Fullerene SAMs

Electronic Supplementary Material (ESI) for Chemical Science. This journal is © The Royal Society of Chemistry 2017

Supporting information for: Rectification of Current Responds to Incorporation of Fullerenes into Mixed-Monolayers of Alkanethiolates in Tunneling Junctions Li Qiu, Yanxi Zhang, Theodorus L. Krijger, Xinkai Qiu, Patrick van ’t Hof, Jan C. Hummelen, and Ryan C. Chiechi∗ Stratingh Institute for Chemistry & Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands E-mail: [email protected]

S1

Contents 1 Experimental details

S2

1.1

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

S2

1.2

Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

S4

2 Electrical Measurements

S7

2.1

Histogram of log |R| and current density . . . . . . . . . . . . . . . . . . . .

S7

2.2

Plots of log |R|, log |J| and log |I| versus V . . . . . . . . . . . . . . . . . . .

S8

3 Characterization

S8

3.1

Contact angle measurement . . . . . . . . . . . . . . . . . . . . . . . . . . .

S8

3.2

XPS thickness measurement . . . . . . . . . . . . . . . . . . . . . . . . . . .

S8

3.3

Estimation of LUPS of FSC11 . . . . . . . . . . . . . . . . . . . . . . . . . S11

3.4

NMR spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S18

References

1 1.1

S22

Experimental details General

General: Chemicals including 11-bromoundec-1-ene, 4-hydroxybenzaldehyde, thioacetic acid, 1-decanethiol (SC10) were obtained from Sigma-Aldrich and used as received with the exception of SC10 which was purified by column chromatography (silica, hexane). The C60 used for the syntheses was 99.5 % (purchased from Solenne BV, Groningen, The Netherlands). All compounds were stored in nitrogen-flushed vials and in the dark. The Au substrates used in this work are made by mechanic Template Stripping (mTS) described in detail elsewhere. S1 In our case, we deposited 200 nm of Ag and 100 nm of Au (99.99%), respectively, by thermal vacuum deposition onto a 300 Silicon wafer (with no-adhesion layer). S2

Using UV-curable Optical Adhesive (OA) Norland 61, we glued 1 cm2 glass chips on the metal surfaces. The mTS procedure provides ultra flat smooth surfaces, which allows selfassembly process to achieve higher yields of working junctions.

Analytical TLC was performed on Merck silica gel 60/kieselguhr F254 and visualization was accomplished by UV light. Column chromatography was performed using silica gel (SiliaFlash P60 Type R12030B, 230-400 mesh). 1 H-NMR and

13

C-NMR were performed on a

Varian Unity Plus (400 MHz) instrument at 25 ◦C, using tetramethylsilane (TMS) as an internal standard. NMR shifts are reported in ppm, relative to the residual protonated solvent signals of CDCl3 (δ = 7.26 ppm) or at the carbon absorption in CDCl3 (δ = 77.0 ppm), and multiplicities are denoted as: s = singlet, d = doublet, t = triplet and m = multiplet. IR measurements were performed on a Nicolet iS50 FT-IR spectrometer. UV-vis absorption spectra were measured with a Jenway 6715 spectrophotometer. High Resolution Mass Spectroscopy (HRMS) was performed on a JEOL JMS 600 spectrometer. Contact Angles (CA) were measured under ambient conditions on a SCA20 Dataphysics instrument with software version 3.60.2. Equilibrium contact angles were obtained by applying 1 µL water droplets on SAMs using the sessile drop method. The contact angle was measured at three different locations on each surface and the results were averaged. XPS measurements were performed using a VG Microtech spectrometer with a hemispherical electron analyzer, and a Mg Kα (1253.6 eV) X-ray source. CP-AFM I-V measurements were performed on a Bruker AFM Multimode MMAFM-2 equipped with a Peak Force TUNA Application Module (Bruker). The SAMs were contacted with an Au-coated silicon nitride tip with a nominal radius of 30 nm (NPG-10, Bruker, tip A: resonant frequency 65 kHz, spring constant: 0.35 N/m; tip B: resonant frequency: 23 kHz, spring constant: 0.12 N/m; tip D: resonant frequency: 18 kHz, spring constant: 0.06 N/m) in TUNA mode with loading force of 1.4 nN (tip A), 0.48 nN (tip B) and 0.24 nN (tip D), respectively. The AFM tip was grounded and for loading force of 1.4 nN, the sample was biased from -1.5 V to +1.5 V and from +1.5 V

S3

to -1.5 V (while for loading force of 0.48 nN and 0.24 nN, the sample was biased from -2 V to +2 V and from +2 V to -2 V) to record the I-V curve (512 points per trace were taken): a max of 30 trace/re-trace cycles per junction were performed. After every junction, the tip was withdrawn and moved to a different spot, and engaged again for a total of 39 (for 1.4 nN of loading force), 20 (for 0.48 nN of loading force) and 10 (for 0.24 nN of loading force) junctions per sample analyzed. Between different samples a new tip was used. The data were analyzed with the same software used for EGaIn using the current I instead of the current density J. The obtained log|I|(V ) plots and log|R|(V ) are shown in Figure S6.

1.2

Synthesis

The synthesis of compound FSC11 is straightforward, as shown in Scheme S1. By treating the commercially available 4-hydroxybenzaldehyde with 11-bromo-1-undecene under basic conditions, 4-(10-Undecenyloxy)benzaldehyde could be obtained in good yield, which was then converted to the thioester 4-(11-thioacetoxyundecyl)benzaldehyde through a free radical-mediated nucleophilic addition(azo-bis-isobutyronitrile (AIBN) as the radical initiator). The Prato reaction S2 then gave the corresponding FSC11-Ac, which experienced dibutyltin oxide-mediated transesterification with methanol to give the target C60-thiol FSC11. S3 New compounds were all fully characterized by means of HRMS, NMR and IR.

4-(10-Undecenyloxy)benzaldehyde. The procedure for the synthesis of this compound was taken from the literature. S4 11-Bromo-1-undecene (4.38 mL, 4.66 g, 20 mmol), 4hydroxybenzaldehyde (2.44g, 20 mmol), tetrabutylammonium iodide (catalytic amount, 0.20 g) and potassium carbonate (13.80 g, 100 mmol) were introduced into acetone (100 mL). After refluxing for 6 h, the mixture was allowed to cool to room temperature and the solids were filtered off. The filtrate was concentrated in vacuo and the crude product was purified by column chromatography (ethyl acetate:hexane = 1:9) to give 5g product as a colorless oil S4

O

O Br H OH

n

9

SH, AIBN O

Bu4NI, K2CO3

O

O

H 9

H

O

o

O

Toluene, 25 C, 6 h

9

S

Acetone, Reflux, 6 h

N

Sarcosine, C60

N

OC11H22SAc

OC11H22SH

Dibutyltin oxide Chlorobenzene/MeOH

Chlorobenzene, 100 oC, 24 h

Reflux, 24 h FSC11-Ac

FSC11

Figure S1: Synthetic route of FSC11 (90%).

4-(11-Thioacetoxyundecyl)benzaldehyde. The procedure for the synthesis of this compound was taken but lightly improved from the literature. S5 4-(10-Undecenyloxy)benzaldehyde (2.74 g; 10 mmol), thioacetic acid (7.13 mL; 100 mmol), and azo-bis-isobutyronitrile (AIBN, 30 mg; 0.18 mmol) were dissolved in 40 mL of toluene. The mixture was degassed with a stream of N2 and then stirred at room temperature for 8 h. The reaction was quenched with 5% aqueous NaHCO3 and extracted three times with ethyl acetate. The combined organic layers were washed with 5% aqueous NaHCO3 and then brine and dried over MgSO4 . Upon filtration and removal of the solvent under reduced pressure, the yellow solid residue was then purified by column chromatography on silica eluting with a gradient of pure toluene to pure chloroform. The crude product obtained was recrystallized from methanol to afford 1.41 g (42%) of the title aldehyde as a white powder.

FSC11-Ac. An oven-dried three-necked, 500 mL round-bottom flask was charged with C60 S5

(1.44 g, 2 mmol), 4-(11-thioacetoxyundecyl)benzaldehyde (700 mg, 2 mmol), sarcosine (720 mg, 8 mmol) and chlorobenzene (200 mL). The reaction mixture was stirred under N2 at 100 ◦C for 24 h. The mixture was concentrated in vacuo to 15 mL, and the crude residue was purified by column chromatography (Silica gel; CS2 followed by toluene) to afford the pure compound as a brown solid. The product was redissolved in 7 mL of chlorobenzene, precipitated with MeOH, washed repeatedly with MeOH and pentane, and dried in vacuo at 50 ◦C. This procedure gave 600 mg (0.55 mmol, 27%) of FSC11-Ac. 1

H-NMR (400 MHz, CS2 / D2 O) δ 7.84 (s, 2H), 7.05 (d, J = 8.1 Hz, 2H), 5.16 (d, J = 9.2

Hz, 1H), 5.07 (s, 1H), 4.46 (d, J = 9.2 Hz, 1H), 4.11 (t, J = 6.3 Hz, 2H), 3.01 (s, 3H), 2.48 (s, 3H), 2.06 1.92 (m, 2H), 1.80 1.64 (m, 4H), 1.52 (s, 14H). 13 C-NMR (100 MHz, CS2 / D2 O) δ 162.1, 159.1, 156.8, 156.4, 156.3, 150.0, 149.6, 149.3, 149.2, 149.1, 149.0, 148.9, 148.7, 148.6, 148.5, 148.3, 148.2, 148.1, 148.0, 147.5, 147.2, 146.0, 145.9, 145.5, 145.4, 145.1, 145.0, 144.9, 144.8, 144.7, 144.5, 144.4, 143.1, 143.0, 142.8, 142.5, 139.6, 139.5, 138.6, 133.1, 131.2, 117.5, 86.0, 80.2, 72.9, 71.7, 70.6, 42.9, 33.1, 33.0, 32.9, 32.8, 32.7, 32.5, 32.3, 32.2, 29.5. IR (cm−1 ): 2923, 2849, 2777, 2326, 1687, 1609, 1506, 1461, 1330, 1243, 1171, 1105, 1029, 946, 831, 702. HRMS(ESI) calcd. for C82 H36 NO2 S[M+H]+ : 1098.24613, found: 1098.24992.

FSC11. The solution of FSC11-Ac (300 mg, 0.27mmol) and dibutyltin oxide (3.42mg, 0.014mmol, 5mol%) in chlorobenzene (60 ml) and methanol (30 ml) was heated to reflux for 24 h under N2 . The mixture was concentrated in vacuo to 15 mL, and the crude residue was purified by column chromatography (Silica gel; toluene/hexane=1/1 followed by toluene) to afford the pure compound as a brown solid. The product was redissolved in 7 mL of chlorobenzene, precipitated with MeOH, washed repeatedly with MeOH and pentane, and dried in vacuo at 50 ◦C. This procedure gave 88 mg (0.55 mmol, 30%) of FSC11. 1

H-NMR (400 MHz, CDCl3 ) δ 7.69 (s, 2H), 6.94 (d, J = 8.2 Hz, 2H), 4.97 (d, J = 8.7 Hz,

1H), 4.88 (s, 1H), 4.24 (d, J = 9.1 Hz, 1H), 3.95 (t, J = 6.5 Hz, 2H), 2.79 (s, 3H), 2.51 (dd, J = 14.7, 7.4 Hz, 2H), 1.83 1.71 (m, 2H), 1.68 1.52 (m, 3H), 1.50 1.21 (m, 14H). 13 C-NMR

S6

(100 MHz, CDCl3 ) δ 161.9, 159.0, 156.8, 156.3, 150.0, 149.9, 149.5, 149.2, 149.0, 148.9, 148.8, 148.7, 148.6, 148.4, 148.2, 148.1, 148.0, 147.9, 147.8, 147.4, 147.3, 147.0, 145.8, 145.6, 145.3, 145.2, 144.9, 144.8, 144.7, 144.6, 144.5, 144.3, 144.2, 142.8, 142.6, 142.2, 139.5, 139.3, 138.4, 133.1, 131.3, 117.2, 85.9, 72.6, 71.6, 70.6, 42.7, 36.7, 32.2, 32.1, 32.0, 31.7, 31.0, 28.7, 27.3. IR (cm−1 ): 2918, 2848, 2773, 1604, 1510, 1461, 1424, 1330, 1243, 1168, 1103, 1025, 908, 829, 702. HRMS(ESI) calcd. for C80 H34 NOS[M+H]+ : 1056.23556, found: 1056.23989.

2 2.1

Electrical Measurements Histogram of log |R| and current density

F S C 1 1 P u re S A M s

5 0

c o u n ts

4 0 3 0 2 0 1 0 0 0 .0

0 .5

lo g |R | 1 .0

1 .5

2 .0

Figure S2: Histograms of log |R| for pure SAMs and FSC11 on AgTS obtained by dividing each value of J at positive bias into the corresponding value at negative bias for every value of |V | for 567 and 650 J/V traces, respectively. While log |R| for FSC11 SAMs (mixed monolayers) produced a single Gaussian centered near 1.5, the data of the pure SAMs are distributed from 0 − 2 and likely comprise multiple peaks. We interpret this difference to competition from the strong fullerene-fullerene and fullerene-Ag interactions (discussed in the main text) that preclude the formation of a well-ordered SAM.

S7

0 .1 2

lo g |R | @

0 .0 8

0 .8 5 V = 2 .1 0

0 .1 0

o n p u re S A M s

0 .9 5 V = 2 .7 9

o n F S C 1 1 S A M s fw d

0 .0 6

C u rre n t (A )

C u rre n t (A )

0 .0 8

lo g |R | @

0 .0 6

re v

0 .0 4 0 .0 2

fw d

0 .0 4

fw d re v

0 .0 2

fw d 0 .0 0

0 .0 0

re v

re v

-0 .0 2

-0 .0 2 -1 .0

-0 .5

0 .0

0 .5

1 .0

-1 .0

-0 .5

0 .0

0 .5

1 .0

P o te n tia l ( V )


Figure S3: I/V data for representative junctions that produce stable I/V curves above 0.5 V showing typical degrees of hysteresis based both on pure FSC11 SAMs (left) and on mixed FSC11 SAMs (right) on AgTS .

2.2

3 3.1

Plots of log |R|, log |J| and log |I| versus V

Characterization Contact angle measurement

The SAM of FSC11 was evaluated with water contact angle measurements, before the exchanging, the SAM of SC10 (left) was determined to be more hydrophobic and showed an average contact angle of 94 ± 1◦ , while after exchanging, the fullerene SAM of FSC11 was formed with an average contact angle of 68 ± 1◦ , which is corresponding closely to values of C60 -SAM reported by Tsukruk and co-workers. S6

3.2

XPS thickness measurement

To measure the thickness of the SAM we acquire the Ag3p3/2 and Ag3d peaks with the sample rotated under 0, 10, 20, 30, 40, and 50 degrees. A Gaussian fit with background is made to the peaks to obtain their intensities. To correct for slow fluctuations in the X-ray source intensity we acquire a spectrum for each peak at 0 degrees in between the measurements where the sample is rotated. These measurements are used to obtain a correction factor γI .

S8

6 0

A fte r e x c h a n g e B e fo re e x c h a n g e

2 0 0

6 0 5 0

5 0

A t - 0 .5 V

1 2 0

2 4 0

4 0

1 6 0

c o u n ts

c o u n ts

1 5 0

7 0

A t + 0 .5 V

4 0

1 2 0

9 0

3 0

6 0

2 0

8 0

2 0

3 0

1 0

4 0

1 0

0

0

-5

-4

lo g |J | -3

-2

-1

3 0

0

0

-4

-3

lo g |J | -2

c o u n ts

A fte r e x c h a n g e B e fo re e x c h a n g e

1 8 0

c o u n ts

2 1 0

0 -1

0

Figure S4: Histograms of current density of FSC11 and SC10 at - 0.5 V (left) and + 0.5 V (right) in the AgTS /FSC11 or SC10//Ga2 O3 /EGaIn junctions. The maximum value of log |J| at −0.5 V drops below −3, while the value at 0.5 V remains almost equal to that of SC10. The suppression of leakage current (at negative bias) compared to the SAM of pure SC10 is caused by the increase in tunneling distance imposed by the fullerene group. At positive bias, the LUPS is sufficiently close to Ef of Ag electrode that charges can be mediated by LUPS of C60 cage and tunneling occurs only through the aliphatic portion of the SAM (followed by hopping between C60 cage and EGaIn), leading to a nearly equal magnitude of J for SAMs of SC10 and FSC11 at 0.5 V. This asymmetry results in an obvious current rectification. This factor was used to normalize the peak intensities to acquire I ∗ = γI I, which was used to fit the thickness of the layer. The values are given in Table S1. Table S1: measured XPS peak intensities (I), correction factor γI , and the corrected peak intensities (I ∗ ) for the Ag3d and Ag3p peaks. sample rotation (◦ ) 0 10 20 30 40 50

I 8358 7945 7349 6479 5050 3086

Ag3 d γI 1.00 1.01 1.00 0.96 0.94 0.93

∗

I 8358 8044 7333 6230 4748 2880

I 3775 2972 3663 3029 1732 1121

Ag3 p3/2 γI 1.00 0.91 0.95 0.93 0.88 0.86

I∗ 3775 2715 3471 2820 1522 965

We measure the intensity of the peaks of electrons that make it from the silver through the SAM, without scattering. The intensity therefore depends on the length of the path through the overlayer, and the inelastic mean free path of the electrons. The intensity at a

S9

5 0 4 0

A u

T S

7 0

A g

T S

6 0

4 0 3 0

2 0

c o u n ts

c o u n ts

5 0 3 0

2 0 1 0 1 0 0

0 0 .4

0 .8

1 .2

lo g |R |

1 .6

2 .0

Figure S5: Histograms of log |R| for FSC11 on AgTS and AuTS obtained by dividing each value of J at positive bias into the corresponding value at negative bias for every value of |V | for 650 and 366 J/V traces, respectively. The blue and red lines are Gaussian fits with peaks and standard deviations of 1.46±0.018 and 0.92±0.017 for AgTS and AuTS respectively. given angle can be expressed as:

−d −L ) = I0 exp( ) λ λ cos(φ) d 1 ln(I ∗ ) = ln(I0 ) − λ cos(φ) I ∗ (φ) = I0 exp(

(S1)

with L the length of the path through the layer, d the thickness of the layer, λ the inelastic mean free path, and φ the angle of rotation of the sample with respect to the analyzer. λ depends on the kinetic energy of the observed electrons and the material the electrons have to move through. We have determined the values of λ, for electrons originating from the Ag3d and Ag3p levels, from measurements on a SAM of SC10 on silver, whose thickness was well studied ((12 ± 3) ˚ A). S7 The values were found to be 8 ˚ A−1 and 8.8 ˚ A−1 for Ag3d and Ag3p respectively. With these values of λ we can make a fit to the corrected intensities to find the thickness of the FSC11 SAM, which was found to be d = 1.8 ± 0.3 nm. This treatment assumes the inelastic mean free path in the FSC11 SAM to be equal to that in the SC10 SAM. The lower packing density of FSC11 could lead to a slight underestimation of the thickness of the layer.

S10

3.3

Estimation of LUPS of FSC11

LUPS energy of FSC11 was determined using a combination of optical and photoelectron spectroscopy. The UV-vis absorption spectrum (Figure S14) of FSC11, which enables the estimation of HOMO-LUMO gap (Eg ). Inset shows the determination of onset wavelength to be 718.13 nm, from which Eg is extrapolated to be 1.73 eV. Ultraviolet photoelectron spectroscopy (UPS, Figure S15) analysis of the SAM bound to AgTS is used to find the Fermi level of the silver, and the HOPS level of the FSC11 relative to the Fermi level. Binding energies are calculated with respect to the vacuum level. The vacuum level is found by summing the secondary electron cutoff and the photon energy (He I, hν =21.2 eV). In Figure S15 the valence band spectrum is shown as measured by UPS, showing the characteristic double peak of HOMO and HOMO-1 of C60 . For this data a smooth background function has been subtracted. A multiple Gaussian peak fit is performed on the data and the width (σ) and center (µ) of the peaks are found from the fit. We take the value of µ + 2σ as the onset of the HOMO, which is found to be -5.45 eV. From the equation ELU M O = EHOM O + Eg (eV), ELU M O is extropolated to be -3.72 eV.

S11

-6 .8

lo a d in g f o r c e : 1 .4 n N

-7 .0

0 .4

-7 .2

lo a d in g f o r c e : 1 .4 n N

0 .0 -0 .4

-7 .6

lo g |R |

lo g |I |

-7 .4 -7 .8

-0 .8

-8 .0 -8 .2

-1 .2

-8 .4 -1 .6

-8 .6 -1 .5

-1 .0

-0 .5

0 .0

0 .5

1 .0

1 .5

-1 .5

-1 .2

-0 .9

-0 .3

0 .0

lo a d in g f o r c e : 0 .4 8 n N

lo a d in g fo r c e : 0 .4 8 n N

-6 .6

-0 .6



0 .4

-6 .9 0 .0 -0 .4

-7 .5

lo g |R |

lo g |I |

-7 .2

-0 .8

-7 .8 -8 .1

-1 .2

-8 .4

-1 .6

-8 .7 -2 .0

-1 .5

-1 .0

-0 .5

0 .0

0 .5

1 .0

1 .5

2 .0

-2 .1

-1 .8

-1 .5


-1 .2

-0 .9

-0 .6

-0 .3

0 .0

-0 .6

-0 .3

0 .0


1 .0 -6 .0



0 .5

-6 .6

0 .0

-6 .9

-0 .5

lo g |R |

lo g |I |

-6 .3

-7 .2

-1 .0

-7 .5

-1 .5

-7 .8

-2 .0

-8 .1

-2 .5

-8 .4

-3 .0

-8 .7 -2 .0

-1 .5

-1 .0

-0 .5

0 .0

0 .5

1 .0

1 .5

2 .0

-1 .8

-1 .5

-1 .2

-0 .9



Figure S6: Plots of log |I| (left) log |R| (right) versus V of FSC11 SAM for CP-AFM measurements at different loading forces of 1.4 nN (up) 0.48 nN (middle) and 0.24 nN (down) (the units of I are mA). CP-AFM measurements employing a rigid Au electrode instead of a conformal, liquid-metal electrode (EGaIn) shows an obvious rectification with log |R| greater than 1, meaning that the origin of rectification for the AgTS /FSC11//Ga2 O3 /EGaIn junction is the SAM and not AgTS or EGaIn. The error bars are standard deviations.

S12

4

C P - A F M - 1 .4 n N C P - A F M - 0 .4 8 n N C P - A F M - 0 .2 4 n N

E G a In (p u re S A M s) E G a In (F S C 1 1 )

|lo g |R ||

3 2 1 0 0 .0

0 .5

1 .0

1 .5

2 .0

P o te n tia l ( V ) Figure S7: Comparison of log |R| vs. |V | plots of EGaIn (black squares and red dots) and CP-AFM (blue, green and magenta symbols) measurements. Each data point is the peak of a Gaussian fit to a histogram of log |R| at that value of |V |. The error bars are the standard deviations of those fits. This same plot is shown without error bars in the Main Text for clarity.

2 .0

0 h 6 h 1 2 2 4 3 6 6 0

1 .6

-4

0 h

lo g |R |

lo g |J |

-2

6 h 1 2 2 4 3 6 6 0

-6

-8 -0 .6

-0 .4

-0 .2

0 .0

0 .2

0 .4

0 .6

1 .2 0 .8

h h h h

h 0 .4

h h

0 .0

h

0 .8

0 .0


0 .1

0 .2

0 .3

0 .4

0 .5


Figure S8: Plots of log|J| (left) and log|R| (right) versus the exchange time for the preparation of FSC11 SAM. The magnitude of log|R| increased gradually with the exchange time below 24 h, while remained almost unchanged since then, indicating the nearly complete FSC11 SAM was achieved after 24 h later (we did not perform the measurement for longer than 60 h because the optical adhesive began to swell).

S13

C 8 S H -F S C 1 1 C 1 0 S H -F S C 1 1 C 1 2 S H -F S C 1 1

-1 -2

lo g |J |

-3 -4 -5 -6 -7 -0 .6

-0 .4

-0 .2

0 .0

0 .2

0 .4

0 .6


Figure S9: Plots of log|J| (left) versus the magnitude of applied bias after 24 h exchange for FSC11 SAM preparation using different passivating thiols with different length of alkane chain. The magnitudes of log|J| are not significantly, which again supporting the mechanism proposed in the manuscript.

lo g |R | lin e a r fit o f lo g |R |

3 .0 2 .5 2 .0

E x c h a n g e tim e : 2 4 h R @ 1 V is d e d u c e d a s 9 4 0

lo g |R |

1 .5 1 .0 0 .5 0 .0

Equation

y = a + b*x

Adj. R-Square

0.99435

-0 .5

Value

-1 .0 0 .0

log |R|

Intercept

log |R|

Slope

0 .1

0 .2

Standard Error

0.1087

0.01858

2.86467

0 .3

0.07196

0 .4

0 .5


Figure S10: A plot and linear fitting of log|R| versus the magnitude of applied bias after 24 h exchange for FSC11 SAM preparation. The linear dependence of log |R| on |V | enables the extrapolation of the value of R at any specific |V |, e.g., ±0.95 V. Comparing deduced value of R = 676 at ±0.95 V to R = 617 from a single ‘hero junction’ that survived sweeping to ±0.95 V offered a close agreement.

S14


2 .5 2 .0

R @

1 V is d e d u c e d a s 8 3 3

lo g |R |

1 .5 1 .0 0 .5 0 .0

Equation

y = a + b*x

Adj. R-Square

0.97774

-0 .5

Value

-1 .0

Standard Error

log |R|

Intercept

0.12158

0.01754

log |R|

Slope

2.79887

0.14058

0 .0

0 .1

0 .2

0 .3

0 .4

0 .5


Figure S11: A plot and linear fitting of log|R| versus the magnitude of applied bias for pure SAMs. The linear dependence of log |R| on |V | gave almost the same slope and similar deduced value of R (833) at ±1.0 V.


3 .0 2 .5 2 .0

3

E x c h a n g e tim e : 3 6 h R @ 1 V is d e d u c e d a s 7 6 4

1 .5

E x c h a n g e tim e : 6 0 h R @ 1 V is d e d u c e d a s 1 4 5 2 2

1 .0

lo g |R |

lo g |R |

lo g |R | lin e a r fit o f lo g |R | 4

0 .5

1

0 .0 Equation

-0 .5

y = a + b*x

Adj. R-Square

0

0.96209 Value

-1 .0 -1 .5 0 .0

log |R|

Intercept

log |R|

Slope

0 .1

0 .2

0.98923 Value

0.03077

2.92856

0.19334

0 .4

y = a + b*x

Adj. R-Square

-0.04564

0 .3

Equation

Standard Error

-1

0 .5

0 .0

log |R|

Intercept

log |R|

Slope

0 .1

0 .2

Standard Error

-0.00409

0.02097

3.16607

0 .3

0.11006

0 .4

0 .5



Figure S12: Plots and linear fits of log|R| versus the magnitude of applied bias after 36 h and 60 h exchange for FSC11 SAM preparation. The plots of log |R| versus |V | for SAMs of FSC11 at different exchange times (i.e., 36 h and 60 h) gave almost the same slope and similar deduced value of R at ±1.0 V, validating the extrapolated value of |R|obsd = 940 employed in the main text.

S15

Figure S13: profiles of water contact angle of SC10 SAM (left, before exchange) and FSC11 SAM (right, after exchange).

Figure S14: UV-vis absorption spectrum of FSC11, which enabled the estimation of HOMOLUMO gap (Ef ). Inset shows the determination of onset wavelength to be 718.13 nm, from which Ef is extrapolated to be 1.73 eV.

S16

3500

UPS data (bg subtracted) multiple peak fit

3000 Intensity (counts/s)

fit HOMO 2500

fit HOMO-1

2000

HOMO HOMOonset

1500

Efermi

1000 500 0 9

8

7

6

5

4

3

Binding energy (eV)

Figure S15: UPS of the FSC11 SAM, relevant energy levels are determined to be: Vacuum level: 0 eV; Fermi level: -3.57 eV; HOMO onset: -5.45 eV.

Figure S16: AFM height profiles of (left) the pure alkanethiol SAM (that is before exchange) and (right) FSC11 SAM (after exchange, the surface of which is comparable to that in the paper. S8 Both films looks like relatively smooth (Ra ≈ 1nm). Although the difference before and after exchange is obvious, One could hardly draw definitive conclusions about the distribution of fullerenes since, in our hands, AFM is only barely capable of resolving 15 nm-wide protein complexes S9 and C60 is nominally 1 nm in diameter. There are qualitative differences before and after exchange, certainly, and there are randomly-distributed spheroids in the post-exchange AFM, which could not be overinterpreted thus far.

S17

8.5

8.0

7.5

7.0

6.5

6.0

5.5

4.0

3.5

3.0

2.5

2.58 4.44 14.00

2.48 2.00 1.98 1.97 1.75 1.73 1.69 1.52

3.01

2.35

4.47 4.45 4.13 4.11 4.10 1.22

5.0 4.5 f1 (ppm)

2.62

9.0

3.19

9.5

1.26 1.17

7.06 7.04

2.34

7.84

PC11SAc-H

5.17 5.15 5.07

NMR spectra

2.28

3.4

2.0

Figure S17: 1 H NMR spectrum of FSC11-Ac

S18

1.5

1.0

0.5

0.0

220 210 200 190 180 170 160 150 140

Figure S18: 130

13 120 110 100 f1 (ppm)

S19 90 80 70

42.88 33.13 33.07 32.99 32.94 32.90 32.84 32.74 32.54 32.32 32.20 29.54

85.97 80.20 72.86 71.67 70.60

162.07 159.13 156.77 156.43 156.34 150.08 148.93 148.74 147.52 147.21 145.42 144.98 144.94 144.86 143.06 143.00 142.84 142.46 139.64 139.48 138.63 133.13 131.24 117.50

PC11SAcC_d2o_CARBON_20160828112617

60 50

C NMR spectrum of FSC11 40 30 20 10 0 -10

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0

S20

4.5 4.0 f1 (ppm) 3.5 3.0 2.5

2.21 2.83 2.03 12.32

2.00

3.09

2.23

1.17

1.02 1.16

2.14

2.22

2.79 2.54 2.52 2.50 2.48 1.80 1.78 1.76 1.74 1.73 1.61 1.59 1.57 1.56 1.44 1.42 1.34 1.32 1.30 1.27

4.25 4.23 3.96 3.95 3.93

4.98 4.96 4.88

6.95 6.93

7.69

PC11SH-H

2.0

Figure S19: 1 H NMR spectrum of FSC11 1.5 1.0 0.5 0.0

220 210 200 190 180 170 160 150 140

Figure S20: 130

13 120 110 100 f1 (ppm)

S21 90 80 70

42.66 36.69 32.19 32.16 32.15 32.07 31.98 31.72 31.03 28.73 27.33

72.61 71.60 70.64

85.86

161.86 159.02 156.75 156.31 149.95 149.94 148.59 147.04 145.23 145.21 145.20 144.81 144.76 144.62 142.55 142.22 138.42 133.11

PC11SHC_cdcl3_CARBON_20160603171611

60 50

C NMR spectrum of FSC11 40 30 20 10 0 -10

References (S1) Weiss, E. A.; Kaufman, G. K.; Kriebel, J. K.; Li, Z.; Schalek, R.; Whitesides, G. M. Si/SiO2 -templated Formation of Ultraflat Metal Surfaces on Glass, Polymer, and Solder Supports: Their Use as Substrates for Self-Assembled Monolayers. Langmuir 2007, 23, 9686–9694. (S2) Maggini, M.; Scorrano, G.; Prato, M. Addition of Azomethine Ylides to C60 : Synthesis, Characterization, and Functionalization of Fullerene Pyrrolidines. J. Am. Chem. Soc. 1993, 115, 9798–9799. (S3) Baumhof, P.; Mazitschek, R.; Giannis, A. A Mild and Effective Method for the Transesterification of Carboxylic Acid Esters. Angew. Chem., Int. Ed. 2001, 40, 3672–3674. (S4) Lee, G. S.; Lee, Y.-J.; Choi, S. Y.; Park, Y. S.; Yoon, K. B. Self-Assembly of βGlucosidase and D-Glucose-Tethering Zeolite Crystals Into Fibrous Aggregates. J. Am. Chem. Soc. 2000, 122, 12151–12157. (S5) Kurzatkowska, K.; Dolusic, E.; Dehaen, W.; Sieron-Stoltny, K.; Sieron, A.; Radecka, H. Gold Electrode Incorporating Corrole as an Ion-Channel Mimetic Sensor for Determination of Dopamine. Analytical chemistry 2009, 81, 7397–7405. (S6) Tsukruk, V. V.; Lander, L. M.; Brittain, W. J. Atomic Force Microscopy of C60 Tethered to a Self-Assembled Monolayer. Langmuir 1994, 10, 996–999. (S7) Li, W.; Virtanen, J. A.; Penner, R. M. Self-Assembly of N-Alkanethiolate Monolayers on Silver Nanostructures: Determination of the Apparent Thickness of the Monolayer by Scanning Tunneling Microscopy. The Journal of Physical Chemistry 1994, 98, 11751– 11755. (S8) Itoh, Y.; Kim, B.; Gearba, R. I.; Tremblay, N. J.; Pindak, R.; Matsuo, Y.; Nakamura, E.; Nuckolls, C. Simple formation of C60 and C60-ferrocene conjugated monoS22

layers anchored onto silicon oxide with five carboxylic acids and their transistor applications. Chemistry of Materials 2011, 23, 970–975. (S9) Casta˜ neda Ocampo, O. E.; Gordiichuk, P.; Catarci, S.; Gautier, D. A.; Herrmann, A.; Chiechi, R. C. Mechanism of Orientation-Dependent Asymmetric Charge Transport in Tunneling Junctions Comprising Photosystem I. J. Am. Chem. Soc. 2015, 137, 8419– 8427.

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