Perylene-based bis-, tetrakis-, and hexakis(terpyridine) ligands and their ruthenium(II)-bis(terpyridine) complexes: Synthesis and photophysical properties

Article abstract of DOI:10.1002/ejoc.201300329

A series of metallodendrimers 9-11, as well as their corresponding ligands, were designed and synthesized. These materials integrate perylene as a functional core with IItpy> termini; both chromophores are known for their photovoltaic pro

Full text of DOI:10.1002/ejoc.201300329

Job/Unit: O30329
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Date: 02-05-13 15:55:58
Pages: 6
SHORT COMMUNICATION
Metallomacromolecules
A family of functional materials bearing a
perylene core and terpyridine branches,
along with their RuII–bis(terpyridine) com-
plexes, was designed and synthesized. Their
structures were elucidated by NMR spec-
troscopy and MS. Their optical properties
showed absorption spectra that ranged
from 250 to 625 nm, which suggests their
possible use as sensitizers for dye-sensitized
solar cells.
H. El-Batal, K. Guo, X. Li,
C. Wesdemiotis,* C. N. Moorefield,
G. R. Newkome* ............................... 1–6
Perylene-Based Bis-, Tetrakis-, and Hexa-
kis(terpyridine) Ligands and Their Ru-
thenium(II)–Bis(terpyridine) Complexes:
Synthesis and Photophysical Properties
Keywords: Supramolecular chemistry
/
Metallomacromolecules / Chromophores /
Dendrimers / Ligand design
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C. Wesdemiotis, G. R. Newkome et al.
SHORT COMMUNICATION
DOI: 10.1002/ejoc.201300329
Perylene-Based Bis-, Tetrakis-, and Hexakis(terpyridine) Ligands and Their
Ruthenium(II)–Bis(terpyridine) Complexes: Synthesis and Photophysical
Properties
Hany El-Batal,[a] Kai Guo,[a] Xiaopeng Li,[b] Chrys Wesdemiotis,*[a,b]
Charles N. Moorefield,[c] and George R. Newkome*[a,b,c]
Keywords: Supramolecular chemistry / Metallomacromolecules / Chromophores / Dendrimers / Ligand design
A series of metallodendrimers 9–11, as well as their corre- troscopy, COSY, and MS. Their photophysical properties re-
sponding ligands, were designed and synthesized. These
materials integrate perylene as a functional core with Ͻtpy-
RuIItpyϾ termini; both chromophores are known for their
photovoltaic properties. The products were fully charac-
terized by a combination of 1H NMR and 13C NMR spec-
vealed a broad absorption spectrum with enhanced molar
absorption coefficients corresponding to the increase in the
number of ϽtpyRuIItpyϾ units, which is indicative of their
potential as candidates for light harvesting.
cause of their potential utilitarian applications[33,34] and
interesting possible topologies, which include macro-
cycles[35] and dendrimers.[29,33,34] Metallodendritic architec-
tures are monodisperse, well-defined branched structures,
and because light-absorbing chromophores can be incorpo-
rated into their core and branches, the resultant materials
can possess enhanced optical characteristics. Our objective
is to synthesize materials with maximized photofunctional
properties through the noncovalent combination of multi-
chromophores.
Herein, we present the synthesis, isolation, and charac-
terization of three novel perylene-containing tpy ligands,[36]
as well as their heteroleptic ϽtpyRuIItpyϾ complexes. The
perylene unit is employed as the core and the ϽtpyRuII-
tpyϾ complex is used as the termini. The structures of these
materials were studied by NMR spectroscopy, MS, UV/Vis
absorption, and photoluminescence.
Introduction
Perylene bis(imide) is an organic chromophore with ex-
ceptional characteristics,[1–3] including high quantum yield,
photoluminescence, thermal and photochemical stability, as
well as good optical and electronic properties,[4] which lead
to applications[5] in fields such as fluorescent markers,[6]
photonics,[7] organic electronics,[8–10] and solar devices.[5–12]
Their use in the construction of multichromophoric dye ar-
rays (cyclic or incorporating branches) embraces the prom-
ise of enhancing light-harvesting efficiency; this goal can be
achieved by instilling a supramolecular[13,14] approach by
using hydrogen-bonding,[15] hydrophobic,[16] and π–π inter-
actions and metal–ligand binding approaches to control the
shape and size of the assembled architectures. Numerous
examples of Ͻligand–M–ligandϾ connectivity have been
reported by Newkome,[17–20] Stang,[21] Schmittel,[22,23] Fu-
jita,[24,25] and others.[26–28]
More specifically, 2,2Ј:6Ј,2ЈЈ-terpyridine[29,30] (tpy) li-
gands have gained increasing utility in metal–ligand coordi-
nation, particularly ϽtpyRuIItpyϾ complexes[20,31,32] be-
Results and Discussion
Construction of the desired complexes necessitated ac-
cess to the requisite amino(mono, bis, and tris)terpyridine
ligands. The mono- and bis(terpyridine)s were prepared by
[a] Department of Polymer Science, The University of Akron,
Akron, OH 44325-4717, USA
[b] Department of Chemistry, The University of Akron,
Akron, OH 44325-4717, USA
[c] The Maurice Morton Institute for Polymer Science, The
University of Akron,
reported procedures. Synthesis of tris(terpyridine) 6
(Scheme 1) was accomplished by the alkylation of phenol
1[37] with N-(3-propyl)phthalimide 2 and K2CO3 in MeCN
at 80 °C for 8 h to give (85%) imide 3, which was next
treated with 4-terpyridinylphenylboronic acid (4) in toluene/
H2O/tBuOH (3:3:1) at 100 °C for 3 d. The crude product
was purified by column chromatography (Al2O3), eluting
with CHCl3, followed by deprotection with hydrazine in
EtOH to afford 6 (80%).
Akron, OH 44325-4717, USA
Fax: +1-330-972-2368
E-mail: wesdemiotis@uakron.edu
newkome@uakron.edu
Homepage: http://www.uakron.edu/chemistry/faculty-staff/
wesdemiotis.dot
http://www.dendrimers.com
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300329 or from
the author.
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Perylene-Based Terpyridine Ligands
δ = 8.12 ppm, whereas hexakis(terpyridine) 12 revealed the
presence of two electronically nonequivalent sets of tpy pro-
tons with a 2:1 integration ratio, four electronically equiva-
lent perylene protons, and a singlet at δ = 3.23 ppm corre-
sponding to CH3. The observed integration ratios for all
the ligands were as anticipated. The identity and purity of
the tpy ligands were further assured by ESI-MS spectra,
which led to peaks at m/z = 1712.8 [M]+ (calcd. m/z =
1717.7) for 10, m/z = 2174.8 [M]+ (calcd. m/z = 2174) for
11, and m/z = 3149.2 [M]+ (calcd. m/z = 3149.2) for 12.
RuIItpy(MeCN)3 13 was constructed by heating terpyrid-
ine 17 at reflux in an ethanol solution of RuCl3·3H2O for
12 h to afford the paramagnetic RuIIItpy adduct, which was
washed with EtOH, dehalogenated, and reduced to RuIItpy-
(MeCN)3 by heating in a AgNO3 solution of MeOH/MeCN
(1:1) at reflux for 12 h (Scheme 3).
Scheme 1. Synthesis of tris(terpyridine) 6. Reagents and conditions:
(a) K2CO3, MeCN, 80 °C, 8 h; (b) PdII, K2CO3, toluene/H2O/
tBuOH (3:3:1), Ar, 100 °C, 72 h; (c) N2H4, EtOH, 80 °C, 8 h.
The two-step synthesis of complexes 14–16 is illustrated
in Scheme 2. Initially, bis(anhydride) 7[38] was treated with
aminoterpyridine 8,[39] 9,[40] or 6 in quinoline at 220 °C for
4 d. The crude products were precipitated by using AcOH,
filtered, washed with water and EtOH, and subsequently
purified by column chromatography (Al2O3), eluting with
CHCl3, followed by recrystallization (CHCl3/MeOH) to af-
ford 10 (67%), 11 (55%), and 12 (40%).
The structures were confirmed by 1H NMR and 13C
NMR spectroscopy, COSY, as well as electrospray ioniza-
1
tion mass spectrometry (ESI-MS). The H NMR spectrum
Scheme 3. Synthesis of RuIItpy adduct 13. Reagents and condi-
tions: (a) RuCl3·3H2O, EtOH, 12 h; (b) AgNO3, MeCN/MeOH
(1:1).
of bis(terpyridine) 10 revealed a singlet at δ = 8.87 ppm
(3Ј,5Ј), two doublets at δ = 8.74 (6,6ЈЈ) and 8.64 ppm (3,3ЈЈ),
two multiplets at 7.78 (4,4ЈЈ) and 7.33 ppm (5,5ЈЈ), and a
single perylene proton at δ = 8.19 ppm. In comparison, the
Reagent 13 was column chromatographed (SiO2), eluting
1H NMR spectrum of tetrakis(terpyridine) 11 showed tpy with a mixture of MeCN/H2O/KNO3 (20:1:1). The 1H
resonance frequencies at δ = 8.70–8.69 (3Ј,5Ј and 6,6ЈЈ), 7.84 NMR spectrum of 13 revealed a singlet at δ = 8.66 ppm
(4,4ЈЈ), and 7.30 ppm (5,5ЈЈ) and a single perylene proton at (3Ј,5Ј), two doublets at δ = 8.94 (6,6ЈЈ) and 8.58 ppm (3,3ЈЈ),
Scheme 2. Synthetic route to ligands 10–12 along with their corresponding ϽtpyRuIItpyϾ complexes 14–16. Reagents and conditions:
–
(a) quinoline, Ar, 220 °C, 4 d; (b) DMF, Ar, 110 °C, 2 d (complexes 14–16 were isolated with NO3 counterions).
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SHORT COMMUNICATION
as well as three singlets at δ = 2.76, 2.49, and 2.13 ppm at δ = 9.87 and 9.54 ppm (for 15). In contrast, the tpyH6,6ЈЈ
corresponding to tpy-CH3 moieties, equatorial MeCN li- resonances showed dramatic upfield shifts relative to those
gands, and axial MeCN ligands, respectively. Heteroleptic of the corresponding free ligands at δ = 6.99 ppm (for 14)
complexes 14–16 were prepared by the reaction of tpy li- and at δ = 7.98–7.94 and 7.87–7.86 ppm (for 15). Hexakis
1
gands 10–12 with adduct 13 (1.2 equiv. per tpy) in DMF adduct 16 exhibited a complicated H NMR spectroscopy
at 110 °C for 48 h; the solvent was removed in vacuo and pattern with the following resonance frequencies: four
complexes 14–16 were column chromatographed (SiO2), tpyH3Ј,5 at δ = 9.04, 8.98, 8.95. 8.94 ppm; perylene proton
eluting with mixtures of MeCN/H2O/KNO3 (30:1:1 for 14, at δ = 8.08 ppm; three CH3 and one C(CH3)3 at δ = 2.98,
80%; 20:1:1 for 15, 70%; 15:1:1 for 16, 55%). Finally, the 2.85, 2.27 and 1.29 ppm, respectively, with the correct inte-
–
counterion was exchanged (NO3– to PF6 ) by modifying the gration ratios. The structures were further confirmed by
–
solubilities from MeOH/CHCl3 (NO3 ) to MeCN/CHCl3 ESI-MS with peaks for multiply charged ions of 14 at m/z
– 3+
and DMF. Complexes 14–16 were characterized by 1H = 902.60 [M – 3PF6 ] (calcd. m/z = 902.60) and m/z =
– 4+
NMR and 13C NMR spectroscopy, COSY, and ESI-MS. 640.70 [M – 4PF6 ] (calcd. m/z = 640.71), which resulted
–
The 1H NMR spectra of both complexes 14 and 10 showed from the loss of PF6 counterions. Tetrakis adduct 15 for-
two sets of distinct resonance frequencies attributed to the mation was confirmed with signals at m/z = 1113.7, 861.9,
internal and terminal tpy ligands. The tpyH3Ј,5Ј resonances 694.0, 674.1, and 484.3 for charge states +4 to +8, respec-
showed slight downfield shifts relative to those of the corre- tively. Finally, hexakis complex 16 (Figure 1) was confirmed
sponding free ligands at δ = 9.22 and 9.16 ppm (for 14) and by the presence of signals at m/z = 1342.9, 1094.9, 917.7,
784.9, 681.6, 598.8, 530.9, and 474.9 for charge states +5 to
+12, respectively.
The absorption (in DMF) and emission spectra (in
CHCl3) of the metallodendrimers and the corresponding li-
gands along with their photophysical data are shown in
Figure 2. It is known that the electronic properties of per-
ylene are unaltered[41] by substituents in the imide position.
Thus, one can expect the UV/Vis spectra of the ligands and
complexes to be a superimposition of perylene and Ͻtpy-
RuIItpyϾ absorptions with peak heights proportional to the
number of termini. Ligands 10–12 are bright-red materials
that show absorption spectra with λmax = 579, 543, and
447 nm corresponding to S0–S1 and S0–S2 transitions[14] in
addition to the expected tpy ligand-centered (LC, πǞπ*)
absorption with λmax = 267 and 289 nm.
In comparison, the emission spectra of ligands 10–12 are
mainly attributed to perylene emission bands with λmax
=
582, 617, and 671 nm. Moreover, ruthenium-containing
heterocomplexes 14–16 are dark-red solids exhibiting bands
at λmax = 497 nm corresponding to allowed metal-to-ligand
charge transfer (1MLCT) transitions [logε = 4.88 (for 14),
4.90 (for 15), 4.92 (for 16)], λmax = 288 and 313 nm corre-
sponding to LC (πǞπ*) absorption [logε = 3.28, 5.25 (for
14); 5.29, 5.30 (for 15); 5.30, 5.32 (for 16)], and λmax
=
Figure 1. ESI-MS of (a) 14, (b) 15, and (c) 16.
Figure 2. Normalized absorption (in DMF) and emission spectra (in CHCl3) of ligands 10–12 and the corresponding complexes 14–16
at 25 °C. The emission spectra were recorded with an excitation wavelength of 580 nm and a slit width of 5 nm (all data normalized with
respect to the highest value). Comparison of the extinction coefficient data can be found in Table S1 (Supporting Information).
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Perylene-Based Terpyridine Ligands
Supporting Information (see footnote on the first page of this arti-
570 nm corresponding to perylene S0–S1 absorption band
[logε = 4.72 (for 14), 4.62 (for 15), 4.44 (for 16)]. The ob-
served progressive increase in the molar extinction coeffi-
cient (14 Ͻ 15 Ͻ 16) at the 288, 313, and 497 nm absorption
bands is consistent with the increase in the number of li-
gands and RuII metal centers.
1
cle): Copies of the H NMR, 13C NMR, and COSY spectra.
Acknowledgments
The authors gratefully thank the National Science Foundation
(NSF) (CHE-1151991-GRN; DMR-0821313, and CHE-1012636-
CW) and the Ohio Board of Regents.
Conclusions
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in vacuo. The residue was column chromatographed (SiO2), eluting
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SHORT COMMUNICATION
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