S1  

Supporting Information

Surface–Confined Heterometallic Triads on the Basis of

Terpyridyl Complexes and Design of Molecular Logic Gates†

Prakash Chandra Mondal,*,†,‡, Vikram Singh,† Yekkoni Lakshmanan Jeyachandran,§ and

Michael Zharnikov*,§

†Department of Chemistry, University of Delhi, Delhi, 110007, India.

‡Department of Chemical Physics, Weizmann Institute of Science, Rehovot, 76100, Israel.

§Applied Physical Chemistry, Heidelberg University, Heidelberg, 69120, Germany.

E-mail: mondalpc@gmail.com (P.C.M)

Email: michael.zharnikov@urz.uni-heidelberg.de (M.Z)

S2  

Materials and Methods (synthesis and fabrication of the triads):

Pyridine-4-carboxaldehyde, 2-acetyl pyridine, RuCl3.3H2O, (NH4)2OsCl6, FeCl2, 3-iodo-n-

propyltrimethoxy-silane and NH4PF6 were purchased from Sigma-Aldrich. Cu(NO3)2.3H2O

was purchased from s. d. fine chemicals (Mumbai, India). Tetra n-butyl ammonium

hexaflurophosohphate was purchased from Alfa-Aesar. The chemicals were used as received

without any further purification. Solvents (AR grade) were purchased from Merk (Mumbai),

s. d. fine chemicals and used without further purification. Teflon-lined autoclaves (25 mL and

50 mL) were purchased from Prakash Scientific, Bangalore, India. ITO-coated glass

substrates (single side coated) were purchased from VIN Karola Instruments (ρ = 7-10 ohm2).

Single-crystal silicon (100) substrates were purchased from Georg Albert PVD-

Beschichtungen (Silz, Germany).

1H and 13C NMR spectra were recorded with JEOL 400 NMR spectrometer (Model No.

JNMECX 400P).

FT-IR spectra (KBr pellets) were recorded with a Perkin Elmer spectrometer in a range of

400–4000 cm-1.

Synthesis of 4’-pyridyl terpyridyl (4’-pytpy):

4’-pyridyl-2,2’:6’,2’’-terpyridine (4’-pytpy) have been synthesized following published

procedureS1 and needle shape white crystals were obtained. The ligand was characterized by

1H, 1H-1H COSY, 13C NMR, elemental analysis, UV-vis and ESI-MS data: δH (400 MHz,

CDCl3), δ/ppm: 8.76 (s, 2H, Ar H), 8.78 (d, J = 8.6Hz, 2H), 8.68 (d, J = 8.05Hz, 2H), 7.8 (d,

J = 8.4Hz, 2H), 7.89 (t, J = 6.8Hz, 2H), 8.75 (d, J = 8.2Hz, 2H), 7.39 (t, J = 6.72, 2H). 13C

NMR (100 MHz, CDCl3), δ/ppm: 118.51, 121.27, 121.59, 124.03, 136.88, 145.83, 147.29,

149.09, 150.44, 155.57, 156.25. EI-MS; m/z (%): 310 (100) (M+). Anal. Calcd for C20H14N4 :

C, 77.1; H, 4.8; N, 18.02. Found: C, 76.5; H, 4.40; N, 17.89. UV-vis λmax/nm (ε/103 dm3 mol-1

cm-1): 254 (8.02).

S3  

Synthesis of Fe-PT, Ru-PT and Os-PT:

The metallo-ligands were prepared via published methodS2 (scheme S1). To prepare Fe-PT,

4'-pyridyl-terpyridyl (98 mg; 0.316 mmol) were dissolved into 10 mL hot methanol and then

FeCl2 (21 mg; 0.158 mmol) in 10 mL methanol was added drop wise and the whole reaction

refluxed with stirring for 4h under N2 atmosphere. Then, the reaction mixture was slowly

cooled to room temperature and it was precipitated out by addition of an excess of a saturated

methanolic solution of NH4PF6 and then it filtered off. The residue was washed with an

excess amount of water followed by diethyl-ether. Then it was recrystallized several times

using acetonitrile and acetone (1:1, v/v) to get the purple colour microcrystalline solid.

Ru-PT and Os-PT were prepared following the similar method. Ru-PT, deep red color

microcrystalline solid was obtained and purified by column chromatography using

acetonitrile and toluene (1:1, v/v), whereas Os-PT, deep brown color microcrystalline solid

was obtained followed by silica column chromatography using acetonitrile, saturated aqueous

KNO3 and water (7:1:0.5, v/v). The complexes were characterized by the help of 1H and 1H-

1H COSY, 13C NMR, ESI mass, FTIR, elemental analysis, UV-vis spectroscopy and cyclic

voltammetry (CV).

Characterization data:

Fe-PT: 1H NMR (400 MHz, CD3CN); δ/ppm: 9.20 (s, Ar, 4H), 9.02 (d, J = 8.0 Hz, 4H), 8.61

(d, J = 11 Hz, 4H), 8.23 (d, J = 10.2 Hz, 4H), 7.90 (t, J = 8.2 Hz, 4H), 7.15 (d, J = 5.8 Hz,

4H), 7.10 (t, J = 7 Hz, 4H). 13C NMR (100 MHz, CD3CN), δ/ppm: 118.29, 122.58, 122.98,

125.04, 128.36, 139.82, 148.75, 152.08, 154.22, 158.77, 161.84. EI-MS; m/z (%): 338 (90)

[M-2PF6]2+, 339 (46) [(M-2PF6)+H+]2+, 821 (30) [(M-PF6)]

+. UV-vis (CH3CN) λmax/nm (ε/103

dm3 mol-1 cm-1): 569 (23.00). FT-IR, KBr (cm-1): 838 (vs), 1408 (m) and 1598 (m). Anal.

Calcd for C40H28N8FeP2F12: C, 45.47; H, 3.63; N, 10.61. Found: C, 45.16; H, 3.34; N, 9.96%.

S4  

Ru-PT: 1H NMR (400 MHz, CD3CN) δ/ppm: 9.03 (s, Ar, 4H), 8.95 (d, J = 6.2 Hz, 4H), 8.65

(d, J = 9 Hz, 4H), 8.11 (d, J =6.2 Hz, 4H), 7.96 (t, J = 8 Hz, 4H), 7.40 (d, J = 6Hz, 4H), 7.18

(t, J = 6 Hz, 4H). 13C NMR (100 MHz, CD3CN), δ/ppm: 118.28, 122.79, 122.86, 125.69,

128.68, 139.09, 146.42, 152.20, 153.36, 156.66, 158.84. EI-MS; m/z (%): 361 (45)

[M−2PF6]2+, 362 (60) [(M-2PF6)+H+]2+. UV-vis (CH3CN) λmax/nm (ε/103 dm3 mol-1 cm-1):

490 (29.77). FT-IR, KBr (cm-1): 839 (vs), 1408 (m) and 1600 (m). Anal. Calcd for

C40H28N8RuP2F12: C, 47.49; H, 2.79; N, 11.08. Found: C, 47.83; H, 3.12; N, 11.28%.

Os-PT: 1H NMR (400 MHz, CD3CN) δ/ppm: 9.06 (s, Ar, 4H), 8.96 (d, J = 6.8 Hz, 4H), 8.65

(d, J = 8.5 Hz, 4H), 8.14 (d, J = 7 Hz, 4H), 7.84 (t, J = 8.4 Hz, 4H), 7.29 (d, J = 6.2Hz, 4H),

7.14 (t, J = 7.5 Hz, 4H). 13C NMR (100 MHz, CD3CN), δ/ppm: 118.28, 122.79, 122.86,

125.69, 128.68, 139.09, 146.42, 152.20, 153.36, 156.66, 158.84. EI-MS m/z (%): 405 (78)

[M−2PF6]2+, 406 (100) [(M-2PF6)+H+]2+. UV-vis (CH3CN) λmax/nm (ε/103 dm3 mol-1 cm-1):

490 (27.45), 674 (8.020). FT-IR, KBr (cm-1): 836 (vs), 1406 (m) and 1596 (m). Anal. Calcd

for C40H28N8OsP2F12: C, 43.64; H, 2.85; N, 10.18. Found: C, 42.83; H, 2.85; N, 10.01%.

Scheme S1: Synthetic scheme for the preparation of Fe-PT, Ru-PT and Os-PT.

S5  

9.2 8.8 8.4 8.0 7.6 7.2 6.8 (ppm)

Fig. S1a: 1H NMR spectrum of Fe-PT in CD3CN.

9.0 8.7 8.4 8.1 7.8 7.5 7.2 (ppm)

Fig. S1b: 1H NMR spectrum of Ru-PT in CD3CN.

S6  

9.0 8.5 8.0 7.5 7.0 (ppm)

Fig. S1c: 1H NMR spectrum of Os-PT in CD3CN.

Activation of the substrates:

Both ITO-coated glass and Si-substrates were cleaned by successive sonication in n-hexane,

acetone, and 2-propanol and dried under an N2 stream. Soda-lime glass (Chase Scientific

Glass, India) was cleaned by immersion in a “piranha” solution (composition of piranha

soltution-7:3 (v/v) conc. H2SO4/30% H2O2) over 1h. [Attention: “piranha” solution is an

extremely dangerous oxidizing agent and should be handled carefully with appropriate

personal protection]. Subsequently, the substrates were rinsed repeatedly with deionized (DI)

water and subjected to RCA cleaning reagent: 1:5:1 (v/v) NH3•H2O/H2O/30% H2O2 at room

temperature for ~ 45 min. The substrates were then washed with sufficient amount of DI

water and dried under an N2 stream. Finally, the substrates were dried in an oven for 2h at

135 °C.

S7  

Formation of the coupling layer and template layers:

Hetero-metallic molecular triads were prepared by successive assembly of the Fe-PT, Ru-PT

and Os-PT complexes using Cu(NO3)2 as the metallo-linker (see Scheme 1). Different

combinations of the M-PT units were prepared. Freshly cleaned glass, ITO-coated glass, and

Si substrates were functionalized with 3-iodo-n-propyltrimethoxy-silane under N2 atmosphere

using Schlenk line, forming the coupling layer (CL).S3 In detail, the substrates were treated

with a dry n-pentane solution of 3-iodo-n-propyltrimethoxy-silane (0.1 mM) at room

temperature for 30 min under N2 atmosphere. Then the substrates were thoroughly washed

with dry n-pentane, and sonicated (for 3 min each) with DCM and isopropanol respectively.

The resulting films were dried properly under a stream of N2 followed by drying in oven at

120ºC for 15 min. Afterwards, the functionalized substrates were loaded into in a teflon-

coated autoclave containing 0.5 mM solution of Fe-PT, Ru-PT or Os-PT in

acetonitrile/toluene (1:1 v/v) and kept at 80 ºC for 52h in dark under N2. Subsequently, the

autoclave was cooled slowly to room temperature. The functionalized substrates were then

taken away, rinsed with acetonitrile, and sonicated for 3 min each in acetonitrile, isopropanol

and acetone to remove any physisorbed materials. The samples were then dried carefully

under N2 before the characterization. In a test experiment, the functionalized substrates were

kept for 72h under the identical reaction conditions and UV-vis spectra showed no further

increase in absorption. However, when the reaction time was only 10h, UV-vis spectra

showed no sufficient growth of films on substrates.

Fabrication of hetero-molecular triads:

Freshly prepared template layers were exposed to 0.5 mM solution of Cu(NO3)2 in dry

acetonitrile for 30 min at room temperature under exclusion of light. The samples were then

washed gently in acetonitrile and under N2 stream. Then, Cu-terminated template layers

S8  

(Cu/M-PT) were immersed in a solution of a different M-PT unit to fabricate hetero-metallic

molecular dyad. The dyad layers were then washed in acetonitrile and under N2. The dyad

layers were further reacted with Cu(NO3)2 to get Cu-terminated dyad layers (dyad/Cu). The

substrates were further immersed in dissimilar M-PT units in acetonitrile at room

temperature. The substrates were washed properly in acetonitrile.

Materials and Methods (characterization):

The above step-wise coordination reactions were monitored by static contact angle (CA)

goniometry, atomic force microscopy (AFM), spectroscopic ellipsometry, X-ray

photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS)

spectroscopy, UV-vis spectroscopy, and cyclic voltammetry. Also, the fabricated triad layers

were characterized by these techniques.

AFM images were recorded on silicon substrates using a Dimension 3100 (Veeco Digital

Instruments, Santa Barbara, CA) device equipped with a Nanoscope IIIa controller (Veeco)

operated in tapping/semicontact mode in air. Aluminium-coated cantilevers with silicon

nitride tips (triangular shaped) were obtained from NanoWorld (length, width and thickness

100, 13.5, 0.5 µm respectively) whose resonance frequency of 70-90 kHz. The spring

constant of the cantilever, k is 0.32 N/m and deflection sensitivity 70 nm/V. The radius of the

tips was less than 10 nm. The topography images were recorded at a scan rate of 0.5 Hz and

samples per line was kept at 512 with slow scan axis enabled. Integral gain and proportional

gain was fixed at 0.35, and 1.5 respectively. Several images of each sample were recorded in

different fields of view (0.5-2.0 μm) to ensure uniformity and reproducibility. The AFM

measurements were done using four tips to validate reproducibility. The average roughness

(analyzed by Nanoscopic 730r1sr2 software package) was estimated as obtained from the

system and unprocessed data, (in nm) after measuring at three different places.

S9  

Static aqueous CA measurements were performed with an automated goniometer (Rame-

Hart, model 100), and microsyringe droplets (advancing drop method) of ca. 4 μL deionized

water (Millipore, Inc.). The measurements were carried out immediately after the preparation

of the samples on silicon substrates. The data were recorded from a minimum of four

different drops at different places over a minimum of three independent samples.

The thicknesses of the samples were measured using a multiple wavelength ellipsometer (M

2000 V from J. A. Woollam Co., Inc.). The data were acquired at a constant incidence angle

of 70º under ambient conditions and analyzed using commercial software (WVASE32).

Parameters A, B and C were 1.4, 0.02, and 0.01, respectively, with mean square error (MSE)

< 10 for a Cauchy model. The SiO2 layer was calibrated to be 15 Å. Before measurements for

the samples, the silicon as standard sample was mounted, aligned and calibrated properly.

The calibration data should be perfectly matched with the theoretically fit data. To measure

the refractive index, probe wavelength of He-Ne laser used in this experiment is at 633 nm.

The optical constants, n (real component) and k (imaginary component) were fixed at 1.45

and 0, respectively. The refractive index for SiO2 was estimated at 1.45, while for the layers it

was in the range of 1.4 to 1.7.

The XPS and NEXAFS spectroscopy experiments were carried out under room temperature

and ultrahigh vacuum (UHV) conditions with a base pressure of at least 1.5×10−9 mbar or

better. The time for the acquisition of the spectra was carefully selected to avoid any

noticeable damage of the samples by the primary X-rays.S4,S5 XPS measurements were

performed using a Mg Kα X-ray source and a LHS 11 analyzer. The spectra acquisition was

carried out in normal emission geometry with an energy resolution of ≈0.9 eV. The X-ray

source was operated at a power of 260 W and positioned ∼1.5 cm away from the samples.

The high-resolution XPS (HRXPS) and NEXAFS spectroscopy measurements were

performed at the HE-SGM beamline (bending magnet) of the synchrotron storage ring

S10  

BESSY II in Berlin, Germany, using a Scienta R3000 spectrometer. The synchrotron light

served as the primary source of X-rays. The acquisition of the HRXP spectra was carried out

in normal emission geometry with an energy resolution of ∼0.3-0.5 eV, depending on the

binding energy range. The energy scale of both XP and HRXP spectra was referenced to the

Si 2p3/2, 1/2 doublet at 99.15 eV.[S6]

The acquisition of the NEXAFS spectra was carried out at both carbon and nitrogen K-edges

in the partial electron yield mode with retarding voltages of −150 and −300 V respectively.

Linear polarized synchrotron light with a polarization factor of ∼91% was used.

The energy resolution was ~0.30 eV at the C K-edge and somewhat lower at the N K-edge.

The incidence angle of x-rays was varied from 90° (E-vector in the surface plane) to 20° (E-

vector nearly normal to the surface) in steps of 10°-20° to monitor the orientational order of

the within the target films. This approach is based on the linear dichroism in X-ray

absorption, i.e., the strong dependence of the cross-section of the resonant photoexcitation

process on the orientation of the electric field vector of the linearly polarized light with

respect to the molecular orbital of interest.S7

The raw NEXAFS spectra were normalized to the incident photon flux by division by a

spectrum of a clean, freshly sputtered gold sample. Further, the spectra were reduced to the

standard form by subtracting a linear pre-edge background and normalizing to the unity edge

jump (determined by a nearly horizontal plateau 40-50 eV above the respective absorption

edges). The photon energy scale was referenced to the most intense π* resonance of highly

oriented pyrolytic graphite (HOPG) at 285.38 eV.S8

UV-vis spectra were recorded with a JASCO (Model No. V670) spectrophotometer. A bare

glass substrate was used to compensate for the background absorption.

Cyclic voltammetry measurements were performed with a CH Instruments potentiostat

(Model 660D). Cyclic voltammograms were measured on 1 mM solutions of the complexes

S11  

in acetonitrile with tetra-n-butylammonium hexafluorophosphate (TBAPF6, 100 mM) as

supporting electrolyte using a glassy carbon as working electrode, a Pt wire as counter

electrode, and Ag/Ag-Cl as reference electrode. In case of the surface based electrochemistry,

ITO-coated glass substrates were used as working electrode, Pt-wire as counter electrode and

Ag/AgCl have been used as reference electrode. The ITO-coated glass substrates with ITO-

coated side kept towards the counter and reference electrodes were dipped into 20 mM

solution of TBAPF6 in acetonitrile which was degassed by N2 bubbling before the

experiments. Scan rate was varied in the 100-1000 mV s-1 range.

Fig. S2: Water contact angle formed on the surface of (a) Fe-PT template layer, and (b) Cu-

terminated Fe-PT-template layer (Fe-PT-Cu) on silicon.

Fig. S3: AFM topography images of (a) template layer (Fe-PT), (b) dyad (Fe-PT/Cu/Ru-PT),

and (c) triad (Fe-PT/Cu/Ru-PT/Cu/Os-PT) layers (c) on Si(100). Scan area was 500 nm× 500

nm for all cases.

S12  

1 2 3

0.4

0.8

1.2

Ro

ug

hn

ess

/ n

m

No. of depostion steps  

Fig. S4: Variation of Rrms (in nm) with deposition steps on silicon surface. Deposition step 1,

2, and 3 are the template layer (Fe-PT), dyad (Fe-PT/Cu/Ru-PT), and triad (Fe-PT/Cu/Ru-

PT/Cu/Os-PT) layers, respectively.

Fig. S5: Si 2p XP spectra of the coupling (CL), template (Fe-PT), dyad (Fe-PT/Cu/Ru-PT),

and triad layers (Fe-PT/Cu/Ru-PT/Cu/Os-PT) on Si(100). The open circles represent the

experimental data.

S13  

Fig. S6: A representative example of the complete set of the NEXAFS spectra. C (a) and N

(b) K-edge NEXAFS spectra of dyad layer (Fe-PT/Cu/Ru-PT) on Si(100). The spectra were

acquired at an X-ray incidence angle of 20°, 55°, and 90° and the difference between the

spectra acquired at X-ray incidence angles of 90° and 20° are shown for each case.

S14  

Fig. S7: A representative example of the complete set of the NEXAFS spectra. C (a) and N

(b) K-edge NEXAFS spectra of Cu-terminated dyad layer (dyad-Cu) assembly on Si(100).

The spectra were acquired at an X-ray incidence angle of 20°, 55°, and 90° and the difference

between the spectra acquired at X-ray incidence angles of 90° and 20° are shown for each

cases.

 

 

 

 

 

 

S15  

Fig. S8: UV-vis spectra of Fe-PT (a), Ru-PT (b) and Os-PT (c) in dry acetonitrile (10-5 M

solution).  

 

Fig. S9: Cyclic voltammograms of Fe-PT (a), Ru-PT (b) and Os-PT (c) in dry acetonitrile (1

mM solution in 100 mM of TBAP6).

S16  

Thermal and Electrochemical Stability of the Template layers:

The template layers were subjected to thermal stress (Figure S10). The samples were placed

inside a sealed glass pressure tube under air. The thermal stability was monitored by keeping

the samples for >1 h at various temperatures (i.e., 30, 55, 80, 125, 150, 180, 210, and 240 oC).

Before each temperature increase, the samples were allowed to attain room temperature and

were analyzed by UV-vis spectrophotometry. Electrochemical stability of the template layers

is illustrated by Figure S11.

Fig. S10: Ex-situ UV-vis monitoring of the thermal stability of the Fe-PT (a), Ru-PT (b) and

Os-PT (c) template layers on glass substrates. The data show that these layers are stable.

Fig. S11: Electrochemical stability of the Ru-PT template layer on ITO-coated glass

substrate. Data are presented after each 100 cycles (scan rate 50 mV s-1).

S17  

Reversibility test:

Fig. S12: UV-vis spectrum (red curve) recorded after addition of Et3N to the triad layer

treated with NOBF4 for 180 s (blue curve). The spectra show 60% reversibility as compared

to the spectrum of the triad layer before the NOBF4 exposure.

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1409-1418.

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(S4) Heister, K.; Zharnikov, M.; Grunze, M.; Johansson, L. S. O.; Ulman, A. Langmuir 2001,

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Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie, MN 1992.

(S7) Stöhr, J. NEXAFS Spectroscopy; Springer Series in Surface Science 25; Springer-

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