Synthesis and spectral analysis of alkyl-substituted 3,3′- bis(dipyrrolylmethenes)

Article abstract of DOI:10.1134/S1070363209110243

Four new alkyl-substituted 3,3′-bis(dipyrrolylmethene) dihydrobromides containing from 4 to 10 alkyl substituents were synthesized. In a highly alkylated ligand of these substances one of the hydrogen atoms of the 3,3′-methylene spacer was substituted wit

Full text of DOI:10.1134/S1070363209110243

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 11, pp. 2425–2434. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © E.V. Antina, G.B. Guseva, N.A. Dudina, A.I. V’yugin, A.S. Semeikin, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79,
No. 11, pp. 1903–1912.
Synthesis and Spectral Analysis
of Alkyl-Substituted 3,3'-Bis(dipyrrolylmethenes)
E. V. Antinaa,b, G. B. Gusevaa, N. A. Dudinaa, A. I. V’yugina, and A. S. Semeikinb
a Institute of Solution Chemistry, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153045 Russia
e-mail: eva@isc-ras.ru
b Ivanovo State University of Chemical Engineering, Ivanovo, Russia
Received February 2, 2009
Abstract―Four new alkyl-substituted 3,3'-bis(dipyrrolylmethene) dihydrobromides containing from 4 to 10
alkyl substituents were synthesized. In a highly alkylated ligand of these substances one of the hydrogen atoms
of the 3,3'-methylene spacer was substituted with a phenyl group. The compounds obtained were studied by IR,
1H NMR, electron absorption, and fluorescent spectroscopy. The increased alkylation degree of pyrroles and
the introduction of an aryl substituent in the 3,3'-spacer causes a significant high-frequency shift of the
1
N–H stretching vibrations in the IR spectra, an upfield shift of the NH-proton signals in H NMR spectra, a
decrease in the auxochromic effects of protons on the aromatic system of chromophore in the composition of
salts. The red shift of maximum of the strong band in electron absorption spectra and the emission spectra of
compounds in DMF, DMSO, C5H5N, C6H6, and CHCl3 was established. The salts obtained are stable in
benzene and chloroform, while in electron–donor solvents the irreversible processes of solvolytic dissociation
of salts to free organic base and HBr take place.
DOI: 10.1134/S1070363209110243
Complexes of dipyrrolylmethenes and linear
oligopyrroles built of pyrrolylmethene domains
because of clearly expressed chromophore and
fluorescent properties and high photo- and
thermostability proved to be promising objects both for
the theoretic studies and the practical application as
limiters of the hard laser radiation, analytic reagents,
fluorescent sensors and markers, and anticancer drugs
[1–3].
The molecular design of dipyrrolylmethene ligands
of the general type a is restricted to varying alkyl
(R,R1) substituents and donor atoms (X) [4] or to the
fusion of cyclic structures to pyrrole fragments b [5, 6].
R'
R
R
R
R
R'
R
R
X
NH
N
N
R
R
R
b
a
R = H, Alk; R' = H, Ar; X = N, O, S.
For the synthesis of linear oligopyrroles the
dipyrrolylmethene domains bound with alkyl bridges
of different architecture and “rigidity” at the 2,2'-, 2,3'-,
or 3,3'-positions (c)–(e) [7] are usually used.
Special interest among the compounds of this group
present the polydentate tetrapyrrole ligands forming
stable binuclear complexes with the functionally
important photophysical properties.
2425

2426
ANTINA et al.
R
R
R
R
Y
R R
Y
R
R
R
R
3
3'
2
2'
HN
N
HN
N
R
R
R
R
R
R
N
HN
N
HN
R
R
R
R
d
c
Y = CH2, (CH2)n, CH≡CH.
R
R
R
R
R
R
R
R
R
R
R
R
R
R
N
N
N
N
N
N
H
H
H
e
Main problems of molecular design consist in
supplying the ligand with the optical properties and the
structural preorganization providing the formation of
stable helicates with p- and d-elements having a set of
spectral characteristics (intense absorption and fluore-
scence emission in the range of phototherapeutic
window) necessary for limiters of the hard laser radia-
tion and photosensitizers used in photodynamic
therapy and photodiagnostics [8]. The development of
the general strategy for the synthesis of new linear
tetrapyrroles with the predictable photophysical
properties requires systematic studies of main trends in
the effect of structural factors on the important
properties of ligands, among them of bis(dipyrrolyl-
methenes) and their complexes.
In extension of the research in the field of di- and
tetrapyrroles [4, 9] we synthesized and identified four
new alkylated 3,3'-bis(dipyrrolylmethenes) III, V–VII.
Here we report on the results of comparative studies of
spectral properties of new 3,3'-bis(dipyrrolylmethenes)
and their analogs I, II, and IV obtained before [9].
Br−
H
H
R10
R9
R6
N
N
+
R11
R7
R2
R1
R8
R3
R4
C
H
+
R5
N
N
H
H
Br−
I−VII
I: R1 = R2 = R3 = R4 = R5 = R6 = R7 = R8 = R9 = R10 = Me; R11 = H; II: R1 = R3 = R4 = R5 = R6 = R7 = R8 = R10 = Me; R2 =
R9 = Et, R11 = H; III: R1 = R3 = R4 = R5 = R6 = R7 = R8 = R10 = Me, R2 = R9 = Et, R11 = Ph; IV: R1 = R2 = = R3 = R5 = R6 =
R8 = R9= R10 = Me, R4 = R7 = Et, R11 = H; V: R1 = R3 = R4 = R5 = R6 = R7 = R8 = R10 = Me, R2 = R9 = R11 = H; VI: R2 =
R3 = R4 = R5 = R6 = R7 = R8 = R9 = Me, R1 = R10 = R11 = H; VII: R4 = R5 = R6 = R7 = Me; R1 = R2 = R3 = R8 = R9 = R10 =
R11 = H.
The analysis of the effect of the molecular structure
on the coordination properties of bis(dipyrrolyl-
methenes) will become the subject of our further
studies. While performing the synthesis of new alkyl-
substituted ligands we presumed that the decrease in
the degree of methylation and the introduction of an
aryl substituent in the spacer should significantly
influence their photophysical and chemical, among
them the coordination, properties due to the changes in
the electron density on the pyrrole rings and
heteroatoms. In the case of compound III containing
aryl substituent in the methylene spacer, and of
substance IV having ethyl groups near the spacer it
was presumable that along with the inductive effects a
significant influence on the ligand properties will be
produced by the steric effects of bulky substituents.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

SYNTHESIS AND SPECTRAL ANALYSIS OF ALKYL-SUBSTITUTED
2427
Scheme 1.
R1
R1
R1
R1
R1
CO2Et
CO2Et
(CH2O)n
HBr
KOH
(CH2OH)2
Me
HN
NH
HN
CO2Et
NH
N
H
Me
Me
IX
Me
Me
VIII
X
HBr
R3
R4
R2
R1
R2
CHO
R2
R1
N
H
R3
R3
XI
+
+
NH
HN
NH
HN
R4
R4
Me
Me
2Br−
Scheme 2.
Me
Me
Ph
Me
Me
Ph
Me
H
H
CO2Et
CO2Et
PhCHO
HBr
KOH
(CH2OH)2
Me
HN
NH
HN
CO2Et
NH
N
H
Me
Me
Me
Me
XII
XIII
XIV
HBr
Et
Me
CH3
CHO
N
H
Me
Me
Me
Me
Ph
H
XV
Et
Me
Et
+
+
NH
HN
NH
HN
Me
Me
Me
2Br−
Compounds I, II, and IV were prepared according
to the procedure [9]. Synthesis of compound III was
carried out as shown in Scheme 1.
Data on the stretching and bending vibrations of the
N–H bonds (νN–H, δN–H) are listed in Table 1.
N–H Stretching vibrations are observed in the range
3434–3480 cm–1. They are sensitive to the features of
the molecular structure. For the decamethylated ligand
dihydrobromide (compound I) this band is located at
3480 cm–1. The decrease in the total +I inductive effect
arising from partial substitution of methyl groups by
ethyls, the introduction of the aryl substituent with the
expressed –I inductive effect in the spacer, and the
Substances V–VIII were synthesized by the
Scheme 2.
Details of the synthetic procedures are described in
the Experimental. Results of the IR studies of
compounds V–VIII in the solid state (Fig. 1) show the
analogous character of the vibration spectra of 3,3'-bis
(dipyrrolylmethene) dihydrobromides (H2L·2HBr.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

2428
ANTINA et al.
decrease in the number of the alkyl substituents from
ten to four causes the shift of νN–H to low frequency by
46 cm–1 due to the decrease in the electron density on
the nitrogen atoms. Considering the reported data [10]
it is possible to analyze the influence of structural
factors on the frequencies of the analogous vibrations
in the IR spectra of pyrrole and its oligo derivatives of
linear or macrocyclic structure. N–H Stretching vibra-
tions in pyrrole are observed at ~3500 cm–1. Frequency
νN–H in porphyrins is decreased by ~190 cm–1 as
compared to that of pyrrole. Similarly to bis-
(dipyrrolylmethenes) the alkylation of porphyrin to
octaalkylporphin causes the high frequency shift of δN–
methene). N–H Stretching vibrations of alkylated di-
pyrrolylmethenes are observed at ~3408–3426 cm–1
with a small shift to high frequency compared with
biladiene-a,c. Destroying the conjugation between two
aromatic π-systems of pyrrole in the molecules of
dipyrrolylmethanes causes a shift to high frequency of
δN–H absorption band (~3428–3448 cm–1 ) as compared
to dipyrrolylmethenes [10]. Hence, the frequencies of
the νN–H stretching vibrations in the compounds under
consideration form the following series: porphyrin <
2,2'-bis(dipyrrolylmethene) < dipyrrolylmethene <
dipyrrolylmethane < 3,3'-bis(dipyrrolylmethene) <
pyrrole. It is important to note the significant
differences in the spectral characteristics of alkylated
3,3'-bis(dipyrrolylmethenes) and their 2,2'-analogs,
biladiene-a,c derivatives. The change in the type of
addition of the methylene spacer to dipyrrolylmethene
fragments from 2,2' to 3,3'-position leads to a
significant increase in the νN–H frequency in the IR
spectrum of 3,3'-isomer dihydrobromides. For ex-
ample, salt I [9] shows the high frequency shift of νN–H
absorption band by 63 cm–1 as compared to deca-
by ~30 cm–1 due to the increase in the electron
H
density on the nitrogen atoms. The introduction of
electron-acceptor aryl substituents in meso-position of
the macroring causes the shift to low frequency of the
νN–H absorption band. Opening of macroring in β-octa-
alkylporphins leads to the increase in frequency of the
νN–H absorption band by ~80 cm–1 in their linear
precursors, decaalkyl-substituted derivatives of
biladiene-a,c [11] regarded as 2,2'-bis(dipyrrolyl-
(a)
60
55
50
45
40
35
25
20
15
3500
3000
2500
2000
1500
1000
500
Wavenumber, cm–1
(b)
55
50
45
40
35
30
25
20
15
10
5
3500
3000
2500
2000
1500
1000
500
Wavenumber, cm–1
Fig. 1. IR spectra of 3,3'-bis(dipyrrolylmethene) dihydrobromides in KBr pellets: (a) compound III, (b) V, (c) VI, and (d) VI.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

SYNTHESIS AND SPECTRAL ANALYSIS OF ALKYL-SUBSTITUTED
(c)
2429
60
50
40
30
20
10
0
3500
3000
2500
2000
1500
1000
500
Wavenumber, cm–1
(d)
50
40
30
20
10
0
–0
3500
3000
2500
2000
1500
1000
500
Wavenumber, cm–1
Fig. 1. (Contd.)
methyl substituted biladiene-a,c [11]. The differencies
observed in the frequencies of the analogous
characteristic vibrations of pyrrole and the related
oligopyrrole compounds reflect qualitatively the
general tendency to the increase in the basicity of
ligands in going from biladiene to dipyrrolylmethene
and 3,3'-bis(dipyrrolylmethene).
domains are characterized by signals at 6.73–7.12 ppm;
the signals of the 3.3'-CH2 spacers are located at 3.52–
5.41 ppm; protons of >NH and >N+H groups give
signals at 12.99–13.86 ppm. Signals of separate groups
of protons in the compounds H2L·2HBr under
investigation remain highly characteristic and do not
overlap with one another. The only exclusion is the
1H NMR spectra of 3,3'-bis(dipyrrolylmethenes) are
presented in the Experimental. The spectral
characteristics (intensity and multiplicity) obtained
reliably confirm the structure of compounds
synthesized. By the example of compounds V–VIII
note the rules of location of signals belonging to the
Table 1. Stretching (νN–H, cm–1) and bending (δN–H, cm–1)
vibrations of N–H bonds in the IR spectra of pyrrole [10]
and compounds I–VIIIa
Compound
νN–H, cm–1
δN–H, cm–1
1
separate groups of protons in H NMR spectra of 3.3'-
Pyrrole
I
3496
3480
3460
3455
3450
3442
3438
3434
–
bis(dipyrrolylmethenes). Depending on the molecular
structure of the ligand the signals of protons belonging
to the separate groups are located in following spectral
ranges: Methyl substituents on pyrrole rings are
characterized by the signals at 1.96–2.71 ppm; CH3-
and –CH2- groups of ethyl substituents give signals at
1.04–1.08 ppm and 2.42–2.54 ppm respectively;
signals of α- and β-protons of pyrrole ring are located
at 6.18–7.90 ppm; CH spacers of dipyrrolylmethene
1611
1614
1616
1615
1614
1617
1614
II
III
IV
V
VI
VII
a Data for compounds I, II, and IV are taken from [9].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

2430
ANTINA et al.
signals were marked previously as a result of chemical
modification of the pyrrole molecule and of its
oligomers like dipyrrolylmethenes, dipyrrolylmethanes,
and porphyrins [10, 12]. The signal of the NH group
I
1
proton in H NMR spectrum of pyrrole is located at
II
7.62 ppm. The methylation of pyrrole ring leads to the
upfield shift of the signal by ~0.9 ppm. The introduc-
tion of the electron–acceptor ester or formyl group in
α-position of the ring causes the downfield shift of the
signal (up to 3.3 ppm). The location of δ(NH) signals
III
IV
1
in H NMR spectra of dipyrrolylmethanes and their
derivatives is observed in the range 7.8–9.8 ppm.
Signals of the NH group protons in 1H NMR spectra of
porphyrins are strongly shifted upfield (from –1.4 to
–4.4 ppm) due to the shielding action of the macro-
cyclic current. Signals of NH protons [δ(NH) and
δ(N+H)] in 1H NMR spectra of the hydrobromides of the
alkylated derivatives of dipyrrolylmethenes and biladi-
ene-a,c are significantly shifted downfield (11.76–
13.53 ppm) as compared to monopyrroles and dipyrrolyl-
methanes. Still larger downfield shift of δ(NH) and
δ(N+H) proton signals (12.99–13.86 ppm) is observed
V
VI
VII
1
in H NMR spectra of 3,3'-bis(dipyrrolylmethene)
dihydrobromides under investigation. Hence, the
downfield shifts of δ(NH) proton signal for pyrrole and
its linear and macrocyclic oligoderivatives form the
following sequence: porphyrin < pyrrole < dipyrro-
lylmethane < dipyrrolylmethene, 2,2'-bis(dipyrrolyl-
methene) < 3,3'-bis(dipyrrolylmethene).
13.8
13.0
δ(NH), δ(N+H), ppm
Fig. 2. Chemical shifts of the NH and N+H protons (δ,
ppm) in 1H NMR spectra of compounds I–VII. Data for the
compounds I, II, and IV are taken from [9].
As known, the chemical shifts of protons in
aromatic compounds depend on the electron density on
hydrogen atom, on the π-electron charge on the atom
bound with this proton, and on the sterical effects
arising from the interaction with substituent and
heteroatom. The separation of these effects in the
molecules of 3,3'-bis(dipyrrolylmethenes) by an
example of a small group H2L·2HBr under study is
connected with serious complications. But it must be
noted that the increase in the downfield shift of δ(NH)
and δ(N+H) proton signals in 1H NMR spectra
coincides with the decrease in the frequency of the
stretching vibrations δN–H in the IR spectra of salts
(Fig. 3a) in the series of compounds I, II, ... VII. It is
evident that the rule observed is caused by the decrease
in the basicity of ligands due to the decrease in the
total +I inductive effect of substituents. The
dependence presented in Fig. 3a can be used for
making the qualitative conclusions on the relative
stability of salts and coordination compounds of the
new structurally similar 3,3'-bis(dipyrrolylmethenes)
on the basis of 1H NMR and the IR spectra.
signals of δ(NH) and δ(N+H) protons. In some cases
depending on the molecular structure and spatial
arrangement of the ligand they can overlap. Analogous
1
features were observed recently in H NMR spectra of
dipyrrolylmethene and biladiene-a,c salts [4, 11]. In
their spectra two separate proton signals δ(NH) and δ
(N+H) usually are observed in the case of partially
alkylated or nonsymmetrically alkylated ligands, and
also in the presence of 2,3'- or 3,3'-spacer in the
dipyrrole molecule. The chemical modification of the
tetrapyrrole molecule is accompanied by strong
changes in the range of the NH group proton signals
(Fig. 2). Successive decrease in the degree of methyla-
tion of the ligands in the series of compounds I, II, ...
VII leads to the downfield shift of the NH proton
signals by 0.71 ppm. The substitution of two methyl
groups by ethyl ones in the ligand I (compounds II,
IV) and the introduction of the electron-acceptor
phenyl group in the spacer (compound III) causes
small (<0.15 ppm) downfield shift of these signals.
Strong alterations in the range of the NH proton
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

SYNTHESIS AND SPECTRAL ANALYSIS OF ALKYL-SUBSTITUTED
(a) (b)
2431
νNH, cm–1
λ
max, nm
III
II
3480
I
500
I
II
III
IV
IV
3460
3440
V
VI
V
490
VI
VII
VII
13.0
13.4
13.8
13.0
13.4
13.8
1/2Σ[δ(NH), δ(N+H)], ppm
1/2Σ[δ(NH), δ(N+H)], ppm
Fig. 3. Dependence of frequencies of the νN–H stretching vibrations (a) in the IR spectra and of the maximum of first absorption
band (λmax) in the electron absorption spectra (b) in DMF on the shift of signals of protons δ(NH) and δ(N+H) in 1H NMR spectra of
compounds I–VII. Data for the compounds I, II, and IV are taken from [9].
Qualitative characteristics of electron absorption
spectra of compounds V–VIII are listed in Table 2.
The salts are stable in benzene and chloroform, but in
the media with the expressed electron-donor properties
(C5H5N, DMSO, DMF) the processes of irreversible
solvolytic dissociation of H2L 2HBr to the free base
take place.
[H4L]Br2(Solv) + 2В(Solv) → H2L(Solv) + 2[В·HBr](Solv)
,
where B is the electron–donor solvent.
The process is accompanied by the characteristic
transformation of the spectrum of salts to the spectrum
of nonprotonated ligand. The first long wave band
undergoes the blue shift by 31–68 nm, and the charge
Table 2. Electron absorption spectra [λ, nm (log ε)] of 3,3'-bis(dipyrrolylmethene) dihydrobromides in organic solvents
Compoundb
IV
Solventа
I
II
III
V
VI
VII
DMF
С1 372–375 ctp, 374–380 ctp, 463 368–380 ctp, 466 370–376 ctp, 360–385 ctp, 370 ctp, 458 370–380 ctp,
456 sh, 496 sh, 500 (5.01)
(4.87)
sh, 501–502 (5.06) 459 sh, 494 455 sh, 492 sh, 491–492 449 sh, 483
(4.82)
(5.08)
(4.96)
С2 456 (4.67)
463 (4.79)
460–462 (4.74)
459 (4.73)
455 (4.73)
446 (4.65)
415
DMSO
С1 367–380 ctp, 370 ctp, 465 sh, 365–385 ctp, 466 375 ctp, 462 360–380 ctp, 374–378 ctp, 375–390 ctp,
465 sh, 503 505 (5.18)
(5.09)
sh, 504 (5.12)
464 (4.77)
sh, 505 (5.14) 456 sh, 495 458 sh, 496 450 sh, 485
(5.14)
(5.12)
С2 463 (4.70)
465 (4.81)
462 (4.78)
458–460
(4.78)
452 (4.69)
417
С5H5N
С1 373–375 ctp, 373–375 ctp, 467 370 ctp, 466 sh, 368–375 ctp, 365–370 ctp,
–
–
462 sh, 499 sh, 500 (5.01)
(4.87)
500 (4.92)
462 sh, 497 459 sh, 491
(4.89)
(4.87)
С2 462 (4.64)
467 (4.80)
465 (4.73)
462 (4.73)
460 (4.69)
449 (4.64)
419
CHCl3
C6H6
С3 364 ctp, 461 363 ctp, 462 sh, 360–377 ctp, 465 363 ctp, 463 350–365 ctp, 373 ctp, 456 355–362 ctp,
sh, 502 (5.43) 505 (5.45)
sh, 505 (5.45)
sh, 504 (5.45) 456 sh, 496 sh, 497 (5.38) 445 sh, 483
(5.44)
С3 365 ctp, 466 365–375 ctp, 465 360–375 ctp, 467 370 ctp, 466 360–380 ctp, p.s.
p.s.
sh, 507 p.s.
sh, 508 p.s.
sh, 508 (5.19)
sh, 508 p.s.
460 sh, 498
p.s.
a
C1 = 1×10–4 M, spectrum of the salt H2L·2HBr; C2 = 1×10–6 M, spectrum of the free base H2L; C3 = 1×10–6–1×10–4 M, spectrum of the
salt H2L·2HBr; b p.s. is poorly soluble compound; sh is shoulder; ctb is charge transfer band. Data for compounds I, II, and IV are taken
from [9].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

2432
ANTINA et al.
low inductive effect of substituents the chromophore
I
system of compound VII exhibits the largest
polarizability. Δλmax in this case reaches 68 nm.
Spectra of the benzene solutions show noticeable (up
to ~8–10 nm) solvatochromic effect as compared to
other solvents. It arises evidently from the polarization
of chromophore by the π-stacking interactions with the
molecules of the solvent. Increase in the degree of
alkylation of the ligand causes the significant (from
19 nm for salt and 48 nm for the free base) red shift of
λmax of the first strong band in the electronic spectrum
(see Fig. 3b).
2
A
500 510 520 λ, nm
1
360
450
530
λ, nm
According to the modern data [1] many coordina-
tion compounds formed by dipyrrolylmethenes exhibit
high fluorescent quantum yields with the long-wave
emission maxima and high photochemical stability.
Due to that the dipyrrolylmethene derivatives are used
as photosensitizers [3], laser dyes [13], fluorescent
markers in the studies of metabolic processes including
the transport of substances through biomembranes
[14]. The ligand by itself may be used as highly
selective and sensitive sensor for cations and anions
[15, 16]. In this work first data are presented on the
fluorescent properties of 3,3'-bis(dipyrrolylmethene)
hydrobromides (Fig. 4, Table 3). The fluorescent
spectrum is almost the mirror reflection of the electron
absorption spectrum of H2L·2HBr in chloroform with
the small (6–8 nm) Stokes’ shift. The maximum of the
strong band in the emission spectrum of salts is
Fig. 4. (1) Electron absorption spectrum [9] and (2) emis-
sion spectrum of compound IV in chloroform.
transfer band disappears. In the dilute solutions (C2 <
5×10–5 M) in electron-donor solvents the deprotonation
of ligand proceeds very quickly, especially in pyridine,
the most electron-donor substance among the solvents
under study. In the spectrum of freshly prepared
solution only the absorption band of free base is
observed. In the concentrated solutions (C1 > 1×10–4
M) the rate of solvolytic dissociation decreases due to
the processes of association, and in the spectrum of
solution characteristic bands of the protonated form of
ligand H2L·2HBr are registered. Nevertheless, at the
prolonged keeping of the solution its spectrum
converts gradually to the spectrum of the free base
H2L. Comparative analysis of the blue shift value
Δλmax = λlmax – λms ax shows the significant increase in the
auxochromic effect of protons on the dipyrrolyl-
methene chromophore π-system of the ligand at the
decrease in the degree of its methylation. Due to the
observed at 491–511 nm. The increase in the degree of
fl
max
alkylation favors the red shift of λ
indicating the
decrease in energy of the lower luminescent state of
the highly alkylated ligands. By an example of
compound II it was shown that the use of aromatic
nonpolar solvent (benzene) instead of chloroform
causes the double increase in the Stokes’ shift resulting
Table 3. Stokes’ shift (Δλ), location of the maximum of the
fl
strong band in the electron absorption spectrum (λambasx) and in
from the significant shift of λmax in the emission
fl
spectrum of the ligand.
the fluorescence spectrum (λ
)
of compounds in
max
chloroform and benzenea
In general in going from structurally alike di-
pyrrolylmethenes and biladiene-a,c [2, 4, 11, 17] to
3,3'-bis(dipyrrolylmethenes) a significant (up to ~30 nm)
red shift of λmax of the intense band in the absorption
and the emission spectra is observed. Results of the
analysis of the photophysical properties show that as
compared to dipyrrolylmethenes and biladiene-a,c
such specific features of molecular structure of 3,3'-bis-
(dipyrrolylmethenes) as the presence of spacer be-
tween the positions 3 and 3' of dipyrrol domains and
the high degree of alkylation improve the practically
important properties of compounds.
abs
fl
Compound
λ , nm
max
λ
max
, nm
Δλ, nm
502
508
6
6
I
II
505
508
505
504
496
497
483
511
520
511
510
503
505
491
12
6
II
III
IV
V
6
7
8
VI
VII
abs
8
a Data on λ for compounds I, II, and IV are taken from [9].
max
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

SYNTHESIS AND SPECTRAL ANALYSIS OF ALKYL-SUBSTITUTED
2433
s (6H, 9-CH3, 11-CH3), 2.60 s (6H, 3-CH3, 17-CH3),
2.35 s (6H, 9-CH3, 11-CH3), 2.15 s (6H, 7-CH3, 13-
CH3). Found, %: C 55.97; H 6.11; N 9.55.
C27H34Br2N4. Calculated, %: C 56.46; H 5.97; N 9.75.
EXPERIMENTAL
IR spectra of 3,3'-bis(dipyrrolylmethene) dihydro-
bromides in KBr pellets were obtained on an Avatar
1
360 FT-IR ESP spectrometer. H NMR spectra in
Bis(2,3,7,9-tetramethyldipyrrolylmethen-8-yl)-
methane dihydrobromide (VI). (M 574.40). A solu-
tion of 1.0 g of 2,2',4,4'-tetramethyl-5,5'-dicarbo-
ethoxydipyrrolylmethane-3,3' (IX, R1 = CH3) and 1.0 g
of KOH in 30 ml of ethylene glycol was boiled for 1 h
and then poured in water. The precipitate formed was
filtered off and dried at room temperature. Yield of
deuterated chloroform were taken on a Bruker 200
spectrometer. Electron absorption spectra in organic
solvents were registered on a SF-103 and Cary 100
spectrophotometers. Fluorescence spectra were measured
on a SLM 4800 and CM 2203 spectrofluorimeters, the
wavelength of the excitation light being equal to the
maximum in the electron absorption spectrum of the
ligand. Organic solvents of the “chemically pure”
grade were purified additionally by routine procedures
[18]. Water content in them was evaluated by Fischer’s
titration. It was no more than 0.02%.
2,2',4,4'-tetramethyldipyrrolylmethane-3,3' X (R1
=
CH3) 0.46 g (78%, M 202). This substance and 0.56 g
of 2-formyl-3,4-dimethylpyrrole XI (R2 = R3 = CH3,
R4 = H) were dissolved in 10 ml of methanol, and 1 ml
of concentrated hydrobromic acid was added with
stirring. The resulting mixture was stirred for 1 h, the
precipitate formed was filtered off, washed with small
amount of methanol, then with ether, and dried at room
temperature. Yield 1.1 g (84.4%), λmax (ε×10–3): 456
2,2',4,4'-Tetramethyl-5,5'dicarbethoxydipyrrolyl-
methane-3.3' (IX, R1=CH3). (M 346.0). A mixture of
5.0 g of 2,4-dimethyl-5-carboethoxypyrrole VIII (R1 =
CH3), 0.5 g of paraformaldehyde, 1 ml of concentrated
hydrobromic acid, and 40 ml of methanol was heated
to boiling and refluxed for 1 h. The mixture obtained
was cooled, diluted with 40 ml of water, the precipitate
obtained was filtered off, washed with water and dried
in air at 70°C. Yield 4.8 g (92%), mp 225–227°C
1
sh, 497 (239.9) (chloroform). H NMR spectrum
(CDCl3, internal TMS), δ, ppm: 13.32 s (2H, N+H),
13.25 s (2H, NH), 7.62 s (2H, 1-CH, 19-CH), 7.02 s
(2H, 5-CHmeso, 15-CHmeso), 3.59 s (2H, 10-CH2,
spacer), 2.71 s (6H, 9-CH3, 11-CH3), 2.28 s (5H, 7-
CH3, 13-CH3), 2.19 s (6H, 3-CH3, 17-CH3), 2.07 s (6H,
2-CH3, 18-CH3). Found, %: C 54.81; H 6.11; N 9.08.
C27H34Br2N4. Calculated, %: C 56.46; H 5.97; N 9.75.
1
(from methanol). H NMR spectrum (CDCl3, internal
TMS), δ, ppm: 8.52 br.s (2H, NH), 4.27 q (4H,
CH2CH3), 3.45 s (2H, ms-H), 2.18 s (6H, 4,4'-CH3),
2.04 s (6H, 2,2'-CH3), 1.33 t (6H, CH2CH3).
Bis(7,9-dimethyldipyrrolylmethen-8-yl)dihydro-
bromide (VII) (M 518.29). A solution of 1.0 g of
2,2'4,4'-tetyramethyl-5,5'-dicarboethoxypyrrolylmethane-
3,3' IX (R1 = CH3) and 1.0 g of KOH in 30 ml of
ethylene glycol was boiled for 1 h and them poured in
water. The precipitate formed was filtered off and
dried at room temperature. Yield of 2,2',4,4'-tetra-
methyldipyrrolylmethane-3,3' X (R1 = CH3) 0.49 g
(83%, M 202). This compound and 0.46 g of of 2-
formylpyrrole XI (R2 = R3 = R4 = H) were dissolved in
10 ml of methanol, and 1.0 ml of concentrated
hydrobromic acid was added with stirring. The mixture
obtained was stirred for 1 h, the precipitate formed was
filtered off, washed with small amount of methanol,
then with ether, and dried at room temperature. Yield
of the target substance 1.08 g (86%), λmax, nm: 445
Bis(1,3,6,9-tetramethyldipyrrolylmethen-8-yl)-
methane dihydrobromide V (M 574.40). A solution
of 1.0 g of 2,2',4,4'-tetramethyl-5,5'-dicarboethoxydi-
pyrrolylmethane-3,3' IX (R1 = CH3) and 1.0 g of KOH
in 30 ml of ethylene glycol was boiled for 1 h. After
that the mixture obtained was poured in water, the
precipitate formed was filtered off and dried at room
temperature. Yield of 2,2',4,4'-tetramethyldipyrrolyl-
methane-3,3' X (R1 = CH3) was 0.55 g (94%, M 202).
The substance obtained and 0.67 g of 2-formyl-3,5-
dimethylpyrrole XI (R2 = R4 = CH3, R3 = H) were
dissolved in 10 ml of methanol and 1.0 ml of
concentrated hydrobromic acid was added at room
temperature. The resulting mixture was stirred for 1 h,
the precipitate formed was filtered off, washed with
small amount of methanol, then with ether, and dried
at room temperature. Yield 1.35 g (86.4%), λmax, nm
1
(sh), 483 (chloroform). H NMR spectrum (CDCl3,
internal TMS), δ, ppm: 13.86 s (2H, N+H), 13.79 s
(2H, NH), 7.90 s (2H, 1-CH, 19-CH), 7.81 s (2H, 2-
CH, 18-CH), 7.77 s (2H, 3-CH, 17-CH), 6.73 s (2H, 5-
CHmeso, 15-CHmeso), 3.63 s (2H, 10-CH2-spacer), 2.69 s
(6H, 9-CH3, 11-CH3), 2.22 s (6H, 7-CH3, 13-CH3);
1
(ε×10–3): 456 (sh), 496 (275.4) (chloroform). H NMR
spectrum (CDCl3, internal TMS), δ, ppm: 13.17 (4H,
2NH, 2N+H). 7.05 s (2H, 5-CHmeso, 15 CHmeso), 6.18 s
(2H, 2-CH, 18-CH), 3.57 s (2H, 10-CH2, spacer), 2.69
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009

2434
ANTINA et al.
(DMSO-d6, internal TMS), δ, ppm: 12.56 s (2H, N+H),
12.46 s 2H, NH), 7.93 s (2H, 1-CH, 19-CH), 7.83 s
(2H, 2-CH, 18-CH), 7.71 s (2H, 3-CH, 17-CH), 6.69,
6.75 s (2H, 5-CHmeso, 15-CHmeso), 3.75 s (2H, 10-CH2-
spacer), 2.83 s (6H, 9-CH3, 11-CH3), 2.34 s (6H, 7-
CH3, 13-CH3). Found, %: C 51.53, H 4.85, N 10.40.
C23H26Br2N4. Calculated, %: C 53.30; H 5.06, N 10.81.
7.39. C37H40Br2N4. Calculated, %: C 62.90, H 6.56, N
7.93.
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XII, 0.6 ml of benzaldehyde, and 1.0 ml of con-
centrated hydrobromic acid in 20 ml of methanol was
refluxed for 1 h. Several minutes after addition of acid
to the boiling solution a precipitate of dipyrrolyl-
methane was formed. It was filtered off, washed with
methanol, and dried. Yield 2.4 g (95%), mp 213–215°C.
1H NMR spectrum (CDCl3, internal TMS), δ, ppm:
8.51 br.s (2H, NH), 7.19 m (5H, Ph), 5.35 s (1H, ms-
H), 4.23 q (4H, OCH2), 2.05 s (6H, 2,2'-CH3), 1.65 s
(6H, 4,4'-CH2), 1.33 t (6H, CH2CH3).
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15. Sessler, J.L., Maeda, H., Mizuno, T., Lynch, V.M., and
Bis(3,3',5,5'-tetramethyl-4'-ethyldipyrrolylmethen-
4-yl)phenylmethane dihydrobromide (III) (M 706.61).
A solution of 1,0 g of ms-phenyl-2,2'4,4'-tetramethyl-
5,5'-dicarboethoxydipyrrolylmethane-3,3' XIII and
1.0 g of KOH was boiled in 30 ml of ethylene glycol.
The mixture obtained was poured in water, and the
precipitate formed was filtered off and dried at room
temperature. Yield of ms-phenyl-2,2',4,4'-tetramethyl-
dipyrrolylmethane-3,3' XIV was 0.65 g (99%), M
278.40. This substance and 0.74 g of 2,4-dimethyl-3-
ethyl-5-formylpyrrole XV were dissolved in 20 ml of
methanol, and 1.0 ml of concentrated hydrobromic
acid was added with stirring. The mixture obtained
was stirred for 1 h, the precipitate of the target product
was filtered off, washed with small amount of
methanol, then with ether, and dried at room tem-
perature. Yield 0.6 g (36%), λmax, nm (ε×10–3): 4.65 sh,
1
505 (281.8) (chloroform). H NMR spectrum. (CDCl3,
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internal TMS), δ, ppm: 13.21 s (2H, 2N+H), 13.02 s
(2H, 2NH), 7.45 m (1H, p-CH-Ph), 7.38 m (2H, o-CH-
Ph), 7.35 m (2H, m-CH-Ph), 7.16 s (1H, 15-CHmeso),
7.12 s (1H, 5-CHmeso), 5.41 s (2H, 10-CHPh, spacer),
2.70 s (6H, 8-CH3, 11-CH3), 2.44 q (4H, J 8 Hz, 2,18-
CH2CH3, 2.28 s (6H, 9-CH3, 11-CH3), 2.27 s (6H, 7-
CH3, 13-CH3), 1.96 s (6H, 3-CH3, 17-CH3), 1.08 t (6H,
J 8 Hz, 18-CH2CH3). Found, %: C 62.50, H 6.41, N
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 11 2009