Synthesis and spectroscopic properties of axial phenoxide and para amino phenoxide incorporated indium (III) porphyrins

Article abstract of DOI:10.1016/j.molstruc.2019.05.120

Tetrakis-4-methoxyphenyl indium(III) porphyrins containing phenolic and para amino phenolic moieties in the apical sites have been successfully prepared and characterized spectroscopically. The phases and structure evolutions of prepared porphyrins were d

Full text of DOI:10.1016/j.molstruc.2019.05.120

Accepted Manuscript
Synthesis and spectroscopic properties of axial phenoxide and para amino phenoxide
incorporated indium (III) porphyrins
Padma Dechan, Gauri Devi Bajju
PII:
S0022-2860(19)30692-1
DOI:
https://doi.org/10.1016/j.molstruc.2019.05.120
MOLSTR 26627
Reference:
To appear in: Journal of Molecular Structure
Received Date: 6 May 2019
Revised Date: 27 May 2019
Accepted Date: 28 May 2019
Please cite this article as: P. Dechan, G.D. Bajju, Synthesis and spectroscopic properties of axial
phenoxide and para amino phenoxide incorporated indium (III) porphyrins, Journal of Molecular
Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.05.120.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis and Spectroscopic Properties of Axial Phenoxide and Para Amino Phenoxide
Incorporated Indium (III) Porphyrins
Padma Dechan and Gauri Devi Bajju*
Postgraduate Department of Chemistry, University of Jammu, Jammu-180006, India
Abstract
Tetrakis-4-methoxyphenyl indium(III) porphyrins containing phenolic and para amino
phenolic moieties in the apical sites have been successfully prepared and characterized
spectroscopically. The phases and structure evolutions of prepared porphyrins were deduced
from powder X-ray diffraction (PXRD). The axial coordination of phenolic moieties induces
1
slight shift of the H NMR signals of indium porphyrin macrocycles. The measurements of
UV-Visible absorptions of porphyrins in CH2Cl2 and CH3COOC2H5 reflects that axially
ligated metal chelates at neutral pH display hyperchromicity of absorption bands compared to
unligated metal porphyrin. The most striking feature was the structural stability of indium
porphyrins under basic (pH = 10) as well as acidic media (pH = 4). On the other hand, the
metal free ligand 5, 10, 15, 20-Tetrakis-(4-methoxyphenyl) porphyrin, H2TMP (I) undergoes
J type aggregation in acidic media (pH = 4). The robustness of indium porphyrins especially
in acidic media are in strong contrary to other sitting atop (SAT) or out of plane (OOP)
complexes which are usually demetallized under acidic pH. All the prepared macro rings
exhibit negative solvatochromism reflected by the blue shift of absorption bands in
CH3COOC2H5 (more polar) than in CH2Cl2 (less polar). The photoluminescence emissions in
indium(III) species are significantly quenched relative to metal free ligand (I) due to internal
heavy atom effect and distortion of ligand plane. The quenching of fluorescence bands are
more pronounced in axially ligated metal porphyrins. The lesser excited state lifetimes of
indium(III) porphyrins relative to free base analog (I) may be ascribed to spin orbit coupling
induced by indium(III) ion in the respective metal chelates.
Key words: axial ligand; indium(III) porphyrins; solvatochromism; sitting atop (SAT);
internal heavy atom effect
Corresponding author: Gauri Devi Bajju*
E-mail: gauribajju@gmail.com
Contact No.: +91 9419145184
Introduction

ACCEPTED MANUSCRIPT
Heavy metal porphyrins exhibit remarkable optical properties. For example, introducing
Indium or Gallium metal into the central porphyrin ring has been reported to generate
desirable photophysical properties such as long lifetime of the excited triplet state, low
fluorescence lifetime, low fluorescence quantum yield (Φf), deactivation directed by the
singlet excited state, and a high quantum yield of singlet oxygen generation which are
essential in an efficient sensitizer for use in photo responsive applications such as
photodyanamic therapy [1-3]. Porphyrins and phthalocyanins offer versatile non linear
optical (NLO) properties due to their extremely high chemical and thermal stability as well as
rich photochemistry [4]. Moreover, the excited state properties of highly pi conjugated
macrocycles can be easily tuned by metal complexation, axial ligation, functionalizations
with various electron withdrawing and electro releasing substituents at the meso and beta
positions of porphyrin ring [4]. In these lines, indium porphyrins (heavy metal porphyrins)
are found to have enhanced optical limiting response [5]. For example, indium-Porphyrin
functionalized with polymethylmethacrylate (InPor-MMA26) shows good reverse saturable
absorption and reasonable positive refraction indicating their potential application in optical
limiting both at picosecond and nanosecond timescale [6]. Similarly, indium porphyrin-
osmium cluster complexes are found to exhibit remarkable optical limiting performance for
sensor protection in the visible region [7, 8]. Optical Limiting Properties of InTPP (indium
tetraphenyl-porphyrin) and axially substituted InTTP (indium tetra-p-tolyl-porphyrin) with
different axial ligands were further investigated and found that axial substitutions influence
the nonlinear optical properties of the metalloporphyrins, mainly by chanting their excited
state absorption cross-section [9]. Besides their enhanced NLO properties, indium porphyrins
have other remarkable applications. For instance, a mesoporous indium-porphyrin
framework, named JLU-Liu7 shows high adsorption performance for small gases and
selectivity for CO2, C2H4, C2H6 and C3H8 over CH4 [10]. Another novel indium porphyrin
framework named as NUPF-3 was found to possess a rarely seen 4-fold interpenetrated pts
framework with segmented pores and dense metalloporphyrin central sites [11]. Due to this
unique feature, NUPF-3 exhibits relative high CO2 uptakes. Moreover, it has good
heterogeneous catalytic property for cyclo addition of CO2 and epoxides under relatively mild
conditions with good recyclability [11]. Since the optical absorption behaviour of porphyrins
are highly sensitive to change in pH of the media [12-14], the structural stability as well as
optical behaviour of indium porphyrins in various media are needed to be investigated to
further explore their potential applications especially in the field which demands their
structural integrity under extreme conditions like presence of acid or base.

ACCEPTED MANUSCRIPT
In our previous article, we had reported that the indium(III) derivative of Tetrakis-4-
methylphenyl porphyrin are easily demetallized under acidic media [14]. It was also reported
that the indium(III) derivative of Tetrakis-4-methoxyphenyl porphyrin on the other hand was
quite stable under such environmental conditions thereby reflecting a property unusual for a
sitting atop (SAT) complex [15, 16]. Inspired by our previous work, we present the synthesis
and spectroscopic properties of Tetrakis-4-methoxyphenyl indium(III) porphyrin
[In(III)TMP]Cl, II coordinated with axial phenolic and para amino substituted phenolic
groups generating the corresponding axially coordinated metal chelates with general formula
[In(III)TMP]OPh, III and [In(III)TMP]OPh-pNH2, IV. The axial substituents with large
pi planes are expected to influence the electronic absorption, emission as well as proton NMR
spectra of unligated metal complex II. The study will clearly reveal particularly the optical
absorption properties of synthesized porphyrins in three different media conditions which is
the main aim of this work. The schematic diagram 1 shows the structures of synthesized
metal chelates III and IV.
y = H (III), NH2 (IV)
Scheme 1 Molecular structures of III and IV
2. Experimental section
2.1 Materials and reagents

ACCEPTED MANUSCRIPT
The analytical reagent (AR) grades chemicals were used for the synthesis of chelating ligand
I and its corresponding metal chelates i.e. II–IV. The AR grade Chloroform, glacial acetic
acid, pyrrole, 4-methoxybenzaldehyde, phenol, 4-amino phenol, propionic acid, concentrated
HCl and KOH pellets were all purchased from Sigma-Aldrich and were used as received. The
metal carrier, InCl3 was also purchased from Sigma Aldrich.
2.2 Measurements and Instrumentation
1
FT-IR was registered on Perkin Elmer Spectrum as KBr pellets. H NMR spectra were
recorded on Bruker spectrometer, model AV 400 N (400 MHZ), using CDCl3 as solvent and
TMS as internal reference. UV-Visible spectra were obtained on PG spectrophotometer;
model T-90, using CH2Cl2 and CH3COOC2H5 as solvents. To introduce basic and acidic
conditions in the organic solvents containing the porphyrin dyes, stock aqueous solutions of
0.1M KOH and 0.1M HCl were used. The pH values of the solutions were measured with a
pH paper. Photoluminescence emission spectroscopic studies were recorded on Cary eclipse
Agilent using CH2Cl2 as solvent at room temperature. The phase purity and crystallite sizes
of the as-prepared samples were determined from powder X-ray diffraction (PXRD) using D8
X-ray diffractometer (Bruker) at a scanning rate of 12° min−1 in the 2θ range from 0° to 50°,
with Cu Kα radiation (λ = 0.15405 nm).
2.3 Synthesis of starting material
The synthesis of the two starting materials I and II according to methods provided in the
literature [18, 19] have been carried in similar manner as discussed previously [14].
2.4 Synthesis of axial phenolic and para amino phenolic coordinated In3+ porphyrins
To a 250mL round bottomed flask containing 15mL methanolic solution of 3.086 ×10−2 mol
of phenol (III) or 3.086 ×10−2 mol of 4-aminophenol (IV) was added 6.602 × 10−4 mol of II
dissolved in 15mL chloroform. The reaction mixtures were then refluxed at 60˚C with
continuous stirring for 1 hour in dark in inert atmospheric conditions. At the end of the
reactions, the mixtures were allowed to cool at room temperature and then filtered. The
residues were washed repeatedly with pure methanol, dried and then finally re-crystallized
using ethylacetate/petroleum ether (8:2) mixtures.
III was obtained as violet solid with 70% yield. FT-IR (KBr, νmax, cm-1): 717.38 γ(C-H)ph,
800.31 γ(C-H)pyrrole, 1338.35 ν(C-N), 1571.70 ν(C=N), 2834 ν(C-H), 1062.58 ν(C-O-C)sym
,

ACCEPTED MANUSCRIPT
1
1243.86 ν(C-O-C)asym, 536.11 ν(In-N), 690.39 ν(In-O). H NMR (CDCl3, 400MHz, δ, ppm):
4.15 (s., 12H, OCH3), 7.31-7.33 (d., 8H, ArHm), 7.36-7.38 (d., 8H, ArHm), 8.05-8.07 (d., 8H,
ArHo), 8.30-8.32 (d., 8H, ArHo), 9.12 (s., 8H, βH), 6.85-6.87 (d., 2H, OPho), 6.94-6.98 (t.,
3H, OPhm,p). UV-Vis (λmax, nm, CH2Cl2): 430 (B band), 563, 606 (Q bands).
IV was obtained as violet solid with 75% yield. FT-IR (KBr, νmax, cm-1): 744.38 γ(C-H)ph,
813.81 γ(C-H)pyrrole, 1338.35 ν(C-N), 1571.70 ν(C=N), 2807.84 ν(C-H), 1091.51 ν(C-O-
C)sym, 1234.21 ν(C-O-C)asym, 520.68 ν(In-N), 669.17 ν(In-O), 3278.39 ν(NH2)sym, 3338.17
1
ν(NH2)asym. H NMR (CDCl3, 400MHz, δ, ppm): 4.15 (s., 12H, OCH3), 7.31-7.33 (d., 8H,
ArHm), 7.36-7.38 (d., 8H, ArHm), 8.05-8.07 (d., 8H, ArHo), 8.30-8.32 (d., 8H, ArHo), 9.12 (s.,
8H, βH), 6.90 (s., 2H, NH2), 6.68-6.70 (d., 2H, OPho), 6.61-6.63 (d., 2H, OPhm). UV-Vis
(λmax, nm, CH2Cl2): 430 (B band), 563, 606 (Q bands).
3. Results and Discussions
3.1 Synthesis
The synthesis of porphyrins I–IV is shown in schematic diagram 2. Porphyrins being highly
photosensitive in nature, the reactions were carried in the dark to avoid the effect of light on
the highly conjugated macro rings. Inert conditions during the metal insertion and apical
coordination of phenolic groups with indium–porphyrin unit were also maintained to ensure
absence of any moisture or oxygen which may interfere with the metallation and apical
ligation processes.

ACCEPTED MANUSCRIPT
Scheme 2 synthetic route for I–IV
3.2 FT-IR Analysis
The axial coordination of phenolic and para amino phenolic moities with the indium(III)
centre of macro ring II were characterized by FT-IR spectroscopy. Fig. 1 represents the FT-
IR spectra of macro rings I–IV. The free base porphyrin I shows N–H stretching vibration at
3317 cm-1. When indium(III) ion is coordinated with the porphyrin ring of I, the
characteristic band due to N–H stretching disappear and a new band due to In–N vibration
appear at ~ 550–500 cm-1. This is attributed to the replacement of two acidic hydrogens by
the metal ion. This also gives information about the presence or absence of I as an impurity in
the metalloporphyrins. The FT-IR spectra of metal chelates III and IV consist of peaks due to
In–O vibrations at 690.39 and 669.17 cm-1 respectively. The FT-IR spectra further reveals no
major changes in the vibration frequencies of aromatic skeleton of I after complexation and

ACCEPTED MANUSCRIPT
axial ligation. A small peak ~ 2800–2900 cm-1 corresponds to C–H stretching vibrations of
macro rings I–IV. The metal complex IV display two characteristic peaks at 3278.39 and
3338.17 cm-1 which are ascribed to NH2 symmetric and asymmetric stretching vibrations
[20].
Fig. 1 FT-IR spectra of I–IV
3.3 1H NMR spectroscopy
1
Fig. 2 and Fig. 3 show the selected regions of the H NMR spectra of II, III and IV. The
complete spectra of free base ligand I and its corresponding indium(III) porphyrins are given
in Fig S1-S4. The insertion of indium(III) ion within the porphyrinic core of I results in the
disappearance of amino proton signal due to the replacement of NH protons by the metal ion.
The coordinated metal ion exerts strong deshielding effect on the porphyrin ring protons
resulting in the downfield shift of the resonance signals. The out of plane coordination of
metal ion with the chelating ligand I results in the magnetic inequivalence of ortho as well as

ACCEPTED MANUSCRIPT
meta phenyl protons. As a result the 1H NMR spectra of metal chelates II, III and IV display
1
two sets of doublets each ascribed for ortho and meta phenyl protons. The H NMR spectra
further reveals that the axial coordination of phenolic group with the indium- porphyrin unit
causes slight downfield shift of the resonance signals relative to the metal chelate containing
the chloro ligand II (Fig. 2). This is attributed to the deshielding effect induced by the axial
phenoxide ion. The ortho (He) and meta/para (Hf) phenyl protons of axial phenolic group
resonates in the upfield region as doublets (δ 6.85/6.87 ppm) and triplets (δ 6.94/6.96/6.98
ppm) respectively. The axial coordination of para amino phenolic group with indium
porphyrin unit on the other hand induces slight upfield shift of resonance signals in
comparison with resonance signals of macro ring II (Fig. 3). The upfield shift of proton
signals in IV is expected to arise due to shielding effect exerted by the electron donating para
amino group which resonates as singlet at δ 6.90 ppm. The other protons i.e. ortho and meta
phenyl protons of para amino substituted phenoxide ion resonates as doublets at δ 6.68/6.70
and 6.61/6.63 ppm respectively.
Fig. 2 The selected regions of the 1H NMR spectra (400 MHz pulse FT) of II (purple) and III
(olive green) at ~ 5 X 10-3 M in CDCl3. Extra peaks at δ 7.2 ppm are due to presence of
undeuterated chloroform

ACCEPTED MANUSCRIPT
1
Fig. 3 The selected regions of the H NMR spectra (400 MHz pulse FT) of II (olive green)
and IV (blue) at ~ 5 X 10-3 M in CDCl3. Extra peaks at δ 7.2 ppm are due to presence of
undeuterated chloroform
3. 4 Powder XRD analysis
In order to determine the structure and phases of the resulting macro rings, powder X-ray
diffraction (PXRD) measurement was performed. Fig. 4 shows the PXRD patterns of I–IV.
All the significant diffraction peaks have been indexed. The XRD data indicates that the
macrocyclic ligand I has face centered cubic geometry (JCPCDS card number 77-0437),
while as its metal derivatives belongs to simple cubic (II, III) and body centered cubic (IV)
symmetries (JCPCDS card number 45-0109). The average crystallite sizes of the samples
were calculated according to Scherrer’s formula (Eq. 1) using the three most intense
diffraction peaks.
D = 0.9λ/βcosθ
(1)
Where D is the crystallite size, λ is the wavelength of the X- ray, β is the FWHM (full width
at half maximum) of the diffraction peak, θ is the diffraction angle and k is the Scherer’s
constant of the order of unity. The average crystalline sizes for I, II, III and IV were found to
be 60.45, 80.56, 71.30 and 36.12 nm respectively. The high intensity of diffraction peaks
particularly for NPs I, II and III reflects their high crystalline nature. In case of IV, the

ACCEPTED MANUSCRIPT
diffraction peaks are comparatively broader which manifests that the NP has comparatively
poor crystalline nature. The degrees of crystallinity of the NPs I–IV are also reflected from
their average crystallite sizes. The crystallite size decreases as peak width increases. The
XRD pattern of I confirms a uniform phase with no impurities. The XRD pattern of II is
significantly different from that of I confirming the change in phase on metal coordination.
The XRD pattern of III is very similar to that of II with diffraction peaks slightly shifted
towards larger 2θ values in former. However, the XRD pattern of IV is completely different
from that of NPs II and III indicating change in phase and formation of a new crystalline
material, with no detectable amounts of starting materials present. The broad diffraction
peaks in IV are further shifted to higher 2θ regions. The reduction in d spacing from I to IV
is due to increase in thickness of porphyrin layers by functionalization with axial phenoxide
and para amino phenoxide ions. The scattering angles and calculated d-spacings of the most
intense scattering peaks are summarised in Table 1.
Table 1 Scattering angles and d-spacings of the most intense scattering peaks
Samples Position FWHM Crystallite Lattice d-spacing Rel. Int.
Area
[°2θ]
6.32
[°2θ]
0.111
0.135
0.192
size (nm)
strain
0.0088
[Å]
13.97117
[%]
100.00
[cts*°2θ]
2557.46
74.9
62.15
44.3
0.0043
0.0038
4.78753
3.53359
10.32
16.74
1045.41
841.47
18.85
25.18
I
78.49
91.25
71.94
80.77
0.0069
0.0027
0.0030
0.0068
11.52828
5.17363
4.65917
82.05
100.00
80.31
308.42
306.02
292.28
7.66
17.12
19.03
0.106
0.092
0.117
II
7.57
0.103
11.66504
100.00
372.69
63.58
00.39
III
IV
17.00
19.07
19.94
21.07
22.60
0.132
0.121
0.377
0.165
0.243
5.20936
4.64968
4.44739
4.21137
3.93028
75.85
74.08
32.41
100.00
30.82
274.79
237.80
167.25
156.17
73.88
69.57
22.36
51.17
34.83
0.0031
0.0094
0.0039
0.0053

ACCEPTED MANUSCRIPT
Fig. 4 The powder XRD patterns of I (green), II (blue), III (red) and IV (magenta)
3.5 Absorption spectroscopy

ACCEPTED MANUSCRIPT
The electronic spectra of porphyrins manifest high sensitivity toward structural modifications
as well as change in the polarity and pH of the surrounding environment.
Fig 5 and Fig. 6 show the UV-Visible absorption spectra of I–IV in pure organic solvents of
CH2Cl2 and CH3COOC2H5. The absorption spectra of I in both the organic solvents consists
of one strong B band in the near UV region ~ λmax 400 nm followed by four weaker Q bands
in the visible region between λmax 500 to 700 nm. Similarly the metal chelates II–IV display
one higher intensity B band ~ λmax 400 nm followed by only two lower intensity Q bands
between λmax 500 to 600 nm. The B and Q bands arise due to S0 to S2 and S0 to S1 (π to π*)
transitions within the highly pi conjugated macro rings. The reduced number of Q bands in
the metal porphyrins is due to increase in symmetry (from D2h to D4h). The lower symmetry
(D2h) of free base porphyrin is ascribed to the presence of two diagonally positioned
hydrogen atoms in its N4 core [21]. The coordination of indium(III) ion with the chelating
ligand I induce bathochromic shift of B band and hypsochromic shift of Q bands as
illustrated by Fig. 5 and Fig. 6. This phenomenon is attributed to ring distortion due to out of
plane coordination of indium(III) ion. The distortion results in the extension of delocalization
by the twisting of four aryl substituents from almost perpendicular orientation closer to the
porphyrin plane [22].
(a)
(b)

ACCEPTED MANUSCRIPT
(c)
Fig. 5 (a) The UV/Vis absorption spectra of I (purple), II (magenta), III (red) and IV (blue)
(b) magnified view of B bands (c) magnified view of Q bands at pH = 7 in CH2Cl2 at ~ 5.0 x
10-5M (arrow signifies increase in intensity)
(a)
(b)

ACCEPTED MANUSCRIPT
(c)
Fig. 6 (a) The UV/Vis absorption spectra of I (blue), II (green), III (magenta) and IV
(purple) (b) magnified view of B bands (c) magnified view of Q bands at pH = 7 in
CH3COOC2H5 at ~ 5.0 x 10-5M (arrow signifies increase in intensity)
Since the axial phenolic and para amino phenolic ligated metal chelates III and IV are now
molecules. It was expected that the axially coordinated metal chelates will have their own
electronic properties and may exhibit profound shifting of the absorption bands. However,
from the experimental observation, it is found that the absorption spectra of uncomplexed
metal porphyrin II and the monoligated complexes i.e. III and IV are very similar with
negligible shift suggesting weak electronic coupling between the two constituent
chromophores (phenolic/para amino phenolic group and indium–porphyrin) in the ground
state [23]. The indium porphyrins however exhibits marked increase in the intensity of
absorption bands relative to free ligand I. The intensity order of B bands of macro rings I–IV
in both the non aqueous solvents follow the trend IV>III>II>I. The trend is almost similar
for the Q bands as II>IV>III>I (CH2Cl2) and IV>III>II>I (CH3COOC2H5). The
hyperchromicity of the absorption bands in the metal chelates relative to free base ligand is
attributed to distortion of ligand plane by out of plane metal coordination [22]. The out of
plane ring distortion is more pronounced when a fifth ligand bind the metal centre in the axial
site. Porphyrins have strong tendency to undergo aggregation in solutions even at very low
concentrations driven mainly by π-π stacking interactions between the two neighbouring
molecules [24, 25]. The magnitude of the π-π interaction reduces in porphyrin coordinated
with metal ions of large ionic radius. In addition when a ligand molecule coordinates with the
metal centre on axial site, the metal is farther displaced away from the ligand plane which
further results in diminished π-π interaction and in fact generally leads to disaggregation [26].

ACCEPTED MANUSCRIPT
This typical phenomenon of supramolecular aggregation and disaggregation is well
manifested in the spectra of I-IV by closely observing the half widths of most intense B
bands. The FWHM of B bands (Table 2) in CH2Cl2 and CH3COOC2H5 follow the order
I>II>III>IV and I>II>IV>III. The broadening of B band in I indicates favourable degree of
aggregation relative to metal chelate II. The sharp and narrow bands in III and IV in turn
reflect lesser degree of aggregation of the axially ligated species [27].
The metal chelates II (CH3COOC2H5), III (CH2Cl2) and IV (CH2Cl2 and CH3COOC2H5)
display hyper porphyrin spectra characterized by appearance of an additional band ~ 300nm.
The extra band at ~ 300 (marked with star symbol) is attributed to charge transfer transition
from allowed npz (filled metal orbital) to π* (empty porphyrin orbital) in the near UV region
[28]. The porphyrin rings I–IV also exhibit marked negative solvatochromism with
absorption bands shifting towards higher energy in more polar solvent. It is known that
solvatochromism arises due to different solvation of the ground and excited states of a
molecule. The negative solvatochromism for I–IV is consistent with the ground state being
more polar than the excited state. This result can be ascribed to a significant degree of charge
transfer existing between the donor (peripheral para methoxy substituted phenyl rings) and
acceptor (porphyrinic N4 core) species in the ground state with electron density pushing back
to the donor from the acceptor moiety during excitation of the molecule resulting in a less-
polar excited state [29].
Effect of pH
The absorption spectra of porphyrins I–IV were also measured under basic as well as acidic
pH in both the organic solvents (Fig. 7 to Fig. 13). The optical behaviour of I in CH2Cl2 under
basic and acidic environment [Fig. S5] was already discussed previously [14]. The present
study will therefore focus on the optical behaviour of I in CH3COOC2H5.
The shape of the absorption spectra of porphyrins I–IV in basic media (pH = 10) are similar
to that under neutral environment (pH = 7) in both the solvents indicating structural stability
of the macro rings at higher pH. The hyperchromicity of the optical bands under basic
conditions [Fig. 7 (left) to Fig. 13 (left)] may be attributed to association and finally
precipitation of the porphyrins in aqueous alkali [30]. The half widths of B bands of metal
porphyrins II–IV in CH2Cl2 under basic media are greater than that in neutral media. On the
other hand, the half widths of B bands of metal chelates II–IV in CH3COOC2H5 at acidic pH
is less than that at neutral pH.

ACCEPTED MANUSCRIPT
In media of high ionic strength (pH = 4), the two inner nitrogen atoms of N4 core of I
undergoes protonation followed by dramatic J type supramolecular aggregation of the
resulting protonated species [31]. The J-aggregation of I results in the appearance of a higher
intensity red shifted band at λmax 451 nm (J band) accompanied by one higher intensity QI
band (which is otherwise forbidden) at λmax 683 nm as illustrated in Fig. 8 (right). The most
striking feature was the optical behaviour of In3+ species under acidic media [Fig. 7 (right) to
Fig. 13 (right)]. The metal ions in the two dyads III and IV remain intact with their macro
rings in media of high ionic strength indicating their remarkable kinetic inertness and
supreme robustness in highly acidic environment. This unique property (acid stability) of the
indium(III) porphyrins is in strong contrary to other SAT complexes which are kinetically
labile in nature. For e.g. the indium(III) derivative of Tetrakis-(4-methylphenyl) porphyrins
are easily demetallized even in slight acidic environment [14]. All these observations clearly
indicate that the judicious choice of chelating ligands may significantly enhance the lifetime
and structural stability of even SAT metalloporphyrins under strongly acidic environment
making them kinetically inert especially towards metal replacement reactions. It is also
worth note that though the indium porphyrins in the present case are chemically stable under
acidic media, the decreasing pH induces marked hypochromicity of the absorption bands of
metalloporphyrins. The hypochromicity of optical bands of metal chelates at lower pH may
be ascribed to peripheral protonation of the monomeric rings. The half widths of B bands of
metal porphyrins in CH2Cl2 under acidic media are greater than that in neutral media. On the
other hand, the half widths of B bands of II–IV in CH3COOC2H5 at acidic pH is less than that
at neutral pH except for macro ring IV which exhibits narrow B band at neutral pH than at
acidic pH. It can be also observed from Table 1 that the FWHM of B bands of macro rings
nearly follow the trends as I>II>III>IV in both the organic solvents under alkaline as well as
acidic environments. The change in neutral pH of the media also influences Hyperporphyrin
behaviour exhibited by the metalloporphyrins. For example, the metal chelate II exhibits no
hyper porphyrin effect in CH3COOC2H5 under neutral pH. However as media becomes
acidic, an additional band ~ 322nm appears in the spectra due to hyperporphyrin effect as
illustrated in Fig. 9 (left). Hyper porphyrin effect is also displayed by III in CH3COOC2H5
under basic [Fig. 10 (right)] as well as acidic media [Fig.11 (right)]. The absorption spectra of
IV in acidic media display an additional band (marked with star symbol) at λmax 363 nm as
illustrated in Fig. 13 (right). This band might be attributed to charge transfer electronic
transitions from para methoxy substituted phenyl rings to the neutral porphyrinic N4 core.

ACCEPTED MANUSCRIPT
Fig. 7 The UV/Vis absorption spectra of I in CH3COOC2H5 under neutral (pH = 7) and basic
(pH = 10) media [left] and under neutral and acidic (pH = 4) media [right] at ~ 5.0 x 10-5M
Fig. 8 The UV/Vis absorption spectra of II in CH2Cl2 [left] and CH3COOC2H5 [right] under
neutral (pH = 7) and basic (pH = 10) media conditions at ~ 5.0 x 10-5M

ACCEPTED MANUSCRIPT
Fig. 9 The UV/Vis absorption spectra of II in CH2Cl2 [left] and CH3COOC2H5 [right] under
neutral (pH = 7) and acidic (pH = 4) media conditions at ~ 5.0 x 10-5M
Fig. 10 The UV/Vis absorption spectra of III in CH2Cl2 [left] and CH3COOC2H5 [right]
under neutral (pH = 7) and basic (pH = 10) media conditions at ~ 5.0 x 10-5M

ACCEPTED MANUSCRIPT
Fig. 11 The UV/Vis absorption spectra of III in CH2Cl2 [left] and CH3COOC2H5 [right]
under neutral (pH = 7) and acidic (pH = 4) media conditions at ~ 5.0 x 10-5M
Fig. 12 The UV/Vis absorption spectra of IV in CH2Cl2 [left] and CH3COOC2H5 [right]
under neutral (pH = 7) and basic (pH = 10) media conditions at ~ 5.0 x 10-5M

ACCEPTED MANUSCRIPT
Fig. 13 The UV/Vis absorption spectra of IV in CH2Cl2 [left] and CH3COOC2H5 [right]
under neutral (pH = 7) and acidic (pH = 4) media conditions at ~ 5.0 x 10-5M
Table 2 FWHM of porphyrins (I-IV) at B band region in neutral, alkaline and acidic media
pH = 7
pH = 10
pH = 4
Solvent
codes
B
bands
(nm)
FWHM B bands FWHM
B
bands
(nm)
FWHM
(cm-1)
(nm)
(cm-1)
(cm-1)
421.22
430.11
430.17
430.19
418.30
427.83
427.56
427.81
11.99
10.35
9.14
8.61
9.70
9.10
10.06
8.54
421.18
430.09
430.35
430.17
417.56
428.07
427.93
428.08
11.47
10.51
9.16
9.48
12.56
8.71
448.7
11.36
12.36
10.024
10.29
13.55
9.06
I
II
III
IV
I
II
III
IV
430.00
430.13
430.22
451.70
428.09
428.28
427.83
CH2Cl2
CH3COOC2H5
8.76
8.55
9.69
9.24
3.5 Emission spectroscopy
The emission spectra of the synthesized macrocycles I–IV illustrated in Fig. 14 were
recorded in CH2Cl2 at 25 ˚C. The macrocyclic ligand I and its three metal chelates II–IV at
390 nm excitation (~ soret band region) manifest both S1 as well as S2 (less common)
fluorescence. The S1 bands have been designated as Q(0,0) and Q(0,1) and that of S2
emission (marked with star symbol) as B(0,0). The high energy S2 emission in I appears at
λmax 436 nm. In the metal chelates II–IV, the bathochromically shifted S2 fluorescence

ACCEPTED MANUSCRIPT
appears as weak band at λmax 458 nm. Similarly, the two S1 bands in I are centered at λmax
655 and 724 nm respectively. In the metal chelates II and III, the S1 emission occurs at λmax
659 and 721 nm. It can be observed from Fig. 14 that the emissions intensity of the Q(0,0)
and Q(0,1) bands in IV decreases significantly and converges to the base line at ~ 750 nm
unlike the other metal complexes. The presence of S2 as well as S1 emissions in these
porphyrins signifies close mirror image relationship between their corresponding absorption
and emission bands. The small stoke shift (Table 3) between the S2 absorption and emission
in macro rings I–IV further reflects that the structures of the near S2 excited porphyrins may
be close to that already in the electronic ground state [32, 22]. Fig. 14 clearly depicts that the
positions of S1 emission bands of the fluorophores II, III and IV are very similar with small
shift suggesting weak excited state interactions between the two chromophoric units
(phenolic/para amino phenolic group and indium–porphyrin). The quenching of emission
bands in indium(III) porphyrins is attributed to combined internal heavy atom effect and
distortion of ligand plane induced by complexation with metal cation of large ionic radius
[33]. Indium(III) is, of course, lying above the N4 core plane ligand. However, it is also more
heavy an atom to exert heavy-atom quenching. The emission intensities of metal chelates
decreases in the order as II>III>IV. This kind of trend might be ascribed to greater degree of
covalency of the empty porphyrin eg (π*) orbital with orbitals on the metal (heavy atom
effect) on going from II to IV [34]. Fig. 15 represents the fluorescence decay profiles of I–
IV. The excited state lifetime of I (7.56 ns) in CH2Cl2 are greater than that of its metal
chelates II-IV (Table 3). This behaviour may be attributed to the spin-orbit coupling induced
by indium(III) ion (heavy metal effect) favouring the population of the triplet state [35].

ACCEPTED MANUSCRIPT
Fig. 14 The emission spectra of I (purple), II (blue), III (green) and IV (magenta) in CH2Cl2
at 25 ˚C, c = 10−5 M
Fig. 15 Fluorescence decays curves of I–IV
Table 3 S1 absorption and emission data of porphyrins I–-IV in CH2Cl2 at 25 ˚C.
Samples
S2 absorption S2 emission
Stoke shift
(nm)
Average lifetime
(nm)
(nm)
436
458
458
458
(ns)
7.56
0.312
0.108
0.796
421.22
430.11
430.17
430.19
14.78
27.89
27.83
27.81
I
II
III
IV
Conclusion
In summary we have synthesized the axial phenolic and para amino phenolic incorporated
indium(III) derivatives of II. The synthesized complexes were successfully characterised by
FT-IR, 1H NMR and UV-Visible spectroscopies. In the 1H NMR spectra, the coordination of
axial phenolic and para amino phenolic group on the metal centre of II causes slight shifting
of the resonance signals. From the UV-Visible absorption data, it is found that the axially
ligated metal chelates exhibits marked hyperchromicity of the optical bands relative to their
free base analog I. A large spectroscopic change is also observed when the porphyrins are
dissolved in organic solvent of different polarity under different pH conditions. The macro
rings exhibits negative solvatochromic behaviour and may serve as potential optical probes.
Upon exciting at 390 nm, the flourophores exhibits both S1 as well as S2 emissions. However,
the emission bands in indium(III) species are significantly quenched due to internal heavy

ACCEPTED MANUSCRIPT
atom effect and distortion of ligand plane. The quenching of emission bands are more
pronounced in macro rings III and IV. The optical absorption and emission measurement
data of axial coordinated macro rings III and IV further reveals weak ground state as well as
excited state electronic interaction between the two chromophoric units (axial phenolic
ligands and the indium–porphyrin). The desirable optical properties like high molar
absorbance, remarkable acid stability and low fluorescence lifetime classifies the two
synthesized dye molecules III and IV as optically efficient sensitizer for their potential use in
many photo sensitive applications like photodyanamic therapy.
Acknowledgments
This research was supported by Council of Scientific and Industrial Research (CSIR) India
(grant No. 09/100(0190)/2016-EMR-I). SAIF Punjab is acknowledged for Powder XRD
data.
References
[1] A. R. da Silva, A. C. Pelegrino, A. C. Tedesco, R. A. Jorge, J. Braz. Chem. Soc. 19
(2008) 491.
[2] O. Ohno, Y. Kaizu, H. Kobayashi, J. Chem. Phys. 82 (1985) 1779.
[3] E. Zenkevich, E. Sagun, V. Knyukshto, A. Shulga, A. Mironov, O. Efremova, R.
Bonnett, S. P. Songca, M. Kassem, J. Photochem. Photobiol. 33 (1996) 171.
[4] M. O. Senge, M. Fazekas, E. G. A. Notaras, W. J. Blau, M. Zawadzka, O. B. Locos, E. M.
Ni Mhuircheartaigh, Adv. Mater. 19 (2007) 2737.
[5] J. M. Perry, K. Mansour, I. Y. S. Lee, X. L. Wu, P. V. Bedworth, C. T. Chen, D. Ng, S. R.
Marder, P. Miles, T. Wada, M. Tian, H. Sasabe, Science 273 (1996) 1533.
[6] K. Ni, D. Liu, Z. Li, Z. Xiao, J. Yang, Y. Song, Proc. SPIE 9297 (2014) 92971N-1.
[7] G. Y. Yang, S. G. Ang, L. L. Chng, Y. W. Lee, E. W. Lau, K. S Lai, H. G Ang, Chem.
Eur. J. 9 (2003) 900.
[8] X. Zhong, Y. Feng, S. L. Ong, J. Hu, W. J. Ng, Z. Wang, CHEM. COMMUN. 9 (2003)
1882.

ACCEPTED MANUSCRIPT
[9] S. G. Ang, H. G. Ang, W. Han, B. W. Sun, M. K. Y. Lee, Y. W. Lee, G. Y. Yang, Proc.
SPIE 4798 (2002) 195.
[10] J. Luo, J. Wang, Y. Cao, S. Yao, L. Zhang, Q. Huo, Y. Liu,
Inorg. Chem. Front. 4 (2017) 139.
[11] L. Xu, M. K. Zhai, X. C. Lu, H. B. Du, Dalton Trans. 45 (2016) 18730.
[12] A. B. Rudine, B. D. DelFatti, C. C. Wamser, J. Org. Chem. 78 (2013) 6040.
[13] I. H. Wasbotten, J. Conradie, A. Ghosh, J. Phys. Chem. B 107 (2003) 3613.
[14] P. Dechan, G. D. Bajju, P. Sood, U. A. Dar, J. Mol. Struct. 1183 (2019) 87.
[15] O. Horvath, R. Huszank, Z. Valicsek, G. Lendvay, COORDIN CHEM REV 250 (2006)
1792.
[16] Z. Valicsek, O. Horváth, K. L. Stevenson, Photochem. Photobiol. Sci. 3 (2004) 669.
[17] L. Xu, Meng-Ke Zhai, Xin-Chao Lu, Hong-Bin Du, Dalton Trans 45 (2016) 18730.
[18] M. Bhatti, W. Bhatti, E. Mast, Inorg. Nucl. 8 (1972) 133.
[19] A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J. Assour, L. Korsakoff, J. Org.
Chem. 32 (1967) 476.
[20] V. Lozovan, V. Ch.Kravtsov, E. B. Coropceanu, P. Rotaru, A. V. Siminel, M. S. Fonari,
Inorganica Chim. Acta, https://doi.org/10.1016/j.ica.2019.03.034
[21] S. Ishihara, J. Labuta, W. V. Rossom, D. Ishikawa, K. Minami, J. P. Hill, K. Ariga,
Phys. Chem. Chem. Phys. 16 (2014) 9713.
[22] Z. Valicsek, O. Horvath, MICROCHEM J 107 (2012) 47.
[23] M. K. Panda, T. Lazarides, G. Charalambidis, V. Nikolaou, A. G. Coutsolelos, Eur. J.
Inorg. Chem. 2015 (2015) 468.
[24] R. J. Abraham, F. Eivazi, Harry Pearson, K. M. Smit, J. Chem. Soc., Chem. Commun. 0
(1976) 698.
[25] R. J. Abraham, F. Eivazi, H. Pearson, K. M. Smith, ChemComm 0 (1976) 699.

ACCEPTED MANUSCRIPT
[26] C. A. Hunter, J. K. M. Sanders, J. Am. Chem. Soc. 112 (1990) 5525.
[27] R. Wiglusz, J. Legendziewicz, A. Graczyk, S. Radzki, P. Gawryszewska, J. Sokolnicki, J
ALLOY COMPD 380 (2004) 396.
[28] P. Sayer, M. Gouterman, C. R. Connell, Acc. Chem. Res 15 (1982) 73.
[29] R. S. Szabadai, J. Roth-Barton, K. P. Ghiggino, J. M. White, D. J. D. Wilson, Aust. J.
Chem 67 (2014) 1330.
[30] A. Neuberger, J. J. Scott, Proc. Royal Soc. Lond. 213 (1952) 307.
[31] Y. Arai, H. Segawa, ChemComm 46 (2010) 4279.
[32] J. Karolczak, D. Kowalska, A. Lukaszewicz, A. Maciejewski, R. P. Steer, J. Phys. Chem.
A 108 (2004) 4570.
[33] Z. Valicsek, O. Horvath, J. Photochem. Photobiol 186 (2007) 1.
[34] M. Gouterman, F. P. Schwarz, P. D. Smith, J. Chem. Phys. 59 (1973) 676.
[35] Z. Valicsek, O. Horváth, G. Lendvay, I. Kikas, I. Skoric, J. Photochem. Photobiol 218
(2011) 143.

ACCEPTED MANUSCRIPT
•
•
Axial coordination of phenolic and para amino phenolic with indium(III) porphyrin
causes hyperchromicity of absorption bands.
Axial phenolic group causes downfield shift of resonance signals whereas axial para
amino phenolic group causes upfield shift of resonance signals of indium(III)
porphyrin.
•
•
•
•
In basic media, the absorption bands of porphyrins are of higher intensity.
In acidic media, the absorption bands of porphyrins are of lower intensity.
The indium(III) porphyrins exhibit remarkable stability under acidic media.
Indium(III) ions induce quenching of fluorescence bands.