Achiral CdSe quantum dots exhibit optical activity in the visible region upon post-synthetic ligand exchange with D- or L-cysteine

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1 This journal is The Royal Society of Chemistry Supporting Information for the manuscript entitled Achiral CdSe quantum dots exhibit optical activity in the visible region upon post-synthetic ligand exchange with D- or L-cysteine Urice Tohgha, Krisztina Varga and Milan Balaz* University of Wyoming, E. University Avenue, Laramie, WY 87, USA. Fax: ; Tel: ; mbalaz@uwyo.edu

2 This journal is The Royal Society of Chemistry Instrumentation. Circular Dichroism (CD). CD spectra were collected at C using a Jasco J-85 spectropolarimeter equipped with a single position Peltier temperature control system. Conditions were as follows: scanning speed nm/min, data pitch.5 nm, DIT s, and bandwidth nm. A quartz cuvette with a cm path length was used for all CD experiments. Each CD spectrum was an average of at least fifteen scans. UVvis absorption spectroscopy. UV-vis spectra were collected at C using a Jasco V- UV-vis double beam spectrophotometer equipped with a single position Peltier temperature control system. A quartz cuvette with a cm path length was used for all UV-vis experiments. Fluorescence spectroscopy. Photoluminescence measurements were done at C using a Varian fluorescence spectrophotometer using a scan rate of nm/min, excitation wavelength 5 nm, with 5. nm excitation and emission slits. A quartz cuvette with a cm path length was used. Fourier Transform Infrared spectroscopy (FTIR). FTIR spectra were acquired at C with a Bruker Platinum ATR single reflection diamond ATR module equipped with a one-finger clamp mechanism. X-Ray. Powder X-Ray diffraction data were collected on a Bruker Axs Smart Apex II CCD Diffractometer. Dynamic Light scattering. DLS data were collected on Brookhaven ZetaPals Particle Size Analyzer. Transition Electron Microscopy. TEM data were recorded on FEI Tecnai F kv Field emission transmission electron microscope. Solution NMR. Solution NMR spectra were acquired on Avance III Bruker spectrometer equipped with a multi-nuclear probe. Solid state NMR (ssnmr). D C cross-polarization (CP) solid-state NMR magic angle spinning (MAS) spectrum was collected on a MHz Avance III Bruker spectrometer equipped with a. mm E free triple resonance HCN probe. The solid state NMR sample was prepared by lyophilizing overnight the L-Cys- CdSe QDs in water. The powder sample was packed into mm Bruker MAS rotor. The MAS spinning rate was maintained at 8. khz, and the variable temperature set point was C. The width of the high power π/ radio frequency (RF) H pulse was. µs, the H- C CP period was. ms, and the spectrum was acquired for ms with 78 khz TPPM H decoupling. Data was processed by MestReNova.. with Hz exponential line broadening. Synthesis of TOPO/OA-CdSe QDs TOPO/OA-CdSe QDs were synthesized using a modified literature procedure (Fig. S). Trioctylphosphine selenide (TOPSe) was prepared by dissolving selenium (.9 g) in trioctylphosphine (TOP,. ml) and ODE (. ml) under nitrogen and sonication (light yellow solution). A stirred mixture of cadmium oxide (CdO,.75 g), trioctylphosphine oxide (TOPO,.7 g), oleic acid (OA,.9 ml) and octadecene (ODE, 7. ml) was heated to C under nitrogen. TOPSe solution ( ml) was swiftly injected into the hot CdO solution. The reaction was stopped by placing the reaction mixture in a chilled toluene. The CdSe QDs were purified by three cycles of precipitating with : absolute S

3 This journal is The Royal Society of Chemistry ethanol/toluene followed by centrifugation at 9, rpm for min. The concentrations of all CdSe QD samples were determined by using size dependent extinction coefficients. TOPO/OA-CdSe QDS Fig. S: Synthetic scheme for synthesis TOPO/OA-CdSe QDs. Synthesis of cysteine capped CdSe QDs by ligand exchange (Scheme S): D- or L-cysteine (. g) was dissolved in DI water (. ml). The ph of the solution was adjusted to with tetramethylammonium hydroxide (TMAH) followed by purging with nitrogen for 5 min. A solution of TOPO/OA-CdSe QDs in toluene (. ml,.5 mm) was added. The mixture was stirred at room temperature under nitrogen in the absence of light. The cysteine capped CdSe QDs transferred to the aqueous layer. The cysteine-cdse nanoparticles were precipitated with isopropanol/di water (:) and centrifuged at, rpm for 5 min. The process was repeated three times and the resulting cysteine-cdse were redissolved in DI water. TOPO/OA-CdSe Cysteine-CdSe Scheme S: Schematic ligand exchange on TOPO/OA-CdSe QDs with chiral cysteines (D- and L- cysteines). S

4 This journal is The Royal Society of Chemistry Size determination of synthesized Cys-CdSe QDs The sizes were determined by using empirical fitting functions developed by Peng et al. as shown below based on the first excitonic absorption wavelength. PENG EQUATION (UV-vis) CdSe: D = (. -9 ) λ ( ) λ + (. - ) λ (.77)λ + (.57) D (nm) is the size of CdSe QDs, λ (nm) is the wavelength of the first excitonic peak. Absorption wavelength = 58. nm (λ in equation above) Estimated size = (. -9 ) (58) ( ) (58) + (. - ) (58) (.77) (58) + (.57) =. nm SCHERRER EQUATION (XRD) Average size was calculated using the Scherrer equation: t =.9λ / (βcosθ) t: average size of the ordered (crystalline) domain β: line broadening at half the maximum intensity (FWHM) in radians θ: Bragg angle λ: X-ray wavelength from Mo source =.79 Å () Peak () Peak () Peak θ = θ = 8 θ = θ = θ = 9 θ = β=. β =.5 β =.7 β (in radians) =. β (in radians) =. β (in radians) =. t=.7 nm t=. nm t=. nm Average size of cysteine-cdse QDs from XRD =.5 nm S

5 Electronic Supplementary Material (ESI) for Chemical Communications This journal is The Royal Society of Chemistry 8.7 nm (%) 9.88 nm (8%).8 nm (9%) Fig. S: DLS results of L-cysteine-capped CdSe in water (Ø =. nm determined from absorption spectrum). Fig. S: Representative sets of TEM micrographs for the L-cysteine-capped CdSe (Ø =. nm determined from absorption spectrum). Fig. S: C solid state NMR spectra of L-cysteine-capped CdSe (Ø =. nm). Asterisk denotes the spinning side band of COO peak. S

6 This journal is The Royal Society of Chemistry L-cysteine-CdSe QDs (9. µm) L-cysteine-CdSe QDs (7. µm) L-cysteine-CdSe QDs (.5 µm) L-cysteine-CdSe QDs (5. µm) L-cysteine-Cdse QDs (. µm) L-cysteine-CdSe QDs (. µm) CD / mdeg 5 L-cysteine-CdSe QDs (9. µm) L-cysteine-CdSe QDs (7. µm) L-cysteine-CdSe QDs (.5 µm) L-cysteine-CdSe QDs (5. µm) L-cysteine-CdSe QDs (. µm) L-cysteine-CdSe QDs (. µm) Fig. S5: Changes in UV-vis absorption (left) and raw circular dichroism (CD, without solvent subtraction, right) spectra with decrease in concentration of L-cysteine-CdSe QDs (DI water). Ø =.5 nm.. CD. Normalized absorbance Normalized CD [Cys-CdSe] / µmol Fig. S: Changes in intensity of UV-vis absorption and CD spectra as a function of decreasing concentration of L-cysteine-CdSe QDs in DI water. Ø =.5 nm. CD / mdeg 8 - o C 8 o C 5 7 CD at o C / mdeg 8 - before heat-cool after st cycle after nd cycle CD / mdeg cycle 5 7 Fig. S7: Left: CD spectra of L-cysteine-capped CdSe (Ø =. nm) in DI water at C and 8 C. Right: Thermal cycle CD spectra of L-cysteine-capped CdSe (Ø =. nm). A solution of L-cysteine-CdSe was heated from C to 8 C then cooled back to C. The heating-cooling cycle was repeated twice consecutively. Inset: The 55 nm CD signal recorded at C nm as a function of heating-cooling cycle. S5

7 This journal is The Royal Society of Chemistry.9.9 L- cysteine-cdse QDs. TOPO/OA-CdSe QDs Transmittance / x Wavenumber / cm Transmittance / x wavenumber / cm - Fig. S8: FTIR spectrum of L-cysteine-CdSe (left) and TOPO/OA-CdSe (right). Ø =. nm. -CH=CH- HDO solvent -propanol solvent Hα Fig. S9: H NMR spectra ( MHz) of oleic acid-capped CdSe (Ø =. nm) in CDCl (top) and solution of L-cysteine-capped CdSe (Ø =. nm) in D O prepared by ligand exchange (bottom). Ligand exchange on L-cysteine-CdSe QDs with -dodecanethiol (DDT-CdSe synthesis): Dodecanethiol (DDT) capped CdSe QDs were synthesized by a phase transfer of cysteine-cdse QDs from water to toluene by replacing the cysteine ligands with DDT ligands. A aqueous solution of L-cysteine-CdSe QDs (. ml, µm) was placed in a round bottom flask and DDT (. ml) was added followed by addition of acetone (.5 ml). The flask was vigorously stirred while heated to 55 C. The phase transfer occurred within min as indicated by the color change of both phases. Toluene (. ml) was added to the flask and the organic layer containing the QDs was decanted and purified by mixing with water, shaking, then centrifuging at, rpm for 5 min. The process was repeated three times and the top toluene layer was collected by a syringe. S

8 This journal is The Royal Society of Chemistry. L-cysteine-Cdse QDs DDT-Cdse QDs nm Fig. S: Absorption spectra of DDT-CdSe (toluene, red curve) and L-cysteine-CdSe (DI water, black curve). Ø =.5 nm. 58nm D-cyst QDs exc 5nm L-cyst QDs exc 5nm 58nm TOPO/OA-CdSe QDs (exc 5nm) 8 9 Intensity Intensity Fig. S: Emission spectra of D-cysteine-CdSe (blue curve) and L-cysteine-CdSe (red curve) in DI water (left) and emission spectra of TOPO/OA-CdSe in toluene (right). Ø =.5 nm.... D-cysteine-CdSe QDs L-cysteine-CdSe QDs 5 57nm D-cysteine-CdSe QDs (exc 5nm) L-cysteine-CdSe QDs (exc 5nm) nm Intensity wavelength /nm Fig. S: Absorption (left) and emission (right) spectra of. nm D-cysteine-CdSe (blue curve) and L- cysteine-cdse (red curve) in DI water. S7

9 This journal is The Royal Society of Chemistry D-cysteine-CdSe QDs L-cysteine-CdSe QDs CD /mdeg Fig. S: CD spectra of. nm D-cysteine-CdSe (blue curve) and L-cysteine-CdSe (red curve) in DI water..5 D-cysteine-CdSe QDs L-cysteine-Cdse QDs 575 nm D-cysteine-CdSe QDs (exc 5nm) L-cysteine-CdSe QDs (exc 5nm). 558nm Intensity Fig. S: Absorption (left) and emission (right) spectra of. nm D-cysteine-CdSe (blue curve) and L- cysteine-cdse (red curve) in DI water. CD / mdeg D-cys-CdSe QDs L-cys-CdSe QDs 5 Fig. S5: CD spectra of. nm D-cysteine-CdSe (blue curve) and L-cysteine-CdSe (red curve) in DI water. References ) Dai, Q.; Li, D.; Chen, H.; Kan, S.; Li, H.; Gao, S.; Hou, Y.; Liu B.; Zou, G. J. Phys. Chem. B,,, ) Yu, W. W.; Qu, L.; Guo, W.; Peng, X. Chem. Mater., 5, 85-8 S8