DFT study of structure, IR and Raman spectra of P0′ and P4′ dendrimers built from octasubstituted metal-free phthalocyanine core

Chemical Physics 358 (2009) 177–183

Contents lists available at ScienceDirect

Chemical Physics journal homepage: www.elsevier.com/locate/chemphys

DFT study of structure, IR and Raman spectra of P00 and P04 dendrimers built from octasubstituted metal-free phthalocyanine core V.L. Furer a,*, I.I. Vandyukova b, A.E. Vandyukov b, J.P. Majoral c, A.M. Caminade c, V.I. Kovalenko b,* a

Kazan State Architect and Civil Engineering University, Zelenaya, 1, Kazan 420043, Tatarstan, Russia A.E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Science, Arbuzov Str., 8, 420088 Kazan, Russia c Laboratorie de Chimie de Coordination, CNRS, 205 route de Narbonne, 31077 Toulouse, Cedex 4, France b

a r t i c l e

i n f o

Article history: Received 15 September 2008 Accepted 13 January 2009 Available online 25 January 2009 Keywords: Dendrimers IR spectra Normal vibrations DFT

a b s t r a c t The IR and Raman spectra of P00 and P04 dendrimers built from an octasubstituted metal-free phthalocyanine core with oxybenzaldehyde terminal groups have been recorded. The phthalocyanine core was used as a probe for analyzing the properties of the internal structure. The structural optimization and normal mode analysis were performed for P00 dendrimer on the basis of the density functional theory (DFT). It was found that the P00 molecule exists in a stable conformation with planar phthalocyanine core. The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. The experimental IR spectra of P1 dendrimer were interpreted by means of potential energy distributions. Relying on DFT calculations a complete vibrational assignment is proposed. The difference IR and Raman spectra of molecules built from the thiophosphoryl and phthalocyanine cores with the same repeating units and terminal groups were studied in order to underline the role of the core functionality on the dendrimer architecture. Ó 2009 Elsevier B.V. All rights reserved.

1. Introduction Phthalocyanines possess unique properties, which led to widespread applications in materials science and nanotechnology including second-order and third-order nonlinear optical activities and optical limiting properties [1,2]. The problem when using such compounds is their stacking tendency to form aggregated species in solution [3–5]. In order to increase solubility dendritic substituents are grafted to the phthalocyanine core [3–5]. It is important for application of the phthalocyanines for instance in photodynamic therapy, because aggregation induces a significant decrease in the photosensitising efficiency [3–5]. Dendrimers are highly branched monodisperse macromolecular compounds [6–9]. A fine control of the shape and properties of dendrimer can be achieved [6–9]. The three structural components of dendrimers, namely an interior core, repeating branching units attached to the core, and functional terminal groups can be tuned at will [6–9]. The concept of site isolation of the active core, leading to enhanced photophysical properties was developed [8]. To yield a better understanding of the effect imparted by each component to the whole structure and the influence of each part on the others, it

* Corresponding authors. Address: Kazan State Architect and Civil Engineering University, Zelenaya 1, Kazan 420043, Tatarstan, Russia. Tel.: +7 8432 104737; fax: +7 8432 387972 (V.L. Furer), tel.: +7 8432 732283; fax: +7 8432 732253 (V.I. Kovalenko). E-mail addresses: [email protected] (V.L. Furer), [email protected] (V.I. Kovalenko). 0301-0104/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2009.01.010

is highly desirable to introduce the density functional theory (DFT) studies of dendrimers. The preparation, IR and Raman spectra of phosphorus dendrimers with thiophosphoryl core built up to 12th generation with terminal aldehyde and P–Cl groups were described [9,10]. Dendrimers with phthalocyanine core gave an opportunity to study a large variety of photo- and physico-chemical properties [11–13]. In this paper we report the IR and Raman spectra study combined with DFT calculations of P00 which is the zero generation dendrimer built from an octasubstituted metal-free phthalocyanine core with oxybenzaldehyde terminal groups [11]. The IR spectra of the fourth generation P04 were also examined. Such generation was chosen because it was shown that the branches of this dendrimer induce a great influence upon the core in terms of isolation and polarity [12]. This work is an extension of the spectroscopic and quantum chemical studies concerning the structure and reactivity of phosphorus-containing dendrimers [10]. The optimized structure parameters of P00 molecules were obtained using DFT techniques. The values of calculated geometric parameters were compared with available experimental data derived by the X-ray analysis [12]. Thus the main aim of this work was to obtain the characteristic spectral features of structural parts of dendrimer: a phthalocyanine core and terminal oxybenzaldehyde groups based on DFT quantum chemical computation. The difference IR and Raman spectra of molecules built from the trifunctional thiophosphoryl and octafunctional phthalocyanine cores with the same repeating units and terminal groups were studied in order

178

V.L. Furer et al. / Chemical Physics 358 (2009) 177–183

to underline the role of the core functionality on the dendrimer architecture. Analysis of IR and Raman spectra of dendrimers combined with DFT calculations is important for investigation of supramolecular properties of dendrimers as containers for different guest molecules. The calculation of electronic density spatial distribution reveals the existence of regions where appropriate environments would attract either ion or a metal atom. The interpretation of IR spectra of non-crystalline dendrimers is important for characterization of their structure. The results that emerge from such an analysis contribute to the understanding of the structure, dynamics and properties of dendrimers.

3. Computational method Calculations of IR spectra of dendrimer P00 were carried out using the gradient-correlated density functional theory with Perdew–Burke–Ernzerhof exchange-correlation functional (DFT/PBE) [14]. This functional is very satisfactory from the theoretical point of view because it does not contain any fitting parameters [15]. The binding energies, geometries and dynamical properties of different molecules calculated with PBE functional [16,17] show the best agreement with experiment. Calculations were performed using three exponential basis with two polarizing functions (TZ2P) [18]. The geometry optimization was also done using B3LYP functional [19], revealing that the method PBE/TZ2P is more accurate (Table 1). The chosen functional and basis sets have clearly provided an accurate method of calculating the dendrimers structural parameters, dipole moments, IR and Raman spectra [20]. The program PRIRODA was used to perform DFT calculations [18]. All stationary points were characterized as minima by analysis of the Hessian matrices. No scaling procedure of wavenumbers or force constants was applied. The minima of the potential surface were found by relaxing the geometrical parameters with standard optimization methods. IR spectra were generated from a list of frequencies and intensities using the Gaussian band shape and half-width r of 10 cm1 for each of N vibration modes calculated. The intensity of each band is Ak in km/mol.

2. Experimental The synthesis and main characteristics of the studied dendrimers were described earlier [9,12]. The molecule P00 contains an octafunctional phthalocyanine core (Pc) and the 4-oxybenzaldehyde –O–C6H4–CHO terminal groups. The molecular structure of the P04 dendrimer is the following: a phthalocyanine core, the bifunctional repeating unit –O–C6H4–CH@N–N(CH3)–P(S)< and the terminal groups are the 4-oxybenzaldehyde fragments (Fig. 1). The analogous molecules built from a trifunctional core S@P(–O–)3 (G00 and G04 ), and the same repeating units and terminal groups were studied in order to underline the role of the core functionality on the dendrimer architecture (Fig. 1). IR spectra in the region 4000–400 cm1 have been recorded with a Vector 22 Bruker FTIR spectrometer. The spectral resolution was set at 4 cm1. Sixty-four scans were added for each spectrum. The studied samples were placed between the KBr plates. The Raman spectra in the region 3500–10 cm-1 were excited by Nd: YAG laser line 1064 nm with power at sample 300 mW and were recorded with an FRA106/S Bruker FT-Raman module with a 4 cm1 resolution.

O

IðmÞ ¼

N X k

( ) Ak ðm  m0 Þ2 pffiffiffiffiffiffi ffi exp  : 2r 2 2pr

The software package SHRINK was used for transformation of quantum mechanical Cartesian force constants to the matrix in redundant internal coordinates and calculation of potential energy distribution (PED) [21].

O

H

H

H

O

O

O

O

O

N

O NH

H

N

N

H

N N

HN

O

N

O

O O

O

H H

O

H

S

P

O

3

O G'0

P'0

Me Pc

CHO

O

O

C N N P H S

Me

Me O

C H

N N P

O

C N N P H S

S

Me O

C N N P H S

O

CHO

2

2

2

2

2

2 8

P'4

Me S

P

O

C N N P H S

Me O

C H

Me

N N P

O

C N N P H S

S

Me O

C N N P H S

O

G'4

Fig. 1. The structures of dendrimers built from phthalocyanine (P00 , P04 ) and thiophosphoryl (G00 , G04 ) cores.

CHO

2

2 3

V.L. Furer et al. / Chemical Physics 358 (2009) 177–183 Table 1 0 Experimental and calculated bond distances (Å A) and bond angles (°) of P00 . Experimental [12,22]

Calculated

Bond distances C(1)–C(2) C(2)–C(4) C(2)–C(6) C(4)–N(1) C(9)–N(4) C(30)–O(1) C(33)–O(1) C(33)–C(34) C(38)–C(81) C(81)–O(9)

1.388 1.453 1.398 1.324 1.263 1.378 1.397 1.375 1.467 1.217

Free base form

Dianionic form

PBE

B3LYP

PBE

B3LYP

1.396 1.452 1.415 1.318 1.368 1.372 1.384 1.399 1.482 1.215

1.461 1.523 1.483 1.382 1.441 1.450 1.466 1.465 1.563 1.264

1.396 1.453 1.414 1.318 1.370 1.381 1.380 1.399 1.478 1.216

1.394 1.480 1.416 1.340 1.352 1.406 1.360 1.404 1.469 1.220

Angles C(1)–C(3)–C(5) C(1)–C(3)–O(3) C(2)–C(4)–N(2) C(2)–C(6)–C(8) C(3)–O(3)–C(45) C(4)–N(1)–C(9) C(4)–N(2)–C(8) C(38)–C(81)–O(9) C(46)–C(45)–C(47) N(1)–C(4)–N(2)

119.8 124.0 108.3 107.4 119.9 121.9 109.8 124.2 121.9 128.4

121.1 118.9 106.0 107.7 119.9 123.3 112.7 125.0 121.0 128.0

121.1 118.5 106.0 105.8 119.0 122.4 112.8 125.2 121.0 128.6

121.2 118.9 106.1 107.9 119.7 122.8 112.5 125.2 120.9 127.2

121.1 119.8 110.0 105.4 118.9 121.8 109.1 126.1 120.3 128.6

Dihedral angles C(1)–C(2)–C(6)–C(7) C(1)–C(2)–C(6)–C(8) C(2)–C(6)–C(8)–N(2) C(2)–C(6)–C(8)–N(3) C(4)–N(1)–C(9)–N(4) C(4)–N(2)–C(8)–C(6) C(4)–N(2)–C(8)–N(3) C(28)–C(30)–O(1)–C(33) C(30)–C(32)–O(2)–C(39) C(30)–O(1)–C(33)–C(35) C(32)–O(2)–C(39)–C(41) C(36)–C(38)–C(81)–O(9)

0.1 179.4 0.0 179.2 0.6 0.3 177.5 64.2 28.9 158.8 141.7 177.4

0.4 179.7 0.1 179.9 0.0 0.0 179.9 32.5 68.4 144.6 163.2 179.8

0.3 179.5 0.0 179.9 0.4 0.1 179.9 29.8 72.8 139.5 165.0 179.6

0.6 178.9 0.2 179.2 0.4 0.1 179.3 35.0 62.8 169.7 148.3 179.8

0.4 179.7 0.0 179.6 0.1 0.0 179.6 79.5 114.0 178.6 175.8 179.5

4. Results and discussion There are no X-ray diffraction experimental data for the entire P00 by, but we can use the geometric parameters of fragments of it, in particular bisformylphthalonitrile from which P00 was synthesised and phthalocyanine [12,22]. To have a deeper insight on the acido/basicity properties of the phthalocyanine ring the liability of core hydrogens were studied. The four pyrrole nitrogen atoms can theoretically undergo protonation/deprotonation reactions (Fig. 2) which modify the symmetry of the phthalocyanine ring and affect particularly UV–visible spec-

R

R

R R

R

R

R

N N

NH

N

N

N

N

NH

N N N N

R R

N N

N

R

R

N

R

R

R R

R

R= O

Fig. 2. The free base and dianionic forms of dendrimer P00 .

CHO

179

tra [12]. The results of full optimization calculations for P00 molecules are presented in Table 1. Although the comparison between gas phase and solid state phase structures is not direct, we can observe a reasonable agreement between theoretical calculations of the free base form of P00 and experimental UV–visible and X-ray diffraction data [12,22] (Table 1). Full optimization yielded the conformer of P00 with planar phthalocyanine ring (Fig. 3). The calculated dihedral angles of phthalocyanine ring are less than 4°. Our data correspond to recent ab initio calculations of phthalocyanine [23]. It was shown that most of the phthalocyanine derivatives have planar conformation [23]. In the molecule P00 each –C6H4–CHO fragment is planar. Thus the molecular conformation is defined by dihedral angles C(32)– C(30)–O(1)–C(33) and C(30)–C(32)–O(2)–C(39), which determine the orientation of terminal groups (Fig. 2). As it follows from the X-ray data the experimental dihedral angles C(32)–C(30)–O(1)– C(33) and C(30)–C(32)–O(2)–C(39) are equal to 64.2° and 151.1°. Full optimization yielded the conformer with dihedral angles 74.1° and 144.5°. The experimental dihedral angles C(30)–O(1)– C(33)–C(35) and C(32)–O(2)–C(39)–C(41) are equal to 158.8° and 141.7° and correspond to calculated values 169.7° and 148.3°. Thus as it follows from the experimental and theoretical data of P00 benzaldehyde groups are not coplanar with phthalocyanine core. The calculated bond distances and angles of the dianionic and free base forms of P00 show little difference and correspond well to the experimental values. The conformations of benzaldehyde groups are slightly different for theoretical structures of the dianionic and free base forms of P00 and in the crystalline state. These deviations may be ascribed to inter-molecular effect. The benzaldehyde terminal groups of P00 dendrimer are out of the phthalocyanine core plane due to steric reasons. However, the phthalocyanine P00 is isolated as a poorly soluble dark-green powder [12]. It was shown that neighboring molecules of octasubstituted phthalocyanines inside the columnar stack by an angle close to 45° [5]. The dendrimer shape can be characterized by ratios I1/I3 and I2/I3 of principal moments of gyration tensor. The difference of these ratios from 1 characterizes the deviation of dendrimer shape from the sphere. For the studied dendrimers the calculated values of ratios I1/I3 and I2/I3 of principal moments of gyration tensor are 0.347 and 0.740 (G00 ), 0.527 and 0.540 (P00 ). Thus the G00 and P00 molecules have highly asymmetric shape and possess open structures. In order to evaluate the interactions between dendrimers and various active substances such as drugs, pesticides, and perfumes, we calculated electronic density spatial distribution for the core and terminal groups. From our calculations it follows that the P00 and P04 dendrimers incorporate C–N polar bonds in the phthalocyanine core with the Hirshfeld charges (in a.u.) on atoms [24] N(1) 0.14, N(1) 0.03, N(4) 0.16 and C(4) 0.10. The oxygen atoms of the terminal group also have negative charges 0.06 (C–O bond) and 0.21 (C@O bond). Thus there are active sites for reaction and interaction in the core of dendrimer and in the terminal groups. Dipole moments may be used for characterization of dendrimer structure. It was shown that the experimental dipole moments of dendrimers built from thiophosphoryl core and 4-oxybenzaldehyde terminal groups increase from 8.27 D (G01 ) to 328 D (G011 ), the highest dipole moment values reported up to now for dendritic structures [25]. The calculated in gas phase dipole moment 8.27 D for the free base form of P00 . Thus the P00 dendrimer has a significant dipole moment which may be attributed to a non-symmetrical distribution of the lone pairs of the oxygen atoms. In this work we calculated the IR spectra of P00 containing the free base neutral and dianionic forms of phthalocyanine core. The experimental and calculated IR and Raman spectra of P00 are represented in Figs. 4 and 5 and Table 2. Thus the phthalocyanine core reveals itself by bands at 746, 879, 1013, 1086, 1274 and

180

V.L. Furer et al. / Chemical Physics 358 (2009) 177–183

Fig. 3. The conformer of dendrimer P00 .

3.0

2.0

2

2.5

Absorbance

2.0

1.5

2

1.0

0.5

1.5

1.0

1

0.5

1

0.0 1800

Raman Intensity/arb. units

3

0.0 1600

1400

1200

1000

800

600

400

Wavenumber/cm -1 Fig. 4. Theoretical spectra of the free base form (1), dianionic form (2), and experimental IR spectra of dendrimer P00 .

1800

1600

1400

1200

1000

Wavenumber/cm

800

600

-1

Fig. 5. Experimental Raman spectra of dendrimers G00 (1) and P00 (2).

181

V.L. Furer et al. / Chemical Physics 358 (2009) 177–183 Table 2 Experimental and corresponded calculated frequencies m (cm1) and intensity I (km/mol) of bands in the IR spectra of P00 in the region 400–1800 cm1. Experiment

Calculation Assignmenta

IR

Raman

Free base form

m

m

m

I

m

I

PED

1698 1594

1700 1602 1576 1544 1521 1501 1462

1743 1590 1571 1550 1518 1501 1466 1440 1422 1413 1394 1354 1336 1307 1273 1213 1224 1181 1167 1156 1128 1119 1085 1015 976 947 884 880 859 830 780 743 729 708 699 691 653 641 629 611 573 569 545 528 503 436 417

451.0 276.6 276.6 50.9 3.6 21.8 740.8 461.3 17.5 6.3 952.1 10.8 18.6 243.9 354.6 213.3 1002.3 38.4 40.6 187.6 259.5 159.7 14.2 251.1 1.3 1.5 97.5 25.4 12.6 27.6 115.4 64.8 9.5 8.3 3.0 8.6 14.0 21.9 7.8 22.6 3.4 2.0 1.5 10.2 10.8 4.0 0.9

1736 1601 1569 1547 1512 1498 1436 1436 1422 1411 1396 1355 1337 1295 1273 1223 1238 1162 1162 1162 1122 1122 1086 997 997 997 876 876 860 833 788 746 703 703 696 696 649 641 630 611 579 565 551 528 500 432 419

432.8 271.8 72.2 5.5 40.2 56.0 753.6 752.8 68.0 178.7 32.5 72.7 59.3 5.7 270.9 370.2 370.2 42.9 42.9 42.9 483.2 483.2 34.2 473.6 473.6 473.6 35.8 35.8 188.1 27.3 12.8 13.2 77.3 77.3 116.6 116.6 56.5 18.1 31.1 28.4 0.1 4.3 7.7 1.3 8.9 5.9 1.5

85 72 60 72 42 58 42 19 64 51 51 29 55 42 65 29 23 42 53 61 26 54 31 32 24 89 53 53 65 79 21 10 29 17 27 48 30 35 32 39 31 36 52 17 30 21 48

1501 1459 1440

1421 1407 1396 1354 1336 1301 1274 1223 1214 1180 1164 1158 1121 1103 1086 1013 970 950 885 879 858 832 783 746

852

727 709 697 686 654 642 628 614 580 569 548 530 502 438 419 a

641 618

Dianionic form

m(C@O) m(CCar), 22 d(CCH) m(CCar), 11 m(CN), 7 d(CCC) m(CN), 7 m(CCpyr), 6 d(CCH) m(CN), 16 m(CCar), 13 m(CCpyr) m(CN), 14 m(CCpyr) d(CCH), 38 m(CCar), 8 d(CCC) m(CCar), 18 m(CN), 7 d(CCH) m(CN), 7 m(CCar), 6 m(CCpyr) d(OCH), 32 m(CCar), 6 d(CCH) d(OCH), 32 m(CCar), 6 d(CCH) m(CN), 25 m(CCar), 21 m(CCpyr) m(CCar), 9 m(CCpyr), 9 d(NCH) m(CN), 16 m(CCpyr), 12 d(NCN) d(CCH), 8 m(CCpyr), 7 m(CCar) m(CN), 21 d(CNH), 13 m(CO) m(CN), 14 m(CO), 15 m(CCar) d(CCH), 14 m(CO), 12 d(CCC) m(CN), 9 m(CCpyr), 7 m(CCar) d(CCH), 22 m(CCar) m(CN), 18 d(CCH), 16 m(CCpyr) d(CCH), 17 m(CCar) d(CCH), 27 m(CCar), 12 m(CN) d(CCC), 24 m(CN), 20 d(CNH) m(CN), 22 d(CNH), 16 d(CCC) q(CH) v(CC), 29 q(CH) v(CC), 29 q(CH) d(CCH), 31 m(CCar) q(CH) m(CCar), 19 d(CCC), 12 m(CCpyr) m(CO), 10 d(COC), 9 m(CC) v(CN), 21 v(CC), 18 q(CH) v(CC), 14 d(CCC), 12 q(CH) v(CN), 18 q(CH), 10 v(CC) v(CN), 25 q(CH), 16 v(CC) d(CCC), 7 d(CCH), 7 d(OCC) v(CN), 26 v(CC), 14 q(CH) v(CC), 25 q(CH), 16 v(CN) d(CCC), 10 d(CCH), 4 d(OCC) d(CCC), 10 d(COC) d(CCC), 17 d(NCN), 22 d(NCC) d(CCC), 13 d(CCH) q(CH), 17 v(CC), 16 d(CCC) q(CH), 28 v(CC), 17 v(CN) v(CC), 15 q(CH), 10 v(CN) v(CC), 40 q(CH)

m, stretch; d, in-plane-bend; q, out-of-plane bend; and v, torsion.

1440 cm1 in the IR spectra of P00 . The 4-oxybenzaldehyde terminal groups are characterized by the well-defined band at 1698 cm1 in the experimental IR spectra of P00 assigned to the C@O stretching vibrations. The characteristic features of the studied IR and Raman spectra of dendrimers built from phthalocyanine P00 , P04 and thiophosphoryl cores G00 , G04 are their similarity to each other (Figs. 5–8). The frequencies of most bands in the IR spectra of P00 , P04 and G00 , G04 dendrimers are just the same only changes of intensity of bands occur. In order to clear up these changes the difference IR spectra of dendrimers were studied (Fig. 5). A dendrimer molecule consists of three types of units: initiator-core (C), repeating unit (R) and terminal group (T):

C 8 ¼ 1; T ¼ 8ðP00 Þ C 8 ¼ 1; R ¼ 120; T ¼ 128ðP04 Þ: C 3 ¼ 1; T ¼ 3ðG00 Þ: C 3 ¼ 1; R ¼ 45; T ¼ 48ðG04 Þ:

A fine control of dendrimer structure enables one to assign bands in the IR spectra to the specific molecular fragments. A clear example of the above opportunity is given when in the difference spectra of dendrimers of the zero generation built from octafunctional phthalocyanine and trifunctional thiophosphoryl cores P00 —G00 compensation is made by band of terminal group. The result of subtraction will be the difference spectra in which by one side of zero line will be situated the bands of the phthalocyanine core (P00 ), and by the other side the bands of the thiophosphoryl core (G00 ):

C 8 þ 8T  8=3ðC 3 þ 3TÞ ¼ C 8  8=3C 3 : In practice experimental IR spectra may not obey such simple and ideal arithmetic. Any differences in spectra must be connected with the changes of the environment of these fragments, variation of the conformational and crystalline state, modification of the intra- and inter-molecular interactions and so on. Analysis of these peculiarities enables one to obtain the unique information about the structure of dendrimers. For example, in the difference IR

182

V.L. Furer et al. / Chemical Physics 358 (2009) 177–183

1.5

3.0

3

P'0

2.5

G'0

1.5

2

2

1.0

Absorbance

Absorbance

2.0

0.5 1.0

1

1

0.5

0.0 0.0 1800

1600

1400

1200

1000

800

600

400

Wavenumber/cm -1 Fig. 6. Difference IR spectra P00 –G00 (3) and IR spectra of P00 (1) and G00 (2).

spectra P00 —G00 bands near 502, 697, 746, 1158, 1214, 1501, 1594 and 1698 cm1 show characteristic EPR-like character. These bands are not fully compensated due to the frequency and intensity dependence on the nature of the dendrimer core. The analysis of the difference IR spectra P00 –G00 enables one to distinguish the bands of the phthalocyanine and thiophosphoryl cores (Fig. 6). The bands on side P00 of the zero line in the difference

3.0

1800

1600

1400

1200

1000

Wavenumber/cm

800

600

400

-1

Fig. 8. Experimental IR spectra of dendrimers P04 (1) and G4 (2).

IR spectra P00 –G00 at 879, 1013, 1274, and 1440 cm1 are connected with vibrations of the phthalocyanine core. The bands on side G00 of the zero line in the difference IR spectra P00 –G00 at 665, 935 cm1 are assigned to vibrations of the thiophosphoryl core. Another example of the above opportunity is given when in the difference IR spectra of dendrimers generations P04 –P00 built from phthalocyanine core compensation is made by band at 1700 cm1, that is by terminal groups (Fig. 7). The result of subtraction will be the difference spectra in which by one side of zero line will be situated the bands of the core (P00 ), and on the side the bands of the repeating units (P00 ):

C 8 þ 120R þ 128T  16ðC 8 þ 8TÞ ¼ 120R  15C 8 : 2.5

3

P'4

Absorbance

2.0

P'0

1.5

2

1.0

0.5

1

0.0 1800

1600

1400

1200

1000

800

600

400

Wavenumber/cm -1 Fig. 7. Difference IR spectra P04 –P00 (3) and IR spectra of dendrimers P04 (1) and P00 (2).

The bands on the P04 side of the zero line in the difference IR spectra P04 –P00 at 605, 624, 658, 728, 784, 836, 919, 952, 1138, 1192, 1299, 1497, 1501, 1597 cm1 are connected with vibrations of the repeating units. It is interesting to compare the IR spectra of dendrimers of the same generation built from the phthalocyanine (P04 ) and thiophosphoryl (G04 ) cores (Fig. 8). Their spectra are similar to each other only small changes of band intensity at 1200 cm1 and in the region 400–600 cm1 occur. For the fourth generation the share of the core becomes negligible, and bands of repeating units and terminal groups altogether determine the spectral pattern of dendrimer. The characteristic feature of the studied IR spectra of the generations G01 –G010 is their similarity to each other [10]. The band half-width and intensity show very little changes for the first four generations and then achieve saturation. The saturation of the band intensity is observed because the ratio of the repeating units and end groups tends to one when the generation numbers increase and reflects strong homogeneity of the dendrimer macromolecules. Thus some structural features of the zero generation dendrimers built from phthalocyanine core obtained in this study are contained for the higher generations of dendrimes and define their properties.

V.L. Furer et al. / Chemical Physics 358 (2009) 177–183

183

5. Summary

References

The IR and Raman spectra of P00 and P04 dendrimers built from an octasubstituted metal-free phthalocyanine core with oxybenzaldehyde terminal groups have been recorded. The structural optimization and vibrational analysis were made for P00 by DFT method. The intensity of the most prominent bands in the IR spectra of P00 is reproduced by our calculations. The calculated absorption curves of P00 as a whole corresponds to the experimental IR spectra in the wide frequency region. Thus the employed DFT method enables one to calculate the structure, charges on atoms, and reproduce the experimental IR spectra of the dendrimer with phthalocyanine core and 4-oxybenzaldehyde end groups. The benzaldehyde terminal groups of P00 are out of the phthalocyanine core plane. The calculated ratios of principal moments of gyration tensor reveal that the P00 and G00 molecules have highly asymmetric shape. IR spectroscopy combined with quantum chemical DFT computation provides unique detailed information about the structure of the technologically relevant materials, which could not be obtained before by any other technique. The analysis of the difference IR spectra of dendrimers enables one to distinguish the bands of the phthalocyanine and thiophosphoryl cores. For the fourth generation the share of the core becomes negligible, and bands of repeating units and terminal groups altogether determine the spectral pattern of dendrimer.

[1] G. de la Torre, C.G. Claessens, T. Torres, Chem. Commun. (2007) 2000. [2] G. de la Torre, P. Vazquez, F. Agullo-Lope, T. Torres, Chem. Rev. 104 (2004) 3723. [3] M. Kimura, K. Narikawa, K. Ohta, K. Hanabusa, H. Shirai, N. Kobayashi, Chem. Mater. 14 (2002) 2711. [4] M. Brewis, G.J. Clarkson, V. Goddard, M. Helliwell, A.M. Holder, N.B. McKeown, Angew. Chem. Int. Ed. 37 (1998) 1092. [5] S. Sergeyev, E. Pouzet, O. Debever, J. Levin, J. Gierschner, J. Cornil, R.G. Aspe, Y.H. Geerts, J. Mater. Chem. 17 (2007) 1777. [6] G.R. Newkome, C.N. Moorefield, F. Vogtle, Dendrimers and Dendrons: Concepts Syntheses Applications, VCH, Weinheim, 2001. [7] J.M.J. Frechet, D.A. Tomalia, Dendrimers and Other Dendritic Polymers, Wiley, New York, 2002. [8] S. Hecht, J.M.J. Frechet, J. Angew. Chem., Int. Ed. 40 (2001) 74. [9] J.P. Majoral, A.M. Caminade, V. Maraval, Chem. Commun. (2002) 2929. [10] V.I. Kovalenko, V.L. Furer, A.E. Vandyukov, R.R. Shagidullin, J.P. Majoral, A.M. Caminade, J. Mol. Struct. 604 (2002) 45. [11] J. Leclaire, Y. Coppel, B. Donnadieu, A.M. Caminade, J.P. Majoral, J. Am. Chem. Soc. 126 (2004) 2304. [12] J. Leclaire, R. Dagiral, S. Fery-Forgues, Y. Coppel, B. Donnadieu, A.M. Caminade, J.P. Majoral, J. Am. Chem. Soc. 127 (2005) 15762. [13] J. Leclaire, R. Dagiral, A. Pla-Quintana, A.M. Caminade, J.P. Majoral, Eur. J. Inorg. Chem. (2007) 2890. [14] C. Lin, K. Wu, R. Sa, C. Mang, P. Liu, B. Zhuang, Chem. Phys. Lett. 363 (2002) 343. [15] J.P. Perdew, K. Burke, M. Erznzerhof, Phys. Rev. Lett. 77 (1996) 3865. [16] M. Erznzerhof, G.E. Scuseria, J. Chem. Phys. 110 (1999) 5029. [17] C. Adamo, V. Barone, J. Chem. Phys. 110 (1999) 6158. [18] D.N. Laikov, Yu.A. Ustynyuk, Russ. Chem. Bull. Int. Ed. 54 (2005) 821. [19] S.Y. Lee, Bull. Korean Chem. Soc. 19 (1998) 93. [20] V.L. Furer, A.E. Vandyukov, J.P. Majoral, A.M. Caminade, V.I. Kovalenko, Chem. Phys. 326 (2006) 417. [21] V.A. Sipachev, J. Mol. Struct. (Theochem). 121 (1985) 143. [22] S. Matsumoto, K. Matsuhama, J. Mizuguchi, Acta Cryst. C55 (1999) 131. [23] A.B.J. Parusel, S. Grimme, J. Porphirins Phthalocyanines. 5 (2001) 1. [24] F.L. Hirshfeld, Theor. Chim. Acc. 44 (1977) 129. [25] M.L. Lartigue, B. Donnadieu, C. Galliot, A.M. Caminade, J.P. Majoral, Macromolecules 30 (1997) 7335.

Acknowledgements Authors are grateful to the Department of Chemistry and Materials Science of Russian Academy of Science for financial support (Program 7). We are also grateful to supercomputer centre of collective use of Kazan Scientific Center RAS for access to computer resources.