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: [email protected] (P.C.M)
Email: [email protected] (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.
REFERENCES
(S1) Winter, A.; van den Berg, A. M. J.; Hoogenboom, R.; Kickelbick, G.; Schubert,
U. S. Synthesis, 2006, 2873-2878.
(S2) Constable, E. C.; Thompson, A. M. W. C. Chem. Soc. Dalton. Trans. 1994, 9,
1409-1418.
(S3) Lin, W.; Lin, W.; Wong, G. K.; Marks, T. J. J. Am. Chem. Soc. 1996, 118, 8034-8042.
(S4) Heister, K.; Zharnikov, M.; Grunze, M.; Johansson, L. S. O.; Ulman, A. Langmuir 2001,
17, 8-11.
(S5) Zharnikov, M. J. Electron Spectrosc. Relat. Phenom. 2010, 178–179, 380-393.
(S6) Moulder, J. F.; Stickle, W. E.; Sobol, P. E.; Bomen, K. D. Handbook of X-ray
Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie, MN 1992.
(S7) Stöhr, J. NEXAFS Spectroscopy; Springer Series in Surface Science 25; Springer-
Verlag: Berlin, 1992.
(S8) Batson, P. E. Phys. Rev. B: Condens. Matter. 1993, 48, 2608-2610.