Supporting Information
Photochemical Stability of Dicyano-Substituted Poly(phenylenevinylenes) with Different
Side Chains
Logan P. Sanow, Jianyuan Sun, Cheng Zhang*
Department of Chemistry and Biochemistry
South Dakota State University, Brookings, South Dakota 57006
TABLE OF CONTENTS
Page
IR spectra of RO-diCN-PPV worked up in MeOH and dilute HCl
S2
1
S2-S3
H-NMR spectra of RO-diCN-PPV and C8-diCN-PPV
IR of RO-diCN-PPV doped with carboxylic acid, phenol, and alkyl alcohol
S3
Light-induced change in polymer molecular weight and GPC elugram profiles
S4-7
C8-diCN-PPV phosphorescence lifetimes
S8
PL spectra of C8-DiCN-PPV and RO-DiCN-PPV
S9
PL spectra of RO-diCN-PPV and RO-diCN-PPV after illumination
S9-10
S1
0.14
0.12
0.08
0.06
absorbance
0.10
0.04
0.02
0.00
4000
3500
3000
2500
2000
wavenumber (cm-1)
1500
1000
500
Figure 1S. The IR spectra of RO-diCN-PPV worked up in MeOH (blue) and worked up with
dilute HCl (red). When the polymers were worked up by a direct precipitation of the basic
reaction mixture in MeOH, the intermediate did not have a chance to be hydrolyzed into the
imide, as a result, an imide peak (1710 cm-1) is not seen in the IR (blue).
1.2
1
0
0.8
-1
0.6
-2
0.4
TGA
0.2
μV (eotherm up)
normalized weight
1
-3
DTA
0
-4
25
125
225
325
Temperature (C°)
425
Figure 2S. Thermal analysis of C8-diCN-PPV. Scan rate: 10 oC/min. N2. (We could obtain flat
baseline for DTA with the Seiko DTA/TGA system)
S2
Logan.396.esp
0.065
0.060
0.055
0.050
Normalized Intensity
0.045
0.040
0.035
0.030
0.025
0.020
0.015
trans
cis
0.010
0.005
8
7
6
Logan.397.esp
5
4
Chemical Shift (ppm)
3
2
1
0.040
0.035
Normalized Intensity
0.030
0.025
0.020
0.015
0.010
trans cis
0.005
8
7
6
5
4
Chemical Shift (ppm)
3
2
Figure 3S. 1H-NMR spectra of RO-diCN-PPV (top) and C8-diCN-PPV in CDCl3.
S3
1
p-methoxybenzoic acid
0.39
p-methoxy phenol
2-hexyl-1-decanol
0.19
absorbance
0.29
0.09
4000
3500
3000
2500
2000
wavenumber (cm -1)
1500
1000
500
-0.01
Figure 4S. IR spectra of RO-diCN-PPV with 15% p-methoxybenzoic acid (blue), 15% p-methoxy
phenol (red), and 15% of 2-hexyl-1-decanol (green).
Time (minutes)
0
50
100
150
200
250
0
Log (normalized absorbance)
-0.2
-0.4
-0.6
-0.8
-1
-1.2
-1.4
-1.6
Figure 5S. Plot of the C8-diCN-PPV carbonyl peak height at 1709 cm-1 (blue) and the OH peak
height at 3370 cm-1 (green) versus (accumulated) film illumination time.
Light-induced change in polymer molecular weight and GPC elugram profiles
S4
GPC elugrams of both polymers of different illumination time (0, 60, 120, 180 minutes) are shown in Figure
6S. Shift in peaks to longer elution time (lower MW) and growth of monomer/oligomer peaks are seen for
both polymers, but more pronounced for C8-diCN-PPV, in agreement with the faster decomposition of
this polymer.
It is also noticed that the two polymers displaced different (opposite) changes in their GPC elugram profile
with illumination. C8-diCN-PPV showed a symmetric peak before illumination. After 60 minutes of
illumination, a high MW shoulder peak appeared and the long MW tail shifted to left and became stronger,
while the main peak shifted to the right (lower MW). On contrary, RO-diCN-PPV showed a clear high MW
shoulder before illumination, which disappeared after 60 minutes of illumination.
0 min
60 min
120 min
180 min
0.5
normalized absorbance
normalized absorbance
0.6
0.5
0.4
0.3
0.2
0.4
0
60
0.3
120
180
0.2
0.1
0.1
0
0
12
14
16
18
11
20
Elution time (min)
13
15
17
Elution time (min)
19
FIGURE 6S. GPC elugrams for C8-diCN-PPV (Top) and RO-diCN-PPV (bottom) at different total
illumination times. The UV-vis detector was set at 310 nm. The integration of absorbance in the
displayed range is normalized for every elugram.
To gain insight into the different behavior, GPC elugrams and 1H NMR spectra were recorded for both
polymers at the early stage of illumination (0, 1, 2, … minutes) to show the evolution of GPC profiles and
to find whether cis/trans content and photoinduced cis-trans isomerization are responsible for the
change. Figure 7S left shows that the new GPC profile of C8-diCN-PPV was established after only two
minutes of illumination, in coincidence with the time taken for this polymer to complete light-induced cistrans isomerization (Figure 8S left). So, the profile change is mostly likely due to the isomerization.
However, if such change happened uniformly to all polymer chains, only a shift of the whole peak to the
left, and no shoulder, should be observed. Since the vinylene units in C8-diCN-PPV are about half cis and
half trans (Figure 8S left), low oligomers containing trans vinylene units (hereafter referred to as trans
oligomers) are mainly responsible for light absorption of this polymer as cis is an less efficient conjugation
unit and is also less planar due to higher steric hindrance (Figure 9S). Polymer chains that contain longer
trans oligomers function as energy traps and get most of the light energy absorbed by the polymer film
and cis-to-trans transformation mainly happen to these polymer chains, leading to a shoulder peak at the
high MW side.
In RO-diCN-PPV, trans dominates (likely as a result of significantly lower energy of trans as compared to
cis), and the polymer has larger MW, so absorption wavelength of all polymer chains are similar (i.e., not
S5
dependent on polymer length) and therefore, all polymer chains underwent cis- trans isomerization and
experienced an increase in trans content. As a result, the retention time decreased from 14.925 min for
the pristine polymer to 14.876 min after illumination of 1 min. As it only took 10 minutes for isomerization
to reach equilibrium (Figure 8S right), cis-to-trans conversion rate decreased fast. From 2 min on,
retention time started to increase (slowly), suggesting that photodegradation started to dominate MW
change. More notably, the high MW shoulder peak weakened along with illumination and disappeared at
4 min. Presumably, the shoulder can be attributed to trans-rich polymers, and trans vinylene units are
more planar and thus less sterically hindered than the cis and react with singlet oxygen faster (Note:
addition of a singlet O2 to C=C is a syn addition, requiring both oxygen atoms to have access to C=C). In
the case of C8-diCN-PPV, although the trans is expected to be more planar than cis (Figure 9S), it has more
steric hindrance than trans of RO-diCN-PPV as CH2 is larger in size than an oxygen atom (Figure 9S).
Therefore, both trans and cis in C8-diCN-PPV are highly non-planar and likely have similar reactivity
toward singlet O2.
0.4
0 min
0 min
1 min
2 min
4 min
8 min
1 min
0.5
2 min
0.4
0.3
0.2
0.1
Normalized Absorbance
Normalized Absorbance
0.6
0
0.3
0.2
0.1
0
10
12
14
16
18
Elution time (min)
20
10
12
14
16
18
Elution time (min)
20
Figure 7S: GPC elugrams for C8-diCN-PPV (left) and RO-diCN-PPV (right) at different total illumination
times. In the elugrams of C8-diCN-PPV, the monomer/dimer peaks are not seen as the samples were left
on bench for 2 days before being used for GPC. The same change was observed for RO-diCN-PPV
samples (not used for the figure shown here). Therefore, the monomer and dimer can evaporate slowly.
S6
1.0
0 min
1
0 min
1 min
0.8
0.8
4 min
2 min
Normalized intensity
2 min
0.6
0.4
0.2
10 min
0.6
15 min
0.4
0.2
0.0
3.5
3
2.5
Normalized Intensity
1 min
0
2
4.5
4
Chemical shift (ppm)
3.5
Chemical shift (ppm)
Figure 8S: The OCH2 regions of 1H NMR spectra of C8-diCN-PPV (left) and RO-diCN-PPV (right) at
different total illumination time in minutes.
C10H21
O
C8H17
NC
C7H15
NC
C7H15
CH2
H2C
CN
CN
CH2
NC
H2C
C7H15
C7H15
NC
C10H21
H
C10H21
O
O
C10H21
H
CN
H
C7H15
O
C10H21
H
CH
H22C
C8H17
CN
O
O
C7H15
O
C10H21
O
C10H21
C10H21
trans
cis
trans
in C8-diCN-PPV
cis
in RO-diCN-PPV
Figure 9S. Trans and cis Structural units in diCN-PPVs. Groups in circles are too close. Their
interactions cause phenyl rings to stay out of the planes of dicyanovinylene.
S7
delay time (ms)
0
LN(normalized PL)
1.5
2
2.5
3
3.5
4
-0.2
-0.4
-0.6
y = -0.2379x + 0.2966
-0.8
Figure 10S. Phosphorescence lifetime in nitrogen (4.2 ms).
delay time (ms)
0
LN(normalized PL)
1
1.5
2
2.5
3
-0.5
-1
y = -0.4245x + 0.2881
-1.5
Figure 11S. Phosphorescence lifetime in air (2.4 ms).
S8
3.5
4
60
PL intensity
50
ROdicnppv
40
C8dicnppv
30
20
10
0
360
410
460
510
560
Wavelength (nm)
610
660
Figure 12S. PL spectra of C8-DiCN-PPV and RO-DiCN-PPV, showing that PL peak intensity of
C8-DiCN-PPV is about 50 % as high as that of RO-DiCN-PPV.
350
photoluminescence
300
0 min
250
1 min
20 min
200
40 min
150
60 min
80 min
100
50
0
480
530
580
wavelength (nm)
630
680
Figure 13S. RO-diCN-PPV PL spectra after 0, 1, 20, 40, 60, and 80 minutes of illumination.
S9
300
0 min
PL intensity
250
1 min
2 min
200
3 min
150
4 min
10 min
100
20 min
30 min
50
0
370
420
470
520
Wavelength (nm)
570
Figure 14S. PL spectra of C8-diCN-PPV after illumination for different amount of time.
S10