Monoanionic Dipyrrin-Pyridine Ligands: Synthesis, Structure and Photophysical Properties

Article abstract of DOI:10.1002/ejic.201500783

A novel monoanionic tetradentate N4 ligand (F₅DPPy) based on a dipyrromethene skeleton as a molecular platform and decorated with pyridine rings at the 1- and 9-positions of the dipyrrin motif has been prepared and characterized. Interestingly, although this ligand is weakly fluorescent, it presents a chelation-enhanced fluorescence effect of around 150 times upon coordination to Zn^II. Time-dependent (TD) DFT calculations reproduce nicely the spectroscopic features of both the ligand and the complex, and analysis of the electron density redistribution in the excited state suggests that a better orbital overlap of the HOMO and LUMO in F₅DPPyZnCl compared with F₅DPPy is responsible for the more intense transitions observed with the former system. As such, this ligand opens interesting perspectives in the design of ratiometric sensors.

Full text of DOI:10.1002/ejic.201500783

FULL PAPER
DOI:10.1002/ejic.201500783
Monoanionic Dipyrrin–Pyridine Ligands: Synthesis,
Structure and Photophysical Properties
Clémence Ducloiset,[a] Pauline Jouin,[a] Elisa Paredes,[a]
Régis Guillot,[a] Marie Sircoglou,*[a] Maylis Orio,[b,c]
Winfried Leibl,[d] and Ally Aukauloo*[a,d]
Keywords: Ligand design / N ligands / Fluorescence / Sensors / Zinc
A novel monoanionic tetradentate N4 ligand (F5DPPy) based
on a dipyrromethene skeleton as a molecular platform and
decorated with pyridine rings at the 1- and 9-positions of the
dipyrrin motif has been prepared and characterized. Interest-
ingly, although this ligand is weakly fluorescent, it presents
a chelation-enhanced fluorescence effect of around 150 times
the ligand and the complex, and analysis of the electron den-
sity redistribution in the excited state suggests that a better
orbital overlap of the HOMO and LUMO in F5DPPyZnCl
compared with F5DPPy is responsible for the more intense
transitions observed with the former system. As such, this
ligand opens interesting perspectives in the design of ra-
upon coordination to ZnII. Time-dependent (TD) DFT calcu- tiometric sensors.
lations reproduce nicely the spectroscopic features of both
preciable quantum yields.[3] The bischelating nature of di-
Introduction
pyrrins and the ease with which the meso-position can be
functionalized with other coordinating functionalities have
been used to develop light-harvesting metal–organic frame-
works (MOFs)[4] or ytterbium(porphyrinate)–BODIPY
conjugates.[5]
The BODIPY class of dyes has gained much attention
since it was recognised that they can be used in a variety
of applications such as biological sensing and labelling, in
electroluminescent devices and as potential candidates for
solid-state solar concentrators, among others.[1] Their chem-
ical stability, high molar absorption coefficients and fluo-
rescence quantum yields are among the main assets of this
class of dyes. It is noteworthy that the enormous synthetic
methodology leading to differently substituted dipyrrinato
organic skeletons has also contributed to a large extent to
reaching a range of targeted functionalities.[2] Dipyrrin-
based metal complexes have also been reported; these show
decreased emission intensities compared with their corre-
sponding boron-based derivatives. However, recent develop-
ments have led to stable luminescent complexes with ap-
The dipyrrin backbone also offers another synthetic han-
dle at the carbon 1- and 9-positions (in the α-positions of
the pyrrolic rings) for the addition of ligating groups,
thereby generating novel pseudo-macrocyclic ligands. Fol-
lowing this strategy, new scaffolds bearing amido,[6,7]
imino[7,8] and phenolate[9] moieties have been synthesized
and coordinated to various transition-metal and/or
group 13 ions. The fluorescent properties of a p-iodo-
phenyl–dipyrrinphenol boronate derivative was reported by
Burgess and co-workers, which gave a quantum yield of
0.41 in chloroform.[9b] Nabeshima et al. described a mes-
ityl–dipyrrinphenol aluminate adduct that can be addition-
ally coordinated through the oxygen atoms of the phenolate
groups to a zinc ion, thus enhancing the fluorescence yield
of the initial species from ΦF = 0.72 to 0.83 in toluene/
MeOH.[9c] It has to be noted though, that the lability of
[a] Institut de Chimie Moléculaire et des Matériaux d’Orsay,
UMR-CNRS 8182, Université Paris-Saclay
91405 Orsay, France
E-mail: marie.sircoglou@u-psud.fr
ally.aukauloo@u-psud.fr
http://www.icmmo.u-psud.fr/Labos/LCI/
[b] Laboratoire de Spectrochimie Infrarouge et Raman, UMR the zinc ion in the latter heteronuclear complex requires the
CNRS 8516, Université des Sciences et Technologies de Lille
presence of a large excess of ZnCl2 under micromolar con-
59655 Villeneuve d’Ascq Cedex, France
centrations. All these above-mentioned studies support the
primary interest in developing novel ligand scaffolds that
ultimately permit the deployment of coordination chemistry
for material science objectives.[10] In our group, we have
been interested in using the dipyrrin core as a molecular
platform to develop a new N4 tetracoordinating cavity. We
describe, herein, the synthesis of a monoanionic ligand
[c] Institut des Sciences Moléculaires de Marseille ISM2, UMR
7313, Aix Marseille Université, CNRS, Centrale Marseille
13397 Marseille Cedex 20, France
[d] Service de Bioénergétique, Biologie Structurale et Mécanismes
(SB2SM), CEA, iBiTec-S, I2BC, UMR 9198
91191 Gif-sur-Yvette, France
Supporting information and ORCID(s) from the author(s) for
this article are available on the WWW under http://dx.doi.org/
10.1002/ejic.201500783.
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where we have introduced two 2-pyridyl groups at the 1-
and 9-positions of the dipyrrin motif. To the best of our
knowledge, this synthetic scaffold can only be found in rare
examples of expanded porphyrin analogues bearing substit-
uents in the β,βЈ-positions,[11] and only one coordination
chemistry study was described for the case of a labile dinu-
clear CoII–pyriporphyrin complex.[12] Interestingly, al-
though our ligand is weakly fluorescent, it presents a chela-
tion-enhanced fluorescence effect of around 150 times upon
coordination to ZnII.
Results and Discussion
The synthetic route to the monoanionic dipyrromethene–
dipyridine ligand (DPPy) is described in Scheme 1. Suzuki
coupling of N-Boc (tert-butyloxycarbonyl) protected (2-
pyrrolyl)boronic acid to 1-bromopyridine in the presence
of [Pd(PPh3)4] and K2CO3 followed by acid deprotection
afforded 2-(2-pyrrolyl)pyridine in 77% yield. Condensation
of 2 equiv. of the pyrrole with 1 equiv. of pentafluorobenz-
aldehyde in the presence of p-toluenesulfonic acid (p-TSA)
followed by treatment with 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ) allowed the desired ligand to be iso-
lated in 46% yield over two steps.
Figure 1. Front and side views of the X-ray crystal structure of
ligand F5DPPy and complex F5DPPyZn. Protons and solvent mol-
ecules are omitted for clarity.
Complexation of the ligand to zinc chloride in THF oc-
curs rapidly in the presence of triethylamine. The 1H NMR
spectrum reveals the disappearance of the NH signal and a
shift of the aromatic proton signals. To determine the coor-
dination mode of the complex in the solid state, single crys-
tals of sufficient quality were grown from a saturated di-
ethyl ether solution, and the complex structure was deter-
mined by single-crystal X-ray diffraction analysis (Fig-
ure 1). The metal atom is tetracoordinated by the four ni-
trogen atoms, which supports the fact that the N2-contain-
ing pyridine ring rotates to bind the metal atom inside the
predefined N4 coordinating cavity. One chloride ion as an
exogenous ligand completes the coordination sphere. The
Zn atom adopts a quasi-square-pyramidal geometry with a
Scheme 1. Synthesis of F5DPPy and its related complexes:
(i) Pd(PPh3)4, K2CO3, 2-bromopyridine, THF, 100 °C, 18 h, 55%;
(ii) HCl, CH2Cl2/H2O, 0 °C, 24 h, 99% ; (iii) pentafluorobenzalde-
hyde, p-TSA, toluene/C2Cl4, 123 °C, 7 d, 46%; (iv) DDQ, THF/
CHCl3, room temperature, 5 h, 99%; (v) 5: ZnCl2, NEt3, THF,
30 min, 96%; 6: Ni(OAc)2·4H2O, toluene, 110 °C, 12 h, 98%.
Single crystals of sufficient quality for X-ray analysis deviation of 0.50 Å from the N4 plane. No noticeable differ-
were obtained from a saturated diethyl ether solution. X- entiation is observed within the C–N or the C–C bonds
ray crystallography analysis revealed that the molecule is of the two rings of the dipyrromethene backbone (see the
almost planar with the two ancillary pyridine N atoms only Supporting Information), thus suggesting a delocalization
slightly deviating from the dipyrrin average plane (p) (N4– of the electron density.
p 0.14 Å, N3–p 0.01 Å). Notably, the pyridyl N2 atom
The electrochemical properties of the free ligand were
points in the opposite direction to the coordinating cavity studied by cyclic voltammetry. On the cathodic side of the
and the perfluorinated phenyl ring is flipped by 63.5° from cyclic voltammogram a quasi-reversible one-electron re-
the ligand backbone plane (Figure 1).
duction wave was observed at –0.88 V versus a saturated
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calomel electrode (SCE; ΔE = 137 mV; Figure 2), account- F5DPPyZnCl was recorded separately and confirmed this
ing for the formation of a rather stable radical anion, the hypothesis (see the Supporting Information).
stability of which is probably due to the presence of the
electron-withdrawing perfluorinated phenyl ring. On the
anodic side, an irreversible oxidation process was noted at
1.4 V. Upon addition of a solution of ZnCl2/NEt3, the cath-
odic wave disappeared, and a new reversible process ap-
peared at –0.68 V versus SCE (ΔE = 144 mV; Figure 2).
Given the silent redox nature of the ZnII ion, this new wave
was attributed to ligand reduction, which became easier
upon complexation. The cyclic voltammogram of
Interestingly, a colour change from red to fluorescing
deep blue was observed in solution upon addition of zinc
chloride to F5DPPy, suggesting a marked modification of
the optical properties of the ligand upon coordination. Ac-
cordingly, monitoring of the formation of the complex by
absorption spectroscopy revealed a 92 nm bathochromic
shift of the spectrum in the visible range as shown by the
decrease in the absorption band at λmax = 511 nm (ε =
17000 Lmol–1 cm–1) along with the concomitant appear-
ance of a double-hump band at λ1,max = 603 nm, λ2
=
563 nm (ε1 = 13700 Lmol–1 cm–1, ε2 = 32600 Lmol–1 cm–1;
Figure 3). To evaluate the suitability of F5DDPy for use as
a fluorescent sensor, emission spectra were also recorded.
As expected, the ligand is poorly fluorescent (λexc = 511 nm,
λΦ = 580 nm, ΦF = 0.002) with a Stokes shift (S) of 69 nm.
Upon coordination, the zinc complex exhibits a strong
emission at 620 nm (λexc = 603 nm, ΦF = 0.31, S = 17 nm).
No such effect was observed with other metals, such as
nickel (see the Supporting Information), as previously ob-
served for other systems.[13] Although the ligand is a modest
fluorescent probe, such a remarkable chelation-enhanced
fluorescence (CHEF) effect could allow its use as a ra-
tiometric sensor. As a comparison, complexation of Zn2+
to a dipyrromethene–diphenolate analogue only led to a
threefold increase in emission with a bathochromic shift of
15 nm.[11]
To interpret such an enhancement in the fluorescence
properties of the tetradentate N4 ligand, theoretical calcula-
tions were performed. The geometry of the two molecules
was optimized by density functional theory (DFT) meth-
ods, and the predicted structures compare reasonably well
with the experimental ones (Figure S5 in the Supporting
Figure 2. Cyclic voltammograms of a solution of F5DPPy (2 mm)
in THF/tBu4NPF6 (0.1 m) (red), upon addition of 0.5 equiv. (pur-
ple) and 1 equiv. (blue) of (ZnCl2, 1.5 NEt3). v = 100 mVs–1, poten-
tial recorded vs. SCE.
Figure 3. (a) UV/Vis spectra of F5DDPy in acetonitrile (13 μm) upon addition of 0–1 equiv. of ZnCl2·1.5NEt3. (b) Emission spectra in
acetonitrile (1.5 μm).
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Information). Inspection of their respective highest occu- system. The structures of the two molecules were then opti-
pied molecular orbitals (HOMO) and lowest unoccupied mized in the first excited state by using TD-DFT methods
molecular orbitals (LUMO) shows that both are delocal- to extract fluorescence emission wavelengths. The results of
ized π-orbitals, which are distributed over the dipyrrin–pyr- these calculations give an emission wavelength of 558 and
idine ligand (Figures S6 and S7 in the Supporting Infor- 583 nm for F5DPPy and F5DPPyZnCl, respectively (ob-
mation). Evaluation of the HOMO–LUMO gap of both served: 580 and 620 nm, respectively). A detailed structural
F5DPPy and F5DPPyZnCl reveals a shift of approximately analysis of the changes implied by the S0ǞS1 transition in
0.1 eV (Table S2 in the Supporting Information), indicating both systems helps to shed some light on the difference be-
that F5DPPyZnCl can be more easily reduced than F5DPPy tween the two emission wavelengths. We observe that fewer
in agreement with the previous cyclic voltammetry study. bonds are affected by the excitation within the F5DPPy
The optical properties of both the free ligand and the corre- framework of the complex compared with that of the ligand
sponding zinc derivative were investigated by using time- (Figure S5 in the Supporting Information), which would ex-
dependent density functional theory (TD-DFT). Our calcu- plain the bathochromic shift observed between these two
lations adequately reproduce the key features of the experi- species. The values of the calculated oscillator strengths
mental UV/Vis spectra of F5DPPy and F5DPPyZnCl; (0.705 and 0.314, respectively) confirm that F5DPPyZnCl is
namely, the two bands at 511 and 603 nm (calculated as 511 a much more fluorescent species than F5DPPy, as observed
and 556 nm, respectively) and the observed bathochromic experimentally. This difference is also consistent with the
shift (Figure 4). Based upon the TD-DFT results, the elec- fact that the complex originally features a better HOMO–
tronic transitions responsible for the prominent UV/Vis LUMO overlapping volume, which was suggested to be a
transitions can be described as HOMO–LUMO transitions factor of fluorescence enhancement and higher light emis-
(Tables S3 and S4 in the Supporting Information). Consis- sion efficiency.[14]
tent with the experimental results, TD-DFT predicts that
the extinction coefficient for the complex is approximately
1.5 times larger than that of the ligand.
Figure 5. Difference electron density sketches of the main UV/Vis
transitions for F5DPPy (left) and F5DPPyZnCl (right) (yellow =
negative, red = positive).
Conclusion
We have reported the synthesis of a novel monoanionic
tetradentate N4 ligand based on a dipyrrin platform. We
have found that this ligand is weakly fluorescent, but upon
chelation with zinc(II) a noticeable increase of about 150
times is observed. As such, this new ligand may give new
possibilities to optimize the optical properties through dif-
ferent substitution patterns. Moreover, this ligand offers a
new coordination set to develop metal complexes for the
activation of small molecules. Efforts are currently being
conducted in this direction.
Figure 4. Predicted UV/Vis spectra (curves) and corresponding
electronic transitions (sticks) of F5DPPy and F5DPPyZnCl.
One way to visualize the electron-density redistribution
in the excited state is a difference electron density plot (Fig-
ure 5, Figures S8 and S9 in the Supporting Information).
This plot shows that the UV/Vis transition in F5DPPy has
significant charge-transfer character with electron density
being donated by one pyrrin–pyridine unit to the other. In
contrast, the UV/Vis transition in F5DPPyZnCl may be
better described as a π–π* one with electron density being
transferred within the ligand backbone. Such analysis is
consistent with the compositions of the MOs involved in
these transitions. Consequently, we can suggest that the bet-
ter orbital overlap of the HOMO and LUMO in
F5DPPyZnCl compared with F5DPPy is responsible for the
Experimental Section
General Procedures and Materials: All commercially available com-
pounds were used as received except for pentafluorobenzaldehyde,
which was freshly distilled prior to use. (N-Boc-2-pyrrolyl)boronic
acid was synthesized according to a literature procedure, and its
more intense UV/Vis transition observed with the former deprotection was performed according to a standard procedure.[15]
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Tetrahydrofuran was dried by distillation from sodium/benzo-
phenone. Chromatography was performed with Merck silica gel 60
(230–400 mesh). NMR spectroscopy chemical shifts (δ) are given
in ppm relative to the residual solvent signal and using hexafluo-
robenzene (δ = –164.9 ppm vs. CFCl3) as an internal standard for
19F NMR spectroscopy. Peak multiplicities are designated by the
following abbreviations: s (singlet), d (doublet), t (triplet), m (mul-
tiplet), br. (broad), p (pseudo), and coupling constants (J) are pro-
vided in Hertz (Hz). CCDC-1400703 (for 3) and -1400704 (for 4)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
6.9 Hz, 2 F, Fortho), –158.64 (pt, J = 21.6 Hz, 1 F, Fpara), –164.29
(pdt, J = 21.6, 6.9 Hz, 2 F, Fmeta) ppm. ESI+-HRMS: calcd. for
C25H16F5N4 [MH+] 467.1290; found 467.1278.
F5DPPyH (4): A solution of 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (270 mg, 1.19 mmol, 1.5 equiv.) in tetrahydrofuran
(50 mL) was added dropwise to dipyrromethane
3 (378 mg,
0.81 mmol, 1 equiv.) in chloroform (80 mL) at room temperature
over 30 min. The dark-red mixture was stirred for 5 h, and the sol-
vents were evaporated to dryness. The residue was dissolved in
dichloromethane and washed with aqueous K2CO3 (1 m; 500 mL).
The aqueous solution was extracted with dichloromethane, and the
combined organic phases were dried with MgSO4, filtered, and the
solvents evaporated to dryness to give 4 as a red solid (374 mg,
0.81 mmol, 99%). Single crystals were obtained by slow solvent
evaporation from a saturated diethyl ether solution. 1H NMR
(CDCl3, 250 MHz): δ = 6.59 (d, J = 4.4 Hz, 2 H, Hpyrrol), 7.10 (d,
J = 4.4 Hz, 2 H, Hpyrrol), 7.29 (m, 2 H), 7.82 (dd, J = 7.8, 1.6 Hz,
2 H), 8.20 (d, J = 8.1 Hz, 2 H), 8.72 (d, J = 4.7 Hz, 2 H), 13.70
(br. s, 1 H, NH) ppm. 13C NMR (CDCl3, 63 MHz): δ = 118.2 (C-
Hpyrrol), 121.6 (C-Hpyridyl), 122.5 (Cq), 123.5 (C-Hpyridyl), 128.1 (C-
Hpyrrol), 135.9 (C-F), 136.8 (C-Hpyridyl), 139.8 (C-F), 142.2 (Cq),
143.1 (Cq), 147.1 (C-F), 150.0 (C-Hpyridyl), 151.0 (Cq), 156.0 (Cq)
ppm. 19F NMR (CDCl3, 235 MHz): δ = –142.12 (m, 2 F, Fortho),
–156.16 (pt, J = 21.3 Hz, 1 F, Fpara), –163.83 (m, 2 F, Fmeta) ppm.
ESI+-HRMS: calcd. for C25H14F5N4 [MH+] 465.1133; found
465.1116. C25H14F5N4 (465.4): calcd. C 64.66, H 2.82, N 12.06;
found C 64.72, H 2.83, N 12.03. UV/Vis (CH3CN): λmax = 511 nm;
ε = 17000 Lmol–1 cm–1.
2-(N-Boc-1H-pyrrol-2-yl)pyridine (1): (N-Boc-2-pyrrolyl)boronic
acid (250 mg, 1.18 mmol, 1 equiv.) and 2-bromopyridine (112.5 μL,
1.18 mmol, 1 equiv.) were dissolved in tetrahydrofuran (10 mL) and
added to [Pd(PPh3)4] (138 mg, 1.19 mmol, 0.1 equiv.) under argon.
Aqueous K2CO3 (3 mL, 1.2 m) was then added, and the biphasic
mixture was stirred vigorously and heated at 100 °C for 18 h. After
cooling to room temperature, water (150 mL) was added to the
reaction mixture, and the aqueous phase was extracted with di-
chloromethane (4ϫ 50 mL). The combined organic extracts were
washed with brine (50 mL), then dried with MgSO4, filtered, and
concentrated. The resulting crude orange oil was purified by col-
umn chromatography on silica gel (petroleum ether/ethyl acetate,
9:1) to yield 1 as a yellow oil (195 mg, 78%). 1H NMR (CDCl3,
250 MHz): δ = 1.36 (s, 9 H, CH3), 6.25 (t, J = 3.3 Hz, 1 H), 6.42
(dd, J = 3.3, 1.8 Hz, 1 H), 7.20 (ddd, J = 12, 4.8, 1.2 Hz, 1 H),
7.36–7.43 (m, 2 H), 7.68 (td, J = 7.5, 1.8 Hz, 1 H), 8.60–8.64 (m,
1 H) ppm.
F5DPPyZnCl (5): Triethylamine (21 μL, 150 μmol, 1.5 equiv.) and
ZnCl2 in diethyl ether (1 m, 100 μL, 100 μmol, 1 equiv.) were added
to compound 4 (46.4 mg, 100 μmol, 1 equiv.) in acetonitrile
(20 mL) at room temperature. The dark-blue solution was stirred
for 30 min, then concentrated under reduced pressure. The green/
blue residue was washed with water (10 mL) to give 5 as a blue
solid (54 mg, 96 μmol, 96%). Single crystals were obtained by slow
solvent evaporation from a saturated diethyl ether/methanol mix-
ture. 1H NMR [(CD3)2CO, 250 MHz]: δ = 7.02 (d, J = 4.5 Hz, 1
H), 7.11 (d, J = 5 Hz, 1 H), 7.64 (dt, J = 5.5, 2.5 Hz, 1 H), 8.14
(m, 2 H), 9.10 (d, J = 5 Hz, 1 H) ppm. ESI+-HRMS: calcd. for
C25H12ClF5N4NaZn [MNa+] 584.9854; found 584.9844. UV/Vis
(CH3CN): λmax = 603 nm; ε = 13700 Lmol–1 cm–1.
2-(2-Pyrrolyl)pyridine (2): Compound 1 (1.27 g, 5.22 mmol) was
dissolved in CH2Cl2, and aqueous HCl (28.5 mL, 3 m) was added
dropwise at 0 °C. The biphasic mixture was vigorously stirred at
room temperature overnight. The aqueous solution was separated
from the organic phase and basified (pH = 12) with aqueous
Na2CO3, then extracted with dichloromethane. The combined or-
ganic phases were dried with MgSO4 and filtered. The solution was
concentrated, and ethyl acetate was added in the same proportion
as dichloromethane. Filtration of the red solution through an alu-
mina pad afforded a colourless solution that was concentrated to
dryness to give 3 as a brown solid (750 mg, 99%). 1H NMR
(CDCl3, 360 MHz): δ = 6.30 (dt, J = 2.6, 3.6 Hz, 1 H), 6.7 (m, 1
H), 6.9 (m, 2 H), 7.03 (dd, J = 2.0, 5.5 Hz, 1 H), 7.54 (d, J =
7.7 Hz, 2 H), 7.62 (td, J = 7.7, 1.6 Hz, 1 H), 8.45 (d, J = 5 Hz, 1
H), 9.8 (br. s, NH) ppm.
Physical Measurements: NMR spectra were recorded in the solvent
indicated with Bruker DPX250, AVX300, AVX360 spectrometers.
High-resolution mass spectrometric data were obtained with a
microTOF-Q II, Bruker Compass. UV/Vis steady-state absorption
spectra were recorded with a Varian Cary 5000 spectrometer.
Steady-state fluorescence spectra were recorded with a Horiba
Fluoromax-4 or a Hitachi F-4500 fluorescence spectrophotometer,
and laser-flash-induced fluorescence was recorded with an Edin-
burgh LP920 laser flash photolysis spectrometer. All experiments
were performed in sealed quartz cuvettes with samples being
purged with argon for 15 min before the experiments. The absolute
yields were determined with Rhodamin 6G (λexc = 480 nm) and
Cresyl Violet perchlorate (λexc = 550 nm) as standards for the li-
gand and the complex, respectively.
Dipyrromethane 3: Compound 2 (249 mg, 1.73 mmol, 2 equiv.) was
dissolved in toluene/tetrachloroethane (1:1; 30 mL) and added to
p-TSA (498 mg, 2.60 mmol, 3 equiv.) and pentafluorobenzaldehyde
(104 μL, 868 μmol, 1 equiv.) in toluene (15 mL). The mixture was
heated at reflux under argon for 7 d, after which it was basified to
pH = 12 with aqueous K2CO3 (1 m). The aqueous phase was ex-
tracted with dichloromethane, and the combined organic phases
were dried with MgSO4, filtered, and the solvents evaporated to
1
dryness to give 3 as a brown solid (370 mg, 0.79 mmol, 46%). H
NMR (CDCl3, 300 MHz): δ = 5.90 (s, 1 H, Hipso), 6.12 (br. s, 2 H,
Hpyrrol), 6.63 (br. s, 2 H, Hpyrrol), 7.01 (t, J = 5.9 Hz, 2 H, Hpyridyl),
7.52 (m, 4 H, Hpyridyl), 8.38 (d, J = 4.7 Hz, 2 H, Hpyridyl), 9.74 (br.
s, 2 H, NH) ppm. 13C NMR (CDCl3, 63 MHz): δ = 33.59 (C-H),
111.06 (C-Hpyrrol), 112.22 (C-Hpyridyl), 119.92 (C-Hpyrrol), 120.67
(C-Hpyridyl), 125.96 (C-Hpyridyl), 127.68 (C-F), 128.98 (C-Hpyridyl),
134.33 (Cq), 139.96 (Cq), 141.40 (C-F), 144.84 (Cq), 147.80 (C-F)
Electrochemical Experiments: Cyclovoltammetry was conducted
under argon by using a PGSTAT 302 potentiostat and a three-
electrode cell using a saturated calomel electrode as a reference
electrode, a Pt counter electrode, and a carefully polished glassy
carbon disk electrode as the working electrode.
Computational Details: All theoretical calculations were based on
ppm. 19F NMR (CDCl3, 235 MHz): δ = –144.43 (dd, J = 21.6, density functional theory (DFT) and were performed with the
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ORCA program package.[16] Full geometry optimizations were car-
ried out for all complexes by using the hybrid functional B3LYP[17]
in combination with the TZV/P[18] basis set for all atoms and by
taking advantage of the resolution-of-the-identity (RI) approxi-
mation in the Split-RI-J variant[19] with the appropriate Coulomb
fitting sets.[20] Increased integration grids (Grid4 in ORCA conven-
tion) and tight SCF convergence criteria were used. Vibrational
frequency calculations were performed to ensure that each geome-
try optimization converged to a real minimum. Solvent effects were
accounted for according to the experimental conditions. For that
purpose, we used acetonitrile as the solvent (ε = 9.08) within the
framework of the conductor-like screening (COSMO) dielectric-
continuum approach.[21] Vertical electronic transitions and dipole
moments were calculated by using time-dependent DFT (TD-
DFT)[22] within the Tamm–Dancoff approximation.[23] To increase
computational efficiency, the RI approximation[24] was used in cal-
culating the Coulomb term, and at least 40 excited states were cal-
culated in each case. Difference transition density plots were gener-
ated for each transition and visualized with the Chemcraft pro-
gram.[25] Excited-state geometry optimizations were performed in
the absence of symmetry constrains making use of analytic gradi-
ents, as implemented for the TD-DFT method in the ORCA pro-
gram package.[26] Fluorescence electronic transitions were calcu-
lated as vertical de-excitations based on the TD-DFT-optimized
geometries of the first excited state.
[6] V. S. Thoi, J. R. Stork, E. T. Niles, E. C. Depperman, D. L. Ti-
erney, S. M. Cohen, Inorg. Chem. 2008, 47, 10533–10541.
[7] E. A. Katayev, N. V. Boev, V. N. Khrustalev, Y. A. Ustynyuk,
I. G. Tananaev, J. L. Sessler, J. Org. Chem. 2007, 72, 2886–2896.
[8] E. A. Katayev, K. Severin, R. Scopelliti, Y. A. Ustynyuk, Inorg.
Chem. 2007, 46, 5465–5467.
[9] a) P. P. Garcia, S. M. Bloom, US Pat. 3691161, 1972; b) H.
Kim, A. Burghart, M. B. Welch, J. Reibenspies, K. Burgess,
Chem. Commun. 1999, 1889–1890; c) C. Ikeda, S. Ueda, T. Na-
beshima, Chem. Commun. 2009, 2544–2546; d) S. Rausaria, A.
Kamadulski, N. P. Rath, L. Bryant, Z. Chen, D. Salvemini,
W. L. Neumann, J. Am. Chem. Soc. 2011, 133, 4200–4203; e)
K. Nakano, K. Kobayashi, K. Nozaki, J. Am. Chem. Soc. 2011,
133, 10720–10723; f) S. El Ghachtouli, K. Wójcik, L. Copey,
F. Szydlo, E. Framery, C. Goux-Henry, L. Billon, M.-F. Char-
lot, R. Guillot, B. Andrioletti, A. Aukauloo, Dalton Trans.
2011, 40, 9090–9093; g) H. Song, S. Rajendiran, E. Koo, B. K.
Min, S. K. Jeong, T. D. Thangadurai, S. Yoon, J. Lumin. 2012,
132, 3089–3092.
[10] R. Sakamoto, T. Iwashima, M. Tsuchiya, R. Toyoda, R. Mats-
uoka, J. F. Kögel, S. Kusaka, K. Hoshiko, T. Yagi, T. Nagay-
ama, H. Nishihara, J. Mater. Chem. A 2015, 3, 15357–15371.
[11] a) R. J. P. Corriu, G. Bolin, J. L. J. E. Moreau, C. Vernhet, J.
Chem. Soc., Chem. Commun. 1991, 211–213; b) F. H. Carre,
R. J. P. Corriu, G. Bolin, J. J. E. Moreau, C. Vernhet, Organo-
metallics 1993, 12, 2478–2486; c) J.-I. Setsune, M. Kawama, T.
Nishinaka, Tetrahedron Lett. 2011, 52, 1773–1777.
[12] J.-I. Setsune, K. Yamato, Chem. Commun. 2012, 48, 4447–4449.
[13] a) Y. Ding, X. Li, T. Li, W. Zhu, Y. Xie, J. Org. Chem. 2013,
78, 5328–5338; b) Y. Ding, Y. Xie, X. Li, J. P. Hill, W. Zhang,
W. Zhu, Chem. Commun. 2011, 47, 5431–5433; c) H.-M. Liu,
P. Venkatesan, S.-P. Wu, Sens. Actuators B 2014, 203, 719–725.
[14] D. Cai, M. A. Marques, B. F. Milne, F. Nogueira, J. Phys.
Chem. Lett. 2010, 1, 2781–2787.
Supporting Information (see footnote on the first page of this arti-
cle): F5DPPyZnOAc synthesis, NMR spectra, crystallographic
data, additional photophysics studies and computational details.
[15] a) X. Hong, M. Mellah, F. Bordier, R. Guillot, E. Schulz,
ChemCatChem 2012, 4, 1115–1121; b) M. Böttger, B. Wieg-
mann, S. Schaumburg, P. G. Jones, W. Kowalsky, H.-H.
Johannes, Beilstein J. Org. Chem. 2012, 8, 1037–1047.
[16] F. Neese, Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2012, 2,
73–78.
[17] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) C. T.
Lee, W. T. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[18] A. Schäfer, C. Huber, R. J. Ahlrichs, J. Chem. Phys. 1994, 100,
5829–5835.
Acknowledgments
This work was supported by the Ministère de l’Education Nation-
ale de la Recherche et de la Technologie (MENRT) (C. D.), the
Laboratoire d’Excellence (LABEX) project Charmmmat, the
French Infrastructure for Integrated Structural Biology (FRISBI)
(ANR-10-INSB-05-01), and the European Cooperation in Science
and Technology (COST) Action (CM1305).
[19] F. Neese, J. Comput. Chem. 2003, 24, 1740–1747.
[20] F. Weigend, Phys. Chem. Chem. Phys. 2006, 8, 1057–1065.
[1] a) R. Ziessel, A. Harriman, Chem. Commun. 2011, 47, 611– [21] A. Klamt, G. Schürmann, J. Chem. Soc. Perkin Trans. 2 1993,
631; b) A. C. Benniston, G. Copley, Phys. Chem. Chem. Phys.
2009, 11, 4124–4131; c) N. Boens, V. Leen, W. Dehaen, Chem.
Soc. Rev. 2012, 41, 1130–1172; d) G. Calzaferri, H. Li, D.
Brühwiler, Chem. Eur. J. 2008, 14, 7442–7449; e) A. Kamkaew,
S. H. Lim, H. B. Lee, L. V. Kiew, L. Y. Chung, K. Burgess,
Chem. Soc. Rev. 2012, 42, 77–88.
799–805.
[22] a) M. E. Casida, in Recent Advances in Density Functional
Methods (Ed.: D. P. Chong), World Scientific, Singapore, 1995;
b) R. E. Stratmann, G. E. Scuseria, M. J. Frisch, J. Chem. Phys.
1998, 109, 8218–8224; R. Bauernschmitt, R. Ahlrichs, Chem.
Phys. Lett. 1996, 256, 454–464.
[23] a) S. Hirata, M. Head-Gordon, Chem. Phys. Lett. 1999, 314,
291–299; b) S. Hirata, M. Head-Gordon, Chem. Phys. Lett.
1999, 302, 375–382.
[24] F. Neese, J. Chem. Phys. 2001, 115, 11080.
[25] Chemcraft, http://chemcraftprog.com.
[26] T. Petrenko, S. Kossmann, F. Neese, J. Chem. Phys. 2011, 134,
054116.
[2] A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891–4932.
[3] a) S. A. Baudron, Dalton Trans. 2013, 42, 7498–7509 and refer-
ences cited therein; b) Y. Ding, Y. Tang, W. Zhu, Y. Xie, Chem.
Soc. Rev. 2015, 44, 1101–1112.
[4] C. Y. Lee, O. K. Farha, B. J. Hong, A. A. Sarjeant, S. T.
Nguyen, J. T. Hupp, J. Am. Chem. Soc. 2011, 133, 15858–
15861.
[5] T. Zhang, X. Zhu, W.-K. Wong, H.-L. Tam, W.-Y. Wong,
Chem. Eur. J. 2013, 19, 739–748.
Received: July 16, 2015
Published Online: October 26, 2015
Eur. J. Inorg. Chem. 2015, 5405–5410
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