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9Dipyrromethenes Дипиррометены
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http://macroheterocycles.isuct.ru
Paper Статья
DOI: 10.6060/mhc213973p
Assignment of the Vibrations of Unsubstituted BODIPY and Aza-BODIPY
Alexander E. Pogonin,@ Darya A. Postnikova, Artyom Y. Shagurin, Danila V. Belov, Sergey D. Usoltsev, and Yuriy S. Marfin
Ivanovo State University of Chemistry and Technology, 153000 Ivanovo, Russian Federation @Corresponding author E-mail: pogonin@isuct.ru
According to quantum chemical calculations generic BODIPY and aza-BODIPY both have planar structure. Assignment of vibrational modes of BODIPY and aza-BODIPY was carried out via potential energy distribution analysis among internal coordinates. Despite obvious similarity ofthe structure and normal modes of the molecules, there are perceptible differences in simulated IR spectra, which were noted. Analysis of the simulated spectra and the experimental data available in literature allowed us to conclude that most of the bands observed in the IR spectra correspond to separate vibrational transitions. The complicated composition of most of the vibrational modes should be noted. The obtained data will also be useful in studies ofsubstituted BODIPY and aza-BODIPY derivatives since it provides solidfoundation for systematic assignment of vibrational bands in these molecules.
Keywords: BODIPY, vibrational spectra, quantum chemical calculation, normal mode.
Интерпретация колебаний незамещенных BODIPY и aza-BODIPY
А. Е. Погонин,@ Д. А. Постникова, А. Ю. Шагурин, Д. В. Белов, С. Д. Усольцев, Ю. С. Марфин
Ивановский государственный химико-технологический университет, 153000 Иваново, Российская Федерация @E-mail: pogonin@isuct.ru
Согласно результатам квантово-химических расчетов молекулы BODIPY и aza-BODIPY имеют плоское строение. Проведено описание колебаний молекул BODIPY и aza-BODIPY на основе анализа распределения потенциальной энергии (РПЭ) форм нормальных колебаний по естественным колебательным координатам. РПЭ нормальных колебаний по внутренним координатам в рассматриваемых молекулах в большинстве случаев имеет сложный характер. Показано, что, несмотря на сходство структур и колебаний молекул BODIPY и aza-BODIPY, существуют заметные отличия теоретических ИК спектров рассматриваемых соединений. Сопоставление рассчитанных ИК спектров и имеющихся в литературе экспериментальных данных показывает, что большинство наблюдаемых полос в ИК спектре могут быть отнесены к отдельным колебательным переходам. При этом большинство колебательных мод имеет сложный характер. Данные, полученные в настоящей работе, полезны для проведения дальнейших систематических исследований колебательных спектров и колебаний в молекулах замещенных BODIPY и aza-BODIPY.
Ключевые слова: BODIPY, колебательные спектры, квантовая химия, нормальные колебания.
Introduction
Constant search for new compounds is an important part of the development in any scientific area. In this regard, synthesis, experimental studies and quantum chemical ((QC) calculations are closely intertwined. Simulations can greatly accelerate the identification, characterization and optimization of materials.™ Matching experimental measurements with theoretical predictions provides good insight into relations between molecular structure and physico-chemical properties, providing a solid ground for further investigations. Currently, QC calculations are often used in dyes chemical physics to simulate electronic absorption and fluorescence spectra. Derivatives of 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) and 4,4'-difluoro-4-bora-3a,4a,8-triaza-s-indacene (aza-BODIPY) have gained increasing interest in two recent decades.[2] This is caused by the fact, that these substances display very promising optical properties: high molar extinction coefficients, fluorescence quantum yields and narrow electronic absorption and emission bands. Alteration of properties of BODIPY and aza-BODIPY is carried out via corresponding substitution pattern modification leading to ultraviolet-visible (UV-Vis) and luminescence bands shift as well as achievement of their sensitive response towards specific solvent parameters.[3-7] Good prediction of these properties is of a paramount importance in the field of dye chemistry.
As for now, vibration spectroscopy is used in BODIPY studies mainly as one of the ways to prove the identity of compounds. However, infrared (IR) and Raman spec-troscopies are versatile techniques for studying the intrinsic properties of various compounds. In the literature, there is a clear lack of data on detailed assignment of the vibra-tional bands for BODIPYs, while many studies focused on the description of vibrations of various larger molecules, e.g. porphyrins[8,9] and phthalocyanines.[1011] Among a few studies dedicated to BODIPYs vibrations, we should mention the work,[12] in which the vibrational frequencies experimentally extracted from two-dimensional electronic spectra (2DES) were compared to the DFT calculated Raman spectra. Differences between calculated Raman active modes and experimental frequencies are explained by the fact that
the QC calculations were performed on the ground state and do not include changes that may occur in the excited electronic state.[12] In the case of literature data on BODI-PYs, most often, attention is paid to individual vibration bands only. In order to get a consistent description of complex BODIPY derivatives and to systematize information about the effect of substitution on spectroscopic properties, we found it important to study generic BODIPY and aza-BODIPY structures. The lack of detailed information on vibrational spectra can be explained by the fact that the generic BODIPY structure had not been synthesized until 2009.[1315]
For big cyclic compounds it is not appropriate to simply assign any experimental peak to the vibration of one certain bond.[16] Sometimes the entire molecule should be considered as a whole for the proper interpretation. QC calculations help assign the bands in experimental vibra-tional spectra. To interpret a model of vibrational spectra a visualization of the nuclei movement and potential energy distribution (PED) analysis were used.[17]
Calculation Details
QC calculations were performed using the Gaussian 03 program[18] in the framework of density functional theory (DFT) method. Optimized geometries and all of the harmonic vibrational frequencies were obtained using B3LYP functional with cc-pVTZ basis set[19] for all atoms. The basis set was taken from Basis Set Exchange software.[20-22] The assignment of vibrational modes was carried out by the PED analysis among internal coordinates using the VibModule progam.[23] Visualization of vibrations is realized by the ChemCraft software. [24]
Results and Discussion
Molecular Structure
The QC calculations predict a C2v equilibrium structures for both BODIPY and aza-BODIPY with planar dipyrromethene moiety. This is in consistent with the information available in the literature.[25-27] Upon the replacement of C8-H group by an N8 atom (BODIPY^aza-BODIPY),
Figure 1. Atom numbering/labeling scheme for BODIPY and aza-BODIPY Макрогетер0циmbl /Macroheterocycles 2021 14(3) 240-248
Table 1. Selected structural parameters of BODIPY from B3LYP calculations and from X-ray data [13-15] in comparison with structural parameters of aza-BODIPY obtained by B3LYP calculations.
Parameters a BODIPY X-ray[13] BODIPY X-ray[14] BODIPY X-ray[15] BODIPY B3LYP aza-BODIPY B3LYP
N4a~C8a 1.390 b 1.381 b 1.400 b 1.390 1.398
C8a-X8 1.384 b 1.376 b 1.394 b 1.386 1.318
C,-C8 1 8a 1.409 b 1.386 b 1.418 b 1.415 1.422
n4-c3 4a 3 1.339 b 1.337 b 1.349 b 1.335 1.332
N-B 1.548 b 1.549 b 1.559 b 1.573 1.572
C1-C2 1.385 b 1.372 b 1.375 b 1.383 1.377
C2-C3 1.398 b 1.391 b 1.404 b 1.408 1.414
B-F 1.392 b 1.392 b 1.396 b 1.382 1.380
N4 -B-N4. 4a 4b 106.5 106.6 106.9 105.5 103.5
C8a-X8-C8b 121.7 123.3 122.3 122.0 119.6
F-B-F 108.6 108.6 109.0 111.3 111.6
C2-C3-N4a-B 177.2 b 177.2 b 177.0 b 180.0 180.0
C8a-N4a-B-N4b 11.1 b 10.6 b 10.8 b 0.0 0.0
N4a-C8a-X8-C8b 2.0 b 0.7 b 2.1 b 0.0 0.0
adistances in A, angles in deg.; b average values for nonequivalent parameters on the same type calculated using data.[13 15,28]
the structure of dipyrromethene moiety is changed, although the binding to the BF2 remains almost the same (Table 1). It should be noted, that BODIPY in its crystalline state is slightly distorted:113-151 the boron atom lies out of the chelate cavity plane of the ligand. The authors[13] named this distortion "saddled". Despite these differences, the structural parameters according to X-ray and QC calculations are in good agreement (Table 1).
Vibrations and Spectra
In order to describe the vibrations, the following axes choices[29] were used: the z-axis is the axis of symmetry, x-axis was chosen perpendicular to the molecule plane and, finally, y is orthogonal to both (Figure 1). The BODIPY molecule belongs to the C2v point group and has 57 vibrational modes: r .. = 20a + 8a /lib, + 18b . In aza-BODIPY there
vib 12 1 2
are 54 fundamental vibrations which have the following distribution in the symmetry classes belonging to the C2v point group: rvib = 19a1 + 8a2 + 10b1 + 17b2. Changes in the dipole moment along the x, y, z axes will happen to vibrations b1, b2, a1, respectively, and thereby allow the vibrations to be IR active. All four symmetry species may be Raman active. Assignments of all vibration bands in the molecules are presented in Tables 2-4. The visualization of all vibrations can be found in the video file located in the supplementary materials. Majority of normal modes are extended over entire molecule. According to the PED, most of the vibrations are comprised of displacements along several internal coordinates, which complicates the frequency assignment. In the variety of complex vibrations, "simple" vibrations ra36 and ra51 should be noted: they originate from B-F stretching (> 80 %) and C8-H8 stretching (~100 %), respectively. Vibra-
tions ff>52-ff>57 can be assigned to C-H stretching in pyrrole moieties. A significant contribution (~40-50 %) to ra5-8 modes is made by in-plane bending motions of a chelate. Out-of-plane modes ra13 and ra15, ra16 and ra18 of BODIPY and aza-BODIPY correspond to asymmetric and symmetric torsional vibrations of pyrrole designated by the authors[30] as Tring. Frequencies related to the C-H out-of-plane bending (% 20 23 24 27 28) lie in the range of 750-1000 cm-1. The majority of modes in the range of 800-1600 cm-1 are strongly coupled in-plane bending motions and stretching in the molecule skeleton.
Calculation results show that two regions with low intensities (0-750 cm-1, 3180-3280 cm-1) and one region with medium to high intensities (750-1700 cm-1) could be distinguished in the obtained spectra (Figure 2-4). In the frequency range 1700-3100 cm-1, fundamental vibrational transitions are absent. The simulation demonstrates that most of the medium and high intensity bands in the spectra correspond to separate vibrational modes. However, the bands 397 cm-1, 597 cm-1 1162 cm-1 (BODIPY), 256 cm-1, 1087 cm-1, 1168 cm-1 (aza-BODIPY) are superpositions of bands corresponding to the separate vibrational transitions (Figures 2, 3). High-intensity bands at 1162 cm-1 (BODIPY) and 1168 cm-1 (aza-BODIPY) are composed of ra36 and ra37 vibrational modes (Figure 2, Table 3). Vibrational mode ra37 is more complicated than ra36: it consists of stretching of B-N, B-F and C-C bonds, but stretching of B-F bonds contributes only to the extent of ~20 %.
The authors[13] showed the location of the main bands in the IR spectrum of BODIPY. It should be noted that the positions of the bands in the obtained theoretical spectrum are in good agreement with the appropriate values
from the experimental spectrum.[13] Correlation between the bands in model and experimental spectra for BODIPY is close to linear one (Figure 5). The obtained scaling coefficient (0.976, Figure 5) is in good agreement with expected value of 0.967[3132] for the B3LYP/cc-pVTZ level of theory.
Low frequency vibrations are interesting for the study of substituted cyclic compounds since they can explain the resulting distortions of the molecules. With the introduction of substituent groups in macrocycles (for example regarding porphyrins[33]) steric hindrance arises that can be released at the expense of geometrical changes in the molecules with the use of low frequency vibrational modes. For BODIPY and aza-BODIPY mode w1 involves primarily displacement of boron atoms out of the chelate plane. Modes ra2-4 are described by out-of-plane skeletal distortions of "butterfly" and "propeller" type. Propeller vibration ra3 (ra4) can be represented as rotations of two pyrrole moieties around the line between C8a (N4a) atom and the center of the bond C2-C3 (C1-C2). It should be recalled that the BODIPY structure in the solid phase[13-15] also has displacement of the boron atom from the chelate plane. Other authors[34] also pointed out the presence of butterfly- and pro -peller-types distortion for BODIPY derivatives.
Differences between the Model Spectra of BODIPY and aza-BODIPY
Influence of the bridge moieties (meso-atoms C8-H8 and N8) on the vibrational spectra of BODIPY and aza-BODIPY manifests itself due to: a) BODIPY has 3 extra vibrations ra29, ra41, ra51, which have been attributed to H8 dependent peaks; b) changes in PED, e.g. changes caused by combining the H8 movement with other displacements in BODIPY; c) structural differences between molecules, which, along with similar PEDs for BODIPY and aza-BODIPY, lead to a shift in the vibration frequencies.
C8-H8 out-of-plane bending and C8-H8 stretching contribute to the extent of ~65 % and ~100 % to the ra29 and ra51 vibrations, respectively. However, ra41 mode is complex: the contribution of C8-H8 in-plane bending is only ~25 %. Only ra41 mode predicted at 1328 cm1 possesses enough intensity in the IR spectrum to be identified as characteristic for BODIPY (Figure 2).
With the assistance of a visual representation analysis (Supplementary Materials), remaining vibratios modes of a BODIPY were found to closely relate to modes of aza-BODIPY (Tables 2-4). PED of appropriate normal modes of two molecules are similar both qualitatively and quantitatively: upon BODIPY^-aza-BODIPY transition, quantitative differences in the contributions of the internal coordinates used in the work (Table 2-4) usually change by no more than ~15 %. However, examples of higher differences in PED should be denoted. Normal modes ra18 and ra20 are described by a sum of out-of-plane bending of C-H and carbon skeleton: whereas for aza-BODIPY the contributions y(C-H) and y(BODIPY) are approximately equal, it was found that for BODIPY just one of the coordinates dominates with the ratio of 70:30. The corresponding bands show an average upshift of 20 cm-1 with change of the meso-atom (Figure 2, region 730-800 cm-1). Contributions of the Cx-Hx stretching coordinates to ff>52-ff>57 also differ in the molecules (Table 4). Frequencies ff>52-ff>57 alter slightly for the considered molecules. Due to the low intensity of the corresponding bands in the region of 3220-3270 cm-1, those differences will be difficult to register in the experiment. In the case of BODIPY, the C8-H8 in-plane bending is coupled with other displacements (Table 4) for normal modes ra38 and ra40. IR intensities for the mode ra40 increase upon BODIPY^-aza-BODIPY transition (Table 3). It was denoted that for BODIPY a large input (~30%) to the whole vibration is contributed by C-H in-plane bending, while for aza-BODIPY the contribution of 5(C-H) decreases to ~10 % and the contribution v(NC) increases by ~15 % as compared to BODIPY.
Figure 2. Simulated IR spectra for BODIPY and aza-BODIPY in the 500-1700 cm-1 range.
Figure 3. Simulated IR spectra for BODIPY and aza-BODIPY in the 0-650 cm-1 range.
Figure 4. Simulated IR spectra for BODIPY and aza-BODIPY in the 3180-3280 cm-1 range.
Despite the close PED of fundamental modes of BODIPY and aza-BODIPY, nine of them are characterized by differences greater than 20 cm-1 (Ml0,l2,20,23,35,38,42,47,50,
Tables 2-4). Upon a change from BODIPY to aza-BODIPY the maximal downshift of 63 cm-1 is observed for ro50 fundamental frequency. The mode originates from X8-C8a stretching (~60 %) and is characterized by large IR intensity (1648 and 1586 cm-1, Figure 2). In addition to the differences denoted above, spectra of the BODIPY and aza-BODIPY also differ in tha area of 1100-1150 cm-1 and 1390-1460 cm-1. The band corresponding to ro35 demonstrates significant contributions of C2-C3 and C1-C8a stretching (~50 %). Apparently, differences in structure of pyrrole moieties due to meso -atom switch lead to a downshift by 27 cm-1. According to the QC calculations, the IR intensity of ro43 vibration band increases sharply upon BODIPY-—-aza-BODIPY transition, which leads to the appearance of 1391 cm-1 band in the simulated spectrum of aza-BODIPY. Moreover, upon BODIPY—aza-
Figure 5. Correlation dependences v = f(ro): v and ro - the positions of the band maxima in the experimental131 and model spectra (Figure 2) for BODIPY, respectively. R - adjusted R squared.
BODIPY transition low-frequency modes (œ1-12) shift upwards (except for œ3). Downshifts of frequencies are found for the C-H out-of-plane (contribution of y(C-H) is about 70 %) modes œ19 20 23 24 27 28 upon BODIPY—aza-BODIPY transition.
Conclusions
Despite the uniquely great interest shown in substituted BODIPYs and aza-BODIPYs, little attention has so far been paid to the parent molecules. This is unacceptable for the systematic study of more complex molecules and the study of the effect of substitution in these molecules. In this work we systematically designated the vibrations
Table 2. Calculated frequencies , cm '), I -intensities (/IR km mol ') and vibrational modes descriptions* for BODIPY and aza-BODIPY in the 0-650 cm-1 range.
i sym BODIPY aza-BODIPY
^IR i) Assignment* ^IR i) Assignment*
1 bi 24.5(i.8) Y(B); rot(Py; N^-C«^)) 38.4(5.i) Y(B); rot(Py; N^-C«^))
2 bi ii4.7(i.3) butterfly ii7.2(i.5) butterfly
3 a2 i34.6(0.0) propeller = rot(Py; C8a-Ct(C2-C3)); rot(BF2) i30.3(0.0) propeller = rot(Py; C8a-Ct(C2-C3)); rot(BF2)
4 a2 i74.3(0.0) propeller = rot(Py; N4a-a(CrC2)); rot(BF2) i87.9(0.0) Propeller = rot(Py; N^-Ct^-C^); rot(BF2)
5 b2 252(3.i) def(BODIPY); wag(F); v(B-N4a) 253.8(3.5) def(BODIPY); wag(F); v(B-N4a)
6 ai 255.7(i.6) def(BODIPY); v(B-N4a) 262.9(3.2) def(BODIPY); v(B-N4a)
7 ai 325.3(6.8) def(m-ring); sci(F-B-F) 326.4(3.6) def(m-ring); sci(F-B-F)
8 a2 327.6(0.0) rot(BF2); wav 33i.4(0.0) rot(BF2); wav
9 b1 393.i(4.3) Y(BODIPY): y(c8, B, Ci, C3); 404(0.0) Y(BODIPY): y(n8, B, Ci, C3);
10 b2 398(9.9) def(m-ring); v(B-N4a); 432.2(27.i) def(m-ring); v(B-N4a);
11 ai 434.9(0.0) breath(m-ring): S(m-ring), v(C8-C8a), v(B-N4a); sci(F-B-F); ^C^); 448.7(0.i) breath(m-ring): S(m-ring), v(N8-C8a), v(B-N4a); v(Ci-C8a); sci(F-B-F);
12 b1 482.3(6.4) y(BF2); y(C8-H); 507.6(0.5) Y(BF2); Y(N8);
13 bi 596.4(i8.9) crown = y(Py); 584.7(i6.3) crown = Y(Py);
14 ai 598.3(4.9) sci(F-B-F); v(B-F); v(B-N4a); S^-B-NJ; 597.5(6.8) sci(F-B-F); v(B-F); v(B-N4a); S(N4a-B-N4b);
15 a2 607.5(0.0) lightning = Y(Py); 602.6(0.0) lightning = Y(Py);
* Based on PED. Coordinates are listed if their contributions are greater than ~10%. Coordinates are presented in descending order of their contributions. The designation "Coord-1: Coord-2, Coord-3means that the displacement along coordinates Coord-2 and Coord-3 are a part of the general displacement Coord-1. Given that the molecules have the symmetry C2v, the following pairs of atoms are symmetrically equivalent: N4a and N4b, C and C7, C2 and C6, C3 and C5, C8a and C8b, Hj and H7, H2 and H6, H3 and H5, two fluorine atoms. Therefore, it is assumed in the assignment that, for example, vibration v(B-N4a) includes both vibration v(B-N4a) and v(B-N4b), etc. The following designations are used: v(X-Y) - stretching of the X-Y bond; 5 - in-plane bending of the fragment indicated in parentheses, including def - deformation of the fragment indicated in parentheses in the molecule plane; y - out-of-plane bending of the fragment or atom indicated in parentheses; rot(fragment; axis) - rotation of the fragment around an axis; butterfly - butterfly-shape nonplanar molecular deformation; rot(BF2) - rotation of the BF2 fragment around an axis B-X8; propeller - propeller-shape nonplanar molecular deformation; wag - wagging deformation in which two fluorine atoms oscillate up and below the plane BF2 with respect to the boron atom; sci(F-B-F) - scissors bending of BF2; fold(fragment; line) - folding of the fragment along the line; wav - wave-shape nonplanar molecule deformation, which can also be considered as chair-shaped folding of the molecule along the lines N4a-C8a and N4b-C8b; breath - breathing deformation of the fragment indicated in parentheses; crown - out-of-plane crown-shape bending of a molecule; lightning - lightning-shape out-of-plane bending of a molecule; m-ring - fragment B-N4a-C8a-X8-C8b-N4b; Py - pyrrole moiety; Ct - center of internuclear distance. The designation "C-H Py" means CrHj, C2-H2, C3-H3.
Table 3. Calculated frequencies , cm 1), IR-intensities (IIR km mol 1) and vibrational modes descriptions* for BODIPY and aza-BODIPY in the 650-1700 cm-1 range.
BODIPY aza-BODIPY
i sym i) Assignment* Exp [i3] i) Assignment*
i6 a2 689.0(0.0) Y(Py): Y(N4a, C8a); 685.i(0.0) Y(Py): Y(N4a, C8a);
i7 b2 706.7(36.4) def(BODIPY); v(C-C): v(C8-C8a); v(B-N4a); 69i 709.5(44.3) def(BODIPY); v(B-N4a);
i8 bi 738.3(i8.2) Y(BODIPY): Y(N4a, C8a, C8); Y(C-H): Y(Ci-Hi); 750.0(33.4) Y(BODIPY): Y(N4a, C8a, N8); Y(C-H): Y(Ci-Hi), Y(C2-H2);
i9 a2 774.4(0.0) Y(C-H): Y(C2-H2), Y(Ci-Hi); Y(BODIPY): Y(C8a); 782.2(0.0) Y(C-H): Y(C2-H2), Y(Ci-Hi); Y(BODIPY): Y(C8a);
20 bi 776.0(84.6) Y(C-H): Y(C2-H2), Y(Ci-Hi); Y(BODIPY): Y(C8a); 2 2 i i 758 796.7(77.4) Y(C-H): Y(C2-H2), Y(Ci-Hi); Y(BODIPY): Y(C8a); 2 2 i i
2i ai 8i4.5(6.0) def(BODIpY): S(C8a-C8-C8b), S(N4a-C8a-C8X S(C8a-Ci-C2); v(N-C); S(C-H); 796.7(0.3) def(BODIpY): S(C8a-N8-C8bX S(N4a-C8a-N8), S(C8a-Ci-C2); ^): V^J;
22 b2 860.8(9.4) def(BODIPY): S^-C^, S(C1-C2-C3); v(B-N4a); v(C-C); 857.3(i.8) def(BODIPY): S(Ci-C2-C3), S(C8a-Ci-C2); V(B-N4a);
Continuation of Table 3.
23 bi 873.7(7.1) Y(C-H): Y^-^), Y^-^); Y(BODIPY); 898.2(0.6) Y(C-H): Y^-^), Y(C1-H1); Y(BODIPY);
24 a2 880.3(0.0) Y(C-H): Y^-^), Y^-H^; Y(BODIPY); 898.2(0.0) Y(C-H): Y^-^), Y(C1-H1); Y(BODIPY);
25 ai 909.2(1.1) def(Py): ^-C^), ^^-C^; 5(C-H Py); V(N4a-C8a); 893.4(0.1) def(Py): 8(C1-C2-C3), 8(N4a-C3-C2); 8(C-H Py); v(N4a-C1a)
26 b2 920.0(7.9) def(BODIPY); 8(C-H); vN<.-CJ; v(B-NJ; 910.6(8.2) def(BODIPY); vCN^Ca* 8(C-H); v(B-NJ;
27 a2 922.2(0.0) Y(C-H Py): y(C3-H3), y(C2-H2), y^-^); fold(Py, C^-C3); 933.0(0.0) Y(C-H Py): y(C2-H2), y(C3-H3), y^-^); fold(Py, C^-C3);
28 b1 922.4(2.0) Y(C-H Py): Y(C3-H3), y(C2-H2), y^-^); fold(Py, C^-C3); 933.3(2.1) Y(C-H Py): y(C2-H2), y(C3-H3), y^-^); fold(Py, C^-C3);
29 b1 952.5(9.5) Y(C8-H8); y(C8); y(C-H Py); - -
30 ai 1004.4(92.9) v(B-F); S(C-H Py); def(BODIPY); 969 999.0(84.3) v(B-F); 8(C-H Py); def(BODIPY);
31 b2 1040.2(1.4) S(C-H): S(C2-H2), 5(C3-H3); v(C-C): v(C2-C3); 1034.2(56.2) 8(C-H): 8(C2-H2), 8(C3-H3); v(C-C): v(C2-C3), v(C1-C2);
32 ai 1071.1(82.7) 5(C-H): 5(C2-H2), 5(C1-H1); v(B-F); v(C-C); 1070.1(74.0) 8(C-H): 8(C2-H2), 8(C1-H1); v(B-F); v(C-C);
33 b2 1086.9(334.9) 5(C-H): 8^1-^); v(C-C): v^-C^; 1063 1087.2(558.7) 8(C-H): 8(C1-H1), 8(C2-H2); v(C-C): v(C1-C2); v(N-C); v(B-NJ;
34 ai 1098.7(46.3) 5(C-H): S(C1-H1), 8(C3-H3); v(C-C): v(C2-C3), v(C1-C2); 1088.6(49.6) 8(C-H): 8(C1-H1); v(C-C): v^), v(C1-C2);
35 b2 1136.8(263.1) v(C-C): v(C2-C3), v(C1-C8a); v(B-NJ; v(N-C); 8(C3-H3); 1112 1110.2(250.0) v(C-C): v(C2-C3), v(C1-C8a); 8(C-H): 8(C1-H1), 8(C3-H3); v(N-C); v(B-NJ;
36 b1 1160.6(241.1) v(B-F); 1166 1169.3(244.3) v(B-F);
37 ai 1168.0 (147.6) v(B-N4a); v(B-F); v(C-C): v^); 1166.9(173.8) v(B-N4a); v(B-F); v(C-C): ^C^);
38 b2 1184.5(32.8) 8(C-H): S^-H,), 8(C2-H2); v(B-NJ; v(C-C); v(N-C): v^^); 1230.3(22.6) 8(C-H): 8(C3-H3), 8(C1-H1), 8(C2-H2); v(N-C): v(N4a-C8a);
39 ai 1260.3(4.0) 8(C-H): 8^-^), 8^-^), 8(C2-H2); 1261.9(12.2) 8(C-H): 8(C3-H3), 8(C1-H1), 8(C2-H2);
40 b2 1279.5(15.2) v(N-C): v(N4a-C3); 8(C-H): S^-H,), 8(C3-H3); v(C-C); 1270.4(100.4) v(N-C): v(N4a-C3); v(C-C); 8(C-H);
41 b2 1328.2(295.4) 8(C-H): 8(C8-H8),8(C3-H3),8(C1-H1); v(N-C): v(N4a-C8a), v(N4a-C3); v(C-C); 1292 - -
42 ai 1357.1(0.6) v(N-C): v(N4a-C3), v(N4a-C8a); v(C-C): v(C1-C2), v(C1-C8a); 1324.2(8.5) v(N-C): v(N4a-C8a), v(N4a-C3); v(C1-C8a);
43 b2 1393.6(8.6) v(C-C): v(CrC8a), v(C1-C2); 8(C-H): 8(C1-H1); v(N-C): v(N4a-C8a); 1391(238.6) v(C-C): v(C1-C8a), v(C1-C2); 8(C-H): 8(C3-H3), 8(C1-H1); v(N-C);
44 ai 1396.9(0.6) v(C-C): v(C8a-C8), v(C1-C2); v(N4a-C8a); 8(C-H): 8(C1-H1); 1387.7(0.3) v(N-C): v^-CJ, 8(C-H): 8^-^); v(C-C): v(CrC2);
45 b2 1437.9(154.6) 8(C-H): 8(C2-H2); v(C-C): ^C^), v(C1-C2); 1397 1420.1(172) 8(C-H): 8(C2-H2), 8(C1-H1); v(C-C): v(C2-C3); v(N-C);
46 ai 1451.3(120.2) v(C-C): v(C2-C3), v(C1-C2); 8(C-H): 8(C2-H2); 1410 1455.4(145.2) v(C-C): v(C1-C2), v(C2-C3); 8(C-H): 8(C2-H2);
47 ai 1531.2(17.9) v(N4a-C3); v(C-C): v(C1-C8a), v^-^ 8(C2,3-H2,3); 1560.2(18.8) v(N-C): v(N4a-C3); S^-H^); v(C-C): v(C1-C8a);
48 b2 1536.6(6.1) 8(C-H): 8(C3-H3); v(C-C): v(CrC2); v(N-C): v(N4a-C3); 1539.3(3.7) 8(C-H): 8(C3-H3), 8(C2-H2); v^-C^; v(N-C): v(N4a-C3);
49 ai 1578.5(0.2) v(C-C): v(C8-C8a), v(C1~C8aX v(crq); 8(CU-HU); v(N-C); 1577.3(4.4) v(C-C): v(C1-C8a), v(C1-C2); v(N-C): v(^- C8a); 8(C1,3-H1,3);
50 b2 1648.1(726.4) v(C-C): v^-CJ, v(C1-C8a); 8(C8-H8); 1605 1585.6(501.1) v(N-C): v(N8-C8a), v(C3-N4a); v(C-C);
* Based on PED. Coordinates are listed if their contributions are greater than ~10%. Coordinate with the largest contribution was placed in the first place. The designation "Coord-l: Coord-2, Coord-3;" means that the displacement along coordinates Coord-2 and Coord-3 are a part of the general displacement Coord-l. Given that the molecules have the symmetry C2v, the following pairs of atoms are symmetrically equivalent: N4a and N4b, C, and C_ C_ and C„ C and C„ C„ and C_, H, and H_ H_ and H„ H and H„ two fluorine atoms. Therefore, it is assumed in assignment that,
1 7 2 6 3 5 8a 8b 1 7 2 6 3 5' ' 0
for example, vibration v(B-N4a) includes both vibration v(B-N4a) and v(B-N4b), etc. A description of the taken designations is given in a footnote to the Table 2.
Table 4. Calculated frequencies , cm 1), IR-intensities (IIR km mol 1) and vibrational modes descriptions* for BODIPY and aza-BODIPY in the 3180-3280 cm-1 range.
i sym BODIPY aza-BODIPY
i) Assignment* i) Assignment*
51 ai 3196.2(1.2) v(C8-H8); - -
52 b2 3234.0(0.5) v(C-H Py): v(Ci-Hi), v(C2-H2), v^-^); 3235.4(4.0) v(C-H Py): v(C3-H,), v(C2-H2);
53 ai 3234.1(1.9) v(C-H Py): v(Ci-Hi), v(C2-H2), v^-^); 3235.7(0.0) v(C-H Py): v(C3-H,), v(C2-H2);
54 b2 3242.0(4.0) v(C-H Py): v(CrH3), v(Ci-Hi); 3248.i(0.0) v(C-H Py): v(Ci-Hi), v(C2-H2), v^-^);
55 ai 3242.4(0.6) v(C-H Py): v(C3-H3), v(Ci-Hi); 3248.4(0.0) v(C-H Py): v(Ci-Hi), v(C2-H2), v(C3-H3);
56 b2 3257.5(2.8) v(C-H Py): v(C2-H2), v(C3-H3), v(CrH,); 3262.2(i.4) v(C-H Py): v(Ci-Hi), v(C2-H2);
57 ai 3257.5(0.2) v(C-H Py): v(C2-H2), v(C3-H3), v^-H,); 3262.3(0.0) v(C-H Py): v(Ci-Hi), v(C2-H2);
* Based on PED. Coordinates are listed if their contributions are greater than ~10%. Coordinate with the largest contribution was placed in the first place. The designation "Coord-1: Coord-2, Coord-3;" means that the displacement along coordinates Coord-2 and Coord-3 are a part of the general displacement Coord-1. Given that the molecules have the symmetry C2v, the following pairs of atoms are symmetrically equivalent: N4a and N4b, C and C7, C2 and C6, C3 and C5, C8a and C8b, H and H7, H2 and H6, H3 and H5, two fluorine atoms. Therefore, it is assumed in assignment that, for example, vibration v(B-N4a) includes both vibration v(B-N4a) and v(B-N4b), etc. A description of the taken designations is given in a footnote to the Table 2.
of unsubstituted BODIPY and aza-BODIPY dyes, modeled and compared their IR spectra.
Acknowledgements. The study of molecular structure of BODIPY and the assignment of vibrational modes were supported by the grant of the President of the Russian Federation (project MK-5965.2021.1.3). The performing QC calculations for aza-BODIPY was supported by the Russian Science Foundation (grant No. 19-73-10107). Comparison of the obtained data for BODIPY and aza-BODIPY was conducted in accordance with the Project FZZW-2020-0007 supported by the Ministry of Science and Higher Education of Russian Federation. The study was carried out using the resources of the Center for Shared Use of Scientific Equipment of the ISUCT (with the support of the Ministry of Science and Higher Education of Russian Federation, grant No. 075-15-2021-671). We thank G.V. Girichev for his help in conducting the calculations using computing resources of the Department of Physics of Ivanovo State University of Chemistry and Technology.
Supplementary materials. The video file with visualization of all vibrations is available on the website https:// macroheterocycles.isuct.ru/en/mhc213973p.
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Received 09.11.2021 Accepted 27.11.2021
