Calculation of the tautomeric properties of 3-formyl-tetrinic acid by the ab initio and DFT methods

Article abstract of DOI:10.1023/A:1011994105199

Quasiline electronic-vibrational spectra of fluorescence and absorption (excitation of fluorescence in selective recording) of the molecules of phthalocyanine deuterated around the periphery of benzene rings (H2Phc-d16) and the center of the macrocycle (D

Full text of DOI:10.1023/A:1011994105199

Journal of Applied Spectroscopy, Vol. 68, No. 3, 2001
EFFECT OF DEUTERATION ON QUASILINE
ELECTRONIC-VIBRATIONAL SPECTRA OF
PHTHALOCYANINE
a
b
b
S. F. Shkirman, N. A. Sokolov, V. K. Konstantinova,
UDC 535.37
a*
and K. N. Solov’ev
Quasiline electronic-vibrational spectra of fluorescence and absorption (excitation of fluorescence in
selective recording) of the molecules of phthalocyanine deuterated around the periphery of benzene
rings (H Phc-d ) and the center of the macrocycle (D Phc) are obtained. The vibrational frequencies
2
16
2
of the ground state are almost insensitive to this deuteration (except for vibrations with the partici-
pation of angular deformations). In excitation spectra, changes in deuteration are more pronounced
due to the effects of nonadiabatic vibronic interaction of the vibrational sublevels of the S state and
1
of the purely electronic level S2.
Keywords: phthalocyanine, deutero derivative, quasiline spectrum, frequency of normal vibration, elec-
tronic-vibrational interaction.
The spectroscopy of phthalocyanine-type molecules continues to attract the attention of researchers in
view of the numerous practical applications of phthalocyanines (many of which are industrial dyes) and their
structural affinity to biologically important tetrapyrrole pigments such as porphyrins and metalloporphyrins.
The metal-free phthalocyanine (H Phc) is one of the first three tetrapyrroles (together with dimethyl ether of
2
protoporphyrin IX and Mg-phthalocyanine) for which quasiline spectra (QLS) of fluorescence were obtained
[
1]. Thereafter, the characteristics of the quasiline spectra of fluorescence and absorption of H Phc were in-
2
vestigated in [2–9].
A detailed interpretation of vibronic quasiline spectra of H Phc is difficult because of its complicated
2
molecular structure. For the solution of such problems by comparing experimentally determined vibrational
frequencies with the data of calculation of normal vibrations, it would be most advantageous to have infor-
mation on the influence of isotopic substitution and, first of all, of deuteration on experimental spectra.
In this work, we present the results of studying the quasiline fluorescence and absorption (fluores-
cence excitation) spectra of two deutero derivatives of H Phc:
2
*To whom correspondence should be addressed.
a
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 F. Skorina
b
Ave., Minsk, 220072, Belarus; e-mail: llum@imaph.bas-net.by; Belarusian State University, Minsk, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 68, No. 3, pp. 315−318, May–June, 2001. Original
article submitted January 26, 2001.
410
0021-9037/01/6803-0410$25.00  2001 Plenum Publishing Corporation

in n-octane matrices at 77 K.
Synthesis of H Phc-d was made via the sodium complex of phthalonitrile-d . The latter was pre-
2
16
4
pared in five stages from o-xylol-d , which in turn was obtained by deuteration of o-xylol in D SO –D O at
4
2
4
2
o
2
0 C by a modified technique [10]. The synthesis of Na Phc-d was made by interaction of phthalonitrile-d
2 16 4
o
with sodium amylate (a solution of metallic sodium in n-amyl alcohol) at 138–140 C. The treatment of
o
Na Phc-d with an aqueous solution of H SO (dilution 1:2 by volume) at 0 C for 2 h with stirring gave
2
16
2
4
o
H Phc-d . For purification purposes, the product was redeposited from concentrated H SO at 0 C. The cen-
2
16
2
4
ter of the molecule was deuterated (production of D Phc) by introducing several drops of CD OD into a
2
3
prepared n-octane solution of H Phc.
2
The quasiline spectrum was recorded on a spectrometric setup (described in [11]) with two mono-
chromators. The quasiline spectra of fluorescence were measured on excitation by total radiation in the 360–
600-nm region. The quasiline spectra of fluorescence excitation were recorded in selective recording of the
intense components of the head "multiplet."
The quasiline spectrum of the fluorescence of H Phc-d is presented in Fig. 1. The head "multiplet"
2
16
consists of the four most intense components. However, we can separate two major quasilines at 690.53 nm
−1
−1
(
14,482 cm ) and 693.49 nm (14,420 cm ). The relative intensity of their "satellites" at 689.81 and 692.46
nm depends respectively on the means of preparation of a sample, and it decreases sharply when the sample
is subjected to slow freezing. We will denote the type of center ("site") with ν = 14,482 cm− by 1, that
1
00
with ν00 = 14,420 cm− by 2, and the "satellites" by 1′ and 2′ (see Fig. 1). The fluorescence excitation spectra
1
of the same object for sites 1 and 2 are shown in Fig. 2.
The results of vibration analysis of the obtained quasiline spectra of H PhC-d are listed in Table 1.
2
16
As is seen, there are marked differences in the vibrational structure of the fluorescence spectra of H Phc and
2
H Phc-d (our data for H Phc agree well with the data of [1–3, 7]). Thus, the frequency of the vibration
2
16
2
−
1
(
most active in the fluorescence spectrum) of an H Phc molecule in the ground state (S ) 683 cm is de-
creased to 668 cm , whereas the frequencies of the vibrations of H Phc 1141 and 1355 cm are decreased
to 1121 and 1330 cm , respectively. Conversely, the group of frequencies in the 1500–1550-cm region
2
0
−1
−1
2
−1
−1
virtually does not change on deuteration of benzene rings. New vibrational frequencies 126, 818, and 855
−1
cm appear in the spectrum of H Phc-d . To interpret the isotopic shifts observed, we will carry out calcu-
2
16
lation of normal vibrations.
Let us focus our attention on the quasiline fluorescence excitation spectrum of impurity centers 1 and
2
of H Phc-d . Earlier [4], an interesting feature was revealed in H Phc. If, for the shortwave site 1 in the
2
16
2
excitation spectrum, one broadened quasiline corresponds to the purely electronic transition S ← S , then
2
0
there is a "doublet" for site 2. This splitting is explained in [4] (see also [12]) by quantum-mechanical inter-
411

Fig. 1. Quasiline fluorescence spectrum of H Phc-d in n-octane at 77
2
16
K. For the head "multiplet" the wavelengths are indicated in nm; for vi-
bronic quasilines the frequencies of normal vibrations are given in cm−
1
(for site 1 with λ00 = 690.5 nm).
Fig. 2. Quasiline fluorescence excitation spectrum of H Phc-d in n-oc-
2
16
tane at 77 K (λrec = 690.5 (a) and 693.5 nm (b)). Given are the frequen-
−
1
cies of normal vibrations (cm ) in the excited state S ; the frequency
1
intervals between the head quasiline and transitions with participation of
the state S are given in square brackets.
2
action of the purely electronic level S with the vibrational sublevel of state S (in the terminology of H.
2
1
Herzberg [13] such an effect is called an electronic-vibrational analog of the Fermi resonance).
An analogous difference is also observed in H Phc-d . Site 1 (Fig. 2a) in the excitation spectrum has
2
16
a very intense and somewhat broadened single quasiline that is separated from the S ← S 0–0-transition by
1
0
−
1
7
8
83 cm . Beyond a doubt, it belongs to the 0–0-transition of S ← S . Three very intense quasilines at 859,
67, and 926 cm (the latter is the most intense one) are observed in site 2 (Fig. 2b); they are located from
2 0
−
1
the 0–0-transition at a much larger distance than that given for site 1. In the quasiline spectrum of fluores-
−
1
cence in this region of vibrational frequencies there is a weak quasiline at 889 cm . We may state that the
−
1
S –S -interval in site 2 comes to about 900 cm (i.e., the values of this interval in sites 1 and 2 differ mark-
2
1
edly), and the frequency of the 0–0-transition of S ← S comes into resonance with the frequency of vi-
2
0
bronic transition with participation of the vibration of B symmetry, which in the state S has the frequency
1
g
1
−
1
8
80 cm and probably corresponds to the indicated vibration in the ground state S . As a result, splitting
0
by the type of the Fermi resonance occurs. We may assume that the low-frequency component of the Fermi
resonance participates in an additional interaction that leads to its splitting into two frequencies.
Investigation of the fluorescence excitation quasiline spectra of sites 1′ and 2′ showed that splitting in
the region of the 0–0-transition of S ← S is also typical of these sites, with splitting being insignificant for
2
0
site 1′ and great for site 2′, but somewhat less than for site 2.
It is seen from Table 1 that in the remaining regions of the absorption spectrum the frequency inter-
vals reckoned from the 0–0-transitions of S ← S of different sites agree satisfactorily with the vibrational
1
0
−
1
frequencies of the ground state and among themselves. The regions 1200–1250 and 1600–1900 cm in site
are an exception. In the first region we observe two intense broadened quasilines; in the second there are
2
−
1
transitions with the participation of frequencies not typical of porphyrazines (the 1607-cm frequency corre-
sponds to the 1602-cm− frequency of site 1 and can belong to the valence C—C vibrations of benzene
1
412

−
1
TABLE 1. Frequencies of Normal Vibrations (in cm ) of an H Phc-d Molecule Active in the Fluorescence and
2
16
Fluorescence Excitation Spectra
(
1)
(2)
(1)
(2)
S0
S
S
S0
S
S
1
1
1
1
−
−
66
104 sh.
111
−
66
−
1121
−
1065
1119
1072
109
114
1123
1
13
26
1139 sh.
1158
−
1161
1
−
−
1
34 sh.
135
179
227
451
558
137
1193
−
1190
−
1
2
4
5
5
6
6
82
28
62
60
92
52
68
181
−
1205 (ampl.)
230
−
1228 (br.)
−
−
455
−
1256 (ampl., br.)
560
−
1330
1384
1277
−
1323
1379
−
−
664
597
1327
−
668
−
1394
−
−
1425 sh. (br.)
1440 (br.)
1480 (v.w.)
1533
7
7
18 sh.
31
56 sh.
713 sh.
725
718 sh.
731
−
1424 (br.)
1453 (br.)
7
1470(?)
−
769
−
1524
1541
1553
−
8
8
18
55
809 sh.
841
891
817 sh.
839 sh.
902 sh.
−
1529
1545 sh.
−
8
89 (v.w.)
1588 sh.
1598
−
−
−
−
907 sh.
929 sh.
−
−
−
1602 (v.w.)
1607
−
−
970 sh.
980 sh.
1032
−
−
−
−
1678 (br.)
1749
−
1
023
1025
−
1926
Note. Characteristics of some of the quasilines: v.w. (very weak), ampl. (amplified), br. (broadened), sh. ("shoul-
der").
rings). It should be noted that the appearance of a larger number of vibronic transitions in the absorption
spectra in comparison with the emission spectrum can be due to the activation of the incompletely symmet-
rical B1g vibrations in an excited state as a result of interaction of the corresponding vibronic levels with the
S2 level.
Deuteration of the center of the H Phc molecule has a weak effect on the quasiline spectrum of fluo-
2
−
1
rescence. We managed to record only the disappearance of the quasiline with the frequency 1357 cm and
the appearance of the 990-cm− frequency in D Phc. Changes in the excitation spectra were more noticeable.
1
2
In particular, this refers to the region of the above-considered vibronic resonance. Site 2 of H Phc displays a
2
well-expressed "doublet" of quasilines offset from the 0—0-transition by 867 and 923 cm− (the latter line is
1
more intense and somewhat broadened asymmetrically from the shortwave side). Deuteration of the center
−
1
complicates the picture: two quasilines of nearly the same intensity at 889 and 904 cm are observed,
−
1
whereas the intensity of the 862-cm quasiline is noticeably smaller than that of the corresponding 867-
−
1
cm quasiline of H Phc. It was noted above that H Phc-d also displays three intense transitions. These
2
2
16
facts point to the complex character of vibronic interaction in the case considered, viz., to the participation of
more than one vibration (it is seen from Table 1 that the data for site 1 of H Phc-d display two vibrations
2
16
−
1
(
891 and 907 cm ) in the corresponding interval).
413

It should be noted that in site 1 the deuteration influences the S –S interval and the shape of the
2
1
−
1
S ← S quasiline. The changes of the S –S interval of 788, 798, and 783 cm in H Phc, D Phc, and
2
0
2
1
2
2
−
1
H Phc-d , respectively, exceed the experimental error (2–3 cm for intense quasilines). These changes can
2
16
be explained only by the fact that the contour of the given quasiline is the envelope of forbidden vibronic
transitions and therefore the observed S –S interval is not a true one.
2
1
In the fluorescence excitation spectra, the region in which one can await the manifestation of defor-
mation vibrations of B1g symmetry with participation of the central N—H bonds (for example, by analogy
with the data for tetrabenzoporphin [14, 15] and tetraazaporphin [16]) is complex and difficult to analyze
because of the vibronic interactions considered above. Nevertheless, for different sites we managed to reveal
−
1
three frequencies of vibrations in the S state that disappear in N-deuteration of H Phc: 905 and 1205 cm
1
2
site 1) and 1110 cm−1 (site 2). The 869, 988, and 1006 cm frequencies appear in this case (the data for
site 1). For comparison, the 907, 1020, and 1228 cm frequencies in tetrabenzoporphin disappear in the
ground state S and the 864, 993, and 1053 cm frequencies appear. Moreover, vibrational frequencies 1361
and 1373 cm of the state S of site 1 were revealed, which disappear in deuteration of the center and may
correspond to the above-noted frequency of the ground state 1357 cm (site 2).
This work was carried out with financial support from the Belarusian Republic Basic Research Foun-
dation (project F98-227).
−1
(
−
1
−
1
0
−
1
1
−
1
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