Synthesis and single crystal structure of a new polymorph of 5, 10, 15, 20-tetrakis-(4-chlorophenyl) porphyrin, H2TTPCl4: Spectroscopic investigation of aggregation of H2TTPCl4

Article abstract of DOI:10.1080/15421406.2018.1512546

5, 10, 15, 20-tetrakis-(4-chlorophenyl) porphyrin, H₂TTPCl₄, has been isolated as a new polymorph following the modified Adler’s method and its X-ray crystal structure solved. The new polymorph (I) crystallises in the monoclinic spac

Full text of DOI:10.1080/15421406.2018.1512546

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Synthesis and single crystal structure of a
new polymorph of 5, 10, 15, 20-tetrakis-(4-
chlorophenyl) porphyrin, H TTPCl : Spectroscopic
2
4
investigation of aggregation of H TTPCl4
2
Padma Dechan, Gauri Devi Bajju, Puneet Sood & Umar Ali Dar
To cite this article: Padma Dechan, Gauri Devi Bajju, Puneet Sood & Umar Ali Dar (2018)
Synthesis and single crystal structure of a new polymorph of 5, 10, 15, 20-tetrakis-(4-chlorophenyl)
porphyrin, H TTPCl : Spectroscopic investigation of aggregation of H TTPCl , Molecular Crystals
2
4
2
4
and Liquid Crystals, 666:1, 79-93, DOI: 10.1080/15421406.2018.1512546
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
018, VOL. 666, NO. 1, 99–113
2
https://doi.org/10.1080/15421406.2018.1512546
Synthesis and single crystal structure of a new polymorph
of 5, 10, 15, 20-tetrakis-(4-chlorophenyl) porphyrin,
H TTPCl : Spectroscopic investigation of aggregation
2
4
of H TTPCl
2
4
a
a
b
a
Padma Dechan
, Gauri Devi Bajju
, Puneet Sood , and Umar Ali Dar
a
b
Postgraduate Department of Chemistry, University of Jammu, Jammu, India; Advanced Materials
Research Centre, Indian Institute of Technology, Mandi, Himachal Pradesh, India
ABSTRACT
2 4
5, 10, 15, 20-tetrakis-(4-chlorophenyl) porphyrin, H TTPCl , has been
isolated as a new polymorph following the modified Adler’s method
and its X-ray crystal structure solved. The new polymorph (I) crystalli-
ses in the monoclinic space group, P2
1
/n with a ¼ 10.1574(5) Å,
ꢀ
3
b ¼ 8.9827(4) Å, c ¼ 20.9350(8) Å, b ¼ 102.532(4) , V ¼ 1864.62(15) Å ,
Z ¼ 2. The previously found polymorph, prepared using Lindsay
method was crystallised in monoclinic space group, P2
1
/a with
ꢀ
a ¼ 15.776 (13) Å, b ¼ 8.646 (3) Å, c ¼ 14.087 (5) Å, b ¼ 96.05 (5) ,
3
V ¼ 1910.7 (3) Å , Z ¼ 2. The main difference between the two
polymorphs seems to be the different packing arrangement of
molecules in their crystal lattices. The dramatic self aggregation
property of new polymorph (I) has also been investigated. The
investigation reveals that under certain conditions of solute con-
centration and pH of the media, the compound exhibits a strong
tendency to exist in a prominent self aggregated state in head-to-
tail type (j-aggregation) molecular alignment. The self association
behaviour of (I) was confirmed by UV-Vis absorption spectra,
performed in chloroform by varying concentrations and pH changes
1
and H NMR spectra, performed in deuterated chloroform at varying
concentrations and their results have been discussed in detail.
Introduction
The synthesis and X-ray crystal structure of H TTPCl belonging to monoclinic space
2
4
group, P2 /a, have been previously reported [1]. The compound was synthesized from
1
p-chlorobenzaldehyde and pyrrole using Lindsay method. The structural data have
discussed in detail the dihedral angles between the pyrrole and phenyl rings as well as
average bond lengths and bond angles between various atoms. The crystal data have
further shown that molecular structure of H TTPCl4 was consequence of steric
2
hinderances between the a-H atoms of the pyrrole and the ortho-H atoms of the phenyl
rings. The packing diagram of the molecules along the [001] axes has also been shown.
However, no further detail regarding the geometry of arrangement of molecules in the
CONTACT Gauri Devi Bajju
gauribajju@gmail.com
Postgraduate Department of Chemistry, University of Jammu,
Jammu 180006, India.
ß 2018 Taylor & Francis Group, LLC

1
00
P. DECHAN ET AL.
unit cell and various inter and intramolecular forces that stabilises the crystal in its 3D
crystal packing have been discussed. No further description of this complex has been
published since, and, indeed, metal free porphyrin chemistry in general appears not
to have been given adequate attention to date, especially if account is taken of the
interesting aspects possibly associated with the packing of molecules. In an attempt to
extend the present knowledge on H TTPCl , we recently reiterated the synthesis of
2
4
H TTPCl following modified Adler’s method [2]. As a result we were able to isolate a
2
4
new crystalline form of H TTPCl belonging to monoclinic space group, P2 /n. Single
2
4
1
crystals of this compound have been obtained and their X-ray crystal structure has
been elucidated.
Porphyrin are known to undergo strong self-aggregation in solutions [3–7] which
enables them to exhibit diverse chemical and photophysical properties [8,9]. Porphyrins
generally aggregate in a parallel manner (plane-to-plane stacking) to form a sandwich-
type arrangement (H-aggregate) or in a head-to-tail arrangement (end-to-end stacking)
to form a J-aggregate [10]. Among the various techniques available for studying
aggregation in solution, UV-vis [11–14] and NMR [13–16] spectroscopies are most
often used. This phenomenon of self aggregation in macrocylic porphyrin compounds
has always attracted us and this led us to investigate whether or not the self aggregation
property is exhibited by the new polymorph (I). Surprisingly, the compound exhibited
prominent self aggregation under certain conditions in solutions as confirmed by UV-
1
Visible and H NMR spectroscopy. The Scheme 1 represents the structure of a mono-
nuclear and j-aggregated H TTPCl .
2
4
Results and discussion
Preparation and crystallisation
Our procedure for the synthesis of solid monoclinic (P2 /n) H TTPCl (I) is different
1
2
4
to that followed previously by Hokelek & Ulku for the monoclinic (P2 /a) form. The
1
previously reported polymorph was prepared from p-chlorobenzaldehyde and pyrrole
by the Lindsey method using boron trifluoride etherate as catalyst. In ours method,
we carried out the acid catalysed condensation reaction between equivalent moles of
pyrrole and 4- chlorobenzaldehyde in the presence of propionic acid solution, followed
by addition of ethylic ether (10 mL) following modified Adler’s method [2] (Scheme 2).
This method afforded us a new polymorph, which crystallized in the form of shiny
violet crystals suitable for X-ray investigation. On completion of reaction, the needle
shaped violet crystals were obtained after leaving the reaction mixture undisturbed at
room temperature for about 10 days.
Single-crystal X-ray data collection and structure determination of (I)
The single crystal of the title compound (I) was examined under a microscope and a
suitable crystal with dimension 0.28 ꢁ 0.133 ꢁ 0.107 was selected for single-crystal X-ray
crystallography. Single-crystal X-ray diffraction data were collected on a CCD Agilent
SUPERNOVA E (Dual) diffractometer. The numerical details relating to the data

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
101
Scheme 1. (a) Structure of H TTPCl monomer (b) Fragment of the structure of j-aggregated H TTPCl .
2
4
2
4
Scheme 2. Synthetic route for (I).
collection, data processing, and refinement of the X-ray structures of the compound are
listed in Table 1 (CCDC number: 1860694).
Crystal structure and crystal packing diagrams of (I)
The Ortep representation of (I) along with the crystallographic labeling scheme is given
in Fig. 1. As expected, the 24 atoms porphyrin core is nearly planar (dihedral angle,
5
.01 Å), which shows a little but no significant distortion. On the contrary, the four
ꢀ
phenyl rings are tilted from the N2/N4/N2/N4 porphyrin core planes by 66.38 (C15)
and 88.67 (C23) showing significant out of porphyrin N4 core plane distortion [Fig. 2
ꢀ
(a)]. And as observed in the previous form [1], the driving force for the out of plane
distortion of peripheral p-chloro phenyl rings seems to be the steric interaction between

1
02
P. DECHAN ET AL.
Table 1. Numerical details of the solution and refinement of the crystal structures of (I).
Compound (I)
Chemical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
44 4 4
C H26CI N
752.49
293 (2)
monoclinic
P2 /n
1
10.1574 (5)
b/Å
8.9827 (4)
c/Å
20.9350 (8)
90.00
102.532 (4)
90.00
ꢀ
a/
ꢀ
b/
ꢀ
c/
3
Volume/Å
1864.62 (15)
Z
q
2
3
calcg/cm
1.340
3.178
ꢃ1
l/mm
F(000)
Crystal size/mm
Radiation
772.0
3
0.28 ꢁ 0.133 ꢁ 0.107
CuKa (k ¼ 1.54184)
ꢀ
2H range for data collection/
9.02 to 133.56
Index ranges
Reflections collected
ꢃ12 ꢄ h ꢄ 11, ꢃ10 ꢄ k ꢄ 7, ꢃ24 ꢄ l ꢄ 23
5828
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F
3271 [Rint ¼ 0.0182, Rsigma ¼ 0.0235]
3271/0/235
1.087
2
Final R indexes [I> ¼2r (I)]
Final R indexes [all data]
Largest diff. peak/hole / e Å
R
R
1
¼ 0.0642, wR
2
2
¼ 0.1935
¼ wR ¼ 0.2113
1
¼ 0.0759, wR
2
ꢃ3
0.70/-0.64
Figure 1. The ORTEP representation of the molecular structure with atom-labeling scheme for
compound (I). Ellipsoids are shown at 50% probability level. Hydrogen atoms are omitted for clarity.
the neighbouring phenyl and pyrrole H atoms [H18 … H16 2.719 Å, H22 … H10 2.819
Å, H3 … H15 3.025, H9-H5 3.060 Å] and the close van der Waals contact between the
pyrrole (N)H atoms [H2-H2 2.432 Å] [Fig. 2 (b)]. The inner NH groups of porphyrin
core are involved in intramolecular bifurcated N— Hꢂꢂꢂ(N,N) hydrogen bonds as shown
in Fig. 2 (b). Hydrogen bonds are listed in Table 2. The observed bond lengths and

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
103
Figure 2. (a) Side view of compound (I) along c axes, showing the out of plane distortion of the periph-
eral p-chloro phenyl rings (b) ORTEP view of compound (I) showing the bifurcated N—Hꢂꢂꢂ(N,N) hydrogen
bonds as red color dashed lines. The contact atoms are shown as blue (N) and pink (H) spheres.
Table 2. Hydrogen bonds for (I).
D—H … A
d(D-H)
0.861
0.861
d(H … A)
2.364
2.364
d(D … A)
2.903
2.923
< (DHA)
121.01
i
i
N2 —H2ꢂꢂꢂN1
ii
i
N2 —H2ꢂꢂꢂN1
120.53
Symmetry code: (i) x, y, z; (ii) 1 ꢃ x, 1 ꢃ y, 1 ꢃ z.
Table 3. Bond lengths (Å).
Cl1-C1
1.740 (3)
1.743 (4)
1.369 (4)
1.365 (4)
1.364 (4)
1.364 (4)
1.395 (4)
1.426 (4)
1.400 (4)
1.431 (4)
1.395 (4)
1.398 (4)
1.496 (4)
1.398 (4)
1.444 (4)
1.449 (4)
C12-C17
C17-C18
C17-C22
C4-C3
1.494 (4)
1.391 (5)
1.374 (5)
1.383 (5)
1.385 (5)
1.345 (5)
1.352 (5)
1.375 (5)
1.367 (6)
1.383 (6)
1.389 (5)
1.383 (5)
1.369 (6)
1.376 (5)
1.343 (6)
Cl2-C20
N1-C11
N1-C8
N2-C14
N2-C13
C14- C7
C14-C15
C13-C12
C13-C16
C7- C14
C7-C8
C4-C5
C9-C10
C15-C16
C3-C2
C2-C1
C1-C6
C18-C19
C5-C6
C19-C20
C22-C21
C20-C21
C7-C4
C11-C12
C11-C10
C8-C9
bond angles (Tables 3 and 4) of the porphyrin macrocycle of present form are not
significantly different from those of previous form.
The main difference between the present and previous form of H TTPCl is very
2
4
likely in the type of crystal packing. Fig. 3 shows the arrangement of the molecules of
present form in the unit cell along the [001] axes. For comparison one can refer the
packing arrangement of molecules in the unit cell of previous form [1] along the same
axes. In the packing diagram representation of present form, each of the eight corners

1
04
P. DECHAN ET AL.
ꢀ
Table 4. Bond angless ( ).
C8-N1-C11
C14-N2-C13
N2-C14-C7
N2-C14-C15
C7-C14-C15
N2-C13-C12
N2-C13-C16
C12-C13-C16
C14-C7-C8
C14-C7-C4
C8-C7-C4
N1-C11-C12
N1-C11-C10
C12-C11-C10
N1-C8-C7
N1-C8-C9
C7-C8-C9
106.0 (2)
109.9 (2)
127.1 (3)
107.2 (3)
125.6 (3)
126.5 (3)
106.9 (3)
126.5 (3)
125.6 (3)
116.2 (3)
118.3 (3)
125.4 (3)
110.1 (3)
124.5 (3)
125.8 (3)
110.1 (3)
124.0 (3)
116.7 (3)
125.5 (3)
117.8 (3)
121.6 (3)
120.3 (3)
C22-C17-C18
C3-C4-C7
C3-C4-C5
118.2 (3)
121.0 (3)
118.3 (3)
120.7 (3)
106.8 (3)
107.9 (3)
108.0 (3)
107.0 (3)
121.5 (4)
119.0 (3)
119.4 (3)
121.5 (3)
119.1 (3)
120.3 (3)
121.3 (3)
119.0 (3)
118.5 (4)
121.3 (4)
119.1 (3)
119.4 (3)
121.5 (3)
119.7 (4)
C5-C4-C7
C10-C9-C8
C16-C15-C14
C15-C16-C13
C9-C10-C11
C2-C3-C4
C1-C2-C3
C2-C1-C11
C2-C1-C6
C6-C1-C11
C19-C18-C17
C6-C5-C4
C20-C19-C18
C5-C6-C1
C17-C22-C21
C19-C20-C12
C21-C20-C12
C21-C20-C19
C20-C21-C22
C13-C12-C17
C11-C12-C13
C11-C12-C17
C18-C17-C12
C22-C17-C12
Figure 3. Packing of molecules of (I) along the [001] axes. Hydrogen atoms are omitted for clarity.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
105
Figure 4. Formation of two sets of offset or slipped multilayer stacks (shown by blue and green
colors) inter-linked by a single unstacked molecule (shown as pink) in (I).
as well as the body of the monoclinic unit cell is occupied by the H TTPCl monomers
2
4
(Fig. 3). The molecules at the corners are shown by blue and green colors while as the
molecule in the body of unit cell is shown as pink for clarity. One can clearly observe
from Fig. 3, that the molecules at the adjacent corners of the unit cell are stacked one
above another in a slightly slipped manner (j-type alignment). Such type of stacking is
not observed in the unit cell of previous polymorph along [001] axes [1]. In another
packing diagram representation of present form (Fig. 4), two sets of offset or slipped
multilayer stacks are formed by the corner occupied molecules that are bridged by a
single body centre occupied molecule. In each set of multilayer stacks, four porphyrin
molecules act remarkably as pairs forming two sets of dimeric pairs (a blue pair and a
green pair). The two porphyrin units in each of the two dimeric pairs are stacked one
above another in a j-type fashion through p–p interactions, with closest atom–atom dis-
tances of 3.51Å [Fig. 5 (a)]. The center-to-center and vertical distance between the two
molecules of porphyrin pairs (blue pairs and green pairs) is measured to be 8.7-8.8 Å
and 5.592 Å. In addition to p-p interactions, there are number of C–Hꢂꢂꢂp (C … C
3.51–3.78 Å) interactions that bound the two molecules in dimeric pairs [Fig. 5 (b)].
The driving force is the enthalpy driven attractive interaction between p-systems leading
to the stacks of molecules. Further, the two porphyrin pairs (blue pair and green pair)
in each of the two set of multilayer stack are inter-connected by a two points C-Hꢂꢂꢂp
(C … C 3.51 Å) interactions (shown by black dashed lines) [Fig. 5(b)]. The driving force
is the directional orientation of the C-H (donor) and C-C (acceptor) species of the
interacting porphyrin molecules of each pair. The existence of C-Hꢂꢂꢂp interactions
resulted in greater degree of slippage of stacked layers. It is interesting to note that the
H TTPCl monomer in the body of unit cell (shown as pink) is not involved in the for-
2
4
mation of stacked layers, however they interact with the molecules forming offset multi-
layers by three types of non covalent forces i.e p-p (C … C 3.51-3.58 Å), C–Hꢂꢂꢂp
(C … C 3.56–3.75 Å) weak C-H … Cl (H … Cl 3.28-3.29 Å) (Fig. 6).
Absorption spectroscopy
Fig. 7 depicts a typical monomeric (blue) and j-aggregated (olive green) absorption
spectra of (I) in chloroform. The typical UV-vis spectra of porphyrins feature two

1
06
P. DECHAN ET AL.
Figure 5. Offset or slipped face-to-face stacking geometry in the crystal lattice of (I) stabilised by
pꢂꢂꢂp (a) and CHꢂꢂꢂp (b) interactions. The atoms involved in directional interactions are shown by
orange (C) and pink (H) spheres. The molecule in the body of unit cell is omitted for clarity.
distinct absorption bands, namely B (or soret) band and Q-bands, that are attributed to
ꢅ
p ꢃ p transition within the highly conjugated porphyrin p-system. To confirm the
aggregation of present form of H TTPCl in pure chloroform, we measured the absorp-
2
4
tion spectra at two different concentrations at room temperature. The absorption spec-
ꢃ6
trum of free base H TTPCl measured at lower concentration i.e. ꢆ 4.0 x 10 M
2
4
exhibited an intense Soret band (B band) at 419 nm and four weak Q bands centered
on 514, 550, 591 and 648 nm respectively (Fig. 7). The spectrum corresponded for non-
aggregated monomeric complex, since no spectral change was observed with significant
dilution of this solution. On measuring the spectra at slightly higher concentration
ꢃ3
ꢆ3.0 ꢁ 10 M, an intense and a narrow absorption B band that was red shifted from
4
19 to 422nm, also followed by very small red shift and increased absorbance of Q
bands was observed. The red shift of absorption bands, especially B band is indicative
of porphyrin self aggregation through head-to-tail molecular ordering [17,18].
On measuring the absorption spectra in acidic media (pH ¼ 4), a split soret bands
appeared [Fig. 8 (a)]. The splitting of the Soret band into two individual Lorentzian
bands located around 420 and 448nm respectively was the result of a tendency to form

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
107
Figure 6. Directional interaction of H TTPCl monomer lying in the body of unit cell (shown as pink)
2
4
with neighbouring monomers (shown as blue and green) occupying each of eight corners of the unit
cell of (I) by (pꢂꢂꢂp) (a), (C-Hꢂꢂꢂp) (b) and (C-HꢂꢂꢂCl) (c) hydrogen bonding interactions. The contact
atoms are shown as orange (C), purple (H) and dark green (Cl) spheres.

1
08
P. DECHAN ET AL.
ꢃ6
Figure 7. (a) The UV/Vis absorption spectra of monomeric (blue, 4.0 x 10 M) and j-aggregated
ꢃ3
H TTPCl (I) (olive green, 3.0ꢁ 10 M) in CHCl at room temperature (b) enlargement of soret band
2
4
3
regions (arrow signifies shift in the monomer B band towards higher wavelength).
Figure 8. (a) The UV/Vis absorption spectra of H TTPCl (I) in CHCl at pH ¼ 4 (green) and pH ¼ 3
2
4
3
(magneta) (b) enlargement of Q band regions.
aggregates. Here the bands centered around 420 and 448nm are attributed to the mono-
meric and that of aggregated H TTPCl . In the acidic media the addition of protons to
2
4
the nitrogen atoms in the center of porphyrin ring induces the partial positive charge
Fig. 9) in the central part of the molecule [19]. The dication generations leds to gradual
(
decrease of the monomer absorption B band at 420nm and appearance of sharp and nar-
row red shifted band (known as j-band) at 448nm. This was also followed by increase in
the intensity of Q I band, which is forbidden otherwise. The red shift of the Soret band

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
109
Figure 9. Structure of the H TTPCl (I) porphyrin dication (H TTPCl42þ) at pH ¼ 4 and lower.
2
4
2
is attributed to a side-by-side aggregation and a formation of J-aggregates. At pH ¼ 3,
the monomer absorption B band diminished completely [Fig. 8 (a)]. and a high intensity
j-band appeared. Also the QII, QIII, QIV bands were almost nearly diminished leaving
behind the high intensity QI band [Fig. 8 (b)]. The QI band was bathochromic shifted
from 647 to 664nm. Therefore in the high ionic strength media, the Q bands were
reduced to only one, red shifted towards 664nm accompanied by significant increase in
intensity. The decrease in the number of Q bands was attributed to increase in the sym-
metry (D2h to D4h) of the porphyrin by protonation, and generation of the dication spe-
cies [19]. It can be noted from Fig. 8 (a) that in the high ionic strength media,
H TTPCl exhibited the spectra of hyper p-type. In addition to the Soret band around
2
4
4
3
00 nm, there appeared an extra absorption band at kmax ꢆ364 nm. The extra band at
64nm may be attributed to the charge transfer transitions from the lone pair p orbitals
*
of the peripheral chlorine atoms to empty p orbitals of porphyrin.
1
H NMR spectroscopy
1
The self aggregation of H TTPCl (I) was also studied by H NMR spectroscopy, and
2
4
1
the results showed that aggregation occurs at high molar concentration. The H NMR
spectra of a typical monomeric (blue) and self aggregated (olive green) H TTPCl in
2
4
deuterated chloroform is shown in Fig. 10 (a). While selected regions of the spectra are
ꢃ5
given in Fig. 10 (b). At low solute concentration i.e. ꢆ 5 X 10 M, notably sharp reso-
nance signals appeared at d 8.87(s), 8.17-8.15(d), 7.79-7.77(d) and -2.84(s) for ortho
(Hc), meta (Hb), beta (Ha) and amino pyrrole protons (Hd). The spectrum corre-
sponded for non- aggregated monomeric complex, since no change in the position as
well as shape of resonance peaks were observed on dilution of the solution. However at
ꢃ3
higher concentration ꢆ 5 X 10 M, the intensities of mononuclear resonance signals
fell off drastically and a broader upfielded peaks appeared. The decrease in the intensity

1
10
P. DECHAN ET AL.
1
ꢃ5
Figure 10. (a) Hmr spectra (400 MHz pulse FT) of monomeric (blue, 5 X 10 M) and j-aggregated
ꢃ3
(
olive green, 5 X 10 M) H TTPCl (I) in CDCl . Extra peaks at d 7.2 p.p.m and 1.5-1.6 p.p.m is due to
2
4
3
presence of undeuterated chloroform and water molecules (b) Magnified view of ortho, meta, beta
and amino pyrrole proton signals.
ꢃ3
followed by slight broadening of resonance signal at ꢆ 5 X 10 M signified that aggre-
gation had already set at this concentration [20]. The shifting of resonance signals was
due to the additional magnetic field generated by the ring current of another macro-
cycle lying in close proximity in aggregated condition [21]. The higher tendency of the
H TTPCl (I) to aggregate in chloroform presumably reflects the lower solvating power
2
4
1
of chloroform for this compound. Because the H NMR spectrum of H TTPCl sharp-
ened up at concentrations around 10 M and lower, this concentration can be roughly
considered as the critical aggregation concentration in this solvent.
2
4
ꢃ5
Conclusion
In summary, we have reported the single crystal molecular structure of second poly-
morph of H TTPCl which crystallizes in the monoclinic space group, P2 /n. In its
2
4
1

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
111
crystal structure, each of the eight corners as well as the body of monoclinic unit cell is
occupied by H TTPCl monomers. The molecules occupying the corners of the unit cell
2
4
formed two sets of offset or slipped (j-type) multilayer stacks that are interlinked by a
H TTPCl molecule lying in the body centre of unit cell by three types of non covalent
2
4
forces i.e. pꢂꢂꢂp, C-Hꢂꢂꢂp and weak intermolecular C-HꢂꢂꢂCl interactions. In each set of
multilayer stacks, four porphyrin molecules form two sets of dimeric pairs. The two
molecules in each dimeric pairs are bound together by various pꢂꢂꢂp and C-Hꢂꢂꢂp inter-
actions and two dimeric pairs are interlinked by a two point C-Hꢂꢂꢂp interactions. The
analysis of the optical absorption spectra of H TTPCl in pure chloroform solution indi-
2
4
ꢃ6
ꢃ3
cated that at low concentration ꢆ 10 M, the molecules exists as simple monomers,
however at higher concentration ꢆ 10 M, they tend to aggregate in a head to tail
manner (j-aggregation). The most important feature observed in the acidic media at
pH ¼ 4, was the appearance of low intensity monomer B band and a sharp high inten-
sity j-band. As the ionic strength of the media increases at pH ¼ 3, the monomer B
band completely disappeared leaving behind a narrow energetic j-band and an intense
1
QI band. The concentration dependent H NMR spectra of H TTPCl revealed that the
2
4
ꢃ5
compound exists as discrete monomers at concentration ꢆ 10 M and lower. Above
this concentration, the compound exhibited dramatic self aggregation leading to signifi-
cant quenching and broadening of resonance signals.
Experimental
Chemicals
The analytical grades chemicals were used for the synthesis of free base H TTPCl (I).
2
4
Pyrrole, 4-chlorobenzaldehyde, propionic acid and diethylether were purchased from
sigma Aldrich and were used as received.
Meaurements
1
UV-Visible spectra were obtained on PG spectrophotometer; model T-90. H NMR
spectra were recorded on Bruker spectrometer, model AV 400 N (400 MHZ), using
CDCl as solvent and TMS as internal reference.
3
Synthesis
The new polymorph of H TTPCl was synthesized following modified Adler’s acid cata-
2
4
lysed condensation method [2] as shown in Scheme 2. To the boiling solution of pro-
pionic acid (50mL) containing 0.05 moles of 4-chlorobenzaldehyde, fitted with a water
condensor, 0.05 moles of pyrrole was added dropwise with vigorous stirring. The mix-
ture was allowed to reflux for 30-40 min, followed by addition of small amount (10mL)
of ethylic ether to cause rapid crystallisation. The reaction was monitored by TLC in a
dichloromethane/n-hexane (30:70 v/v) system. After completion of the reaction, the
reaction mixture was allowed to cool at room temperature and then left undisturbed for
about 10 days. A needle shaped shine violet crystals of (I) were obtained in 65% yield.

1
12
P. DECHAN ET AL.
Solution and refinement of the crystal structure of compound (I)
Reflection data were measured at 293(2) K. The crystal was mounted under paratone oil
and to get relative intensity data, the single crystal analysis was collected on a CCD
Agilent SUPERNOVA E (Dual) diffractometer using monochromated Cu-Ka radiation
(
k ¼ 0.154184 Å) at 293(2) K. Using Olex2 [22], the structure was solved with the
ShelXS [23] structure solution program using Direct Methods and refined with the
ShelXL [23] refinement package using Least Squares minimisation. The positions of all
the atoms were obtained by direct method. All non hydrogen atoms were refined aniso-
tropically. The remaining H- atoms were refined with isotropic temperature factors,
1
.2 Ueq of their parent atoms. Crystallographic data (cif) has been deposited with the
Cambridge Structural Data Centre (CCDC) with reference number- 1860694.
Acknowledgment
This research was supported by CSIR (Council of Scientific and Industrial Research) India (grant
No. 09/100(0190)/2016-EMR-I).
ORCID
Padma Dechan
Gauri Devi Bajju
http://orcid.org/0000-0003-2783-4884
http://orcid.org/0000-0002-6143-8853
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