Synthesis and photophysical properties of novel pyrene-metalloporphyrin dendritic systems

Article abstract of DOI:10.1039/c9dt00855a

A novel series of dendronized porphyrins bearing pyrene units in the periphery (Porph-O-G_n) and their metal complexes (M-[Porph-O-G_n]) are reported. The pyrene-containing Frechet-type dendrons up to the first generation were synthesized and further reacted with 5-phenol-10,15,20-triphenylporphyrin via an esterification reaction to afford the desired pyrene-labeled dendronized porphyrins. Later, these compounds were used as ligands to produce the corresponding complexes of Zn²⁺, Cu²⁺, Mg²⁺ and Mn³⁺. With the compounds in hand, the optical and photophysical properties of the dendritic metalloporphyrins were studied by absorption and fluorescence spectroscopy. The quantum yields, F?rster radius and efficiency of energy transfer were determined and discussed as a function of the structure and the donor-acceptor distances, finding an efficient energy transfer from the pyrene moiety to the metallated porphyrin core in each case.

Full text of DOI:10.1039/c9dt00855a

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[Manuscript submitted for publication as an article in Dalton transactions]
Synthesis and Photophysical Properties of Novel Pyrene-
Metalloporphyrin Dendritic Systems
Sandra M. Rojas-Montoya1, Mireille Vonlanthen1, Pasquale Porcu1, Gabriel Flores-Rojas1,
Andrea Ruiu1, David Morales-Morales2* and Ernesto Rivera1*
1) Instituto de Investigaciones en Materiales, Universidad Nacional
Autónoma de México, Circuito Exterior Ciudad Universitaria
C.P. 04510, Ciudad de México, México.
2) Instituto de Química, Universidad Nacional
Autónoma de México, Circuito Exterior Ciudad Universitaria
C.P. 04510, Ciudad de México, México.
Email: riverage@unam.mx (E.R.) and damor@unam.mx (D.M-M)
---------------------------------------------------------------------------------------------------------
*Author to whom correspondence should be addressed

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Abstract
A novel series of dendronized porphyrins bearing pyrene units in the periphery (Porph-O-
Gn) and their metal complexes (M-[Porph-O-Gn]) are reported. The pyrene-containing
Frechet-type dendrons up to first generation were synthesized and further reacted with 5-
phenol-10,15,20-triphenylporphyrin via an esterification reaction to afford the desired
pyrene-labeled dendronized porphyrins. Later, these compounds were used as ligands to
produce the corresponding complexes of Zn2+, Cu2+, Mg2+ and Mn3+. With the compounds
in hand, the optical and photophysical properties of the dendritic metalloporphyrins were
studied by absorption and fluorescence spectroscopies. The quantum yields, Förster radius
and efficiency of energy transfer were determined and discussed in function of the structure
and the donor-acceptor distances, finding an efficient energy transfer from the pyrene
moiety to the metallated porphyrin core in each case.
Keywords: Dendrimers, Pyrene substituents, Metalloporphyrin, Photophysical properties,
Fluorescence.

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1. Introduction
Dendrimers have represented a motif of great importance and focus of multiple studies
during the last decades due to their notable physical and chemical properties.1–3 They
display promising applications in various fields of materials science ranging from the
elaboration of electroactive and photoactive devices to biological applications for the
administration and release of drugs as well as their use as catalysts in potentially relevant
organic transformations.4–11 Particularly relevant results the field of photoactive
dendrimers, where their photophysical properties can be modulated by careful design of
their architectures. The photoactive units might be located either at the core, in the dendritic
building units or at the periphery, giving rise to different photophysical phenomena, such as
fluorescence resonance energy transfer (FRET) and charge transfer (CT). Being these
processes very important in the design and development of photovoltaic devices.12–17
One of the most commonly used chromophores in dendritic and polymeric
structures is the Pyrene due to its unique and outstanding optical and luminescent
properties.18–25 Moreover, it exhibits the ability to form excimers when its local
concentration increases.25,26 Thus, there are many reports of dendritic and polymeric
architectures incorporating this chromophore and has also been covalently linked to diverse
acceptor groups.27–31
On the other hand, the porphyrin chromophore is among the most investigated
acceptor in dendritic structures due to its versatility and its use in different fields such as
photodynamic therapy, catalysis, non-linear optics and fluorescent switches.32–39 In
addition, one of the most important applications of this chromophore is the design of solar
cells based on molecular systems mimicking to those involved in photosynthesis, acting as
sensitizers of light absorption.40,41 Thus, a large variety of dendritic structures with donor-

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acceptor groups containing porphyrin have been reported,42–44 some of which have been
contributions of our research group, focusing on the study of dendritic structures based on
the pyrene-porphyrin pair of chromophores for energy transfer purposes leading to
astonishing energy transfer efficiencies close to 100%.45–47
Natural porphyrin derivatives with important biological activity for dioxygen
transport and photosynthesis, are based on metalloporphyrin moieties. Complexes of iron,
magnesium and cobalt are found in heme, chlorophyll and vitamin B12, respectively.48,49
Artificial metalloporphyrin complexes such as meso substituted porphyrins are easy to
synthesize and modify. The main feature of these systems is that they exhibit a strong
absorption band in the UV-vis spectrum (Soret band) in the blue region as well as low
intensity Q bands near the red region.50 Changes in the absorption spectra are observed
depending on the metal ion coordinated to the porphyrin ligand.51 It is due to these
photophysical as well as to their redox properties that metalloporphyrins have found
applications in analytical chemistry and catalysis in oxidation reactions as well as building
blocks in the production of metal organic framework.52–58
Thus, in this work, we studied the effect of the metallation of some porphyrins on
the energy transfer from a pyrene moiety. Here, Zn, Cu, Mg, and Mn ions were complexed
to pyrene-labeled dendronized porphyrins. Since metallation strongly affects the optical and
electrochemical properties of the porphyrin chromophore, the UV-vis and fluorescence
properties of all the compounds was studied.

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2. Experimental Section
2.1 General Notes
For the synthesis of the porphyrins, dendrons of zero and first generation Py1G0Br
and Py2G1Br were used.46,59 All the reagents were purchased from Aldrich and used as
received. The solvents employed were purified by simple distillation. The purifications by
means of chromatographic columns were carried out in neutral alumina or silica gel packed
in glass columns, and the eluting solvents for the purifications were determined by thin
layer chromatography. The NMR spectra were recorded on a Bruker Avance 400 MHz,
1
operating at 400 and 100 MHz for H and 13C{1H}, respectively. Matrix-assisted laser
desorption ionization time-of-flight (MALDI-TOF) measurements were conducted with a
Bruker Daltonics Flex Analysis spectrometer. Elemental analyses were done on a Flash
2000 instrument from Thermo Scientific. Absorption spectra of the different compounds
were scanned on a Unicam UV300 spectrophotometer. The absorption spectra were
acquired with a 1 cm path length quartz cell to determine the molar absorption coefficient
of the constructs at the Soret band and at 344 nm for the pyrene band, respectively. The
steady-state fluorescence spectra were recorded in a Fluorolog3 Horiba spectrofluorometer
with Xenon lamp as light source. The slit widths in the excitation and emission
monochromators were adjusted to 1 and 1 nm, respectively. The concentration for all the
compounds was 1.0 × 10-7 and 1.3 × 10-6 M for the porphyrin and pyrene respectively.
Time-resolved fluorescence measurements were performed on Horiba instrument using
Time Correlated Single Photon Counting (TCSPC) and equipped with a NanoLED-350 nm
for pyrene excitation and a NanoLED-425 nm for porphyrin excitation. All decays were
acquired using a time per channel of 219 ps or 55 ps depending on the range of the

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measured lifetime. The instrument response function (IRF) was measured with a LUDOX
solution in water.
2.2 Synthetic procedures for the free-base monosubstituted porphyrins 2.2.1 Synthesis
of 5,10,15,20-tetraphenylporphyrin (TPP) (1) and 5-(4-hydroxyphenyl)-10,15,20-
triphenylporphyrin (Porph-OH) (2)
Compounds 1 and 2 were synthesized according to the method published by our
research group60,61 following the general procedure reported by Lindsey62 for the synthesis
of porphyrins. Symmetric porphyrin 1 was obtained as a purple solid (1.99 g, 17%) and
1
asymmetric porphyrin 2 was obtained also as a purple solid (1.66 g, 14%). TPP (1) δ H
(400 MHz; CDCl3) −2.76 (2H, s, NH), 7.72-7.79 (12H, m, H1, H3), 8.22 (8H, d, J = 7.6 Hz,
H2), 8.86 (8 H, s, H7). δ 13C (100 MHz; CDCl3) 76.7, 77.0, 77.4, 120.2, 126.7, 127.7,
134.6, 142.3. UV-Vis: λmax (THF) / nm 418 ε / dm3 mol-1 cm-1 451,000), 513, 548, 593
and 649 nm. Analysis Elemental: Found: C, 85.91; N, 8.99; H, 4.86. C44H30N4: requires C,
85.97; N, 9.11; H, 4.92%. Porph-OH (2) δ 1H (400 MHz; CDCl3) −2.79 (2H, s, NH), 7.20
(2H, d, J = 8.4 Hz, H3’), 7.74-7.79 (9H, m, H1, H2), 8.07 (2H, d, J = 8.6 Hz, H2’), 8.20-
13
8.23 (6H, m, H3) 8.84-8.89 (8H, m, H7, H8, H12, H13). δ C (100 MHz; CDCl3) 112.9,
120.1, 120.2 ,126.8, 127.8, 129.3, 134.7, 134.8, 135.6, 142.3, 158.7. UV-Vis: λmax (THF) /
nm 418 (ε / dm3 mol-1 cm-1 451 000), 513, 548, 593 and 649 nm.
2.2.2 Synthesis of 5,10,15-triphenyl-20-(4-(4-(pyren-1-yl)butoxy)phenyl) porphyrin
(Porph-0-PyG0) (3)
Py1G0Br (96 mg, 0.28 mmol) and Porph-OH (180 mg, 0.28 mmol) were dissolved in
100 mL anhydrous acetone, then K2CO3 (197 mg, 1.43 mmol) and 18-ether crown-6 in

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catalytic amounts were added to the reaction mixture and allowed to reflux for 72 hours
under inert atmosphere. After this time, the reaction mixture was cooled down to room
temperature and concentrated under vacuum. The crude product was dissolved in
dichloromethane and washed with water. The organic phase was concentrated at reduced
pressure and the crude product purified by flash column chromatography (SiO2,
Hexane/CH2Cl2: 9/1 then CH2Cl2/MeOH: 9.5/0.5). The final product was obtained as a
purple solid (245mg, 96%). δ 1H (400 MHz; CDCl3) −2.74 (2H, s, NH)¸ 2.18-2.31 (4H, m,
H6', H7'), 3.59 (2H, t, J= 7.4 Hz, H8'), 4.35 (2H, t, J= 6.0 Hz, H5'), 7.29 (2H, d, J = 7.3 Hz,
H3'), 7.76-7.83 (9H, m, H1, H3), 8.0-8.09 (4H, m, Hpy), 8.14 (2H, d, J = 8.1 Hz, H2'),
8.19-8.26 (10H, m, 4Hpy, 6H2), 8.43 (1H, d, J = 8.4 Hz, Hpy), 8.85-8.91 (8H, m, H7, H8,
H12, H13). δ 13C (100 MHz; CDCl3) 28.4, 29.4, 33.3, 68.1, 76.7, 77.1, 77.3, 112.7, 119.9,
120.0, 120.1, 123.4, 124.7, 124.8, 124.9, 125.1, 125.2, 125.8 , 126.7, 127.3, 127.5, 127.7,
128.7, 129.9, 130.9, 131.4, 134.4, 134.5, 135.6, 136.6 , 142.2, 158.9. MS (ESI) m/z
calculated for C64H46N4O [M]+: 887.10; found 887.37). UV-Vis: λmax (THF) / nm 344,
417, (ε / dm3 mol-1 cm-1 63 000, 467 000), 512, 549, 592 and 648 nm. Analysis Elemental:
Found: C, 86.39; N, 6.35; H, 5.29. C64H46N4O: requires C, 86.65; N, 6.32; H, 5.23%. Rf
(Hexane/CH2Cl2: 1/1) = 0.57.
2.2.3 Synthesis of 5-(4-((3,5-bis(4-(pyren-1-yl)butoxy)benzyl)oxy)phenyl)-10,15,20-
triphenylporphyrin (Porph-0-Py2G1) (4)
Py2G1Br (113 mg, 0.16 mmol) and Porph-OH (100 mg, 0.16 mmol) were dissolved
in 100 mL of anhydrous DMF, then K2CO3 (109 mg, 0.79 mmol) and 18-crown-6 ether
were added in catalytic amounts to the reaction mixture and allowed to reflux for 72 hours
under inert atmosphere. After this time, the resulting reaction mixture was cooled to room

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temperature and concentrated under vacuum. The crude product was dissolved in
dichloromethane and washed with water. The organic phase was concentrated at reduced
pressure and the product purified by column chromatography (SiO2, Hexane/CH2Cl2: 8/2
then CH2Cl2/MeOH: 9/1). The product was obtained as a purple fluffy solid (180 mg,
90%). δ 1H (400 MHz; CDCl3) -2.52 (2H, s, NH), 2.09 (8H, m, H10', H11'), 3.45 (4H, t, J =
7.6 Hz, H12'), 4.13 (4H, t, J = 6.2 Hz, H9'), 5.18 (2H, s, H5'), 6.63 (1H, t, J = 2.1 Hz, H8'),
6.83 (2H, d, J = 2.1 Hz, H7'), 7.38 (2H, d, J = 8.6 Hz, H3'), 7.83-7.88 (9H, m, H1, H3),
7.91 (2H, d, J = 7.8 Hz, Hpy), 7.96-8.17 (14H, m, Hpy), 8.22 (2H, d, J = 8.6 Hz, H2'), 8.33
(2H, d, J = 9.3 Hz, Hpy), 8.36-8.39 (6H, m, H2), 8.99-9.07 (8H, m, H7, H8, H12, H13).δ
13C (100 MHz; CDCl3) 28.3, 29.2, 33.2, 67.9, 70.3, 76.7, 77, 77.3, 101.08, 106.1, 113.2,
120, 120.1, 123.4, 124.7, 124.83, 124.86, 125, 125.1, 125.8, 126.6, 126.7, 127.2, 127.5,
127.7, 128.6, 129.8, 130.9, 131.4, 134.6, 134.8, 135.6, 136.5, 139.3, 142.2, 160.5. MS
(MALDI-TOF) m/z calculated for C91H68N4O3 [M]+: 1265.57; Found 1265.55. UV-Vis:
λmax (THF) / nm 344, 418, (ε / dm3 mol-1 cm-1 101 000, 456 000), 512, 549, 592 and 648
nm. Analysis Elemental: Found: C, 64.34; N, 4.41; H, 5.45. C91H68N4O3: requires C, 86.36;
N, 4.43; H, 5.42%. Rf (Hexane/CH2Cl2: 4/6) = 0.4.
2.3 Synthetic procedures for the monosubstituted metalloporphyrins
2.3.1 General methodologies for the metallation reactions
A. The corresponding porphyrin and the metal salt were dissolved in DMF under
inert atmosphere and heated to 110°C. The reaction was monitored by UV-Vis
spectroscopy. It was observed that the reaction was finished after 3 hours. The purification
of the metallated porphyrins was carried out by precipitation using a mixture
dichloromethane/hexane.

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B. The corresponding porphyrin and the metal salt were dissolved in DMF under
inert atmosphere and heated to reflux. The reaction was monitored by UV-Vis
spectroscopy. It was observed that the reaction was finished after 12 hours. The purification
of the metallated porphyrins was carried out by precipitation using a mixture
dichloromethane/hexane.
2.3.2 Synthesis M-[TPP] series
Zn-TPP (1a): TPP (300 mg, 0.48 mmol) and Zn(CH₃CO2)₂·2H₂O (448 mg, 2.44
mmol), following the metallation method A. Compound 1a was obtained as a light purple
solid (147mg, 45%). δ 1H (400 MHz; CDCl3) 7.72-7.79 (12H, m), 8.21-8.24 (8H, m), 8.95
(8 H, m). MS (MALDI-TOF) m/z calculated for C44H28ZnN4 [M+H]+: 678.12; Found
678.16. UV-Vis: λmax (THF) / nm 423 ( ε / dm3 mol-1 cm-1 661,500), 556 and 593 nm.
Analysis Elemental: Found: C, 77.86 ; N, 8.23; H, 4.08. C44H28ZnN4: requires C, 77.93; N,
8.26; H, 4.16%.
Cu-TPP (1b): TPP (200 mg, 0.33 mmol) and CuCl2·4H2O (438 mg, 3.26 mmol),
following the metallation method A. Compound 1b was obtained as a dark purple solid
(161mg, 72%). MS (MALDI-TOF) m/z calculated for C44H28CuN4 [M]+: 676.27; Found
676.25. UV-Vis: λmax (THF) / nm 415 ( ε / dm3 mol-1 cm-1 439 500), 540 nm. Analysis
Elemental: Found: C, 78.13; N, 8.16; H, 4.09. C44H28CuN4: requires C, 78.15; N, 8.12; H,
4.17%.
48
Mg-TPP (1c): TPP (300 mg, 0.48 mmol) and MgCl2·4H2O (2094 mg,
9.77 mmol) in basic medium using triethylamine (988 mg, 1.36 mL, 9.768 mmol),
following the metallation method B. Compound 1c was obtained as a green solid (172mg,
1
56%). δ H (400 MHz; CDCl3) 7.71-7.75 (12H, m), 8.21-8.24 (8H, m), 8.84 (8 H, m). MS

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(MALDI-TOF) m/z calculated for C44H28MgN4 [M]+: 637.03; Found 637.02. UV-Vis:
λmax (THF) / nm 429 ( ε / dm3 mol-1 cm-1 552 500), 571 and 613 nm. Analysis Elemental:
Found: C, 82.93 ; N, 8.74; H, 4.38. C44H28MgN4: requires C, 82.96; N, 8.80; H, 4.43%.
MnCl-TPP (1d): TPP (300 mg, 0.48 mmol) and MnCl2·4H2O (483 mg, 2.44
mmol), following the metallation method B. Compound 1d was obtained as a green solid
(153 mg, 45%). MS (ESI) m/z calculated for C44H28MnN4Cl [M-Cl]+: 667.17; Found
667.17. UV-Vis: λmax (THF) / nm 369, 396, 476 ( ε / dm3 mol-1 cm-1 35 000, 31 500, 69
000), 586 and 623 nm. Analysis Elemental: Found: C, 75.14; N, 7.92; H, 4.00.
C44H28MnN4Cl: requires C, 75.16; N, 6.89; H, 4.01%.
2.3.3 Synthesis M[Porph-O-Py G0] series
Zn-Porph-O-PyG0 (3a): Porph-O-PyG0 (150 mg, 0.17 mmol) and
Zn(CH₃CO2)₂·2H₂O (117 mg, 0.85 mmol), following the metallation method A.
Compound 3a was obtained as a light purple solid (162 mg, 84%). δ 1H (400 MHz; CDCl3)
2.17-2.27 (4H, m), 3.54-3.61 (2H, m), 4.31-4.35 (2H, m), 7.26 (2H, m), 7.73-7.81 (9H, m),
8.05-8.12 (6H, m), 8.21-8.23 (9H, m), 8.39-8.43 (1H, m), 8.97-8.94 (8H, m). MS (MALDI-
TOF) m/z calculated for C64H44ZnN4O [M+H]+: 950.46; Found 951.92. UV-Vis: λmax
(THF) / nm 344, 424, ( ε / dm3 mol-1 cm-1 55 000, 579 000), 556 and 593 nm. Analysis
Elemental: Found: C, 80.85 ; N, 5.86; H, 4.64 %. C64H44ZnN4O: requires C, 80.88; N, 5.89;
H, 4.67%.
Cu-Porph-O-PyG0 (3b): Porph-O-PyG0 (150 mg, 0.17 mmol) and CuCl2·4H2O
(227 mg, 1.69 mmol), following the metallation method A. Product 3b was obtained as a
dark purple solid (130 mg, 80%). MS (MALDI-TOF) m/z calculated for C64H44CuN4O

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[M+H]+: 948.60; Found 948.92. UV-Vis: λmax (THF) / nm 344, 416, ( ε / dm3 mol-1 cm-1
50 000, 495 000), 540 nm. Analysis Elemental: Found: C, 80.97; N, 5.87; H, 4.64.
C64H44CuN4O: requires C, 81.03; N, 5.91; H, 4.68 %.
Mg-Porph-O-PyG0 (3c): Porph-O-PyG0 (300 mg, 0.34 mmol) and MgCl2·4H2O
(1451 mg, 6.77 mmol) in basic medium using triethylamine (685 mg, 0.94 mL, 6.77 mmol),
following the metallation method B. Product 3c was obtained as a green solid (202 mg,
1
65%). δ H (400 MHz; CDCl3) 1.70-2.16 (4H, m), 3.52-3.56 (2H, m), 4.24-4.29 (2H, m),
7.27 (2H, m), 7.70-7.76 (9H, m), 7.97-8.11 (6H, m), 8.15-8.20 (9H, m), 8.38-8.41 (1H, m),
8.84-8.88 (8H, m). MS (MALDI-TOF) m/z calculated for C64H44MgN4O [M]+: 909.36;
Found 909.88. UV-Vis: λmax (THF) / nm 344, 430, ( ε / dm3 mol-1 cm-1 48 000, 453 000),
571 and 613 nm. Analysis Elemental: Found: C, 84.48 ; N, 6.12; H, 4.83. C64H44MgN4O:
requires C, 84.53; N, 6.16; H, 4.88%.
MnCl-Porph-O-PyG0 (3d): Porph-O-PyG0 (300 mg, 0.34 mmol) and MnCl2·4H2O
(335 mg, 1.69 mmol), following the metallation methodology B. Product 3d was obtained
as a green solid (132 mg, 40%). MS (ESI) m/z calculated for C64H44MnN4OCl [M-Cl]+:
940.02; Found 939.29. UV-Vis: λmax (THF) / nm 344, 369, 396, 474 ( ε / dm3 mol-1 cm-1
79 000, 50 000, 50 500, 96 500), 580 and 623 nm. Analysis Elemental: Found: C, 78.75; N,
5.68; H, 4.57. C64H44MnN4OCl: requires C, 78.80; N, 5.74; H, 4.55%.
2.3.4 Synthesis M[Porph-O-Py2 G1] series
Zn-Porph-O-Py2G1 (4a): Porph-O-Py2G1 (50 mg, 0.039 mmol) and
Zn(CH₃CO2)₂·2H₂O (55 mg, 0.395 mmol), following the metallation method A. The
metallated porphyrin product was purified by column chromatography (Al2O3, CH2Cl2 then
CH2Cl2/MeOH: 9/1). Compound 4a was obtained as a purple solid (42 mg, 81%). δ 1H (400

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MHz; CDCl3) 1.97-2.08 (8H, m), 3.39-3.43 (4H, m), 4.03-4.07 (4H, m), 5.21-5.29 (2H, m),
6.42-6.46 (1H, m), 6.71-6.72 (2H, m), 7.69-7.77 (2H, m), 7.74-8.07 (18H, m), 8.10 (2H,
m), 8.19-8.27 (6H, m), 8.90-9.96 (8H, m). MS (MALDI-TOF) m/z calculated for
C91H66ZnN4O3 [M+H]+: 1,328.90; Found 1,330.55. UV-Vis: λmax (THF) / nm 344, 424
( ε / dm3 mol-1 cm-1 99 000, 614 500), 556 and 593 nm. Analysis Elemental: Found: C,
82.21 ; N, 4.18; H, 4.17. C91H66ZnN4O3: requires C, 82.25; N, 4.22; H, 5.01%.
Cu-Porph-O-Py2G1 (4b): Porph-O-Py2G1 (50 mg, 0.039 mmol) and CuCl2·4H2O
(106 mg, 0.7908 mmol), following the metallation method A. The metallated porphyrin
product was purified by column chromatography (Al2O3, Hexane/CH2Cl2: 8/2 then
Hexane/CH2Cl2: 1/1). Compound 4b was obtained as a red solid (41 mg, 78%). MS
(MALDI-TOF) m/z calculated for C91H66CuN4O3 [M+H]+: 1,327.07; Found 1,329.61. UV-
Vis: λmax (THF) / nm 344, 416 ( ε / dm3 mol-1 cm-1 83 000, 434 500), 540 nm. Analysis
Elemental: Found: C, 82.46; N, 4.24; H, 5.04. C91H66CuN4O3: requires C, 82.36; N, 4.22;
H, 5.01%.
Mg-Porph-O-Py2G1 (4c): Porph-O-Py2G1 (50 mg, 0.039 mmol) and MgCl2·4H2O
(254 mg, 1.186 mmol) in basic medium triethylamine (120 mg, 0.165 mL, 1.186 mmol).
following the metallation method B. The metallated porphyrin product was purified by
column chromatography (Al2O3, CH2Cl2 then CH2Cl2/MeOH: 9.5/0.5). Compound 4c was
1
obtained as a green solid (20 mg, 40%). δ H (400 MHz; CDCl3) 1.93-2.09 (8H, m), 3.38-
3.43 (4H, m), 4.00-4.06 (4H, m), 5.13-5.19 (2H, m), 6.43-6.45 (1H, m), 6.70-6.71 (2H, m),
7.68-7.77 (2H, m), 7.69-8.08 (18H, m), 8.11 (2H, m), 8.18-8.28 (6H, m), 8.81-9.96 (8H,
m). MS (MALDI-TOF) m/z calculated for C91H66MgN4O3 [M+H]+: 1,287.83; Found
1,289.71. UV-Vis: λmax (THF) / nm 344, 430 ( ε / dm3 mol-1 cm-1 83 500, 506 000), 571

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and 613 nm. Analysis Elemental: Found: C, 84.83 ; N, 4.31; H, 5.13. C91H66MgN4O3:
requires C, 84.87; N, 4.35; H, 5.17%.
MnCl-Porph-O-Py2G1 (4d): Porph-O-Py2G1 (50 mg, 0.039 mmol) and
MnCl2·4H2O (59 mg, 0.29 mmol) following the metallation method B. The metallated
porphyrin product was purified by column chromatography (Al2O3, CH2Cl2/Hexane 9:1
then CH2Cl2/MeOH: 9.5/0.5). Compound 4d was obtained as a green solid (43 mg, 81%).
MS (MALDI-TOF) m/z calculated for C91H66MnN4O3Cl [M-Cl]+: 1318.49; Found
1,320.62. UV-Vis: λmax (THF) / nm 344, 369, 396, 474 (ε / dm3 mol-1 cm-1 123 000, 59
000, 52 500, 119 000), 580 and 623 nm. Analysis Elemental: Found: C, 80.75; N, 4.13; H,
4.88. C91H66MnN4O3Cl: requires C, 80.73; N, 4.14; H, 4.91%.
3. Results and Discussion
3.1. Synthesis and Characterization
Compounds 1 and 2 were synthesized according to the method previously published
by us60,61 and following the synthetic route reported by Lindsey62. A mixture of pyrrole,
benzaldehyde and 4-hydroxybenzaldehyde in anhydrous dichloromethane was reacted in
the presence of borontrifluoride dietherate and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
to obtain the corresponding porphyrinic units (Scheme 1).
The synthesis of compounds 3 and 4 was carried out by a convergent synthesis,
using compound 2 as the porphyrinic core and the corresponding pyrene labeled dendron of
zero and first generation, previously reported by us too.46,59 Compound 2 and the
corresponding bromide of generation zero and one were reacted by a Williamson reaction
protocol, using K2CO3 as base and acetone as solvent to produce zero generation

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dendronized porphyrin 3 and using DMF as solvent to obtain the first generation
dendronized porphyrin 4.
In order to find the proper reaction conditions for the metallation of the porphyrins,
reactions were performed using the free-base TPP and various solvents such as acetone,
dichloromethane, chloroform, leading to successful metallations affording the different M-
[TPP] complexes. However, the resulting dendrimers turned out to be poorly soluble in the
above-mentioned solvents, leading to choose DMF as the best solvent for their synthesis.
Metalloporphyrins were synthesized using zinc acetate63,64 or copper 65, magnesium
65
and manganese chlorides 66. In the case of the porphyrins including Zn, Cu and Mg,
neutral M(II) complexes were obtained, whereas in the case of the Mn-porphyrins
derivatives the metal ion was found in a Mn(III) oxidation state, this being inferred from
the UV-Vis spectra/data previously reported.67,68 In good agreement with Mn(II) being
reported to be unstable and easily oxidized to Mn(III).
For each of the reactions, the free base porphyrins were dissolved in DMF until the
solutions became homogeneous and then the corresponding metallic salt was added. The
reaction mixture was sonicated in order to properly dissolve all components and heated
according to the conditions reported in the experimental section. These reactions were
carried out under an inert atmosphere and monitored by UV-Vis spectroscopy.

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(Z)
(Z)
H
O
H
O
NH
N
N
N
N
N
N
I
OH
+
X
HN
(Z)
OH
(Z)
1
X= 2H
2
1a X= Zn
II
1b X= Cu
1c X= Mg
1d X= Mn
(Z)
N
N
N
III
2
X
O
N
(Z)
3
X= 2H
3a X= Zn
3b X= Cu
3c X= Mg
3d X= Mn
II
O
O
(Z)
N
N
N
IV
2
X
O
N
(Z)
4
X= 2H
4a X= Zn
II
4b X= Cu
4c X= Mg
4d X= Mn
Scheme 1. General scheme of synthesis. Reaction conditions: I. (1) CH2Cl2, Pyrrole, rt, 15
min (2) BF3-OEt2, rt, 15 min (3) DDQ, rt, 1h. 1) 17%, 2) 14% II. DMF, M-[ L ], heating.
III. Acetone, Py1G0Br, K2CO3, 18-C-6, reflux, 72h, 96%. IV. DMF, Py2G1Br, K2CO3, 18-
C-6, reflux, 72h, 90%.

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1
The H NMR spectrum of Porph-O-PyG0 (Figure 1) shows a signal at 8.91-88.85
ppm due to protons H7, H8, H12 and H13 of the porphyrin nucleus. In the region of 8.26-
819 are the signals corresponding to 6 protons of the H2 phenolic ring and between 7.83
and 7.76 a signal corresponding to the porphyrinic protons (H1, H3) integrates to 9 protons.
The signal corresponding to the protons H2' and H3' appears as doublets at 8.14 and 7.29
ppm respectively, integrating to two protons each. Two triplets due to the protons H5' and
H8' can be observed at 4.35 and 3.59 integrating for 2 protons α and 2 protons δ of the
aliphatic chain. In the same way, we observe a multiple signal between 2.31 and 2.18 ppm
due to the protons H6’ and H7’ integrating for 4 protons. The internal NH protons of the
porphyrin appear at -2.74 ppm integrating for two protons. The signals corresponding to the
pyrene protons were observed in the spectrum as a doublet at 8.43 ppm integrating for one
proton, a multiplet at 8.26- 8.19 ppm integrating for 4 protons as well as a multiplet at 8.09-
8.0 ppm integrating for 4 protons, correspond to the total of expected protons for the pyrene
ring. On the other hand, the 1H spectrum of Porph-O-Py2G1 (Figure 2) is similar to that of
the generation zero compound, with an additional singlet at 5.18 ppm corresponding to the
benzylic protons H5' integrating to two protons, a doublet at 6.83 ppm due to the ortho
protons of the benzyl ring H7' integrating for 2 protons, a triplet at 6.63 ppm corresponding
to the proton for the benzyl ring H8' integrating for one proton, the signals of the aliphatic
chain integrate for 4 protons α and 4 protons δ. Likewise an increase in the integration of
protons β and γ of the same chain (8 protons) and of the pyrene protons is observed,
integrating for 18 protons.

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Figure 1. 1H NMR spectrum and assignment of signals for compound 3.
Figure 2. 1H NMR spectrum and assignment of signals for compound 4.

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The characterization of the metallated porphyrins was performed by absorption and
mass spectrometry techniques in order to confirm the formation of the desired structures. In
the absorption spectra of the complexes, the reduction from 4 to 2 Q bands is a good
indication that the metallation reactions occurred. Furthermore the formation of the
complexes was confirmed by MALDI-TOF mass spectrometry using dithranol as a matrice.
In each case the expected mass was obtained.
3.2. Absorption spectra of the dendronized porphyrins
The UV-Vis absorption spectra of all the compounds were measured using THF as
solvent. In the absorption spectra of the free-base porphyrins 1, 3 and 4, the characteristic
Soret band as well as the Q bands of this chromophore were observed (Figure 3 A-C). The
Soret band is observed at 416 nm with high molar absorption coefficients (Table 1),
corresponding to the S0 → S2 transition. Four bands of low intensity (Q bands) were
observed at 513, 548, 593 and 649 nm, which are due to the S0 → S1 transition.
Additionally, the absorption spectra of compounds 3 and 4 show a characteristic band for
the pyrene chromophore at 344 nm, arising from the S0 → S2 transition. An increase of the
molar absorption coefficient of this band was observed according to the number of pyrene
units present in the constructs (Table 1).
When comparing the absorption spectra of the free-base porphyrin with those of the
metallated porphyrins, various changes can be observed, such as a shift of the Soret band as
well as a reduction in the number of Q bands. Those changes are characteristic for the
metallation of porphyrins and are a good indication that the metallation occurred in the

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corresponding porphyrins. All the absorption wavelengths and molar absorption
coefficients of the metalloporphyrins are reported in Table 1.
The absorption spectra of the metallated porphyrins show an intense Soret band
with a hypsochromic shift for the Cu complexes (Figure 3 G-I) and a bathochromic shift
for Zn (Figure 3 D-F) and Mg complexes (Figure 3 J-L). Two Q bands of lower intensity
are observed in the case of Zn and Mg and only one Q band is observed in the case of Cu.64
For the porphyrin-Mn(III) derivative the absorption spectra changed drastically (Figure 3
M-O), here the Soret band is divided in two with lower molar extinction coefficients, both
67
bands appearing at 369 and 476 nm, respectively.
This can be due to a stronger
interaction between the metal and the porphyrin Q bands 69
As observed in the free-base porphyrin series, the absorption spectra of the pyrene
labeled dendronized metalloporphyrin compounds exhibit an additional band at 344 nm
corresponding to the S0 → S2 transition of the pyrene chromophore with an increase in its
molar absorption coefficient according to the number of pyrene units in the molecular
construct. In the case of the porphyrin metallated with Mn, the absorption bands of
metallated porphyrin center overlap with the absorption bands of the pyrene chromophore.
However, the obtained molecular coefficient corresponds to the sum of the individual
components indicating that no interaction is taking place in the ground state. This
observation is true for all the compounds presented in this study.

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Figure 3. Normalized absorption spectra recorded in THF. A) Free base porphyrin 1. B)
Free base porphyrin 3. C) Free base porphyrin 4. D) 1 and Zn-porphyrin 1a. E) 3 and Zn-
porphyrin 3a. F) 4 and Zn-porphyrin 4a. G) 1 and Cu-porphyrin 1b. H) 3 and Cu-porphyrin
3b. I) 4 and Cu-porphyrin 4b. J) 1 and Mg-porphyrin 1c. K) 3 and Mg-porphyrin 3c. L) 4

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and Mg-porphyrin 4c. M) 1 and Mn-porphyrin 1d. N) 3 and Mn-porphyrin 3d. O) 4 and
Mn-porphyrin 4d.
Table 1. Absorption coefficients of the porphyrinic compounds with their respective absorption
bands.
Pyrene and Soret Bands
Q Bands
λ (nm) c
λ (nm) a
ε (dm3 mol-1 cm-1)
Compound
b
1
416
423
415
429
344
36967
39667
47667
344
417
344
424
344
416
344
430
344
369
396
474
344
418
344
424
344
416
344
430
344
369
396
451 000
661 500
439 500
552 500
23 400
35 000
31 500
69 000
63 000
467 000
55 000
579 000
50 000
495 000
48 000
453 000
79 000
50 000
50 500
96 500
101 000
456 000
99 000
614 500
83 000
434 500
83 500
506 000
123 000
59 000
52 500
513, 548, 593,649
556, 593
54064
1a 63,64
1b 65
1c 65
571, 613
1d 66
586, 623
3
513, 548, 593, 649
556, 593
3a
3b
3c
540
571, 613
3d
580, 623
4
512, 549, 592, 648
4a
4b
4c
556, 593
540
571, 613.
580, 623.
4d

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476
119 000
aMaximum absorption wavelength of the pyrene unit and the Soret band for each
b
compound. Values of the absorption coefficients calculated at the pyrene unit and Soret
band of the porphyrin. c Absorption wavelength for Q bands.
3.3 Emission Spectra of the dendronized porphyrins
The fluorescence emission spectra of the free-base and metallated porphyrins were
measured in THF at room temperature by taking the necessary precautions as previously
reported by our research group.46 Excitations were performed at 344 nm for the pyrene
band as well as at the wavelength corresponding to the Soret band of each compound. All
measurements were made with the same absorbance of approximately 0.05 at the excitation
wavelength.
The obtained fluorescence spectra are shown in Figures 4 when the excitation was
performed at the Soret band and in Figure 5 when excited at the wavelength of the pyrene
band (344 nm). In all spectra, the emission is reported as absolute fluorescence intensity,
which means that the total integration of the emission spectra corresponds to the calculated
quantum yield listed in Table 2.
When the Soret band is excited, the transitions S(1,0) → S(0,0) for the free base
porphyrins are observed approximately at 652 nm and for the porphyrin derivatives
including Zn, Mg and Cu at 600, 630 and 650 nm respectively. The transitions of lower
energy S(1,0)→S(0,1) for the non-metallated porphyrins are observed at approximately 717
nm and for those metallated with Zn, Mg and Cu at 655, 680 and 714 respectively (Figures
S9-S12, Supporting Information).
A comparison of the quantum yields of the series of compounds studied when
excited at the wavelength of the Soret band, higher values were observed for the complexes

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with magnesium followed by those of zinc. The complexes of copper and manganese
exhibited very weak or no fluorescence at all. Increasing the generation of the dendrimer
leads to a slight decrease in the quantum yields of all the metallated porphyrin series.
Furthermore, when the compounds were excited at the pyrene band (344nm),
residual emission from pyrene at 376 nm as well as emission from the porphyrinic moiety
were observed. The calculated quantum yields between 0.002 and 0.026 for the emission of
pyrene revealed a drastic quenching compared with the quantum yield of 1-pyrenbutanol
(Py-But-OH, φ=0.524) (Table 2). This indicates that a very efficient energy transfer form
pyrene to the metallated porphyrins is taking place in all cases. The quantum yield of the
porphyrinic moiety when excited at 344 nm is lower than when excited directly at the
corresponding Soret band. However, as observed for the direct excitation of the porphyrin
moiety, the complexes of Mg exhibit higher quantum yields. The same trend is observed for
the emission of the metalloporphyrin series through direct excitation , following this order:
Mg > Zn > Cu >> Mn (Figure 5).

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Figure 4. Emission spectra recorded in THF: A) Free base porphyrin 1 and metalation
series 1a, 1b, 1c, 1d excited at the Soret band (see Table 1). B) Free base porphyrins 3 and
metalation series 3a, 3b, 3c, 3d excited at the Soret band (see Table 1). C) Free base
porphyrins 4 and metalation series 4a, 4b, 4c, 4d excited at the Soret band (see Table 1).
Figure 5. Emission spectra in THF of free base and metallated porphyrins series excited at 344 nm.
The sharp peak at 688 nm corresponds to the harmonic (double the excitation wavelength).

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Table 2. Quantum yields and FRET efficiencies of porphyrin compounds.
φ (Porph)
φ (Pyrene)
λEx=344 b
φ (Porph)
λEx=344 c
λEm-max (nm) a
λEx=Soret
Band d
EFret
e
Compound
2
-
652
-
-
-
-
0.094
-
-
-
-
-
-
-
-
Py-But-OH
376
-
0.524
-
1
650
600
652
617
nd
-
0.110
0.064
0.015
0.217
nd
1a
1b
1c
1d
3
-
-
-
-
-
-
-
-
-
-
-
-
375
375
375
376
375
376
376
376
376
376
652
603
652
618
nd
0.021
0.026
0.007
0.009
0.006
0.002
0.005
0.002
0.009
0.005
0.010
0.004
0.001
0.012
nd
0.110
0.061
0.002
0.194
nd
0.96
0.95
0.99
0.98
0.98
0.99
0.99
0.99
0.98
0.99
3a
3b
3c
3d
4
652
602
nd
0.005
0.004
0.0002
0.011
nd
0.060
0.053
nd
4a
4b
4c
4d
618
0.185
nd
nd
a Excitation wavelength for the pyrene and the Soret bands for each compound. b Quantum yields were determined
usingquininein1MH2SO4 solutionasstandard(φ=0.54)70,71. c Quantumyieldoftheporphyrincorethathassuffered
FRETfromanexcitedpyrenetotheporphyrin, usingTPPinaTHFsolutionasstandard(φ=0.11). dQuantumyields
were determined using TPP in THF solution as standard (φ=0.11). e FRET efficiencies were calculated with the
subsequent equation: EFRET=1−I(Py+Porphyrin)/I(Py), where I(Py+Porphyrin) is the integration of the residual
emission of pyrene when linked to the porphyrin acceptor and I(Py) is the integration of the emission of pyrene in the
absence of the porphyrin acceptor. nd: Indicates that the compound is not presenting emission at the specified
wavelength.
The Förster radius for pyrene-porphyrin donor-acceptor pair was calculated using
equation 1 in order to ensure that FRET can take place in the constructs.
1
푅0 = 9790(푘2푛2휙퐷퐽(휆))6
(퐄퐪.ퟏ)
Where R0 is the Förster radius, k is the orientation factor, n is the refractive index of
the solvent, φD is the quantum yield of the donor and J(λ) is the overlap integral of the
pyrene/porphyrin pair of chromophores. The spectral overlap was calculated using
equation 2:

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∫∞퐹퐷 (휆)휀퐴(휆)휆4푑휆
0
퐽(휆) =
(퐄퐪. ퟐ)
∫∞퐹퐷(휆)푑휆
0
where FD(λ) is the fluorescence of the normalized emission spectra of the donor at λ, εA(λ)
is the extinction coefficient of the acceptor at λ.70
In order to calculate the Förster radius in the constructs of the series of compound 3-
3d and 4-4d, the optical properties of the separate donor and acceptor groups were taken
into account. The superposition integral for the specific donor-acceptor pair was calculated
starting from the absorption spectra of the 1a, 1b, 1c, 1d acceptor series and the emission
spectrum of 1-pyrenbutanol (Py-But-OH) as donor. Compounds with the highest Förster
radius were 1 and Cu complex 1b with values of 4.8 nm each. In the case of the Zn 1a and
Mg 1c complexes, the Förster radius was very similar, giving calculated values of 4.6 and
4.5 nm, respectively. The lowest spectral overlap was observed for the Mn complex 1d,
where the Förster radius resulted to be the smallest of this series with a value of 3.9 nm. In
a previous report from our group, the distance between donor and acceptor in a similar type
of compound was calculated in its extended conformation. A distance of 3 nm was
calculated for first generation dendrimers. 46 The constructs in solution will not be found in
this conformation but rather in a coiled conformation, allowing both chromophores to get
even closer to each other. Since the distance between the chromophores is smaller than the
estimated Förster radius, it can be concluded that in all cases an efficient energy transfer is
taking place between the pyrene and the metallated phorphyrin acceptor.
By exciting the dendronized porphyrin compounds at 344 nm, energy transfer from
the pyrene containing dendrones to the metallated porphyrin core can be observed. The

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fluorescence intensity of the acceptor ([M]-Porphyrin) is observed at naked eye, since the
emission wavelength in the red part of the spectrum is very different than the one from the
pyrene donor, indicating that the FRET is taking place from the pyrene group. The obtained
values for the FRET efficiencies are reported in Table 2. In all cases, those values are
almost equal to one, suggesting the efficient energy transfer in the metallated pyrene
dendronized porphyrin.
3.4 Time-Resolved Fluorescence Measurements
Time-resolved fluorescence measurements for all the compounds were performed in THF by Time
Correlated Single Photon Counting (TCSPC) experiments. Decay profiles were measured by
excitation at 344 nm for the pyrene moiety and at 425 nm for the porphyrin moieties and recorded at
the wavelengths corresponding to the emission of the pyrene donor and the metalloporphyrin
acceptor, respectively. The lifetime data of all the compounds of this study are reported in Tables 3
to 5. The data were fitted using Decay Analysis Software (DAS6) from Horiba Scientific and
Instrument Response Function (IRF). Values between 1 and 1.5 were obtained for 2 and the plots
of the residuals showed a random distribution corroborating that good fits were obtained in all
cases.

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Table 3: Pre-exponential factors and decay times for the pyrene momomer recorded at 378 nm in THF
for all the constructs.
<>
2
Compound
a1
a2
a3
a4
1 (ns)
2 (ns)
3 (ns)
4(ns)
(ns)
0.1
2.4
3.7
0.4
1.4
3.1
0.7
0.6
1.0
1.0
3
32.952
2.050
1.317
2.240
2.259
0.327
1.309
0.405
0.880
0.864
0.06
0.16
0.21
0.18
0.17
0.80
0.25
0.34
0.35
0.35
0.036
0.012
0.028
0.016
0.022
0.031
0.015
0.007
0.011
0.011
3.90
7.38
9.26
2.61
7.11
5.56
4.84
2.57
5.43
6.07
0.037
0.060
0.021
0.005
0.013
0.010
0.005
0.002
0.008
0.008
20.57
77.60
35.52
15.31
33.56
28.22
24.65
0.011
-
77.39
-
1.23
1.09
1.2
3a
3b
3c
3d
4
0.020 193.77
0.004 112.62
0.012 189.24
0.003 164.39
0.002 179.08
1.08
1.21
1.39
1.14
1.33
1.13
1.17
4a
4b
4c
4d
14.35 0.0004 125.11
25.09
26.63
0.003 116.84
0.003 124.76

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Table 4: Decay times for the porphyrin moiety recorded at ex = 344 nm and em = maximum of the
porphyrin emissiona in THF for all the constructs after the FRET process has occur.
<>
(ns)
<>
(ns)
2
2
Compound
Compound
3
11.6
1.8
nd
1.29
1.59
nd
4
12.2
1.8
nd
1.26
1.92
nd
3a
3b
3c
3d
4a
4b
4c
4d
6.4
nd
1.24
nd
6.4
nd
1.33
nd
a
See Table 2. nd Indicates that the compound is not presenting emission at the specified
wavelength.
Table 5: Decay times for the porphyrin moieties recorded at ex = Soret Banda and em = maximum
of the porphyrin emissionb in THF for all the constructs.
<>
(ns)
<>
(ns)
<>
(ns)
2
2
2
Compound
Compound
Compound
1
12.5
2.0
1.14
1.39
1.30
1.16
nd
3
11.9
1.7
1.18
1.25
1.38
1.18
nd
4
12.0
1.8
nd
1.16
1.42
nd
1a
1b
1c
1d
3a
3b
3c
3d
4a
4b
4c
4d
10.3c
7.0
10.4c
6.3
6.3
nd
1.3
nd
nd
nd
a
b
c
See Table 1. See Table 2. Decays of the porphyrin metallated with Cu were found to be bi-
exponential; 1b a1= 0.007; 1= 2.2; a2= 0.041 2= 11.7; 3b a1= 0.010; 1= 3.1; a2= 0.044 2= 12.0. nd
Indicates that the compound is not presenting emission at the specified wavelength.