DFT study of Raman spectra of phosphorus-containing dendrimers built from thiophosphoryl core

Vibrational Spectroscopy 68 (2013) 61–70

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DFT study of Raman spectra of phosphorus-containing dendrimers built from thiophosphoryl core V.L. Furer a,∗ , A.E. Vandyukov b , J.P. Majoral c , A.M. Caminade c , V.I. Kovalenko b,∗∗ a b c

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

a r t i c l e

i n f o

Article history: Received 25 March 2013 Received in revised form 8 May 2013 Accepted 21 May 2013 Available online 4 June 2013 Keywords: Phosphorus-containing dendrimers Raman spectra

a b s t r a c t The FT-Raman spectra of the first and second generations of phosphorus-containing dendrimers with terminal benzaldehyde and P–Cl groups have been recorded and analyzed. The structural optimization and normal mode analysis were performed for dendrimers on the basis of the density functional theory (DFT). The calculated geometrical parameters, harmonic vibrational frequencies and Raman scattering activities are predicted in a good agreement with the experimental data. The experimental Raman spectra of dendrimers were interpreted by means of potential energy distribution. Relying on DFT calculations the lines of the core, repeating units and terminal groups of dendrimers were assigned. The influence of the encirclement on the line frequencies and intensities was studied and due to the predictable, controlled and reproducible structure of dendrimers the information, usually inaccessible is obtained. The strong line at 1600 cm−1 show marked changes of intensity in dependence of aldehyde ( CH O) or azomethyne ( CH N) substituents in the aromatic ring. The polarizabilities and lipophilicity of the eleven generations of dendrimers were estimated based on the calculated values of the first generations. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Dendrimers represent a unique class of molecules with a regular branched structure [1,2]. Molecules of dendrimers have mainly three dimensional structure, emanating from one center – the core, with exponentially increasing number of repeating units and terminal groups [1,2]. Dendrimers are perspective materials for the coordination chemistry, agrochemistry, catalysis, the storage and delivery of drugs [1,2]. Phosphorus-containing dendrimers share several properties with other types of dendrimers, for instance concerning catalysis, creation of new materials, modifications of surface of materials [3–5]. In addition they have also qualities never reported up to now for other dendrimers, such as a high dipole moment value and the ability to form hydrogels even at low concentrations in water [3,4]. Such compounds having a hydrophobic interior and hydrophilic surface should have promising applications [3,4]. However IR and Raman spectra of dendrimers up to now were used mainly for the analytical purposes [6–8].

∗ Corresponding author. Tel.: +7 843 2104737; fax: +7 843 2387972. ∗∗ Corresponding author. Tel.: +7 843 273228; fax: +7 843 2732253. E-mail addresses: [email protected], [email protected] (V.L. Furer), [email protected] (V.I. Kovalenko). 0924-2031/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.vibspec.2013.05.013

We recently reported the preparation and IR and Raman spectra of phosphorus-containing dendrimers built up to the 12th generation with terminal aldehyde groups [9,10]. The 12 generations of the one series were used to study the connection between the peculiarities of the structure of this type of compounds and its vibrational spectra. IR and Raman spectra of phosphorus-containing dendrimers were interpreted by normal mode calculation [9,10]. Study of Raman spectra of dendrimers is important for investigation of supramolecular properties of phosphorus-organic dendrimers as containers for different guest molecules. It enables to reveal the active sites of the dendrimer molecules for nucleophilic and electrophilic attack. The interpretation of Raman spectra is important for characterization the structure of non-crystalline dendrimers. The experimental line widths in the Raman spectra may be applied to study conformational dynamics of dendrimers. The dependence of line broadening in the vibrational spectra on the generation number is established [10]. Analysis of spectra enables one to characterize local flexibility of repeating units and terminal groups of dendrimers. In this work we try to show the value of FT-Raman spectroscopy for characterization of phosphorus-containing dendrimers. The FT-Raman spectra of dendrimers were calculated on basis of quantum-chemical density functional (DFT) calculations. The control growth of dendrimers with increase of generation number

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V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70

enables one to distinguish the lines in the Raman spectra assigned to the specific molecular fragments. Thus the main goal of this study was to obtain the characteristic spectral features of structural parts of dendrimer: a core, repeating units and terminal aldehyde and P–Cl groups based on analysis of Raman spectra. We report a systematic Raman spectra investigation in order to derive the actual molecular structure of dendrimers and to understand why it is possible to obtain phosphorus-containing dendrimers of such high generation number. The results that emerge from such an analysis contribute to comprehension of structure, dynamics and properties of dendrimers. 2. Experimental Synthesis and main characteristics of the studied phosphoruscontaining dendrimer were described earlier [3–5]. The (G0 ) molecules contain the following parts of the dendrimers: the trifunctional core S P( O )3 and the 4-oxibenzaldehyde fragments O C6 H4 CHO as the terminal groups (Fig. 1). The molecular structure of two series generations are the following: a trifunctional core S P( O )3 , repeating unit O C6 H4 CH N N(CH3 ) P(S), and terminal groups are 4-oxibenzaldehyde fragments O C6 H4 CHO (Gi ), or chlorine atoms (Gi ) (Fig. 1). Raman spectra in the region 3500–100 cm−1 were excited by Nd:YAG laser line 1064 nm with power at sample 50 mW and were recorded with an FRA106/S Bruker FT-Raman module with a 4 cm−1 resolution. 3. Computational method Calculations of Raman spectra of dendrimers were carried out using the gradient-correlated density functional theory with Perdew–Burke–Ernzerhof exchange-correlation functional (DFT/PBE) [11]. This functional is very satisfactory from the theoretical point of view, because it verifies a lot of the exact conditions for the exchange-correlation hole and it does not contain any fitting parameters [12]. The comparison of the computed with PBE functional binding energies, geometries and dynamical properties of different molecules show the best agreement with experiment [13,14]. Calculations were performed using three exponential basis with two polarizing functions (TZ2P) [15,16]. This basis set was chosen in order to obtain the most advantageous relation of accuracy and computation time. Its peculiarity is that the same set of exponents is used for all values of angle moment in atom. The program PRIRODA was used to perform DFT calculations [17]. The minima of the potential surface were found by relaxing the geometric parameters with standard optimization methods. All stationary points were characterized as minima by analysis of Hessian matrices. The software package SHRINK [18] was used for the transformation of quantum mechanical Cartesian force constants to the matrix in dependant internal coordinates and calculation of potential energy distribution. No scaling procedure of frequencies or force constants was applied. The selected functional and basis set was checked by calculation of geometry and IR spectra of dendrimers [9]. Spectra were generated from a list of frequencies and intensities using Lorentzian band shape and width at half-height  of 15 cm−1 for each of N vibration modes calculated. An assignment of bands was fulfilled on the basis of calculated potential energy distribution (PED). 4. Results and discussion The geometric parameters of (G0 ), G1 in crystalline state were defined by the X-ray diffraction method [5]. In the molecule (G0 ) each C6 H4 CH O fragment is planar (Fig. 2 and Table 1). Thus

the molecular conformation is defined by three core dihedral angles SPOC and three dihedral angles POCC which determine the orientation of terminal groups. As it follows from the Xray data the core dihedral angle of G 0 S(1) P(1) O(2) C(10), S(1) P(1) O(3) C(16) and S(1) P(1) O(1) C(4) are equal to −0.9◦ , −32.8◦ and 67.3◦ . The experimental dihedral P(1) O(1) C(4) C(5), P(1) O(2) C(10) C(11) and angles P(1) O(3) C(16) C(17) of terminal groups are equal to −100.7◦ , 98.7◦ and −88.8◦ . Full optimization yielded the conformer with core dihedral angles S(1) P(1) O(2) C(10), S(1) P(1) O(3) C(16) and S(1) P(1) O(1) C(4): −3.4◦ , −56.8◦ and 54.4◦ , and the dihedral angles of terminal groups P(1) O(1) C(4) C(5), P(1) O(2) C(10) C(11) and P(1) O(3) C(16) C(17): −81.6◦ , 111.2◦ and −104.8◦ (Fig. 2 and Table 1). Thus the most stable theoretical conformation of (G0 ) is somewhat different as compared to crystalline state. The calculated bond distances (in Å) 1.917 (P(1) S(1)), 1.642 (P(1) O(1)), 1.396 (C(4) O(1)), 1.214 (C(2) O(5)) correspond well to the experimental values 1.887, 1.573, 1.392 and 1.200. The theoretical bond angles (in degrees) S(1) P(1) O(1) (120.0), P(1) O(1) C(4) (121.0), O(1) C(4) C(5) (120.0) are also in close agreement with the experimental values 119.1, 125.1, 117.8. The molecule G1 as a whole looks like a three blade propeller when examined in the direction of terminal P S groups and each O C6 H4 CH N N(CH3 ) P arm is planar (Fig. 2 and Table 2). The most stable theoretical conformation of G1 is slightly different as compared to crystalline state. The calculated bond distances (in Å) 1.918 (P(1) S(1)), 1.642 (P(1) O(1)), 1.401 (C(1) O(1)), 1.922 (P(2) S(2)), 2.076 (P(2) Cl(1)), 1.716 (P(2) N(2)), 1.358 (N(1) N(2)), 1.463 (N(2) C(8)), 1.290 (C(7) N(1)) correspond well to the experimental values 1.877, 1.579, 1.403, 1.887, 1.982, 1.624, 1.402, 1.439, 1.270. The theoretical bond angles (in degrees) S(1) P(1) O(1) (118.7), P(1) O(1) C(1) (121.5), O(1) C(1) C(2) (119.3) are also in close agreement with the experimental values 117.7, 130.8, 123.4. Thus experimental and theoretical data suggest that steric congestion does not disturb the construction of dendrimers even for the highest generations, and that terminal groups are readily available for further reactions. The dendrimer shape can be characterized by ratios I1 /I3 and I2 /I3 of principal moments of gyration tensor. Their values are 0.343 and 0.748 (G0 ), 0.550 and 0.550 (G1 ), 0.516 and 0.519 (G1 ), 0.723 and 0.725 (G2 ), correspond to disk like anisotropic shape of dendrimer molecules and reflect their symmetry. Thus the flat and anisotropic shape of the repeated units of the studied dendrimer defines the ability of molecules to pack with each other to form the most probable disk-like shape. Polarizabilities may be used for characterization of dendrimer structure and electronic properties of molecules. The polarizability derivatives define the intensity of lines in Raman spectra and nonlinear properties of molecules. A dendrimer molecule consists of three types of units: initiator-core (C), repeating unit (R), and terminal group (T). The functionality of these original molecules, which become the initiator-core, determines the multiplicity of the core juncture (c), and the number of dendrons. The repeating unit has multiple juncture (r) at its outer end to join the terminal groups, as a rule r = 2, but it may be equal to 3, 4, 5 etc. The general “formula” of dendrimer molecule of n generation: Gn = C + Rn + Tn , where Rn the number of repeating units, Tn the number of terminal groups. The number of repeating units Rn = c(rn − 1)/(r − 1)R, and the number of terminal groups Tn = crn T may be calculated for each generation number n of dendrimer. In this work the phosphorus-containing dendrimers of eleven generations with trifunctional thiophosphoryl (c = 3), bifunctional repeating units (r = 2) have been analyzed. The ratio of Tn /Rn and

V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70

Cl

S

P

Me

63

Cl

N N

CH

N

S O P

N

P O O

CH

N

S

Me

CHO

Cl Cl

P

N

N

CH

O S

CH O

Cl

P

N

N Me

Cl

S

Me

CH

Me S O N P O

Me N N

CH

G2

S

O O

P

CHO

CHO H C

CH

Me

N N

N

Me N S P O

P

O S P O O

S Cl

Cl

O

CH

CH N

Me

N

N

CH N

CH

N

S P

Cl

N

Me S O N P O

Me S P O O

CHO

CHO

Cl N P

Me S 1

Cl

CHO

Cl

2

S Cl Me P N Cl N

CH

S

O P O O

CH

CH N

N

Me S Cl N P Cl

O H O

O

S P O O

H

Me N S P Cl

H O

Cl

4

3 Fig. 1. Structure of G2 (1), G1 (2), G1 (3), and G0 (4).

the only initiator-core altogether determines the spectral pattern of dendrimer: C = 1, R1 = 3R, T1 = 6T (G1 ); C = 1, R2 = 9R, T2 = 12T (G2 );

At first stage the polarizabilities of dendrimers were computed by DFT method and the values (in Å3 ) 5.8 (G0 ), 23.3 (G1 ), 20.9 (G1 ), and 55.6 (G2 ) were obtained (Table 7). Then comparison of the polarizabilities of (G0 ) and (G1 ) molecules lead to the quantities 1.93 and 3.1 Å3 for the oxybenzaldehyde terminal group and repeated units. The polarizability of the PCl2 terminal group may be estimated as 2.3 Å3 .

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V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70

Fig. 2. Structure and atomic numbering of G2 (1), G1 (2), G1 (3) and G0 (4).

Then we can estimate the polarizabilities of dendrimers by simple summation the corresponding increments of the fragments of molecules (Table 3). Remarkably, the values of the polarizabilities versus generation increase from 23.3 (G1 ) to 33,168.3 (G11 ) and  ). The polarizabilities for (G ) are from 5.8 (G0 ) to 30,895.0 (G11 i less than for Gi dendrimers. Polarizabilities approximately doubled each time when going to the next generation. The dipole moments of dendrimers increase in the same exponential fashion [5]. Lipophilicity is a very important molecular descriptor that often correlates well with the bioactivity of chemicals [21]. The logarithm of the partition coefficient (log P) correlates with water solubility [21]. Lipophilicity can be measured by log P, which reflects the equilibrium partitioning a molecule between an apolar and a polar phase. In the present study we calculated log P for dendrimer molecules with HyperChem software [22] and obtained the rather high negative values −4.9 (G0 ), −4.0 (G1 ), −17.6 (G1 ), and −15.9 (G2 ) (Table 7). Then we can estimate the lipophilicity of dendrimers by simple summation the corresponding increments of the fragments of molecules (Table 3). The values of the lipophilicity versus

generation increase from −4.0 (G1 ) to −12,157.3 (G11 ) and from  ). Thus the dendrimers of all generations −4.9 (G0 ) to −26,042.7 (G11 have strongly negative log P values and they are hydrophobic. The lipophilicity of this dendrimer has a tremendous importance for its geometry and shape in water. Our results demonstrate that the internal structure of dendrimers plays a crucial role when considering biological properties. Experimental and theoretical Raman spectra of studied dendrimers are represented at Figs. 3–10 and Tables 4–7. The comparison of spectra of dendrimers G1 , (G1 ) and G2 show that they are similar to each other. It may be expected, because the vibrations of the same repeating units reveal their self in the Raman spectra of all studied dendrimers. The assignment of lines was fulfilled on the basis of the calculated potential energy distribution. The medium intensity lines at 1701 and 1702 cm−1 in the Raman spectra of (G0 ) and (G1 ) are assigned to C O stretching vibrations of aldehyde groups (Figs. 3 and 5). The strong lines at 1597 cm−1 (G0 ), 1604 cm−1 (G1 ), 1602 cm−1 (G1 ), and 1603 cm−1 (G2 ) refer to the CC stretching

V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70

65

Table 1 Experimental and calculated (DFT/PBE TZ2P) bond distances (Å) and bond angles (◦ ) of G0 .

Bond distances P(1) S(1) P(1) O(1) P(1) O(2) P(1) O(3) C(4) O(1) C(10) O(2) C(16) O(3) C(1) O(4) C(2) O(5) C(3) O(6) Angles S(1) P(1) S(1) P(1) S(1) P(1) P(1) O(1) P(1) O(2) P(1) O(1) O(1) C(4) C(4) C(5)

O(1) O(2) O(3) C(4) C(10) C(4) C(5) C(6)

Dihedral angles S(1) P(1) O(1) C(4) S(1) P(1) O(2) C(10) S(1) P(1) O(3) C(16) P(1) O(1) C(4) C(5) P(1) O(2) C(10) C(11)

Experimental

Calculated

1.887 1.573 1.555 1.572 1.392 1.394 1.408 1.158 1.200 1.207

1.917 1.642 1.654 1.640 1.396 1.404 1.397 1.214 1.214 1.214

Experimental C(1) C(2) C(3) C(4) C(4) C(5) C(6) C(7) C(8)

C(7) C(13) C(19) C(5) C(9) C(6) C(7) C(8) C(9)

1.494 1.465 1.468 1.353 1.380 1.347 1.344 1.382 1.401

Calculated 1.484 1.483 1.484 1.400 1.397 1.389 1.405 1.402 1.393

119.1 115.6 119.2 125.1 127.8 124.4 117.8 119.6

120.0 116.5 120.4 121.0 121.9 124.4 120.0 118.9

C(5) C(6) C(7) C(4) C(5) C(6) C(7)

C(6) C(7) C(8) C(9) C(4) C(7) C(1)

C(7) C(8) C(9) C(8) C(9) C(1) O(4)

121.2 120.5 115.3 117.3 122.1 119.9 126.9

120.5 119.7 120.4 118.8 121.7 120.3 125.0

67.3 −0.9 −32.8 −100.7 98.7

54.4 −3.4 −56.8 −81.6 111.2

P(1) O(1) C(4) C(5) C(6)

O(3) C(4) C(5) C(6) C(7)

C(16) C(17) C(5) C(6) C(6) C(7) C(7) C(1) C(1) O(4)

−88.8 173.7 −0.1 176.9 174.4

−104.8 −176.7 0.2 179.8 180.0

vibrations of para-substituted aromatic ring (Figs. 3–6). The lines at 1581 cm−1 (G1 ), 1578 cm−1 (G1 and G2 ) are assigned to (C N) vibrations of hydrazone fragment (Figs. 4–6). The lines at 1205 cm−1 (G0 ), 1217 cm−1 (G1 ), 1219 cm−1 (G1 and G2 ) are assigned to the stretching vibrations of the C C, C O bonds and aromatic ring. The lines at 1153 cm−1 (G0 ), 1168 cm−1 (G1 ), 1165 cm−1 (G1 and G2 ) are attributed to CCH bend. The weak lines at 1143 cm−1 (G1 ) and 1144 cm−1 (G2 ) are assigned to C N

and N N stretching vibrations. The weak lines at 935 cm−1 (G0 ), 959 cm−1 (G1 ), 965 cm−1 (G1 ), and 956 cm−1 (G2 ) are connected with the stretching of P O bonds. The lines at 524, 481, 395 cm−1 (G1 ) and 530, 481, 392 cm−1 (G2 ) are connected with asymmetric and symmetric stretching vibrations of P Cl bonds. The location of P S stretching vibrations usually is not definitely obtained due to its low intensity in the IR spectra and strong

Table 2 Experimental and calculated (DFT/PBE TZ2P) bond distances (Å) and bond angles (◦ ) of G1 . Experimental Bond distances P(1) S(1) P(1) O(1) P(1) O(2) P(1) O(3) C(1) O(1) C(9) O(2) C(17) O(3) C(1) C(2) C(2) C(3) Angles S(1) P(1) S(1) P(1) S(1) P(1) P(1) O(1) P(1) O(2) P(1) O(3) O(1) C(1) C(1) C(2) C(2) C(3)

O(1) O(2) O(3) C(1) C(9) C(17) C(2) C(3) C(4)

Dihedral angles S(1) P(1) O(1) C(1) S(1) P(1) O(2) C(9) S(1) P(1) O(3) C(17) P(1) O(1) C(1) C(2) P(1) O(2) C(9) C(10) P(1) O(3) C(17) C(18) O(1) C(1) C(2) C(3) C(1) C(2) C(3) C(4)

1.877 1.579 1.578 1.577 1.403 1.403 1.404 1.367 1.363

Calculated 1.918 1.642 1.642 1.642 1.401 1.401 1.401 1.398 1.389

Experimental C(3) C(4) C(7) N(1) N(2) P(2) P(2) P(2) P(2)

C(4) C(7) N(1) N(2) C(8) N(2) S(2) Cl(1) Cl(2)

1.386 1.463 1.270 1.402 1.439 1.624 1.887 1.982 2.009

117.7 117.8 117.8 130.8 130.8 130.9 123.4 119.1 121.3

118.7 118.8 118.8 121.5 121.5 121.4 119.3 119.4 120.7

C(3) C(4) C(7) N(1) N(1) N(2) N(2) N(2)

C(4) C(7) N(1) N(7) N(2) P(2) P(2) P(2)

C(7) N(1) N(2) P(2) C(8) S(2) Cl(1) Cl(2)

60.6 60.6 60.5 27.0 27.0 27.1 175.4 −0.2

43.8 45.1 44.3 90.1 90.8 90.5 176.5 0.1

C(2) C(3) C(4) C(7) N(1) N(1) N(1)

C(3) C(4) C(7) N(1) N(2) N(2) N(2)

C(4) C(7) N(1) N(2) P(2) P(2) P(2)

C(7) N(1) N(2) P(2) S(2) Cl(1) S(2)

Calculated 1.409 1.463 1.290 1.358 1.463 1.716 1.922 2.076 2.079

122.4 119.5 119.2 112.7 121.8 115.4 105.0 105.5

122.0 120.7 120.0 114.5 123.4 115.7 103.5 103.7

177.3 10.1 178.6 178.5 179.4 53.1 −51.7

180.0 0.3 179.9 179.1 179.7 51.7 −52.4

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V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70

Table 3 Polarizabilities ˛ (Å3 ) and log P values for dendrimers. log P

Generation

˛

log P

−4.0 −15.9 −39.7 −87.2 −182.3 −372.3 −752.5 −1512.8 −3033.5 −6074.7 −12,157.3

G 0 G 1 G 2 G 3 G 4 G 5 G 6 G 7 G 8 G 9 G 10 G 11

5.8 20.9 51.1 111.4 232.1 473.6 956.5 1922.2 3853.7 7716.8 15,442.9 30,895.0

−4.9 −17.6 −43.1 −93.9 −195.7 −399.2 −806.3 −16,203.3 −3248.5 −6504.8 −13,017.5 −26,042.7

23.3 55.6 120.3 249.9 509.1 1027.5 2064.3 4137.9 8285.1 16,579.5 33,168.3

613

1229

1566

632 579

713

959

1245 1217 1168

50

654

884 848 1001

1195 1135

1412 1385 1341

0 1800

100

938

1

50

2

1189 1141

1747

1223

1597

580

Raman intensity (a.u.)

665 633

855

150

973

1421 1392

150

100

2

1246 1205 1153

1701

200

1581

200

Raman intensity (a.u.)

1581 cm−1 assigned to the CCar and C N stretching vibrations. The medium-intensity lines at 524, 481, 395 cm−1 in the Raman spectra of G1 are the characteristic features of terminal P Cl bonds. The line at 1702 cm−1 refer to C O stretching vibrations of aldehyde terminal groups. The different phases of dendrimers can be nicely distinguished by Raman spectroscopy. The studied dendrimers are amorphous compounds except the G0 and G1 generations which have the crystalline structure [5]. The intense narrow lines in the Raman spectra of G0 , G1 in the crystalline state are substituted by wide lines in the spectra of amorphous dendrimer G2 . For example line at 1581 cm−1 includes vibrations of repeating units in the Raman spectra of G1 , and its full width at half height (FWHH) is equal to 6.55 cm−1 . This line shifts to the frequency 1578 cm−1 in the Raman spectra of G2 and its FWHH value changes to 9.07 cm−1 . Even more pronounced are the changes for the line at 395 cm−1 of terminal P Cl groups with FWHH equal to 14.35 cm−1 in the Raman spectra of G1 . This line shifts to the frequency 392 cm−1 in the Raman spectra of G2 , and its FWHH value changes to 48.87 cm−1 . Thus, the orientation of

1597

dependence on the electronic properties of the substituents [19]. There are two lines at 633 and 665 cm−1 in the Raman spectra of G0 (Fig. 7). The first line may be connected with bending vibration of benzene ring. The second line is due to P S stretching of a core. In the Raman spectra of G1 three lines at 627, 638 and 652 cm−1 are observed in this region (Fig. 8). The lines at 627 and 652 cm−1 may be connected with vibrations of P S bond. The line at 652 cm−1 disappears in the Raman spectra of G2 and is ascribed to (P S) vibrations of a core, because in these generations the relative contribution of a core is very small (Fig. 10). The line at 627 cm−1 in the Raman spectra of G1 shifts to 621 cm−1 in the experimental Raman spectra of G2 and may be assigned to (P S) vibrations of repeating units. In the Raman spectra of G1 the complex pattern is observed in this region due to the presence of different types of P S bonds in this dendrimer (Fig. 9). Thus the dendrimer core S P( O )3 , reveal itself by the weak line at 959 cm−1 assigned to the P–O stretch and by the mediumintensity line at 652 cm−1 of P S stretch in Raman spectra of G1 . The repeating units show lines in Raman spectra of G1 at 1604 and

1592

G1 G2 G3 G4 G5 G6 G7 G8 G9 G10 G11

1604

˛

Generation

1

0

1600

1400

1200

1000

800

600

400

-1

Raman shift, cm

Fig. 3. Theoretical (1) and experimental Raman spectra of

1600

1400

1200

1000

800

600

-1

Raman shift, cm G0

(2).

Fig. 4. Theoretical (1) and experimental Raman spectra of G1 (2).

400

100

1600

1400

1200

800

600

256

331 304

416 383 356

148

185 372 338 315 268 245

454 424

494

800

400

600

Fig. 7. Theoretical (1) and experimental Raman spectra of G0 (2) in the region 800–100 cm−1 .

Fig. 5. Theoretical (1) and experimental Raman spectra of G1 (2).

with vibrations of terminal benzaldehyde groups are higher than that for the repeating units and reflect some degree of conformational disorder in this part of dendrimer molecules. In general the rather small FWHH values of lines in Raman spectra of dendrimers reflect their homogeneity. The aromatic fragments are located both in repeating unit and terminal benzaldehyde groups. That enables one to define in the

1603

395

PCl2 terminal groups in the crystalline and amorphous dendrimers, are different due to the conformational disorder. The line at 1578 cm−1 in the Raman spectra of G1 , of G1 and of G2 refers to vibrations of repeating units and its FWHH values is less than 10 cm−1 . From this data it follows that the rather rigid repeating units with little conformational freedom lead to the perfect microstructure of studied dendrimers. The FWHH values of lines at 1165, 1602 and 1702 cm−1 in the Raman spectra of G1 connected

1000

800

600

-1

Raman shift, cm

Fig. 6. Theoretical (1) and experimental Raman spectra of G2 (2).

172 225 207

255 315

438 361

564

524

652 638 627

494

613

182 255

317

430 422

558

700

527

5

741

481

790

695 629 579

910

1331 1407

1233 1173 1141

1200

2

1

0

0 1400

10

677

Raman intensity (a.u.)

639 621

956

886

1239 1219 1165

1410 1591

1 1566 1490

15

2

712 695

1578

20

50

1600

200

Raman shift, cm

-1

150

400 -1

Raman shift, cm

Raman intensity (a.u.)

462

580 538 508

777

1000

481

1800

100

1

0

0

200

2

654

25

1

1141

1229

1747

50

632

1588

50

739 713

Raman intensity (a.u.)

1219 1165

1702

100

75

579

2

1590

Raman intensity (a.u.)

150

713

1578

194

155

633

200

67

665

1602

V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70

400

800

600

400

Raman shift, cm

200 -1

Fig. 8. Theoretical (1) and experimental Raman spectra of G1 (2) in the region 800–100 cm−1 .

V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70 Table 4 Experimental and corresponding calculated (DFT/PBE TZ2P) frequencies  (cm−1 ) and relative intensities I (a.u.) of lines in the Raman spectra of G0 in the region 1800–100 cm−1 .

284

2

573

497

418

604 589

671 636

615

10 704

Raman intensity (a.u.)

15

735 718

326

20

192

640 624

68

5

178

322

420

486

753

511

1

0 800

600

400

200 -1

Raman shift, cm

Fig. 9. Theoretical (1) and experimental Raman spectra of G1 (2) in the region 800–100 cm−1 .

2

481

362

530

572

40

719 706

174

320

629

1

579

723

695

20

289

Raman intensity (a.u.)

481

331 302

639 621

60

0 800

Calculated

␯



1701 m 1597 m 1503 w 1421 w 1392 w 1304 w 1291 w 1246 m 1205 m 1153 w 1098 w 1011 w 973 m 961 vw 946 w 935 w 855 m 835 m 784 m 739 w 731 vw 713 vw 665 m 633 w 612 vw 580 vw 538 vw 528 vw 508 vw 462 vw 454 vw 442 vw 416 vw 383 vw 356 vw 331 vw 304 vw 256 vw 214 vw 194 vw 185 vw 155 vw

1747 1597 1481 1412 1385 1341 1270 1267 1223 1135 1085 1001 961 960 939 884 848 835 777 723 719 713 654 632 606 579 530 514 494 454 442 424 415 381 372 338 315 245 222 192 185 148

I

Assignment

56.5 77.5 1.1 2.4 12.7 4.2 2.3 3.8 100.0 21.5 3.6 3.8 0.9 0.4 6.9 6.9 42.1 16.1 10.8 8.4 0.7 1.9 43.2 8.8 2.8 1.1 3.1 4.0 8.1 7.3 5.2 4.0 1.8 4.4 6.6 7.6 8.1 6.9 1.4 3.3 6.6 15.0

81 (C O) 68 (CCar ), 27 ı(CCH) 52 ı(CCH), 41 (CCar ) 49 ı(CCH), 47 (CCar ) 55 ı(CCH), 42 (CCar ) 87 ı(CCH) 88 ı(CCH) 87 ı(CCH) 38 (CO), 28 (CCar ) 68 ı(CCH), 14 (CCar ) 64 ı(CCH), 21 (CCar ) 61 ı(CCH), 35 (CCar ) 89 (CH) 94 (CH) 94 (CH) 50 (PO), 16 (CO) 20 (CCar ), 15 (CC) 94 (CH) 34 (P S) 21 (PO), 18 (CH) 21 (PO), 18 (CH) 48 (CH), 27 (CC) 13 (P S), 11 (PO) 55 ı(CCC), 19 ı(CCH) 59 ı(CCC), 21 ı(CCH) 18 (PO), 14 ı(OCC) (P S) 25 ı(POC), 16 (PO) 12 ı(POC), 10 (CC) 46 (CC), 11 ı(OPC) 27 (CC), 10 ı(OCC) 19 ı(OCC), 13 (CC) 24 ı(OCC), 10 (CC) 84 (CC) 28 (PO), 15 ı(OPO) 18 ı(OCC), 11 (PO) 42 (PO), 21 (CC) 77 (CC), 10 ı(OPO) 16 ␦(OCC), 14 (CC) 26 (CC), 10 ı(OCC) 65 (CC), 9 (PO) 37 (CH), 30 (CC), 9 (PO) 38 (CH), 29 (CC), 8 ı(OPO)

249

392

182

absolute identical experimental conditions the effects of influence of encirclement on its structure. The account of the relation number of terminal groups and repeated units gives the additional opportunity of line assignment in Raman spectra of dendrimers. The relative intensity of lines at 3073 and 1602 cm−1 assigned to CH and CC stretching vibrations of benzene ring show marked difference in

Experimental

600

400

200 -1

Raman shift, cm

Fig. 10. Theoretical (1) and experimental Raman spectra of G2 (2) in the region 800–100 cm−1 .

dependence of aldehyde ( CH O) or azomethyne ( CH N ) substituents in the aromatic ring in terminal group and repeating units of dendrimers [20]. For example ratio I1602 /I3073 falls down from 46.2 for G2 , 8.8 for G1 . It is interesting to note that the whole number of aromatic groups in these compounds is equal to 9, but in case of G2 molecule all of them belong to the repeating units and in G1 molecules 3 groups are located in the repeating units and 6 ones belong to the terminal groups. Thus, the changes of electronic structure of aromatic system in P(S) O C6 H4 CH N N(Me) , P(S) O C6 H4 CH O fragments markedly affect the intensity of 1602 cm−1 line in the Raman spectra, while line at 3073 cm−1 assigned to CH vibrations of phenyl ring practically dose not changes. The intensity of P S stretching vibrations in Raman spectra of dendrimers changes due to the differences in close surroundings of the groups. There are four types of P S groups: in initiator-core, in repeating unit, and pair of two types of terminal groups. The relative intensity of lines at 638 and 619 cm−1 assigned to CCC bending of benzene ring and P S stretching vibrations show marked difference in dependence of substituents in the terminal groups and repeating units of dendrimers. For P S stretching vibrations in a core the ratio I665 /I633 is equal to 1.54 for G0 , the ratio I652 /I638 is equal to 1.59 for G1 . For P S

V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70 Table 5 Experimental and corresponding calculated (DFT/PBE TZ2P) frequencies  (cm−1 ) and relative intensities I (a.u.) of lines in the Raman spectra of G1 in the region 1800–100 cm−1 . Experimental

Calculated (DFT/PBE TZ2P)

␯



1604 s 1581 m 1505 vw 1461 vw 1447 vw 1421 w 1408 w 1372 w 1311 w 1295 w 1245 m 1217 m 1173 m 1168 m 1143 w 1104 vw 1085 vw 959 w 920 vw 886 w 844 vw 817 vw 794 w 756 vw 712 w 695 w 652 w 638 w 627 w 564 vw 550 vw 524 w 481 w 438 vw 423 vw 395 m 315 vw 300 vw 255 vw 225 w 207 vw 172 w

1592 1566 1489 1457 1457 1432 1406 1386 1330 1276 1229 1205 1189 1141 1139 1128 1088 956 938 885 827 825 788 741 722 700 677 634 613 570 558 527 494 430 422 361 317 306 255 231 208 182

I

Assignment

100.0 23.3 2.6 1.0 0.8 0.2 1.2 0.5 6.7 2.1 19.3 5.7 6.9 17.4 6.0 13.0 3.5 0.1 8.7 1.9 0.1 0.1 0.9 0.9 0.1 1.7 3.2 0.5 10.1 0.1 0.8 0.2 0.1 0.2 0.1 11.9 0.5 1.1 0.7 0.2 1.7 1.5

61 (CCar ), 16 ı(CCH) 42 (CCar ), 26 (C N), 14 ı(CCH) 51 ı(CCH), 31 (CCar ) 68 ı(CCH), 31 (CCar ) 68 ı(CCH), 31 (CCar ) 88 ı(HCH), 10 ı(NCH) 47 (CCar ), 35 ı(CCH) 46 ı(NCH), 27 ı(HCH), 12 (CCar ) 65 (CCar ) 85 ı(CCH) 26 (CC), 16 ı(CCH), 17 ı(NCH) 45 (CO), 15 ı(CCH), 12 (CCar ) 25 ı(NCH), 18 (CN), 15 (PN) 54 ı(CCH), 20 (CO), 17 (CCar ) 38 (NN), 29 (CN) 38 (NN), 29 (CN) 51 ı(CCH), 21 (CCar ) 39 (PO), 19 (CH), 14 (CCar ) 34 (NN), 20 ı(NCH), 18 (PN) 21 (CCar ), 20 (PO), 13 ı(NNC) 71 (CH) 79 (CH) 20 (P S), 20 (PO) 43 (P S), 16 (PN) 30 (CH), 26 (CC) 34 (P S), 9 (PN) 19 (P S), 17 (PN), 11 (CN) 58 ı(CCC), 12 ı(CCH) 24 ı(CCC), 22 (P S), 12 (PN) 18 ı(CCC), 17 ı(POC) 21 ı(POC), 18 (P S) 61 (PCl) 53 (PCl) 14 ı(OCC), 13 (CC), 12 (PO) 14 ı(OCC), 14 (CC), 13 (PO) 53 (PCl) 24 (CH), 22 (PN), 20 (NN) 19 ␹(PN), 19 ␹(NN), 16 (CH) 54 (CH), 11 ı(NPCl) 46 (CH), 16 ı(NPCl), 7 ı(SPCl) 26 (CC), 10 ı(OCC) 26 (CN), 19 (CC), 15 ı(SPCl)

Table 6 Experimental and corresponding calculated (DFT/PBE TZ2P) frequencies  (cm−1 ) and relative intensities I (a.u.) of lines in the Raman spectra of G1 in the region 1800–100 cm−1 . Experimental  1702 m 1602 s 1578 m 1503 vw 1469 vw 1448 vw 1421 w 1409 w 1371 w 1304 w 1295 w 1231 m 1219 m 1165 m 1103 vw 1015 vw

Calculated  1747 1590 1588 1489 1460 1459 1435 1411 1387 1329 1276 1229 1210 1141 1099 1002

I

Assignment

4.8 100.0 55.5 2.5 1.1 1.0 0.6 0.4 0.7 4.3 3.0 27.1 14.3 25.7 0.4 0.8

84 (C O) 62 (CCar ), 17 ı(CCH) 36 (CCar ), 36 (C N), 7 ı(CCH) 47 ı(CCH), 31 (CCar ) 68 ı(CCH), 16 ı(NCH) 68 ı(CCH), 16 ı(NCH) 88 ı(HCH) 45 (CCar ), 41 ı(CCH) 57 ı(NCH), 39 ı(HCH) 68 (CCar ) 80 ı(CCH) 26 (CC), 16 ı(CCH), 17 ı(NCH) 45 (CO), 12 ı(CCH), 12 (CCar ) 59 ı(CCH), 20 (CO), 16 (CCar ) 51 ı(CCH), 21 (CCar ) 38 ı(CCC), 35 (CCar ), 22 ı(CCH)

69

Table 6 (Continued) Experimental

Calculated





965 vw 918 vw 888 vw 854 w 833 vw 800 vw 751 vw 735 vw 718 vw 671 vw 640 w 624 w 604 vw 589 vw 497 vw 418 vw 326 vw 284 vw 192 vw

960 911 882 846 828 806 753 733 716 657 636 627 615 573 486 420 322 290 178

I

Assignment 0.1 3.4 1.6 2.3 0.5 0.8 1.2 1.0 0.3 2.5 2.8 1.1 7.9 12.0 0.4 0.1 0.9 0.5 1.2

48 (PO), 23 (CO), 18 (CCar ) 27 (PN), 21 (NN), 21 ı(NCH) 48 (PO), 23 (CO), 18 (CCar ) 79 (CH) 79 (CH) 65 (CH) 43 (P S), 16 (PN) 38 (P S), 17 (PO) 38 (P S), 17 (PO) 58 ı(CCC), 12 ı(CCH) 58 ı(CCC), 12 ı(CCH) 60 ı(CCC), 18 ı(CCH) 24 ı(CCC), 22 (P S), 12 (PN) 18 ı(CCC), 17 ı(POC) 85 (PC) 14 ı(OCC), 14 (CC), 13 (PO) 21 (PN), 16 (CN), 15 (CH) 19 (PN), 19 (NN), 16 (CH) 38 (CH), 32 ı(SPO), 13 (CC)

Table 7 Experimental and corresponding calculated (DFT/PBE TZ2P) frequencies  (cm−1 ) and relative intensities I (a.u.) of lines in the Raman spectra of G2 in the region 1800–100 cm−1 . Experimental  1603 s 1578 m 1506 vw 1466 vw 1445 vw 1419 v 1410 v 1370 v 1334 vw 1305 v 1239 m 1219 m 1165 m 1144 v 1102 vw 1082 v 1051 vw 1017 vw 956 v 915 vw 886 v 848 vw 811 vw 793 vw 767 vw 742 vw 719 vw 706 vw 639 v 621 v 572 vw 530 vw 481 vw 454 vw 392 vw 331 vw 302 vw 249 vw 240 vw 232 vw 182 vw

Calculated  1591 1566 1490 1457 1457 1413 1407 1360 1331 1329 1233 1226 1173 1141 1115 1087 1087 1001 955 910 876 830 805 790 763 739 723 695 634 629 579 529 481 444 362 326 299 254 236 234 174

I

Assignment

100.0 16.1 7.6 1.2 0.5 1.4 1.5 1.3 31.9 3.0 42.3 1.8 0.6 15.0 5.7 0.8 0.8 0.8 0.1 3.1 2.8 1.7 0.6 4.8 2.8 3.6 0.4 22.0 0.8 16.8 19.8 0.6 31.2 0.6 32.3 1.4 1.4 0.1 6.0 0.6 7.5

51 (CCar ), 19 (C N), 17 ı(CCH) 42 (CCar ), 26 (C N), 14 ı(CCH) 46 ı(CCH), 36 (CCar ) 69 ı(CCH), 15 ı(NCH) 69 ı(CCH), 15 ı(NCH) 88 ı(HCH), 10 ı(NCH) 52 (CCar ), 33 ı(CCH) 30 (CCar ), 22 ı(NCH), 12 ı(CCH) 65 (CCar ) 85 ı(CCH) 21 (CC), 20 (CCar ), 19 ı(CCH) 23 (CO), 19 ı(CCH), 19 (CCar ) 41 (CO), 17 ı(CCH) 38 (NN), 31 (CN) 51 ı(CCH), 21 (CCar ) 35 ı(CCH), 25 (CCar ) 43 ı(CCH), 19 (CCar ) 34 (CCar ), 32 ı(CCH), 31 ı(CCC) 79 (CH) 34 (NN), 20 ı(NCH), 18 (PN) 36 (CH), 30 (PO) 71 (CH) 79 (CH) 20 (P S), 20 (PO) 43 (P S), 16 (PN) 43 (P S), 16 (PN) 18 (CC), 14 (P S), 10 (CH), 24 (P S), 19 (PN), 11 (CN) 33 (P S), 15 (PO) 64 ı(CCC), 15 ı(CCH) 18 ı(CCC), 17 ı(POC) 74 (PCl) 76 (PCl) 14 ı(OCC), 13 (CC), 12 (PO) 76 (PCl) 24 (CH), 22 (PN), 20 (NN) 19 (PN), 19 (NN), 16 (CH) 54 (CH), 11 ı(NPCl) 54 (CH), 11 ı(NPCl) 46 (CH), 16 ı(NPCl), 7 ı(SPCl) 26 (CN), 19 (CC), 15 ı(SPCl)

70

V.L. Furer et al. / Vibrational Spectroscopy 68 (2013) 61–70

stretching vibrations connected with PCl2 terminal groups the ratio I627 /I638 is equal to 0.82 for G1 , and fall down to 0.63 (G2 ). For P S stretching vibrations connected with benzaldehyde terminal groups the ratio I624 /I640 is equal to 2.43 for G 1 . Although the calculated curves of isolated dendrimer molecules are much simpler than the experimental Raman spectra the intensity of most prominent lines is reproduced by our computations (Figs. 3–10). The differences between theoretical and experimental spectra may be attributed to some defects in dendrimer molecules and imperfection of the used method. 5. Summary The FT Raman spectra of the first generations of phosphoruscontaining starburst dendrimers with terminal aldehyde and P Cl groups were compared. The influence of the encirclement on the band frequencies and intensity is studied and due to the predictable, controlled and reproducible structure of the dendrimers the information usually inaccessible is obtained. The strong line at 1602 cm−1 show marked changes of intensity in dependence of aldehyde ( CH O) or azomethyne ( CH N ) substituents in the aromatic ring. The analysis of Raman spectra enables one to assign the characteristic lines P S stretching vibrations for the bonds in a core, in repeating unit and in terminal groups of dendrimers. Thus the structural features of the first and second generations of dendrimers built from thiophosphoryl core obtained in this study are contained for the higher generations of dendrimes and define their properties. Raman spectroscopy provides unique

detailed information about the structure of the technologically relevant materials, which could not be obtained before with any other technique. References [1] G.R. Newkome, C.N. Moorefield, F. Vogtle, Dendrimers and Dendrons: Concepts, Syntheses, Applications, VCH, Weinheim, 2001. [2] J.M.J. Frechet, D.A. Tomalia, Dendrimers and other Dendritic Polymers, Wiley, New York, 2002. [3] J.P. Majoral, A.M. Caminade, V. Maraval, Chem. Commun. (2002) 2929. [4] A.M. Caminade, J.P. Majoral, Prog. Polym. Sci. 30 (2005) 491. [5] M.L. Lartigue, B. Donnadieu, C. Galliot, A.M. Caminade, J.P. Majoral, Macromolecules 30 (1997) 7335. [6] A.P. Davis, G. Ma, H.C. Allen, Anal. Chem. Acta 496 (2003) 117. [7] M. Wells, R.M. Crooks, J. Am. Chem. Soc. 118 (1996) 3988. [8] I. Grabchev, V. Bojinov, J.M. Chovelon, Polymer 44 (2003) 4421. [9] V.L. Furer, A.E. Vandyukov, J.P. Majoral, A.M. Caminade, V.I. Kovalenko, J. Mol. Struct. 919 (2009) 366. [10] V.L. Furer, I.I. Vandyukova, C. Padie, J.P. Majoral, A.M. Caminade, V.I. Kovalenko, J. Mol. Struct. 886 (2008) 1. [11] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865. [12] M. Ernzerhof, G.E. Scuseria, J. Chem. Phys. 110 (1999) 5029. [13] C. Adamo, V. Barone, J. Chem. Phys. 110 (1999) 6158. [14] M. Ernzerhof, G.E. Scuseria, J. Chem. Phys. 111 (1999) 911. [15] T.H. Dunning Jr., J. Chem. Phys. 55 (1971) 716. [16] A.D. McLean, G.S. Chandler, J. Chem. Phys. 72 (1980) 5639. [17] D.N. Laikov, Yu.A. Ustynyuk, Russ. Chem. Bull. Int. Ed. 54 (2005) 821. [18] V.A. Sipachev, J. Mol. Struct. (Theochem.) 121 (1985) 143. [19] I.W. Larkin, J. Chem. Soc. Faraday Trans. II 69 (1973) 1278. [20] A.R. Katrizky, R.D. Topsom, Chem. Rev. 77 (1977) 639. [21] E. Benfenati, G. Gini, N. Piclin, A. Roncaglioni, M.R. Var, Chemosphere 53 (2003) 1155. [22] HyperChem(TM) Professional 7.51, Hypercube, Inc., Gainesville, Florida, USA, 2002.