Synthesis and photochemical characteristics of novel tribenzoporphyrazines possessing peripherally annulated tetrahydrodiazepine and diazepine rings

Article abstract of DOI:10.1016/j.poly.2010.12.049

Novel tribenzoporphyrazines possessing peripherally annulated tetrahydrodiazepine and diazepine rings were synthesized and characterized, and the substituent effects on their absorption spectra in various solvents and on singlet oxygen generation were stu

Full text of DOI:10.1016/j.poly.2010.12.049

Polyhedron 30 (2011) 1004–1011
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and photochemical characteristics of novel tribenzoporphyrazines
possessing peripherally annulated tetrahydrodiazepine and diazepine rings
b
a
c
d
Tomasz Goslinski a, , Jaroslaw Piskorz , Dawid Brudnicki , Andrew J.P. White , Maria Gdaniec ,
⇑
Wojciech Szczolko a, Ewa Tykarska a
a Department of Chemical Technology of Drugs, Poznan University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan, Poland
b Department of Inorganic and Analytical Chemistry, Poznan University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan, Poland
c Department of Chemistry, Imperial College, London SW7 2AZ, United Kingdom
d Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel tribenzoporphyrazines possessing peripherally annulated tetrahydrodiazepine and diazepine rings
were synthesized and characterized, and the substituent effects on their absorption spectra in various
solvents and on singlet oxygen generation were studied. Solvatochromic effects of tribenzoporphyrazines
dissolved in a range of protic and aprotic solvents were evaluated by monitoring the changes in the UV–
Vis spectra. The correlation between the Q-band shift towards longer wavelengths and the refractive
index of the solvent indicated that the solvatochromic effects are mainly a result of solvation rather than
coordination processes. The potential photosensitizing activity of novel tribenzoporphyrazines was eval-
uated by measuring the ability of singlet oxygen production, which is the result of the interaction
between an activated photosensitizer and oxygen. This experiment proves promising photosensitizing
activity of novel styryldiazepinotribenzoporphyrazine, which is an efficient singlet oxygen generator
with a UD value of 0.44, although this value is a little lower than that of zinc phthalocyanine.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 27 November 2010
Accepted 31 December 2010
Available online 19 January 2011
Dedicated to D.Sc. Joanna Zeidler.
Keywords:
Diazepine
Linstead macrocyclization
Porphyrazine
Solvatochromic effect
Spectroscopy
1. Introduction
in the 1H-form, even after acidic solvation in CF3COOH. These mac-
rocycles are far from being entirely planar, and the mutual struc-
Porphyrazines (pzs), including tribenzoporphyrazines, are
synthetic analogs of porphyrins, which are present in nature. Their
structural modifications embrace metal inclusion to the macrocy-
cle core and peripheral substitution, which results in a significant
modulation of their electrochemical and optical properties.
Peripherally modified pzs can be substituted in the b positions
with sulfur, oxygen and nitrogen residues or have five-, six- and
seven-membered rings bound to both b,b positions [1,2]. Porphyr-
azines have been investigated as sensitizers for photodynamic
therapy [3], metal ion and gas sensors [4], precursors for optical
data recording systems, electrochromic displays, magnetic, elec-
tronic and conductive materials for nanotechnology [5–9].
tural and electronic interaction between planar porphyrazine and
non-planar diazepine rings is of great interest. Following Donzello
et al. [12], the UV–Vis spectra of these macrocycles in basic, acidic
and neutral media confirmed the multifaceted participation of the
external diazepine rings through tautomeric and protonated forms
to electron sharing within the entire metal-macrocycle framework.
Non-linear optical investigations have shown that diazepinopor-
phyrazine complexes behave in solution like reverse-saturable
absorbers (RSA), which show reduced transmittance with
increased irradiation. Lately low-symmetry tribenzoporphyrazines
with annulated 6H-1,4-diazepine rings have been synthesized and
subjected to spectroscopic studies [13,14]. In addition to the stud-
ies embracing the diazepinoporphyrazines, Barrett and Hoffman
[15] have published the synthesis, characterization and photo-
chemistry of novel tetrahydrodiazepinoporphyrazine and its seco-
derivative.
For more than 10 years Ercolani and Stuzhin [1,10,11] have
reported the synthesis, characterization and applications of a
new class of porphyrazines carrying peripherally annulated diaze-
pine rings. The 1,4-diazepine ring, that contains six
p-electrons
annulated to the free-base porphyrazine and its numerous metal
complexes, exists in the stable 6H-tautomeric form and has been
considered as quasi-aromatic. Complexes of Mn(II) and Li(I) exist
Donzello et al. [10] suggested that the physical properties of
this new class of complexes can be modulated by operating appro-
priate substitutions in the 5, 6 and 7 positions of the external dia-
zepine rings. This study aims to present a strategy leading to
further functionalised diazepino- and tetrahydrodiazepino-
porphyrazines. The newly synthesized tribenzoporphyrazines
⇑
Corresponding author. Tel.: +48 61 854 66 33; fax: +48 61 854 66 39.
E-mail address: tomasz.goslinski@ump.edu.pl (T. Goslinski).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.12.049

T. Goslinski et al. / Polyhedron 30 (2011) 1004–1011
1005
were studied for the substituent effects on their absorption spectra
2.1.3. 6-Ethoxycarbonylmethyl-4,5,6,7-tetrahydro-1,4,5,7-tetra-
in different solvents and on singlet oxygen generation.
methyl-1H-1,4-diazepine-2,3-dicarbonitrile (6)
NaH (60% in mineral oil, 0.068 g, 1.7 mmol) was suspended in
DMF (15 mL) and stirred for 30 min at ꢀ15 °C. Next, 5 (0.200 g,
0.763 mmol) in DMF (5 mL) was added over 30 min, and then the
mixture was stirred for another 30 min. (CH3)2SO4 (0.170 mL,
1.80 mmol) in DMF (2 mL) was added dropwise over 15 min at
ꢀ15 °C. The mixture was stirred for 2 h, poured into ice water
(50 mL) and then extracted with dichloromethane (3 ꢁ 50 mL).
The solvent was evaporated and the residual solid was chromato-
graphed (n-hexane–ethyl acetate 7:1 to 7:3) to give yellowish
crystals of meso compound 6 (0.180 g, 81%): Mp 69–70 °C, Rf 0.32
(n-hexane–ethyl acetate, 7:5). IR (neat) cmꢀ1: 2976, 2936, 2203,
1729, 1562, 1174, 1030. 1H NMR (400 MHz; CDCl3) dH, ppm: 4.18
(q, 2H, 3J = 7 Hz, CH2CH3), 3.50 (dq, 2H, 3J = 6 Hz, 2 ꢁ CHCH3),
2.93 (s, 6H, 2 ꢁ NCH3), 2.45 (m, 1H, CHCH2), 2.36 (d, 2H,
3J = 8 Hz, CH2CO), 1.29 (t, 3H, 3J = 7 Hz, CH2CH3), 1.19 (d, 6H,
3J = 7 Hz, 2 ꢁ CHCH3); 13C NMR (100 MHz; CDCl3) dC, ppm: 172.0
(CO), 115.1, 114.9, 61.0, 58.7, 39.4, 35.6, 32.7, 14.5, 14.2 (CH2CH3).
MS (EI) m/z: 290 [M]+Å. MS (ES): 313 [M+Na]+, 329 [M+K]+, 275
[MꢀCH3]ꢀ. HRMS (EI) m/z: 290.1737 (calc. for [M]+Å 290.1743).
Anal. Calc. for C15H22N4O2: C, 62.05; H, 7.64; N, 19.30. Found: C,
62.11; H, 7.67; N, 19.21%.
2. Experimental
2.1. Synthesis
The known compounds ethyl 3-acetyl-4-oxopentanoate (2a)
[16–18], ethyl 4-oxo-4-phenyl-3-(phenylcarbonyl)butanoate (2b)
[19], 5-methyl-7-phenyl-6H-1,4-diazepine-2,3-dicarbonitrile (9)
[20] and 5-[(E)-2-(4-methoxyphenyl)ethenyl]-7-phenyl-6H-1,4-
diazepine-2,3-dicarbonitrile (11a) [21] were synthesized according
to the literature procedures and their modifications.
2.1.1. 5,7-Dimethyl-6-ethoxycarbonylmethyl-6H-1,4-diazepine-2,3-
dicarbonitrile (4)
Diketone 2a (5.880 g, 31.60 mmol), diaminomaleonitrile
3
(3.420 g, 31.60 mmol) and oxalic acid dihydrate (0.200 g,
1.59 mmol) in benzene (63 mL) were refluxed under a Dean–Stark
receiver for 41 h. The solvent was then evaporated and the residual
solid was chromatographed (n-hexane–ethyl acetate, 7:3 to 7:4).
Crystallization from n-hexane–ethyl acetate gave yellowish crys-
tals of 4 (1.000 g, 12%): Mp 147–149 °C, Rf 0.42 (n-hexane–ethyl
acetate, 1:1). IR (neat) cmꢀ1: 2987, 2927, 2223, 1731, 1446, 1173,
1022, 948, 878. 1H NMR (400 MHz; CDCl3) dH, ppm: 4.26 (q, 2H,
3J = 7 Hz, CH2CH3), 3.27 (d, 2H, 3J = 8 Hz, CH2CO), 2.15 (s, 6H,
2 ꢁ CH3), 1.90 (t, 1H, 3J = 8 Hz, CH), 1.32 (t, 3H, 3J = 7 Hz, CH2CH3).
13C NMR (100 MHz; CDCl3) dC, ppm: 169.6 (CO), 152.6, 122.0,
114.2, 61.9 (OCH2), 53.8, 32.0, 22.2, 14.1 (CH2CH3). MS (EI)
m/z: 258 [M]+Å, 229 [MꢀCH3CH2]+, 213 [MꢀCH3CH2O]+, 185
[MꢀCH3CH2OCO]+, 171 [MꢀCH3CH2OCOCH2]+. MS (ES) m/z: 259
[M+H]+. HRMS (EI) m/z: 258.1116 (calc. for [M]+Å 258.1117). Anal.
Calc. for C13H14N4O2: C, 60.45; H, 5.46; N, 21.69. Found: C, 60.53;
H, 5.35; N, 21.55%.
Crystal data for 6: C15H22N4O2, M = 290.37, orthorhombic, Pca21,
a = 18.9315(7), b = 9.2846(3), c = 8.8695(3) Å, V = 1559.00(9) Å3,
Z = 4, Dc = 1.237 g cmꢀ3
,
l
(Mo K
T = 130 K, Xcalibur, Eos diffractometer, 2180 independent reflec-
tions, 1779 reflections with I > 2 (I), Rint = 0.025, hmax = 25.3°,
a
) = 0.09 mm–1, colorless prism,
r
R1(obs) = 0.033, wR2(all) = 0.068, 195 parameters, 1 restraint.
2.1.4. Tetrakis(6-pentoxycarbonylmethyl-4,5,6,7-tetrahydro-1,4,5,7-
tetramethyl-1H-1,4-diazepino)[2,3-b;20,30-g;200,300-l;2000,3000-q]porphy-
razinatozinc(II) (7)
Diazepine
6 (0.196 g, 0.676 mmol), zinc acetate (0.062 g,
0.34 mmol), pentanol (2 mL) and DBU (0.100 mL, 0.676 mmol)
were added together and stirred for 16 h at 130 °C. The solvent
was then evaporated with toluene and the residual oil was chro-
matographed three times (n-hexane–ethyl acetate 7:3 to 1:1) to
give a blue unseparable mixture of the diastereoisomeric porphyr-
azines 7 (0.017 g, 7%): Rf 0.21 (n-hexane–ethyl acetate 7:3). UV–Vis
Crystal data for 4: C13H14N4O2, M = 258.28, monoclinic, P21/c,
a = 9.0074(2), b = 13.4610(3), c = 11.5446(3) Å, b = 108.826(3)°,
V = 1324.88(6) Å3, Z = 4, Dc = 1.295 g cmꢀ3
,
l
(Mo K
colorless blocks, T = 173 K, OD Xcalibur 3 diffractometer, 4423 inde-
pendent reflections, 3398 reflections with I > 2 (I), Rint = 0.022,
a ,
) = 0.09 mmꢀ1
r
hmax = 32.3°, R1(obs) = 0.039, wR2(all) = 0.121, 174 parameters.
(dichloromethane) kmax, nm (log
e): 348 (4.47), 560 (4.33). IR (neat)
cmꢀ1 2928, 1733, 1578, 1465, 1377, 1275, 1167. 1H NMR
:
2.1.2. 5,7-Dimethyl-6-ethoxycarbonylmethyl-4,5,6,7-tetrahydro-1H-
1,4-diazepine-2,3-dicarbonitrile (5)
(500 MHz; d5-pyridine) dH, ppm: 4.26 (overlapped, 8H, 8 ꢁ CHCH3),
4.24 (s, 24H, 8 ꢁ NCH3), 4.17 (t, 3J = 7 Hz, 8H, 4 ꢁ OCH2), 3.16 (m,
4H, 4 ꢁ CHCH2), 2.81 (m, 8H, 4 ꢁ CH2CO), 1.56 (m, 8H,
4 ꢁ OCH2CH2), 1.52 (m, 24H, 8 ꢁ CHCH3), 1.22 (m, 16H,
4 ꢁ CH2CH2CH3), 0.79 (t, 3J = 6 Hz, 12H, 4 ꢁ CH2CH3). 13C NMR
(126 MHz; d5-pyridine) dC, ppm: 173.6 (CO), 152.1, 152.0, 136.7,
136.3, 64.5, 60.5, 41.9, 38.5, 32.3, 28.4, 28.0, 22.2, 16.7, 13.8
(CH2CH3). MS (MALDI TOF) m/z 1394 [M + H]+.
NaBH4 (0.204 g, 5.40 mmol) was added in three portions to a
suspension of diazepine 4 (0.664 g, 2.57 mmol) in methanol
(20 mL) at ꢀ5 °C over 45 min. The mixture was then stirred for an-
other 1.5 h at room temperature. The solvent was evaporated and
the residual solid was diluted with water (20 mL) and extracted
with ethyl acetate (total amount 250 mL). Chromatography (n-hex-
ane–ethyl acetate, 7:1 to 1:1) gave diazepine 5 (0.607 g, 90%): Mp
149–150 °C, Rf 0.82 (n-hexane–ethyl acetate, 2:3). IR (neat) cmꢀ1
:
2.1.5. (6-Pentoxycarbonylmethyl-4,5,6,7-tetrahydro-1,4,5,7-tetra-
3342, 2984, 2209, 1730, 1536, 1460, 1277, 1175. 1H NMR
(300 MHz; CDCl3) dH, ppm: 4.13 (q, 2H, 3J = 7 Hz, CH2CH3), 3.48
(bs, 2H, 2 ꢁ NH), 2.99 (q, 2H, 3J = 6 Hz, 2 ꢁ NHCH), 2.22 (s, 3H,
CHCH2CO), 1.26 (t, 3H, 3J = 7 Hz, CH2CH3), 1.22 (d, 6H, 3J = 7 Hz,
2 ꢁ CHCH3). 1H NMR (400 MHz; DMSO-d6) dH, ppm: 5.95 (s, 2H,
2 ꢁ NH), 4.04 (q, 2H, 3J = 7 Hz, CH2CH3), 2.88 (q, 2H, 3J = 6 Hz,
2 ꢁ NHCH), 2.03 (overlapped, 2H, CH2CO), 2.01 (overlapped, 1H,
CHCH2), 1.17 (t, 3H, 3J = 7 Hz, CH2CH3), 1.08 (d, 6H, 3J = 6 Hz,
2 ꢁ CHCH3). 13C NMR (75 MHz; CDCl3) dC, ppm: 173.6 (CO),
116.4, 109.4, 60.8, 58.3, 47.1, 26.0, 20.7, 14.1 (CH2CH3). 13C NMR
(100 MHz; DMSO-d6) dC, ppm: 173.3 (CO), 117.2, 107.9, 60.0,
57.3, 48.0, 25.8, 19.9, 14.0 (CH2CH3). MS (ES) m/z: 261 [MꢀH]ꢀ,
285 [M+Na]+. Anal. Calc. for C13H18N4O2: C, 59.53; H, 6.92; N,
21.36. Found: C, 59.32; H, 6.56; N, 21.17%.
methyl-1H-1,4-diazepino)[2,3-q]tribenzo[b,g,l]porphyrazinatozinc(II)
(8)
Diazepine
6 (0.102 g, 0.350 mmol), phthalonitrile (0.448 g,
3.50 mmol), zinc acetate (0.353 g, 1.92 mmol) and DBU
(0.575 mL, 3.85 mmol) were added to pentanol (3 mL) and refluxed
for 24 h. The reaction mixture was cooled to room temperature and
the solvent was evaporated with toluene (2 ꢁ 50 mL). The residual
oil was chromatographed twice (n-hexane–ethyl acetate 7:5 and n-
hexane–ethyl acetate 7:1 to 7:1.5) to give the light blue porphyr-
azine 8 (0.036 g, 13%): Rf 0.70 (n-hexane–ethyl acetate, 7:5). UV–
Vis (DMSO): kmax, nm (log e
): 349 (4.21), 667 (4.31). 1H NMR
(400 MHz; d5-pyridine) dH, ppm: 9.75 (m, 4H, ArH), 9.54 (d, 2H,
3J = 6 Hz, ArH), 8.18 (m, 6H, ArH), 4.51 (s, 6H, 2 ꢁ NCH3), 4.38
(dq, 2H, 3J = 7 Hz, 2 ꢁ CHCH3), 4.18 (t, 2H, 3J = 7 Hz, OCH2), 3.26

1006
T. Goslinski et al. / Polyhedron 30 (2011) 1004–1011
(m, 1H, CHCH2), 2.92 (d, 2H, 3J = 7 Hz, CH2CO), 1.68 (d, 6H, 3J = 7 Hz,
2 ꢁ CHCH3), 1.55 (p, 2H, 3J = 7 Hz, OCH2CH2), 1.18 (m, 4H,
CH2CH2CH3), 0.74 (t, 3H, 3J = 7 Hz, CH2CH3). 13C NMR (100 MHz;
d5-pyridine) dC, ppm: 173.8 (CO), 154.6, 154.1, 153.9, 153.0,
139.4, 139.2, 139.0, 136.8, 129.6, 129.5, 64.8, 61.5, 42.7, 39.5,
32.4, 28.6, 28.2, 22.4, 17.2, 14.0 (CH2CH3). MS (MALDI TOF) m/z
781 [M+H]+.
0.38 (dichloromethane–methanol, 20:1), Rf (reversed phase) 0.30
(methanol–tetrahydrofurane, 10:1). UV–Vis (DMSO) kmax nm
(log
): 358 (4.55), 658 (4.52), 692 (4.55). 1H NMR (400 MHz; d5-
,
e
pyridine) dH, ppm: 9.72 (s, 6H, ArH), 8.95 (d, 2H, 3J = 7 Hz, ArH),
8.26 (dh, 1H, @CH), 8.21 (m, 2H, ArH), 8.16 (m, 2H, ArH), 8.10 (m,
2H, ArH), 7.89 (d, 1H, 3J = 16 Hz, @CH), 7.68 (t, 2H, 3J = 7 Hz, ArH),
7.60 (d, 1H, 3J = 7 Hz, ArH), 7.10 (s, 2H, ArH), 3.95 (s, 3H, OCH3),
3.84 (s, 6H, 2 ꢁ OCH3). 13C NMR (100 MHz; d5-pyridine) dC, ppm:
156.5, 154.3, 141.6, 140.6, 140.3, 140.0, 139.9, 139.7, 137.8,
132.1, 131.5, 130.3, 130.2, 130.0, 129.9, 129.7, 129.3, 129.1,
129.0, 128.4, 123.4h, 105.8, 60.8, 56.2, 37.2. MS (MALDI TOF) m/z:
821 [M+H]+.
2.1.6. 5-[(E)-2-(2,4-Dimethoxyphenyl)ethenyl]-7-phenyl-6H-1,4-
diazepine-2,3-dicarbonitrile (11b)
Dinitrile 9 (0.200 g, 0.848 mmol), 2,4-dimethoxybenzaldehyde
(0.141 g, 0.848 mmol), piperidine (4 drops) and benzene (8.5 mL)
were refluxed for 16 h. The color of the reaction mixture changed
from yellow to red-brown. After the solvent had been evaporated,
the dry residue was chromatographed in dichloromethane and
crystallized from dichloromethane–n-hexane to give a bright red
precipitate (yellowish-orange after being dissolved in dichloro-
methane) of 11b (0.135 g, 41%): Mp 233–235 °C dec, Rf 0.31 (n-
hexane–ethyl acetate, 7:5), 0.20 (dichloromethane). UV–Vis
2.2. Photochemical and solvatochromic studies
All measurements were carried out on a Hitachi U-1900 spec-
trophotometer. All solvents were obtained from commercial sup-
pliers and were used without further purification, with the
exception of acetone, ethyl acetate, methanol, ethanol, n-hexane,
pyridine and dichloromethane, which were distilled prior to mea-
surements. UV–Vis spectra were recorded in the range 300–
900 nm.
(dichloromethane) kmax, nm (log e): 252 (4.35), 311 (4.33), 427
(4.36). 1H NMR (400 MHz; DMSO-d6) dH, ppm: 8.18 (d, 2H,
3J = 7 Hz, ArH); 7.92 (d, 1H, 3J = 16 Hz, @CH), 7.61 (t, 2H, 3J = 8 Hz,
ArH), 7.54 (t, 2H, 3J = 8 Hz, ArH), 6.97 (d, 1H, 3J = 16 Hz, @CH),
6.59 (s, 1H, ArH), 6.57 (d, 1H, ArH), 5.74 (bs, 1H, N@C–CHeq),
3.88 (s, 3H, OCH3), 3.81 (s, 3H, OCH3), 2.17 (bs, 1H, N@C–CHax).
13C NMR (100 MHz; DMSO-d6) dC, ppm: 163.5, 160.0, 151.9,
151.1, 140.6, 133.0, 132.9, 130.8, 130.5, 129.0, 123.6, 122.0,
121.8, 116.2, 116.0, 115.9, 106.6, 98.3, 55.8, 55.6, 39.5h. MS (ES)
m/z: 381 [MꢀH]ꢀ, 383 [M+H]+, 405 [M+Na]+. Anal. Calc. for:
The photooxidation reaction of 1,3-diphenylisobenzofuran
(DPBF) was used to determine singlet molecular oxygen (1Dg) gen-
eration by the photosensitizers following lately presented method-
ologies [22–24]. The kinetics of DPBF photooxidation were studied
by observing the decrease of the absorbance at kmax = 417 nm. The
efficiency of singlet oxygen generation was measured in DMSO
solutions (3.0 mL) (no oxygen bubbled) using the relative method
with zinc phthalocyanine (ZnPc, Sigma–Aldrich) as a reference
and DPBF as a scavenger for singlet oxygen. Solutions of the sensi-
tizers (absorbance < 0.2 at the irradiation wavelength) ZnPc
C
23H18N4O2 ꢁ 0.25H2O: C, 71.40; H, 4.82; N, 14.48. Found: C,
71.38; H, 4.59; N, 14.47%.
2.1.7. 5-Phenyl-7-[(E)-2-(3,4,5-trimethoxyphenyl)ethenyl]-6H-1,4-
diazepine-2,3-dicarbonitrile (11c)
(0.82 ꢁ 10ꢀ5 mol/dm3),
8
(2.45 ꢁ 10ꢀ5 mol/dm3), 12 (1.95 ꢁ
10ꢀ5 mol/dm3) in DMSO containing DPBF (3.35 ꢁ 10ꢀ5
,
Dinitrile 9 (0.208 g, 0.882 mmol), 3,4,5-trimethoxybenzalde-
hyde (0.173 g, 0.882 mmol), piperidine (5 drops) and benzene
(20 mL) were refluxed for 24 h. The color of the reaction mixture
changed from yellow to red-brown. After the solvent had been
evaporated, the dry residue was chromatographed using dichloro-
methane–methanol 10:1 and n-hexane–ethyl acetate 2:3. Next the
solid residue was crystallized from n-hexane–ethyl acetate to give
a bright red precipitate (yellowish-orange after being dissolved in
dichloromethane) of 11c (0.233 g, 64%): Mp 190 °C dec, Rf 0.82
(dichloromethane–methanol, 10:1), 0.47 (n-hexane–ethyl acetate,
4.60 ꢁ 10ꢀ5, 4.64 ꢁ 10ꢀ5 mol/dm3, respectively) were prepared in
the dark and irradiated in their Q-band region with light from an
ordinary Philips lamp (230 V, 75 W). High-energy wavelengths
were filtered out by passing the incident beam through a cut-off
Schott KC17 filter (650 nm). The distance between the lamp and
the UV–Vis cuvette was 30 cm and the light intensity was set to
8.5 mW/cm2 (measured by a radiometer RD 0.2/2 with a TD probe,
Optel). Measurements of the sample and reference under the same
conditions enabled quantum yield calculations by direct compari-
son of the slopes in the linear region of the semi-logarithmic plots
of ln A0/A vs. irradiation time obtained (in seconds) for the samples
and the corresponding slopes obtained for the reference. The sin-
glet oxygen quantum yields UD(sample) = (ksample/kZnPc) ꢂ (AZnPc/Asam-
ple)ꢂUD(ZnPc), where UD(ZnPc) is the singlet oxygen quantum yield for
2:3). UV–Vis (dichloromethane) kmax, nm (log e): 255 (4.29), 323
(4.28), 409 (4.34). 1H NMR (400 MHz; DMSO-d6) dH, ppm: 8.22
(d, 2H, 3J = 7 Hz, ArH), 7.91 (d, 1H, 3J = 16 Hz, @CH), 7.60 (m, 1H,
ArH), 7.54 (t, 2H, 3J = 7 Hz, ArH), 7.10 (d, 1H, 3J = 16 Hz, @CH),
7.03 (s, 2H, ArH), 5.75 (s, 1H, N@C–CHeq), 3.81 (s, 6H, 2 ꢁ OCH3),
3.68 (s, 3H, OCH3), 2.21 (s, 1H, N@C–CHax). 13C NMR (100 MHz;
DMSO-d6) dC, ppm: 153.1, 151.3, 150.7, 145.5, 140.1, 133.2,
132.8, 130.5, 130.1, 129.0, 123.8, 123.4, 122.4, 116.0, 115.8,
106.1, 60.1, 56.0, 39.5h. MS (ES) m/z: 413 [M+H]+, 435 [M+Na]+.
Anal. Calc. for: C24H20N4O3: C, 69.89; H, 4.89; N, 13.58. Found: C,
69.65; H, 5.13; N, 13.30%.
the reference (ZnPc) in DMSO
(UD(ZnPc) = 0.67) [25], ksample
(k9 = 0.0005 sꢀ1 and k12 = 0.0041 sꢀ1) and kZnPc (0.0029 sꢀ1) are
the DPBF photobleaching rates in the presence of the samples
and reference, respectively. AZnPc and Asample are the absorbances
at the Q-band (area under the absorption spectra from 520 to
800 nm) of the samples and the reference, respectively.
2.3. Crystallography
2.1.8. {5-Phenyl-7-[(2E)-(3,4,5-trimethoxyphenyl)ethenyl]-6H-1,4-
diazepino}[2,3-q]tribenzo[b,g,l]porphyrazinatomagnesium(II) (12)
Magnesium (0.063 g, 2.6 mmol), butanol (40 mL) and a catalytic
amount of iodine were refluxed for 24 h. Then diazepine 11c
(0.100 g, 0.243 mmol) and phthalonitrile (0.307 g, 2.40 mmol)
were added and the reaction mixture was refluxed for 21 h. After
Celite filtration, butanol was evaporated off with toluene. The solid
residue was chromatographed (dichloromethane–methanol 35:1
to 10:1). Subsequent chromatography using a reversed phase col-
umn (methanol–tetrahydrofuran 10:1) gave 12 (0.028 g, 14%). Rf
Single crystals of 4 and 6 were obtained at room temperature by
slow evaporation of ethyl acetate–n-hexane solutions. The struc-
tures were solved by direct methods with SHELXS97 and were
refined with SHELXL97 by full matrix least-squares based on F2
[26]. All non-hydrogen atoms were refined anisotropically. All H
atoms were generated geometrically, with C–H = 0.93–0.98 Å, and
refined as riding on their carriers, with Uiso(H) = 1.2Ueq(C) and
1.5Ueq(C) for methyl groups. Details on data collection and refine-
ment, fractional atomic coordinates, anisotropic displacement

T. Goslinski et al. / Polyhedron 30 (2011) 1004–1011
1007
parameters, full list of bond lengths and angles in CIF format have
been deposited at the Cambridge Crystallographic Data Centre.
3. Results and discussion
3.1. Synthesis
Following the procedure of Tanaka et al. [19], the 1,3-diketones
1a and 1b were coupled with ethyl bromoacetate by treatment
with NaH in THF to give 2a and 2b, respectively (Scheme 1). Sub-
sequent condensation of 2a with diaminomaleonitrile (3), accord-
ing to the method reported by Begland et al. [27] using oxalic
acid in benzene, led to the novel dicyanodiazepine 4.
X-ray study showed that the 6-substituted dicyanodiazepine
ring of 4 has a non-planar molecular structure (Fig. 1). The diaze-
pine ring exhibits a slightly distorted boat conformation with a
mirror plane through atom C6 and bisecting bond C2–C3. The
dinitrile side of the ring is flattened due to the aromatic character
of this part of the ring. Both methyl groups are located on the same
side of the ring, opposite to the hydrogen at C6 which is placed axi-
ally over the diazepine ring. The other C6-ethoxycarbonylmethyl
substituent approaches an equatorial position. Conformational as-
pects of trisubstituted 1,4-diazepine-2,3-dicarbonitriles have been
examined so far for various derivatives differentiated at the C5, C6
and C7 positions, and revealed that their conformation is a conse-
quence of the C6 center chirality and ring atropoisomerism. These
compounds typically prefer a conformation in which the C6 substi-
tuent (provided it is not a t-butyl group) is in the equatorially dis-
posed position [28]. In the solid state 4 is present in the form of the
6H tautomer, similarly to the previously obtained diazepine com-
pounds [11]. Unfortunately, condensation of 2b with 3 using oxalic
acid in benzene or P2O5 in ethanol did not lead to diazepine prod-
uct formation (no examples have been found in the literature [29])
and only mono-condensed intermediates were isolated.
Fig. 1. The molecular structures of 4 and 6 showing the atom-labeling scheme
(displacement ellipsoids are shown at the 50% probability level). The methyl and
methylene hydrogens are omitted for clarity.
that the dinitrile part (N1, C2, C3, N4) of the ring and C6 are copla-
nar with C5 and C7, forming up-and-down waves. Interestingly,
the configurations at C5 and C7 indicate that this molecule is in
fact a meso achiral diastereoisomer (Fig. 1). According to the
X-ray structures of 4 and 6, and a 1H–1H NOESY NMR study of 5
(Table 1S, Fig 1S, Supplementary data), it seems that the reduction
Dicyanodiazepine 4 was reduced to the tetrahydrodiazepine 5
using sodium borohydride in methanol, and the latter was dime-
thylated to 6 using the conditions (NaH, (CH3)2SO4 in DMF) re-
ported by Baum and co-workers [15]. An X-ray study showed
R
N
R
R
N
N
N
N
N
N
N
O
O
O
O
NH2
NH2
(i)
(ii)
(iii)
O
O
O
+
O
O
O
N
R
N
R
R
3
4
5
R = H
1a
1b
2a
2b
R = CH3
R = C6H5
R = CH3
(iv)
6
R = CH3
R = C6H5
R
N
N
N
N
N
N
N
N
N
N
N
N
(v)
(vi)
N
N
Zn
N
R
R
6
N
N
Zn
N
R
N
N
N
N
N
N
N
N
R
8
R = CH2COOC5H11
7
R = CH2COOC5H11
Scheme 1. Reagents and conditions: (i) 2a [16–18] – NaH, THF, 0 °C, 1 h; next BrCH2COOC2H5, rt, 48 h (83%); 2b [19] – NaH, THF, 0 °C, 1 h; next BrCH2COOC2H5, rt, 48 h (74%);
(ii) (CO2H)2 (cat.), benzene, reflux, 41 h (12%); (iii) NaBH4, CH3OH, ꢀ5 °C, 45 min; next rt, 1.5 h (90%); (iv); NaH, DMF, ꢀ15 °C, 1 h; next (CH3)2SO4, ꢀ15 °C, 2 h 15 min (81%);
(v) Zn(OAc)2, DBU, nPeOH, 130 °C, 16 h (7%); (vi) phthalonitrile, Zn(OAc)2, DBU, nPeOH, 130 °C, 24 h (13%).

1008
T. Goslinski et al. / Polyhedron 30 (2011) 1004–1011
reaction of 4 involves the diastereoselective addition of a hydride
to C5 and C7 from the less crowded, concave side of the ring.
Compound 6 was used in a macrocyclization reaction with zinc
acetate and DBU in pentanol to give the novel symmetrical por-
phyrazine 7 in 7% overall yield as a mixture of stereoisomers. Var-
ious NMR techniques were found to be useful to fully characterize
the structure of 7 (Table 2S, Fig 2S, Supplementary data). Mixed
macrocyclization of 6 with a 10-fold excess of phthalonitrile,
applying zinc acetate and DBU in pentanol, gave the novel light
blue tribenzoporphyrazine 8 in 13% overall yield. Tribenzopor-
phyrazine 8 was separated from Zn(II)–phthalocyanine by column
chromatography on silica using n-hexane–ethyl acetate, 7:1 to
7:1.5.
Ar
N
N
N
N
N
N
N
N
(i)
H
O
+
Ar
9
10a-c
11a-c
OCH3
OCH3
OCH3
OCH3
OCH3
Ar:
b
a
c
H3CO
Tribenzoporphyrazine 8 protons present in the
a-positions of
the annulated benzene rings were observed in the lowest field re-
gion at 9.54 and 9.75 ppm, whereas b-protons appeared as a mul-
tiplet at 8.18 ppm (Table 3S, Fig. 3S, Supplementary data). Such
protons shifts present for benzo-fused rings to the porphyrazine
core have been lately explained by a strong deshielding effect of
N
OCH3
OCH3
OCH3
N
N
N
N
N
the macrocyclic p
-ring current [13]. The 1H–1H COSY spectrum of
(ii)
Mg
N
N
11c
8 revealed connectivities in the benzo-fused part, C5–C6–C7 frag-
ment of tetrahydrodiazepine ring and a pentoxy fragment of the
pentoxycarbonylmethyl substituent. The 1H–1H NOESY cross-
peaks gave information on the spatial orientation of the C5- and
C7-methyl groups and C5- and C7-hydrogens, as well as the C6-
pentoxycarbonylmethyl group and C6-hydrogen. For the C5- and
C7-methyl groups, with a 1H signal at 1.68 ppm, a large nuclear
Overhauser effect (NOE) to the neighboring C6–CH2 protons reso-
nating at 2.92 ppm and N–CH3 protons resonating at 4.51 ppm
was observed. A parallel weak NOE signal was observed between
the C6–H proton and C5- and C7-methyl groups, while the C6-H
proton showed a large NOE to the neighboring C5- and C7–H pro-
tons. Moreover, the C6–CH2CO protons gave a weak NOE signal to
the OCH2 protons resonating at 4.18 ppm, belonging to the pent-
oxycarbonylmethyl group. Other NOE effects for N–CH3 and the
adjacent benzo-fused part with 1H signals respectively at 4.51
and 9.54 ppm were observed. The NMR 1H–1H NOESY experiment
suggests that the tetrahydrodiazepine tribenzoporphyrazine 8 is a
meso-diastereoisomer, similar to that observed for the precursor
meso-dinitrile 6.
A synthetic study indicated that a direct approach leading to
novel diazepinoporphyrazines using diaminomaleonitrile conden-
sation with modified aromatic diketones (like 2b, Scheme 1)
cannot be applied. In order to obtain novel functionalized diazepi-
noporphyrazines, an attempt was made to check the reactivity of
styryldicyanodiazepines in the macrocyclization reaction, which
were recently synthesized by Horiguchi and co-workers
[21,30,31]. Although styryldicyanodiazepines have been known
for 10 years, no attempt, to our knowledge, has been made so far
to use them as precursors for the preparation of styryldiazepino-
porphyrazines [29].
Firstly, a two-step synthesis of the known dicyanodiazepine 9
was performed by the Horiguchi et al. procedure (Scheme 2)
[21]. Condensation reactions of 9 with 4-methoxybenzaldehyde
(10a), 2,4-dimethoxybenzaldehyde (10b) and 3,4,5-trimethoxy-
benzaldehyde (10c) gave the known diazepine 11a [21] and novel
diazepines 11b and 11c, respectively. Macrocyclization reaction
trials using diazepines 11a–11c revealed that the number and po-
sition of the methoxy groups have an influence on the reactivity in
the macrocyclization reactions. Diazepine 11c, containing a trime-
thoxyphenyl substituent, showed the best reactivity, but under
Linstead conditions gave an inseparable mixture of isomers that
were difficult to characterize. Consequently, a mixed macrocycliza-
tion reaction of diazepine 11c with a 10-fold excess of phthalonit-
rile led to the novel styryldiazepinotribenzoporphyrazine 12,
which was successfully separated from Mg(II)-phthalocyanine
N
N
12
Scheme 2. Reagents and conditions: (i) 11a – [21]; 11b – piperidine (cat.), benzene,
reflux, 16 h (41%); 11c piperidine (cat.), benzene, reflux, 24 h (64%); (ii)
phthalonitrile, Mg(OnBu)2, nBuOH, reflux, 21 h (14%).
–
using silica gel 90 C18-reversed phase for column chromatography
with methanol–tetrahydrofurane 10:1.
Tribenzoporphyrazine 12 protons present in the a-positions of
the annulated benzene rings were observed in the lowest field re-
gion at 9.72 ppm, whereas the b-protons appeared as multiplets at
8.10, 8.16 and 8.21 ppm, which is similar to 8 and corresponds to
the literature data [13]. The 1H–1H COSY spectrum of 12 revealed
connectivities in the benzo-fused part, vinyl part and C5-phenyl
ring. The vinyl part protons belonging to the styryl substituent at
C7 resonate at 8.26 and 7.89 ppm with a 3J value of 16 Hz, very
characteristic for trans-isomerism present in a styryl moiety (Table
4S, Fig. 4S, Supplementary data). The 1H–1H NOESY cross-peaks
gave information on the spatial orientation of the C7 substituted
styryl moiety. For the vinyl proton at 8.26 ppm, a large NOE signal
to the neighboring protons belonging to the benzo-fused part at
9.72 ppm and a weaker NOE signal to the C5-phenyl group protons
at 8.95 ppm were observed. For 12, no signals attributable to the
C6–CH2 protons of the diazepine ring (CH2 in 6H- or CH and NH
in the 1H-tautomeric form) were observed. Donzello et al. [13]
found out that the rates of the possible tautomerism and/or confor-
mational transformation of the diazepine ring are comparable with
the nuclear relaxation time, causing strong line broadening and the
disappearance of the resonance signals.
3.2. Solvatochromic effects
The solvatochromic effects of tribenzoporphyrazines 8 and 12
dissolved in a range of protic and aprotic solvents were evaluated
by monitoring the changes in the UV–Vis spectra (Fig. 2). The elec-
tronic absorption spectra of 8 and 12 revealed a broad intensity
Soret band (B-band) in the range 352–365 nm and an intense,
broad, diffused or split Q-band in the range 600–750 nm, which re-
sulted from the symmetry reduction of the
The significant intensity of this band is a result of
in the macrocyclic system [2,11–13], when going from a symmet-
rical to a low symmetry porphyrazine. As both tribenzoporphyra-
p
-chromophore [13].
p
ꢀ
p⁄ transitions

T. Goslinski et al. / Polyhedron 30 (2011) 1004–1011
1009
Fig. 2. Normalized UV–Vis spectra of 8 and 12 in different solvents.
Fig. 3. Plot of the wavelength kmax of the Q-band vs. the refractive index of the
solvent described by the rational function F = (n2 ꢀ 1)/(2n2 + 1) for (a) 8; (b) 12
(sub-band Q1); (c) 12 (sub-band Q3); where n stands for the refractive index of the
solvent: (1) 1-chloronaphthalene, (2) dimethyl sulfoxide, (3) dichloromethane, (4)
dioxane, (5) tetrahydrofuran, (6) triethylamine, (7) ethanol, (8) acetone, (9)
acetonitrile, (10) ethyl acetate, (11) methanol, (12) pyridine, and (13) n-hexane.
zines are unsymmetrical, the Q-band region is relatively broad and
may overlap with nꢀp⁄ transitions as a result of partial conjuga-
tion of N atom lone pairs of the boat-shaped diazepine rings in
the 6H-form with the central p-chromophore. Broad research per-
formed by Ercolani and Stuzhin [12] on a group of symmetrical dia-
zepine annulated porphyrazines indicated the nꢀp⁄ transitions can
mix with
pꢀ
p⁄ transitions and gain in intensity, appearing in the
chloroform was used as the solvent. It is noteworthy that the pre-
viously obtained tribenzoporhyrazines, possessing an annulated
6H-diazepine ring, revealed in the Q-band two well-separated
absorptions appearing at 650–660 and 690–700 nm [13].
The correlation between the Q-band shift towards longer
wavelengths and the refractive index of the solvent was tested to
evaluate the solvatochromic effects [23]. The wavelength corre-
sponding to the maximum of the Q-band, kmax, was plotted against
the rational function F = (n2 ꢀ 1)/(2n2 + 1) of the solvent’s refrac-
tive index n (Fig. 3), according to known procedures [23,32]. This
dependence is linear, even though the influence of the solvent’s
dielectric constant on the solvatochromic shift is neglected here.
Simultaneously, it was checked that for 8 and 12 the Q-band shift
Q-band. A spectral feature characteristic for diazepinoporphyra-
zines is an additional sub-band present in the Q-band region.
The positions and intensities of some bands in 8 and 12, espe-
cially the Q-band, were also affected by the type of solvent used
and aggregation (Table 5S, Supplementary data). For 8, the Q-band
was present at kmax = 635–677 nm. It was found that the Q-band’s
red shift was the greatest when chloroform was used as the solvent
and an additional Q-band split (635 and 677 nm) was observed. For
dioxane, besides the Q-band at 663 nm, an additional band at
727 nm was observed. As follows from Fig. 2, for 12 Q-band com-
ponents of similar or different intensities, Q1–Q3, were present
at kmax = 645–659 nm, 669–699 and 668–729, respectively. The
separation of the resulting sub-bands, which is further discussed
for Q1 and Q3, strongly depends on the properties of the solvent,
which eliminated vibrational structure as the origin of this split.
In the UV–Vis spectra of 12, recorded in ethyl acetate, triethyl-
amine, ethanol, pyridine, benzene, tetrahydrofurane, dioxane,
1-chloronaphthalene and chloroform, the intense Q-band was split
into three sub-bands (Q1–Q3). In the UV–Vis spectra of 12
recorded in acetonitrile, acetone and dimethyl sulfoxide, the Q1-
and Q3-sub-bands were found, whereas in toluene, chlorobenzene,
methanol and dichloromethane, the Q1- and Q2-sub-bands were
observed. It was found that the Q-band red shift was greatest when
was not correlated with the dipole moments (l) of the solvents
tested. A linear correlation for 8 between the Q-band shifts and
1/F values with the correlation index R2 = 0.9474 was found for
nine solvents (Fig. 3). A better correlation between the Q-band
shifts and 1/F values suggests that the solvatochromic effects for
8 are mainly the result of solvation rather than coordination pro-
cesses [23]. Changes in the UV–Vis spectra of tribenzoporphyrazine
12 and relations between the Q-band shifts (kmax), including
Q1- and Q3-sub-bands and 1/F values, are shown in Fig. 3 and
are presented in Table 5, Supplementary data. It was found
that the correlation indices for 10 solvents between Q1- and

1010
T. Goslinski et al. / Polyhedron 30 (2011) 1004–1011
Q3-sub-band shifts and 1/F values were R2 = 0.9143 and
R2 = 0.9275, respectively. Summarizing, the linear nature of the
plot suggests that the red shifts in the Q-band are mainly a result
of solvation rather than coordination and there is no correlation
between the coordinating strength of the solvent and the red shift.
A coordinating solvent, such as tetrahydrofuran, gives nearly the
same Q-band shift (653 nm) as benzene and dichloromethane
(652 nm), confirming that coordination of the solvent does not play
a significant role in the red shift.
phyrazines 8 and 12 were irradiated with light above 650 nm.
Upon interaction with singlet oxygen, DPBF was oxidized and
decomposed, and this was observed in the UV–Vis spectra as a de-
crease of the absorbance at 417 nm (Fig. 4). This band is a result of
DPBF maximum absorption and tribenzoporphyrazine Soret-band
overlapping.
The lack of change in the Q-band intensity during irradiation of
12 indicates its good stability and resistance. DPBF was completely
oxidized by 12 in 10 min, while the same effect using zinc phtha-
locyanine (ZnPc) as a reference was reached after 20 min. This
experiment shows promising photosensitizing activity for the
new tribenzoporphyrazine 12, which is an efficient singlet oxygen
generator with a UD value of 0.44, although it is a little lower than
that of ZnPc (UD = 0.67 [25]).
Tribenzoporphyrazine 8, upon singlet oxygen generation mea-
surement, showed a lower activity, with completed oxidation of
DPBF after 104 min and a UD value of 0.08. A small change in
the Q-band intensity of 8 due to phototransformation (a decrease
of the Q-band at 667 nm and an increase of the X-band at 730–
740 nm) was observed, but this process occurs much slower than
the singlet oxygen production. Changes in absorptions of 8 during
the 104 min time of this experiment did not exceed 2.1%.
3.3. Singlet oxygen generation
The potential photosensitizing activity of the obtained novel
tribenzoporphyrazines was evaluated by measuring the ability
for singlet oxygen production, which is the result of an interaction
between an activated photosensitizer and oxygen. DPBF (1,3-diph-
enylizobenzofuran) was used as a chemical quencher, which
undergoes a cycloaddition reaction with singlet oxygen to produce
an endoperoxide [22,24,33]. Solutions of DPBF and tribenzopor-
4. Conclusion
Novel tribenzoporphyrazines possessing peripherally annulated
tetrahydrodiazepine and diazepine rings were synthesized and
characterized. NMR NOESY and X-ray diffraction experiments
established that the precursor dinitrile, the tetrahydrodiazepine
annulated tribenzoporphyrazine, was obtained as a meso-diastero-
isomer. A synthetic study indicated that the recently synthesized
styryldicyanodiazepines may be treated as precursors for the
preparation of tribenzoporphyrazines possessing an annulated sty-
ryldiazepine ring.
The novel tribenzoporphyrazines were studied for the substitu-
ent effects on their absorption spectra in various solvents and on
singlet oxygen generation. Solvatochromic effects of the tribenzo-
porphyrazines dissolved in a range of protic and aprotic solvents
were evaluated by monitoring the changes in the UV–Vis spectra.
The correlation between the Q-band shift towards longer
wavelengths and the refractive index of the solvent was tested
to evaluate the solvatochromic effects. This indicated that the
solvatochromic effects for annulated tetrahydrodiazepino- and
styryldiazepino-tribenzoporphyrazines are mainly the result of sol-
vation, rather than coordination processes.
The potential photosensitizing activity of the novel tribenzopor-
phyrazines was evaluated by measuring the ability for singlet
oxygen production, which is the result of an interaction between
the activated photosensitizer and oxygen. This experiment
proves promising photosensitizing activity of the novel sty-
ryldiazepinotribenzoporphyrazine, which is an efficient single oxy-
gen generator with a UD value of 0.44, although it is a little lower
than that of zinc phthalocyanine. Tetrahydrodiazepinotribenzopor-
phyrazine showed a lower activity for singlet oxygen generation
(UD = 0.08). The direction of this research will be continued and
reported in due course.
Acknowledgements
This study was supported by the Polish Ministry of Science and
Higher Education Grant No. N405 031 32/2052. T.G. thanks the
British Council and the Polish Ministry of Science and Higher Edu-
cation for the opportunity to participate in the British-Polish Young
Scientific Programme (YSP). T.G. thanks Professor A.G.M. Barrett
from the Imperial College in London and Professor S. Sobiak from
Fig. 4. Changes in the UV–Vis spectra under aerobic conditions in DMSO for: (a)
DPBF and ZnPc within 20 min; (b) DPBF and 8 within 104 min; (c) DPBF and 12
within 10 min; ZnPc – zinc phthalocyanine.

T. Goslinski et al. / Polyhedron 30 (2011) 1004–1011
1011
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