Structure and dynamics processes in free-base chlorins controlled by chemical modifications of macroring and aryl groups in: Meso -positions

Article abstract of DOI:10.1039/c7ra02217d

In this work we present the synthesis, detailed structural characterization and analysis of molecular motion for unsymmetrical pyrrolidine-fused chlorins employing NMR, UV spectroscopy and DFT theoretical calculations. In samples, the meso-rings were modified by substitution of hydrogen by fluorine in ortho1 and meta positions 2. The sample with perfluorinated ring 3 and phenyl derivative 4 were used as reference species. The assignment of signals was performed employing 2D NMR techniques. The rotational dynamics was examined by means of ¹H and ¹⁹F variable-temperature (VT) 1D NMR spectroscopy and 2D EXSY experiments. The synergism of steric effect between pyrrolidine ring and meso-rings is unambiguously proved. Models 1 and 3 behave very similar, aromatic rings are rigid in temperature range 233-373 K. For sample 2 and 4 the distinct molecular dynamics was revealed. The barrier of rotation depends on localization of ring in the chlorin structure. Those which are bonded in the neighborhood of pyrrolidine ring are more rigid compared to those localized on the opposite site. The temperature is a trigger which sequentially releases the rotation of aromatic group in the desired localization. Introduction of fluorine in labeled position has influence on static geometry defined by saddling angles.

Full text of DOI:10.1039/c7ra02217d

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Structure and dynamics processes in free-base
chlorins controlled by chemical modifications of
macroring and aryl groups in meso-positions†
Cite this: RSC Adv., 2017, 7, 24795
*
J. S´niechowska, P. Paluch and M. J. Potrzebowski
In this work we present the synthesis, detailed structural characterization and analysis of molecular motion
for unsymmetrical pyrrolidine-fused chlorins employing NMR, UV spectroscopy and DFT theoretical
calculations. In samples, the meso-rings were modified by substitution of hydrogen by fluorine in ortho 1
and meta positions 2. The sample with perfluorinated ring 3 and phenyl derivative 4 were used as
reference species. The assignment of signals was performed employing 2D NMR techniques. The
rotational dynamics was examined by means of 1H and 19F variable-temperature (VT) 1D NMR
spectroscopy and 2D EXSY experiments. The synergism of steric effect between pyrrolidine ring and
meso-rings is unambiguously proved. Models 1 and 3 behave very similar, aromatic rings are rigid in
temperature range 233–373 K. For sample 2 and 4 the distinct molecular dynamics was revealed. The
barrier of rotation depends on localization of ring in the chlorin structure. Those which are bonded in
the neighborhood of pyrrolidine ring are more rigid compared to those localized on the opposite site.
The temperature is a trigger which sequentially releases the rotation of aromatic group in the desired
localization. Introduction of fluorine in labeled position has influence on static geometry defined by
saddling angles.
Received 22nd February 2017
Accepted 28th April 2017
DOI: 10.1039/c7ra02217d
rsc.li/rsc-advances
to the structure of tetrapyrrolic compounds enhances their
photodynamic activity and controls chemical and spectroscopic
properties.6–9 The most important chemical modication is
Introduction
Chlorins (hydroporphyrins) belong to the big family of por-
phyrinoids, an intriguing class of macrocyclic heteroorganic
compounds widely distributed in the nature. Due to unique
physical and chemical properties porphyrinoids play a key role
in important biological processes including cell respiratory,
light harvesting, and electron transfer. They are also a mean-
ingful class of compounds from the practical point of view,
intensively studied for application in catalysis,1 electronics,2
supramolecular chemistry3 and materials science.4 In addition,
they are used as photosensitizers5 and anticancer or antibacterial
drugs6 in medicine. Excellent spectroscopic features of chlorins
are reasons why these compounds found number of spectacular
applications e.g. in photodynamic therapy, light-energy
conversion systems or synthetic models of photosynthetic
reaction centers.
replacement of hydrogen by uorine atoms or uorinated
moieties in the aromatic residues for meso-position. Skillful
introductions of uorine substituents into chlorins may
increase photostability, lipophilicity and high level of singlet
oxygen generation.10 It is well established that photonic prop-
erties of porphyrinoids are modulated by rst-order molecular
structure and conformation of meso-aryl groups with respect to
the macroring plane. When the aromatic groups of tetra-meso-
aryl-substituted porphyrin are coplanar with the macrocycle
then aryl ring would be a part of porphyrin chromophore. Great
efforts are being concentrated on the improvement of their
properties and what follows on their possible applications.
The porphyrinoid derivatives have recently attracted much
attention as components of nanomolecular machines; rotors,11,12
wheels,13 and gyroscopes.14 Application of the porphyrinoids in the
construction of different types of functional molecular systems
was reviewed by Michl and coworkers,15 Kay, Leigh, Zerbetto16 and
others.17 Both metal free, as well as metal complexes of porphyrins,
are used as building units of advanced machines. For instance,
molecular oscillator based on supramolecular complexes of
metalloporphyrin and fullerenes was described by Tashiro et al.18
Molecular gear assembling metalloporphyrins and cavitand were
reported by Kobayashi and coworkers.19 Systems based on tin(IV)
porphyrins as stator bearing at the meso-position, a monodentate
Chlorins strongly absorb light in the near infrared part of
electromagnetic spectrum and are relatively photostable.
Introduction of halogen atoms (bromine, chlorine, or uorine)
Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences,
Sienkiewicza 112, 90-363 Lodz, Poland. E-mail: marekpot@cbmm.lodz.pl
† Electronic supplementary information (ESI) available: NMR spectra, assignment
of pyrrolidine-fused chlorine 2 and 3, absorption spectroscopy, HRMS analysis of
compounds, Cartesian coordinates of computed structures of pyrrolidine-fused
chlorines, NBO analysis. See DOI: 10.1039/c7ra02217d
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Cavaleiro's37 discovery that porphyrins could act as dipolarophiles,
we synthesized target compounds. The synthesis of compounds
is a multi-step sequence and synthetic route is presented in
Scheme 1. The starting porphyrins 5 and 6 were synthesized
according to procedures described in the literature. Porphyrin 5
was prepared from aldehyde and pyrrole with a mixture of
nitrobenzene and acetic acid38 as a solvent. For porphyrin 6 we
adopted Adler and Longo procedure39 involving the heating of
equimolar amounts of the uorinated aldehyde and pyrrole in
reuxing propionic acid. In both methods crude products
were crystallized. Compounds 7 and 8 were purchased from
PorphyChem. Treatment of free-base porphyrins 5–8 with cooper
acetate in chloroform afforded the corresponding copper
complex of porphyrins. Nitration at b-position was achieved by
the reaction of copper(II) nitrate with complex 9–12 in mixture
acetic acid/acetic anhydride in chloroform in reux temperature.
Subsequent demetallation under strong acid conditions afforded
the expected b-nitro-tetra-aryloporphyrins 17–20. Aer that, the
porphyrins were converted to pyrrolidine-fused chlorins by the
reaction with azomethine ylide generated in situ from sarcosine
and paraformaldehyde.
Fig. 1 Structure of pyrrolidine-fused chlorins 1–4.
coordinating site and tridentate chelate on the different handles as
rotors were shown.20,21 Dynamics processes of porphyrinoids are
also key element in construction of molecular switches and
sensors.22 Ishihara et al. have reviewed number of derivatives
which can be used for this purpose.23 Unique complexation
properties of cyclic zinc(II) bisporphyrin with exible linker were
employed for synthesis of molecular switches with controllable
photo and electro properties.24 The photomolecular switches with
strong absorption properties of porphyrinoids were also
reported.25
The porphyrinoid derivatives can undergo complex motions
including positional displacements of submolecular compo-
nents and/or local molecular dynamics both in the liquid and
solid states. Knowledge about the nature of these processes and
tools for controlling the motion in molecular machines is a key
information determining the synthetic strategy. The best
recognized dynamics process in porphyrinoids is rotation of
aromatic rings in meso-position. Gottwald and Ullman26 were
the rst to observe rotation of the phenyl rings in meso-tetra-
phenylporphyrin. This problem was discussed in detail for
different porphyrin derivatives in review articles and
textbooks.27–29
Geometry of unsymmetrical chlorins – theoretical models
The starting point for discussion of structure and dynamic
processes for derivatives under investigation is knowledge
about preferable conformation. The static and dynamic aspects
of the conformation of meso-tetra-arylporphyrinoids were dis-
cussed in number of papers where different methodologies
were employed. In the case when the sample forms crystals with
quality suitable for monocrystal studies the X-ray crystallography
is mainly used for search of conformation. When the crystalli-
zation process fails, the alternative approaches are theoretical
calculations. It is a case of samples researched in our project as
we were not able to grow good quality crystals.
The local molecular motion of meso-aryl rings can be
restricted or eliminated by hindrance effect. In the most
common approach introducing the bulky group at b-position of
pyrrolic ring and steric interactions with adjacent residue has
inuence on the rotation barrier. Such phenomenon was re-
ported in detail by Noss et al.30 and by other authors for number
of chemically modied porphyrins. To the best of our knowledge
the literature about dynamics process in chlorins is rather
limited. Stolzenberg et al.31 reported activation barriers for
meso-aryl group rotation in metal-free and titanyl hydro-
porphyrins. It was found that activation barriers in these
Computer methods allow analyzing both the conformation
of the meso-phenyl rings and the deformation of the porphyrinoid
macrocycle, as well as the barriers of rotation of the meso-phenyl
rings (atropisomerism). The measure of nonplanar distortions
is shown by the saddling dihedral angles labelled as c1, c2, c3,
c4 (for notation used see Table 1). It is interesting to note that
values of these angles differ between derivatives. The largest
values suggesting the macrocycle deformation are found for
sample 2 and 4 while in contrast samples 1 and 3 are almost
planar. Moreover, comparison of sample 1 and 2 reveals that the
position of uorine atoms in the aryl ring is a crucial factor
inuencing the nonplanarity/planarity of macroring. Ortho-
uorines strongly interact with macrocycle leading to the at-
tening of structure. This effect in pictorial form is shown in
Fig. 2.
compounds ranged from 15.6 to 18.6 kcal molꢀ1
.
In this paper we show how dynamic processes in the chlorins
can be controlled and sequentially modulated by combination of
steric effects in macrocyclic framework and aryl residues in meso-
position. For this purpose we employ derivatives as shown in Fig. 1.
Another interesting structural feature is conformation of aryl
rings with respect to the macroring plane. In each case aryl
groups are in gauche conformation. However, more detailed
analysis and measurement of the torsional angles between the
planes of aryl groups shows intriguing features related to the
Results and discussion
Synthesis of unsymmetrical chlorins
It is well-known that 1,3-dipolar cycloaddition32–36 is an useful position of uorine in rings. The c5, c6 torsional angles are
method of transformation of porphyrins into chlorins. Based on dened as shown in Table 1. As one can see the values for
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Scheme 1 Synthetic route.
Table 1 Saddling dihedral angles of pyrrolidine-fused chlorins 1–4
Compound
c1
c2
4.65
9.65
4.98
c3
3.09
11.57
3.76
c4
1.07
9.25
1.68
c5
c6
1
2
3
4
1.31
5.19
2.28
5.68
12.56
31.98
14.36
33.79
11.14
29.25
10.95
32.83
10.12
12.04
10.05
samples 2 and 4 again are very similar. It clearly proves that and the band maxima of absorption and molar absorbance
uorine atoms which are not in direct contact with macroring coefficients were summarized in Table 2.
weakly interact with it. During further comparison of the values
The absorption spectra of 1–4 differ in respect of the posi-
of c5 and c6 we noted that the largest distinction is seen for tions and the intensity ratios of the bands as well as a molar
compound 3. It suggest that bulky uorine groups located in the absorbance coefficient. The positions of the Soret band are
neighbourhood of nitro residue “feel” the steric effect.
Concluding, the theoretical calculations and computed models
clearly show that position of substitution of uorine in the
meso-aromatic ring has strong inuence on the preferable
conformation. Thus we can anticipate that molecular dynamics
of these groups will also be distinctive.
Correlation between molecular structure and optical
properties
The absorption spectra of synthesized pyrrolidine-fused chlor-
ins 1–4 were measured in dichloromethane and toluene. Fig. 3
Fig. 2 DFT (B3LYP/6-311++g(d,p)) optimized structures of chlorins 1
shows the absorption spectra in toluene at room temperature and 2.
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Fig. 3 (Left) Absorption spectra at room temperature of pyrrolidine-fused chlorins 1–4 in toluene solution. (Right) Expansion of 440–690 nm
region of spectra. Molar concentrations of the chlorins 1–4 were roughly the same.
nearly identical with each other. Compared to the chlorin 4, the
Soret bands for uorinated analogues were moved, but the
shis are not signicant. Major changes are noticeable for Q
band. It is apparent from the absorption bands that small shis
in the absorption maxima occur as the results of substitution
and amount of uorine atoms in the chlorins. With the increase
in the number of uorine atoms in the molecule, the strongest
absorption bands are shied bathochromically compared to the
non-uorinated chlorin 4. The number and location of uorine
atoms affects also the intensity of the absorption. The highest
value of molar absorbance coefficient at room temperature in
toluene is related to chlorin 2, the next very close is for sample 4.
NMR studies of chlorins 1–4
The crucial information which is prerequisite for discussion of
local molecular motion is the precise assignment of meso-aryl
groups and their localization in the structure of chlorins. The
notation which we used in this project for labeling of A, B, C, D
aryls in meso-positions is shown in Scheme 2.
NMR spectroscopy is a technique which provides straight-
forward structural information about geometry of compounds.
For chlorins 1–4 we have carried out NMR measurements
at ambient temperature employing 1D and 2D homo- and
heteronuclear correlations. In the case of samples 1–3 which are
uorine derivatives, 19F nucleus is an additional structural
1
probe invaluable in further studies. Fig. 4 shows standard H
and 19F NMR spectra for sample 1.
For each sample a broad singlet at ꢀ1.5 to ꢀ3.5 ppm rep-
Table 2 Molar absorbance coefficient of the chlorins 1–4
resenting inner pyrrolic NH groups was observed. In all
0
0
compounds signals for H3, H21, H21 and H22, H22 found in the
range 2–6 ppm are well resolved and can be unambiguously
assigned (Fig. 4a). The spin system pattern clearly conrms that
N-methylpyrrolidine ring is connected to C2 and C3 carbons. In
other case, for substitution at C7/C8 or C12/C13 as well C17/C18
the six spin system should be observed.
Molar absorbance
Soret band
[nm]
coefficient [dm3 molꢀ1 cmꢀ1
]
Compound
in toluene
1
2
3
4
408
409
408
411
141 040
180 726
120 968
163 822
The detailed description of strategy used for assignment of
A, B, C, D aryl residues we show employing sample 1 and sample
4. In other cases the employed methodology is similar. To
specify the describing of the spatial alignment for moieties
under investigation we adopted the convention assuming that
the pyrrolidine ring is above macroring plane while nitro group
is below. Consequently, uorine or hydrogen atoms in meso-aryl
rings which are at the same side as the nitro substituent were
denoted as down, and up when they are on the opposite side.
In analysis of uorinated samples, homonuclear 1H–1H,
19F–19F 2D NMR correlations and experiments based on H–19F
1
Heteronuclear Overhauser Effect (HOESY) were found to be the
most informative. The 19F–19F COSY spectrum carried out with
proton decoupling (Fig. 5) allowed us to assign pairs of uorine
atoms belonging to individual meso-aryl rings. As can be seen, the
inuence of pyrrolidine ring and nitro group on 19F chemical
shis of neighbouring aryls in meso-position is signicant. The
distinction of d19F for up and down uorine atoms is ca. 1 ppm.
Scheme 2 General labeling and numeration in chlorins.
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Fig. 4 (a) 1H NMR spectrum of chlorin 1 and expansion of 2–6 ppm region showing H21/H21 , H22/H22 and H23 protons. (b) 19F NMR spectrum of
chlorin 1 recorded in toluene-d8 at 600 MHz.
0
0
Next, we carried out 1H–19F HOESY experiment (Fig. 6) and weaker correlation between H22 –FA-up. At the rst glance
0
assuming that this correlation, showing dipolar interactions by this correlation via 7 bonds is very surprising. However
space will enable us to distinguish spatial localization of uo- inspection of DFT optimized (at B3LYP/6-311++g(d,p) level)
0
0
rine atoms. The analysis began with H3, H21, H21 and H22, H22 structure gives reasonable explanation of this effect. Distance
˚
˚
0
0
signals for which the assignment is unquestionable. The posi- between H21 –FD-up is 2.50 A and H22 –FA-up is 3.22 A. In this case
tion of FD-up is concluded on the base of correlation between H21 the so called “J coupling through space” operates due to existence
0
and H21 (Fig. 6), while FA-up on correlation between H22 and of an interaction between antibonding orbitals. Such coupling
H
22 . FA-down shows the correlation peak with H3. FD-up and is well described in literature mostly in case of 19F–19F and
0
FD-down correlate with H18. In the same way H7 correlates with
A-up and FA-down. Correlation between H17 and two uorine signals
provides information about assignment of FC-up and FC-down
F
.
Position of FC-up and FC-down is assigned by correlation with H13.
Assignment of FB-up and FB-down was not possible, but these two
signals were assigned via correlation between H8 and H12.
Interesting effects were observed in 1H–19F HETCOR (Fig. 7)
0
spectrum which shows a strong correlation between H21 –FD-up
Fig. 5 19F{1H}–19F{1H} DQF-COSY spectrum of chlorin 1 recorded in Fig. 6 1H–19F HOESY spectrum of chlorin 1 recorded in toluene-d8.
toluene-d8. The spectrum obtained at 600 MHz spectrometer.
The spectrum obtained at 600 MHz spectrometer.
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Fig. 8 Most diagnostic part of 1H–1H COSY spectrum of compound 4
recorded at 243 K in toluene-d8. The spectrum obtained at 600 MHz
spectrometer.
Fig. 7 1H–19F HETCOR spectrum of chlorin 1 recorded in toluene-d8.
The spectrum obtained at 600 MHz spectrometer.
1H–19F coupling but also for 19F–15N, 19F–31P, 19F–77Se.40 H21
–
0
F
D-up interaction also causes additional (1.8 Hz) splitting of H21
signal in 19F non decoupled 1H spectrum. H22 –FA-up interaction
is much weaker and causes only little line broadening in 19F non
decoupled 1H spectrum (this coupling cannot be easily directly
measured and we estimated it to be 0.5 Hz).
0
9
The most diagnostic part of 1H–1H ROESY spectrum of
For structural assignment of sample 4 we employed classical
Fig.
1
NMR strategy based on the analysis of homonuclear 2D H–1H
compound 4 recorded at 243 K in toluene-d8. The spectrum obtained
at 600 MHz spectrometer.
COSY (Fig. 8) and 1H–1H ROESY spectra (Fig. 9). As in the
previous case we begun the structural study with diagnostic
0
0
signals H3, H21, H21 and H22, H22 . Knowing the chemical shis
of these signals it was possible to assign protons in b-pyrrolic
position. Proton in o-HA-up position was assigned by correlation
overlapping even in 2D experiment, and additional complica-
tion caused by chemical exchange, it was impossible to assign
meta and para protons of phenyl rings.
1
1
0
with H22 and H22 protons in H– H ROESY spectrum. Having in
mind o-HA-up correlation it was further possible to assign H7
proton in b-pyrrolic positions. In the similar way we assigned
Dynamics of meso rings
1
Having the set of assigned H and 19F signals, we were able to
H
18 using correlation with o-HD-up. Correlation between H18 and
o-HD-up as well H8 and H17 was done using 1H–1H COSY
experiment and their correlation with previously assigned H7
and H18. It was impossible to assign positions of up and down o-
protons in B and C rings. Both up/down protons were assigned
by correlation with H8 or H17 for C and B rings respectively in
1H–1H ROESY spectrum. H12 and H13 signals were assigned by
correlation with o-protons of C or B ring. Due to high
investigate the molecular dynamics of meso-aryl rings in rela-
tion to their position in the structure and in function of
temperature. In all cases we have carried out variable-
temperature (VT) NMR measurements in the range of 233 to
353 K (sample 1 and 2) and in the range of 283–353 K (sample 3)
employing toluene-d8 as solvent. Fig. 10 shows the 1D 19F VT
NMR spectra for samples 1–3.
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Fig. 11 Arrhenius plot for exchange rate of 19F signals of B (blue
square) and C (red triangle) rings for sample 2.
0.8 kcal molꢀ1 for B and C rings, respectively. These energies are
very close to each other and similar to data available in litera-
ture for another porphyrinoids (subporphyrins,41 porphyrins,
metalloporphyrins and metallo-chlorins15). Our studies unam-
biguously proved that the substitution in b-position have
signicant inuence on molecular dynamics of meso-rings. This
dynamic process can be controlled by synthesis of derivatives
substituted by uorine atom in assumed position of aromatic
group.
Further evidence conrming the distinct molecular motion
of meso aromatic groups for uorine derivatives 1–3 was ob-
tained by employing 19F{1H}–19F{1H} 2D EXSY experiment
(Fig. 12). Using this technique it is possible to observe correla-
tion between the exchanged signals even in slow chemical
exchange regime.
For sample 1 and 3 even at 353 K it was not possible to
observe correlation signals. It means that all rings are static in
the 233–353 K temperature range. It is worth to express that in
the case of 2,6-disubstituted phenyl rings, 1 steric hindrance
caused by substitution of aromatic groups has great inuence
on the rotation barrier and excludes dynamic processes in each
pyrrolidine-fused chlorin in meso-position.
The case of sample 2 is different. As we mentioned above, 1D
NMR analysis proved the molecular motion of B and C meso-
rings. To answer whether A and D rings are completely static in
NMR time scale, or if they exhibited small mobility, we per-
formed 19F{1H}–19F{1H} EXSY experiment at temperature 353 K.
In this case it was easy to observe the exchange signals between
Fig. 10 1D 19F VT NMR spectra in the range of 233–353 K of
compound (a) 1 and (b) 2. In case compound 3 (c) due to low solubility
of this compound spectra were measured starting from 283 K. The
spectra were recorded in toluene-d8 at 600 MHz.
In the case of sample 1 and sample 3 the line broadening of
19F signals caused by rotation of uorophenyl rings in meso-
positions is not observed. The only visible thermal effect is
a small change of chemical shis (temperature dri). This
temperature shi effect may be caused by changing the solva-
tion sphere and change of interactions between chlorin and
toluene molecules. Sample
2 behaves differently when
compared to 1 and 3. In this case we observed line shape effect
for uorine atoms representing B and C rings. This process
begun at 303 K. Starting from 318 K it was not possible to
observe multiplicity (doublet) of signals for B and C rings. Near
temperature 338 K signals representing B and C rings are very
broad. At 353 K we monitored two separated, quite broad
signals for averaged B and C uorine atoms. These signals
sharpened when temperature was further increased. It is worth
to express that line broadening was not observed for uorine
atoms representing A and D rings. It suggests that these resi-
dues are rigid in the broad range of temperature. Going further
with analysis of molecular motion for B and C rings we calcu-
lated (from line shape tting) exchange barriers in temperature
range 308–373 K. Having these values it was possible to calcu-
late the activation energy (Ea) of rotation from Arrhenius plot
(Fig. 11). The Ea values were found to be 18.5 ꢁ 0.5 and 17.7 ꢁ
FA-up–FA-down and FD-up–FD-down, so these signals were in slow
exchange limit. It means that B and C rings are much more
mobile than A and D rings, but all of the rings exhibit mobility
at 353 K in NMR time scale.
In the case of sample 4 we do not have such an excellent
NMR probe for analysis of molecular motion as uorine
nucleus. Thus the basic source of information is 1H NMR
spectroscopy. Fig. 13 shows the aromatic region of meso-resi-
dues in the 233–353 K temperature range.
In this case it was possible to observe lineshape effect for
ortho signals of B and C ring starting from temperature 293 K.
Coalescence of HB-up–HB-down and HC-up–HC-down pairs of signals
were observed at temperature 333 K. Further increasing of
temperature caused reducing of line widths. For A ring it was
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Fig. 12 19F{1H}–19F{1H} 2D EXSY spectra recorded for compound 1 (left), 2 (middle), 3 (right) at temperature 373 K, 353 K, 373 K, respectively. The
spectra obtained in toluene-d8 at 600 MHz spectrometer.
possible to observe lineshape effect for protons in ortho position activation energy than A ring due to additional hindrance
in A ring starting from 333 K, but it was not possible to observe caused by nitro group. Of course both of these rings have larger
coalescence. It was not possible to observe lineshape effect for D rotation activation energy then B and C ring, caused by strong
ring signals. Unfortunately, it was not possible to determine the inuence of additional N-methylpyrrolidine ring near to A and
precise value of rotation barrier due to complex 5 spin system D rings. It means that substitution at meta position has no
for each ring, additionally complicated by strong overlapping of signicant steric or electronic effect for rotation barrier.
meta and para signals. In this case we estimated only Gibbs free
energy from coalescence temperature. It was ca. ꢀ16 kcal molꢀ1
Conclusions
for B and C rings. In this case we observed similar behaviour of
meso-rings like in case 3,5-diuorophenyl analogue – B and C The major aim of our investigation is to understand and explain
rings have the smallest rotational barrier, A ring has higher the inuence of modications of the structures of uorinated
rotational barrier and D ring has the highest rotational barrier. pyrrolidine-fused chlorins on the dynamic processes. These
This observation is easy to understand – D ring has higher compounds were synthesized and characterized in detail. The
rotational dynamic of aryl rings in meso-position of chlorins was
examined by VT 1H and 19F 1D NMR spectroscopy and 19F
{1H}–19F{1H} 2D EXSY experiments. The calculated activation
energies for aryl substituents in our compounds were very
similar to other porphyrinoids. We proved that even small
modication in aryl rings may have an effect on rotation of
these rings. Our results show that introduction of atoms even as
small as uorine in ortho position in aryl rings causes an
inhibitation of rotation. This is due to the increased steric bulk
of the hydrogens in b-pyrrolic positions and uorine atoms.
Natural Bond Orbital (NBO) analysis did not reveal specic
interactions between the electron-lone-pairs of uorine atoms
and the p-cloud of the macroring (see ESI†).46 In nonuorinated
chlorin a rotational dynamic of aryl ring can be controlled by
temperature.
Experimental details
General information
The chlorins 1–4 were prepared using chemicals which were
purchased from Sigma Aldrich, TCI and used without further
purication. Reagent grade solvents were purchased from
Polish Chemicals Reagents and were distilled prior to use. Silica
gel columns for chromatography were prepared with silica
(Kieselgel 60, 200–400 mesh). All NMR experiments were run on
Fig. 13 1H VT spectra in the 233–373 K temperature range recorded in
toluene-d8 for chlorin 4. The spectra obtained at 600 MHz
spectrometer.
a 600 MHz Bruker Avance III spectrometer equipped with BBOF
1
probhead operating at 600.13, 564.69, 150.92 MHz for H, 19F
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and 13C nuclei, respectively. 2D 1H–19F HOESY, 19F–19F EXSY 1037.1 [M + H]+. Compound 12 (0.28 g, yield: 92%), MS (MALDI
and 2D 1H–1H ROESY experiments were measured with 200 ms TOF) m/z ¼ 677.3 [M + H]+.
mixing time. 1H–19F 2D HETCOR correlation was optimized for
10 Hz 1H–19F coupling constants. VT experiment was carried
General procedures for the nitration complexes of
porphyrins44
automatic with automatic mode (using modied au zgvt script)
with at least 20 min stabilization of temperature at target
temperature with automatic shimming and probhead tuning
aer temperature equilibration. The following abbreviations
were used to describe peak splitting patterns when appropriate:
br ¼ broad singled, s ¼ singlet, d ¼ doublet, t ¼ triplet, q ¼
quartet, dd ¼ doublet of doublets, bm ¼ broad multiplet and m
¼ multiplet. Coupling constants J are reported in Hz. UV-VIS
spectra were obtained on Specord S600 “Analytik jena AG”.
Mass spectra of obtained compounds were registered by
MALDI-TOF Mass Spectrometer – PerSeptive. All calculations
were carried out using the Gaussian09 program package.42 For
geometry optimization of all structures B3LYP and basis set 6-
311++ g(d,p) have been used.
Synthesis of porphyrin 5. Porphyrin 5 was prepared in
accordance to a previously described method,38 with the
following procedure. 2,6-Diuorobenzaldehyde (6.96 mL, 0.06
mol) was dissolved in a mixture of nitrobenzene (105 mL) and
acetic acid (210 mL) and the temperature was raised to 120 ꢂC.
Aerwards, pyrrole (4.2 mL, 0.06 mol) was added. The mixture
was stirred for 1 h. Then, the mixture was cooled and 30 mL
In round bottom ask cooper complex of porphyrin (0.4 mmol)
was dissolved in chloroform (275 mL) and the solution is heated
to reux. Aerwards, Cu(NO3)2$2.5H2O (2 mmol) in mixture of
acetic acid (5.5 mL) and acetic anhydrate (27.5 mL) was added.
The reaction was stirred for 2 h in reux with TLC monitoring
aer which it was washed with water, saturated solution of
sodium biscarbonate and the organic layer was dried with
MgSO4/Na2CO3. Aer evaporating the solvent, the products
were isolated by column chromatography (using a chloroform/
n-hexane as the eluent) to give: compound 13: 0.28 g, yield 80%,
MS (MALDI TOF) m/z ¼ 866.2 [M + H]+. Compound 14 0.26 g,
yields 78%, HRMS (ES+/TOF) m/z: [M + H]+ calcd for C44H22F8-
N5O2CuNa 887.0605; found 887.0582, MS (MALDI TOF) m/z ¼
866.2 [M + H]+. Compound 15 0.32 g, yield 75%, MS (MALDI
TOF) m/z ¼ 1082.1 [M + H]+. Compound 16 0.23, yield 80%, MS
(MALDI) m/z ¼ 722.3 [M + H]+.
General procedures of demetallation of copper complex45
Procedure A (for compound 17 and 18). To cooper complex
methanol was added. The crystals were ltered off and washed of b-nitro-porphyrin (0.3 mmol) dissolved in chloroform (27
with water and methanol. A sample was recrystallized from mL), concentrated H2SO4 (2 mL) was added. CF3COOH (4 mL)
dichloromethane/methanol to afford 0.34 g (11%) porphyrin as was then added to this stirred mixture. The reaction was
dark purple crystals. 1H NMR (500 MHz, CDCl3) d ꢀ2.77 (bs, continued with stirring at room temperature for 2 h, aer which
2H), 7.37–7.40 (m, 8H), 7.77–7.83 (m, 4H), 8.88 (s, 8H). MS the mixture was poured onto water (100 mL). The water phase
(MALDI TOF) m/z ¼ 759.6 [M + H]+.
was extracted with chloroform. The combined organic layers
Synthesis of porphyrin 6. The synthesis of the porphyrin 6 were dried with MgSO4/Na2CO3. Aer evaporating the solvent,
has been adapted from the synthesis reported by Alder et al.39 the residue was chromatographed (eluent : chloroform/n-
1
with slight modication. To a reuxing propionic acid (60 mL) hexane 1 : 3). Compound 17: 0.23 g, yield: 95%, H NMR (600
a 3,5-diuorobenzaldehyde (6.72 mL, 0.06 mol) and pyrrole (4.2 MHz, DMF-d7) d ꢀ2.61 (bs, 2H), 7.73–7.76 (m, 2H), 7.86–7.90 (m,
mL, 0.06 mol) was added. The reaction mixture was vigorously 6H), 8.21–8.30 (m, 8H), 9.15 (q, J ¼ 4.8 Hz, 2H), 9.42 (d, J ¼
stirred for 1 h in reux. Aer that, reaction was cooled to room 4.8 Hz, 1H) 9.47–9.51 (m, 3H), 9.79 (s, 1H), 13C NMR (151 MHz,
temperature and 30 mL methanol was added. The purple crys- DMF-d7):
d 111.73–112.26, 115.52, 117.03–117.65, 128.40,
tals were ltered off and washed with water and methanol, then 129.14, 129.40, 130.56, 130.66, 131.19, 133.00–133.31, 133.87,
dried. Porphyrin was obtained as purple crystals in 0.39 g 12% 135.76, 156.15, 161.53, 163.16, 163.55. HRMS (ES+/TOF) m/z: [M
yields. 1H NMR (500 MHz CDCl3) d ꢀ2.96 (bs, 2H), 7.29–7.34 (m, + H]+ calcd for C44H22F8N5O2 804.1646; found 804.1639, MS
4H), 7.75–7.79 (m, 8H), 8.91 (s, 1H). MS (MALDI TOF) m/z ¼ (MALDI TOF) m/z ¼ 804.7 [M + H]+. Compound 18: 0.22 g. Yield:
759.6 [M + H]+.
93%, 1H NMR (600 MHz, CDCl3) d ꢀ2.76 (bs, 2H), 7.27–7.29 (m,
2H), 7.32–7.38 (bm, 3H), 7.77–7.82 (m, 8H), 8.78 (q, J ¼ 4.7 Hz,
2H), 9.00 (t, J ¼ 5.1 Hz, 2H), 9.04 (d, J ¼ 4.9 Hz, 1H), 9.12 (d, J ¼
5.0 Hz, 1H), 9.13 (s, 1H); 13C NMR (151 MHz, CDCl3): d 104.06,
104.23, 104.37, 104.39, 104.473, 104.64, 104.70, 104.80, 117.85,
General procedures for synthesis of copper complexes of
porphyrins43
A mixture of porphyrin (0.45 mmol) in chloroform (34 mL) and 117.97, 118.10, 118.39–118.41, 118.61, 118.65–118.69, 118.74,
Cu(OAc)2$H2O (2.25 mmol) in methanol (17 mL) was stirred for 118.79, 120.69, 128.39, 129.05, 129.65, 130.09, 131.78, 135.24,
2 h at room temperature. Reaction was monitored by TLC 142.22, 142.46, 143.64, 143.86, 144.12, 145.62, 153.20, 160.53–
(hexane : chloroform 4 : 1) aer which the reaction mixture was 160.76, 162.20–162.42. HRMS (ES+/TOF) m/z: [M + H]+ calcd for
poured onto water and extracted with chloroform. The organic
C44H22F8N5O2 804.1646; found 804.1632, MS (MALDI TOF) m/z
layer was dried over Na2SO4. Aer evaporation of solvent to ¼ 804.7 [M + H]+.
dryness afforded dark pink solid of: compound 9 (0.34 g, yield:
Procedure B (for compound 19 and 20). To cooper complex
93%), MS (MALDI TOF) m/z ¼ 821.5 [M + H]+. Compound 10 of b-nitro-porphyrin (0.3 mmol) concentrated H2SO4 (2 mL) was
(0.33 g, yield: 90%), MS (MALDI TOF) m/z ¼ 821.5 [M + H]+. added. CF3COOH (4 mL) was then added to this stirred mixture.
Compound 11 (0.41 g, yield: 89%), MS (MALDI TOF) m/z ¼ The reaction continued with stirring at room temperature for
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1.5 h, aer which the mixture was poured onto water and 4.5 Hz, 2H), 8.72 (dd, J ¼ 1.3 Hz, 4.7 Hz, 1H), 8.77 (dd, J ¼ 1.1 Hz,
saturated solution of sodium biscarbonate. The water phase 4.8 Hz, 1H). 13C NMR (151 MHz, CDCl3): d 41.08, 63.52, 64.29,
was extracted with chloroform. The combined organic layers 66.58, 103.82, 104.2, 104.90, 105.28, 110.27, 110.70, 115.80,
were dried with MgSO4 and Na2CO3. Aer evaporating the 117.02–117.442, 120.76, 121.67, 125.11, 125.36, 128.09, 128.58,
solvent, the residue was chromatographed (eluent : chloroform/ 132.98, 133.41, 135.13, 135.74, 140.14, 140.35, 141.25, 144.15–
n-hexane 1 : 3). Compound 19: yield: 0.28 g, 90%, 1H NMR (600 144.34, 152.67, 153.42, 156.24, 159.49, 160.56–160.65, 161.30,
MHz, CDCl3) d ꢀ2.78 (s, 2H), 8.82 (q, J ¼ 4.7 Hz, 2H), 9.03–9.08 161.80, 162.22–162.31, 162.80, 163.00, 163.46. HRMS (ES+/TOF)
(bm, 4H), 9.18 (s, 1H), 13C NMR (151 MHz, CDCl3): d 103.27, m/z: [M + H]+ calcd for C47H29F8N6O2 861.2224; found 861.2216,
104.17, 104.45, 106.36, 113.31, 114.40–115.09, 128.42, 128.62, MS (MALDI TOF) m/z ¼ 861.8 [M + H]+. Compound 3: eluent:
129.68, 131.20, 135.36, 136.83, 138.52, 140.51, 140.79, 141.69, diethyl ether : chloroform 1 : 5, 0.058 g yield 55%, 1H NMR (600
141.88, 142.63, 143.38, 143.61, 143.82, 145.67, 145.97, 147.29, MHz, CDCl3) d ꢀ2.14 (d, J ¼ 16.5, 2H), 2.38–2.41 (m, 4H), 3.00
147.64, 153.67, 156.86, 162.57, 169.56, MS (MALDI TOF) m/z ¼ (d, J ¼ 11.4 Hz, 1H), 3.37–3.40 (t, J ¼ 8.4 Hz, 1H), 4.45 (d, J ¼
1020.5 [M + H]+. Compound 20: 0.19 g, yield: 95%, 1H NMR (600 11.5 Hz, 1H), 5.69 (t, J ¼ 9.0 Hz, 1H), 8.37 (dd, J ¼ 4.8 Hz, 1.5 Hz,
MHz, CDCl3) d ꢀ2.58 (bs, 2H), 7.73–7.83 (bm, 12H), 8.21–8.27 1H), 8.55 (d, J ¼ 4.8 Hz, 1H), 8.58 (q, J ¼ 4.6 Hz, 1H), 8.78 (d, J ¼
(m, 6H), 8.28 (d, J ¼ 7.2 Hz, 2H), 8.75 (q, J ¼ 4.6 Hz, 2H), 8.92 (t, J 4.2 Hz, 1H), 8.84 (d, J ¼ 4.7 Hz, 1H). 13C NMR (151 MHz, CDCl3):
¼ 4.6 Hz, 2H), 8.97 (d, J ¼ 4.9 Hz, 1H), 9.04 (d, J ¼ 4.9 Hz, 1H), d 40.90, 61.94, 63.69, 64.09, 96.50, 96.73, 69.50, 69.73, 105.47,
9.08 (s, 1H), 13C NMR (151 MHz, CDCl3): d 120.10, 120.58, 106.50, 107.63, 112.90, 114.85–115.37, 124.59, 125.30, 128.03,
120.85, 123.01, 126.88, 126.91, 126.96, 127.07, 128.01, 128.23, 128.67, 133.03, 133.523, 135.51, 136.37, 136.71, 137.40, 138.42,
128.40, 128.54, 128.92, 129.47, 129.91, 131.86, 134.56, 134.70, 139.11, 140.09, 140.28, 141.44, 142.18, 143.14, 143.96, 145.05,
134.71, 135.03, 135.05, 135.42, 137.97, 139.33, 140.20, 140.38, 145.50, 145.67, 146.70, 147.11, 147.34, 148.34, 153.25, 154.13,
141.11, 141.33, 141.57, 146.04, 153.09, 156.37, 156.57, MS 157.51, 161.77. HRMS (ES+/TOF) m/z: [M + H]+ calcd for
(MALDI TOF) m/z ¼ 661.7 [M + H]+.
C47H17F20N6O2 1077.1094; found 1077.1082. MS (MALDI TOF)
m/z ¼ 1077.7 [M + H]+. Compound 4: eluent: diethyl ether-
: chloroform 1 : 5, 0.062 g yield 57%, 1H NMR (600 MHz,
CDCl3) d ꢀ1.95 (bs, 2H), 2.21 (t, J ¼ 6 Hz, 1H), 2.28 (s, 3H), 2.90
General procedure for the 1,3-dipolar cycloadditions
The synthetic procedure has been reported by Cavaleiro et al.32 (d, J ¼ 12 Hz, 1H), 3.24 (t, J ¼ 9.0 Hz, 1H), 4.05 (d, J ¼ 11.4 Hz,
with slight modication. In round bottom ask a toluene (20 1H), 5.71 (t, J ¼ 9.0 Hz), 7.18–7.30 (m, 3H), 7.64–7.78 (m, 13H),
mL) solution of the b-nitro-5,10,15,20-tetraarylporphyrin (0.01 7.93–7.940 (m, 1H), 8.00 (d, J ¼ 7.2 Hz, 1H), 8.08–8.25 (m, 6H),
mmol), sarcosine (2 equiv), and paraformaldehyde (5 equiv) was 8.45 (d, J ¼ 4.2 Hz, 1H), 8.59 (q, J ¼ 4.2 Hz, 2H), 8.71 (d, J ¼
heated at reux for 5 h under a nitrogen atmosphere. Aer 2.5 h 4.2 Hz, 1H), 8.77 (d, J ¼ 4.8 Hz, 1H). 13C NMR (151 MHz, CDCl3):
the additional portions of sarcosine (2 equiv), and para- d 41.14, 63.79, 64.67, 66.99, 105.53, 112.16, 112.54, 122.98,
formaldehyde (5 equiv) were added and the reaction mixture 123.98, 124.85, 125.15, 125.26, 126.64, 126.70, 126.79, 127.43,
was reuxed for another 2.5 h period. Aer being cooled to 127.79, 127.80, 127.92, 127.93, 128.10, 128.18, 128.44, 128.46,
room temperature and evaporated, the reaction mixture was 128.67, 128.99, 132.27, 132.77, 133.15, 133.23, 133.84, 133.91,
applied on the top of a silica gel column. Compound 1: 133.98, 134.09, 135.60, 136.19, 137.81, 138.72, 140.60, 140.86,
eluent : chloroform, 0.047 g yield 43%, 1H NMR (600 MHz, 141.59, 141.62, 141.75, 153.07, 153.84, 156.37, 159.57, 717.8, MS
CDCl3) d ꢀ1.97 (bs, 2H), 2.32 (s, 3H), 2.41 (t, J ¼ 9.2 Hz, 1H), 3.06 (MALDI TOF) m/z ¼ [M + H]+.
(d, J ¼ 11.4 Hz, 1H), 3.33 (t, J ¼ 8.4 Hz, 1H), 4.37 (d, J ¼ 11.7 Hz,
1H), 5.70 (t, J ¼ 8.9 Hz, 1H), 7.26–7.36 (bm, 9H), 7.71–7.78 (bm,
Acknowledgements
4H), 8.32 (d, J ¼ 3.0 Hz, 4H), 8.51 (s, 1H), 8.59 (d, J ¼ 7.3 Hz, 2H),
8.74 (d, J ¼ 3.2 Hz, 1H), 8.80 (d, J ¼ 3.5 Hz, 1H). 13C NMR (151
MHz, CDCl3): d 41.06, 62.30, 64.06, 64.63, 98.95, 105.75, 108.93,
110.18, 110.97, 111.11–111.41, 111.57, 111.59, 111.72, 111.87,
112.31, 112.45, 116,12, 116.26, 116.40, 118.03, 118.17, 118.22,
118.33, 118.50, 118.58, 124.16, 124.96, 127.64, 128.19, 128.32,
129.00, 131.03, 131.44, 132.31, 132.61, 133.14, 135.44, 136.29,
140.01, 153.15, 154.11, 156.96, 160.85, 161.23, 161.32, 161.7,
161.82, 162.23, 162.51, 163.00, 163.35, 163.45, 163.90. HRMS
(ES+/TOF) m/z: [M + H]+ calcd for C47H29F8N6O2 861.2224; found
861.2207, MS (MALDI TOF) m/z ¼ 861.8 [M + H]+. Compound 2:
This research has been nancially supported by the Polish
National Center of Sciences (Grant No. 2013/11/N/ST5/02040).
We gratefully thank the Tomasz Pawlak for help with NBO
analysis.
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