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DFT study of structure, IR and Raman spectra of the fluorescent “Janus” dendron built from cyclotriphosphazene core
Journal of Molecular Structure 1005 (2011) 25–30
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DFT study of structure, IR and Raman spectra of the fluorescent ‘‘Janus’’ dendron built from cyclotriphosphazene core V.L. Furer a,⇑, I.I. Vandyukova b, A.E. Vandyukov b, S. Fuchs c, J.P. Majoral c, A.M. Caminade c, V.I. Kovalenko b,⇑ a b c
Kazan State Architect and Civil Engineering University, Zelenaya, 1, Kazan 420043, Russia A.E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Science, Arbuzov Str., 8, Kazan 420088, 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 5 May 2011 Received in revised form 1 August 2011 Accepted 1 August 2011 Available online 18 August 2011 Keywords: Dendrimers IR spectra Normal vibrations DFT Raman spectra
a b s t r a c t The FTIR and FT-Raman spectra of the zero generation dendron, possessing five fluorescent dansyl terminal groups, cyclotriphosphazene core, and one carbamate function G0v were studied. The structural optimization and normal mode analysis were performed for G0v dendron on the basis of the density functional theory (DFT). The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. It was found that dendron molecule G0v has a concave lens structure with slightly non-planar cyclotriphosphazene core. The experimental IR and Raman spectra of G0v dendron were interpreted by means of potential energy distributions. Relying on DFT calculations a complete vibrational assignment is proposed. The frequency of m(NH) band in the IR spectrum reveal the presence of H-bonds in the G0v dendron. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Dendrimers are highly branched monodisperse macromolecular compounds [1–3]. A fine control of the shape and properties of dendrimer can be achieved [1–3]. 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 [1–3]. Dendrons are dendritic molecules having one function located at the core and several other functions located on the surface. The synthesis of ‘‘Janus’’ dendrimers bearing fluorescent groups on one side and water-solubilizing functions on the other, which should be useful for labeling materials or biological entities was described [4]. The key point for the synthesis such dendrimers is the coupling of two different dendrons by their core. The strategy is based on the non-symmetrical functionalization of hexachlorotriphosphazene N3P3Cl6 to synthesize AB5 type compounds, where A is the function usable for the coupling with another dendron and B is the functional terminal group; thus, five functions remain available for growing, instead of two for ‘‘classical’’ dendrons [4]. Besides their usefulness for the synthesis of complex dendritic architectures, ⇑ Corresponding authors. Tel.: +7 8435104737; fax: +7 8432387972 (V.L. Furer), tel.: +7 8432732283; fax: +7 8432732253 (V.I. Kovalenko). E-mail addresses: [email protected] (V.L. Furer), [email protected] (V.I. Kovalenko). 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.08.001
dendrons offer other possible users for elaborating new materials, depending on the function located at the core [5–7]. The techniques used for characterizing such macromolecular compounds should afford not only their chemical composition but also their morphology, shape and homogeneity. NMR spectrometry, mass spectrometry, size exclusion chromatography, dynamic light scattering and various microscopies (TEM, AFM) have provided important information about the structure of these compounds [9], but FTIR spectroscopy should afford additional information [10]. In this paper we report the IR and Raman spectra study combined with DFT calculations of G0v which is the zero generation dendron built from a cyclotriphosphazene core with five dansyl terminal groups and one carbamate function [4]. We choose dansyl group as the fluorescent label since it was already find suitable for labeling dendrimers [11]. The presence of carbamate groups is important since they offer a wide range of possibilities to obtain water-solubilizing functions onto the surface of dendrimers [12,13]. Our aim was to combine the experimental results with density functional theory (DFT) quantum chemical calculations to interpret IR and Raman spectra of dendrimers. During full optimization we were able to find local minimum conformer of G’0v and its IR spectra using DFT techniques. We have obtained structural parameters for dendron G’0v and compared them to the experimental values. Thus the main aim of this work was to characterize the core and terminal groups of dendrimers based on IR and Raman
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correlation hole and it does not contain any fitting parameters [15]. The comparison of the computed with PBE functional binding energies, geometries and dynamical properties of different molecules show the best agreement with experiment [16,17]. Calculations were performed using three exponential basis with two polarizing functions (TZ2P) [18,19]. 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 [20]. 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 [21] 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 [22]. Spectra were generated from a list of frequencies and intensities using Gaussian band shape and width at half-height r of 20 cm1 for each of N vibration modes calculated. An assignment of bands was fulfilled on the basis of calculated potential energy distribution (PED).
spectra study and DFT analysis. The results that emerge from such an analysis contribute to the understanding of the structure, dynamics and properties of dendrimers. 2. Experimental The synthesis and main characteristics of dendron G0v were described earlier [8]. The dendron G0v contains the cyclotriphosphazene core (NP)3, one carbamate group –O–C6H4–(CH2)2–NH –CO–OC(CH3)3, and five dansyl terminal groups –O–C6H4–– (CH2)2–NH–SO2C10H6–N(CH3)2 (Fig. 1). The dendron G0v was obtained as white powder. 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 typical resulting sample thickness was measured to be about 10 lm. Raman spectra in the region 3500–10 cm1 were excited by Nd: YAG laser line 1064 nm with power at sample 50 mW and were registered with an FTIR spectrometer VERTEX 70 equipped with RAM II Bruker FT-Raman module. The 1064 nm excitation of Raman spectra was used for utmost suppression of fluorescence of dendron sample. 3. Computational method
4. Results and discussion Calculations of IR spectra of G0v 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 verifies a lot of the exact conditions for the exchange–
The dendron G0v is amorphous and lack long-range order in the condensed phase. Thus, its molecular structure is impossible to determine by X-ray diffraction. But we can use the geometric parameters of relative cyclotriphosphazene and dansyl molecules
N N
O O
S
S O NH
O N H
O N
P
O
N
N S H O
P O O P N O O
NH
O
O
O
O
S
NH
NH O S O
O N
N Fig. 1. Structure of dendron molecule G0v.
N
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V.L. Furer et al. / Journal of Molecular Structure 1005 (2011) 25–30
in crystalline state defined by the X-ray diffraction method [23,24]. It was shown that the cyclotriphosphazene ring is slightly non-planar, with two nitrogen atoms displaced by 0.15 Å in opposite directions from the plane of the other four (three phosphorous and one nitrogen) atoms [23]. There are no differences among chemically equivalent bond lengths [23]. Although the comparison between gas phase and condensed phase structures is not direct, we can observe a reasonable agreement between theoretical calculations of G0v and the experimental X-ray diffraction data for the crystal phase of hexaphenoxycyclotriphosphazene [23] and dansyl derivative [24] (Table 1). Full optimization yielded the conformer of G0v with slightly non-planar cyclotriphosphazene ring (Fig. 2). The calculated dihedral angles of cyclotriphosphazene ring are less than 7°. Our data correspond to recent ab initio calculations of phosphazenes [25]. It was shown that most of cyclotriphosphazene derivatives have planar ring conformations [25]. The calculated for G0v molecule bond distances (in Å) P(1)N(1) (1.608), P(1)O(1) (1.634), S(1)N(4) (1.706), S(1)O(7) (1.469), and C(1)O(1) (1.401), correspond well to the experimental values 1.574, 1.583, 1.617, 1.425, and 1.395. The theoretical bond angles (in°) N(1)P(1)N(3) (119.9), P(1)N(1)P(2) (119.2), O(1) P(1)O(2) (103.5), O(1)C(1)C(2) (117.4), P(1)O(1)C(1) (124.6) are also in close agreement with the experimental values 117.3, 121.3, 100.1, 118.8, and 128.7. Our calculations show that G0v molecule has a concave lens structure with slightly non-planar cyclotriphosphazene core. The dendron shape can be characterized by ratios I1/I3 and I2/I3 of principal moments of gyration tensor. Their values 0.36 and 0.80
correspond to disk like anisotropic shape of dendron G0v molecules. Thus the flat and anisotropic shape of the cyclotriphosphazene core defines the ability of dendrons to pack with each other to form the most probable disk-like shape. The host–guest chemistry is usually based on electrostatic interactions between dendrimer surface and charged particles. In order to evaluate the interactions between dendrons 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 studied molecule G0v incorporate strong P–N polar bonds in the core with Hirshfeld [26] atomic charges (in a.u.) on atoms N(1) (0.29), P(1) (0.43). The oxygen atoms of the carbamate unit O(16), O(17) have negative charges 0.10, 0.28. The O(8) and O(9) atoms of SO2 group have charges 0.25 and 0.24 respectively, the S(1) atom has rather large positive charge 0.43. The N(4) and N(9) atoms of dansyl group have charges 0.12 and 0.04. Other atoms of G0v have charges less than 0.1. Dipole moments may be used for characterization of dendrons structure. The calculated in gas phase dipole moment of G0v is equal to 18.95 D. Thus G0v dendron has a significant dipole moment which may be attributed to a non-symmetrical distribution of the dansyl arms. The branches of this dendron induce a great influence upon the core in terms of isolation and polarity. Lipophilicity is a very important molecular descriptor that often correlates well with the bioactivity of chemicals [27]. The logarithm of the partition coefficient (logP) correlates with water solubility [27]. Lipophilicity can be measured by logP, which reflects the equilibrium partitioning a molecule between an apolar and a
Table 1 0 Experimental and calculated bond distances (Å A) and bond angles (°) of G0v. Exp.[23,24]
Calc.
Exp.[23,24]
Calc.
Bond distances P(1)–N(1) P(1)–N(3) P(1)–O(1) P(2)–N(1) P(2)–N(2) P(3)–N(2) P(3)–N(3) S(1)–N(4) S(1)–O(7)
1.574 1.581 1.583 1.572 1.573 1.574 1.575 1.617 1.425
1.608 1.605 1.634 1.609 1.605 1.608 1.613 1.706 1.469
N(4)–C(32) N(9)–C(66) N(9)–C(69) O(6)–C(10) O(17)–C(112) C(1)–O(1) O(16)–C(112) S(1)–C(41) S(1)–O(18)
1.411 1.421 1.446 1.404 1.200 1.395 1.341 1.772 1.425
1.472 1.412 1.457 1.403 1.219 1.401 1.369 1.833 1.467
Angles N(1)–P(1)–N(3) N(1)–P(2)–N(2) N(2)–P(3)–N(3) P(1)–N(1)–P(2) P(1)–N(3)–P(3) P(2)–N(2)–P(3) O(1)–P(1)–O(2) P(1)–O(1)–C(1) P(1)–O(2)–C(7) O(1)–C(1)–C(2) P(3)–O(6)–C(101) S(1)–N(4)–C(32)
117.3 117.9 116.6 121.3 121.3 122.4 100.1 128.7 123.5 118.8 124.4 125.5
119.9 120.3 119.7 119.2 120.0 119.9 103.5 124.6 127.5 117.4 119.5 120.0
N(4)–S(1)–O(7) N(4)–S(1)–O(18) N(4)–S(1)–C(48) N(9)–C(73)–C(51) O(6)–C(101)–C(102) C(111)–O(16)–C(112) O(8)–S(1)–O(9) O(16)–C(112)–O(17) O(17)–C(112)–N(14) C(66)–N(9)–C(69) C(76)–N(9)–C(77)
105.2 108.2 106.5 123.5 118.8 115.4 115.4 125.2 123.4 115.6 109.4
105.3 109.7 102.8 118.8 119.3 115.3 122.1 125.3 124.1 116.9 111.3
Dihedral angles P(1)–N(1)–P(2)–N(2) P(1)–N(3)–P(3)–N(2) P(1)–O(1)–C(1)–C(2) P(2)–N(1)–P(1)–N(3) P(2)–N(2)–P(3)–N(3) P(3)–N(2)–P(2)–N(1) P(3)–N(3)–P(1)–N(1) P(3)–O(6)–C(101)–C(102) N(1)–P(1)–O(1)–C(1) N(1)–P(1)–O(2)–C(7) N(3)–P(3)–O(6)–C(31) N(4)–S(1)–C(41)–C(42)
4.3 9.9 172.8 9.3 4.8 11.8 16.6 81.9 174.7 20.6 174.7 58.9
10.6 2.1 112.0 12.1 0.6 4.9 7.9 85.6 165.6 53.5 165.7 71.9
N(9)–C(66)–C(44)–C(42) S(1)–C(41)–C(42)–C(44) S(1)–N(4)–C(32)–C(31) O(1)–C(1)–C(2)–C(4) O(6)–C(101)–C(102)–C(103) O(17)–C(112)–N(14)–C(108) C(1)–C(2)–C(4)–C(6) C(2)–C(4)–C(6)–C(31) C(4)–C(6)–C(31)–C(32) C(32)–N(4)–S(1)–C(41) C(44)–C(66)–N(9)–C(60)
178.5 174.3 150.7 174.1 173.7 176.9 0.7 176.9 77.6 56.2 155.1
175.7 179.0 80.3 175.3 177.9 174.2 0.2 176.8 73.6 67.7 157.7
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V.L. Furer et al. / Journal of Molecular Structure 1005 (2011) 25–30
Fig. 2. Optimized geometry and atom numbering for G0v.
Absorbance
625 570
791
2
684
537 499
839
888
1018
1120 1079
1323 1268
1454 1409
1691
1.5
1574
1505
2.0
955
1181 1163 1145
polar phase. In the present study we calculate logP for G0v dendron with HyperChem software and obtained the rather high value 24.86 which is due to hydrogen bonding. The IR spectra were calculated for the most stable conformation of G0v (Fig. 3). The assignment of bands was fulfilled on the basis of the calculated potential energy distribution (PED) (Table 2). The IR and Raman spectra of G0v are represented in Figs. 4–6. The strong band at 3291 cm1 with weak shoulder at 3430 cm1 are observed in this region of IR spectrum of G0v (Fig. 5). These bands refer to m(NH) vibrations of dansyl and carbamate group
1.0
1
0.5
0.0 1800
1600
1400
1200
1000
800
600
Wavenumber/cm -1 Fig. 3. Theoretical (1) and experimental (2) IR spectra of G0v.
400
respectively. The band of the free m(NH) bond is not observed in the IR spectrum of G0v, and thus all NH groups participate in hydrogen bond. The weak absorptions, assigned to the aromatic CH stretching mode at 3078, 3054, and 3035 cm1, are seen in the IR spectrum of G0v (Fig. 5). The medium-intensity line at 3074 cm1, arising from this vibrations presents in the Raman spectrum of G0v (Fig. 5). The CH3 asymmetric stretching frequencies are established at 2998 cm1 in the Raman spectrum of G0v. The bands at 2944 and 2856 cm1 in the IR spectrum and lines at 2940 and 2866 cm1 in the Raman spectrum of G0v are connected with asymmetric and symmetric stretching vibrations of CH2 groups. The well-separated doublet 1691, 1709 cm1 of the amide I band of carbamate group is observed in the IR spectra of G0v (Fig. 3). The band of the free m(C@O) bond is not observed in the IR spectrum of G0v, and thus all C@O groups participate in hydrogen bond. This doublet may be ascribed to different types of H-bonds. The bands at 1610, 1588, 1574, 1505, and 1478 cm1 in the IR spectrum and the lines at 1610, 1576, and 1479 cm1 in the Raman spectrum of G0v refer to CCar stretch and CCH bending vibrations of aromatic ring. The band at 1454 cm1 in the IR spectrum of G0v is connected with CH2 bending vibrations. The intense line at 1356 cm1 in the Raman spectrum of G0v is assigned to CCar stretch and CCH bending vibrations of aromatic ring of dansyl group. The broad medium-intensity band at 1323 cm1 in the IR spectrum of G0v is assigned to the asymmetric stretch of the SO2 group. The very strong band and complex bands in the experimental IR spectrum of G0v at 1163, 1181, 1200, 1232, 1256, and 1268 cm1 and the medium-intensity lines at 1162, 1174, 1205, and 1237 cm1 in the Raman spectrum of G0v refer to the C–O, P–N and C–C stretch. The band at 1120 cm1 in the IR spectra of G0v may be connected with the symmetric stretch of the SO2 group. The strong band at 954 cm1 in the experimental IR spectrum of G0v is assigned to P–O stretching vibrations. The medium-intensity band at 888 cm1 in the IR spectrum of G0v refers to the symmetric
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V.L. Furer et al. / Journal of Molecular Structure 1005 (2011) 25–30
1079
1018
1073 1047 1015 1003
955 944 888 874 839
839 826 798
791
684 625
570
537 499
a
762 725 684 641 627 602 585 579 573 552 547 539 501 490 465 444
m, stretch; d, in-plane bend; q, out-of-plane bend; and v, torsion.
COC stretch. The band at 791 cm1 in the IR spectrum of G0v represents C–H out-of-plane vibrations of aromatic ring. The band at 625 cm1 in the IR spectrum and line at 627 cm1 in the Raman spectrum of G0v include contribution of CCC bend. The lines in low frequency region of Raman spectrum of G0v at 585, 538, 501, 465, 462, 395, 346 and 290 cm1 may be assigned to the bending vibrations of skeleton. Thus, a core (NP)3, of dendron shows band at 1237 cm1 in the Raman spectrum of G0v assigned to PN stretch. Carbamate group reveal itself by well defined doublet at 1709 and 1691 cm1 in the
0.6
539
640 626
0.2
839
1407
0.4
0.0
1800
1600
1400
1200
1000
800
600
400
Wavenumber/cm-1 Fig. 4. Experimental Raman spectra of G0v.
2.5
2.0 2 2788
1102 1094
d(HCH), 11 d(NCH) d(HCH), 8 d(NCH) d(HCH), 7 d(CCH) d(HCH), 28 d(CCH), 20 m(CCar) d(HCH), 10 d(NCH) d(HCH), 15 d(CCH) m(CCar), 39 d(CCH), 5 d(CCC) m(CCar), 8 d(CCC), 6 d(CCH) m(S = O), 13 d(NCH), 9 d(CCH) m(CN), 16 d(CCH), 16 d(NCH) d(CCH), 14 m(CC), 13 d(NCH) d(CCH), 14 m(CC), 13 d(NCH) m(C–C), 18 m(PN), 14 m(C–O) m(CCar), 32 d(CCH), 9 d(CCC) m(C–C), 20 m(CCar), 6 m(C–O) d(CCH), 6 m(C–O), 5 d(HCH) m(P–N), 21 m(C–O), 20 d(CCH) d(CCH), 22 m(CCar), 19 m(CN) d(CCH), 13 d(NCH), 9 m(CCar) d(CCH), 14 m(CCar), 8 d(NCH) d(NCH), 6 d(HCH) m(S = O) m(CCar), 26 d(NCH), 12 d(CCH) d(NCH), 12 m(CCar), 6 d(CCH) d(CCH), 28 d(HCH), 24 m(CCar) m(CCar), 18 m(CN), 17 d(NCH) d(CCH), 11 m(C–C) d(CCH), 31 m(CCar), 27 d(CCC) m(PO), 10 m(PN), 6 m(CCar) q(CH), 6 v(CC) m(PO), 4 m(C–O) m(PO) m(CCar), 14 m(C–C), 11 m(S–N) q(CH), 14 m(PN), 7 m(C–N) q(CH), 7 d(HCH), 4 m(C–C) m(P–N), 24 m(P = S), 9 q(CH) m(P–O), 16 m(P–N), 4 d(PNP) v(CC), 19 q(CH), 10 m(P–O) v(CC), 19 q(CH), 15 v(CN) d(CCC), 18 d(CCH), 7 m(CCar) d(CCC), 17 d(CCH), 8 m(CCar) m(CCar), 10 m(SC), 8 m(CN) v(CN), 8 m(C–O), 8 d(SN) m(P = S), 14 m(P–O), 12 d(POC) v(CC), 23 q(CH), 4 v(SN) v(SN), 12 v(CN), 11 m(SN) d(CCC), 11 d(POC), 7 d(OSC) d(CCC), 7 d(OSC), 5 d(CCN) d(CCC), 11 v(CN), 8 m(SN) d(CCC), 16 d(CNC), 11 m(CN) v(CC), 38 q(CH) d(OCC), 22 v(CO), 11 d(CCC)
0.8
1.5
1.0
0.5
2788
1120
1177 1175 1162 1143
m(C@O), 9 d(CNH) m(CCar), 23 d(CCH) m(CCar), 24 d(CCH) m(CCar), 12 d(CCH), 8 d(CCC) d(CCH), 37 m(CCar), 6 m(C–O)
2855
1163 1145
1205
61 66 68 71 46 71 75 81 37 73 71 47 82 66 43 47 47 22 32 27 17 27 36 38 66 71 78 29 61 36 23 71 33 59 87 76 88 17 14 65 25 56 20 37 56 54 22 10 18 35 14 21 27 16 33 47 24
2866
1237 1232 1200 1181
460.4 25.1 27.8 7.7 158.6 18.5 7.8 2.5 50.1 50.2 0.6 1.2 24.3 94.3 32.7 4.6 9.5 214.4 5.1 237.0 528.9 582.8 33.2 23.2 5.2 29.1 100.3 3.5 6.3 74.9 26.2 103.7 27.5 36.8 28.7 151.2 35.2 143.1 127.5 106.6 232.2 64.1 52.7 4.7 15.2 21.1 30.2 18.3 6.9 34.3 26.2 84.2 9.3 34.2 4.7 5.8 6.0
2940 2944
1306 1268 1256
1771 1608 1584 1576 1496 1479 1458 1457 1442 1434 1421 1410 1352 1315 1303 1260 1259 1244 1230 1199 1180 1178 1170 1162 1140 1133 1104 1093 1082 1079 1046 1017 1006 951 941 893 885 843 821 794 785 769 725 674 636 634 604 584 577 565 553 546 533 504 490 459 444
3074
1323
Assignmenta
1205 1143 1094
1409
1479 1462 1458 1443 1438 1420 1407 1356
I
3291
1454
1610 1589 1576
m
1576
m
1479 1441
Raman
m
1610
IR 1691 1610 1588 1574 1505 1478
1.0
Calculation
Intensity
Experiment
1356
Table 2 Experimental and corresponded calculated frequencies m (cm1) and intensity I (km/ mole) of bands in the IR spectra of G0v in the region 400–1800 cm1.
1
0.0 3600
3400
3200
3000
2800
2600
Wavenumber/cm -1 Fig. 5. Experimental Raman (1) and IR (2) spectra of G0v.
IR spectrum of G0v, connected with amide I vibration. Dansyl terminal groups may be identified by the intense in Raman spectrum line at 1356 cm1, assigned to CC stretching vibrations of naphthalene ring. Although the calculated absorption curve of isolated molecules of G0v is much simpler than the experimental IR spectrum the intensity of most prominent bands is reproduced by our computations (Fig. 3). Thus DFT calculations may be used for interpretation of spectra of dendrimers. 5. Summary The IR and Raman spectra of G0v dendron built from a cyclotriphosphazene core with dansyl and carbamate terminal groups
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the technologically relevant materials, which could not be obtained before by any other technique. The analysis of IR and Raman spectra of dendrons enables one to distinguish the bands of a cyclotriphosphazene core, dansyl and carbamate terminal groups.
290
0.6
References
539
395
465
0.2
584
Intensity
501
0.4
0.0
600
550
500
450
400
350
300
250
200
Wavenumber/cm -1 Fig. 6. Experimental Raman spectra of G0v.
have been recorded. The structural optimization and vibrational analysis were made for G0v by DFT method. The intensity of the most prominent bands in the IR spectrum of G0v is reproduced by our calculations. The calculated absorption curves of G0v as a whole corresponds to the experimental IR spectrum in the wide frequency region. Thus the employed DFT method enables one to calculate the structure, charges on atoms, and reproduce the experimental IR spectrum of the dendron G0v. The calculated ratios of principal moments of gyration tensor reveal that the G0v molecules have highly asymmetric shape. IR spectroscopy combined with quantum chemical DFT computation provides unique detailed information about the structure of
[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] G.R. Newkome, V. Shreiner, Polymer 49 (2008) 1. [4] S.C. Zimmerman, F. Zeng, D.E.C. Reichert, S.V. Kolotuchin, Science 271 (1996) 1095. [5] C.J. Hawker, J.M.J. Frechet, J. Chem. Soc. Chem. Commun. (1990) 1010. [6] C.J. Hawker, K.L. Wooley, J.M.J. Frechet, J. Macromol. Symp. 77 (1994) 11. [7] V. Maraval, R. Laurent, B. Donnadieu, M. Mauzac, A.M. Caminade, J.P. Majoral, J. Am. Chem. Soc. 122 (2000) 2499. [8] S. Fuchs, A. Pla-Quintana, S. Mazares, A.M. Caminade, J.P. Majoral, Org. Lett. 21 (2008) 4751. [9] A.M. Caminade, R. Laurent, J.P. Majoral, Adv. Drug. Deliv. Rev. 57 (2005) 2130. [10] J.M. Chalmers, P.R. Griffiths (Eds.), Comprehensive Review on Vibrational Spectroscopy, Handbook of Vibrational Spectroscopy, Wiley, New York, 2002. [11] I. Bury, B. Donnio, J.-L. Gallani, D. Guillon, Langmuir 23 (2007) 619. [12] A.M. Caminade, J.P. Majoral, Phosphazenes: a worldwide insight, in: M. Gleria, R. de Jaeger (Eds.), NOVA Science Publishers, New York, 2004, p. 713 (Chapter 30). [13] J.P. Majoral, A.M. Caminade, V. Maraval, Chem. Commun. (2002) 2929. [14] J.P. Perdew, K. Burke, M. Erznzerhof, Phys. Rev. Lett. 77 (1996) 3865. [15] M. Erznzerhof, G.E. Scuseria, J. Chem. Phys. 110 (1999) 5029. [16] C. Adamo, V. Barone, J. Chem. Phys. 110 (1999) 6158. [17] M. Erznzerhof, G.E. Scuseria, J. Chem. Phys. 111 (1999) 911. [18] T.H. Dunning Jr., J. Chem. Phys. 55 (1971) 716. [19] A.D. McLean, G.S. Chandler, J. Chem. Phys. 72 (1980) 5639. [20] D.N. Laikov, Yu.A. Ustynyuk, Russ. Chem. Bull. Int. Edit. 54 (2005) 821. [21] V.A. Sipachev, J. Mol. Struct. (Theochem.) 121 (1985) 143. [22] V.L. Furer, A.E. Vandyukov, J.P. Majoral, A.M. Caminade, V.I. Kovalenko, J. Mol. Struct. 919 (2009) 366. [23] W.C. Marsh, J. Trotter, J. Chem, A. Soc, Inorg. Phys. Theor. (1971) 169. [24] H. Wu, P. Zhou, J. Wang, L. Zhao, C. Duan, New J. Chem. 33 (2009) 653. [25] A.B. Chaplin, J.A. Harrison, P.J. Dyson, Inorg. Chem. 44 (2005) 8407. [26] F.L. Hirshfeld, Theor. Chim. Acc. 44 (1977) 129. [27] E. Benfenati, G. Gini, N. Piclin, A. Roncaglioni, M.R. Var, Chemosphere 53 (2003) 1155.
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
DFT study of structure, IR and Raman spectra of the fluorescent ‘‘Janus’’ dendron built from cyclotriphosphazene core V.L. Furer a,⇑, I.I. Vandyukova b, A.E. Vandyukov b, S. Fuchs c, J.P. Majoral c, A.M. Caminade c, V.I. Kovalenko b,⇑ a b c
Kazan State Architect and Civil Engineering University, Zelenaya, 1, Kazan 420043, Russia A.E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Science, Arbuzov Str., 8, Kazan 420088, 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 5 May 2011 Received in revised form 1 August 2011 Accepted 1 August 2011 Available online 18 August 2011 Keywords: Dendrimers IR spectra Normal vibrations DFT Raman spectra
a b s t r a c t The FTIR and FT-Raman spectra of the zero generation dendron, possessing five fluorescent dansyl terminal groups, cyclotriphosphazene core, and one carbamate function G0v were studied. The structural optimization and normal mode analysis were performed for G0v dendron on the basis of the density functional theory (DFT). The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. It was found that dendron molecule G0v has a concave lens structure with slightly non-planar cyclotriphosphazene core. The experimental IR and Raman spectra of G0v dendron were interpreted by means of potential energy distributions. Relying on DFT calculations a complete vibrational assignment is proposed. The frequency of m(NH) band in the IR spectrum reveal the presence of H-bonds in the G0v dendron. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction Dendrimers are highly branched monodisperse macromolecular compounds [1–3]. A fine control of the shape and properties of dendrimer can be achieved [1–3]. 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 [1–3]. Dendrons are dendritic molecules having one function located at the core and several other functions located on the surface. The synthesis of ‘‘Janus’’ dendrimers bearing fluorescent groups on one side and water-solubilizing functions on the other, which should be useful for labeling materials or biological entities was described [4]. The key point for the synthesis such dendrimers is the coupling of two different dendrons by their core. The strategy is based on the non-symmetrical functionalization of hexachlorotriphosphazene N3P3Cl6 to synthesize AB5 type compounds, where A is the function usable for the coupling with another dendron and B is the functional terminal group; thus, five functions remain available for growing, instead of two for ‘‘classical’’ dendrons [4]. Besides their usefulness for the synthesis of complex dendritic architectures, ⇑ Corresponding authors. Tel.: +7 8435104737; fax: +7 8432387972 (V.L. Furer), tel.: +7 8432732283; fax: +7 8432732253 (V.I. Kovalenko). E-mail addresses: [email protected] (V.L. Furer), [email protected] (V.I. Kovalenko). 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.08.001
dendrons offer other possible users for elaborating new materials, depending on the function located at the core [5–7]. The techniques used for characterizing such macromolecular compounds should afford not only their chemical composition but also their morphology, shape and homogeneity. NMR spectrometry, mass spectrometry, size exclusion chromatography, dynamic light scattering and various microscopies (TEM, AFM) have provided important information about the structure of these compounds [9], but FTIR spectroscopy should afford additional information [10]. In this paper we report the IR and Raman spectra study combined with DFT calculations of G0v which is the zero generation dendron built from a cyclotriphosphazene core with five dansyl terminal groups and one carbamate function [4]. We choose dansyl group as the fluorescent label since it was already find suitable for labeling dendrimers [11]. The presence of carbamate groups is important since they offer a wide range of possibilities to obtain water-solubilizing functions onto the surface of dendrimers [12,13]. Our aim was to combine the experimental results with density functional theory (DFT) quantum chemical calculations to interpret IR and Raman spectra of dendrimers. During full optimization we were able to find local minimum conformer of G’0v and its IR spectra using DFT techniques. We have obtained structural parameters for dendron G’0v and compared them to the experimental values. Thus the main aim of this work was to characterize the core and terminal groups of dendrimers based on IR and Raman
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V.L. Furer et al. / Journal of Molecular Structure 1005 (2011) 25–30
correlation hole and it does not contain any fitting parameters [15]. The comparison of the computed with PBE functional binding energies, geometries and dynamical properties of different molecules show the best agreement with experiment [16,17]. Calculations were performed using three exponential basis with two polarizing functions (TZ2P) [18,19]. 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 [20]. 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 [21] 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 [22]. Spectra were generated from a list of frequencies and intensities using Gaussian band shape and width at half-height r of 20 cm1 for each of N vibration modes calculated. An assignment of bands was fulfilled on the basis of calculated potential energy distribution (PED).
spectra study and DFT analysis. The results that emerge from such an analysis contribute to the understanding of the structure, dynamics and properties of dendrimers. 2. Experimental The synthesis and main characteristics of dendron G0v were described earlier [8]. The dendron G0v contains the cyclotriphosphazene core (NP)3, one carbamate group –O–C6H4–(CH2)2–NH –CO–OC(CH3)3, and five dansyl terminal groups –O–C6H4–– (CH2)2–NH–SO2C10H6–N(CH3)2 (Fig. 1). The dendron G0v was obtained as white powder. 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 typical resulting sample thickness was measured to be about 10 lm. Raman spectra in the region 3500–10 cm1 were excited by Nd: YAG laser line 1064 nm with power at sample 50 mW and were registered with an FTIR spectrometer VERTEX 70 equipped with RAM II Bruker FT-Raman module. The 1064 nm excitation of Raman spectra was used for utmost suppression of fluorescence of dendron sample. 3. Computational method
4. Results and discussion Calculations of IR spectra of G0v 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 verifies a lot of the exact conditions for the exchange–
The dendron G0v is amorphous and lack long-range order in the condensed phase. Thus, its molecular structure is impossible to determine by X-ray diffraction. But we can use the geometric parameters of relative cyclotriphosphazene and dansyl molecules
N N
O O
S
S O NH
O N H
O N
P
O
N
N S H O
P O O P N O O
NH
O
O
O
O
S
NH
NH O S O
O N
N Fig. 1. Structure of dendron molecule G0v.
N
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V.L. Furer et al. / Journal of Molecular Structure 1005 (2011) 25–30
in crystalline state defined by the X-ray diffraction method [23,24]. It was shown that the cyclotriphosphazene ring is slightly non-planar, with two nitrogen atoms displaced by 0.15 Å in opposite directions from the plane of the other four (three phosphorous and one nitrogen) atoms [23]. There are no differences among chemically equivalent bond lengths [23]. Although the comparison between gas phase and condensed phase structures is not direct, we can observe a reasonable agreement between theoretical calculations of G0v and the experimental X-ray diffraction data for the crystal phase of hexaphenoxycyclotriphosphazene [23] and dansyl derivative [24] (Table 1). Full optimization yielded the conformer of G0v with slightly non-planar cyclotriphosphazene ring (Fig. 2). The calculated dihedral angles of cyclotriphosphazene ring are less than 7°. Our data correspond to recent ab initio calculations of phosphazenes [25]. It was shown that most of cyclotriphosphazene derivatives have planar ring conformations [25]. The calculated for G0v molecule bond distances (in Å) P(1)N(1) (1.608), P(1)O(1) (1.634), S(1)N(4) (1.706), S(1)O(7) (1.469), and C(1)O(1) (1.401), correspond well to the experimental values 1.574, 1.583, 1.617, 1.425, and 1.395. The theoretical bond angles (in°) N(1)P(1)N(3) (119.9), P(1)N(1)P(2) (119.2), O(1) P(1)O(2) (103.5), O(1)C(1)C(2) (117.4), P(1)O(1)C(1) (124.6) are also in close agreement with the experimental values 117.3, 121.3, 100.1, 118.8, and 128.7. Our calculations show that G0v molecule has a concave lens structure with slightly non-planar cyclotriphosphazene core. The dendron shape can be characterized by ratios I1/I3 and I2/I3 of principal moments of gyration tensor. Their values 0.36 and 0.80
correspond to disk like anisotropic shape of dendron G0v molecules. Thus the flat and anisotropic shape of the cyclotriphosphazene core defines the ability of dendrons to pack with each other to form the most probable disk-like shape. The host–guest chemistry is usually based on electrostatic interactions between dendrimer surface and charged particles. In order to evaluate the interactions between dendrons 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 studied molecule G0v incorporate strong P–N polar bonds in the core with Hirshfeld [26] atomic charges (in a.u.) on atoms N(1) (0.29), P(1) (0.43). The oxygen atoms of the carbamate unit O(16), O(17) have negative charges 0.10, 0.28. The O(8) and O(9) atoms of SO2 group have charges 0.25 and 0.24 respectively, the S(1) atom has rather large positive charge 0.43. The N(4) and N(9) atoms of dansyl group have charges 0.12 and 0.04. Other atoms of G0v have charges less than 0.1. Dipole moments may be used for characterization of dendrons structure. The calculated in gas phase dipole moment of G0v is equal to 18.95 D. Thus G0v dendron has a significant dipole moment which may be attributed to a non-symmetrical distribution of the dansyl arms. The branches of this dendron induce a great influence upon the core in terms of isolation and polarity. Lipophilicity is a very important molecular descriptor that often correlates well with the bioactivity of chemicals [27]. The logarithm of the partition coefficient (logP) correlates with water solubility [27]. Lipophilicity can be measured by logP, which reflects the equilibrium partitioning a molecule between an apolar and a
Table 1 0 Experimental and calculated bond distances (Å A) and bond angles (°) of G0v. Exp.[23,24]
Calc.
Exp.[23,24]
Calc.
Bond distances P(1)–N(1) P(1)–N(3) P(1)–O(1) P(2)–N(1) P(2)–N(2) P(3)–N(2) P(3)–N(3) S(1)–N(4) S(1)–O(7)
1.574 1.581 1.583 1.572 1.573 1.574 1.575 1.617 1.425
1.608 1.605 1.634 1.609 1.605 1.608 1.613 1.706 1.469
N(4)–C(32) N(9)–C(66) N(9)–C(69) O(6)–C(10) O(17)–C(112) C(1)–O(1) O(16)–C(112) S(1)–C(41) S(1)–O(18)
1.411 1.421 1.446 1.404 1.200 1.395 1.341 1.772 1.425
1.472 1.412 1.457 1.403 1.219 1.401 1.369 1.833 1.467
Angles N(1)–P(1)–N(3) N(1)–P(2)–N(2) N(2)–P(3)–N(3) P(1)–N(1)–P(2) P(1)–N(3)–P(3) P(2)–N(2)–P(3) O(1)–P(1)–O(2) P(1)–O(1)–C(1) P(1)–O(2)–C(7) O(1)–C(1)–C(2) P(3)–O(6)–C(101) S(1)–N(4)–C(32)
117.3 117.9 116.6 121.3 121.3 122.4 100.1 128.7 123.5 118.8 124.4 125.5
119.9 120.3 119.7 119.2 120.0 119.9 103.5 124.6 127.5 117.4 119.5 120.0
N(4)–S(1)–O(7) N(4)–S(1)–O(18) N(4)–S(1)–C(48) N(9)–C(73)–C(51) O(6)–C(101)–C(102) C(111)–O(16)–C(112) O(8)–S(1)–O(9) O(16)–C(112)–O(17) O(17)–C(112)–N(14) C(66)–N(9)–C(69) C(76)–N(9)–C(77)
105.2 108.2 106.5 123.5 118.8 115.4 115.4 125.2 123.4 115.6 109.4
105.3 109.7 102.8 118.8 119.3 115.3 122.1 125.3 124.1 116.9 111.3
Dihedral angles P(1)–N(1)–P(2)–N(2) P(1)–N(3)–P(3)–N(2) P(1)–O(1)–C(1)–C(2) P(2)–N(1)–P(1)–N(3) P(2)–N(2)–P(3)–N(3) P(3)–N(2)–P(2)–N(1) P(3)–N(3)–P(1)–N(1) P(3)–O(6)–C(101)–C(102) N(1)–P(1)–O(1)–C(1) N(1)–P(1)–O(2)–C(7) N(3)–P(3)–O(6)–C(31) N(4)–S(1)–C(41)–C(42)
4.3 9.9 172.8 9.3 4.8 11.8 16.6 81.9 174.7 20.6 174.7 58.9
10.6 2.1 112.0 12.1 0.6 4.9 7.9 85.6 165.6 53.5 165.7 71.9
N(9)–C(66)–C(44)–C(42) S(1)–C(41)–C(42)–C(44) S(1)–N(4)–C(32)–C(31) O(1)–C(1)–C(2)–C(4) O(6)–C(101)–C(102)–C(103) O(17)–C(112)–N(14)–C(108) C(1)–C(2)–C(4)–C(6) C(2)–C(4)–C(6)–C(31) C(4)–C(6)–C(31)–C(32) C(32)–N(4)–S(1)–C(41) C(44)–C(66)–N(9)–C(60)
178.5 174.3 150.7 174.1 173.7 176.9 0.7 176.9 77.6 56.2 155.1
175.7 179.0 80.3 175.3 177.9 174.2 0.2 176.8 73.6 67.7 157.7
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V.L. Furer et al. / Journal of Molecular Structure 1005 (2011) 25–30
Fig. 2. Optimized geometry and atom numbering for G0v.
Absorbance
625 570
791
2
684
537 499
839
888
1018
1120 1079
1323 1268
1454 1409
1691
1.5
1574
1505
2.0
955
1181 1163 1145
polar phase. In the present study we calculate logP for G0v dendron with HyperChem software and obtained the rather high value 24.86 which is due to hydrogen bonding. The IR spectra were calculated for the most stable conformation of G0v (Fig. 3). The assignment of bands was fulfilled on the basis of the calculated potential energy distribution (PED) (Table 2). The IR and Raman spectra of G0v are represented in Figs. 4–6. The strong band at 3291 cm1 with weak shoulder at 3430 cm1 are observed in this region of IR spectrum of G0v (Fig. 5). These bands refer to m(NH) vibrations of dansyl and carbamate group
1.0
1
0.5
0.0 1800
1600
1400
1200
1000
800
600
Wavenumber/cm -1 Fig. 3. Theoretical (1) and experimental (2) IR spectra of G0v.
400
respectively. The band of the free m(NH) bond is not observed in the IR spectrum of G0v, and thus all NH groups participate in hydrogen bond. The weak absorptions, assigned to the aromatic CH stretching mode at 3078, 3054, and 3035 cm1, are seen in the IR spectrum of G0v (Fig. 5). The medium-intensity line at 3074 cm1, arising from this vibrations presents in the Raman spectrum of G0v (Fig. 5). The CH3 asymmetric stretching frequencies are established at 2998 cm1 in the Raman spectrum of G0v. The bands at 2944 and 2856 cm1 in the IR spectrum and lines at 2940 and 2866 cm1 in the Raman spectrum of G0v are connected with asymmetric and symmetric stretching vibrations of CH2 groups. The well-separated doublet 1691, 1709 cm1 of the amide I band of carbamate group is observed in the IR spectra of G0v (Fig. 3). The band of the free m(C@O) bond is not observed in the IR spectrum of G0v, and thus all C@O groups participate in hydrogen bond. This doublet may be ascribed to different types of H-bonds. The bands at 1610, 1588, 1574, 1505, and 1478 cm1 in the IR spectrum and the lines at 1610, 1576, and 1479 cm1 in the Raman spectrum of G0v refer to CCar stretch and CCH bending vibrations of aromatic ring. The band at 1454 cm1 in the IR spectrum of G0v is connected with CH2 bending vibrations. The intense line at 1356 cm1 in the Raman spectrum of G0v is assigned to CCar stretch and CCH bending vibrations of aromatic ring of dansyl group. The broad medium-intensity band at 1323 cm1 in the IR spectrum of G0v is assigned to the asymmetric stretch of the SO2 group. The very strong band and complex bands in the experimental IR spectrum of G0v at 1163, 1181, 1200, 1232, 1256, and 1268 cm1 and the medium-intensity lines at 1162, 1174, 1205, and 1237 cm1 in the Raman spectrum of G0v refer to the C–O, P–N and C–C stretch. The band at 1120 cm1 in the IR spectra of G0v may be connected with the symmetric stretch of the SO2 group. The strong band at 954 cm1 in the experimental IR spectrum of G0v is assigned to P–O stretching vibrations. The medium-intensity band at 888 cm1 in the IR spectrum of G0v refers to the symmetric
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V.L. Furer et al. / Journal of Molecular Structure 1005 (2011) 25–30
1079
1018
1073 1047 1015 1003
955 944 888 874 839
839 826 798
791
684 625
570
537 499
a
762 725 684 641 627 602 585 579 573 552 547 539 501 490 465 444
m, stretch; d, in-plane bend; q, out-of-plane bend; and v, torsion.
COC stretch. The band at 791 cm1 in the IR spectrum of G0v represents C–H out-of-plane vibrations of aromatic ring. The band at 625 cm1 in the IR spectrum and line at 627 cm1 in the Raman spectrum of G0v include contribution of CCC bend. The lines in low frequency region of Raman spectrum of G0v at 585, 538, 501, 465, 462, 395, 346 and 290 cm1 may be assigned to the bending vibrations of skeleton. Thus, a core (NP)3, of dendron shows band at 1237 cm1 in the Raman spectrum of G0v assigned to PN stretch. Carbamate group reveal itself by well defined doublet at 1709 and 1691 cm1 in the
0.6
539
640 626
0.2
839
1407
0.4
0.0
1800
1600
1400
1200
1000
800
600
400
Wavenumber/cm-1 Fig. 4. Experimental Raman spectra of G0v.
2.5
2.0 2 2788
1102 1094
d(HCH), 11 d(NCH) d(HCH), 8 d(NCH) d(HCH), 7 d(CCH) d(HCH), 28 d(CCH), 20 m(CCar) d(HCH), 10 d(NCH) d(HCH), 15 d(CCH) m(CCar), 39 d(CCH), 5 d(CCC) m(CCar), 8 d(CCC), 6 d(CCH) m(S = O), 13 d(NCH), 9 d(CCH) m(CN), 16 d(CCH), 16 d(NCH) d(CCH), 14 m(CC), 13 d(NCH) d(CCH), 14 m(CC), 13 d(NCH) m(C–C), 18 m(PN), 14 m(C–O) m(CCar), 32 d(CCH), 9 d(CCC) m(C–C), 20 m(CCar), 6 m(C–O) d(CCH), 6 m(C–O), 5 d(HCH) m(P–N), 21 m(C–O), 20 d(CCH) d(CCH), 22 m(CCar), 19 m(CN) d(CCH), 13 d(NCH), 9 m(CCar) d(CCH), 14 m(CCar), 8 d(NCH) d(NCH), 6 d(HCH) m(S = O) m(CCar), 26 d(NCH), 12 d(CCH) d(NCH), 12 m(CCar), 6 d(CCH) d(CCH), 28 d(HCH), 24 m(CCar) m(CCar), 18 m(CN), 17 d(NCH) d(CCH), 11 m(C–C) d(CCH), 31 m(CCar), 27 d(CCC) m(PO), 10 m(PN), 6 m(CCar) q(CH), 6 v(CC) m(PO), 4 m(C–O) m(PO) m(CCar), 14 m(C–C), 11 m(S–N) q(CH), 14 m(PN), 7 m(C–N) q(CH), 7 d(HCH), 4 m(C–C) m(P–N), 24 m(P = S), 9 q(CH) m(P–O), 16 m(P–N), 4 d(PNP) v(CC), 19 q(CH), 10 m(P–O) v(CC), 19 q(CH), 15 v(CN) d(CCC), 18 d(CCH), 7 m(CCar) d(CCC), 17 d(CCH), 8 m(CCar) m(CCar), 10 m(SC), 8 m(CN) v(CN), 8 m(C–O), 8 d(SN) m(P = S), 14 m(P–O), 12 d(POC) v(CC), 23 q(CH), 4 v(SN) v(SN), 12 v(CN), 11 m(SN) d(CCC), 11 d(POC), 7 d(OSC) d(CCC), 7 d(OSC), 5 d(CCN) d(CCC), 11 v(CN), 8 m(SN) d(CCC), 16 d(CNC), 11 m(CN) v(CC), 38 q(CH) d(OCC), 22 v(CO), 11 d(CCC)
0.8
1.5
1.0
0.5
2788
1120
1177 1175 1162 1143
m(C@O), 9 d(CNH) m(CCar), 23 d(CCH) m(CCar), 24 d(CCH) m(CCar), 12 d(CCH), 8 d(CCC) d(CCH), 37 m(CCar), 6 m(C–O)
2855
1163 1145
1205
61 66 68 71 46 71 75 81 37 73 71 47 82 66 43 47 47 22 32 27 17 27 36 38 66 71 78 29 61 36 23 71 33 59 87 76 88 17 14 65 25 56 20 37 56 54 22 10 18 35 14 21 27 16 33 47 24
2866
1237 1232 1200 1181
460.4 25.1 27.8 7.7 158.6 18.5 7.8 2.5 50.1 50.2 0.6 1.2 24.3 94.3 32.7 4.6 9.5 214.4 5.1 237.0 528.9 582.8 33.2 23.2 5.2 29.1 100.3 3.5 6.3 74.9 26.2 103.7 27.5 36.8 28.7 151.2 35.2 143.1 127.5 106.6 232.2 64.1 52.7 4.7 15.2 21.1 30.2 18.3 6.9 34.3 26.2 84.2 9.3 34.2 4.7 5.8 6.0
2940 2944
1306 1268 1256
1771 1608 1584 1576 1496 1479 1458 1457 1442 1434 1421 1410 1352 1315 1303 1260 1259 1244 1230 1199 1180 1178 1170 1162 1140 1133 1104 1093 1082 1079 1046 1017 1006 951 941 893 885 843 821 794 785 769 725 674 636 634 604 584 577 565 553 546 533 504 490 459 444
3074
1323
Assignmenta
1205 1143 1094
1409
1479 1462 1458 1443 1438 1420 1407 1356
I
3291
1454
1610 1589 1576
m
1576
m
1479 1441
Raman
m
1610
IR 1691 1610 1588 1574 1505 1478
1.0
Calculation
Intensity
Experiment
1356
Table 2 Experimental and corresponded calculated frequencies m (cm1) and intensity I (km/ mole) of bands in the IR spectra of G0v in the region 400–1800 cm1.
1
0.0 3600
3400
3200
3000
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IR spectrum of G0v, connected with amide I vibration. Dansyl terminal groups may be identified by the intense in Raman spectrum line at 1356 cm1, assigned to CC stretching vibrations of naphthalene ring. Although the calculated absorption curve of isolated molecules of G0v is much simpler than the experimental IR spectrum the intensity of most prominent bands is reproduced by our computations (Fig. 3). Thus DFT calculations may be used for interpretation of spectra of dendrimers. 5. Summary The IR and Raman spectra of G0v dendron built from a cyclotriphosphazene core with dansyl and carbamate terminal groups
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the technologically relevant materials, which could not be obtained before by any other technique. The analysis of IR and Raman spectra of dendrons enables one to distinguish the bands of a cyclotriphosphazene core, dansyl and carbamate terminal groups.
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Intensity
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Wavenumber/cm -1 Fig. 6. Experimental Raman spectra of G0v.
have been recorded. The structural optimization and vibrational analysis were made for G0v by DFT method. The intensity of the most prominent bands in the IR spectrum of G0v is reproduced by our calculations. The calculated absorption curves of G0v as a whole corresponds to the experimental IR spectrum in the wide frequency region. Thus the employed DFT method enables one to calculate the structure, charges on atoms, and reproduce the experimental IR spectrum of the dendron G0v. The calculated ratios of principal moments of gyration tensor reveal that the G0v molecules have highly asymmetric shape. IR spectroscopy combined with quantum chemical DFT computation provides unique detailed information about the structure of
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