Supporting information
Ligand exchange leads to efficient triplet energy transfer to
CdSe/ZnS Q-Dots in a Poly(N-vinylcarbazole) matrix
nanocomposite.
Adis Khetubol1, Sven Van Snick2, Antti Hassinen3, Eduard Fron1, Yuliar
Firdaus1 Lesley Pandey1, Charlotte David1, Karel Duerinckx1, Wim Dehaen2,
Zeger Hens3, Mark Van der Auweraer1a
1
KULeuven, Chemistry Department, Division of Molecular Imaging and Photonics, Laboratory of
Photochemistry and Spectroscopy, Celestijnenlaan 200F, B2404, 3001, Leuven, Belgium
2
KULeuven, Chemistry Department, Division of Molecular Design and Synthesis, Laboratory of
Organic Synthesis, Celestijnenlaan 200F, B2404, 3001, Leuven, Belgium
3
Ghent University, Physics and Chemistry of Nanostructures, Krijgslaan 281-S3, 9000, Gent,
Belgium
A Synthesis and characterization of the ligands
Methyl-6-bromohexanoate 1: This compound was prepared according to General Procedure
1 using 6-bromohexanoic acid (5000 mg, 25.6 mmol) and 100 mL methanol, yielding 1 as a
yellow oil (5262 mg, 98%). 1H NMR (300 MHz, CDCl3): δ 1.49 (qu, J = 3.96Hz, 2H), 1.66
(qu, J = 5.67 Hz, 2H), 1.88 (qu, J = 5.10 Hz, 2H), 2.33 (t, J = 5.49Hz, 2H), 3.41 (t, J =
5.07Hz, 2H), 3.67 (s, 3H).
Methyl-11-bromoundecanoate 2: This compound was prepared according to General
Procedure 1 using 11-bromoundecanoic acid (5000 mg, 18.9 mmol) and 100 mL methanol,
yielding 2 as a yellow oil (5232 mg, 99%). 1H NMR (300 MHz, CDCl3): δ 1.29 (bs, 10H),
a
To whom all correspondence should be addressed
Mark.vanderauweraer@chem.kuleuven.be
1.42 (bs, 2H), 1.62 (bs, 2H), 1.85 (qu, J = 6.39 Hz, 2H), 2.30 (t, J = 7.29 Hz, 2H), 3.40 (t, J =
7.32 Hz, 2H), 3.67 (s, 3H).
6-Carbazol-9-yl-hexanoic acid 3: This compound was prepared according to General
Procedure 2 using K2CO3 (3182 mg, 17.9 mmol), CH3CN (50 mL), carbazole (1000 mg, 5.9
mmol) and methyl-6-bromohexanoate 1 (1500 mg, 7.2 mmol), yielding 3 as a white solid
(563.8 mg, 33%). Mp: 113.1 °C. 1H NMR (300 MHz, CDCl3): δ 1.43 (qu, J = 8.28 Hz, 2H),
1.66 (qu, J = 7.38 Hz, 2H), 1.89 (qu, J = 7.38 Hz, 2H), 2.31 (t, J = 7.38 Hz, 2H), 4.29 (t, J =
7.11 Hz, 2H), 7.22 (m, 2H), 7.39 (m, 4H), 8.08 (d, J = 7.74 Hz, 2H). 13C NMR (75 MHz,
CDCl3): δ 24.4 (CH2), 26.7 (CH2), 28.6 (CH2), 33.8 (CH2), 42.7 (CH2), 108.5 (CH), 118.8
(CH), 120.4 (CH), 122.8 (C), 125.6 (CH), 140.3 (C), 179.6 (C). HREIMS: calcd for
C18H19NO2 [M]+, 281.14161; found 281.14188.
11- Carbazol-9-yl-undecanoic acid 4: This compound was prepared according to General
Procedure 2 using K2CO3 (1591 mg, 8.9 mmol), CH3CN (25 mL), carbazole (500 mg, 3.0
mmol) and methyl-11-bromoundecanoate 2 (1002 mg, 3.6 mmol), yielding 4 as a grey solid
(332.2 mg, 31%). Mp: 89.7 °C. 1H NMR (300 MHz, CDCl3): δ 1.24 (bs, 12H), 1.60 (m, 2H),
1.85 (m, 2H), 2.32 (t, J = 7.41 Hz, 2H), 4.28 (t, J = 7.17 Hz, 2H), 7.22 (m, 2H), 7.41 (m, 4H),
8.08 (d, J = 7.74 Hz, 2H). 13C NMR (75 MHz, CDCl3): δ 24.6 (CH2), 27.3 (CH2), 28.9 (CH2),
29.1 (CH2), 29.3 (CH2), 29.4 (CH2), 33.9 (CH2), 43.0 (CH2), 108.6 (CH), 118.7 (CH), 120.3
(CH), 122.7 (C), 125.5 (CH), 140.4 (C), 179.9 (C). HREIMS: calcd for C23H29NO2 [M]+,
351.2198; found 351.2182.
Mark.vanderauweraer@chem.kuleuven.be
B Fluorescence Quantum yields and decays of the ZnS:CdSe quantum dots
PL intensity (a.u.)
10000
QD solution in CB;
exc= 460 nm; em= 480 nm
QDs (LCA)
QDs (C6)
QDs (C11)
1000
100
10
20
30
40
50
60
70
80
90 100 110
Decay time (ns)
Fig. S1 Fluorescence decay of CdSe/ZnS QDs in CB solutions. The excitation and recorded
emission were 460 and 480 nm respectively.
The fluorescence decays were analyzed as a sum of three exponentials (eq S1). As the
exact origin of this non-exponential decay is not known and outside the scope of this
manuscript no direct physical meaning should be given to decay times and amplitudes.
I t   A1 exp   t   A2 exp   t   A3 exp   t 
 1 
 2 
 3
eq S1
Those parameters are just used to calculate the average decay time (eq S2)
  A1 1  A2 2  A3 3
eq S2
Table S1: Fluorescence decay times and amplitudes of the CdSe/ZnS QDs in CB solution for
the decays shown in Figure S1.
Samples
A1 (%)
A2 (%)
A3 (%)
τ1 (ns)
τ2 (ns)
QDs (LCA)
23.4
29.3
QDs (C6)
16.0
29.7
47.3
2.1
54.3
2.1
Mark.vanderauweraer@chem.kuleuven.be
τ3 (ns)
<> (ns)
8.5
20.8
12.8
9.5
21.4
14.8
QDs (C11)
18.0
29.5
52.5
2.1
8.8
22.1
14.7
The average decay times show that replacing LCA by C6 or C11 does not lead to
fluorescence quenching due to hole injection from the valence band of the excited QD into
the HOMO of PVK. The small increase in average decay time could be due to stronger
interaction of C6 and C11 with the ZnS surface leading to a reduction of defect sites.
Assuming an identical radiative decay rate for the QDs the combination of the average decay
times with the fluorescence quantum yield of 0.55±0.05 for the LCA capped QDs yields a
fluorescence quantum yield of 0.63±0.06 and 0.62±0.06 for C6 and C11 capped QDs.
We will now calculate the fluorescence quantum yield for triplet transfer for QDs
covered with C11 ligands. Upon excitation at 330 nm the fluorescence quantum yield of the


carbazole emission of QDs covered with C11 ligands amounts to  f   0f 1   sENT where
 0f and  SENT are respectively the fluorescence quantum yield of the unquenched ligand and
the quantum yield of singlet energy transfer to the QDs. With  0f  0.45 ±0.05 and  SENT =
0.108, as determined from the fluorescence decays,  f = 0.40±0.04. The fluorescence
quantum yield of the QD emission upon excitation at 330 nm,  330
f ,QD , is that of the carbazole
emission of the QDs covered with C11 ligands multiplied by the ratio between the area under
the emission band of the QDs and that of carbazole which amounts to 1.2±0.2. This gives a
fluorescence quantum yield,  330
f ,QD , of 0.49±0.15 for the QD emission. The fluorescence
quantum yield of the QD emission due to singlet energy transfer,  Sf ,QD , is given by
440
 Sf ,QD   SENT  440
f ,QD where  f ,QD is the fluorescence quantum yield of the QDs upon direct
excitation at 440 nm and which amounts to 0.62 ±0.15. Hence  Sf ,QD amounts to
0.067±0.007. Tf ,QD , the fluorescence quantum yield of the QDs upon excitation at 330 nm
Mark.vanderauweraer@chem.kuleuven.be
S
due to triplet energy transfer, amounts then to Tf ,QD  330
f ,QD   f ,QD or 0.49±0.15T
0.067±0.007=0.42±0.16. This corresponds to Tf ,QD   ISC TENT  440
f ,QD where  ISC and  ENT
correspond to the quantum yield of intersystem crossing in the C11 ligand on the QD and the
quantum yield for triplet energy transfer respectively.  ISC   0ISC 1   sENT  where  0ISC
corresponds to the quantum yield for intersystem crossing in free C11 ligands. Assuming that
in the free ligands the excited state of carbazoles decays either by fluorescence or intersystem
crossing1 ,  0ISC  1   0f . With  0f  0.45  0.05  0ISC amounts to 0.55±0.05. Hence

T
ENT

Tf ,QD
 440
f ,QD  ISC
or 1.4±0.5.
PL intensity (a.u.)
10000
QDs (C11) in solution
doped PVK film with 30% QDs(C11)
doped polystyrene film with 30% QDs(C11)
exc = 440 nm; em= 490 nm
1000
10
20
30
40
50
60
70
80
90
Decay time (ns)
Figure S2: Fluorescence decays of C11 capped CdSe/ZnS QDs in CB solution and PVK and
polystyrene films. The excitation and recorded emission were 440 and 490 nm respectively.
Mark.vanderauweraer@chem.kuleuven.be
Table S2: Fluorescence decay times and amplitudes of the fluorescence decays of C11
capped CdSe/ZnS QDs in Figure S2.
Samples
A1 (%)
A2 (%)
A3 (%)
τ1 (ns)
τ2 (ns)
τ3 (ns)
< > ns
QDs (C11) solution
20.4
34.3
45.3
1.5
9.6
20.0
12.7
Doped PVK film
32.1
47.8
20.0
1.0
6.3
19.0
7.1
Doped polystyrene 18.0
29.5
52.5
2.2
7.5
21.5
7.1
film
Table S2: Fluorescence decay times and amplitudes of the fluorescence decays of C11
capped CdSe/ZnS QDs in Figure S2.
The fluorescence decays were analyzed as a sum of three exponentials (eq S1). As the
exact origin of this non-exponential decay is not known and outside the scope of this
manuscript no direct physical meaning should be given to decay times and amplitudes. Those
parameters are just used to calculate the average decay time (eq S2). Assuming an identical
radiative decay rate for the QDs the combination of the average decay times with the
fluorescence quantum yield of 0.55±0.05 for the LCA capped QDs in CB yields a
fluorescence quantum yield of 0.54±0.05, 0.31±0.03 and 0.30±0.03 for C11 capped QDs in
CB, PVK and polystyrene films. Although the average fluorescence decay time and quantum
yield are decreased in PVK compared to a solution in CB one should note that a similar
decrease was found for C11 capped QDs in a polystyrene matrix, hence this decrease is not
due to hole injection from the valence band of the excited QD into the HOMO of PVK. It
remains possible that this effect is due to a loss of ligands upon formation of the polymer
film. The small difference in average fluorescence decay time and quantum yield for QDs
used in table S1 and S2 reflects the batch to batch fluctuations of the obtained QDs.
Mark.vanderauweraer@chem.kuleuven.be
We will now calculate the fluorescence quantum yield for triplet transfer in a PVK
film with a loading of 10 wt% of QDs with C11 ligands. Upon excitation at 330 the
fluorescence quantum yields of the carbazole emission of the PVK film loaded with QDs


covered with C11 ligands amounts to  f   0f 1   sENT . With  0f  0.16 ±0.03 and  SENT
= 0, as determined from the fluorescence decays,  f = 0.16±0.03. The fluorescence
quantum yield of the of the QD emission upon excitation at 330 nm,  330
f ,QD , is that of the
carbazole emission in the PVK film with QDs covered with C11 ligands multiplied by the
ratio between the area under the emission band of the QD and that of carbazole which
amounts to 0.28±0.05. This gives a fluorescence quantum yield  330
f ,QD of 0.045±0.018 for the
QD emission. The fluorescence quantum of the QD emission due to singlet energy
440
transfer,  Sf ,QD , is given by  Sf ,QD   SENT  440
f ,QD where  f ,QD is then fluorescence quantum
yield of the QDs upon direct excitation at 440 nm and which amounts to 0.31 ±0.06.  Sf ,QD
amounts to zero as  SENT = 0. The fluorescence quantum yield of the QDs upon excitation at
S
330 nm due to triplet energy transfer amounts then to Tf ,QD  330
f ,QD   f ,QD or 0.045±0.018.
0
s
This corresponds to Tf ,QD   ISC TENT  440
f ,QD . As  ISC   ISC 1   ENT  and assuming that in
the excited state of carbazoles in pristine PVK film decays either by fluorescence or
intersystem crossing,1  0ISC  1   0f . With  0f  0.16  0.03 ,  0ISC amounts to 0.84±0.03.
Hence 
T
ENT

 Tf ,QD
 440
f ,QD  isc
or 0.17±0.09.
Mark.vanderauweraer@chem.kuleuven.be
1. Barltrop, J.A.; Coyle, J.D. Principle of Photochemistry, Wiley, Chichester Eng. and
Newyork, 1978 / Barltrop, J.A.; Coyle, J.D. Excited States in Organic Chemistry. Wiley,
London and Newyork, 1975.
Mark.vanderauweraer@chem.kuleuven.be