Density Functional Theory Study of Poly(o-phenylenediamine

Article pubs.acs.org/JPCC

Density Functional Theory Study of Poly(o‑phenylenediamine) Oligomers Habib Ullah,† Anwar-ul-Haq Ali Shah,*,† Khurshid Ayub,‡ and Salma Bilal§ †

Institue of Chemical Sciences, University of Peshawar, 25120 Peshawar, Pakistan Department of Chemistry, COMSATS Institute of Information Technology, University Road, Tobe Camp, 22060 Abbottabad, Pakistan § National Centre of Excellence in Physical Chemistry, University of Peshawar, 25120 Peshawar, Pakistan ‡

S Supporting Information *

ABSTRACT: Density functional theory (DFT) and timedependent DFT (TD-DFT) calculations have been performed to gain insight into the structure of poly(o-phenylenediamine) (POPD). Both reported structures of POPD, ladder (L)- and polyaniline (P)-like, are investigated theoretically through the oligomers approach. The simulated vibrational properties of 5POPD(L) and 5POPD(P) at B3LYP/6-31G (d) along with their assignments are correlated with experimental frequencies. Vibrational spectra show characteristic peaks for both POPD(L) and POPD(P) structures and do not provide any conclusive evidence. Excited-state properties such as band gap, ionization potential, electron affinities, and HOMO−LUMO gaps of POPD(L) and POPD(P) from monomers to five repeating units are simulated. UV−vis spectra are simulated at the TD-B3LYP/6-31+G (d, p) level of theory, supportive to the ladder-like structure as the major contributor. Comparison of the calculated data with the experimental one strongly suggests that the ladder-like structure is the predominant contributor to the molecular structure of POPD; however, a small amount of POPD(P) is also believed to be present.

■

INTRODUCTION Conducting polymers have gained much attraction over the last few decades due to their versatile technological application in electronic devices,1 sensors,2 electromagnetic shielding,3 corrosion protection,4 and optical and electronic devices.5 Conducting polymers can be classified on the basis of synthesis, nature, conduction mechanism, and so on. On the basis of conduction mechanism, electroactive polymers have been classified into two main groups: electron-conducting polymers and redox polymers.6 Redox polymers have certain merits over electron-conducting polymers, although the conductivity of redox polymers is lower when compared with electron conducting polymers because of the hopping mechanism.7 Poly(o-phenylenediamine) (POPD) is a redox polymer,8 and it has gained much application in the corrosion inhibition of biofilms.9 POPD, when polymerized as thin transparent layers on metal surface, it enhances the charge-transfer resistance.10 POPD, in its oxidized state, pertains conductivity even at high electrode potential.11 Besides the above-mentioned properties, POPD also finds applications in fuel cells,12 rechargeable batteries,13 electrochromic display material, and biosensors.14−17 POPD is generally synthesized by polymerization of ophenylenediamine, an aniline derivative with an amino group at its ortho position. The molecular properties of POPD are © 2013 American Chemical Society

remarkably different from polyaniline. Different suggestions are reported about the structure of POPD; it contains 2,3diaminophenazine repeat unit in a ladder-like fashion,18 or an open polyaniline (PANI)-like structure,19 as shown in Figure 1.

Figure 1. Two different structural representation of POPD.

On the basis of vibrational spectral analysis, it has been reported recently that PANI-like segments also contribute to the molecular structure of POPD.18 This inference was based on the presence of a peak at 1390 cm−1 in the Raman spectrum of POPD. The presence of the peak at 1390 cm−1 does confirm the presence of PANI-like structure; however, it does not negate the presence of the ladder-like structure. Because these Received: November 22, 2012 Revised: January 16, 2013 Published: January 30, 2013 4069

dx.doi.org/10.1021/jp311526u | J. Phys. Chem. C 2013, 117, 4069−4078

The Journal of Physical Chemistry C

Article

Figure 2. Optimized geometry of 5POPD(L).

Figure 3. Optimized geometry of 5POPD(P).

findings were based on in situ Raman studies, we became interested in carrying out a detailed theoretical vibrational and excited-state properties analysis of POPD for both PANI and ladder-like to confirm its structure. For theoretical analysis, we opted for density functional theory (DFT) and time-dependent (TD) DFT because of the reliability of DFT for predicting the geometric and electronic properties of oligomers and polymers. DFT can reliably be used for oligomers up to small-size polymers.20−24 Moreover, in the recent years, theoretical vibrational spectroscopy has emerged as a decisive tool for the structure determination of several polymers. An excellent knowledge of vibrational properties can be obtained about a molecule if suitable quantum mechanical method is used.25 The study focused on the interpretation of IR, Raman spectra, and other spectroscopic properties of oligomers and polymers has been the area of extensive exploration.6,20,23,26−31 The literature reveals that DFT at B3LYP/6-31G (d) level of theory21−23,26,30−34 can accurately calculate the geometric and electronic (band structure and excited state) properties due to its electron correlation effect. Our confidence based on the literature led us to use the B3LYP method of DFT with 6-31G (d) basis set to calculate the molecular properties of the oligomers. We have simulated the geometric, vibrational, and excited-state properties such as ionization potential (IP), electron affinities (EAs), energies of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), and band gap of POPD for both ladder- and PANI-like structures from monomer (POPD) up to five repeating units (5POPD). The

simulated data of both structures are compared with experimental data to elucidate the exact structure. For convenience, the ladder-like oligomers are denoted as nPOPD(L) and PANI-like oligomers are denoted as nPOPD(P), where n is the number of repeating unit. For UV−vis calculations, TDDFT calculations have been used at B3LYP/6-31G (d).

■

METHODS All calculations were performed using Gaussian 09.35 The visualization of results was done using Gabedit36 and MarvinView 5.9.1.37 The optimized geometries of all molecules were obtained by gradient minimization at Becke threeparameter (exchange), Lee, Yang, and Parr both local and nonlocal (correlation; DFT) (B3LYP)38 of DFT39,40 method with 6-31G (d) basis set without any symmetry constraints. The geometry optimizations were considered to be complete when the stationary point was located. The optimized structures were confirmed to be true minima by frequency analysis (no imaginary frequencies). The IE, EA, HOMO, LUMO, and band gap calculations were performed on these optimized structures. The oligomers properties were extrapolated to polymer through second-degree polynomial fit equation.26 A scaling factor 0.9613 was applied to the calculated frequency, which is required for better correlation of the computed value with the experimental one.28,41 Five repeating units of POPD represent its polymeric nature quite well; therefore, calculations are restricted up to 5POPD. Frequencies are assigned manually using Gabedit. The band gap (or the π−π* lowest electron transition) was estimated as the 4070



Article

attachments, which result in a ladder-like structure). The B3LYP/6-31G (d) optimized structure of 5POPD(P) contains all nitrogen atoms of the backbone on a common plane in a zigzag manner, whereas the 5POPD(L) is nearly planar Infrared Spectra of 5POPD(L). The theoretical simulated IR spectra of POPD(L) from monomer up to five repeating units are given in Figure 5. In general, the errors in the

difference between the HOMO and LUMO orbital energies. The negative of HOMO is estimated as IP,23,41 whereas the negative of LUMO is estimated as EA.24,38 The UV−vis spectra of the selected oligomers are simulated at TD-DFT using B3LYP/6-31G+(d, p). All calculations were performed in the gas phase.

■

RESULTS AND DISCUSSION Optimized Geometric Structure. We have optimized the structure of POPD(L) from monomer up to 5POPD(L); the optimized geometric structure of 5POPD(L) is given in Figure 2 and the Cartesian coordinates of the optimized 5POPD(L) are given in the Supporting Information. The optimized structure of 5POPD(L) is almost planar. The calculated values may be slightly different from experimental results because of the condensed phase nature of solid polymers.42 Several important simulated geometric parameters (bond lengths, bond angles, and dihedral angles) at B3LYP/6-31G (d) level of theory are given in Supporting Information Table 1 (ST1). The C−C bond length is found to be in the range of 1.39 to 1.41 Å, the C−H bond length is 1.08 Å, the C−N is 1.40 to 1.41 Å, and the N−H bond is 1.01 Å. The C−C−H bond angles are in the range of 119.03 to 120.60°, those of C−C−C are 119.15 to 121.60°, those of H−N−H are 109.14 to 109.19°, and those of C−N−H are 109.14 to 116.59°. The dihedral angles of C−C−N-C are in the range of −178.04−177.47°. The optimized geometric structure of 5POPD(P) is given in Figure 3. (See Figure S2 in the Supporting Information for details.) The important optimized geometric parameters are given in ST2. The optimized bond lengths of C−C and C−N of both structures are given in Figure 4. The C−C bond length

Figure 5. Scaled IR spectra of POPD(L) from monomer to five repeating units.

calculations are systematic; therefore, a scaling factor (0.9613) was applied to the calculated frequencies.30,41 All quoted theoretical results are thus scaled values. The majors band peaks of 5POPD(L) along with their experimental bands and approximate assignments are given in Table 1. About 15−10 cm−1 difference was found between experimental and calculated frequencies. The spectrum of 5POPD(L) is mainly composed of 15 bands peaking at 3441, 3345, 3076, 3037, 1619, 1614, 1343, 1315, 1307, 1268, 1265, 1249, 1230, 606, and 480 cm−1. The calculated 3441 and 3345 cm−1 band are assigned to N−H stretching, and 3076 and 3037 cm−1 are C−H stretching. The calculated 1619 cm−1 that corresponds to CC stretching and C−H bending correlates with the experimental 1636 cm−1. Some other important vibrations are 1614 and 1343 cm−1 (C C stretching), 1315 cm−1 (C−N stretching), 1307 cm−1 (H−C and H−N wagging), 1268 cm−1 (H−C/H-N wagging and C C stretching), 1265 cm−1 (C−N stretching), 1249 cm−1 (H−N, H−C wagging, and C−C−C scissoring), and 1233 cm−1 (H− N, H−C wagging, and CC stretching). The calculated 606 cm−1 correlates with the observed 614 cm−1 bending for rings deformation. The last 480 cm−1 band is concerned with H−N out-of-plane bending. Simulated four bands peaked at 1619, 1315, 1265, and 606 cm−1 and showed strong correlation with experimental data, evidence of the contribution of ladder-like structure.

Figure 4. Bond lengths of C−C and C−N of 5POPD(L) and 5POPD(P).

is found to be in the range of 1.39 to 1.41 Å, the C−H bond length is 1.08 Å, the C−N bond length is 1.39 to 1.43 Å, and the N−H bond is 1.01 Å. The C−C−H bond angles are in the range of 118.46−120.64°, those of C−C−C are 118.57− 122.20°, those of H−N−H are 108.27−113.17°, and those of C−N−H are 111.27−115.38°. The dihedral angles of C−C− N−C are in the range of −162.72 to 162.65°. N−C bond lengths of ladder-like structure are small as compared with PANI-like structure due to fixed NH2 (two side 4071



Article

Table 1. Experimental IR, Raman, and Calculated Frequencies (in cm−1) of 5POPD(L)a experimental18 S no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Raman

calculated frequency IR

scaled

unscaled

3441 3345 3076 3037 1619 1614 1588 1440 1343

3579 3479 3199 3159 1685 1678 1652 1498 1398

1315 1307 1268 1265 1249 1230 1186 647 606

1368 1359 1319 1316 1299 1279 1234 674 631

480

499

3700−3000

1636 1606 1575 1473 1400 1390 1319

1269 1248 1166 647 603

1287

614 578

approximate assignment νH−N νH−N νH−N νH−C νH−C νCC(Q), βC−H νCC νCC(B) νC−N N(Ring)P, νCC(B) νC−N+νC−N(Q) Wag H−C; H−N Wag H−C; H−N, νCC νC−N(B) Wag H−C; H−N, cis C−C−C, νC−N Wag H−C; H−N, νCC β H−C Def(ring) Def(ring) β H−C β H−N

ν: stretching; Wagg: Wagging; cis: scissoring; β: bending; B: benzoid; Def: deformation mode; P: phenazine-type structures; and Q: quinoid type ring. a

Infrared Spectra of 5POPD(P). The theoretical calculated IR spectra of 5POPD(P) are plotted along with their short chain analogue in Figure 6. The approximate assignments of

major bands of 5POPD(P) along with their experimental frequencies are given in Table 2. The 3403 and 3056 cm−1 bands are associated with H−N and H−C stretching, respectively. The calculated 1630 cm−1 shows correlation with the observed 1630 cm−1. A peak at 1575 cm−1 is assigned to CC, C−H stretching, and N−H scissoring. Other major bands are 1614 cm−1 (H−N−H scissoring), 1499 cm−1 (CC stretching and H−N, H−C wagging), 1417 cm−1 (CC stretching), 1230 cm−1 (CN stretching and H−C, H−N wagging), and 826, 730, and 653 cm−1 (H−N and H−C out-ofplane bending). The simulated 1307 and 1267 cm−1 bands correlate with observed 1319 and 1287 cm−1 (C−N stretching), respectively. The band peak at 638 cm−1, which is ring deformation, correlated with the observed 614 cm−1. The simulated 587 cm−1 correlates with observed 578 cm−1 and corresponds to H−N out-of-plane bending. Again the same four bands peak as that of 5POPD(L); 1619, 1315, 1265, and 606 cm−1 are simulated in 5POPD(P), which are quite interesting and confusing too. Examining the data of Table 1, one cannot elucidate the exact structure of POPD. 5POPD(P) and 5POPD(L) structures are very similar, and they contain similar types of bonds except that the former has NH2 moieties spread over chain in addition to NH, whereas the ladder-like structure has only NH groups available. A way to experimentally distinguish the 5POPD(P) and 5POPD(L) is to analyze the region between 3500 and 3000 cm−1, where these two structures should appear differently; however, the experimental spectrum shows a broad peak in this region. Therefore, the structure elucidation is very limited. Raman Spectra of 5POPD(L). The theoretical Raman spectra of 5POPD(L) (Figure 7) and their comparison with the experimental spectrum of POPD (Table 1) indicate that the experimental 1606 cm−1 is correlated with the calculated 1614 cm−1 band, which is CC stretching. The simulated CC

Figure 6. Scaled IR spectra of POPD(P) from monomer to five repeating units. 4072



Article

Table 2. Experimental IR, Raman, and Calculated Frequencies (in cm−1) of 5POPD(P)a experimental18 S no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 a

Raman

calculated frequency IR

scaled

unscaled

3403 3056 1630 1575 1614 1499 1488 1417 1395

3539 3179 1696 1639 1678 1559 1548 1475 1452

1387 1307 1267 1267 1230 1145 826 730 645 638 653 638 587 480

1443 1360 1319 1319 1279 1192 859 759 671 664 679 664 611 499

3700−3000

1606 1575

1636

1473 1400 1390

1269 1248

1319 1287 1287

1166

647

603

614 578

approximate assignment νH−N νH−N νH−C νCC(Q), νC−H νCC(Q), νC−H cis H−N−H νCC, Wag H−C; H−N νC−N, Wag H−N N(Ring)P, νCC(B) νCC, Wag H−C; H−N νC−N+νCC, Wag H−C; H−N νC−N(Q) νC−N(B) νC−N νCN, Wag H−C; H−N β H−C β H−N, β H−C β H−N, β H−C Def(ring) Def(ring) β H−N, β H−C Def(ring) β H−C β H−N

ν: stretching; Wagg: Wagging; cis: scissoring; β: bending; B: benzoid; Def: deformation mode; P: phenazine-type structures; Q: quinoid type ring.

experimental C−N stretching at 1473 is 33 cm−1 higher than the calculated 1440 cm−1 band. The next prominent band at 1269 cm−1 (C−N stretching) is very similar to our calculated 1265 cm−1. Another band at 1248 cm−1 is also strongly correlated with the calculated 1249 cm−1 (H−N and H−N wagging, C−C−C scissoring, and C−N is stretching). Two weak bands at 647 and 603 cm−1 correspond to ring deformation and are similar to our calculated 647 and 606 cm−1 bands, respectively. The theoretical and experimental results show correlation with one another and cannot conclude which alternative is dominant. Raman Spectra of 5POPD(P). A comparison of Raman spectra of POPD(P) from monomer up to five repeating units is given in Figure 8. Correlations of major experimental Raman bands with theoretical data along with their approximate assignments are listed in Table 2. The most intense band in the Raman spectra of POPD is at 1473 cm−1, which has contribution from C−N stretching and N−H wagging. This assignment of band is similar to the calculated 1488 cm−1. The two shoulder peaks around 1473 are 1575 and 1269 cm−1, which are associated with CC, C−H, N−H, and C−N stretching. The 1575 cm−1 band is exactly similar to the calculated 1575 cm−1, and 1269 cm−1 is also strongly correlated with the simulated 1267 cm−1. In the lower region of spectra, two bands at 647 and 603 cm−1, which are due to ring deformation, can be correlated to the calculated 645 and 638 cm−1, which are also concerned with ring deformation. From the analysis of the correlation Table 3 and Figures 9 and 10, the contribution of both PANI and ladder-like structures is concluded. Vibrational spectroscopy is a key characterization for structure elucidation, but due to smaller difference between the two structures, the results are not so

Figure 7. Scaled Raman spectra of POPD(L) from monomer to five repeating units.

stretching, which appear at 1588 cm−1, is strongly correlated with the experimental Raman band at 1575 cm−1. The 4073



Article

Figure 9. Scaled IR spectra of 5POPD(P) (red) and 5POPD(L) (black).

Figure 8. Scaled Raman spectra of POPD(P) from monomer to five repeating units.

useful. We cannot conclude safely which alternative is dominant because both the IR and Raman (correlation of experimental and theoretical) results contribute both structures. So, here in our case, frequency calculation cannot give us exact conclusion. HOMO and LUMO Energy and Band Gap. The HOMO and LUMO of 5POPD(L) and 5POPD(P) calculated at B3LYP/6-31G (d) are shown in Figure 11. The HOMO and LUMO of 5POPD(L) are extended to all carbons, hydrogens, and nitrogens and form a ladder like structure and involve delocalization over the entire molecule framework. Where in the 5POPD(P) half of the atoms do not contribute to the electron density in the HOMO and LUMO, therefore, no delocalization over the entire framework of 5POPD(P) takes place. The HOMO and LUMO energies of both types of POPD, from monomer up to infinite repeating units, are given in the Tables 4 and 5 and also in Figure 12 and 13. The extrapolating oligomer data plot up to polymer is given in the Supporting Information (S10−S19). Data for oligomers are

Figure 10. Scaled Raman spectra of 5POPD(P) (red) and 5POPD(L) (black).

extrapolated to polymers, and the plots are given in the Supporting Information along with correlation coefficients. With increasing conjugation, energy of HOMO increases, whereas the energy of LUMO decreases, and this causes

Table 3. Correlation of the Experimental IR, Raman, and Calculated Frequencies (in cm−1) of 5POPD(L) and 5POPD(P) experimental

calculated frequencies

experimental

calculated frequencies

S no.

IR

5POPD(L)

5POPD(P)

Raman

5POPD(L)

5POPD(P)

1 2 3 4 5 6 7 8 9

3700−3000 3700−3000 1636 1400 1319 1287 614 578

3441 3345 1619 1440 1315 1265 606

3403

1606 1575 1473 1390 1269 1248 1166 647 603

1614 1588 1440

1575 1488

1265 1249 1187 647 606

1267 1267 1145 645 638

1630 1417 1307 1267 638 587

4074



Article

Figure 11. Molecular orbitals at isovalue = 0.02 of 5POPD(L) and 5POPD(P).

decrease in the band gap. The HOMO−LUMO energy differences of 5POPD(L) and 5POPD(P) are 3.21 and 4.3 eV, respectively, and these correspond to ππ* transition energies. The band gap of 5POPD(L) and 5POPD(P) oligomers is extrapolated to polymer through second-degree polynomial fit equation. The band gap is obtained from the difference of the orbital energies (valence and conduction band). The experimental band-gap value of POPD is 2 eV calculated by Saraswathi et al.43 and significantly correlates well with the calculated band gap of POPD(L), which is 2.4 eV, whereas POPD(P) has 3.95 eV. UV−Visible Spectroscopy. The theoretical simulated UVvis spectra of 5POPD(L) and 5POPD(P) at TDDFT-B3LYP/ 6-31 +G (d, p) level of theory are given in Figure 14. Oscillator strength is used as a measure of the relative strength of the electronic transitions within atomic and molecular systems;44 therefore, it serves the same purpose as absorbance. 5POPD(L) has vertical transition energy (should correspond to λmax value, but this is an approximation) at 424 nm whereas 5POPD(P) has vertical transition energy at 323 nm. The experimental UVvis spectrum of a thin film polymer of POPD, reported by Muthirulan et al. shows two peaks: an intense peak at 428 nm and a small peak at 295 nm. The theoretical simulated λmax

Table 4. IPs, EAs, HOMOs, LUMOs, and Band Gaps of POPD(L) n, rep. unit

IP (eV)

EA (eV)

HOMO (eV)

LUMO (eV)

band gap (eV)

1 2 3 4 5 ∞

4.44 3.88 3.55 3.41 3.21 2.7

−0.83 −0.33 −0.15 −0.07 0 0.22

−4.44 −3.88 −3.55 −3.41 −3.21 −2.7

0.83 0.33 0.15 0.07 0 −0.22

5.27 4.21 3.7 3.48 3.21 2.4

Table 5. IPs, EAs, HOMOs, LUMOs, and Band Gaps of POPD(P) n, rep. unit

IP (eV)

EA (eV)

HOMO (eV)

LUMO (eV)

band gap (eV)

1 2 3 4 5 ∞

4.44 4.56 4.47 4.41 4.36 4.11

−0.83 −0.18 0.01 0.04 0.06 0.16

−4.44 −4.56 −4.47 −4.41 −4.36 −4.11

0.83 0.18 0.01 −0.04 −0.06 −0.16

5.27 4.74 4.48 4.37 4.3 3.95

4075



Article

Figure 12. Development of band structure of 5POPD(L) from energy levels of oligomers. (The monomer is used as a repeat unit).

Figure 13. Development of band structure of 5POPD(P) from energy levels of oligomers. (The monomer is used as a repeat unit.)

Figure 14. Calculated UV−vis spectra of 5POPD(L) (red) and 5POPD(P) (black).

spectrum is for an oligomer of five repeating units whereas the experimental UV-vis spectrum is for an infinite thin film polymer. Electronic Properties like IP and EA. The IP and EA obtained from the negative of the DFT orbital (HOMO and LUMO) energy (Koopman’s theorem) with typical exchange correlation functionals is usually small as compared with experimental values. The implementation of hybrid functionals (B3LYP), which accounts for the effects of self-interaction, is used to achieve better correlation. The IP and EA of both types of POPDs are listed in Tables 4 and 5, respectively. These Tables show that all of the IPs from monomers up to five repeating units are positive values, whereas some of the EA values are in negative. The negative EA means that the anionic state is unbound.

value of 5POPD(L) and 5POPD(P) at 424 and 323 nm, respectively show strong correlation with experimental POPD's band peaked at 42845 and 295 nm. The peak at 295 nm in the experimental UV-vis spectra of POPD is concerned with π→π* transition of the benzenoid rings while 428 nm suggests the existence of quinoid imine units, confirming a mixture of two structures.45 So, 428 and 295 nm band peaks are clear evidence of the existence of POPD(L) and POPD(P), respectively. However, the peak at 295 nm is very small, which indicates that POPD(P) is a small contributor to the real structure. The experimental UV-vis spectra of POPD (428 nm peak) has about 4 and 28 nm (295 nm peak) difference from that of simulated UV-vis spectra of 5POPD(L) and 5POPD(P), respectively. This distinction is due to the difference in the length of polymer and gas phase simulation. The simulated 4076


The Journal of Physical Chemistry C Because no experimental IP or EA of POPD is reported in the literature so far, correlation cannot be achieved. The simulated IP and EA will be fruitful for the future experimentalists.

CONCLUSIONS We have carried out quantum mechanical calculation for the structure elucidation POPD at both TD-DFT and DFTB3LYP/6-31G (d) level of theory for both PANI and ladderlike from monomer up to five repeating units. The B3LYP/631G (d) optimized geometry of 5POPD(P) contains all nitrogen atoms of the backbone in a zigzag fashion, and the whole structure seem to be bend, whereas the optimized geometry of 5POPD(L) is quite close to planarity. Subsequent to optimization, vibrational and other excited-state properties like HOMO, LUMO, IP, EA, and band gap have been calculated at the above-mentioned level of theory. From the correlation of simulated IR and Raman frequencies of 5POPD(L) and 5POPD(P) with experimental, it is concluded that the contribution of both PANI and ladder-like structure is present, and no conclusion in favor of either structure could be drawn. The UV−vis spectra were calculated at TD-DFT (B3LYP/6-31+G (d, p) method. From the comparison of simulated band gap and UV−vis spectra of 5POPD(L) and 5POPD(P) with the experimental data of POPD, it is concluded that the real molecular structure of POPD has major contribution from the ladder-like structure, whereas the PANI structure has a small contribution. The intense experimental band of POPD (428 nm) is in good agreement with the calculated 5POPD(L) (424 nm). The simulated extrapolated (through second-degree polynomial fit equation) band gap value of POPD(L), which is 2.4 eV, also correlates well with the experimental 2 eV value, as compared with POPD(P), which is 3.95 eV.

■

REFERENCES

(1) Cai, Z.; Martin, C. R. J. Am. Chem. Soc. 1989, 111, 4138−4139. (2) Kaneto, K.; Kaneko, M.; Min, Y.; MacDiarmid, A. G. Synth. Met. 1995, 71, 2211−2212. (3) Lu, W. K.; Elsenbaumer, R. L.; Wessling, B. Synth. Met. 1995, 71, 2163−2166. (4) Tan, C.; Blackwood, D. Corros. Sci. 2003, 45, 545−557. (5) He, H.; Zhu, J.; Tao, N. J.; Nagahara, L. A.; Amlani, I.; Tsui, R. J. Am. Chem. Soc. 2001, 123, 7730−7731. (6) Gospodinova, N.; Terlemezyan, L. Prog. Polym. Sci. 1998, 23, 1443−1484. (7) Goyette, M. A.; Leclerc, M. J. Electroanal. Chem. 1995, 382, 17− 23. (8) Malinauskas, A. Synth. Met. 1999, 107, 75−83. (9) Atta, N. F.; Galal, A.; Mark, H. B., Jr.; Yu, T.; Bishop, P. L. Talanta 1998, 47, 987−999. (10) Wang, F.; Luo, J.; Yang, K.; Chen, J.; Huang, F.; Cao, Y. Macromolecules 2005, 38, 2253−2260. (11) Holze, R. Electrochim. Acta 2011, 56, 10479−10492. (12) MacDiarmid, A.; Yang, L.; Huang, W.; Humphrey, B. Synth. Met. 1987, 18, 393−398. (13) Handbook of Advanced Electronic and Photonic Materials and Devices: Conducting Polymers; Nalwa, H. S., Ed.; Academic Press: San Diego, 2001; Vol. 8. (14) Shah, A. A.; Holze, R. Electrochim. Acta 2006, 52, 1374−1382. (15) Shah, A. A.; Holze, R. Electrochim. Acta 2008, 53, 4642−4653. (16) Shah, A. A.; Holze, R. J. Solid-State. Electrochem. 2007, 11, 38− 51. (17) Guimard, N. K.; Gomez, N.; Schmidt, C. E. Prog. Polym. Sci. 2007, 32, 876−921. (18) Bilal, S.; Shah, A. A.; Holze, R. Electrochim. Acta 2011, 56, 3353−3358. (19) Mattoso, L.; Manohar, S.; MacDiarmid, A.; Epstein, A. J. Polym. Sci., Part A.: Polym. Chem. 1995, 33, 1227−1234. (20) Alemán, C.; Domingo, V. M.; Fajarí, L.; Juliá, L.; Karpfen, A. J. Org. Chem. 1998, 63, 1041−1048. (21) Romanova, J.; Petrova, J.; Tadjer, A.; Gospodinova, N. Synth. Met. 2010, 160, 1050−1054. (22) Salzner, U.; Aydin, A. J. Chem. Theor. Comput. 2011, 7, 2568− 2583. (23) Salzner, U.; Pickup, P.; Poirier, R.; Lagowski, J. J. Phys. Chem. A 1998, 102, 2572−2578. (24) Salzner, U. J. Phys. Chem. A 2008, 112, 5458−5466. (25) Louarn, G.; Lapkowski, M.; Quillard, S.; Pron, A.; Buisson, J.; Lefrant, S. J. Phys. Chem. 1996, 100, 6998−7006. (26) Salzner, U. J. Phys. Chem. A 2010, 114, 5397−5405. (27) Alemán, C.; Ferreira, C. A.; Torras, J.; Meneguzzi, A.; Canales, M.; Rodrigues, M. A. S.; Casanovas, J. Polymer 2008, 49, 5169−5176. (28) Casado, J.; Hernández, V.; Ramirez, F.; López Navarrete, J. J. Mol. Struct. (THEOCHEM) 1999, 463, 211−216. (29) Förner, W. J. Mol. Struct. (THEOCHEM) 2004, 682, 115−136. (30) Mishra, A. K.; Tandon, P. J. Phys. Chem. B 2009, 113, 9702− 9707. (31) Mishra, A. K.; Tandon, P. J. Phys. Chem. B 2009, 113, 14629− 14639. (32) Liu, S. S.; Bian, L. J.; Luan, F.; Sun, M. T.; Liu, X. X. Synth. Met. 2012, 162, 862−867. (33) Ma, J.; Li, S.; Jiang, Y. Macromolecules 2002, 35, 1109−1115. (34) Romanova, J.; Petrova, J.; Ivanova, A.; Tadjer, A.; Gospodinova, N. J. Mol. Struct. (THEOCHEM) 2010, 954, 36−44.

ASSOCIATED CONTENT

S Supporting Information *

Tables of selected optimized geometric parameters, optimized geometries along with Cartesian coordinates of POPD(L) and POPD(P) from monomer to five repeating units, and extrapolating data plots through second-order polynomial fit equation. This material is available free of charge via the Internet at http://pubs.acs.org.

■

ABBREVIATIONS

DFT, density functional theory; PANI, polyaniline; B3LYP, Becke Three-Parameter and Lee Yung Pur; POPD(L), poly(ophenylenediamine) ladder-like; POPD(P), poly(o-phenylenediamine) PANI-like; HOMO, highest occupied molecular orbital; LUMO, lowest unoccupied molecular orbital

■

■

■

Article

AUTHOR INFORMATION

Corresponding Author

*Tel: +92 91 9216652. E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. Funding Sources

We acknowledge the Higher Education Commission (HEC) of Pakistan and University of Peshawar for financial support to the project. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We gratefully thank Professor Dr. Ulrike Salzner for helpful discussions. 4077



Article

(35) Frisch, M.; Trucks, G.; Schlegel, H.; Scuseria, G.; Robb, M.; Cheeseman, J.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al. Gaussian 09, revision C. 01; Gaussian, Inc.: Wallingford, CT, 2009. (36) Allouche, A.-R. Gabedit, 2007. http://gabedit.sourceforge.net; accessed April 1, 2012. (37) Csizmadia, P. Marvin, 1999. http://www.chemaxon.com/ marvin; accessed Oct 9, 2012. (38) Becke, A. D. Phys. Rev. A 1988, 38, 3098−3100. (39) Yanai, T.; Tew, D. P.; Handy, N. C. Chem. Phys. Lett. 2004, 393, 51−57. (40) Andersson, M.; Uvdal, P. J. Phys. Chem. A 2005, 109, 2937− 2941. (41) Foresman, J. B.; Frisch, Æ. Exploring Chemistry with Electronic Structure Methods; Gaussian: Pittsburgh, PA, 1996. (42) Rani, A. U.; Sundaraganesan, N.; Kurt, M.; Cinar, M.; Karabacak, M. Spectrochim. Acta, Part A: Mol. Biomol. Spectr. 2010, 75, 1523−1529. (43) Sivakkumar, S.; Saraswathi, R. J. Appl. Electrochem. 2004, 34, 1147−1152. (44) Scholes, G. D. Annu. Rev. Phys. Chem. 2003, 54, 57−87. (45) Muthirulan, P.; Rajendran, N. Surf. Coat. Technol. 2011, 206, 2072−2078.

4078


Density Functional Theory Study of Poly(o-phenylenediamine

Recommend Documents