CdSe/CdS Conjugated Polymer Core Shell Hybrid Nanoparticles by a Grafting From Approach

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1 Supporting information CdSe/CdS Conjugated Polymer Core Shell Hybrid Nanoparticles by a Grafting From Approach Tjaard de Roo, Steffen Huber, and Stefan Mecking* Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Konstanz, Germany Materials: Deionized water was distilled under a nitrogen atmosphere and THF and toluene were distilled from sodium/benzophenone ketyl under a nitrogen atmosphere. CdO (99.998%), dodecylphosphonic acid (95%) and Se (granules, %) were purchased from ABCR. CsF (99%) was purchased from Acros. Oleic acid (technical grade, 90%), oleyl amine (technical grade, 70%), 1-octadecene (technical grade, 90%) trioctylphosphine (technical grade, 90%), sulfur (99.999%, Riedel de Haën) and 18 crown 6 (99%) were purchased from Sigma Aldrich. (4- iodophenyl)phosphonic acid was purchased from SiKÉMIA. (4-bromophenyl)phosphonic acid was provided by M. Krumm and was synthesized according to literature. 1,2 P t Bu 3 was provided by MCAT Konstanz. All chemicals were used as received unless stated otherwise. [Pd(P t Bu 3 ) 2 ] was synthesized according to a literature procedure. 3 2-(5-bromo-3-(2-ethylhexyl)thiophen-2-yl)- 4,4,5,5-tetramethyl-1,3,2-dioxaborolane was synthesized similar to a literature known procedure. 4 Methods: All manipulations of air- and/or water sensitive compounds were carried out under inert atmosphere using standard glove box and Schlenk techniques. Glassware were dried at 80 C for at least 24 h. Ensemble emission spectra and quantum yields were measured using a Hamamatsu Absolute PL Quantum Yield Measurement System C equipped with an integrating sphere. TEM images were obtained on a JEOL JEM2200FS (200 kv). Gel permeation chromatography (GPC) was carried out on a Polymer Laboratories PL-GPC 50 with two PLgel 5 μm MIXED-C columns in THF at 50 C with RI detection against polystyrene standards. S1

2 Absorption spectra were recorded on a Varian Cary 100 scan spectrometer. NMR spectra were recorded on a Varian Unity INOVA 400 and on a Bruker Avance 400 spectrometer. 1 H NMR chemical shifts were referenced to the solvent signal. MALDI-TOF mass spectra were recorded in CHCl 3 on a Bruker Microflex MALDI-TOF with alpha-cyano-4-hydroxycinnamic acid as matrix. Synthesis of 2-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2- dioxaborolane: 2-(7-Bromo-9,9-dioctyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was synthesized according to a slightly modified literature procedure. 5 Instead of adding tri-iso-propyl borate and pinacol in a second step, iso-propoxyboronic acid pinacol ester was used, directly leading to the desired boronic acid ester. Synthesis of CdSe quantum dots: CdSe quantum dots were synthesized according to a previously reported procedure. 6 A solution of 0.5 M Cd(oleate) 2 in oleic acid was prepared by dissolving 145 mg of CdO in 2 ml of oleic acid at 170 C. After complete dissolution, the temperature was decreased to 80 C and 3 ml of 1- octadecene and 1 g of dodecylphosphonic acid were added. The mixture was degassed for two hours under vacuum (ca. 0.1 mbar). Simultaneously, a 1 M solution of trioctylphosphineselenide (TOPSe) was prepared by dissolving 118 mg of selenium in 1.5 ml of trioctylphosphine in an ultrasonic bath. After addition of 1.5 ml of oleyl amine, the solution was degassed under vacuum (ca. 0.1 mbar) for two hours at 70 C. For the synthesis of CdSe QDs, the degassed Cd-precursor was heated to 240 C. After quickly injecting the Se-precursor and stirring of the solution for 7 minutes, the solution was cooled down to 50 C. 40 ml of ethanol were added to precipitate the QDs followed by centrifugation for 5 minutes at 2500 g. The obtained QD pellet was suspended in 10 ml of hexane and centrifuged again at 2500 g for 5 minutes. The supernatant containing the QDs was removed from the pellet consisting of excess dodecylphosphonic acid and the QDs were precipitated by adding 40 ml of ethanol. After another centrifugation step and removal of the supernatant solution, the QD pellet was dispersed in 10 ml of toluene, resulting in a concentration of approximately 1*10-4 mmol/ml. The concentration of the CdSe QDs was determined by the method published by Yu et al. 7 S2

3 Figure S1. TEM image of CdSe quantum dots. The inset shows the photoluminescence spectrum. Synthesis of CdSe/CdS core-shell quantum dots: A 0.1 M solution of Cd(oleate) in oleic acid and octadecene was prepared by dissolving 435 mg of CdO in 6 ml of oleic acid at 170 C and addition of 24 ml of octadecene. A 0.1 M S- precursor was prepared by dissolving 96 mg of S in 30 ml of octadecene at 70 C. Both precursor solutions were degassed for 2 hours at 0.1 mbar at 70 C. 9.0 ml of the QD core dispersion, 12 ml of oleyl amine and 24 ml of octadecene were added to a 500 ml round bottom flask. By applying vacuum, the toluene was removed and the QD core solution was additionally degassed for 1 h at 70 C at 0.1 mbar. For the shell synthesis, 1.68 ml of the Cdprecursor were added to the QD core solution at 70 C and the mixture was heated to 240 C. After 10 minutes at this temperature, 1.68 ml of the S-precursor were added drop wise. In 10- minute intervals, 2.76 ml Cd, 2.76 ml S, 3.90 ml Cd, 3.90 ml S, 5.22 ml Cd, 5.22 ml S, 6.78 ml Cd, 6.78 ml S and 8.52 ml Cd precursor solutions were added drop wise by a syringe pump. After the last addition, the solution was stirred at 240 C for 20 minutes and then cooled down to room temperature in a water bath. By addition of 100 ml of ethanol, the core/shell QDs were S3

4 precipitated and centrifuged. The supernatant solution was discarded and the QD pellet was dispersed in 10 ml of toluene. The concentration of the CdSe/CdS core-shell QDs was derived from the amount of CdSe cores used in the shell synthesis, assuming that all the cores are transferred into core-shell QDs, leading to a concentration of 9*10-5 mmol/ml. Figure S2. TEM image of CdSe/CdS quantum dots. The inset shows the photoluminescence spectrum. S4

5 General procedure for the functionalization of CdSe/CdS core-shell quantum dots with (4- halophenyl)phosphonic acid: For the functionalization of core-shell QDs with (4-bromophenyl)phosphonic acid or (4- iodophenyl)phosphonic acid, 1 ml of the oleyl amine functionalized QDs were precipitated from toluene by addition of ethanol and centrifuged. The QDs were then redispersed in THF and again precipitated. These last steps were repeated until the QDs were not redispersible anymore in THF. To the QD pellet, 2 ml of THF and 8 mg of (4-bromophenyl)phosphonic acid or 10 mg of (4-iodophenyl)phosphonic acid were added, respectively, resulting in a good dispersibility of the QDs after a few seconds in an ultrasonic bath. The amount of phosphonic acid that can bind to the QD surface was determined by NMR. By adding successive amounts of phosphonic acid to the QDs (precipitated several times) and recording 31 P NMR spectra between the additions, the amount of phosphonic acid that can bind to the QD surface was determined. For 1 ml of QD dispersion, the addition of 10 mg of (4-iodophenyl)phosphonic acid still results in a very broad 31 P NMR signal between 10 and 14 ppm, indicating that all of the phosphonic acid is bound to the QDs. By further increasing the amount of phosphonic acid in small portions, a sharp 31 P NMR signal on top of the broad signal is observed, indicating the presence of nonbound phosphonic acid. This also results in a sharp signal at 28 ppm, which can be assigned to dodecylphosphonic acid. The latter is used during the synthesis of the CdSe cores and is relocated at the surface of the shell. Considering the QD concentration, 10 mg of (4-iodophenyl)phosphonic acid per 1 ml of QD dispersion are equivalent to approximately 350 (4-iodophenyl)phosphonic acid ligands per single nanocrystal. S5

6 Figure S3. Bottom red 31 P- NMR spectrum: (4-iodophenyl)phosphonic acid in THF-d 8. Center green 31 P NMR spectrum: CdSe/CdS quantum dots functionalized with 10 mg of (4- iodophenyl)phosphonic acid (around 350 ligands per QD). Top blue 31 P NMR spectrum: Functionalized saturated QDs with additional 46 mg of (4-iodophenyl)phosphonic acid. The sharp signal at 13 ppm can be assigned to nonbound (4-iodophenyl)phosphonic acid and the sharp signal at 28 ppm to dodecylphosphonic acid that was displaced from the QD surface. Synthesis of the surface bound initiator complex: 1 ml of a QD dispersion functionalized with (4-bromophenyl)phosphonic acid or (4- iodophenyl)phosphonic acid in toluene or in THF was degassed by applying three freeze-pumpthaw cycles. Afterwards, 0.75 equiv of [Pd(P t Bu 3 ) 2 ] (vs (4-bromophenyl)phosphonic acid) or 0.75 equiv of [Pd(dba) 2 ] with 1.5 equiv of P t Bu 3 (vs (4-iodophenyl)phosphonic acid) were added and the mixture was heated up to 75 C for 4.5 hours (bromo aryl) or to 50 C for 2 hours (iodo aryl), respectively. S6

7 Polymerization procedure: In a 100 ml Schlenk tube, 100 mg (0.17 mmol, 1 equiv) of monomer, 102 mg (0.17 mmol, 4 equiv) of CsF and 355 mg (1.346 mmol, 8 equiv) of 18 crown 6 were dissolved in 25 ml of THF and 1 ml of water. After degassing the solution by 3 freeze-pump-thaw cycles, the QD/initiator dispersion was quickly added. After 1 hour at 0 C (polyfluorene) or -20 C (polythiophene), the polymerization was quenched by addition of ml of methanol. The hybrid particles were collected by centrifugation and the pellet was redispersed in 10 ml of toluene. For end-capping experiments, the polymerization was quenched after 1 hour polymerization time by the addition of 20 equiv of 2-[3,5-bis(trifluoromethyl)phenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (vs 1 equiv of [Pd(P t Bu 3 ) 2 ]), stirred for another 30 minutes at 0 C, followed by the addition of methanol to precipitate the hybrid particles. Sample preparation for GPC and MALDI-TOF MS analysis: In order to analyze the polymer formed in the surface initiated polymerization, the hybrid particles were dispersed in toluene and the CdSe/CdS quantum dots were destroyed by addition of concentrated HCl (extreme caution, H 2 Se, H 2 S and HF is formed). After stirring for one hour, water was added and the ph was adjusted to ph~6 with a saturated K 2 CO 3 solution. The polymer was extracted from the aqueous phase with chloroform. After removal of the solvent, the polymer was dissolved in 1 ml of chloroform and precipitated with 4 ml of methanol. After centrifugation, the supernatant was discarded and the isolated polymer was dried under reduced pressure. S7

8 dw_dlogm Mn: PDI: Mw Figure S4. GPC trace (UV-detection at 375 nm) of polyfluorene isolated after treating the hybrid particle dispersion with concentrated HCl and thereby stripping off the polymer. Figure S5. MALDI-TOF mass spectrum of polymer obtained after polymerizing with the (4- bromophenyl)phosphonic acid@qds/[pd(p t Bu 3 ) 2 ] system from the supernatant after removing the hybrid particles by centrifugation. The identified polyfluorene species are listed on the right. S8

9 Figure S6. Bottom MALDI-TOF mass spectrum: Polyfluorene isolated after quenching the polymerization with 20 equiv of 2-[3,5-bis(trifluoromethyl)phenyl]-4,4,5,5-tetramethyl-1,3,2- dioxaborolane (vs 1 equiv of [Pd(P t Bu 3 ) 2 ]), collecting the nanocrystals by centrifugation and destroying the latter by addition of concentrated hydrochloric acid. The main species carries a phenylphosphonic acid initiating end-group and a 3,5-bis(trifluoromethyl)phenyl terminating end-group. Only minor amounts of phenylphosphonic acid functionalized polymer terminated with a proton is observed, indicating that the chain ends were still active as the end-capper was introduced. Top MALDI-TOF mass spectrum: Polyfluorene isolated from the supernatant after centrifuging off the nanocrystals. The identified polyfluorene species are depicted on the right. S9

10 Intensity Figure S7. 19 F NMR spectrum of isolated polyfluorene after quenching the polymerization with 20 equiv (vs [Pd(P t Bu 3 ) 2 ]) of 2-[3,5-bis(trifluoromethyl)phenyl]-4,4,5,5-tetramethyl-1,3,2- dioxaborolane, centrifuging off the nano crystals and destroying the latter by addition of concentrated hydrochloric acid Wavelength [nm] Figure S8. Red line: Photoluminescence spectrum of a highly diluted CdSe/CdS/polyfluorene hybrid particle dispersion in toluene (λ exc : 400 nm). Black spectrum: Photoluminescence spectrum of the same sample after addition of 5 µl of concentrated HCl and stirring for 2 hours. S10

11 A strong increase in polyfluorene emission intensity is observed. This indicates an energy transfer from the surface bound polyfluorene to the inorganic nanocrystal. Figure S9. MALDI-TOF mass spectrum of isolated polyfluorene obtained after quenching the polymerization with methanol, collecting the hybrid particles by centrifugation and destroying the inorganic core by addition of concentrated HCl. The polymerization was initiated from (4- iodophenyl)phosphonic acid functionalized QDs with [Pd(dba) 2 ] and P t Bu 3. S11

12 dw_dlogm Figure S10. MALDI-TOF mass spectrum of isolated polythiophene after initiation by (4- iodophenyl)phosphonic 2 ]/P t Bu 3 and quenching with methanol after 1 hour at -20 C, centrifuging off the nanocrystals and destroying the latter with hydrochloric acid. The identified polythiophene species with varying end-groups are depicted on the right. Phenylphosphonic acid terminated polythiophene is not observed Mn: 4500 PDI: Mw 10 4 Figure S11. GPC trace of isolated polythiophene that was obtained after quenching the polymerization with methanol, centrifuging off the nanocrystals and destroying the latter with hydrochloric acid. S12

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14 Reaction of 2-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2- dioxaborolane with [Pd(P t Bu 3 ) 2 ] monitored by 31 P NMR: Figure S12. Reaction of 2-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2- dioxaborolane with [Pd(P t Bu 3 ) 2 ] at 40 C in THF-d 8 monitored by 31 P NMR. The reaction toward the oxidative addition product is very slow, however, also very selective. The sharp signal at 64 ppm can be assigned to free P t Bu 3 and the broad signal at 63 ppm to the formed complex. S14

15 Figure S13. Room temperature 1 H 31 P-HMBC spectrum of the reaction of 2-(7-bromo-9,9-dioctyl- 9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane with [Pd(P t Bu 3 ) 2 ] after 16 hours at 40 C. The broad 31 P NMR signal at 63 ppm can be assigned to the three coordinate complex formed by oxidative addition of [Pd(P t Bu 3 ) 2 ] into the C-Br bond of the monomer. The coupling of the phosphine ligand to the aromatic region can be clearly observed. S15

16 Reaction of 2-(5-bromo-3-(2-ethylhexyl)thiophen-2-yl)-4,4,5,5-tetramethyl-1,3,2- dioxaborolane with [Pd(P t Bu 3 ) 2 ] monitored by 31 P NMR: Figure S14. Reaction of 2-(5-bromo-3-(2-ethylhexyl)thiophen-2-yl)-4,4,5,5-tetramethyl-1,3,2- dioxaborolane with [Pd(P t Bu 3 ) 2 ] in THF-d 8 at 40 C monitored by 31 P NMR. During the reaction, the formed complex precipitates as a yellow solid. The signal at 64 ppm can be assigned to free P t Bu 3. S16

17 Figure S15. 1 H NMR spectrum of the yellow precipitate formed during the reaction of 2-(5- bromo-3-(2-ethylhexyl)thiophen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane with [Pd(P t Bu 3 ) 2 ], measured in benzene. The integrals are in agreement with the integrals expected for the complex formed by oxidative addition of [Pd(P t Bu 3 ) 2 ] into the C-Br bond of the thiophene monomer. S17

18 TEM analysis of hybrid particles and physical mixtures of QDs and polymer: Figure S16. TEM image of a physical mixture of CdSe/CdS and benzyl alcohol terminated polyfluorene. TEM image a physical mixture of polyfluorene and QDs, comparable to the samples generated by surface initiated polymerizations. The mixture was prepared by polymerizing 2-(7-bromo-9,9- dioctyl-9h-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane with the initiator complex [(bromo){4 [(tetrahydro 2H pyran 2 yloxy)methyl]phenyl}(tri tert butylphosphine) palladium] in the presence of (4-bromophenyl)phosphonic acid functionalized CdSe/CdS quantum dots. The reaction conditions are similar to the conditions used for surface initiated polymerizations except that an external initiator was added instead of [Pd(P t Bu 3 ) 2 ] or [Pd(dba) 2 /P t Bu 3 ]. Phase separation of the polymer and the nanocrystals and agglomeration of the latter is observed. S18

19 Figure S17. TEM image of CdSe/CdS/polyfluorene hybrid particles. Large interparticle distance between nanocrystals can be observed. Nanocrystals are randomly distributed over the TEM grid, indicating a good stabilization by the polymer ligands. Phase separation and agglomeration of the nanocrystals is prevented by the direct binding of the conjugated polymer to the nanocrystal surface. S19

20 Figure S18. TEM image of a physical mixture of CdSe/CdS quantum dots and nonfunctionalized polythiophene. TEM image of a physical mixture of CdSe/CdS/polythiophene. The surface initiated polymerization with the (4-iodophenyl)phosphonic acid@qds/[pd(dba) 2 ]/P t Bu 3 system only yields nonfunctionalized polythiophene. The nanocrystals agglomerate during TEM sample preparation due to a phase separation between the polymer and the nanocrystals. (1) Kalek, M.; Jezowska, M.; Stawinski, J. Adv. Synth. Catal. 2009, 351, (2) McKenna, C. E.; Higa, M. T.; Cheung, N. H.; McKenna, M.-C. Tetrahedron Lett. 1977, 18, (3) Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, (4) Jayakannan, M.; Lou, X.; van Dongen, J. L. J.; Janssen, R. A. J. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, (5) Zhang, X.; Tian, H.; Liu, Q.; Wang, L.; Geng, Y.; Wang, F. J. Org. Chem. 2006, 71, (6) Negele, C.; Haase, J.; Budweg, A.; Leitenstorfer, A.; Mecking, S. Macromol. Rapid Commun. 2013, 34, (7) Yu, W. W.; Qu, L.; Guo, W.; Peng, X. Chem. Mater. 2003, 15, S20