3.1. Electronic Structure
Table 1 shows the experimental and calculated ionization energy (In) values for compounds I–III, as well as the contributions of the orbits of the oxygen atom O, the carbonyl carbon atoms of the Cβ, the CH group at the γ-position, the methyl groups and the OH groups (compound I), NH2 (compound II), NHMe (compound III), denoted as X. For the filled orbits, the contributions of the Mulliken atomic populations are given, and for the vacant MO, the relative sums of the squares of the coefficients of the base orbits. Orbitals are mixed if the sum of the Mulliken atomic populations for each of the fragments is greater than 20%. The “+” sign indicates binding and the “–” sign indicates anti-binding.
In the row of compounds I–III, a correlation of the nature of the three upper filled MOs is observed. According to the OVGF/cc-pVTZ method, the substitution of the OH group with the NH2 group leads to a decrease in I1-3 by 0.72–1.12 eV and destabilization of the energy of affinity for the electron by 0.41 eV (Table 1). The substitution of the amino group for the NMe group determines a reduction of I1-3 by 0.15–0.51 eV, but has no appreciable effect on the energy of the electron affinity. Therefore, the substitution of the OH group with the NH2 and NMe groups causes a decrease in the HOMO→Lumo energy gap value by 0.54 and 0.94 eV, respectively, which leads to a bathochromic shift in the absorption spectra (Fig. S1).
The transition from ligands (Compound I–III) to spiroborates (Compound IV–VI) stabilizes the energy of affinity for the electron by 1.4–2.0 eV (Fig. 2, Table 1). At the same time, π3 MOs are stabilized by 0.8–1.0 eV, which leads to a decrease in the energy interval π3→π4 by 0.7–1.1 eV. For the remaining upper filled ligand orbits, there is also stabilization of levels at 0.4–1.7 eV. This is due to the transfer of electron density 1.04–1.08 e from the ligand to dihydroxyphinylene.
Fig. 1 shows the MO forms needed for further discussion. Table 1 presents experimental and calculated In values for compounds IV–VI, types of valence MOs KS, as well as contributions of atomic orbits localized on fragments of the molecule (ligand – O(X)C3H, dihydroxyphenylene – PhO2B, substitute – 2Me). The types of the Kohn-Sham molecular orbitals are determined relative to the Mulliken atomic populations. Type π orbitals are divided into localized on the ligand and on dihydroxyphenylene (indicated by the supreme index X). The correlation diagram of In (OVGF/cc–pVTZ) in Fig. 2 is provided to demonstrate the electronic effects of substitution.
Table 1 Relative vertical ionization energies (eV) of the highest occupied MOs (denoted as H,…, H–n) and electron affinities of the lowest unoccupied MO (denotes as L) in IV-VI computed using the Hartree-Fock approach at the level of the Koopmans' theorem (HF), the OVGF and DFT/CAMB3LYP methods (cc-pVDZ basis set). The Mulliken populations of the molecular fragments in the molecular orbitals (percent) are also shown.
MO, type
|
Contribution, %
|
Ionization energies, eV
|
PhO2B/2O
|
O(X)C3H/OX
|
2Me
|
HF
|
OVGF
|
CAMB3LYP
|
|
Compound IV
|
|
L, a2 π4
|
1/0
|
83/13
|
16
|
–1.61
|
0.18
|
1.00
|
|
H, b2 π2X
|
99/14
|
1/0
|
0
|
7.47
|
7.12
|
6.51
|
|
H–1, a2 π3X
|
100/6
|
0/0
|
0
|
8.42
|
8.06
|
7.43
|
|
H–2, b1 π3
|
3/2
|
94/21
|
3
|
10.43
|
9.66
|
9.00
|
|
H–3, b2 π1X
|
94/19
|
5/4
|
1
|
12.17
|
10.71
|
10.12
|
|
H–4, a1 σX
|
100/19
|
0/0
|
0
|
12.64
|
11.05
|
10.60
|
|
H–5, b2 n–
|
10/0
|
73/48
|
17
|
13.21
|
11.47
|
10.61
|
|
H–7, b1 σX
|
95/25
|
3/1
|
1
|
13.43
|
11.81
|
10.74
|
|
H–6, a2
|
84/70
|
13/10
|
3
|
13.64
|
11.73
|
11.14
|
|
H–8, b1
|
100/66
|
0/0
|
0
|
13.89
|
12.04
|
11.93
|
|
H–9, a1 σX
|
98/24
|
2/1
|
0
|
14.78
|
12.90
|
12.36
|
|
H–11, a2 π2
|
18/14
|
46/41
|
36
|
15.20
|
13.57
|
12.49
|
|
H–10, a1 n+
|
19/4
|
62/37
|
19
|
15.23
|
13.45
|
12.73
|
|
H–12, b1 π1
|
19/5
|
38/28
|
43
|
15.31
|
13.80
|
12.96
|
|
Compound V
|
|
L, π4
|
1/0
|
87/19
|
12
|
–2.23
|
0.41
|
0.40
|
|
H, π2X
|
99/15
|
1/1
|
0
|
7.36
|
6.99
|
6.37
|
|
H–1, π3X
|
100/6
|
0/0
|
0
|
8.36
|
7.97
|
7.34
|
|
H–2, π3
|
3/2
|
94/27
|
2
|
9.63
|
8.90
|
8.32
|
|
H–3, π1X
|
91/20
|
8/6
|
2
|
12.02
|
10.55
|
9.94
|
|
H–4, σ X
|
100/20
|
0/0
|
0
|
12.53
|
10.92
|
10.01
|
|
H–5, σ X + π2
|
60/39
|
34/22
|
6
|
13.10
|
11.48
|
10.33
|
|
H–6, n–
|
17/0
|
68/43
|
16
|
13.23
|
11.54
|
10.56
|
|
H–7, σ X
|
81/39
|
15/12
|
3
|
13.33
|
11.62
|
10.71
|
|
H–8, σ X
|
99/53
|
1/1
|
0
|
13.74
|
11.93
|
11.05
|
|
H–9, σ X
|
49/37
|
39/27
|
12
|
14.25
|
12.58
|
11.78
|
|
H–10, σ X
|
97/23
|
2/1
|
1
|
14.67
|
12.78
|
11.83
|
|
H–11, Me + π1
|
20/10
|
36/30
|
44
|
14.95
|
13.39
|
12.34
|
|
H–12, n+ + σ X
|
50/18
|
24/15
|
26
|
15.19
|
13.48
|
12.56
|
|
Compound VI
|
|
L, π4
|
1/0
|
84/17
|
15
|
–2.17
|
0.38
|
0.38
|
|
H, π2 X
|
99/15
|
1/1
|
0
|
7.38
|
6.99
|
6.39
|
|
H–1, π3 X
|
100/6
|
0/0
|
0
|
8.39
|
7.99
|
7.37
|
|
H–2, π3
|
3/2
|
94/28
|
2
|
9.37
|
8.60
|
8.07
|
|
H–3, π1 X
|
88/20
|
10/7
|
2
|
12.02
|
10.54
|
9.93
|
|
H–4, σ X
|
100/20
|
0/0
|
0
|
12.54
|
10.91
|
10.02
|
|
H–5, π2
|
19/14
|
74/35
|
7
|
12.77
|
11.40
|
10.33
|
|
H–6, n– + π1 X
|
20/1
|
66/37
|
14
|
13.00
|
11.35
|
10.53
|
|
H–7, σ X
|
90/41
|
8/5
|
2
|
13.29
|
11.56
|
10.57
|
|
H–8, σ X
|
95/56
|
4/1
|
1
|
13.73
|
11.90
|
11.07
|
|
H–9, σ X
|
80/54
|
17/4
|
3
|
13.85
|
12.05
|
11.26
|
|
H–10 σ X
|
91/22
|
7/2
|
2
|
14.67
|
12.79
|
11.84
|
|
H–11, n+ + σ X
|
27/9
|
65/10
|
8
|
14.88
|
13.39
|
12.26
|
|
H–12, Me + π1
|
21/12
|
35/30
|
44
|
14.92
|
13.32
|
12.38
|
|
Table 2 Relative vertical ionization energies (eV) of the highest occupied MOs (denoted as H,…, H–n) and electron affinities of the lowest unoccupied MO (denotes as L) in I-III computed using the Hartree-Fock approach at the level of the Koopmans' theorem (HF), the OVGF and DFT/CAMB3LYP methods (cc-pVDZ basis set). The Mulliken populations of the molecular fragments in the molecular orbitals (percent) are also shown.
MO, type
|
Contribution. %
|
|
Ionization energies. eV
|
O
|
2Cβ
|
CγH
|
2Me
|
X
|
HF
|
OVGF
|
CAMB3LYP
|
Expt data
|
Compound I
|
L, π4
|
15
|
49
|
3
|
25
|
8
|
‒2.80
|
‒1.22
|
0.04
|
-
|
H, π3
|
13
|
15
|
51
|
4
|
17
|
9.49
|
8.90
|
8.26
|
9.08
|
H–1, n-
|
60
|
9
|
9
|
13
|
9
|
11.39
|
9.76
|
8.88
|
9.69
|
H–2, π2
|
37
|
16
|
1
|
25
|
21
|
13.71
|
12.50
|
11.50
|
12.5
|
H–3, n+
|
11
|
12
|
25
|
8
|
43
|
14.63
|
13.02
|
11.87
|
|
H–4, Me–π1
|
8
|
10
|
3
|
51
|
29
|
14.83
|
13.41
|
12.29
|
13.2
|
H–5, Me–σ
|
10
|
11
|
9
|
67
|
3
|
14.90
|
13.61
|
12.40
|
|
H–6, Me
|
2
|
4
|
1
|
88
|
5
|
15.54
|
14.46
|
13.10
|
14.2
|
H–7, σ+Me
|
15
|
21
|
11
|
42
|
11
|
16.07
|
14.56
|
13.44
|
|
H–8, σ
|
8
|
15
|
1
|
73
|
4
|
16.47
|
14.63
|
13.56
|
|
H–9, Me+π2
|
15
|
25
|
5
|
37
|
17
|
16.26
|
15.13
|
13.87
|
|
H–10, π1+Mе
|
6
|
26
|
7
|
45
|
16
|
17.04
|
15.52
|
14.48
|
|
Compound II
|
L, π4
|
15
|
55
|
6
|
14
|
10
|
‒3.17
|
‒1.63
|
–0.43
|
–
|
H, π3
|
13
|
11
|
48
|
2
|
25
|
8.54
|
7.95
|
7.43
|
8.24
|
H–1, n–
|
66
|
8
|
9
|
13
|
3
|
10.70
|
9.04
|
8.17
|
8.98
|
H–2, π2
|
32
|
21
|
0
|
18
|
30
|
12.59
|
11.38
|
10.58
|
11.2
|
H–3, π1–Me
|
14
|
18
|
8
|
39
|
21
|
13.65
|
12.38
|
11.51
|
12.0
|
Compound III
|
L, π4
|
14
|
55
|
5
|
13
|
13
|
‒3.18
|
‒1.59
|
–0.47
|
|
H, π3
|
13
|
9
|
47
|
2
|
29
|
8.26
|
7.59
|
7.15
|
7.81
|
H–1, n–
|
66
|
8
|
8
|
13
|
5
|
10.58
|
8.89
|
8.07
|
8.74
|
H–2, π2
|
26
|
23
|
2
|
12
|
37
|
12.08
|
10.87
|
10.20
|
10.6
|
H–3, π1–Me
|
21
|
20
|
9
|
36
|
15
|
13.35
|
12.11
|
11.27
|
11.6
|
According to the calculated data of the DFT method, in compound IV, the π-orbitals of acetylacetone and dihydroxyphenylene are not mixed up to 13.5 eV, where the mixing is negligible. A similar pattern is observed due to the mutually perpendicular arrangement of the planes of acetylacetone and dihydroxyphenylene. Thus, the types of MOs of Compound IV can be divided into two groups: localized on acetylacetone and on dihydroxyphenylene. The OVGF/cc–pVTZ method showed that the highest occupied molecular orbital (HOMO) (I1 = 7.12 eV), HOMO-1 (I2 = 8.06 eV), and HOMO-3 (I4 = 10.71 eV) corresponded to πX -orbitals, and HOMO-4, HOMO-6, and HOMO–9 are σX-orbitals of dihydroxyphenylene. There are also two MOs at 11.73 eV and 12.04 eV localized mainly on oxygen atoms of dihydroxyphenylene. The three filled π-orbitals of acetylacetone correlate with I3, I11 and I13 at 9.66, 13.57 and 13.8 eV, respectively. The n– and n+ orbitals, located predominantly on oxygen atoms, were determined by the OVGF/cc–pVTZ method as I6 = 11.47 eV and I12 = 13.45 eV, respectively. The lowest unoccupied molecular orbital (LUMO) is defined as the π-orbital of acetylacetone, and the energy of electron affinity is 0.18 eV.
The replacement of an oxygen atom with an NH group (compound V) leads to the stabilization of the LUMO level by 0.23 eV and the destabilization of the HOMO level by 0.13 eV (Table 1, Fig. 2). These orbitals are localized on fragments located relative to each other at an angle close to 90°, so a decrease in the energy gap by 0.36 eV should not affect the optical spectra of the connections, since in the considered complexes, the transition π2X→π4 is prohibited by the selection rules for symmetry C2v. While destabilization of the π3 level by 0.76 eV leads to a decrease in the π3 – π4 interval, which causes a bathochromic shift of the long-wave band in the absorption spectrum. Replacing the NH- group with NMe- (compound VI) destabilizes the π3 level by 0.30 eV. At the same time, in all spiroborates, MOs localized on the dioxyphenylene fragment change their energy within the range of 0.01–0.03 eV (Table 1, Fig. 2), and the change in the energies of the electron levels of the ligands is associated with the replacement of the oxygen atom in the structure of the ligand of the NH- and NMe-group. The addition of the dioxyphenylene moiety stabilizes the n– orbital by mixing (in the order of 10–18%) with π1X. Mixing π2X MO with oxygen AO (15%) destabilizes the orbital, resulting in the inversion of π 2 X and π 3 X MOs.
According to the calculated data, energy splitting of C 1s-electron levels is observed in the studied complexes (Fig. S2). Depending on the energy, the levels of C 1s-electrons can be divided into three groups C 1s, C 1s' and C 1s'' (Fig. S2). The first group includes the levels of carbon atoms in the meta and para positions of the benzene cycle (colored green and red, respectively). Group C1s' includes the levels of methyl group carbon atoms and the benzene cycle in the ortho- position. The electron levels of carbonyl carbon atoms are colored yellow and designated as C 1s''. The deviation from C2v symmetry when replacing an oxygen atom with NH- and NMe-groups, as well as the transfer of the charge from the substituent to the carbon atom at the β-position and methyl groups (about 35%) leads to the cleavage of degenerate levels of C1s' and C1s''.
According to the calculated data, the point group of symmetry of the molecule of boron acetylacetonate of 1,2-dihydroxyphenylene (compound – IV) is close to C2v. The deviation of the plane of acetylacetone from the plane perpendicular to the dihydroxyphenylene group is 8.2°. When replacing an oxygen atom in the α-position with NH- and NMe-groups (compounds V and VI), the deviation of the plane of acetylacetone from the plane perpendicular to the dihydroxyphenylene group is 0.8° and 0.4°, respectively. The interatomic distances B-O1 and B-O2 (1.43 Å) are less than B-O3 and B-O4 (1.51 Å), and when O4 is replaced with an NH group, the distances B-O1 and B-O2 increase to 1.45 Å, with B –N = 1.55 Å and B-O3 = 1.5 Å.
3.2. Photoelectronic spectra
Earlier, the authors of this paper published a thorough analysis of X-ray photoelectron spectroscopy (XPS) data for Complex IV [57]. In this paper, the results of calculations of complexes I–III, IV, VI are compared with ultraviolet photoelectron spectroscopy and XPS spectra to obtain comprehensive information about electronic levels and identify substitution effects.
In accordance with the simulation results using the methods DFT/CAMB3LYP/cc-pVTZ (Koopmans extended theorem) and OVGF/cc-pVTZ, the bands “1” and “2” in compound I are determined by single-electron ionization processes (Fig. 3). Arm “3 '” corresponds to two electronic levels. The bands “3”, “4” and “5” are due to two, five and two cationic states, respectively.
In compounds II and III, bands “1” and “2” are determined by single-electron ionization processes, and there is an increase in energy intervals between I3 and I4 (Fig. 3, Table 1), compared to I. Therefore, the band “3” in II and III corresponds to one electronic level. In Compounds II and III, arm “4 '” is caused by ionization from a single orbital, and band 4 is related to two and three cationic states, respectively.
In the XPS spectra of the valence region of compounds IV and VI, two intensity maximums are observed in the energy range from 1.0 to 13.0 eV, two maximums in the energy range from 13.0 to 22.0 eV, and one maximum at 28.0 eV (Fig. 4). The relative intensities and contours of the components are determined by the distribution of the density of electronic states and the relative ionization cross-sections of 2s- and 2p-levels (σs, σp). For the source Mg Kα, the ratio σs:σp for carbon is 17.9, for oxygen 5.8 and for nitrogen 10.6, and the ratio σp (C):σp(N):σp(O) is 1.0 : 3.2 : 8.9 [58].
The results of quantum chemical modeling by the methods of DFT/CAMB3LYP/cc-pVTZ and OVGF/cc-pVTZ showed that the maximums “1” and “2” in the spectra of both compounds, as well as the inflections “1'” and “1''” in the spectra, are due to the predominant ionization with O 2p AOs. The “3” maxima correspond to mixed C 2s / O 2p AOs. The “4” maxima are determined by ionization from C 2s orbitals. The “5” maximum in compound IV is determined by ionization with four MOs with predominant contributions of O 2s AOs. In compound VI, two maxima are observed in the last band of the spectrum. At the same time, the contribution to the “5” maximum is given by O 2s and N 2s AOs.
On the X-ray spectra of C 1s-electrons of complexes IV and VI (Fig. S3), two components C 1s and Cβ 1s are present. The calculated energy values that determine the half-width and the position of the maximums of the bands in the scale of communication energies are presented on the XPS spectra of C 1s-electrons of compounds IV and VI (Fig. S3). For C1s electrons in compounds, the low-energy group of levels is due to ionization from the carbon atoms of the benzene cycle. The levels of the two carbonyl carbon atoms are shifted by 3.5–4.5 eV, and the central group of levels corresponds to the remaining carbon atoms. The overlapping bands of the two groups of levels in the range of Eb 284.0–286.5 eV cause a half-width of 2.3–2.5 eV for the entire band with a maximum at 285.5 eV. On the XPS spectra of C 1s levels, a good correspondence is observed between the differences in energy and the relative areas of the Gaussians with the calculated energies and the number of electronic levels (Fig. S3).
For both complexes, as for most boron chelate complexes [59, 60], the binding energy of 1s-electrons of the boron atom is 193.1 eV (Table S1), which, according to the table data [61], is characteristic of a high degree of oxidation of the boron atom. The concentration values obtained experimentally showed a good agreement with the concentrations according to the gross formula. The deviation did not exceed 2.2 % for carbon and oxygen and 0.7 % for boron and nitrogen.
3.3. Excited states
To interpret the absorption spectra of compounds IV–VI (Fig. 5), Table 3 presents the calculated characteristics of significant transitions in comparison with the experimental data of the absorption spectroscopy method. To assess the effect of the dioxyphenylene moiety on the spectral-luminescent characteristics of compounds IV–VI (Fig. 5), Table 3 presents the results of calculations of excited states of ligands I–III.
In the spectra of compounds IV–VI, the intense band corresponds to the excited state S2 (Fig. 5, Table 3). This state with an oscillator force of 0.205 is determined by the transition π3→π4. The excited states S1, S3, and S4 (S5 for compound IV) are prohibited by the selection rules and have a low oscillator strength according to the simulation results. Despite this, the spectra of compounds V and VI show a low-intensity maximum in the long-wave part of the spectrum. Since the selection rules are strict for ideal C2v symmetry, this phenomenon for compounds V and VI is explained by a deviation from C2v symmetry by replacing one oxygen atom with an NH- or NMe-group. In the short-wave part of the theoretical spectrum, a band defined by the excited state of the phenylene (transition π3X→π4X) should also be observed.
Table 3. Excited states in IV–VI calculated and experimental. The oscillator strength is indicated in brackets.
Compd
|
State
(№)
|
Transition
|
hν, eV
|
ADC(2)
|
EOM-DLPNO
|
TDDFT/
CAMB3LYP
|
Expl data
|
IV
|
1
|
π2 X → π4
|
3.41
(0.0020)
|
3.91
(0.0035)
|
3.38
(0.0039)
|
3.56
|
2
|
π3→ π4
|
4.48
(0.2054)
|
4.33
(0.2892)
|
4.58
(0.0315)
|
4.40
|
3
|
π3 X → π4
|
4.71
(0.0197)
|
4.68
(0.0400)
|
4.97
(0.2456)
|
|
4
|
n–→ π4
|
5.04
(0.0026)
|
5.07
0.0014
|
5.21
(0.1010)
|
|
5
|
π2 X → π4X
|
5.10
(0.0902)
|
5.39
(0.0751)
|
5.30
(0.0212)
|
|
V
|
1
|
π2 X → π4
|
3.81
(0.0001)
|
4.25
(0.0012)
|
3.78
(0.0002)
|
3.55
|
2
|
π3→ π4
|
4.49
(0,1911)
|
4.27
(0.2646)
|
4.87
(0.2191)
|
4.33
|
3
|
π2 X → π4X
|
5.00
(0,0294)
|
4.66
(0.0511)
|
5.02
(0.0040)
|
|
4
|
π3 X → π4
|
5.25
(0,1186)
|
5.82
(0.1419)
|
5.21
(0.1667)
|
|
5
|
n–→ π4
|
5.90
(0,0000)
|
5.91
(0.0009)
|
5.87
(0.0230)
|
|
VI
|
1
|
π2 X → π4
|
3.77
(0.0001)
|
4.14
(0.3026)
π3→ π4
|
3.83
(0.0002)
|
3.51
|
2
|
π3→ π4
|
4.34
(0.2303)
|
4.25
(0.0019)
π2 X → π4
|
4.71
(0.2678)
|
4.11
|
3
|
π2 X → π4X
|
4.98
(0.0294)
|
4.25
(0.0016)
π2 X → π4
|
5.05
(0.0022)
|
|
4
|
π3 X → π4
|
5.22
(0.1195
|
5.25
(0.0560)
|
5.22
(0.1697)
|
|
5
|
n–→ π4
|
5.85
(0.0002)
|
5.83
(0.0192)
π3 X → π4
|
5.85
(0.0217)
|
|
The replacement of the oxygen atom with an NH group (complex V) leads to a bathochromic shift of 0.07 eV, and the replacement of the NH group with NMe increases the shift to 0.29 eV, which is consistent with the calculated data on the change in the energy interval between MO π3 and π4.
Table 4 presents the results of simulating the excited states of compounds I–III according to the ADC(2)/cc–pVTZ, DLPNO/cc–pVTZ, and TDDFT/CAMB3LYP/cc-pVTZ methods. In absorption spectra I–III, the long-wave bands correspond to the excited state with a transition of π3→π4. According to the calculations and experiment data, there is a decrease in the energies of the excited states S1 and S2 during the transition from I to II and III, which correlates with the data on changes in the value of the HOMO→LUMO energy gap.
Table 4 Excited states in I–III calculated and experimental. The oscillator strength is indicated in brackets.
Compd.
|
State
(№)
|
Transition
|
hν, eV
|
ADC(2)
|
EOM-DLPNO
|
TDDFT/
CAMB3LYP
|
Expl data
|
I
|
1
|
n– → π4
|
4.17
(0.0004)
|
4.22
(0.0006)
|
4.45
(0.0005)
|
4.53
|
2
|
π3 → π4
|
5.06
(0.2646)
|
4.85
(0.3601)
|
5.23
(0.3023)
|
II
|
1
|
n– → π4
|
4.02
(0.0002)
|
4.08
(0.0005)
|
4.31
(0.0003)
|
4.22
|
2
|
π3 → π4
|
4.79
(0.3037)
|
4.46
(0.3629)
|
4.98
(0.3301)
|
III
|
1
|
n– → π4
|
3.97
(0.0002)
|
4.09
(0.0004)
|
4.31
(0.0004)
|
3.99
|
2
|
π3 → π4
|
4.49
(0.3398)
|
4.18
(0.3939)
|
4.77
(0.3814)
|
For all compounds, a qualitative correspondence between the experimental and calculated absorption spectra is observed (Fig. 5). The DLPNO method, in comparison with the ADC(2) and TDDFT methods, allowed a better agreement with the experiment for the oscillator forces and the absolute values of the energies of the excited states (Table 5). Despite this, this method overestimates the energy of the forbidden transition in the range of 3.4–3.6 eV by an average of 0.5 eV, which leads to difficulties in interpreting the absorption spectra. Due to the well-chosen parameters of the CAMB3LYP function, the TDDFT calculation data on the oscillator forces are better consistent with the experiment compared to the ADC(2). However, the TDDFT method significantly inflates the transition energy π3→π4, so the interpretation of the spectra was carried out according to the ADC method (2).
Table 5 Deviations of the calculated data for the energies of excited states from the experimental data for compounds I–VI
Method
|
Error, eV
|
I
|
II
|
III
|
IV
|
V
|
VI
|
TDDFT/CAMB3LYP
|
0.71
|
0.76
|
0.79
|
0.60
|
0.65
|
0.60
|
ADC(2)
|
0.54
|
0.57
|
0.51
|
0.08
|
0.19
|
0.22
|
EOM-DLPNO
|
0.33
|
0.25
|
0.21
|
0.08
|
0.05
|
0.00
|