Synthesis, spectroscopic and photophysical properties of novel styryldiazepinoporphyrazine

Article abstract of DOI:10.1016/j.inoche.2012.02.001

A novel porphyrazine possessing two styryl substituents conjugated with each of four diazepine rings was synthesized and characterized using UV-vis, MS MALDI and various NMR techniques. Solvent effects on the electronic absorption spectra of this porphyrazine were determined in protic and aprotic solvents. The changes observed in the electronic absorption spectra seem to result mainly from solvation as there was no correlation between the coordinating strength of the solvent and the red shift. Also the potential photosensitizing activity of this novel porphyrazine was evaluated by measuring its ability to generate singlet oxygen, which was found to reach the yield (Φ_Δ) of 0.11 in DMF.

Full text of DOI:10.1016/j.inoche.2012.02.001

Inorganic Chemistry Communications 20 (2012) 13–17
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, spectroscopic and photophysical properties of novel
styryldiazepinoporphyrazine
c
b,
a
Jaroslaw Piskorz a, Ewa Tykarska b, , Maria Gdaniec , Tomasz Goslinski , Jadwiga Mielcarek
⁎
⁎
a
Department of Inorganic and Analytical Chemistry, Poznan University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan, Poland
Department of Chemical Technology of Drugs, Poznan University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan, Poland
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel porphyrazine possessing two styryl substituents conjugated with each of four diazepine rings was
synthesized and characterized using UV–vis, MS MALDI and various NMR techniques. Solvent effects on
the electronic absorption spectra of this porphyrazine were determined in protic and aprotic solvents. The
changes observed in the electronic absorption spectra seem to result mainly from solvation as there was no
correlation between the coordinating strength of the solvent and the red shift. Also the potential photosensitizing
activity of this novel porphyrazine was evaluated by measuring its ability to generate singlet oxygen, which was
found to reach the yield (ΦΔ) of 0.11 in DMF.
Received 17 December 2011
Accepted 8 February 2012
Available online 21 February 2012
Keywords:
Diazepine
Porphyrazine
Linstead macrocyclization
Solvatochromic effects
Singlet oxygen
© 2012 Elsevier B.V. All rights reserved.
Porphyrazines (Pzs) belong to macrocyclic compounds which do
not exist in nature. Beginning from their first synthesis performed
by Linstead over seventy years ago [1], many of them have been
synthesized and researched. Pzs can be modified in the macrocyclic
core with various metal ions and/or in the periphery with different
alkyl, aromatic, nitrogen, oxygen, and sulfur containing groups and
annulated rings [2,3].
Pzs possessing peripherally annulated diazepine rings have been
subjected to advanced physical–chemical studies and exhibited inter-
esting electronic properties. Many spectroscopic studies concerning
tetrakis-2,3-(5,7-diphenyl-1,4-diazepino)porphyrazine and its vari-
ous metal complexes have been performed in basic, neutral and acidic
solutions, and have confirmed the conjugation of the diazepine ring
with macrocyclic core. The UV–vis spectra of these macrocycles
revealed a broad Q-band, which in most of the solvents, was divided
into two sub-bands located in the range of 630–640 nm and 660–
680 nm. The presence of an additional band at 660–680 nm is the re-
sult of n−π* transition between N atom's lone pairs of the diazepine
rings and π-electrons of the macrocycle core [4–6]. As a continuation
of these studies Donzello et al. [7] obtained tribenzoporphyrazine
containing annulated 5,7-diphenyl-6H-1,4-diazepine ring and its
magnesium complex which exhibited significant Q-bands red shift
up to 715 and 700 nm, respectively. The long Q-band absorption
wavelengths observed for diazepinoporphyrazines suggest that
these macrocycles might be considered as potential photosensitizers
for photodynamic therapy (PDT), as light of longer wavelength is
capable of deeper penetration of irradiated tissue [8].
Combination of macrocyclic and stilbenoid chromophors in one
molecular system can be used, e.g. for development of artificial
light-harvesting materials. In the recent years a number of styryl
substituted phthalocyanines [9–12] and tetrapyrazinoporphyrazines
have been prepared and studied [13–15]. We have recently reported
the synthesis of a diazepinoporphyrazine derivative possessing styryl
and phenyl substituents at C5 and C7 positions of the diazepine ring
[16]. It has been found that tribenzoporphyrazine with annulated 5-
phenyl-7-[(E)-2-(3,4,5-trimethoxyphenyl)ethenyl]-6H-1,4-diazepine
ring, showing maximum wavelengths of the Q-band components at
645–659, 669–699 and 668–729 nm, exhibits interesting spectroscopic
properties. Moreover, the promising efficiency of singlet oxygen gener-
ation by this macrocyclic system was observed (ΦΔ=0.44).
In this paper we aim to present synthesis and spectroscopic character-
ization of a novel symmetrical magnesium diazepinoporphyrazine
possessing two styryl substituents conjugated with each of four seven-
membered diazepine rings. Known compound, 5,7-dimethyl-6H-1,4-
diazepine-2,3-dicarbonitrile (3) was used in the condensation reaction
with 3,4,5-trimethoxybenzaldehyde (4) to give a novel dinitrile contain-
ing two styryl groups conjugated with diazepine ring (5) [17] following
well established synthetic methodologies (Scheme 1) [18,19].
Crystallographic analysis revealed conformational polymorphism
of 5 [20]. The differences in the structure arise from conformational
freedom around two single bonds of the styryl substituents (Fig. 1).
⁎
Corresponding authors. Tel.: +48 61 854 66 33; fax: +48 61 854 66 39.
E-mail addresses: etykarsk@ump.edu.pl (E. Tykarska),
tomasz.goslinski@ump.edu.pl (T. Goslinski).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.02.001

14
J. Piskorz et al. / Inorganic Chemistry Communications 20 (2012) 13–17
Scheme 1. Reagents and conditions: (i) oxalic acid, benzene, reflux, 4 h [18], (45%); (ii) —
piperidine (cat.), benzene, reflux, 7 h (42%); (iii) Mg(OnBu)2, nBuOH, reflux, 20 h (9%).
Fig. 1. The molecular structure of two polymorphic forms of 5 and labeling scheme.
Atoms of 5b are labeled analogously as in 5a. Arrows indicate the bonds for which dif-
ferent conformation is observed in the two polymorphs. Thermal ellipsoids are shown
at the 50% probability level.
Two different conformations are observed at the bonds linking the
two styryl substituents with the heterocyclic rings. In the polymorph
5a the two styryl groups are similarly oriented relative to the
ring with the torsion angles C2A-C1A-C5-N4 and C2B-C1B-C7-N1
of 166.6(2)° and 167.8(2)°, respectively. In the polymorph 5b the
corresponding torsion angles are 163.0(1)° and −6.2(2)° showing dif-
ferent orientation of the two substituents. The dihedral angles between
the two benzene-ring planes are 39.7° and 88.9° for 5a and 5b, respec-
tively and this difference results mainly from the changes in the torsion
angle values at the second single bond of the styryl substituents (Table
1S, Supplementary data).
Subsequent macrocyclization reaction of 5,7-disubstituted 1,4-
diazepine-2,3-dicarbonitrile 5 following Linstead conditions [1,3] led
to a novel magnesium porphyrazine (6) [21] which was characterized
using UV–vis, MS MALDI and various NMR techniques. 1H NMR
spectrum of Pz 6 revealed two characteristic doublet signals at 8.46
and 8.20 ppm (3J=16 Hz) belonging to eight vinyl groups, a singlet
resonating at 7.07 ppm for sixteen phenyl protons, two broad slightly
distinguished doublet signals at 6.68 and 6.05 ppm for C6-CH2 eight
geminal protons, and two singlets at 3.99 and 3.88 ppm for seventy
two protons from methoxy groups. Moreover, variable-temperature
NMR resonances received from geminal C6-CH2 protons of the diazepine
ring were found within the regions of: 6.61–6.72 and 5.94–6.07 ppm at
the temperature range studied (273→333 K). The flat broad signals of
C6\CH2 group present at 6.72 and 6.07 ppm at 273 K were shifted
upfield when the temperature was raised to 333 K and appeared as
sharp doublets at 6.61 and 5.94 ppm with 2J=12 Hz (Fig. 2). Following
Angeloni and Ercolani study [5], the presence of two doublets from
C6\CH2 protons indicates that all diazepine rings are in the 6H tauto-
meric form. Noteworthy, the C6\CH2 geminal proton resonances of
5,7-disubstituted 1,4-diazepine-2,3-dicarbonitrile 5 appeared at 1.83
and 4.96 ppm and were assigned as axial and equatorial, respectively.
The downfield shift of these protons to 6.68 and 6.05 ppm for Pz 6 indi-
cates an increase of the diazepine rings planarity, causing deshielding
effect resulting from an expansion of the macrocyclic core π-electron
conjugation, which is consistent with the data previously obtained for
zinc complex of tetrakis-2,3-(5,7-diphenyl-6H-1,4-diazepino)porphyr-
azine [4].
Solvent effects on the electronic absorption spectra of Pz 6 were
determined in protic and aprotic solvents. The UV–vis spectra revealed
a broad intense Soret band with the wavelength of the maximum
absorption (λmax) in the range of 368–391 nm and broad Q-band with
λmax in the range of 660–704 nm. The positions and intensities of the
bands were affected by the type of solvent used with the most significant

J. Piskorz et al. / Inorganic Chemistry Communications 20 (2012) 13–17
15
Fig. 2. 1H NMR spectrum of porphyrazine 6 in pyridine-d5. Variable temperature 1H NMR spectra embracing the region 5.9–6.8 ppm are presented in the inset above. Symbols * and
x indicate residual peaks of pyridine and water, respectively.
changes observed in the Q-band region of the recorded spectra (Fig. 3,
Table 5S, Supplementary data).
and DPBF in DMF or DMSO were irradiated with monochromatic
light at wavelengths adjusted to the maximum absorption of the Q-
bands. The kinetics of subsequent oxidation of DPBF by singlet oxygen
was studied by monitoring of the absorbance decrease at 417 nm and
used for calculation of singlet oxygen generation yield value
(ΦΔ =0.11) in DMF. A decreased generation of singlet oxygen in
DMSO seems to result from aggregation.
As the broad and split Q-band present in the structure of Pz 6 is not
typical of symmetrical complexes, its aggregation behavior at different
concentrations was studied in the UV–vis in DMSO and DMF (Fig. 4S,
Supplementary data). The statistical analysis of the linear correlations
between absorbance values of the Q1- and Q2-sub-bands and concentra-
tions of the Pz 6 revealed that the Beer–Lambert law was not obeyed in
the range of all nine concentrations studied for both solvents. However,
when the analyses were repeated for the lowest six concentrations, the
Beer–Lambert law turned out to be obeyed for DMF solutions. The
studies indicate that the Pz 6 aggregates appear both in DMF and
DMSO solutions, with stronger tendency in DMSO, which might explain
decreased singlet oxygen generation of the latter described above. In
addition, it has been recently shown by Tarakanov et al. for 5,7-(4-tert-
butylphenyl) substituted diazepinoporphyrazines that the observed
broad and split Q-band may result from dimerization and strong exciton
coupling between two adjacent Pz units [26].
It was found that the Q-band red shift was the largest when pyridine
was used as a solvent, whereas the strongest hypsochromic shift was
observed in acetonitrile and methanol. Noteworthy, in the UV–vis
spectra recorded in acetone, chloroform, dimethylformamide, dimethyl
sulfoxide, dioxane and pyridine, the Q-band split into two sub-bands
(Q1, Q2) was observed at λmax =661–671 and 696–704 nm, respectively.
The relationships between the wavelength of the maximum absorption
of Q1- and Q2-sub-bands and the dipole moment or 1/F value of the
solvent were evaluated in order to determine processes that can be
responsible for the observed changes in the Q-band region of the
spectrum. The 1/F value is a rational function of the solvent's refractive
index (n), calculated from the equation F=(n2−1)/(2n2+1) [22]. A
linear correlation between Q1-band shifts and 1/F values with the corre-
lation index (r2) of 0.90 was found for nine solvents including acetone,
acetonitrile, benzene, chlorobenzene, dimethylformamide, ethanol,
methanol, pyridine and toluene. Moreover, a parallel relationship be-
tween Q2-band and 1/F value with r2=0.94 was observed for 5 out of
7 solvents (acetone, chloroform, dichloromethane, dioxane and pyridine)
(Fig. 2S, Supplementary data). On the other hand, the Q-band shifts were
not correlated with the dipole moments of the solvent. The linear
correlation between the Q-band shifts and 1/F values and a lack of
corresponding relationship with dipole moments, may indicate that the
changes observed in the electronic absorption spectra are mainly a result
of solvation, and there is no correlation between the coordinating
strength of the solvent and the red shift [22].
In summary, a new 5,7-disubstituted 1,4-diazepine-2,3-dicarbonitrile
was obtained, characterized and used for the synthesis of a novel
porphyrazine containing two styryl substituents coupled with each of
four diazepine rings. Significantly, X-ray study revealed two different
polymorphic structures of this 5,7-disubstituted 1,4-diazepine-2,3-
dicarbonitrile. The novel porphyrazine was characterized using UV–vis,
MS MALDI and various NMR techniques. An examination of solvent
effects indicated that the changes observed in the electronic absorption
spectra are mainly a result of solvation, and that there is no correlation
The potential photosensitizing activity of Pz 6 was evaluated by
measuring its ability to generate singlet oxygen. The relative method,
with zinc(II) phthalocyanine as
a reference and DPBF (1,3-
diphenylisobenzofuran) as a chemical quencher for singlet oxygen,
was applied (Fig. 3S, Supplementary data) [23–25]. Solutions of 6

16
J. Piskorz et al. / Inorganic Chemistry Communications 20 (2012) 13–17
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[17] Procedure for the synthesis of 5,7-bis[(E)-2-(3,4,5-trimethoxyphenyl)ethenyl]-
6H-1,4-diazepine-2,3-dicarbonitrile (5): dinitrile 3 (2.152 g, 12.5 mmol), 3,4,5-
trimethoxybenzaldehyde (4, 4.905 g, 25 mmol) piperidine (8 drops) and benzene
(100 ml) were refluxed for 7 hours. The colour of the reaction mixture changed
from yellow to red-brown. After being allowed to cool to room temperature,
the mixture was evaporated with toluene. The dry residue was chromatographed
using dichloromethane–methanol 50:1 to 20:1. Next the solid residue was
crystallized from dichloromethane–n-hexane to give dark orange crystalline
Fig. 3. The changes of the Q-band absorption for 6 in various solvents.
between the coordinating strength of the solvent and the red shift. The
potential photosensitizing activity of novel porphyrazine was expressed
by the singlet oxygen generation value of 0.11 in DMF. A decreased
generation of singlet oxygen in DMSO seems to result from aggregation.
Further experiments aiming to obtain novel analogs of potential usage
for PDT are in progress.
solid (yellowish-orange when dissolved in dichloromethane) of
42%): Rf 0.89 (dichloromethane–methanol, 10:1). UV–Vis (dichloromethane): λmax
nm (logε) 359 (4.69), 425 (4.42). MS (ES pos) m/z 529 [M+H]+, 551 [M+Na]+. MS
5 (2.763 g,
,
(ES neg) m/z 527 [M−H]− 563 [M+Cl]− 1H NMR (400 MHz; CDCl3): δH, ppm 7.55
.
(d, 2H, 3J=16 Hz, C5(7)\CH_CH), 6.79 (d, overlapped, 2H, 3J=16 Hz, C5(7)\
CH_CH), 6.77 (s, overlapped, 4H, 4×ArH), 4.96 (s, 1H, N_C\CHeq), 3.87 (s, 6H,
2×OCH3), 3.86 (s, 12H, 4×OCH3), 1.83 (s, 1H, N_C\CHax). 13C NMR (100 MHz;
CDCl3): δC, ppm 153.6, 149.5, 144.5, 141.2, 129.7, 123.7, 123.1, 115.4, 105.7, 61.0,
56.2, 39.8. Anal. Calc. for C29H28N4O6: C, 65.90; H, 5.34; N, 10.60. Found: C, 65.69; H,
5.40; N, 10.98%.
Acknowledgments
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Weigert, Hydrogen cyanide chemistry. VIII. New chemistry of diaminomaleonitrile.
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[20] Crystal data for 5: two polymorphic forms were obtained by slow evaporation of
dichloromethane–propanol (1:1) (5a, dark orange crystals with mp. 236–237 °C
dec) and ethyl acetate–hexane (1:1) (5b, yellow crystals with mp 232–233 °C dec).
The authors acknowledge financial support for the project from
the Polish Ministry of Science and Higher Education (NN401 067238).
Appendix A. Supplementary materials
Supplementary data to this article can be found online at doi:10.
1016/j.inoche.2012.02.001. The following publications refer to the ex-
perimental data contained in the Supporting Information [27].
(5a):
C29H28N4O6, M=528.55, triclinic, P-1, a=9.6434(7)Å, b=11.3819(6)Å,
c=12.4798(9)Å, α=88.093(5)°, β=74.017(7)°, γ=89.538(5)°, V=1316.1(2)Å3,
Z=2, Dc=1.334 g cm−1, μ(MoKα)=0.095 mm−1, T=130 K, 4641 independent
reflections, 3661 reflections with I>2σ(I),
Rint=0.030, θmax= 25.0°, R1(obs.)
=0.039, wR2(all)=0.092, 358 parameters. CCDC 858633. (5b): C29H28N4O6,
References
M=528.55, monoclinic, P21/n, a=13.4790(3)Å, b=14.5163(3)Å, c=13.8322(3)
Å, β=101.363(2)°, V=2653.4(1)Å3, Z=4, Dc=1.323 g cm−1
,
μ(MoKα)
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=0.094 mm−1, T=130 K, 4671 independent reflections, 3830 reflections with
I>2σ(I), Rint =0.032, θmax= 25.0°, R1(obs.)=0.036, wR2(all)=0.087, 358 parame-
ters. CCDC 858634.
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ethenyl}-6H-1,4-diazepino][2,3-b;2′,3′-g;2″,3″-l;2‴,3‴-q]
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17
porphyrazinatomagnesium(II)] (6): magnesium (0.048 g, 2,00 mmol), n-butanol
(100 ml) and one crystal of iodine were refluxed for 6 hours. Next 5 (1.056 g,
2 mmol) was added and the reaction mixture was refluxed for the next 20 hours,
and celite filtrated. In addition, celite was washed with dichloromethane, and sol-
vents were evaporated. Residual solid was chromatographed twice in dichloro-
methane–methanol, 50:1 to 10:1. Subsequent chromatography using reversed
phase (methanol–tetrahydrofuran, 20:1) gave dark green porphyrazine 6 (0.097 g,
9%): Rf 0.74 (dichloromethane–methanol, 10:1), Rf (reversed phase) 0.41 (metha-
nol–tetrahydrofuran, 20:1). UV–Vis (dichloromethane): λmax, nm (logε) 383
(5.10), 703 (4.76). MS (MALDI pos) m/z 2140 [M+H]+. MS (MALDI neg) m/z
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2138 [M−H]− 1H NMR (500 MHz; pyridine-d5): δH, ppm 8.46 (d, 8H, 3J=16 Hz,
.
8×C5(7)\CH_CH), 8.20 (d, 8H, 3J=16 Hz, 8×C5(7)\CH_CH), 7.07 (s, 16H,
16×ArH), 6.68 (d, 4H, 2J=10 Hz, 4×N_C\CH2), 6.05 (d, 4H, 2J=10 Hz,
4×N_C\CH2), 3.99 (s, 24H, 8×OCH3), 3.88 (s, 48H, 16×OCH3). 13C NMR
(126 MHz; pyridine-d5): δC, ppm 154.5, 153.9, 147.6, 142.3, 140.1, 139.1, 132.3,
129.1, 105.6, 60.5, 56.0, 39.2.
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