Design of flexible dendritic systems bearing donor-acceptor groups (pyrene-porphyrin) for FRET applications

Article abstract of DOI:10.1016/j.dyepig.2021.109382

Herein, we report the synthesis and characterization of a novel series of dendritic compounds, bearing peripheral pyrene groups and a porphyrin core, of zero and first generation with different spacer lengths. These compounds were further metallated with

Full text of DOI:10.1016/j.dyepig.2021.109382

Dyes and Pigments 191 (2021) 109382
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Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Design of flexible dendritic systems bearing donor-acceptor groups
(pyrene-porphyrin) for FRET applications
a
a
a
˜
´
´
Yoliztli Banales-Leal , Andrea García-Rodríguez , Fabian Cuetara-Guadarrama ,
Mireille Vonlanthena, Kendra Sorroza-Martíneza, David Morales-Moralesb, Ernesto Riveraa
,
*
a
´
´
Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, Mexico City, CP 04510, Mexico
b
´
´
Instituto de Química, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, Mexico City, CP 04510, Mexico
A R T I C L E I N F O
A B S T R A C T
Keywords:
Herein, we report the synthesis and characterization of a novel series of dendritic compounds, bearing peripheral
pyrene groups and a porphyrin core, of zero and first generation with different spacer lengths. These compounds
were further metallated with Zn(II) and Mg(II). The optical properties of these dendritic molecules were studied
by absorption and fluorescence spectroscopy. After metallation, the dendritic porphyrins exhibited a red shift in
the Soret absorption band and a blue shift in the emission band. All compounds exhibited high energy transfer
efficiency, reaching values of EFRET above 99%.
Energy transfer (FRET)
Optical properties
Dendrimer
Pyrene
Porphyrin
1. Introduction
In addition, the porphyrin chromophore motif has been widely
applied in photodynamic therapy, catalysis, non-linear optics, fluores-
In the last decades dendritic molecules have attracted much atten-
tion, being motif of multiple studies to investigate their outstanding
physical and chemical properties [1–4]. Hence, dendrimers and den-
drons are promising compounds for the elaboration of electroactive and
photoactive devices, for their biological applications in the adminis-
tration and controlled drug delivery, as well as for their potential use as
catalysts for organic transformations [5–11]. Moreover, the photo-
physical properties of photoactive dendrimers can be finely tuned by the
careful design of their architectures, allowing the location of the pho-
toactive units either in the core, in the dendritic building units or at the
periphery. This permit the observation of fluorescence resonance energy
transfer (FRET) and charge transfer (CT), photophysical phenomena
that are very important in the development of photovoltaic devices
[12–16].
cent switches, etc [28–32]. One of the most notable applications of
porphyrins, has been their incorporation as acceptor in many dendritic
structures, as part of the design of solar cells based on photosynthesis
mimicking molecular systems (acting as sensitizers of light absorption)
[33–35]. Hence,
a large number of dendritic structures with
donor-acceptor groups having porphyrin chromophores has been re-
ported [36,37]. Some important contributions from our research group
have been reported on the study of dendritic structures based on the
pyrene-porphyrin donor-acceptor pair for energy transfer purposes,
leading to energy transfer efficiencies close to 100% [38–43].
Furthermore, important biological porphyrin derivatives for dioxy-
gen transport and photosynthesis are based on metalloporphyrins. Some
relevant examples are the iron, magnesium and cobalt complexes found
in the heme, chlorophyll and vitamin B12, respectively [44–47]. In
addition, artificial metalloporphyrin complexes such as meso
substituted porphyrins can be synthesized and modified in a facile
manner. The two main features of these systems are the appearance of a
strong absorption band in the blue region of the UV–vis spectrum (Soret
band), and low intensity Q bands near the red region [48,49]. The co-
ordination of the porphyrin with a metal ion provokes changes in the
observed absorption spectra, therefore changing the photophysical and
redox properties [50,51]. Metalloporphyrins have been used in analyt-
ical chemistry, catalysis (i.e. oxidation reactions) and as building blocks
In this sense, and due to its unique and outstanding optical and
photophysical properties, pyrene has been widely used as fluorescent
probe in various dendritic and polymeric structures [17–20]. It is worth
mentioning that this chromophore can produce either inter or intra-
molecular excimers, by increasing its local concentration or by inter-
acting with another pyrene unit present in the same molecule,
respectively [21–23]. Thus, dendritic and polymeric architectures
bearing pyrene, covalently linked to diverse acceptor groups have been
reported [24–27].
* Corresponding author.
E-mail address: riverage@unam.mx (E. Rivera).
https://doi.org/10.1016/j.dyepig.2021.109382
Received 6 October 2020; Received in revised form 22 February 2021; Accepted 6 April 2021
Available online 17 April 2021
0143-7208/© 2021 Elsevier Ltd. All rights reserved.

˜
Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
for the production of metal organic frameworks (MOF’s) [52–57].
We have previously studied the effect of metallation (Zn, Cu, Mg, and
Mn) of some pyrene-labeled dendronized porphyrins on their energy
transfer from the pyrene moiety [41]. The UV–vis and fluorescence
properties of the series of compounds have been studied and these sys-
benzaldehyde (1.94 mL, 19.0 mmol), benzyltributylammonium chloride
(BTBAC) (12.3 mg, 0.039 mmol) were mixed and some drops of EtOH
were added and the mixture was stirred for 15 min. After this time,
borontrifluoride diethyl etherate (BF3∙OEt) (0.32 mL, 2.5 mmol) was
added and the mixture was further stirred for 15 min. Finally, 2,3-
dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (4.33 g, 19 mmol) was
added and the reaction was allowed to continue for 2 h. Trimethylamine
(5 mL) was added to quench the reaction. The crude product was puri-
fied by column chromatography (neutral alumina), using a mixture of
hexanes/CH2Cl2 as eluent, increasing gradually the polarity until hex-
anes/CH2Cl2 7:3 was reached. The desired product 2 was obtained as a
purple solid (0.65 g, 14%). 1H NMR (δ ppm, 400 MHz, CDCl3): 8.91–8.86
(m, 8H), 8.31–8.17 (m, 6H), 8.12 (d, J = 8.6 Hz, 2H), 7.80–7.72 (m, 9H),
7.28 (d, J = 8.7 Hz, 2H), 4.30 (t, J = 6.2 Hz, 2H), 4.24 (q, J = 7.2 Hz,
2H), 2.70 (t, J = 7.1 Hz, 2H), 2.31 (quint, J = 6.5 Hz, 2H), 1.35 (t, J =
7.1 Hz, 3H), ꢀ 2.79 (s, 2H). 13C NMR (δ ppm, 100 MHz, CDCl3): 190.9
(CHO), 142.3 (C2, C–NH), 135.8 (C3), 134.9 (C4, phenol), 129.2 (C5,
phenyl groups), 127.8 (C6, phenyl groups), 126.8 (C7, C-meso-
porphyrin), 120.1 (C8, phenol), 113.8 (C9, C- endo-porphyrin). MALDI-
TOF: m/z calculated for C50H40N4O3 [M]+: 744.31 found [M]+: 744.51.
Elemental Anal. Calcd (%) for C50H40N4O3: C, 80.62; H, 5.41; N, 7.52.
Found: C, 80.66; H, 5.38; N, 7.47.
´
tems include Frechet type rigid dendrons. Therefore, in this work we
have performed the synthesis of a new series of pyrene dendronized
porphyrins of zero and first generations. These Newkome type den-
drimers bear a flexible structure with the aim of facilitating the further
encounter of the pyrene-porphyrin donor-acceptor pair [58,59].
2. Experimental part
2.1. General notes
All the reagents employed in the synthesis were purchased from
Merck Sigma Aldrich and used as received. The solvents used in the
reactions were purified by simple distillation in the presence of a drying
agent (CaH2 for dichloromethane). The products were purified by col-
umn chromatography in silica gel and the composition of the eluting
solvent was selected after thin layer chromatography (TLC) experi-
ments. All compounds were characterized by 1H and 13C NMR spec-
troscopy in CDCl3. NMR spectra were recorded on a Bruker Avance 400
MHz, working at 400 MHz and 100 MHz for 1H and 13C, respectively.
Chemical shifts are reported in parts per million. Multiplicity is given as
s (singlet), d (doublet), t (triplet), q (quadruplet), quint (quintuplet) or m
(multiplet). MALDI-TOF mass spectra were recorded on a Bruker Dal-
tonics Flex Analysis employing dithranol as matrix. FAB analyses were
recorded on an MStation JMS-700 instrument. Elemental analyses were
performed in a Thermo Scientific Flash 2000 elemental analyzer, using a
Mettler Toledo XP6 Automated-S Microbalance and sulfanilamide as
standard (Thermo Scientific BN 217826, attained values N = 16.40%, C
= 41.91%, H = 4.65%, and S = 18.63%; certified values N = 16.26%, C
= 41.81%, H = 4.71%, y S = 18.62%). Absorption spectra were recorded
on a Unicam UV300 spectrophotometer using quartz cells with a width
of 1 cm and THF (spectrometric grade) as solvent. Fluorescence spectra
were carried out on a Horiba Fluorolog 3 spectrophotometer with a
Xenon lamp. The slit width for excitation and emission were set up to 1
nm in both cases.
2.2.3. Synthesis of porphyrin 3
Porphyrin 2 (161.0 mg, 0.217 mmol) and KOH (36.6 mg, 0.652
mmol) were dissolved in a mixture of THF/ethanol 3:1 and heated to
reflux for 3 h. Afterwards, the solvent was evaporated under reduced
pressure. The crude product was dissolved in a mixture of THF/CH2Cl2
1:1 and washed with aqueous HCl (1 N) until pH 5 was reached. The
product was extracted with water and the organic phase dried over
MgSO4 and concentrated under reduced pressure. The obtained solid
was purified by recrystallization in methanol to afford porphyrin 3 as a
purple solid (115.2 mg, 74%). 1H NMR (δ ppm, 400 MHz, CDCl3): 12.26
(s, br, 1H), 8.87–8.83 (m, 8H), 8.21 (m, 6H), 8.12 (d, J = 8.6 Hz, 2H),
7.80–7.72 (m, 9H), 4.28 (t, J = 6.2 Hz, 2H), 2.79 (t, J = 7.4 Hz, 2H),
2.38–2.30 (m, 2H), ꢀ 2.77 (s, 2H). 13C NMR (δ ppm, 100 MHz, CDCl3):
173.5 (CO), 158.8, 142.4, 135.6, 134.8, 134.7, 129.3, 127.8, 126.8,
120.2, 120.1, 112.9, 60.7 (CH2), 31.1 (CH2), 24.0 (CH2). FAB+: m/z
calculated for C48H36N4O3 [M]+: 716.28 found [M]+: 716.51. Elemental
Anal. Calcd (%) for C48H36N4O3: C, 80.43; H, 5.06; N, 7.82. Found: C,
80.36; H, 5.03; N, 7.77.
2.2. Synthesis of the dendritic porphyrin core
2.2.1. Synthesis of ethyl-4-(4-formylphenoxy) butanoate (1)
2.3. Synthesis of the dendritic porphyrins including pyrene fragments 4a,
4b and 4c
Compound 1 was synthesized according to the literature [60]. A
mixture of 4-hydroxybenzaldehyde (1.00 g, 8.3 mmol) and K2CO3,
(1.40 g, 9.6 mmol) was dissolved in anhydrous DMF (5 mL). Then, ethyl
4-bromobutyrate (1.90 g, 9.6 mmol) was added dropwise. The mixture
was heated to 100 ◦C for 5 h. The solvent was removed under reduced
pressure, and the crude was redissolved in CH2Cl2 (30 mL) and washed
with distilled water (3 x 20 mL). The crude product was dried with
Na2SO4, the solution filtrated, and the solvent removed under reduced
pressure. The product was purified by column chromatography using a
mixture hexanes/ethyl acetate 7:3 as eluent. The pure product 1 was
obtained as a yellow liquid (1.63 g, 92%). 1H NMR (δ ppm, 400 MHz,
CDCl3): 9.86 (s, 1H), 7.83 (d, 2H, J = 8.7 Hz), 6.99 (d, 2H, J = 8.7 Hz),
4.13 (q, 2H, J = 7.1 Hz), 4.10 (t, 2H, J = 6.2 Hz), 2.53 (t, 2H, J = 7.2 Hz),
2.15 (quint, 2H, J = 6.7 Hz), 1.26 (t, 3H, J = 7.1 Hz). 13C NMR (δ ppm,
100 MHz, CDCl3): 190.9 (CHO), 173.1 (CO), 164.0 (C), 132.1 (CH),
130.1 (C), 114.8 (CH), 67.2 (CH2), 60.6 (CH2), 30.7 (CH2), 24.5 (CH2),
14.3 (CH3). Elemental Anal. Calcd (%) for C13H16O4: C, 66.09; H, 6.83.
Found: C, 66.05; H, 6.85.
2.3.1. Synthesis of porphyrin 4a
Porphyrin 3 (300.0 mg, 0.420 mmol) and 1-pyrenebutanol (137.6
mg, 0.502 mmol) were dissolved in anhydrous DMF (5 mL) at 5 ◦C.
Then, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) (96.5 mg,
0.502 mmol), N,N-diisopropylethylamine (DIPEA) (0.09 mL, 0.502
mmol) and hydroxybenzotriazole (HOBt) (67.8 mg, 0.502 mmol) were
added. The reaction mixture was allowed to react at room temperature
with stirring for 36 h. The solvent was removed under reduced pressure
and the crude product was extracted with CH2Cl2/water. The organic
phase was dried over MgSO4 and the solvent was removed under
reduced pressure. The crude product was purified by column chroma-
tography using CH2Cl2 as eluent to obtain the desired product 4a as a
purple solid (235.9 mg, 57%). 1H NMR (δ ppm, 400 MHz, CDCl3):
8.87–8.83 (m, 8H), 8.28 (d, J = 8.4 Hz, 1H), 8.23 (d, J = 8.7 Hz, 6H),
8.12–8.06 (m, 6H), 7.97–7.88 (m, 4H), 7.80–7.73 (m, 9H), 7.23 (d, J =
8.3 Hz, 2H), 4.28–4.23 (m, 4H), 3.42 (t, J = 6.1 Hz, 2H), 2.69 (t, J = 7.4
Hz, 2H), 2.30–2.27 (m, 2H), 2.03–1.89 (m, 4H), ꢀ 2.76 (s, 2H). 13C NMR
(δ ppm, 100 MHz, CDCl3): 173.7 (CO), 159.0, 142.4, 136.6, 135.9,
134.9, 134.7, 131.2, 131.1, 130.2, 129.0, 128.1, 128.0, 127.6, 127.4,
126.1, 125.5, 125.3, 125.2, 125.17, 125.15, 124.9, 123.4, 120.2, 120.1,
112.9, 67.4 (CH2), 64.8 (CH2), 33.4 (CH2), 31.7 (CH2), 29.0 (CH2), 28.5
2.2.2. Synthesis of porphyrin 2
A volume of 600 mL of anhydrous CH2Cl2 was poured into a round
bottom flask under inert atmosphere and protected from light. Then,
compound 1 (1.50 g 13.5 mmol), pyrrole (1.76 mL, 25.5 mmol),
2

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Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
(CH2), 25.3 (CH2). FAB+: m/z calculated for C68H52N4O3 [M]+: 972.40
found [M]+: 972.62. Elemental Anal. Calcd (%) for C68H52N4O3: C,
83.92; H, 5.39; N, 5.76. Found: C, 83.96; H, 5.42; N, 7.73.
136.6, 135.9, 134.9, 134.7, 131.2, 131.1, 130.2, 129.0, 128.2, 128.0,
127.6, 127.4, 126.1, 125.5, 125.3, 125.2, 125.17, 125.15, 124.9, 123.4,
120.4, 120.1, 112.9, 67.5 (CH2), 64.8 (CH2), 33.4 (CH2), 31.7 (CH2),
29.0 (CH2), 28.6 (CH2), 25.3 (CH2). MALDI-TOF: m/z calculated for
C68H50N4O3Zn [M]+: 1034.32 found [M]+: 1034.47. Elemental Anal.
Calcd (%) for C68H50N4O3Zn: C, 78.79; H, 4.86; N, 5.41. Found: C,
78.76; H, 4.89; N, 5.38.
2.3.2. Synthesis of porphyrin 4b
Porphyrin 3 (300.0 mg, 0.420 mmol) and 1-aminopyrene (108.9 mg,
◦
0.502 mmol) were dissolved in anhydrous DMF (5 mL) at 5 C. Then,
EDC (96.5 mg, 0.502 mmol), DIPEA (0.09 mL, 0.502 mmol) and HOBt
(67.8 mg, 0.502 mmol) were added. The resulting reaction mixture was
allowed to react at room temperature with stirring for 24 h. Then, the
solvent was evaporated under reduced pressure and the crude product
extracted with CH2Cl2/water. The organic phase was then dried with
MgSO4 and the solvent removed under vacuum. The crude product was
purified by column chromatography using different mixtures of CH2Cl2/
methanol, gradually increasing the polarity until a ratio of CH2Cl2/
methanol 95:5 was reached. The desired product 4b was obtained as a
purple solid (295.3 mg, 77%). 1H NMR (δ ppm, 400 MHz, CDCl3):
8.87–8.80 (m, 8H), 8.52 (d, J = 8.4 Hz, 1H), 8.23 (d, J = 8.7 Hz, 6H),
8.20–7.97 (m, 10H), 7.83–7.75 (m, 9H), 7.38 (d, J = 8.3 Hz, 2H), 4.50 (t,
J = 6.1 Hz, 2H), 3.04 (t, J = 6.1 Hz, 2H), 2.60–2.57 (m, 2H), ꢀ 2.75 (s,
2H). 13C NMR (δ ppm, 100 MHz, CDCl3): 175.9 (CO), 150.8, 150.6,
150.5, 143.2, 135.9, 134.8, 131.2, 131.1, 130.2, 129.0, 128.1, 128.0,
127.6, 127.4, 126.1, 125.5, 125.3, 125.2, 125.17, 125.15, 124.9, 123.5,
120.2, 120.1, 112.9, 67.3 (CH2), 33.1 (CH2), 25.2 (CH2). FAB+: m/z
calculated for C64H45N5O2 [M]+: 915.36 found [M]+: 915.69. Elemental
Anal. Calcd (%) for C64H45N5O2: C, 83.91; H, 4.95; N, 7.64. Found: C,
83.86; H, 5.92; N, 7.60.
2.4.2. Synthesis of the Zn(II) metalloporphyrin 5b
Metalloporphyrin 5b was synthesized following the procedure
described for metalloporphyrin 5a. Porphyrin 4b (50.0 mg, 0.055
mmol), Zn(CH3COO)2⋅2H2O (50.1 mg, 0.275 mmol) and anhydrous
DMF (2 mL). Reaction time 8 h. Metalloporphyrin 5b was obtained as a
purple solid (50.0 mg, 95%). 1H NMR (δ ppm, 400 MHz, CDCl3):
8.96–8.90 (m, 8H), 8.72–8.23 (m, 8H), 8.14–7.89 (m, 9H), 7.83–7.73
(m, 9H), 7.20 (d, J = 8.3 Hz, 2H), 4.33 (t, J = 6.1 Hz, 2H), 2.75 (t, J =
6.1 Hz, 2H), 2.36–2.34 (m, 2H). 13C NMR (δ ppm, 100 MHz, CDCl3):
175.8 (CO), 150.8, 150.5, 143.2, 135.9, 134.8, 131.2, 131.1, 130.2,
129.0, 128.1, 128.0, 127.6, 127.3, 126.1, 125.5, 125.3, 125.2, 125.18,
125,11, 124.9, 123.5, 120.2, 120.1, 112.9, 67.3 (CH2), 33.2 (CH2), 25.2
(CH2). MALDI-TOF: m/z calculated for C64H43N5O2Zn [M]+: 977.27
found [M]+: 977.44. Elemental Anal. Calcd (%) for C64H43N5O2Zn: C,
78.48; H, 4.43; N, 7.15. Found: C, 78.45; H, 4.39; N, 7.13.
2.4.3. Synthesis of the Zn(II) metalloporphyrin 5c
Metalloporphyrin 5c was synthesized following the procedure
described for metalloporphyrin 5a. Porphyrin 4c (15.0 mg, 0.016
mmol), Zn(CH3COO)2⋅2H2O (16.1 mg, 0.080 mmol) and anhydrous
DMF (2 mL). Reaction time 12 h. Metalloporphyrin 5c was obtained as a
purple solid (50.0 mg, 96%). 1H NMR (δ ppm, 400 MHz, CDCl3):
8.91–8.86 (m, 8H), 8.20–8.16 (m, 8H), 8.14–7.87 (m, 9H), 7.77–7.71
(m, 9H), 7.06 (d, J = 8.3 Hz, 2H), 5.34 (d, J = 5.4 Hz, 2H), 4.34 (t, J =
6.1 Hz, 2H), 2.47 (t, J = 6.1 Hz, 2H), 2.28–2.21 (m, 2H). 13C NMR (δ
ppm, 100 MHz, CDCl3): 175.3 (CO), 150.9, 150.6, 150.5, 135.9, 134.96,
134.92, 131.7, 131.6, 131.5, 131.1, 129.4, 128.7, 128.0, 127.9, 127.7,
127.0, 125.5, 125.3, 125.2, 125.17, 125.15, 123.9, 123.4, 120.2, 120.1,
111.9, 67.6 (CH2), 42.5 (CH2), 33.6 (CH2), 25.8 (CH2). MALDI-TOF: m/z
calculated for C65H45N5O2Zn [M]+: 991.29 found [M]+: 991.46.
Elemental Anal. Calcd (%) for C65H45N5O2Zn: C, 78.58; H, 4.57; N, 7.05.
Found: C, 78.56; H, 4.53; N, 7.08.
2.3.3. Synthesis of porphyrin 4c
Porphyrin 3 (300.0 mg, 0.420 mmol) and 1-pyrenemethylamine
hydrochloride (134.9 mg, 0.502 mmol) were dissolved in anhydrous
DMF (5 mL) at 5 ◦C. EDC (96.5 mg, 0.502 mmol), DIPEA (0.09 mL,
0.502 mmol) and HOBt (67.8 mg, 0.502 mmol) were added. The
resulting reaction mixture was allowed to react at room temperature
with stirring for 24 h. The solvent was evaporated at reduced pressure
and the crude product extracted with CH2Cl2/water. The organic phase
was then dried over MgSO4 and the solution concentrated under reduced
pressure. The crude product was purified by column chromatography
using a mixture of hexanes/ethyl acetate 8:2. The desired product 4c
was obtained as a purple solid (306.5 mg, 66%). 1H NMR (δ ppm, 400
MHz, CDCl3): 8.85–8.79 (m, 8H), 8.33 (d, J = 8.4 Hz, 1H), 8.23–7.88 (m,
16H), 7.77–7.75 (m, 9H), 7.10 (d, J = 8.3 Hz, 2H), 5.23 (d, J = 5.4 Hz,
2H), 4.28–4.25 (m, 2H), 2.61–2.57 (m, 2H,), 2.38–2.34 (m, 2H), ꢀ 2.77
(s, 2H). 13C NMR (δ ppm, 100 MHz, CDCl3): 172.3 (CO), 158.9, 142.6,
135.9, 134.9, 131.7, 131.6, 131.5, 131.1, 129.4, 128.7, 128.0, 127.9,
127.7, 127.0, 125.5, 125.3, 125.2, 125.17, 125.15, 124.9, 123.4, 120.2,
120.1, 112.9, 67.5 (CH2), 42.5 (CH2), 33.6 (CH2), 25.9 (CH2). FAB+: m/
z calculated for C65H47N5O2 [M]+: 929.37 found [M]+: 929.80.
Elemental Anal. Calcd (%) for C65H47N5O2: C, 83.94; H, 5.09; N, 7.53.
Found: C, 83.96; H, 5.11; N, 7.48.
2.4.4. Synthesis of the Mg(II) metalloporphyrin 6a
Porphyrin 4a (50.0 mg, 0.051 mmol), Mg(CH3COO)2⋅4H2O (570.7
mg, 2.550 mmol) and triethylamine (0.24 mL, 1.785 mmol) were dis-
solved in anhydrous DMF (3 mL) under inert atmosphere. The mixture
◦
was heated to 140 C and the reaction progress monitored by UV–Vis
spectroscopy until completion after 48 h. The solvent was evaporated
and the crude metallated porphyrin was purified by precipitation using a
mixture of CH2Cl2/hexanes. The product was separated by filtration.
The metalloporphyrin 6a was obtained as a green solid (49.5 mg, 96%).
1H NMR (δ ppm, 400 MHz, CDCl3): 9.00–8.97 (m, 8H), 8.32–8.28 (m,
7H), 8.15–7.89 (m, 10H), 7.86–7.78 (m, 9H), 7.28 (d, J = 8.3 Hz, 2H),
4.34–4.30 (m, 4H), 3.47 (t, J = 6.1 Hz, 2H), 2.75 (t, J = 7.4 Hz, 2H),
2.36–2.32 (m, 2H), 2.09–2.05 (m, 2H), 1.98–1.93 (m, 2H). 13C NMR (δ
ppm, 100 MHz, CDCl3): 174.6 (CO), 150.8, 150.4, 137.6, 136.9, 134.9,
134.7, 131.2, 131.1, 130.2, 129.5, 128.4, 128.0, 127.6, 127.4, 126.1,
125.5, 125.3, 125.2, 125.17, 125.15, 124.9, 123.4, 120.4, 120.1, 112.9,
67.5 (CH2), 64.8 (CH2), 33.7 (CH2), 31.7 (CH2), 29.0 (CH2), 28.6 (CH2),
25.3 (CH2). MALDI-TOF: m/z calculated for C68H50N4O3Mg [M]+:
994.37, found [M]+: 994.56. Elemental Anal. Calcd (%) for
2.4. Synthesis of the dendritic Zn(II) 5a, 5b, 5c and Mg(II) 6a, 6b, 6c
metalloporphyrins including pyrene fragments
2.4.1. Synthesis of Zn(II) metalloporphyrin 5a
Porphyrin 4a (50.0 mg, 0.05 mmol) and Zn(CH3COO)2⋅2H2O (47.2
mg, 0.257 mmol) were dissolved in anhydrous DMF (2 mL) under inert
atmosphere and the resulting solution was heated to 110 ◦C. The reac-
tion was monitored by UV–Vis spectroscopy until completion after 12 h.
The purification of the metallated porphyrin was carried out by pre-
cipitation, using a mixture of CH2Cl2/hexanes. The product 5a was then
separated by filtration (50.1 mg, 94%). 1H NMR (δ ppm, 400 MHz,
CDCl3): 8.94–8.91 (m, 8H), 8.26–8.21 (m, 7H), 8.09–7.93 (m, 10H),
7.80–7.73 (m, 9H), 7.23 (d, J = 8.3 Hz, 2H), 4.28–4.24 (m, 4H), 3.41 (t,
J = 6.1 Hz, 2H), 2.69 (t, J = 7.4 Hz, 2H), 2.31–2.25 (m, 2H), 2.04–1.85
(m, 4H). 13C NMR (δ ppm, 100 MHz, CDCl3): 173.6 (CO), 159.0, 142.4,
C
68H50N4O3Mg: C, 82.05; H, 5.06; N, 5.63. Found: C, 81.98; H, 5.04; N,
5.59.
2.4.5. Synthesis of the Mg(II) metalloporphyrin 6b
Metalloporphyrin 6b was synthesized following the procedure
described for metalloporphyrin 6a. Porphyrin 4b (50.0 mg, 0.055
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Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
mmol), Mg(CH3COO)2⋅4H2O (584.2 mg, 2.730 mmol), triethylamine
(0.27 mL, 1.910 mmol) and anhydrous DMF (3 mL). Reaction time 50 h.
The metalloporphyrin 6b was obtained as a green solid (49.5 mg, 95%).
1H NMR (δ ppm, 400 MHz, CDCl3): 8.96–8.94 (m, 8H), 8.23–8.20 (m,
7H), 8.13–7.79 (m, 10H), 7.78–7.72 (m, 9H), 7.29 (d, J = 8.3 Hz, 2H),
4.33 (t, J = 6.1 Hz, 2H), 2.75 (t, J = 6.1 Hz, 2H), 2.36–2.34 (m, 2H). 13C
NMR (δ ppm, 100 MHz, CDCl3): 176.3 (CO), 151.4, 151.3, 150.5, 141.2,
136.9, 134.7, 131.1, 131.0, 130.2, 129.0, 128.1, 128.0, 127.6, 127.3,
126.1, 125.5, 125.3, 125.2, 125.18, 125.11, 124.9, 123.5, 120.2, 120.1,
112.9, 68.3 (CH2), 34.2 (CH2), 26.2 (CH2). MALDI-TOF: m/z calculated
for C64H43N5O2Mg [M]+: 937.33, found [M]+: 937.53. Elemental Anal.
Calcd (%) for C64H43N5O2Mg: C, 81.92; H, 4.62; N, 7.46. Found: C,
81.88; H, 4.58; N, 7.48.
2H), 1.96–1.84 (m, 6H), 1.22 (s, 3H), ꢀ 2.92 (s, 2H). 13C NMR (δ ppm,
100 MHz, CDCl3): 175.3 (CO), 172.4 (CO), 159.4, 142.1, 136.1, 135.0,
134.1, 130.3 129.7, 129.0, 127.8, 126.1, 120.9, 120.7, 120.6, 68.1 (C),
57.3 (C), 33.2 (CH2), 31.5 (CH2), 29.9 (CH2), 29.0 (CH2), 26.1 (CH2).
FAB+: m/z calculated for C58H51N5O8 [M]+: 947.39, found [M]+:
947.90. Elemental Anal. Calcd (%) for C58H51N5O8: C, 73.63; H, 5.43; N,
7.40. Found: C, 73.60; H, 5.40; N, 7.36.
2.5.3. Synthesis of porphyrin 9
Porphyrin 8 (50.0 mg, 0.058 mmol), 1-pyrenemethylamine chlo-
rhydrate (PyCH2NH2) (46.6 mg, 0.174 mmol), (2-(1H-benzotriazol-1-
yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) (88.0 mg,
0.232 mmol) and DIPEA (0.12 mL, 0.696 mmol) were dissolved in
anhydrous DMF (3 mL) under inert atmosphere. The resulting mixture
was stirred at room temperature for 36 h, concentrated under reduced
pressure and redissolved in CH2Cl2. The organic phase was washed with
water and the resulting solution dried over MgSO4 and concentrated
under reduced pressure. The crude product was purified by column
chromatography in silica gel, using a solvent mixture of CH2Cl2/meth-
anol 95:5 as eluent. The desired product 9 was obtained as a purple solid
(45.8 mg, 50%). 1H NMR (δ ppm, 400 MHz, CDCl3): 8.88–8.85 (m, 4H),
8.76 (d, J = 4.8 Hz, 2H), 8.69 (d, J = 4.8 Hz, 2H), 8.22–8.19 (m, 6H),
7.88–7.62 (m, 38H), 6.95 (d, J = 8.2 Hz, 2H), 6.87 (s, 1H), 6.49 (t, J =
5.4 Hz, 3H), 4.77 (d, J = 5.4 Hz, 6H), 3.86 (t, J = 5.9 Hz, 2H), 2.31 (t, J
= 7.2 Hz, 2H), 2.25 (t, J = 7.5 Hz, 6H), 2.14–2.05 (m, 6H), 2.00–1.96
(m, 2H), ꢀ 2.84 (s, 2H). 13C NMR (δ ppm, 100 MHz, CDCl3): 190.6 (CO),
173.1 (CO), 142.0, 136.2, 136.1, 136.0, 135.2, 131.5, 131.1, 130.3,
130.1, 129.7, 129.0, 128.8, 127.8, 127.7, 127.6, 127.4, 126.9, 126.1,
125.3, 125.2, 125.1, 125.0, 124.9, 123.4, 120.9, 120.7, 120.6, 79.9 (C),
57.9 (C), 41.2 (CH2), 33.2 (CH2), 31.5 (CH2), 31.3 (CH2), 29.9 (CH2),
26.1 (CH2). MALDI-TOF: m/z calculated for C109H84N8O5 [M]+: 1585.88
found [M]+: 1586.25. Anal. Calcd (%) for C109H84N8O5: C, 82.55; H,
5.34; N, 7.07. Found: C, 82.51; H, 5.36; N, 7.03.
2.4.6. Synthesis of the Mg(II) metalloporphyrin 6c
Metalloporphyrin 6c was synthesized following the procedure
described for metalloporphyrin 6a. Porphyrin 4c (15.0 mg, 0.016
mmol), Mg(CH3COO)2⋅4H2O (172.6 mg, 0.800 mmol), triethylamine
(0.80 mL, 0.560 mmol) and anhydrous DMF (3 mL). Reaction time 50 h.
Metalloporphyrin 6c was obtained as a green solid (14.8 mg, 96%). 1H
NMR (δ ppm, 400 MHz, CDCl3): 8.85–8.78 (m, 8H), 8.33 (d, J = 8.4 Hz,
1H), 8.24–8.05 (m, 10H), 7.97–7.88 (m, 6H), 7.79–7.73 (m, 9H), 7.10
(d, J = 8.3 Hz, 2H), 5.21 (d, J = 6.8 Hz, 2H), 4.24 (t, J = 6.1 Hz, 2H),
2.57 (t, J = 6.1 Hz, 2H), 2.36–2.32 (m, 2H). 13C NMR (δ ppm, 100 MHz,
CDCl3): 176.4 (CO), 151.3, 150.6, 150.3, 136.5, 134.9, 134.9, 131.8,
131.2, 131.1, 131.0, 129.4, 128.7, 128.0, 127.9, 127.8, 127.3, 127.0,
126.5, 125.3, 125.2, 125.1, 124.9, 123.9, 123.45, 121.4, 121.2, 111.9,
67.2 (CH2), 42.4 (CH2), 33.5 (CH2), 25.7 (CH2). FAB+: m/z calculated
for C65H45N5O2Mg [M]+: 951.34, found [M]+: 951.59. Elemental Anal.
Calcd (%) for C65H45N5O2Mg: C, 81.97; H, 4.76; N, 7.35. Found: C,
81.95; H, 4.78; N, 7.33.
2.5. Synthesis of the dendritic porphyrins 7, 8 and 9
2.5.1. Synthesis of porphyrin 7
2.6. Metallation of the dendritic porphyrin 9
Porphyrin 3 (50.0 mg, 0.069 mmol) and di-tert-butyl 4-amino-4-[2-
(tert-butoxycarbonyl)ethyl]heptanedioate (aminotriester) (43.5 mg,
0.139 mmol) were dissolved in anhydrous DMF (5 mL) at 5 ◦C [61,62].
Then, EDC (26.8 mg, 0.139 mmol), DIPEA (0.04 mL, 0.209 mmol) and
HOBt (18.9 mg, 0.139 mmol) were added. The resulting reaction
mixture was allowed to react with stirring at room temperature for 36 h.
The solvent was evaporated under reduced pressure and the crude
product extracted with a solvent mixture of CH2Cl2/water. The organic
phase was dried over MgSO4 and the solution concentrated under vac-
uum. The crude product was purified by column chromatography in
silica gel, using hexanes/ethyl acetate 7:3 as eluent. The desired product
7 was obtained as a purple solid (63.5 mg, 82%). 1H NMR (δ ppm, 400
MHz, CDCl3): 8.92–8.79 (m, 8H), 8.22 (d, J = 8.4 Hz, 6H), 8.11 (d, J =
8.4 Hz, 2H), 7.81–7.72 (m, 9H), 7.29 (d, J = 8.4 Hz, 2H), 6.11 (s, 1H),
4.30 (t, J = 5.9 Hz, 2H), 2.51 (t, J = 7.3 Hz, 2H), 2.33–2.25 (m, 8H), 2.05
(dd, J = 8.9, 6.7 Hz, 6H), 1.45 (s, 27H), ꢀ 2.77 (s, 2H). 13C NMR (δ ppm,
100 MHz, CDCl3): 173.4 (CO), 172.2 (CO), 159.1, 142.6, 136.0, 134.9,
134.7, 128.0, 127.1, 126.8, 120.2, 120.1, 112.9, 81.1 (C), 67.7 (C), 34.2
(CH2), 31.3 (CH2), 30.5 (CH2), 30.3 (CH2), 28.5 (CH2), 25.9 (CH3).
FAB+: m/z calculated for C70H75N5O8 [M]+: 1113.56, found [M]+:
1113.85. Elemental Anal. Calcd (%) for C70H75N5O8: C, 75.45; H, 6.78;
N, 6.28. Found: C, 75.41; H, 6.74; N, 6.30.
2.6.1. Synthesis of the Zn(II) metalloporphyrin 10
Metalloporphyrin 10 was synthesized following the procedure
described for metalloporphyrin 5a. Porphyrin 9 (16.0 mg, 0.010 mmol),
Zn(CH3COO)2⋅2H2O (18.5 mg, 0.102 mmol) and anhydrous DMF (2
mL). Reaction time 12 h. The metallated porphyrin 10 was obtained as a
purple solid (45.8 mg, 50%). 1H NMR (δ ppm, 400 MHz, CDCl3):
8.88–8.85 (m, 4H), 8.76 (d, J = 4.8 Hz, 2H), 8.69 (d, J = 4.8 Hz, 2H),
8.22–8.19 (m, 6H), 7.88–7.62 (m, 38H), 6.95 (d, J = 8.2 Hz, 2H), 6.87 (s,
1H), 6.49 (t, J = 5.4 Hz, 3H), 4.77 (d, J = 5.4 Hz, 6H), 3.86 (t, J = 5.9 Hz,
2H), 2.31 (t, J = 7.2 Hz, 2H), 2.25 (t, J = 7.5 Hz, 6H), 2.14–2.05 (m, 6H),
2.00–1.96 (m, 2H), ꢀ 2.84 (s, 2H). 8.82–8.71 (m, 8H), 8.53 (t, J = 5.7 Hz,
3H), 8.21–7.73 (m, 44H), 7.43 (s, 1H), 7.29 (d, J = 8.2 Hz, 2H), 4.92 (d,
J = 5.5 Hz, 6H), 4.19 (t, J = 6.5 Hz, 2H), 2.38 (t, J = 7.2 Hz, 2H),
2.24–2.20 (m, 6H), 2.11–1.98 (m, 8H). 13C NMR (δ ppm, 100 MHz,
CDCl3): 189.3 (CO), 172.4 (CO), 142.1, 136.3, 136.2, 136.0, 135.2,
131.6, 131.2, 130.15, 130.11, 129.7, 129.5, 128.9, 127.9, 127.7, 127.6,
127.4, 126.9, 126.18, 126.13, 125.3, 125.2, 125.1, 125.0, 124.9, 123.4,
120.9, 120.7, 120.6, 81.1(C), 57.8 (C), 41.1 (CH2), 33.3 (CH2), 31.6
(CH2), 31.3 (CH2), 29.9 (CH2), 25.7 (CH2). MALDI-TOF: m/z calculated
for C109H82N8O5Zn [M]+: 1649.25, found [M]+: 1649.43. Calcd (%) for
C
109H82N8O5Zn: C, 79.38; H, 5.01; N, 6.79. Found: C, 79.41; H, 4.98; N,
6.77.
2.5.2. Synthesis of porphyrin 8
Porphyrin 7 (60.0 mg, 0.053 mmol) was dissolved in formic acid (2
mL) (98% v/v) under stirring for 12 h. The remaining acid was evapo-
rated under reduced pressure and the product washed with toluene. The
pure product was obtained as a purple solid (47.9 mg, 96%). 1H NMR (δ
ppm, 400 MHz, CDCl3): 8.85 (m, 8H), 8.22 (d, J = 7.2 Hz, 6H), 8.12 (d, J
= 8.2 Hz, 2H), 7.88–7.79 (m, 9H), 7.36 (d, J = 8.2 Hz, 2H), 4.25 (t, J =
6.3 Hz, 2H), 2.42 (t, J = 7.3 Hz, 2H), 2.23–2.14 (m, 6H), 2.12–2.09 (m,
3. Results and discussion
3.1. Synthesis
The synthesis of the zero generation pyrene porphyrin derivatives 4a
to 4c is shown in Scheme 1. 4-Hydroxybenzaldehyde was reacted in the
presence of ethyl 4-bromobutyrate under Williamson reaction
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Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
Scheme 1. Synthesis of zero generation pyrene dendronized porphyrins 4a–4c, and metallated complexes 5a–5c and 6a–6c.
conditions to give intermediate ethyl-4-(4-formylphenoxy) butanoate
(1) [60]. To construct the porphyrin core, the methodology reported by
Lindsey and coworkers was followed [63–65]. Compound 1 was reacted
in the presence of benzaldehyde and pyrrole using BF3⋅OEt2 as catalyst
at highly diluted concentration, followed by an oxidation with DDQ to
obtain the desired porphyrin compound 2 [39]. Compound 2 was hy-
drolyzed under basic conditions to give the corresponding carboxylic
acid 3. For the synthesis of 4a, 4b and 4c, compound 3 was esterified
using EDC, HOBt and DIPEA in the presence of 1-pyrenebutanol,
1-aminopyrene and 1-pyrenemethylamine, respectively.
dendronized porphyrin 9.
Metallation reactions were performed as previously reported by us
[41]. Zinc acetate was used to metallate zero and first generation pyrene
dendronized porphyrins, while magnesium acetate was used to metal-
late the zero generation porphyrins (Scheme 1 and Scheme 2). The
complexation reactions were monitored by UV–Vis spectroscopy. The
coordination was confirmed by the disappearance of two Q bands
together with a red shift of the Soret band.
3.2. Characterization of the compounds
First generation of Newkome type pyrene dendronized porphyrin 9
(Scheme 2) was synthesized starting from the esterification of com-
pound 3 with aminotriester to give porphyrin 7 [61,62]. Hydrolysis of
compound 7 under basic conditions gave compound 8. Pyrene was
incorporated through amide formation using HBTU and DIPEA in the
presence of 1-pyrenemethylamine to obtain first generation pyrene
Analysis by 1H NMR of all the pyrene dendronized porphyrins pro-
duced similar NMR spectra (Fig. 1). All compounds exhibited two signals
between δ = 8.90 and 8.70 ppm, corresponding to the protons of the
porphyrin core, whereas signals due to the phenyl groups were observed
at δ = 8.23 and 7.76 ppm.
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Dyes and Pigments 191 (2021) 109382
Scheme 2. Synthesis of first generation pyrene dendronized porphyrins 9 and 10.
In addition, for the compounds including the pyrene units (com-
pounds 4a–c and 9), signals of the protons of this moiety were observed
between δ = 8.40 and 7.70 ppm and partially overlapped with those of
the porphyrin moiety. A signal corresponding to the protons at the meso
position of the porphyrin substituted benzylic ring can be observed be-
tween δ = 7.10 and 7.00 ppm. Furthermore, for all compounds three
more signals were observed in the aliphatic region due to the ethyl 4-(4-
formylphenoxy) butanoate fragment at δ = 4.30, 2.60 and 2.30 ppm,
with slight shift variations for the different compounds. Additionally, in
the case of 1-pyrenebutanol, a series of aliphatic signals can be observed
at δ = 3.40, 2.00 and 1.90 ppm. When 1-pyrenemethylamine was
employed as spacer, a signal due to the methylene group was observed at
δ = 5.20–4.80 ppm. The dendritic porphyrin compounds 7 to 10,
showed two signals corresponding to the methylene groups of the
aliphatic chain between δ = 2.30 and 2.05 ppm. Finally, a signal at
ꢀ 2.70 ppm (which shifts to ꢀ 2.80 ppm in some of the compounds),
corresponding to the inner protons of the free-base porphyrins was also
observed. This signal completely disappeared once the porphyrins have
been metallated, being a clear indication that the inner protons have
been replaced by the metal. The characterization of the whole series of
compounds was complemented by FAB+, MALDI-TOF mass spectrom-
etry and elemental analyses. All these results are in agreement with the
proposed structures.
3.3. Optical properties of the studied compounds
The optical properties of the pyrene dendronized porphyrins were
determined by absorption spectroscopy in the UV–vis range in THF so-
lution. This solvent was selected since the obtained dendritic com-
pounds are totally soluble, avoiding the formation of aggregates.
Moreover, the use of viscous solvents such as DMSO or DMF was avoided
since they slow down the encounter between the donor (pyrene) and the
acceptor (porphyrin) groups thereby affecting the velocity and making
more difficult the energy transfer (FRET).
The optical properties of the compounds are summarized in Table 1.
All compounds exhibit the S0→S2 band of pyrene at 344 nm, as well as
the typical bands of the porphyrin: a Soret band at about 418 nm, fol-
lowed by four Q bands between 450 and 700 nm for the free-base
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Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
Fig. 1. 1H NMR spectrum and assignment of signals for compound 4a.
porphyrins and only two Q bands for the metalloporphyrins.
Table 1
The obtained absorption spectra of the pyrene dendronized por-
phyrins bearing butylpyrenyl (4a, 5a, 6a) and methynepyrenyl (4c, 5c,
6c and 9) groups correspond to the sum of the absorption bands of
pyrene and porphyrin moieties, which suggests that there is no signifi-
cant interaction between both chromophores in the ground state.
Interestingly, dendronized porphyrins bearing pyrene directly linked to
Optical properties of the series of compounds.
Compound
Pyrene and Soret bands
Q bands
λ (nm)a
λ (nm)a
ε
(Mꢀ 1 cmꢀ 1
)
b
2
418
344
418
344
418
344
418
344
424
345
424
344
424
344
430
344
430
344
430
344
418
344
424
486,000
50,000
513, 548, 593, 647
514, 550, 592, 648
4a
459,500
44,000
4b
4c
5a
5b
5c
6a
6b
6c
9
515, 550, 592, 648
514, 548, 592, 648
557, 596
452,000
54,000
443,000
42,000
565,000
35,000
556, 596
452,000
46,000
556, 596
457,000
51,500
571, 613
504,000
36,5000
452,000
52,500
572, 612
572, 614
474,500
141,500
493,500
132,000
440,000
514, 548, 592, 648
555, 597
10
a
Maximum absorption wavelength for pyrene, Soret band and Q bands of
each compound.
b
Molar extinction coefficient calculated for pyrene and Soret band.
Fig. 2. Normalized absorption spectra of the free-base pyrene dendronized
porphyrins (4a, 4b, 4c, and 9) in THF.
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Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
amide group (4b, 5b and 6b), showed a significant broadening in the
absorption band of the pyrene, caused by electron delocalization. In
Fig. 2, the absorption spectra of zero and first generation pyrene
dendronized porphyrins 4a–c and 9, respectively is presented.
at 653 nm (Fig. 5A). This band was blue shifted to 603 nm in the Zn(II)
metallated compound 5c and to 618 nm for the Mg(II) derivative 6c. The
second emission band of lower energy appeared at 715 nm for the free-
base porphyrin 4c, whereas this band was blue-shifted for the Zn(II) and
Mg(II) metallated porphyrins, 5c and 6c, exhibiting this band at 654 and
673 nm, respectively.
The molar extinction coefficients (ε) were calculated using the Beer-
Lambert law by plotting a curve of absorbance vs concentration and the
results are shown in Table 1. The obtained values for the molar extinc-
tion coefficients of the Soret band of the porphyrin moiety are comprised
between 443,500 and 486,000 Mꢀ 1 cmꢀ 1, which is in accordance with
When these compounds were excited at 344 nm (Fig. 5B), residual
pyrene monomer emission was observed at 375 nm, followed by the
emission of the porphyrin moiety. This last emission revealed that an
energy transfer phenomenon is occurring from pyrene to porphyrin.
The quantum yields of the pyrene dendronized porphyrins were
determined using the following equation [67]:
the reported
[66].
ε
value of the tetraphenylporphyrin (470,000 Mꢀ 1 cmꢀ 1
)
In the absorption spectra of all pyrene dendronized porphyrins, a
bathochromic shift of the Soret band was observed after the metallation
with either zinc or magnesium (Fig. 3). In all cases the band corre-
sponding to the pyrene moiety was not affected, and the presence of only
two Q bands confirmed that the coordination with the metal occurred.
Finally, compounds 9 and 10 behaved similarly exhibiting a higher
molar extinction coefficient value for the absorption band at 344 nm
than their generation zero analogs, since the number of pyrenes is
significantly increased (Fig. 4). The absorbance ratio Apy (344 nm)/Apor
(Soret 418 nm) for the zero and first generation pyrene dendronized
porphyrins, 4c and 9 was calculated to be 0.11 and 0.29, respectively.
Being the Apy/Apor value for compound 9 three times higher due to its
three-fold pyrene content.
As Fx nx
Ax Fs nx
ΦF(x) = ( )( )( )2ΦF
(1)
(s)
where s stands for standard and x for sample, A is the absorbance at the
excitation wavelength, F is the area under the emission spectra, n is the
refraction index of the solvent and ΦF(s) is the quantum yield of the
standard. To determine the quantum yield, a quinine solution in H2SO4
(1 M) was employed (Φ = 0.55) as a standard for the pyrene moiety and
tetraphenylporphyrin in toluene (Φ = 0.11) was used for the porphyrin
core [68,69]. The results are summarized in Table 2.
3.5. FRET efficiency of the compounds
3.4. Emission properties of the studied compounds
The FRET efficiency (EFRET) was calculated for all compounds and
resulted to be almost quantitative. The results showed that there is an
efficient energy transfer phenomenon from the donor (pyrene) to the
acceptor (porphyrin), when the donor is excited at 344 nm. From the
analysis of the emission spectra, it was observed that the pyrene emis-
sion (λex = 344 nm) decreases considerably from a quantum yield value
of 0.542 for 1-pyrenebutanol to about 0.003, with the appearance of the
emission bands of the porphyrin. The calculated FRET efficiencies were
The fluorescence emission spectra were recorded in THF (A = 0.05)
at room temperature. The excitation wavelengths were 344 nm for the S0
→ S2 transition of the pyrene moiety, 418, 424, and 430 nm for the Soret
band of the free-base, Zn(II)- and Mg(II)-metallated porphyrins,
respectively. The obtained emission spectra are shown in Fig. 5.
The free-base porphyrin 4c exhibited a S(1,0) → S(0,0) emission band
Fig. 3. Normalized absorption spectra recorded in THF.
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Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
Fig. 4. Comparison of normalized absorption spectra of zero and first generation pyrene dendrimers recorded in THF.
Fig. 5. Absolute emission spectra recorded in THF for the free-base 4c and metallated porphyrins 5c and 6c. A) Excitation wavelength corresponding to the Soret
band (see Table 1). B) Excitation wavelength 344 nm. The sharp peak at 688 nm corresponds to the harmonic (double the excitation wavelength).
above 99%. The flexibility of the structures of the pyrene dendronized
Table 2
porphyrins of zero and first generations allowed the encounter of donor
Quantum yields and FRET efficiency of the compounds.
and acceptor chromophores favoring the energy transfer. Moreover, as
Compound
λemission-max
Φ
Φ
Φ
EFRcET
previously reported by our group, no excimer emission was observed
from the pyrene moiety [41,43]. This is due to the rate constant of the
energy transfer is much faster than the rate constant for the excimer
formation.
(nm)a
(pyrene)
λex = 344
nm
(porphyrin)
λex = 344
nm
(porphyrin)
λex = Soret
bandb
(%)
PyOHd
4a
375
375
376
375
375
376
375
375
376
375
376
–
0.542
0.002
0.002
0.002
0.003
0.003
0.003
0.003
0.003
0.003
0.003
–
–
–
The optical properties of these flexible free-base and metallated
dendronized porphyrins were compared to those of a previously re-
ported series bearing more rigid structures. When comparing zero gen-
eration dendronized porphyrins (free base 4a-c, Zn-metallated 5a-c and
Mg-metallated 6a-c) to their rigid homologues (Ref [41]: free base 3,
Zn-metallated 3a and Mg-metallated 3c), it can be observed that the
absorption and emission wavelengths are very similar. In the case of the
first generation dendronized porphyrins, the flexible dendritic molecule
reported here (free-base 9) and its homologue with a more rigid
dendronized porphyrin (Ref [41]: free-base 4) presented similar ab-
sorption and emission wavelengths. However, the flexible dendronized
porphyrins reported in this work exhibited higher EFRET, with values
between 99.4 -99.6%, than the more rigid dendronized porphyrins
previously reported [41], which showed EFRET values between 96 and
99%. From these results, it was concluded that better EFRET were reached
with more flexible structures, which facilitate the encounter between
the donor and acceptor groups in the dendritic molecules.
651
652
652
602
603
603
618
618
618
652
0.047
0.053
0.065
0.037
0.035
0.032
0.102
0.086
0.086
0.032
0.091
0.093
0.086
0.075
0.058
0.063
0.159
0.251
0.243
0.089
99.6
99.6
99.5
99.5
99.5
99.5
99.5
99.5
99.5
99.4
4b
4c
5a
5b
5c
6a
6b
6c
9
a
Emission wavelengths for the pyrene and the Soret bands of each compound.
Excitation at absorption wavelength corresponding to the Soret band (See
b
Table 1).
c
FRET efficiencies were calculated using the following equation: FRET = 1 –
(IDA/ID), where IDA is the integration of the residual emission of the donor when
linked to the acceptor and ID is the integration of the emission of the donor in the
absence of the acceptor.
d
1-Pyrenebutanol.
9

˜
Y. Banales-Leal et al.
Dyes and Pigments 191 (2021) 109382
[11] Tomalia DA, Nixon LS, Hedstrand DM. The role of branch cell symmetry and other
critical nanoscale design parameters in the determination of dendrimer
encapsulation properties. Biomolecules 2020;10(4):642.
4. Conclusions
A novel series of zero and first generation dendritic compounds,
bearing peripheral pyrene groups and a porphyrin core connected with
spacers of different lengths, were synthesized and fully characterized.
These compounds were further metallated with Zn(II) and Mg(II), as was
evidenced by UV–vis absorption where two porphyrin Q bands were
observed instead of the four bands observed for the free-base porphyrin.
The Soret absorption band of the metallated compounds exhibited a red
shift compared with their free-base analogs, whereas, the emission band
was blue shifted. When excited at 344 nm, emission of the porphyrin
moiety and low intensity residual emission of pyrene were observed.
This was a clear indication that FRET occurred. All the studied com-
pounds showed outstanding energy transfer efficiencies, reaching EFRET
values above 99%.
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Author statement
˜
Yoliztli Banales-Leal: Investigation, Data Curation, Validation,
[22] Yip J, Duhamel J, Bahun GJ, Adronov A. A study of the dynamics of the branch
ends of a series of pyrene-labeled dendrimers based on pyrene excimer formation.
J Phys Chem B 2010;114(32):10254–65.
Formal Analysis, Visualization Andrea García-Rodríguez: Methodol-
´
´
ogy, Investigation, Formal Analysis Fabian Cuetara-Guadarrama:
Methodology, Visualization, Writing - Review & Editing Mireille Von-
lanthen: Methodology, Visualization, Investigation, Writing - Review &
Editing Kendra Sorroza-Martínez: Investigation, Data Curation,
Formal Analysis. David Morales-Morales: Resources, Writing Original
Draft, Supervision, Project Administration Ernesto Rivera: Resources,
Writing Original Draft, Supervision, Project Administration, Funding
Acquisition.
[23] Raimbault J, Casier R, Little H, Duhamel J. Hydrophobic and elastic forces
experienced by a series of pyrene end-labeled poly(ethylene oxide)s interacting
with sodium dodecyl sulfate micelles. Macromolecules 2018;51(15):5933–43.
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Pyrene-excimers-based antenna systems. Chem Eur J 2009;15(3):754–64.
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optical, electrochemical properties and conductivity of trans- and cis-poly(1-
ethynylpyrene): a comparative investigation. Polymer 2005;46(13):4789–98.
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[26] Illescas J, Caicedo C, Zaragoza-Galan G, Ramírez-Fuentes YS, Gelover-Santiago A,
Rivera E. Synthesis, characterization and optical properties of novel well-defined di
(1-ethynylpyrene)s. Synth Met 2011;161(9–10):775–82.
[27] Hall T, Whitton G, Casier R, Gauthier M, Duhamel J. Arborescent poly(l -glutamic
acid)s as standards to study the dense interior of polypeptide mesoglobules by
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Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[29] DeRosa MC, Crutchley RJ. Photosensitized singlet oxygen and its applications.
Coord Chem Rev 2002;233–234:351–71.
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Acknowledgements
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[31] Krieger A, Fuenzalida Werner JP, Mariani G, Grohn F. Functional supramolecular
porphyrin-dendrimer assemblies for light harvesting and photocatalysis.
Macromolecules 2017;50(9):3464–75.
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The authors are grateful to Miguel Angel Canseco, Gerardo Cedillo,
[32] Chen J, Fan T, Xie Z, Zeng Q, Xue P, Zheng T, Xue P, Zheng T, Chen Y, Luo X,
Zhang H. Advances in nanomaterials for photodynamic therapy applications: status
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´
˜
´
María de los Angeles Pena Gonzalez and Elizabeth Huerta Salazar for the
technical assistance in the characterization of the compounds. Lucero
Ríos and Carmen García for MALDI-TOF measurements. We are grateful
to PAPIIT-DGAPA (Project IN101119) and CONACyT (Project 279380)
for the financial support.
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11