Tropylium cation-fused aromatic [26]dicarbaporphyrinoids with NIR absorptions: Synthesis, spectroscopic and theoretical characterization

Article abstract of DOI:10.1142/S1088424619501001

An easy and efficient synthetic methodology for two hitherto unknown tropylium-cation-fused Hückel aromatic [26] dicarbaporphyrinoids has been developed by acid-catalyzed Lindsey type condensation of bithiophene/biselenophene diol with azulene using BF3 · Et2O followed by oxidation with chloranil and/or DDQ. Both the macrocycles have been achieved in moderately good yields. Their structures, aromaticity and optical properties have been elucidated by NMR, UV-vis-NIR spectroscopic analyses and in-depth theoretical calculations. Both the macrocycles exhibited strongly diatropic characteristics with the UV-vis spectra closely resembling the spectra for true porphyrins. Detailed structural analyses using 1H-1H COSY, ROESY and DFT level theoretical investigations indicated fully conjugated [26]π main conjugation pathway being benefitted bythe tropylium character of the seven membered rings.

Full text of DOI:10.1142/S1088424619501001

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2019; 23: 1–10
DOI: 10.1142/S1088424619501001
Published at http://www.worldscinet.com/jpp/
Tropylium cation-fused aromatic [26]dicarbaporphyrinoids
with NIR absorptions: Synthesis, spectroscopic
and theoretical characterization
Krushna C. Sahooa, Mohandas Sangeethab, Dandamudi Usharani*b,c
and Harapriya Rath*a
aSchool of Chemical Sciences, Indian Association for the Cultivation of Science, 2A/2B Raja SC Mullick Road,
Jadavpur, Kolkata 700032, India
bDepartment of Food Safety and Analytical Quality Control Laboratory, CSIR-Central Food Technological
Research Institute, Mysuru, Karnataka, 700020, India
cAcademy of Scientific and Innovative Research (AcSIR), CSIR-HRDG, Gazhiabad, Uttarpradesh, India
Dedicated to Professor Atsuhiro Osuka on the occasion of his 65th birthday.
Received 3 June 2019
Accepted 17 July 2019
ABSTRACT: An easy and efficient synthetic methodology for two hitherto unknown tropylium-cation-
fused Hückel aromatic [26] dicarbaporphyrinoids has been developed by acid-catalyzed Lindsey type
.
condensation of bithiophene/biselenophene diol with azulene using BF3 Et2O followed by oxidation
with chloranil and/or DDQ. Both the macrocycles have been achieved in moderately good yields. Their
structures, aromaticity and optical properties have been elucidated by NMR, UV-vis-NIR spectroscopic
analyses and in-depth theoretical calculations. Both the macrocycles exhibited strongly diatropic
characteristics with the UV-vis spectra closely resembling the spectra for true porphyrins. Detailed
structural analyses using 1H–1H COSY, ROESY and DFT level theoretical investigations indicated fully
conjugated [26]p main conjugation pathway being benefitted by the tropylium character of the seven
membered rings.
KEYWORDS: Hückel topology, core modification, carbaporphyrinoids, aromaticity, NIR absorption,
DFT calculations.
the major UV-vis absorptions to longer wavelengths, a
INTRODUCTION
particularly valuable feature that could have wide range
The ever-expanding applications in biological and
of applications [1]. Designing such NIR-absorbing and/
opto-electronical fields such as photodynamic therapy
or emitting systems is of considerable interest due to
agents, solar energy conversion materials, materials
their immense biomedical applications such as tissue
for nano-molecular devices, and nonlinear optical
diagnostics, photodynamic therapy dyes and microscopic
materials has urged synthetic chemists to exploit more
imaging agents [2]. Very recently we reported the first
and more efficient methodologies for synthesis of
ever aromatic [30] heteroannulenes with strong NIR
functionalized porphyrins. In such endeavors, p-system
extension of porphyrins offers the possibility of shifting
absorption that have been well benefitted from the
presence of intriguing resonance hybrid structures
having rigid ethynylene-cumulene moieties (Csp
Csp)
[3]. An alternative strategy to arrive at NIR absorptive
dyes is ring fusion on the porphyrin ring. To gain
more insights into the effects due to ring fusion on the
porphyrin ring, many efforts have been made toward the
*Correspondence to: Dr. Harapriya Rath, tel.: +9133-2473-
4971, fax: +9133-2473-2805, email: ichr@iacs.res.in; Dr.
Dandamudi Usharani, tel.: +91821-251-4972, e-mail: ushad@
cftri.res.in.
Copyright © 2019 World Scientific Publishing Company

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K. C. SAHOO ET AL.
synthesis of p-extended porphyrins in the last decade
[4]. Among the p-extended porphyrinoids, linearly
fused aromatic rings exhibited significant advantages
on the red-shifting effect although due to the extreme
instabilities of pyrroles bearing linearly-fused acenes
such as benzene, naphthalene and anthracene, synthesis
of the acene-fused porphyrins still required expedient
tactics [5]. Nevertheless, it still remains a challenge
to conveniently enlarge the conjugated system and
introduce versatile functional groups on the periphery for
applications in different fields. Another way of altering
the cavity size and perturbing electronic structure of
the macrocycles is replacement of carbon(s) in place
of pyrrole nitrogen(s), the so called Carbaporphyrins
[6]. In common with N-confused porphyrins [7], these
compounds have a CNNN core that can facilitate
the generation of organometallic derivatives [8]. For
instance, benzocarbaporphyrins and tropiporphyrins with
indene or cycloheptatriene units in place of a pyrrole ring
readily form silver (III) complexes and some gold (III)
derivatives [9].
Among all the known carbaporphyrins, introduction
of an azulene moiety to the porphyrinoid framework
(Chart 1) is of particular interest because of the unusual
electronic properties of this bicyclic system [10]. Synthe-
sis of azuliporphyrin and its heteroanalogues have been
found to exhibit borderline macrocyclic aromaticity from
dipolar canonical forms that simultaneously give the
structure carbaporphyrin and tropylium aromatic charac-
teristics [11]. A perusal of the literature reveals the non-
aromatic features of dithia- and dioxa-diazuliporphyrins
which are easily oxidizable to their radical cations and
consequently to aromatic dications [12]. It must also be
emphasized that azuliporphyrins afford Ni (II), Pd (II)
and Pt (II) complexes in addition to stable iridium (III)
and rhodium (III) derivatives [13]. It is worth mention-
ing that even though core-modified ring-expanded het-
eroannulenes have been extensively studied because of
their suitability for various applications [14], inclusion of
azulene moieties in ring-expanded heteroannulenes has
remained hitherto unexplored. The combination of azu-
lene p systems with porphyrin macrocyclic frameworks
leading to redox switchable materials along with fasci-
nating metal complexes has thus inspired us to check the
viability in expanded porphyrins and hence the undertak-
ing of the work has been presented in this manuscript.
RESULTS AND DISCUSSION
Synthesis of the desired macrocycles is based on
the fact that azulene favors electrophilic substitution
in 1 and 3 positions that are structurally analogous
to the a-positions in pyrrole. Using Lindsey type
[3] condensation, a 1:1 molar ratio of azulene and
bithiophene diol were stirred in dichloromethane under
.
dilute conditions using BF3 Et2O as a catalyst followed
by oxidation with DDQ. Column chromatographic
separation over basic alumina followed by repeated
silica gel (200–400 mesh) chromatographic separation
and preparative thin layer chromatography (PTLC)
yielded 8% of extra pure macrocycle [9]2+ as green
solid while macrocycle [10]2+ was obtained as green
solid in 10% yield. Macrocycles [9]2+ and [10]2+, to the
best of our knowledge are the first of the kind to have
a 26p macrocyclic conjugation pathway in an expanded
dicarbaporphyrinoid. Here, it is worthy to mention
that, as proposed by Latos-Grażyński and co-workers
Chart 1. Representative structures of azulene-incorporated porphyrinoids
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TROPYLIUM CATION-FUSED AROMATIC [26]DICARBAPORPHYRINOIDS WITH NIR ABSORPTIONS
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Scheme 1. Synthesis of macrocycles [9]2+ and [10]2+
where controlled addition of oxidant and/or reductant
both the macrocycles [15]. Also the effect of heteroatom
substitution (S/Se) is realized through the red shift of the
absorptions in the visible region and NIR region of the
electromagnetic spectrum for [10]2+ compared to [9]2+.
In order to account for the isolated macrocycles
not being the neutral forms 9/10, DFT-level geometry
optimization has been carried out for a thorough
understanding of the electronic structures of 9/10 at
the B3LYP/6-31G (d, p) level of theory (B1) using
the Gaussian 16 program [16]. In-depth theoretical
calculations on various isomers of 9 and 10 indicated
that tetrathiophene or tetraselenophene are more stable
in non-inverted forms (Fig. 2). An increase in the number
of inverted thiophene rings further reduced the stability
of the macrocyclic ring due to repulsion of inner CH’s
of thiophene with the inner CH’s of the azulene rings
(Figs S10–S11). The close inspection of geometric
structure of the most stable isomer of 9 indicated the
local aromatic nature of the azulene moieties. It is worthy
to note that the Ca–Cb and Cb–Cb distances for thiophene
rings and C–C bond lengths of the azulene rings are very
similar to reported crystal structures of 5a and 5b [12] and
the Ca–Ca bond distance of the bithiophene ring is close
to the original tetrathia rubyrin [14c]. While the azulene
rings are out of the plane where mean plane deviation
with respect to meso carbons of macrocycle is 42.5° and
41.5° for 9 and 10. Moreover, in order to gain insight
into the electronic absorption spectral patterns of 9 and
10, we performed TD-DFT calculations at the B1 level
led to redox switchable chromophore, in our case using
a mild oxidant or a strong oxidant in excess amount or
stoichiometric amount led to formation of [9]2+ and [10]2+.
We strongly believe that, unlike the lower congeners
reported by Latos-Grażyński, neither neutral forms 9 and
10 nor the intermediate cation radical is stable enough to
be isolated for both macrocycles [9]2+ and [10]2+.
Both macrocycles [9]2+ and [10]2+ described above
were characterized by MALDI-TOF mass, UV-vis-NIR,
1H and 2D NMR spectroscopy and in-depth theoretical
calculations at the DFT level. MALDI-TOF mass
analyses confirmed the proposed compositions for the
macrocycles.
The presence of two azulene rings introduces an
element of cross-conjugation that would be expected
to disrupt macrocyclic aromaticity. However, for
macrocycle [9]2+, a Soret like absorption at 587 nm
and weak Q-band-like absorptions at 702 and 788 nm
followed by a broad absorption band at 1305 nm has
been observed, while the electronic absorption spectrum
of [10]2+ is indeed extremely similar in shape and
structure to the spectrum of [9]2+ exhibiting a Soret like
absorption at 620 nm and weak Q-band-like absorptions
at 735 and 802 nm followed by a broad absorption band
at 1385 nm. The e value for the Soret type band is on the
order of 105 M-1cm-1 for both the macrocycles (Fig. 1).
These observations from the electronic absorption
spectra confer porphyrinic nature with aromaticity for
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K. C. SAHOO ET AL.
Fig. 1. UV-vis-NIR absorption spectra of macrocycles (a) [9]2+ and (b) [10]2+ in dichloromethane
of theory [17]. The simulated UV-vis spectra in presence
of dichloromethane for 9 and 10 did not show any NIR
absorption bands (Figs S12–S15) as we observed in the
steady-state absorption spectra (Fig. 1) of our isolated
macrocycles. To gain deeper insight into the aromaticity
of 9 and 10, we conducted Nucleus-Independent
Chemical shift (NICS) [18] calculation. The NICS(0)
values at the center of the macrocycles were estimated to
be 2.22 and 2.21 ppm respectively (Fig. S16), indicating
the meager antiaromatic character. Additionally, the
localized aromatic character of the azulene and thio-
phene rings (Fig. S17) has been clearly illustrated by
Anisotropy of the Induced Current Density (ACID)
plots [19] which seems to be in line with the proposed
conjugated pathway observed in neutral forms of 5a
and 5b [12]. Further investigation of inverted thiophene
conformations for both 9a and 10a also convinced us of
the apparent nonaromaticity of macrocycles.
For an interpretation of the observed steady state
electronic absorption spectra, one is urged to invoke
p-electron delocalization motif with the isolated
macrocycles being [9]2+ and [10]2+. These can have
greater degree of combined carbaporphyrin and tropy-
lium character as shown in Scheme 2, leading to charge
delocalization rather than charge separation and hence
accounting for the porphyrinic nature with aromaticity
as inferred from electronic absorption spectrum (Fig. 1).
Therefore,wecarriedouttheoreticalcalculationstounder-
stand the most stable isomer of the macrocycles [9]2+ and
[10]2+. Figure 3 summarizes DFT optimized geometry
of the most stable conformer of [9]2+. Figure S19
summarizes all plausible conformers of [9]2+. It is to
be noted that for the most stable conformer of [9]2+ the
C–C bond lengths of the tropylium ring are delocalized
(1.395–1.398Å), more like a tropylium cation. Moreover,
in the optimized geometry of the most stable conformer
of [9]2+, the delocalization of both the bithiophene rings
is extended through the carbocyclic rings thereby leading
to a 26p electron conjugation pathway as depicted in
the Scheme 2. The simulated UV-vis spectra (Fig. 4)
in the presence of dichloromethane for [9]2+ and [10]2+
were found to coincide with the steady-state absorption
spectra. On the basis of calculations, it has been envisaged
that the strong Soret-like band and very weak Q-type
bands observed in the steady state electronic absorption
spectra of [9]2+ and [10]2+ mainly involve HOMO-1,
HOMO, LUMO and LUMO+1 orbital transitions
(Table S9–S10). The broad bands at 1305 nm and 1385 nm
are a consequence of electronic vertical transition of
HOMO and LUMO orbitals. The nature of HOMO and
LUMO orbitals of [9]2+ and [10]2+ clearly indicate an
extended p delocalization of the bithiophene ring with
carbaporphyrin leading to lower HOMO–LUMO energy
and the characteristic NIR absorption bands as observed
in other expanded porphyrins [3, 14c]. In contrast to the
frontier orbitals of expanded carbaporphyrinoids [9]2+
(Fig. 4), the nature of LUMO orbitals of 5a are azulene
p* orbitals (Fig. S25a).
Further evidence of the aromaticity of [9]2+ and [10]2+
has been elucidated through NICS(0) values at the
center of the macrocycles which were found to be -8.54
ppm and -9.38 ppm respectively, indicating aromatic
character. Figure 5 clearly depicts distinct clockwise ring
currents in the AICD plots of [9]2+ and [10]2+, supporting
the macrocyclic aromaticity. Furthermore, the estimated
Harmonic Oscillator Model ofAromaticity (HOMA) [20]
values of 0.860, 0.801 for [9]2+ and [10]2+ and degenerate
frontier molecular orbital (FMOs) with energy level
diagrams (Fig. S23) are well matched with their aromatic
nature.
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TROPYLIUM CATION-FUSED AROMATIC [26]DICARBAPORPHYRINOIDS WITH NIR ABSORPTIONS
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Fig. 2. Structural parameters of optimized geometries (a) 9 and (b) 9a conformers in front and side view at B3LYP/6-31G(d, p) level
of theory. Note that key bond length (Å) parameters are given for 9 in bold and for 10 in italics. Relative free energies (kcal/mol) are
given in parenthesis. Hydrogen atoms are omitted for clarity sake
Scheme 2. 26p Conjugation pathway for macrocycles [9]2+ and [10]2+
Fig. 3. DFT optimized geometries of most stable conformer of [9]2+ (a) front, (b) side view and structural parameters of optimized
geometries at B3LYP/6-31G(d, p) level of theory. Note that key bond length (Å) parameters are given for [9]2+ in bold and for [10]2+
in italics. Hydrogen atoms are omitted for clarity sake
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K. C. SAHOO ET AL.
Fig. 4. TD-DFT absorption spectrum of [9]2+ and the corresponding frontier orbitals that have major contributions in electronic
transitions
Fig. 5. Anisotropy of the Induced Current Density (AICD) plot at B3LYP/6-31G (d, p) level of theory for [9]2+ (a) and [10]2+ (b)
Finally, the NMR spectrum of [9]2+ displayed charac-
teristic features of an aromatic macrocycle in the solution
state in strong support for the above-discussed theoretical
results. The diatropic ring current of the macrocycle
clearly distinguished the protons present in the core
and on the periphery of the macrocycle. We anticipated
the typical downfield resonances of the b -thiophene
CH’s, the tropylium character of the seven membered
ring and an upfield resonance for the inner CH’s of
insight into structural rigidity without any conceivable
conformational fluxionality. At 298 K in CDCl3, the H
1
NMR spectrum of [9]2+ exhibited sharp signals with
assignable spectral features that are consistent with the
most stable conformation without any heterocyclic ring
inversion. In the 2D COSY spectra (Fig. 6a), the multiplet
at 9.98 exhibits two sets of correlations with the broad
peak at 9.22 and 9.12 ppm. In the 2D ROESY spectra
(Fig. 6b), the broad peaks at 9.22 ppm and 9.12 ppm
exhibit correlations with the signals at 2.09 ppm. Thus,
these peaks have been unequivocally assigned as –CH
1
five-membered rings. The H NMR spectral patterns
upon lowering the temperature (Fig. S9) provided an
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TROPYLIUM CATION-FUSED AROMATIC [26]DICARBAPORPHYRINOIDS WITH NIR ABSORPTIONS
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Fig. 6. 1H–1H 2D COSY (a), 1H–1H 2D ROESY (b) and Complete 1H NMR spectra (c) of [9]2+ in CDCl3 at 298 K
peaks (a, b′) of bithiophene rings and the later signals as
o-Me respectively and hence accounting the multiplet at
9.98 as –CH protons a′ and b of bithiophene rings.
DFT optimized geometry of the most stable conformer
of [9]2+. The decreased macrocyclic symmetry is fully
supported by the magnetically nonequivalent nature of
each individual proton in the macrocyclic conjugation
pathway resonating separately in their respective 1H NMR
spectra. The calculated Dd value from chemical shift is
found to be 12.10 ppm, thus suggesting aromaticity in
this macrocycle [21]. Extreme insolubility of macrocycle
There are two closely spaced singlets at 7.44 and 7.40
ppm. The signal at 7.44 ppm exhibits bond correlations
with an o-Me peak at 2.09 ppm and a p-Me peak at
2.70 ppm, respectively, thus accounting the former signal
as m-CH of same mesityl ring. The singlet at 7.40 ppm
exhibits bond correlations with a p-Me peak at 2.70 ppm,
thus accounting the former signal as m-CH of same
mesityl ring. The two well resolved doublets at 7.67
and 7.03 ppm exhibit bond correlations with each other
in 2D COSY spectra, while the former doublet exhibits
dipolar coupling with an o-Me peak at 2.09 ppm in 2D
ROESY spectra, clearly revealing the former doublet
as –CHs of seven-membered tropylium rings labelled
as d, d′ and later doublet as e, e′ respectively. The two
most shielded peaks at -2.19 and -2.22 ppm have been
assigned as inner –CHs of five membered rings. These
observations clearly reveal two types of magnetically
non-equivalent tropylium units that presumably reflect a
different degree of distortion from planarity in solution
state, whereas both the tropylium rings are tilted inward
with the mean plane deviation being 35.78° for the
1
[10]2+ made the recording of H NMR extraordinarily
difficult. Although a definite proof from single crystal
X-ray diffraction analysis is lacking at this stage for
the macrocycles [9]2+ and [10]2+, DFT level analysis
has clearly supported our experimental spectroscopic
observations (Fig. S23).
In conclusion, the present manuscript provides
conformational rigidity of two highly stable [26]
dicarbaporphyrinoids. Excellent agreement between the
theoretically determined properties and the experimental
spectroscopic measurements are key to the evidence of
strong aromaticity with NIR absorption. Our results are in
accordance with the fact that inclusion of azulene moieties
into macrocyclic core does not necessarily initiate
borderline aromaticity. Rather, depending upon the types
of macrocycles under investigation, strong aromaticity
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K. C. SAHOO ET AL.
can be induced via extra stable tropylium cations. Further
development of such dynamic carbaporphyrinoids is
currently under progress in our laboratory.
calculations were carried out using the Gaussian 16
(A.03) program suite [27].
Synthesis
MATERIALS AND METHODS
5,5′-Bis-(mesitylhydroxymethyl)-2,2′-bithiophene (6).
To a solution of N,N,N′,N′-tetramethylethylenediamine
(2.7 mL, 18 mmol) in dry tetrahydrofuran (40 mL),
n-butyllithium (11 mL, 18 mmol) was added followed
by 2,2′-bithiophene (1 g, 6 mmol) under nitrogen
atmosphere. The reaction mixture was stirred at room
temperature for one hour and later heated under reflux
for one hour. The reaction mixture was then allowed to
attain 25°C. Mesitaldehyde (2.2 mL, 15 mmol) in dry
tetrahydrofuran was added dropwise to the reaction
mixture at 0°C. After addition was over, the reaction
mixture was allowed to attain 25°C. Then saturated
ammonium chloride was added and it was extracted with
ether or chloroform (100 mL). The organic layers were
combined and washed with brine (100 mL) and dried over
anhydrous sodium sulfate. The crude product obtained on
evaporation was recrystallized from dry toluene, which
afforded the pale solid. Yield 1.40 g (57%). mp 137°C
(decomposed). Anal. calcd. for C28H30O2S2: C, 72.69; H,
6.54; S, 13.86%. Found: C, 72.93; H, 6.57; S, 13.85. 1H
NMR (400 MHz; CDCl3; Me4Si): dH ppm 6.91 (d, J =
4Hz, 2H), 6.86 (s, 4H), 6.51 (d, J = 4Hz, 2H), 6.4 (s, 2H),
2.33 (s, 12H), 2.28 (s, 6H), 1.57 (brs, OH, 2H). 13C{1H}
NMR (100 MHz; CDCl3; Me4Si): dC ppm 20.3, 20.8,
69.3, 122.2, 123.5, 130.0, 131.9, 135.3, 136.7, 137.8,
150.2. MS (EI): m/z 463.1757 (calcd. for [M + H]+).
5,5′-Bis-(mesitylhydroxymethyl)-2,2′-biselenophene
(7). A similar procedure as mentioned above was
followed with biselenophene (1 g, 3.8 mmol), n-butyl-
lithium (7.5 mL, 11.4 mmol) and mesitaldehyde
(1.4 mL, 9.5 mmol) to obtain 7. The crude product
was precipitated out by hexane and purified by silica
gel column chromatography using the mixture of ethyl
acetate — hexane (20:80) solution. The solvent was
evaporated and a light yellow solid was obtained. Yield
1.50 g (67%). mp 137°C (decomposed). Anal. calcd. for
C28H30O2Se2: C, 60.44; H, 5.43; Se, 28.38%. Found: C,
60.95; H, 5.57. 1H NMR (400 MHz; CDCl3; Me4Si): dH
ppm 6.9 (d, J = 3.96 Hz, 2H), 6.78 (s, 4H), 6.5 (m, 2H),
6.29 (s, 2H), 2.27 (s, 12H), 2.2 (s, 6H). 13C{1H} NMR
(100 MHz; CDCl3; Me4Si): dC ppm 20.6, 29.8, 69.8,
124.7, 126.3, 130.2, 135.3, 137.0, 137.9, 138.3, 148.8.
MS (EI): m/z 579.0054 (calcd. for [M+ + Na]+).
Electronic absorption spectra were measured using
1
a UV-vis-NIR spectrophotometer. H, and 13C NMR
spectra were recorded on a spectrometers (operating
1
at 500.13/700.13 MHz for H and 125.77/176.05 MHz
for 13C) using the residual solvents as the internal
1
references for H (CHCl3 (d = 7.26 ppm), CH2Cl2 (d =
5.32 ppm). MALDI-TOF MS data were recorded using
a Bruker Daltonics Flex Analyzer and ESI HR-MS data
were recorded using a Waters QTOF Micro YA263
spectrometer. All solvents and chemicals were of reagent
quality, obtained commercially and used without further
purification except as noted. For spectral measurements,
anhydrous dichloromethane was obtained by refluxing
and distillation over CaH2. Dry THF was obtained by
refluxing and distillation over pressed sodium metal.
Thin layer chromatography (TLC) was carried out on
alumina sheets coated with silica gel 60 F254 and gravity
column chromatography was performed using Silica Gel
230–400 mesh.
Computational chemistry
Electronic structure calculations of core modified
dicarbaporphyrinoids 9, 10, [9]2+ and [10]2+ were carried
out using density functional theory (DFT) with Becke’s
three-parameter hybrid exchange functional and the
Lee-Yang-Parr correlation functional (B3LYP) [16] and
the 6-31G (d, p) basis set for all the atoms (B1) [17].
Further harmonic vibrational frequencies were computed
on optimized geometries of all isomers to verify the
nature of the stationary points. To evaluate the absorption
spectra of 9, 9a, 10, 10a, [9]2+ and [10]2+, time-dependent
TD-DFT calculations [22] were performed in the presence
of dichloromethane using the polarizable continuum
model (PCM) with the integral equation formalism
variant (IEFPCM) [23] at the B1 level of theory. The
effective p-electron delocalization through the system is
confirmed by the NMR shielding values and the negative
value of nuclear independent chemical shift (NICS)
[18] calculated by using the gauge-independent atomic
orbital (GIAO) [24] method based on the optimized
geometries at the B1 level using tetramethylsilane as a
reference standard. The magnitude and direction of the
induced ring current when an external magnetic field is
applied orthogonal to the macrocycle plane is displayed
with AICD [19] plots by employing the continuous set of
gauge transformations (CSGT) [25]method. The relative
energies and Gibb’s free energies of isomers 9, 92+, 10
and 102+ were optimized at the B1 level and single point
energy calculations were performed at the B3LYP/6-
311+G(d, p) level of theory (B2) [26]. Note that all these
Compound [9]2+. Under nitrogen atmosphere and
in dark conditions, a solution of compound 6 (462 mg,
1 mmol) and azulene (128 mg, 1 mmol) in 250 mL dry
dichloromethane was stirred for 30 min. Afterward, a
.
catalytic amount of BF3 Et2O (0.1 mL) was added to
the reaction mixture and stirred at room temperature
for 90 min. Then chloranil (614 mg, 2.5 mmol) was
added and opened to air and the mixture was refluxed
for another 1 h. The solvent was removed under reduced
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TROPYLIUM CATION-FUSED AROMATIC [26]DICARBAPORPHYRINOIDS WITH NIR ABSORPTIONS
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followed by repeated silica gel column chromatography
with a mixture of 1% methanol — dichloromethane
solution. After recrystallization, the title compound was
yielded as dark green solids. Yield. ~101mg. mp 300°C
(decomposed). Anal. calcd. for C76H64S4: C, 82.57; H,
5.84; S, 11.60%. Found: C, 82.97; H, 5.97; S, 11.06. 1H
NMR (500 MHz; CDCl3; Me4Si): dH ppm -2.19 (s, 1H,
CH); -2.22 (s, 1H, CH); 2.09 (s, 24H, o-CH3); 2.70 (s,
12H, p-CH3); 7.03 (m, 4H, -CH tropylium); 7.25 (brs,
2H, -CH tropylium); 7.40 (s, 4H, -CH mesityl); 7.44 (s,
4H, -CH mesityl); 7.67 (m, 4H, -CH tropylium); 9.12 (d,
J = 4.2 Hz, 2H, thiophene b-H); 9.22 (d, J = 4.2 Hz, 2H,
thiophene b-H); 9.98 (m, 4H, thiophene b-H). UV-vis
2. (a) Waignright M. Color. Technol. 2010; 126: 115–
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Proc. Natl. Acad. Sci. USA. 2018; 115: 4465–4470
and references therein.
-1
5
(ϵ [M-1 cm × 10 ]): l, nm, 587 (4.5), 702 (0.81), 788
(0.86), 1305 (0.29). MS (MALDI-TOF): (m/z) 1104.279
(calcd. for [M]+).
.
Compound [10]2+. Under nitrogen atmosphere and
in dark conditions, a solution of compound 7 (556 mg,
1 mmol) and azulene (128 mg, 1 mmol) in 250 mL dry
dichloromethane was stirred for 30 min. Afterward, a
3. Sahoo KC, Kumaraswami M, Usharani D and Rath
H. J. Org. Chem. 2019; 84: 5203–5212.
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A. Angew. Chem., Int. Ed. 2001; 40: 619–621. (d)
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267–288. (e) Panda PK, Kang Y-J and Lee C-H.
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.
catalytic amount of BF3 Et2O (0.1 mL) was added to
the reaction mixture and stirred at room temperature
for 90 min. Then chloranil (614 mg, 2.5 mmol) was
added and opened to air and the mixture was refluxed
for another 1 h. The solvent was removed under
reduced pressure and the compound was filtered by
basic alumina followed by repeated silica gel column
chromatography with the a mixture of 1% methanol —
dichloromethane solution. After recrystallization, the
title compound was yielded as dark green solids. Yield.
~101mg. mp 300 °C (decomposed). Anal. calcd. for
C76H64Se4: C, 70.59; H, 4.99; Se, 24.42%. Found: C,
-1
70.98; H, 5.01. UV-vis (ϵ [M-1 cm × 105]): l, nm,
.
620 (4.5), 735 (0.91), 802 (0.96), 1385 (0.32). MS
(MALDI-TOF): (m/z) 1296.451(calcd. for [M] +).
5. Mori H, Tanaka T and Osuka A. J. Mat. Chem. C
2013; 1: 2500–2519, and references therein.
Acknowledgments
6. Lash TD. Chem. Rev. 2017; 117: 2313–2441.
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KCS thanks CSIR, New Delhi for senior research
fellowship. HR thanks DST-SERB (EMR/2016/004705),
New Delhi, India for research grant. MS thanks CFTRI
for research fellowship. DU thanks CFTRI for computing
facilities.
Supporting information
1
MS spectra, H and 13C NMR spectra of precursors,
Low VT NMR spectra, theoretical data and X, Y, Z
coordinates are given in the supplementary material.
This material is available free of charge via the Internet
at http://www.worldscinet.com/jpp/jpp.shtml.
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