Singlet-singlet energy transfer in carbazole-porphyrin dyads and triads

Article abstract of DOI:10.1016/j.dyepig.2017.05.018

Donor-π-Acceptor (D-π-A) type carbazole-porphyrin dyads and triads were synthesized in good yields through palladium catalyzed coupling reactions. The length of the spacer between the D (carbazole) and A (porphyrin) was varied from “phenylethyne” to “ethyne linkage”. The effect of the linker length on the spectral properties of these D-π-A dyads and triads was studied. The N-butyl-3-ethynyl-carbazole was coupled with different porphyrins bearing either one or two meso-p-iodophenyl group/meso-bromo groups using palladium catalyst. All the dyads and triads were characterized by MALDI-MS, NMR, UV–vis absorption, fluorescence and cyclic voltammetry techniques. The S₁ emission dynamics were analyzed by time-resolved spectroscopy (TCSPC); an efficient energy transfer up to 84% was observed from donor groups to the porphyrin core. Electrochemical studies revealed that, compounds having freebase porphyrin components are difficult to reduce as indicated by the cathodic shift in their reduction potentials. On the contrary, the compounds having zinc porphyrin components are easy to reduce as reflected by the anodic shift in their reduction potentials. The lowest HOMO-LUMO gap was found for the dyad which has short linker between D and A.

Full text of DOI:10.1016/j.dyepig.2017.05.018

Accepted Manuscript
Singlet-singlet energy transfer in carbazole-porphyrin dyads and triads
Naresh Balsukuri, Iti Gupta
PII:
S0143-7208(17)30291-7
10.1016/j.dyepig.2017.05.018
DYPI 5980
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 13 February 2017
Revised Date: 5 April 2017
Accepted Date: 5 May 2017
Please cite this article as: Balsukuri N, Gupta I, Singlet-singlet energy transfer in carbazole-porphyrin
dyads and triads, Dyes and Pigments (2017), doi: 10.1016/j.dyepig.2017.05.018.
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ACCEPTED MANUSCRIPT
Manuscript Title:
Singlet-Singlet Energy Transfer in Carbazole-Porphyrin Dyads and Triads
Graphical Abstract

ACCEPTED MANUSCRIPT
Singlet-Singlet Energy Transfer in Carbazole-Porphyrin Dyads and Triads
Naresh Balsukuria and Iti Gupta*a
aIndian Institute of Technology Gandhinagar, Village Palaj, Simkheda, Gandhinagar,
Gujarat- 382355, India. *Corresponding author, e-mail: iti@iitgn.ac.in
ABSTRACT
Donor-Acceptor (D-π-A) type carbazole-porphyrin dyads and triads were synthesized in good
yields through palladium catalyzed coupling reactions. The length of the spacer between the D
(carbazole) and A (porphyrin) was varied from “phenyl-ethyne” to “ethyne linkage”. The effect
of the linker length on the spectral properties of these D-π-A dyads and triads was studied. The
N-butyl-3-ethynyl-carbazole was coupled with different porphyrins bearing either one or two
meso-p-iodophenyl group /meso-bromo groups using palladium catalyst. All the dyads and triads
were characterized by MALDI-MS, NMR, UV-vis absorption, fluorescence and cyclic
voltammetry techniques. The S1 emission dynamics were analyzed by time-resolved
spectroscopy (TCSPC); an efficient energy transfer up to 84% was observed from donor groups
to the porphyrin core. Electrochemical studies revealed that, compounds having freebase
porphyrin components are difficult to reduce as indicated by the cathodic shift in their reduction
potentials. On the contrary, the compounds having zinc porphyrin components are easy to reduce
as reflected by the anodic shift in their reduction potentials. The lowest HOMO-LUMO gap was
found for the dyad which has short linker between D and A.
Key Words: Carbazole, Porphyrin, Cyclic Voltammetry, Energy Transfer, D-π-A systems
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Introduction
The artificial light harvesting antenna systems have been a matter of interest from decades and
inspired the research to create better molecules for its employment [1-4]. To mimic natural light
harvesting systems like chlorophylls, many model compounds based on porphyrins or
phthalocynines have been synthesized and studied [5-11]. Due to their strong absorption
coefficient in visible region, porphyrins have been used to construct dyads or higher arrays to
achieve intramolecular photoinduced processes [12-14]. The selective excitation of the donor
moiety in such D-A type systems is imperative to understand the energy transfer processes.
Among model donor-acceptor (D-A) systems, porphyrin based hetero-dyads are popular as
selective excitation of donor unit is possible in such systems [15-19]. Amalgamation of different
chromophore with porphyrin is one of the ways to achieve selective excitation in such porphyrin
conjugates [20, 21]. Previous works reported by our group have shown that carbazole and
phenothiazine can be covalently linked to corroles/porphyrins/aza-BODIPYs to make D-A type
systems [22-24]. Substitution of energy donor moieties at the meso-positions of porphyrin is
practically useful synthetic strategy [25] to make D-A type porphyrin based systems. Senge et al.
[26] have reported the synthesis of carbazole bridged porphyrin dimers and their metal
complexes and utilized them further to make single layer organic light emitting diods (OLEDs).
Carbazole derivatives are well known dyes with high electronic absorption and efficient
fluorescent emission [27]. Due to their high photostability and elongated molecular shape they
have been used extensively in organic photovoltaics [28, 29]. Recently, meso-carbazole
substituted porphyrins and porphyrin dimers linked with carbazole have been tested for dye
sensitized solar cell applications [30-32]. A theoretical study by Ren and coworkers [33] on
meso-carbazole substituted porphyrins revealed through bond energy transfer in the system,
where carbazole group act as donor and central porphyrin core acts as acceptor. The porphyrin
based dyads, triads and higher arrays have been well characterized by spectroscopic/
photophysical methods and the energy levels of individual components can be tuned by
substitution, metallation or core-modification [34-36]. By means of time resolved fluorescence
technique, the singlet energy levels of donor and acceptor components can be determined and by
observing the decay of the donor, singlet-singlet energy transfer process can be studied. The
study of photoinduced energy /electron transfer processes in such D-A systems are of high
relevance to the issues of conversion of light energy and molecular electronics.
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Our aim in this work is to understand the photoinduced energy transfer process in a series
of dyads and triads where individual components are connected via “ethyne” or “phenyl-ethyne”
spacer. Herein, we report the synthesis of five D-π-A type porphyrin dyads and triad having one
or two donor groups (N-butylcarbazole) at their meso-positions. The spacer length was varied
from “ethyne” to “phenyl-ethyne” in the dyads and triads. The effect of the spacer length on
these compounds was studied by UV-vis absorption, fluorescence spectroscopies and cyclic
voltammetry. Both time-resolved and steady state fluorescence studies suggested effective
energy-transfer from donor groups to porphyrin ring in these molecules. HOMO-LUMO gap for
all the dyads and triads was also calculated by cyclic voltammetry data.
Results and discussion
Synthesis
Scheme 1. Synthesis of compound 1. Reagents and conditions: (a) n-butylbromide, 50% aqueous NaOH solution,
benzene, 80 oC, 2h, (95%); (b) KI, KIO3 80 oC, 2h, (62%); (c) PdCl2(PPh3)2, PPh3, CuI, NEt3, THF,
ethynyltrimethylsilane, RT, 48h, (56%); (d) NaOH, Ethanol, 1h, (87%).
The order to prepare dyads 4 and 5, the key precursors viz: compounds 1 and 3 were prepared as
shown in Schemes 1 and 2 respectively. Compound 1 was prepared in 47% yield [37] from 9H-
carbazole in four steps (Scheme 1) as per the literature reported methods. The meso-bromo
functionalized porphyrin 3 was prepared in five steps by following known procedures (Scheme
2). Initially, 5-H-10,15,20-tris-(p-tolyl)porphyrin [38] was prepared and then brominated with N-
bromosuccinamide and catalytic amount of pyridine in chloroform. Crude reaction mixture was
purified by neutral alumina column chromatography and pure 5-bromo-10,15,20-tris-(p-
tolyl)porphyrin (compound 3) was obtained in 76% yield [39]. The synthetic strategy for the
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preparation of dyads 4 and 5 is shown in Scheme 3. The key precursors: 9-butyl-3-ethynyl-
carbazole (1) and 5-bromo-10,15,20-tris-(p-tolyl)porphyrin (3) were reacted at 50 oC for 4h in
Scheme 2. Synthesis of compound 3. Reagents and conditions: (a) TFA, RT, 30 min, (30%); (b) EtMgBr, dry
o
toluene, 0 C, 30 min, p-tolylchloride, RT, 15 min, (46%); (c) NaBH4, CHCl3/MeOH (2:1), RT, 2h, (66%); (d)
DCM, TFA, RT, 2h, DDQ, 30 min, (10%); (d) NBS, CHCl3, RT, 30 min, Pyridine (76%).
o
Scheme 3. Synthesis of dyads 4 and 5. Reagents and conditions: (a) Pd2(dba)3, AsPh3, Et3N/Toluene, 50 C, 4h,
(54%); (b) Zn(CH3COO)2.2H2O, CHCl3/MeOH (2:1), 4h, (70%).
the presence of Pd2(dba)3 in toluene/triethylamine (TEA) mixture under inert atmosphere [40].
As the reaction progressed the colour of the reaction mixture changed from purple to dark green
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and a new green spot was observed on TLC (thin layer chromatography). Reaction was stopped
after 4h when starting materials disappeared on TLC. The crude dyad 4 was purified by neutral
alumina column chromatography using 30% dichloromethane (DCM)/Petroleum ether (PE)
mixture, as green solid in 54% yield. Dyad 5 was formed when dyad 4 was reacted with zinc
(II)acetate in chloroform (CHCl3)/MeOH mixture (2:1) for 4h at room temperature (Scheme 3).
After purification on neutral alumina with 20% DCM/PE mixture, dyad 5 was isolated as dark
green solid in 70% yield. In order to make dyad 9, initially 5,15-dibromo-10,20-
dimesitylzinc(II)porphyrin (8) was prepared [41] in four steps as shown in Scheme 4. The 5,15-
H-10,20-dimesitylporphyrin (6) was synthesized and treated with N-bromosuccinimide in the
presence of pyridine in chloroform to produce brominated product (7). Further stirring with
zinc(II) acetate in the mixture of chloroform and methanol for 2 hours, gave crude compound 8
[41]. Neutral alumina column chromatography produced porphyrin 8 in 86% yields as purple
solid.
Scheme 4. Synthesis of compound 9. Reagents and conditions: (a) TFA, RT, 30 min, (25%); (b) CHCl3, BF3.OEt2,
3h, RT, DDQ, 1h, Et3N, 30 min, (19%); (c) NBS, CHCl3, RT, 30 min, Pyridine, (69%); (d) Zn(CH3COO)2.2H2O,
CHCl3/MeOH (2:1), RT, 2h, (86%); (e) Pd2(dba)3, AsPh3, RT, Et3N/Toluene, 50 oC 4h (48%).
Dyad 9 was prepared by reacting compound 1 with porphyrin 8 under similar palladium coupling
conditions [40] (Scheme 4). The reaction mixture colour changed to dark green after 1h
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indicating the formation of product. Reaction was stopped after 4h and crude dyad 9 was purified
by neutral alumina column chromatography; pure dyad was obtained in 48% yield as green solid.
Scheme 5. Synthesis of compound 10. Reagents and conditions: (a) TFA, RT, 30 min, (22%); (b) DCM, TFA, RT,
2h, DDQ, 30 min, (12%).
o
Scheme 6. Synthesis of traids 11 and 12. Reagents and conditions: (a) Pd2(dba)3, AsPh3, Et3N/Toluene, 50 C 4h,
(60%); (b) Zn(CH3COO)2.2H2O, CHCl3/MeOH (2:1), RT, 4h, (82%).
In order to make triads 11 and 12 firstly, we have prepared 5,15-bis(p-iodophenyl)-10,20-
dimesitylporphyrin (10) as shown in Scheme 5. Porphyrin 10 was synthesized by condensing
mesitaldehyde and p-iodobenzaldehyde in DCM with catalytic amount of TFA (trifluoroacetic
acid) followed by oxidation with DDQ (2,3-dichloro-5,6-dicyanochlorobenzene). The crude
porphyrin 10 [42] was obtained as purple solid in 12% yield after neutral alumina column
chromatography. For the synthesis of triad 11, one equivalent of porphyrin 10 and two
equivalents of compound 1 were treated in the similar palladium coupling conditions [40]
(Scheme 6) described above. This time colour of the reaction mixture changed from dark purple
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to deep red indicating the formation of triad. The crude triad 11 was obtained as dark red solid in
60% yield after neutral alumina column chromatography. The zinc metallation of triad 11 under
similar reaction conditions described for dyad 5, produced triad 12 (Scheme 6). The neutral
alumina column purification produced triad 12 as dark red solid in 82% yield. All the dyads and
triads were characterized by MALDI-MS or ESI-MS techniques (Supplementary Information).
The observation of strong molecular ion peak [M+H]+ for all the target molecules in mass
analysis confirmed their formation. The structures of dyads and triads were also confirmed by
1H-NMR and 13C-NMR (supplementary information). The proton NMR spectra of dyads and
triads (4, 5 and 9) showed β-pyrrolic protons between 9.82 to 7.87 ppm as three/four sets of
signal. The seven aromatic protons of N-butylcarbazole group showed up between 8.25 to 7.30
ppm and nine alkyl protons appeared as four sets of signals between 4.32 to 0.97 ppm. The
proton NMR spectra of triads 11 and 12 displayed two sets of doublet corresponding to eight β-
pyrrolic protons between 8.94 to 8.80 ppm. Dyad 4 and triad 11 exhibited characteristic upfield
signal at -2.67 and -2.57 ppm respectively, for the two N-H protons of the porphyrin core.
Absorption studies
Table 1. UV-Vis absorption data of dyads and triads recorded in toluene. The concentration was 10-5 M.
Compound
Soret band
λab (nm) (log ε)
444 (5.47)
Q-bands
λ (nm) (log ε)
Sh 539 (4.20), 587 (4.68), 678 (4.28)
571 (4.21), 621 (4.49)
4
5
452 (5.42)
453 (5.12)
576 (4.06), 628 (4.26)
9
424 (5.60)
427 (5.59)
516 (4.35), 552 (4.13), 595 (3.81), 652 (3.88)
551 (4.31), 592 (3.57)
11
12
Carbazole is an electron rich moiety which absorbs in the range of 290-350 nm, and it may act as
electron/energy donor in the dyads [43]. Whereas, porphyrin absorbs in the range of 400-700 nm
and it may act as electron/energy acceptor in the dyads and triads. The UV-vis spectra of all
dyads and triads were recorded in toluene and data is presented in Table 1. A comparison of UV-
vis spectra of dyad 4 and triad 11 along with monomer tetraphenylporphyrin (H2TPP) is shown
in Figure 1. Generally porphyrins shows one strong Soret band at about 400-420 nm (S0-S2
transitions) and four weak Q-bands (S0-S1 transitions) at about 500-700 nm.
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1.0
0.8
0.6
0.4
0.2
0.0
H TPP
2
4
11
400
450
500
550
600
650
700
Wavelength (nm)
Figure 1. Comparison of absorption spectra of 4, 11 and H2TPP in toluene.
1.0
ZnTPP
5
9
12
0.8
0.6
0.4
0.2
0.0
400
450
500
550
600
650
Wavelength (nm)
Figure 2. Comparison of normalized absorption spectra of 5, 9 and 12 and ZnTPP in toluene.
Dyad 4 showed one Soret band at 444 nm and two well-defined Q bands at 587 and 678 nm. The
Soret and Q bands of dyad 4 were significantly red shifted by 24-30 nm with respect to the
parent H2TPP; this suggest better communication between the donor carbazole and poprhyrin
acceptor because of short ethyne linkage. On the other hand, triad 11 exhibited only marginal red
shifts (4 nm) in absorption bands as compared to the H2TPP, this can be attributed to the longer
phenyl-ethyne linker between carbazole and porphyrin units. The absorption spectra of dyads 5,
9 and triad 12 along with their monomer zinc(II)-tetraphenylporphyrin (ZnTPP) are shown in
Figure 2. Dyads 5 and 9 exhibited strong Soret bands at 452 and 453 nm respectively; whereas
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the two Q-bands appeared in the range of 571 to 628 nm for both the dyads. Similarly, triad 12
showed high energy Soret band at 427 nm and two Q-bands at 551 and 592 nm. Compared to
Zn-TPP monomer [45], dyads 5 and 9 displayed 30 nm bathochromic shifts in their Soret bands;
whereas triad 12 showed only 5 nm red shifted Soret band. No distinct absorption band
corresponding to N-butylcarbazole moiety was observed in all the compounds (4, 5, 9, 11 and
12). The absorption studies of all these compounds indicated that in dyads 4, 5 and 9 the
carbazole has strongly affected the electronic properties of the porphyrin unit due to short meso-
ethyne linkage between the donor and acceptor. Also, in case of triads 11 and 12 the absorption
properties of porphyrin unit are not much affected because of the longer phenyl-ethyne linker
between the donor and acceptor. A close look to the Figures 1 and 2 clearly shows only minor
changes in the band shapes and wavelength maxima for 11 and 12 respectively, with their
corresponding monomers. This observation reflects that the two monomeric units retained their
individual identities and interacts weakly in triads.
Emission studies
Fluorescence spectra of all the compounds were recorded in toluene and the emission quantum
yields and energy transfer data are presented in Table 2. Quantum yields of dyad 4 and triad 11
were calculated by comparing the emission with H2TPP (Φf = 0.11) by exciting at first Q-band at
515 nm [46-48]. For the emission quantum yields of compounds 5, 9 and 12, the ZnTPP was (Φf
= 0.033) used as a standard [46-48]. The emission spectra of compounds 4 and 11 are shown in
Table 2. Fluorescence data of dyads and triads recorded in toluene.
Compound
H2TPP
ZnTPP
Carbazoleb
4
Excitation (λex)
515 nm
550 nm
330 nm
515 nm
300 nm
550 nm
350 nm
550 nm
350 nm
515 nm
300 nm
550 nm
350 nm
Emission (λem)
651 nm, 717 nm
597 nm, 647 nm
372 nm, 385 nm
682 nm, 747 nm
681 nm, 752 nm
629 nm, 680 nm
629 nm, 680 nm
618 nm, 670 nm
618 nm, 669 nm
655 nm, 719 nm
655 nm, 720 nm
601 nm, 648 nm
602 nm, 648 nm
ETE (%)
Donor (Φf)
Acceptor (Φf)
__
__
0.11
__
__
__
0.033
__
0.127
__
0.19a
0.16b
84%
62%
48%
75%
64%
__
__
__
__
0.077a
0.048b
0.014a
0.006b
0.20a
5
9
11
12
0.15b
0.056a
0.036b
a: Quantum yield of acceptor excited at acceptor; b: Quantum yield of acceptor excited at donor.
b: λex = 330 nm in toluene, anthracene (Φf = 0.25 in Ethanol) was used as standard.
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1.0
0.8
0.6
0.4
0.2
0.0
4
11
H TPP
2
650
700
750
800
Wavelength (nm)
Figure 3. Comparison of normalized emission spectra of dyads 4, 11 & H2TPP (λex = 515 nm) in toluene.
Figure 3; also the fluorescence spectra of compounds 5, 9 and 12 are shown in Figure 4.
The nature of emission spectra of porphyrins may be explained by Gouterman theory, which
indicates the two emission bands as mirror image of Qx (1,0) and Qx (0,1) band of absorption
[46-48]. Upon excitation at 515 nm, dyad 4 showed two emission bands corresponding to
porphyrin unit emission at 682, 747 nm; whereas triad 11 exhibited fluorescence bands at 655,
719 nm (Figure 3). The first and second emission bands of dyad 4 were significantly red shifted
by 32 and 20 nm respectively as compared to the H2TPP monomer; whereas triad 11 did not
show any shift in emission.
5
9
12
1.0
0.8
0.6
0.4
0.2
0.0
ZnTPP
600
650
700
750
Wavelength (nm)
Figure 4. Comparison of normalized emission spectra of dyads 5, 9 and 12 (λex= 550 nm) in toluene.
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The Zn metallated dyads 5, 9 and triad 12 also showed two emission bands as shown in Figure 4.
The emission bands of dyad 5 were observed at 629 and 680 nm; dyad 9 exhibited two
fluorescence bands at 618 and 670 nm. Similarly, triad 12 showed two emission bands at 601 and
648 nm. As compared to ZnTPP, larger red shifts of 31-33 nm were observed in both the
emission bands of dyad 5. Similarly, dyad 9 also showed about 21-23 nm red shifts in the
emission bands as compared to ZnTPP. From Table 2, it has been observed that quantum yields
of dyad 4 (Φf = 0.19) and triad 11 (Φf = 0.20) are higher than the monomer H2TPP. Similarly,
the calculated quantum yields of zinc metallated dyads 5 (Φf = 0.077) and triad 12 (Φf = 0.056)
were higher than the ZnTPP. On the other hand, dyad 9 have shown low quantum yield (Φf =
0.014 ) than ZnTPP, it may be attributed to the presence of meso-bromo group causing heavy
atom effect [49, 50]. In General, maximum red shifts of the emission bands were observed for
the dyads 4 and 5 among all the compounds, due to short ethyne linkage between donor
carbazole and acceptor porphyrin unit.
The steady state fluorescence studies indicated efficient energy transfer in all the
porphyrin carbazole dyads and triads (4, 5, 9, 11 & 12). Since, carbazole donor absorbs around
290-350 nm and porphyrin absorbs between 400-700 nm. The selective excitation on carbazole is
possible in all dyads and triads. For qualitative energy transfer studies, the emission spectra were
recorded for same compound exciting at two different wavelengths. When 1:1 mixture of
compound 1 and porphyrin 3 is excited at 300 nm (Figure 5); very intense emission peaks were
Figure 5. (a) Comparison of emission spectra of dyad 4, a 1:1 mixture of corresponding monomers (1 and 3) in
toluene (λex = 300 nm). (b) Overlay of carbazole donor 1 emission and acceptor porphyrin 3 absorption.
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observed only from compound 1 (donor molecule) at 358 and 376 nm; and no emission was
observed from porphyrin 3 upon excitation at 300 nm (Figure 5). However, when dyad 4 was
excited at 300 nm, the emission of carbazole unit was drastically decreased and strong emission
from porphyrin unit was observed at 681 and 752 nm, indicating that energy is transferred from
donor carbazole to acceptor porphyrin core. The efficiency of energy transfer from carbazole to
porphyrins in all the compounds was calculated by using below mentioned formula and the data
is presented in Table 2.
φf of acceptor in the molecule excited at the donor
ETE % =
X 100
φf of acceptor in the molecule excited at the acceptor
The quantum yields of porphyrin carbazole conjugates in all the compounds were calculated at
two different wavelengths i. e. excited at donor (where the donor absorb strongly) and excited at
acceptor (porphyrin core). The ETE (%) gives the idea of the total energy transfer including the
loss in energy by non-radiative decays during the energy transfer process [51]. The calculated
values of total energy transfer values were in the range of 62% to 84%, indicating an efficient
energy transfer from donor units to acceptor unit in all the compounds (Table 2). In the case of
dyad 9, total energy transfer values was found to be lower (48%) due to heavy atom effect.
Time resolved florescence measurements
The singlet excited state lifetimes τ of dyads and triads (4, 5, 9, 11 and 12) and associated
reference compounds: monomer 1, H2TPP and ZnTPP were monitored by time-resolved
fluorescence technique [52, 53]. All the compounds were excited both at 445 and 330 nm
corresponding to their monomeric porphyrin and carbazole moieties respectively. The data were
collected at different wavelengths corresponding to the emission peak maxima of donor
(carbazole) and acceptor (porphyrin) in dyads. The fluorescence decay profiles of all the
compounds are shown in Figure 6 and the data are tabulated in Table 3. The fluorescence decays
of porphyrin units in the compounds 4 and 11 were fitted to single exponential and the observed
lifetimes were 7.9 and 9.7 ns respectively. These values are closer to the monomer H2TPP singlet
state lifetime (9.2 ns). The fluorescence decays of compounds 4 and 11, collected at carbazole
unit (384 nm) were fitted to double exponential and observed lifetimes τ1 (corresponding
to carbazole unit) [22, 23], were reduced from 8.9 ns (free carbazole 1) to 1.4 and 1.2 ns
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respectively (Table 3). The other minor component of fluorescence decays of compounds 4 and
11 were attributed to the monomeric porphyrin impurities present in the solution. In case of
carbazole-zinc porphyrin dyads 5, 9 and triad 12 the fluorescence decays of zinc-porphyrin units
were also fitted to single exponential and the observed lifetimes were in the range of 0.1 to 2.2
ns. These values are closer to the monomer ZnTPP singlet state lifetime (1.9 ns). The
fluorescence decays of compounds 5, 9 and 12, collected at carbazole unit (384 nm) were fitted
to double exponential and observed lifetimes τ1 (corresponding to carbazole unit) were in the
range of 1.2 and 1.3 ns (Table 3).
Figure 6. Lifetime decay profiles of (a) compouds 4, 11; (b) compouds 5, 9 and 12 in toluene. The excitation
wavelengths used were 445 nm (acceptor) and 330 nm (donor) and data was collected at different wavelengths
depending on their corresponding emission maxima.
Table 3. Singlet excited state lifetimes of dyads and triads and monomers in toluene.
a
b
Compound
H2TPP
ZnTPP
Carbazole
λex
λem (max)
τ1 (ps)
9200
1980
8900
7880
1650
100
9700
2270
1425c
1374c
1390c
1226c
1260c
τ2 (ps)
--
--
--
--
--
2070
--
405
405
300
445
445
445
445
445
330
330
330
330
330
654
597
384
682
630
618
655
601
384
384
384
384
384
4
5
9
11
12
4
5
9
11
12
--
7750d
7422d
7766b
6840d
7220d
a: laser excitation source wavelength, b: data collected at their respective emission maxima
c & d: these data fitted to biexponential curve.
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Table 4. Efficiency and rates of energy transfer in dyads and triads.
Compound Ja (cm6 mmol-1)
kENT-1 (ps)
1697
kTS-1 (ps)
92543
71615
71615
7352
kTB-1(ps)
1728
1663
1703
1763
1706
χTB
χTS
ΦΕΝΤ
0.84
0.84
0.84
0.86
0.85
9.64 x10-14
0.98
0.97
0.96
0.80
0.86
0.02
0.03
0.04
0.20
0.14
4
5
9
11
7.46 x10-14
1626
1647
1422
1468
7.46 x10-14
3.16 x10-14
4.54 x10-14
10562
12
a: spectral overlap term calculated by using PhotochemCAD software (see ESI, S15-S19).
Again, the singlet state lifetimes of carbazole unit in the compounds 5, 9 and 12 were much
shorter than the free monomer 1 lifetime (8.9 ns). The major short component (1.2 to 1.4 ns
range) observed in all the compounds was attributed to carbazole unit. The quenched lifetime of
carbazole in all the compounds was due to the singlet-singlet excitation energy transfer from
carbazole donor to porphyrin acceptor. The rate of energy transfer (kENT) and the efficiency of
energy transfer (φENT) were calculated in these compounds (4, 5, 9, 11 and 12) by following
reported methods [54, 55]. The kENT values were in the range of 1422 to 1697 ps and φENT values
calculated in all the compounds were between 84 to 86% (Table 4). The energy transfer rates and
efficiency for dyads 5, 9 and 12 were much slower and less efficient as compared to the
porphyrin dyads reported by Lindsey’s and Osuka’s groups [56, 57]. The TS (through space)
energy transfer contribution can be evaluated in terms of Förster mechanism [54, 55]. A Förster
process is mediated by the donor-acceptor distance and orientation as well as their emission and
absorption spectral overlap characteristics (J, spectral overlap term, Table 4). J is the spectral
overlap integral which is calculated by PhotochemCAD software (Supplementary Information,
S11-S16). As per the Förster’s equation [55-57] through space energy transfer rates (
through bond energy transfer rates ( TB) were calculated for all the compounds. The relative
contributions of TS ( TS) and TB ( TB) energy transfer to the overall rate were calculated using
kTS) and
k
χ
χ
reported methods and the data are summarized in Table 4. An inspection of Table 4 reveals that
the TS rates are much slower and TB contributions are between 80-98% of the observed rate.
Also, the TS contributions estimated for all compounds were also found to be very minor (Table
4); supporting the predominant contribution of TB only. The prevailing through bond (TB)
energy transfer process is common in D-π-A systems bridged by unsaturated linkers. The rates of
TB energy transfers in all the compounds were in the range of 1.6 to 1.7 ns-1, which were much
14

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slower than the reported porphyrin dyads [26]. Similarly, the calculated rates of TB energy
transfers in all the compounds were in the range of 11-92 ns-1 (Table 4).
Electrochemical studies
Table 5. Electrochemical redox data (V vs SCE) of dyads and triads in DCM and energy levels calculated
from optical and CV data.
Compound
E1/2(ox)/V
E1/2(red)/V
HOMO
LUMO
∆E [eV]
Optical ∆E
I
II
I
II
[eV]
[eV]
(from CV)
[eV]
__
__
__
__
1.03
0.80
0.91
0.72
0.80
0.90
0.84
1.30
1.09
1.16
1.18
1.13
1.14
1.13
-1.23
-1.25
-1.14
-1.24
-0.97
-1.27
-1.31
-1.55
-1.67
-1.53
-1.65
-1.57
-1.62
-1.53
H2TPP
ZnTPP
__
__
__
__
-5.33
-5.14
-5.22
-5.32
-5.26
-2.98
-3.18
-3.45
-3.15
-3.11
2.35
1.96
1.77
2.17
2.15
2.65
2.65
2.63
2.81
2.79
4
5
9
11
12
The cyclic voltammetric measurements of all compounds (4, 5, 9, 11 and 12) were carried out
under nitrogen atmosphere at the scan rate of 50 mV/s using 0.1 M tetrabutylammonium
perchlorate as supporting electrolyte. The redox potential data of all the compounds and a
comparison of reduction waves are shown in the Table 5 and Figure 7 respectively. The
presence of electron rich carbazole moiety in dyads and triads is expected to shift the redox
potentials of porphyrin unit. Therefore, it is important to characterize the electrochemical
behavior of these compounds. The reported CV of H2TPP [58] comprised of two oxidation and
Figure 7. Comparison of the reduction waves of dyads and triads in DCM containing 0.1 M TBAP as a supporting
electrolyte, recorded at a 50 mV/s scan speed (V vs. SCE).
15

ACCEPTED MANUSCRIPT
two reduction processes (Table 5). Dyad 4 showed two irreversible oxidations at 0.91 and 1.16 V
along with two reduction processes, one reversible at -1.14 V and one irreversible at -1.53 V.
Triad 11 exhibited two reversible oxidations at 0.90 and 1.14 V along with two reversible
reductions at -1.27 and -1.62 V. Dyad 5 displayed two irreversible oxidations at 0.72 V and 1.18
V along with one irreversible reduction at -1.24 and one reversible reduction at -1.65 V.
Similarly, dyad 9 and triad 12 showed two irreversible oxidations between 0.80 and 1.13 V.
Also, dyad 9 and triad 12 displayed two irreversible reductions between -0.97 to -1.57 V (Table
5). The oxidation and reduction potential values of all the compounds, having carbazole donor
and free base porphyrin /zinc porphyrin as acceptors are very different from their corresponding
monomers, suggesting that the coupling with carbazole moiety at the meso position affected the
electronic properties of the porphyrin units in all the compounds. In the case of compounds 4 and
11 the reduction potentials are shifted to more negative side, indicating that it’s difficult to
reduce the free base porphyrin core in these compounds, as compared to the H2TPP. On the other
hand, for compounds 5, 9 and 12 the reduction potential values are less negative than that of
ZnTPP [59, 60], suggesting that these compounds are easy to reduce compared to ZnTPP. In the
case of compounds 4 and 11 oxidation potentials experienced cathodic shifts, suggesting that it is
easy to oxidize the porphyrin ring in these compounds compared to the H2TPP monomer.
Figure 8. HOMO-LUMO energy levels of dyads and triads calculated from CV data.
16

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On the contrary, the oxidation potentials of compounds 5, 9 and 12 experienced anodic shifts,
indicating that they are difficult to oxidize as compared to the ZnTPP monomer. For organic
molecules HOMO energy level indicates the energy required to extract an electron from a
molecule, which is an oxidation process. Similarly, LUMO energy level indicates the energy
necessary to inject an electron to a molecule which implies reduction process. The HOMO and
LUMO levels of compounds (4, 5, 9, 11 and 12) were approximated from the electrochemical
data are [61] given in Table 5. As per the literature reports, the electrochemically measured
HOMO-LUMO gap of tetraarylporphryins is 2.25 ±0.15 V and it is independent of the central
metal ions [62]. Another report by Kadish and co-workers suggested that, the HOMO-LUMO
gap of teraarylporphyrins partially dependent on the nature of central metal ion, substituents on
the ring and planarity of the ring [63]. As evident from the energy level diagram (Figure 8), the
HOMO-LUMO gap for dyad 4 was slightly higher than that of free base porphyrin (H2TPP).
Whereas, the band gap in triad 11 was slightly lower than that of the H2TPP [64]. On the other
hand, the measured band gap of ZnTPP is 2.15 V and triad 12 exhibit similar bandgap value
(Figure 8). In case of dyads 5 and 9 the band gap values were 1.96 to 1.77 V respectively. The
calculated values of HOMO-LUMO gap for dyads 5 and 9 were lower than that of the ZnTPP,
indicating greater effect of donor carbazole unit on the zinc porphyrin unit in these compounds.
Also, the optical band gap [65] was calculated for all the compounds from the absorption data
(Table 5). Among all the compounds, the triads 11 and 12 exhibited higher optical band gap of
2.81 and 2.79 eV respectively, as compared to the dyads. The optical band gap values were found
to be 2.63 to 2.65 eV for dyads 4, 5 and 9 this observation was in sync with red shifted
absorption spectra of these dyads.
Photoinduced electron transfer
In addition to intramolecular singlet excitation energy transfer (EET), the photoinduced electron
transfer (PET) quenching interaction may also be possible in these D-A porphyrins. Hence we
evaluated the relationships of energy levels for dyads and triads using fluorescence and redox
potential data (Table 5). The singlet state energy (S1) for the carbazole donor was calculated
from its absorption and emission data; the charge-separated state has been estimated from the
first oxidation and first reduction potentials of the dyads and triads [66]. In order to understand
17

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the possibility of photoinduced electron transfer processes (PET) in all the compounds, we have
calculated free energy of this process by the following equation [66].
∆GPET (D-A) = ECT (D-A) – E0-0 (D)
∆GPET (D-A) is the free energy change during the electron transfer from Donor to Acceptor. ECT
(D-A) is the energy of the charge transfer state of D-A molecule [dyads and triads] obtained from
the 1st oxidation and 1st reduction potentials as determined by cyclic voltammetry measurements.
E0-0 (D) is the zero-zero excitation energy obtained from the average of the frequencies of the
longest wavelength absorption maxima and the shortest wavelength emission maxima of the
donor N-butylcarbazole. These values are calculated using above mentioned equation for all the
compounds and the data is presented in Table 6.
Table 6. Energies of the singlet and charge transfer states and free energy change for PET process.
Molecules
Eo-o
ECT (D-A)
ꢀ
GPET (D-A)
__
__
N-Butylcarbazole
Compound 4
Compound 5
Compound 9
Compound 11
Compound 12
3.55
__
2.05 eV
1.96 eV
1.77 eV
2.17 eV
2.15 eV
-1.50 eV
-1.59 eV
-1.78 eV
-1.38 eV
-1.40 eV
__
__
__
__
Figure 9. Generalized energy level diagram of triads (a) 11 and (b) 12; various energy levels were obtained by
absorption, emission and redox data. (EET = excitation energy transfer, PET = photoinduced electron transfer)
The energy level diagram of triads 11 and 12 having carbazole (CBZ) as donor and core
porphyrin acceptors (H2P) and (ZnP) respectively is shown in Figure 9. The intramolecular EET
18

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from CBZ donor group to H2P or ZnP porphyrin acceptor is thermodynamically favoured
process; the singlet state energy of free carbazole is higher (3.55 eV) than that of the freebase
(1.94) or zinc porphyrin (2.07) core in 11 and 12 respectively [67]. The PET reaction from CBZ
to core porphyrin H2P or ZnP can not be ruled out based on thermodynamic considerations, when
excited at the donor. This PET reaction leads to a charge-transfer state of the type CBZ+._(H2P)-. or
CBZ+._(ZnP)-. and the values of free energy change
∆G(PET) for triads 11 and 12 were -1.38 and -
1.40 eV respectively. We believe that the co-occurrence of strong intramolecular EET and less
prominent PET may be responsible for the quenched emission of donor moiety in these triads
when excited at 350 nm. Similar observations were made for D-π-A dyads 4, 5 and 9; also the
energy level diagrams are provided in the supplementary information (Supplementary
Information, S13).
Conclusions
In conclusion, carbazole-porphyrin dyads and triads were synthesized and studied by absorption,
electrochemical and fluorescence techniques. The S1 emission dynamics were analyzed by time-
resolved spectroscopy (TCSPC); an efficient energy transfer up to 84% was observed from donor
groups to the porphyrin core. D-
cathodic shifts in oxidation potentials as compared to H2TPP, thus making them easy to oxidize.
Whereas, D- -A systems having carbazole-zinc porphyrin unit exhibited anodic shifts in
π-A systems having carbazole-freebase porphyrin unit exhibited
π
oxidation potentials as compared to ZnTPP, thus making them difficult to oxidize.
Acknowledgements
Financial support from SERB (EMR/2015/000779) Govt. of India is greatly acknowledged. NB
thanks IIT Gandhinagar for fellowship and infrastructural support. Authors are grateful to Prof.
H. Furuta, Kyushu University for MALDI-MS measurements.
Supporting Information
The characterization data like MALDI-MS, 1H and 13C NMR spectra of selected compounds are
available. Energy transfer calculation details and PET figure are also available for selected
compounds.
19

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Experimental
Instrumentation and Reagents
Unless otherwise mentioned, all the reagents and solvents were purchased from Aldrich, Acros
Organics or Merck and used without further purification. Silica gel (60-120 mesh size) and
neutral alumina (Brockmann Grade I-II) used for column chromatography were procured from
Merck. The NMR spectra of compounds in CdCl3 solution were recorded with Bruker Avance III
500 MHz NMR spectrometer. The ESI-MS data for few compounds (starting materials) were
recorded (in positive ion mode) with Waters Synapt-G2S ESI-Q-TOF Mass instrument. MALDI
mass data for dyads and triads were recorded on Bruker Daltonics MALDI-TOF instrument.
Absorption spectra were recorded with Shimadzu UV-1700 and Fluorescence emission studies
were performed using Horiba-JobinYvon Fluolorog-3 Spectrometer. Cyclic voltammetry (CV)
studies were carried out with an electrochemical system [CH1660E, CH instruments, USA]
utilizing the three electrode configuration consisting of a glassy carbon (working electrode),
platinum wire (auxiliary electrode) and saturated calomel (reference electrode) electrodes. The
experiments were done under nitrogen atmosphere in dry DCM using 0.1
M
tetrabutylammonium perchlorate as supporting electrolyte. All potentials were calibrated vs.
saturated calomel electrode by the addition of ferrocene as an internal standard, taking E ½
(Fc/Fc+) = 0.3 V vs. SCE.
Synthesis
Compound 1: In a clean round-bottomed flask N-butylcarbazole-3-trimethylsilane (672 mg,
2.10 mmol) was dissolved in ethanol (84 ml). After 10 min NaOH solution (2.25 mL, 1.9 M) was
added to reaction and the reaction mixture was stirred for 4 h at room temperature. Reaction
mixture was extracted with diethyl ether and dried over anhydrous Na2SO4 and solvent was
evaporated by using rotary evaporator under reduced pressure. The desired product was purified
by column chromatography on silica gel 10% DCM/PE mixture. Removal of solvent produced
1
compound 1 as brown solid in 87% yield (450 mg). Rf = 0.35 (silica, DCM/PE 1:5); H NMR
(CDCl3, 500 MHz,
δ ppm): 8.25 (s, 1H), 8.07 (d, J = 8 Hz, 1H), 7.58 (d, J = 8.5 Hz, 1H), 7.48 (t,
J = 8 Hz, 1H), 7.40 (d, J = 8 Hz, 1H), 7.33 (d, J = 8.5 Hz, 1H), 7.23 (s, 1H), 4.29 (t, J = 7 Hz,
2H), 3.08 (s, 1H), 1.81-1.87 (m, 2H), 1.36-1.42 (m, 2H), 0.94 (t, J = 7.5 Hz, 3H).
20

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Compound 3: In a clean round-bottomed flask under N2 conditions 5,10,15-tri-p-tolylporphyrin
(100 mg, 0.17 mmol) was dissolved in CHCl3(43 mL). After 5 min N-bromosuccinimide (NBS)
o
(30 mg, 0.17 mmol) and pyridine (170 uL) was added to reaction mixture at 0 C for 15 min.
Acetone (3.5 mL) was added to quench the reaction. The reaction mixture was evaporated by
using rotary evaporator under reduced pressure. The desired product was purified by column
chromatography on neutral alumina 15% DCM/PE mixture. Removal of solvent produced
1
compound 2 as purple solid in 76% yield (86 mg). Rf = 0.38 (silica, DCM/PE 1:4); H NMR
(CDCl3, 500 MHz,
δ ppm): 9.65 (d, J = 4 Hz, 2H), 8.91 (s, 2H), 8.80 (s, 4H), 8.06 (t, J = 7.5 Hz,
6H), 7.53-7.57 (m, 6H), 2.71 (s, 6H), 2.69 (s, 3H), -2.75 (s, 2H).
Compound 6: In a clean round-bottomed flask under N2 conditions 5-H dipyrromethane (600
mg, 4.10 mmol) and 2,4,6-trimethylbenzaldehyde (0.60 mL, 4.10 mmol) were dissolved in 400
mL of CHCl3 and then reaction mixture was treated with BF3.OEt2 (0.16 mL, 1.33 mmol). The
mixture was stirred for 3 h at room temperature. DDQ (171.61 mg, 0.75 mmol) was added stirred
at room temperature for 3h. Et3N (0.57 mL) was added and stirred for further 30 min. The
reaction mixture was passed through neutral alumina and concentrated by using rotary
evaporator under reduced pressure. The desired product was purified by column chromatography
on neutral alumina 15-20% DCM/PE mixture. Removal of solvent produced compound as purple
1
solid in 19% yield (424 mg). Rf = 0.40 (silica, DCM/PE 1:4); H NMR (CDCl3, 500 MHz,
δ
ppm): 10.21 (s, 2H), 9.31 (d, J = 4.5 Hz, 4H), 8.87 (d, J = 4.5 Hz, 4H), 7.31 (d, J = 8 Hz, 4H),
2.65 (s, 6H), 1.84 (s, 12H), -3.05 (s, 2H).
Compound 7: 5,15-dimesitylporphyrin (100 mg, 0.18 mmol) was dissolved in CHCl3 (10 mL)
and then N-bromosuccinimide (NBS) (65 mg, 0.36 mmol) and pyridine (0.12 mL) were added.
The reaction mixture was stirred for 30 min at room temperature and quenched with acetone. The
reaction mixture was evaporated by using rotary evaporator under reduced pressure. The desired
product was purified by column chromatography on neutral alumina 20% DCM/PE mixture.
Removal of solvent produced compound as purple solid in 69% yield (88 mg). Rf = 0.38 (silica,
DCM/PE 1:4); 1H NMR (CDCl3, 500 MHz,
4H), 7.29 (s, 4H), 2.64 (s, 6H), 1.82 (s, 12H), -2.53 (s, 2H).
δ ppm): 9.54 (d, J = 5 Hz, 4H), 8.68 (d, J = 4.5 Hz,
21

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Compound 10: 5-mesityldipyrromethane (200 mg, 0.75 mmol) and 4-iodobenzaldehyde (176
mg, 0.75 mmol) were dissolved in DCM (70 mL) under N2 conditions and then TFA (0.10 mL,
1.34 mmol) was added to reaction mixture slowly over 30s. DDQ (171.61 mg, 0.75 mmol) was
added after 30 min and the reaction mixture was stirred at room temperature for further 1h. The
reaction mixture was passed through neutral alumina and concentrated by using rotary
evaporator under reduced pressure. The desired product was purified by column chromatography
on neutral alumina 25% DCM/PE mixture. Removal of solvent produced compound 10 as purple
1
solid in 12% yield (84 mg). Rf = 0.38 (silica, DCM/PE 1:4); H NMR (CDCl3, 500 MHz,
δ
ppm): 8.76 (d, J = 4.5 Hz, 4H), 8.70 (d, J = 5 Hz, 4H), 8.08 (d, J = 8 Hz, 4H), 7.95 (d, J = 8.5
Hz, 4H), 7.28 (s, 1H), 2.63 (s, 6H), 1.82 (s, 12H), -2.67 (s, 2H).
Dyad 4: In a clean and dry 50 mL 3-neck round-bottomed flask, 5-bromo-10,15,20-tris-(p-tolyl)
porphyrin 3 (30 mg, 0.04 mmol) was taken under nitrogen atmosphere. Then 3-ethynyl-9-
butylcarbazole (12 mg, 0.04 mmol) was added followed by dry toluene (15 mL) and TEA (4
mL). After this, Pd2(dba)3 (6 mg) and AsPh3 (14 mg) were added and reaction mixture was
o
heated at 50 C for 4 h. Solvent was removed from the reaction mixture on rotary evaporator.
The desired product was purified by column chromatography on neutral alumina using 30%
DCM/PE mixture. Removal of the solvent produced dyad 4 as green solid in 54% yield (20 mg).
Mp> 300 oC; Rf = 0.33 (silica, DCM-hexane 2:3); 1H NMR (CDCl3, 500 MHz,
δ ppm): 9.82 (d,
J = 4.5 Hz, 2H), 8.93 (d, J = 5 Hz, 2H), 8.75 (m, 5H), 8.24 (d, J = 7.5 Hz, 1H), 8.08-8.11 (m,
5H), 8.05 (d, J = 8 Hz, 2H), 7.56 (d, J = 7.5 Hz, 4H), 7.50-7.53 (m, 4H), 7.43 (d, J = 8 Hz, 1H),
7.29-7.32 (m, 1H), 4.32 (t, J = 7.5 Hz, 2H), 2.70 (s, 6H), 2.67 (s, 3H), 1.87-1.93 (m, 2H), 1.42-
1.46 (m, 2H), 0.98 (t, J = 7.5 Hz, 3H), -2.24 (s, 2H); 13C NMR (CDCl3, 125 MHz,
δ ppm):
141.00, 140.43, 139.25, 139.02, 137.44, 137.42, 134.50, 134.38, 129.38, 127.51, 127.42, 126.21,
124.05, 123.27, 122.65, 121.48, 120.98, 120.70, 119.50, 114.12, 109.07, 109.02, 100.60, 98.57,
+
90.45, 43.06. 31.16, 29.70, 21.49, 20.58, 13.86. MALDI-MS: C59H47N5 [M]+:
calcd. m/z 825.3831, found. m/z 825.9623.
Dyad 5: Dyad 4 (20 mg, 0.024 mmol) and Zn(OAc)2.2H2O (36 mg, 0.16 mmol) taken in 100 mL
round bottom flask. Then CHCl3/MeOH (2:1, 8 mL) mixture was added in the RB and the
reaction mixture was stirred for 4 h at room temperature. Then the reaction was stopped and
solvent was evaporated under reduced pressure. The desired product was purified by column
22

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chromatography on neutral alumina using 20% DCM/PE mixture. Removal of solvent produced
o
dyad 5 as green solid in 70% yield (15 mg). Mp> 300 C; Rf = 0.42 (silica, DCM-hexane 1:3);
1H NMR (CDCl3, 500 MHz,
δ ppm): 9.89 (d, J = 4 Hz, 2H), 9.02 (d, J = 4.5 Hz, 2H), 8.87 (s,
4H), 8.68 (s, 1H), 8.16 (d, J = 7.5 Hz, 1H), 8.10 (d, J = 7.5 Hz, 4H), 8.05 (d, J = 7.5 Hz, 3H),
7.57 (d, J = 7.5 Hz, 4H), 7.53 (d, J = 7.5 Hz, 2H), 7.44-7.49 (m, 3H), 7.38 (d, J = 8 Hz, 2H), 4.30
(t, J = 7 Hz, 2H), 2.72 (s, 5H), 2.69 (s, 4H), 1.87-1.92 (m, 2H), 1.42-1.46 (m, 2H), 0.97 (t, J =
7.5 Hz, 3H); MALDI-MS: C59H46N5Zn + [M+H]+: calcd. m/z 888.3045, found. m/z 888.1944.
Dyad 9: In a clean and dry 50 mL 3-neck round-bottomed flask, Zn 5,15-dibromo-10,20-
dimesitylporphyrin 8 (40 mg, 0.05 mmol) was taken under nitrogen atmosphere. Then 3-ethynyl-
9-butylcarbazole (32 mg, 0.13 mmol) was added followed by dry toluene (15 mL) and TEA (4
mL). After this, Pd2(dba)3 (7 mg) and AsPh3 (14 mg) were added and reaction mixture was
o
heated at 50 C for 4 h. Solvent was removed from the reaction mixture on rotary evaporator.
The desired product was purified by column chromatography on neutral alumina using 40%
DCM/PE mixture. Removal of the solvent produced dyad 9 as green solid in 48% yield (24 mg).
Mp> 300 oC; Rf = 0.33 (silica, DCM-hexane 2:3); 1H NMR (CDCl3, 500 MHz,
δ ppm): 9.81 (d,
J = 4.5 Hz, 2H), 9.61 (d, J = 4.5 Hz, 2H), 8.79 (d, J = 4.5 Hz, 2H), 8.73 (d, J = 5 Hz, 3H), 8.24
(d, J = 7.5 Hz, 1H), 8.08 (d, J = 8.5 Hz, 1H), 752-7.57 (m, 2H), 7.48 (d, J = 8.5 Hz, 1H), 7.30-
7.34 (m, 5H), 4.41 (t, J = 7.5 Hz, 2H), 2.65 (s, 6H), 1.92-1.98 (m, 2H), 1.84 (s, 12H), 1.45-1.48
(m, 2H), 1.01 (t, J = 7.5 Hz, 3H). ESI-MS: C56H48BrN5Zn + [M+2H]+: calcd. m/z 933.2385,
found. m/z 933.3842.
Traid 11: In a clean and dry 50 mL 3-neck round-bottomed flask, 5,15-bis(4-iodophenyl)-10,20-
dimesitylporphyrin 10 (40 mg, 0.04 mmol) was taken under nitrogen atmosphere. Then 3-
ethynyl-9-butylcarbazole (26 mg, 0.10 mmol) was added followed by dry toluene (14 mL) and
TEA (3 mL). After this, Pd2(dba)3 (6 mg) and AsPh3 (13 mg) were added and reaction mixture
o
was heated at 50 C for 4 h. Solvent was removed from the reaction mixture on rotary
evaporator. The desired product was purified by column chromatography on neutral alumina
using 30% DCM/PE mixture. Removal of the solvent produced triad 11 as red solid in 60% yield
(30 mg). Mp> 300 oC; Rf = 0.33 (silica, DCM-hexane 2:3); 1H NMR (CDCl3, 500 MHz,
δ ppm):
8.85 (d, J = 4.5 Hz, 4H), 8.72 (d, J = 4.5 Hz, 4H), 8.44 (s, 2H), 8.23 (d, J = 8 Hz, 4H), 8.16 (d, J
= 7.5 Hz, 2H), 7.96 (d, J = 8 Hz, 4H), 7.77-7.79 (m, 2H), 7.48-7.52 (m, 2H), 7.42-7.45 (m, 4H),
23

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7.28 (t, J = 7 Hz, 6H), 4.33 (t, J = 7 Hz, 4H), 2.62 (s, 6H), 1.87-1.92 (m, 4H), 1.85 (s, 12H),
13
1.39-1.46 (m, 4H), 0.97 (t, J = 7.5 Hz, 6H), -2.57 (s, 2H); C NMR (CDCl3, 125 MHz,
δ ppm):
141.60, 140.96, 140.33, 139.44, 138.45, 137.84, 134.61, 129.87, 129.44, 127.84, 126.20, 124.27,
123.46, 123.05, 122.59, 120.64, 119.46, 118.88, 118.59, 113.28, 109.03, 108.90, 92.23, 87.64,
43.07, 31.18, 21.68, 20.62, 13.92. MALDI-MS: C86H73N6 + [M+H]+: calcd. m/z 1189.5897,
found. m/z 1189.9305.
Triad 12: Triad 11 (20 mg, 0.017 mmol) and Zn(OAc)2.2H2O (24 mg, 0.11 mmol) taken in 100
mL round bottom flask. Then CHCl3/MeOH (2:1, 5 mL) mixture was added in the RB and the
reaction mixture was stirred for 4 h at room temperature. Then the reaction was stopped and
solvent was evaporated under reduced pressure. The desired product was purified by column
chromatography on neutral alumina using 40% DCM/PE mixture. Removal of solvent produced
triad 12 as green solid in 82% yield (18 mg). Mp> 300 oC; Rf = 0.42 (silica, DCM-hexane 1:3);
1H NMR (CDCl3, 500 MHz,
δ ppm): 8.94 (d, J = 4.5 Hz, 4H), 8.81 (d, J = 4.5 Hz, 4H), 8.44 (s,
2H), 8.24 (d, J = 8 Hz, 4H), 8.15 (d, J = 7.5 Hz, 2H), 7.96 (d, J = 8 Hz, 4H), 7.77-7.79 (m, 2H),
7.48-7.52 (m, 2H), 7.43-7.46 (m, 4H), 7.28 (m, 6H), 4.34 (t, J = 7.5 Hz, 4H), 2.63 (s, 6H), 1.87-
13
1.93 (m, 4H), 1.85 (s, 12H), 1.40-1.48 (m, 4H), 0.98 (t, J = 7.5 Hz, 6H); C NMR (CDCl3, 125
MHz,
δ ppm): 150.10, 149.99, 142.44, 140.98, 140.32, 139.29, 139.03, 137.56, 134.52, 132.26,
130.97, 129.71, 129.43, 127.73, 126.17, 124.23, 123.22, 123.08, 122.63, 120.61, 119.80, 119.55,
119.43, 113.40, 109.00, 108.86, 92.04, 87.73, 43.08, 31.17, 29.71, 21.63, 20.59, 13.87. MALDI-
MS: C86H72N6 Zn+ [M+2H]+: calcd. m/z 1254.9440, found. m/z 1254.06.
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