
2011;6:1706–27.
[77] Shigeta Y, Kobayashi A, Yoshida M, Kato M. Crystal engineering of vapochromic
porous crystals composed of Pt(II)-diimine luminophores for vapor-history sensors.
Cryst Growth Des 2018;18:3419–27.
[51] Zhou GJ, Wang Q, Wong WY, Ma DG, Wang LX, Lin ZY. A versatile color tuning
strategy for iridium(III) and platinum(II) electrophosphors by shifting the charge-
transfer states with an electron-deficient core. J Mater Chem 2009;19:1872–83.
[52] Ebina M, Kobayashi A, Ogawa T, Yoshida M, Kato M. Impact of a carboxyl group on
a cyclometalated ligand: hydrogen-bond- and coordination-driven self-assembly of
a luminescent platinum(II) complex. Inorg Chem 2015;54:8878–80.
[53] Liang AH, Li YH, Zhu WG, Wang YF, Huang F, Wu HB, Cao Y. Novel cyclometalated
platinum(II) complex containing carrier-transporting groups: synthesis,
luminescence and application in single dopant white PLEDs. Dyes Pigments 2013;
96:732–7.
[78] Shigeta Y, Kobayashi A, Ohba T, Yoshida M, Matsumoto T, Chang HC, Kato M.
Shape-memory platinum(II) complexes: intelligent vapor-history sensor with
ONÀ OFF switching function. Chem Eur J 2016;22:2682–90.
[79] Kobayashi A, Fukuzawa Y, Noro SI, Nakamura T, Kato M. Stepwise vapochromism
observed for a simple terpyridine-platinum(II) complex with a thiocyanato ligand.
Chem Lett 2009;38:998–9.
[80] Taylor SD, Norton AE, Hart RT, Abdolmaleki MK, Krause JA, Connick WB. Between
red and yellow: evidence of intermediates in a vapochromic Pt(II) salt. Chem
Commun 2013;49:9161–3.
[54] Yu JT, He KQ, Li YH, Tan H, Zhu MX, Wang YF, Liu Y, Zhu WG, Wu HB. A novel
near-infrared-emitting cyclometalated platinum(II) complex with donor-acceptor-
acceptor chromophores. Dyes Pigments 2014;107:146–52.
10