H. Lu et al.
Dyes and Pigments 193 (2021) 109463
2
.3. Synthesis of PM
AMP (5 g, 1.79 mmol) and glacial AcOH (20 ml) were mixed in 100
ml round-bottom flask. Maleic anhydride (0.5 g, 5.1 mmol) was dis-
solved in glacial AcOH (5 ml) and dropped into the mixture. Then the
◦
mixture was heated to 160 C for 6 h with magnetic stirring [28]. After
cooling down to room temperature, glacial AcOH was removed by rotary
2 2
evaporator. Crude product was redissolved in CH Cl (50 ml) and
washed with saturated sodium chloride aqueous solution (150 mL,
thrice). Organic layer was dried with anhydrous sodium sulfate for 3 h
and then filtered. The solvent was removed to obtain the desired prod-
1
uct, which is brown viscous oily liquid with 90% yield. H NMR (CDCl
3
,
3
2
6
00 MHz, ppm): δ 0.43–0.57 (t, J = 8.5 Hz, 2H, Si–CH
H, Si–CH –CH ), 3.47–3.52 (t, J = 7.3 Hz, 2H, Si–CH
.67–6.68 (s, 2H, -CH
2
),1.54–1.65 (m,
–CH –CH ),
3
CH- in maleimade). C NMR (CDCl , 100 MHz,
2
2
2
2
2
–
–
13
ppm): δ 169.81, 132.99, 40.92, 34.71, 21.53, 14.22, 0.10. Mn = 3310
(
PDI = 1.2).
◦
ꢀ 1
Fig. 1. The TGA trace of PMDF recorded at a heating rate of 10 C min under
2
.4. Synthesis of 7,9-diphenyl-8H-cyclopenta[a]acenaphthylen-8-one
nitrogen atmosphere.
(
DCA)
3
.2. Structure characterization
DCA was synthesized through reaction of acenaphthenequinone and
,3-diphenylpropan-2-one according to literature [29]. Acenaph-
thenequinone (5.47 g, 0.03 mol) and 1,3-diphenylpropan-2-one (6.3 g,
1H NMR spectra were recorded on Bruker 300 (300 MHz) spec-
1
trometer without tetramethylsilane as internal reference and shown in
0
2
.03 mol) were dissolved in ethanol (60 mL) and placed in three-neck
50 mL round-bottom flask equipped with reflux condenser and mag-
Fig. 2. At 0.05, 0.51, and 1.57 ppm, resonance peaks of –Si–CH ,
3
–Si–CH –, and –Si–CH –CH –, respectively, were easily distinguished in
2
2
2
netic stirrer. When the mixture solution was heat to reflux, KOH (0.8 g)
which dissolved in ethanol (5 mL) solution was dropwise added via a
drop funnel. The mixture immediately turned black. After dropwise
addition of KOH ethanol solution completed, the mixture was kept in
reflux for 2 h and then cooled down to room temperature. After filtered,
black precipitate was obtained. The crude product was washed with
PM (H1, H2, H3, and H4 in Fig. 2A) and PMDF (H7, H8, H9, and H10 in
Fig. 2B), thereby confirming presence of alkylsilane groups. Chemical
shifts at 6.67 and 6.68 ppm were assigned to double bonds in maleimide
–
–
groups in PM (H5 and H6 in Fig. 2A). Peak of –CH
CH- of maleimide
groups disappeared in PMDF (Fig. 2B), and aromatic hydrogens
appeared at 7.28–7.92 ppm. These results indicated that efficient
grafting of aromatic groups into polysiloxane chains occurred via Diel-
s–Alder reaction.
ethanol several times to obtain pure product, which is purple-black solid
1
powder with yield of 90%. H NMR (CDCl
3
, 300 MHz, ppm): δ 8.08 (d, J
=
7.1 Hz, 2H), 7.86 (m, 6H), 7.62 (t, J = 7.5 Hz, 2H), 7.56 (t, J = 7.6 Hz,
13
4
1
H), 7.43 (t, J = 7.0 Hz, 2H). C NMR (CDCl
3
, 100 MHz, ppm): δ 201.7,
3.3. Optical properties
54.2, 132.1, 131.5, 131.4, 129.0, 128.6, 128.3, 127.8, 121.7, 120.9.
+
ꢀ 6
HRMS: m/z calcd. for C27
H
16O, 357.1235 [M + H] , found: 357.1260
UV–vis absorption spectrum of PMDF in THF solution at 1 × 10
+
◦
ꢀ 1
[
M + H] . Melting point: 291 C.
mol L was shown in Fig. 3a. Absorption peaks at around 226 and 277
nm originated from
π
- * transitions of aromatic group. After observing
π
UV–vis absorption spectra, we further investigated optical properties in
pure THF solutions at different concentrations.
2
.5. Synthesis of PMDF
As shown in Fig. 3b, PMDF was dissolved in THF at concentrations of
PM (1 g, 0.33 mmol) and DCA (0.3 g, 0.84 mmol) were mixed in
ꢀ 3
ꢀ 4
ꢀ 5
ꢀ 6
1
× 10 , 1 × 10 , 1 × 10 , and 1 × 10 mol/L, respectively. As
◦
phenyl ether (25 ml). The mixture was heated to 150 C and kept for 24
h. Crude product was precipitated in methanol, washed three times by
water and methanol, and then dried under vacuum to obtain a dark
concentration increased, fluorescence emission peak of PMDF exhibited
gradual red-shift from 404 nm to 461 nm, and the emission intensity
simultaneously increased. The details can be found in Table 1. The
green oily liquid with 74% yield. 1H NMR (CDCl
, 300 MHz, ppm): δ
), 1.51–1.56 (m, 2H, Si–CH –CH ),
–CH –CH ), 7.28–7.92 (16H, ArH in
, 100 MHz, ppm): δ 164.7, 137.8,
36.6, 134.9, 131.7, 129.4, 128.4, 127.9, 127.3, 127.1, 126.9, 122.8,
ꢀ 3
3
emission intensity of solution at high concentration (1 × 10 mol/L)
0
.47–0.57 (t, J = 8.5 Hz, 2H, Si–CH
.48–3.53 (t, J = 7.4 Hz, 2H, Si–CH
2
2
2
was fifteen times stronger than that of solution at lower concentration
3
2
2
2
ꢀ 6
(
1 × 10 mol/L), indicating PMDF shows aggregation-induced emis-
1
3
aromatic units). C NMR (CDCl
3
sion (AIE) feature. Furthermore, the emission intensity curve of PMDF in
THF mixed with different content of water was measured and shown in
Fig. S1a. As the water content increased to 70%, the emission intensity
dramatically increased to 135% of the initial value. This emission in-
tensity behavior confirmed that PMDF is an AIE-active polymer. The size
distribution of PMDF aggregates was shown in Fig. S1b and the average
size was 76 nm. The red-shift of emission peak and the emission intensity
enhancement of PMDF could be attributed to the restriction of intra-
molecular rotation of 7,11-diphenyl-8H-acenaphth[1,2-f] isoindole-
8,10 (9H)-dione in PMDF. It can significantly suppress non-radiative
path and enhance the molecular rigidity, leading to stronger emission
intensity and longer emission wavelength. To further study the effect of
siloxane structure, we synthesized PMDF with different MWs of poly-
1
1
22.1, 121.2, 120.4, 45.7, 35.9, 20.1, 0.15. Mn = 3962 (PDI = 1.2).
3
. Results and discussion
3
.1. Thermal stability
Thermal properties of PMDF were characterized by thermal gravi-
metric analyzer (TGA) under a nitrogen atmosphere. As shown in Fig. 1,
◦
decomposition temperature of PMDF was 363 C; this value corresponds
◦
ꢀ 1
to a weight loss of 5% at heating rate of 10 C min . The peak
◦
decomposition temperature was found to be 480 C. These high thermal
decomposition temperatures suggest PMDF has excellent thermal
stability.
siloxane backbone (160, 1500, 3000 and 6000) using
α
,
ω
-bis(amino-
propyl)polydimethylsilioxane with different MWs. The emission
3