Characterizations of 5,10,15,20 tetra(4-hydroxyphenyl)-porphyrin polymer (polyTHPP):
(a)
40
30
5,10,15,20 tera(4hydroxyphenyl)porphyrin (THPP)
20
10
0
(b)
50
40
30
20
10
0
-10
-20
-10
-20
0.0
0.2
0.4
0.6
0.8
Scan1
Scan3
Scan5
1.0
Scan 1
Scan 3
Scan 5
0.0
0.2
0.4
0.6
0.8
1.0
Figure S1. Electrochemical polymerization and deposition of THPP on Au and ITO electrodes
(IDE).
C yclic voltammograms (CV) of scan1, scan3 and scan5 respectively measured during
1

electrochemical polymerization of THPP on, ( a) Au and ( b) ITO as WE electrodes. Inset shows the molecular stracure of THPP.
Figure S1(a) and S1(b) show the cyclic voltammograms (CV) during electrochemical polymerization of THPP on gold and ITO as WE electrodes, respectively. The CV was run from 0V to +1.0 V up to 5 scans and at a potential scan rate 0.05 V s
-1
. Repeated scan reveals the shifting of the redox peak from 0.7V
, which is related to an increase in the number of porphyrin molecules per cm
-2
area ( will be discussed later). Same behavior of electrochemical polymerization of zinc tetrakis(4-hydroxyphenyl)porphyrin has been also reported by Tom J.
Savenije et.al
1
.
Interestingly , we found that growth of the deposited film on Au electrode was not observed after 10 scan, but on ITO, the film kept growing . The highest thickness of the film on ITO was obtained 282 nm after 30 scans, where thickness was measured using profilometer.
(1)
2

(2)
(3)
Figure S2. Surface morphology of polyTHPP on Au and ITO.
On Au electrode, surface morphology after (1) , 5 th
Scan (2) and 10 th
scan of CV, respectively. (3) on ITO after 10 th
scan of CV.
Figure S3. The EDX analysis of polyTHPP film shows the presence of Cl.
3

The evolution of surface morphology was analyzed by AFM and SEM after each scan. Figure S2 shows the surface morphology of polyTHPP on Au and ITO . The surface morphology studies reveal granular surface morphology for films grown on both ITO and gold. The morphology studies further reveal porous morphology for the film grown on Au after five scans which indicates poor stickiness of the polymer after 5scan — this explains why there is no further growth of layer on Au after 10 scans. Such porous morphology was not observed for the layer deposited on ITO with number of scans (Fig S2(3)). Therefore, for present studies, the number of scan was limited to five scans during the deposition of polyTHPP on Au electrode by CV. The presence of counter ion (ClO
4
) in the film is confirmed from observed Cl peak in EDX analysis
(Fig. S3)
0.57V
1.15V
0.00
-0.08
-0.25 V
-1.19 V
-0.16
Scan5
Scan1
-0.24
-3.0
-1.5
0.0
1.5
3.0
Figure S4. Electrochemical characterization poly THPP film . CV of polyTHPP after first scan, five scans recorded only in 0.1M LiClO
4
electrolyte showing two oxidation peaks (0.57 V and
1.15V) and two reduction peaks (-0.25 V and -1.19V)
4

The redox property of the deposited film was stuided by CV which was run in 0.1M LiClO
4 methanol solution where the film coated electrode was working electrode, Pt as counter electrode and Ag/AgCl as reference electrode. Figure S3 shows the CV of poly- THPP film grown on
ITO electrode after first scan and five scans. The figure shows double redox peak of the polymer which is related to the redox peaks of the monomer solution. Thus, after polymerization, the core structure of porphrin does not change significantly and retains redox properties of monomer. The number of molecule deposited on the film was calculated from the area under the first oxidation peak as after first oxidation, second oxidations take place. The number of molecules deposited per cm
2
after 1scan is 7.75X10
12 which increases to 9.59x10
12 after 5 scans. Thickness measurements by ellipsometer reveal that 45±5 nm thick film grown after five scans of CV. We also investigated the solubility of the polymer which was found to be insoluble in common organic solvents (methanol, acetone, isopropanol, acetonitrile) and inorganic solvent (HCl, water). However, the polymer was found to be soluble in concentrated sodium hydroxide which is also reported in literature
2
.
(1) Spectroscopic characterization of the Films.
(a)
5

5th scan
1st scan
400 600 800
Wave length (nm)
1000
(b)
400 600
860 nm
800
1000
1603 cm-1
(c)
500 1000 1500 2000
2500
6

0 500 1000 1500 2000 2500
Figure S4.
Spectroscopic characterization of the Films. (a) UV-Vis spectra of films deposited on ITO after 1 st
scan, 5 scans and 10 scans showing characteristics absorption peaks of THPP.
Inset shows the UV-Vis spectra of the dropcast monomer film. ( b) and (c).
The Raman spectra of polyTHPP and the dropcast monomer THPP film showing characteristics bands of porphyrin ring.
UV-Vis spectra of films deposited on ITO after 1 scan, 5 scans, 10 scans of CV show absorption peaks at 433 nm, 515nm, 654 nm, and 860 nm, which increase and broaden with scan
(Fig. S4a). The bands are also broadened and sifted in comparison with the corresponding bands of dropcast film of the monomer ( inset in Fig. S4a). These changes in the spectra are understood from observed increase of number molecule on electrode with scans. The UV-Vis spectra are in resemblance with reported UV-Vis electrochemically polymerized porphyrin monomer
[1,3]
. Raman spectroscopy studies of electrochemically polymerized film reveal characteristics bands at 1375 cm
-1
, 1477 cm
-1
, 1536 cm
-1
, 1603 cm
-1
of porphyrin which match well the reported Raman spectra of porphyrin polymer
[3]
(Fig. S4b). Furthermore, these bands
7

match with the bands (1378 cm
-1
, 1471 cm
-1
, 1538 cm
-1
, 1594 cm
-1
) of the drop cast film of
THPP monomer (Fig. S4c).
Theoretical calculations reveal that the electron density of the highest occupied molecular orbital
(HOMO) lies all over the THPP molecule. The HOMO shows that the electron density lies on meta carbon in phenyl group of phenol moiety ( 3-position with respect to OH). Thus, this meta carbon in phenyl group would be involved during polymerization. This mechanism of polymerization has been reported in literature, where the mechanism has been verified by substituting hydrogen atom at para postion by other group
1,3
.
(2) Calculation of HOMO and LUMO of the polymer :
To understand the distribution of electron density across the THPP molecule, we calculated the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies using ab initio molecular orbital theory method, as implemented in GAMESS software
.The geometries and the total energies of THPP were optimized under the density functional theory using the linear combination of atomic orbital approach. For this purpose, basis set was a standard 6-31G+(d, p) [4]. Becke’s three-parameter functional was used for calculating exchange–correlation energy[4], where this functional consists of Hartree–Fock exchange,
Becke’s exchange and the Lee–Yang–Parr correlation functional. All calculations were carried out in Anupam super computer at Bhabha Atomic Research Centre, Mumbai, India.
Here we used electrochemical method to evaluate the energy levels of HOMO and LUMO of the THPP polymer. In this method, the onset potentials of oxidation and reduction peak were taken from the CV of the polyTHPP film. Then, these values were used in empirical equation 4
8

The theoretically calculated values of the monomer are -4.67 eV for HOMO) and -3.78 eV
LUMO.
We also calculated HOMO and LUMO value of the polyTHPP from oxidation and reduction potential obtained from the cylic volatgramm of the film using the equation
E HOMO/LUM0 = [−e(E onset(vs.Ag/AgCl)
− E onset(Fc/Fc+ vs Ag/AgCl)
)] − 4.8
(1) where the ferrocene value of −4.8eV with respect to the vacuum level is defined as zero.
The electrochemically measured HOMO at -4.53 eV and LUMO at -3.9eV of the polymer matches well with the theoretically obtained values of the monomer.This indicates why oxidation and reduction peaks of polymer are not deviated from that of monomer. This also confirms that core structure of the THPP does not change due to polymerization.
(3) Energy level diagram of PolyTHPP/IDE
Based on the calculated HOMO and LUMO, energy level diaram can be represented as
(a)
LUMO
(-3.9eV)
-5.1eV
HOMO
(-4.53eV)
0.5eV
Au
Au
At V=0
(b)
9

e-
LUMO
-5.1eV
HOMO
(c)
Au
V>-1V
Au
LUMO
-5.1eV
HOMO e-
Au
V> 1 V
Au
Figure S5.
Pictorial representation of energy levels diagrams for Au/polyTHPP/Au structure at different applied bias. a) at V=0V, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are at -4.5eV and -3.90 eV, respectively where as Fermi
10

level of Au ia at -5.1eV. b) and c) at V>-1V, and V>1V, respectively. The slopes of the levels showing voltage drop across the film under applied bias.
Fabrication of ineterdigitated electrodes.
Interdigitated microelectrodes were fabricated on 4-inch oxidized silicon wafers using photolithography. Ti/Au(20nm/150nm) was deposited via electron beam deposition. Lift –off was performed to remove excess metal to reveal electrodes that were 10µm width at a pitch of
5µm. Finally, the devices were cleaned and diced as individual die for polymerization.
11

Figure S6. Steps involved in the fabrication of IDE . The four steps process to fabricate IDE
12

FRA analysis of polyTHPP on IDE
(a)
10
10Hz
8
6
4
1MHz
2
At 0V
Measured
Fitted
0
(b)
13

(c)
2.0
10
8
6
4
1MHz
2
0
0
1.5
Q
Q
5 10
Measured
Calculated
10Hz
15
Measured
Fitted
(d)
1.0
0.5
1MHz
0.0
0.0
0.5
1.0
1.5
10Hz
2.0
14

0.6
0.4
0.2
1MHz
At 3 V
10 Hz
0.0
0.0
0.2
0.4
0.6
0.8
Figure S7.
Frequency response analysis (FRA). Measured and fitted Nyquist plot of imaginary impedance (Z
 ) vs real impedance(Z′) at
(a) 0 V, (b) 2 V, (c) 2.5 V and (d) 3V. The inset in each figure shows the equivalent circuit, where symbols have their usual meaning used in FRA.
The impedance of a conducting polymer film arises from the following elements :
1.Resistance due to metal polymer interface (Rp)
2. Diffusion of counter ion through the film to maintain electrical neutrality - which manifests as Warburg impedance (W) at low frequency region in FRA analysis.
3. Capacitance of film between two metal electrodes, geometrical capacitance (Cg)
Thus, the equivalent electronic circuit for conducting polymer between two metal electrodes comprises of geometrical capacitance in parallel with polarization resistance which is in series with W.
In present studies, at 0V, the equivalent circuit consist of R, C and W which match the elements present in any conducting polymer
5
( Fig. S6(a))
15

The analyses of FRA data reveal that with increase of voltage, W changes to a constant phase element(Q) in parallel with charge resistance (Rct) in the voltage range 2V to 3V (Fig. S6(b) and
(c)). Above 3.V, the impedance circuit shrink to capacitance and resistance (RC) ( Fig S6(d) )
References
16

17