Tetraguanidino-functionalized phenazine and fluorene dyes: Synthesis, optical properties and metal coordination

Article abstract of DOI:10.1039/c4dt03572k

In this work the first phenazine derivatives with guanidino substituents were prepared and their structural and electronic properties studied in detail. The guanidino groups decrease the HOMO-LUMO gap, massively increase the quantum yield for fluorescence and offer sites for metal coordination. The yellow-orange colored 2,3,7,8-tetraguanidino-substituted phenazine shows intense fluorescence. The wavelength of the fluorescence signal is strongly solvent dependent, covering a region from 515 nm in Et₂O solution (with a record quantum yield of 0.39 in Et₂O) to 640 nm in water. 2,3-Bisguanidino-substituted phenazine is less fluorescent (maximum quantum yield of 0.17 in THF), but exhibits extremely large Stokes shifts. In contrast, guanidino-functionalized fluorenes emit only very weakly. Subsequently, the influence of coordination on the electronic properties and especially the fluorescence of the phenazine system was analysed. Coordination first takes place at the guanidino groups, and leads to a blue shift of the luminescence signal as well as a massive decrease of the luminescence lifetime. Luminescence is almost quenched completely upon Cu^I coordination. On the other hand, in the case of Zn^II coordination the fluorescence signal remains strong (quantum yield of 0.36 in CH₃CN). In the case of strong zinc Lewis acids, an excess of metal compound leads to additional coordination at the phenazine N atoms. This is accompanied by significant red-shifts of the lowest-energy transition in the absorption and fluorescence spectra. Pentanuclear complexes with two phenazine units were isolated and structurally characterized, and further aggregation leads to chain polymers. This journal is

Full text of DOI:10.1039/c4dt03572k

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Transactions
PAPER
Tetraguanidino-functionalized phenazine and
fluorene dyes: synthesis, optical properties and
metal coordination†
Cite this: Dalton Trans., 2015, 44,
3467
Elvira Bindewald,a Roxana Lorenz,a Olaf Hübner,a Dominik Brox,b
Dirk-Peter Herten,b Elisabeth Kaifera and Hans-Jörg Himmel*a
In this work the first phenazine derivatives with guanidino substituents were prepared and their structural
and electronic properties studied in detail. The guanidino groups decrease the HOMO–LUMO gap, mas-
sively increase the quantum yield for fluorescence and offer sites for metal coordination. The yellow-
orange colored 2,3,7,8-tetraguanidino-substituted phenazine shows intense fluorescence. The wave-
length of the fluorescence signal is strongly solvent dependent, covering a region from 515 nm in Et2O
solution (with a record quantum yield of 0.39 in Et2O) to 640 nm in water. 2,3-Bisguanidino-substituted
phenazine is less fluorescent (maximum quantum yield of 0.17 in THF), but exhibits extremely large
Stokes shifts. In contrast, guanidino-functionalized fluorenes emit only very weakly. Subsequently, the
influence of coordination on the electronic properties and especially the fluorescence of the phenazine
system was analysed. Coordination first takes place at the guanidino groups, and leads to a blue shift of
the luminescence signal as well as a massive decrease of the luminescence lifetime. Luminescence is
almost quenched completely upon CuI coordination. On the other hand, in the case of ZnII coordination
the fluorescence signal remains strong (quantum yield of 0.36 in CH3CN). In the case of strong zinc Lewis
acids, an excess of metal compound leads to additional coordination at the phenazine N atoms. This is
accompanied by significant red-shifts of the lowest-energy transition in the absorption and fluorescence
spectra. Pentanuclear complexes with two phenazine units were isolated and structurally characterized,
and further aggregation leads to chain polymers.
Received 20th November 2014,
Accepted 8th January 2015
DOI: 10.1039/c4dt03572k
www.rsc.org/dalton
density on the aromatic system and the quantum yield of fluo-
rescence by suppressing nonradiative relaxation processes.
Introduction
Amino-substituted phenazines and fluorenes are important There are also other applications that make phenazines attrac-
dyes. Hence the phenazine derivative mauveine (Perkin’s dye, tive for modern chemistry, spanning from organic electronics
which actually was shown to be a mixture of several com- (phenazines have been integrated in solar cell3 and organic
pounds which differ in the number of methyl groups) was the light emitting diode (OLED)4 devices) to sensors (e.g. pH5 or
first commercialized synthetic dye.1 Although its last commer- metal sensing6,7) and pharmaceutical purposes (especially
cial use (coloring of British stamps) ended in 1901, mauveine DNA intercalation). Fluorenes are attractive building blocks in
was of great importance for the development of the modern polymers, and polyfluorenes are electrically conductive and
chemical industry.2 Other known phenazine dyes include electroluminescent.8 Hence fluorenes and polymers including
safranin and Neutral red. All these compounds feature amino fluorene units are intensively applied in OLED devices.9 Fluo-
substituents. The amino functions increase the electron rene and triphenylene derivatives have been integrated into
porous covalent organic frameworks with distinct optical and
electronic properties.10,11
The influence of metal coordination on the optical pro-
perties of fluorophores was intensively studied in the past.12,13
Photoluminescent sensors based on the photo-induced elec-
tron transfer (PET) mechanism were built by linking fluoro-
phors (through a spacer) to ionophores, which are responsible
for metal coordination.14,15 In its bound state, the ionophore
usually forms a chelating complex with the metal ion. For
aAnorganisch-Chemisches Institut, Im Neuenheimer Feld 270; Ruprecht-Karls-
Universität Heidelberg, 69120 Heidelberg, Germany.
E-mail: hans-jorg.himmel@aci.uni-heidelberg.de; Fax: +49-6221-545707
bCellnetworks Cluster and Inst. for Physical Chemistry, Im Neuenheimer Feld 267;
Ruprecht-Karls-Universität Heidelberg, 69120 Heidelberg, Germany
†Electronic supplementary information (ESI) available. CCDC 1016464–1016468,
1016832, 1034621. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4dt03572k
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Scheme 1 The new GFA compounds 1 and 2 and the previously reported GFAs 3 and 4.
example, for zinc sensing,13 the ionophore often contains lysts, e.g. in lactide polymerization20 or Heck-type reactions.21
pyridyl groups.16 In classical PET probes, the HOMO energy of Generally only the imino-N atom of the guanidine binds to the
the free (uncoordinated) ionophore (e.g. “formed” by N donor metal, since the lone-pairs on the amino N atoms are engaged
atom lone pairs) is slightly higher than the relevant orbital in π-interactions. However, in exceptional cases the amino
energy of the fluorophore, so that intramolecular electron group also binds to the metal, leading to additional hemilabile
transfer (through the spacer) upon photoexcitation of the metal–ligand bonding which is of interest for catalytic appli-
fluorophore leads to fluorescence quenching. In the bound cations.22 A detailed analysis of the guanidine-metal bonding
(metal coordinated) ionophore the HOMO energy is then on the basis of a experimental charge-density study revealed σ-
drawn down below the fluorophore orbital energy, leading to as well as π-bonding contributions, in line with the observed
strong fluorescence. This is termed CHEF (chelation enhanced elongation of the CvN imino bond upon coordination.23 Our
fluorescence) effect. On the other hand, coordination of tran- group recently established guanidino-functionalized aromatic
sition metals with unpaired electrons such as Cu2+ (like compounds (GFAs) as a new class of strong organic electron
coordination of heavy metal ions) generally leads to fluo- donors.24,25 The Lewis-structures of two representatives,
rescence quenching.17
namely 1,2,4,5-tetrakis(tetramethylguanidino)benzene, 3,26
In this work we report the first phenazine and fluorene and 2,3,5,6-tetrakis(tetramethylguanidino)pyridine, 4,27 are
derivatives with guanidino substituents, namely 2,3,7,8-tetra- shown in Scheme 1. According to cyclic voltammetric (CV)
kis(tetramethylguanidino)-phenazine (1) and 2,3,6,7-tetrakis- experiments, both compounds exhibit a similar electron-donor
(tetramethylguanidino)-fluorene (2). The guanidino groups, capacity with an E1/2 value (in CH2Cl2) of −0.76 V versus Fc/Fc+
which outperform in several aspects the amino groups, fulfil (Fc = ferrocene) for two-electron oxidation. On the other hand,
several tasks. They massively increase the quantum yield for 4 but not 3 could be used in photochemical reductive C–C
fluorescence in the phenazine derivative. In addition, they coupling reactions.28 We have analysed in some detail the
increase the solubility in organic solvents and also in aqueous effect of alkylation of the pyridine N atom on the electronic
solutions, and prohibit, at least to some extent, aggregation properties of 4. Alkylation leads to a red-shift of the lowest-
processes which could lead to quenching of the fluorescence. energy electronic transition (LUMO ← HOMO excitation). We
Many previous experiments with guanidino-substituted aro- show in this work that coordination at the N atoms of the phe-
matic compounds by our group showed that the guanidino nazine core of compound 1 also changes the electronic
groups increase significantly the HOMO energy and decrease properties.
the HOMO–LUMO gap. Last but not least, they offer sites for
metal coordination. In this work, the coordination chemistry
and optical properties (absorption and emission spectra) will
be addressed in particular.
Results and discussion
Synthesis and structural characterization
Neutral guanidines as well as guanidinates were shown to
be excellent ligands, which were applied in coordination
The new GFA 1 was synthesized in a three step reaction start-
chemistry for manifold purposes.18 CuI complexes of tripodal ing with 1,2,4,5-tetraamino-benzene. Heating an aqueous solu-
tris(2-guanidinylethyl)amine ligands were used for the prepa- tion of 1,2,4,5-tetraamino-benzene·4HCl in the presence of
ration of end-on bonded superoxo-complexes which exhibit a
NaOAc (sodium acetate) and under a stream of compressed air
rich chemistry.19 Other guanidine ligands were used as cata- gave deep purple-colored 2,3,7,8-tetraamino-phenazine-tri-
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Scheme 2 Synthesis of the new compounds 1 and 2.
starting with 2,7-dinitrofluorene (see Scheme 2).30 Guanidiny-
lation was again achieved with activated tetramethyl-urea in
the presence of NEt3. The structures of compounds 1, 2 and 5,
as derived from single-crystal X-ray diffraction, are visualized
in Fig. 1. The imino CvN bond distances adopt characteristic
average values of 1.300 Å in 1, 1.293 Å in 2 and 1.317 Å in 5.
These values generally increase upon metal coordination (see
below). According to 1H NMR studies the guanidino groups are
highly flexible,31 so that at room temperature all 48 methyl
protons in 1 and 2 and all 24 methyl protons of 5 exhibit the
same chemical shift.
Scheme 3 Lewis structure of the new bisguanidine 5.
We also measured CV curves to study the redox activity of
the new compounds. Fig. S1 (see ESI†) displays the CV curve
for compound 1. It contains four oxidation waves, centered at
−0.12, 0.08, 0.38 and 0.63 V vs. Fc/Fc+ (Fc = ferrocene),
showing that the compound could be oxidized at a lower
potential than ferrocene. Three reduction waves of different
intensity appear at −0.39, −0.23 and 0.24 V. The curve shows
that the guanidino groups indeed turn phenazine into an elec-
tron donor. On the other hand, they clearly indicate a non-
reversible redox behaviour, in contrast to the fully reversible
oxidation processes for compounds 3 and 4.26,27 On the basis
of this result, the further discussion focuses on the optical pro-
perties rather than the redox-chemistry.
hydrochloride,
a reaction which was already previously
described.29 Then this compound was reacted with activated
tetramethyl-urea (the “Vilsmeier” salt 2-chloro-1,1,3,3-tetra-
methylformamidinium chloride, [ClC(NMe2)2]Cl) to yield 1 in
the form of an orange-colored solid. Deeply orange-colored
crystals suitable for a single-crystal X-ray diffraction analysis
were obtained from Et2O solutions. We also synthesized the
corresponding bisguanidine 1,2-bis(tetramethylguanidino)-
phenazine, 5 (see Scheme 3), from 1,2-diamino-phenazine
(also an orange-colored solid at ambient conditions). The
amino precursor to compound 2, namely 2,3,6,7-tetramino-
fluorene-tetrahydrochloride, was synthesized according to the
literature (with minor modifications, see Experimental details)
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Fig. 2 Effect of added HCl (a) and NaOH (b) on the electronic absorp-
tion spectra of an aqueous solution of compound 1.
Fig. 1 Molecular structures of (a) the phenazine derivative 1 and (b) the
corresponding bisguandine 5, as well as (c) the fluorene derivative 2.
Vibrational ellipsoids drawn at the 50% probability level. Hydrogen
atoms omitted for sake of clarity. Selected structural parameters (bond
distances in Å, bond angles in °): For 1: N1–C1 1.395(4), N1–C7 1.302(4),
N2–C7 1.390(4), N3–C7 1.363(4), N4–C2 1.403(4), N4–C12 1.298(4),
N5–C12 1.382(4), N6–C12 1.390(4), N7–C4 1.346(4), N7’–C5 1.354(4),
C1–C2 1.457(5), C1–C6 1.382(4), C2–C3 1.371(5), C3–C4 1.426(4), C4–
C5 1.435(4), C5–C6 1.417(4), C1–N1–C7 121.4(3), C2–N4–C12 119.0(3).
For 5: N1–C1 1.382(4), N1–C13 1.321(4), N2–C13 1.361(4), N3–C13
1.357(4), N4–C12 1.389(4), N4–C18 1.312(4), N5–C18 1.372(4), N6–C18
1.379(4), N1⋯HO1 2.039(4), N7⋯HO2 2.059(3), C1–N1–C13 121.6(3),
C12–N4–C18 122.5(3). For 2: N1–C1 1.412(3), N1–C14 1.293(3), N2–C14
1.381(3), N3–C14 1.382(3), N4–C2 1.406(3), N4–C19 1.299(3), N5–C19
1.391(3), N6–C19 1.367(3), N7–C7 1.408(3), N7–C24 1.287(3), N8–C24
1.375(3), N9–C24 1.390(3), N10–C8 1.412(3), N10–C29 1.291(3), N11–
C29 1.381(3), N12–C29 1.394(3), C1–N1–C14 119.85(18), C2–N4–C19
119.79(17), C7–N7–C24 123.12(17), C8–N10–C29 121.27(17).
turned out to be soluble in several organic solvents and also
water, yielding yellow-orange colored solutions. The electronic
absorption spectrum of an aqueous solution of 1 is shown in
Fig. 2. It contains strong bands at 229, 300 (with a shoulder at
311), 432 and 484 nm. Due to the high basicity of guanidines,
a large portion of the molecules is protonated. Addition of HCl
to the solution leads to a decrease of the 484 nm band, and an
increase of the 432 nm band. Upon addition of 12 equivalents
of HCl the 484 nm band is extinguished (see Fig. 2a). On the
other hand, addition of NaOH leads to the increase of the
band at higher wavelength (the maximum shifts slightly from
484 nm to 493 nm) at the expense of the 432 nm band
(Fig. 2b). On the basis of these results we assign the 484 nm
band to the unprotonated compound, and the band at 432 nm
to the protonated species. The corresponding emission spectra
are shown in Fig. 3. Without acid or base addition, the fluo-
rescence quantum yield in water is 0.02. HCl addition leads to
fluorescence quenching, and NaOH addition to a massive
increase of the fluorescence signal. Hence only the unproto-
nated, but not the protonated species shows fluorescence. The
Optical properties
Next we studied the optical properties of the two new GFA
compounds 1 and 2 and of bisguanidine 5. Compound 1
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emission maximum after addition of 10 eq. of HCl is reached
at λmax = 634 nm, leading to a substantial Stokes shift of
4510 cm−1 32
Since the compound offers two different sites for
.
protonation (the N atoms in the phenazine heterocycle and the
imino N atom of the guanidino group), we studied protonation
in some more detail. Addition of an ammonium salt (NH4)X
(X = PF6 or BF4) led to twofold protonation. Crystals of the salt
[1H2](BF4)2 were grown and the structural elucidation showed
protonation exclusively at the guanidino groups (see Fig. S2 in
the ESI†). On the other hand, quantum chemical calculations
(B3LYP/6-311G**) predict a preference for the proton to bind
to the N atom of the heterocycle. Hence the Gibbs free energy
change (at 298 K, 1 bar) for tautomerization of 1H+ in the gas-
phase according to Scheme 4 was calculated to be −23 kJ
mol−1. Similar results were previously obtained for 2,3,5,6-
tetrakis(tetramethylguanidino)pyridine, for which protonation
at the pyridine N atom is favoured by −24 kJ mol−1 (ΔG value
at 298 K, 1 bar).27
Subsequently we studied the influence of different solvents
on the absorption and emission spectra. In Fig. 4a, the light
emitted from several solutions, excited with UV light, is visual-
ized. It can be seen that the emission intensity and also the
wavelength vary. The intensity is particularly high in Et2O, for
which we determined a quantum yield of fluorescence of 0.39.
To the best of our knowledge, this is the highest quantum
yield measured for a molecular simple phenazine derivative.
For comparison, Safranine O exhibits a quantum yield of 0.06
in H2O and 0.29 in EtOH,33 and dipyrido[3,2-a:2′,3′-c]phena-
zine of 0.009 in CH2Cl2.34 Fig. 4b shows the absorption and
emission spectra (excited at 480 nm) of 1 in CH3CN and Et2O.
The emission maximum is reached at 515 nm, being thus
strongly blue-shifted by more than 100 nm with respect to
aqueous solution. The absorption maximum for the corres-
ponding electronic transition is located at 484 nm, at the same
position than in H2O, and thus the Stokes shift in Et2O solu-
tion (2130 cm−1) is much smaller than in aqueous solutions of
the compound. For comparison, Fig. 4b also includes the UV/
Vis spectrum of unsubstituted phenazine in CH3CN. The
decrease of the HOMO–LUMO gap by the guanidino groups
manifests itself in a massive red-shift of the lowest-energy
band (located around 363 nm in phenazine, but 484 nm in 1).
Table 1 gives an overview over the wavenumbers for absorption
and emission and the Stokes shifts in several solvents.
Fig. 3 Effect of added HCl (a) and NaOH (b) on the electronic emission
spectra of an aqueous solution of compound 1.
At this stage, it appeared to us attractive to compare the
optical properties of compound 1 bearing four guanidino
Scheme 4 The two tautomeric forms of 1H+ (which presumably are in equilibrium in solution). The structure on the right is more stable in the gas-
phase according to quantum chemical calculations, but protonation experiments gave only evidence for protonation at the guanidino groups.
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Fig. 4 (a) Photos showing the emission of solutions of compound 1 in different organic solvents. (b) Electronic absorption and emission spectra for
solutions of compound 1 in CH3CN and in Et2O solution. (c) Calculated HOMO and LUMO energies (B3LYP/6-311G**) of 1 relative to unsubstituted
phenazine.
groups with that of compound 5 bearing only two guanidino Especially intense emission signals were observed in Et2O and
groups. Fig. S3 in the ESI† shows photos of the emission from THF. However, the quantum yields of 0.11 determined in Et2O
solutions of 5 in different solvents, excited with UV light, and and 0.17 in THF are smaller than for 1. The lowest-energetic
some representative absorption and emission spectra. band in the absorption spectrum of 5 (at 393 nm in CH3CN,
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Table 1 Comparison of absorption and emission wavelengths (in nm)
and Stokes shifts (in cm−1) for 1, [1(ZnCl2)2], 5 and [5(ZnCl2)2] and
different solvents
Stokes
Compound
Solvent λmax, abs
λmax, em shift32
1
Et2O
302, 444s, 464
515
546
568
640
2130
2220
3060
5040
CH2Cl2 311, 487
CH3CN 221, 309, 484
H2O
229, 300, 311s, 432,
484
pH ≫ 7 493a
pH ≪ 7 432a
634
583
4510
6000
[1(ZnCl2)2]
CH3CN 228, 316, 458, 484
CH2Cl2 228, 319, 459, 486
506
512
898
1050
[(1)2(ZnCl2)5] CH2Cl2 581a
599
517
5
Et2O
CH3CN 233, 276, 393
THF 227, 278, 435
277, 433
568
599
588
5490
8750
5980
[5(ZnCl2)2]
CH3CN 231, 283, 302, 424,
442
514
498
3170
2390
THF
231, 286, 304, 425,
445
a Only the lowest-energy band is listed.
Table 2 Comparison of quantum yield Φ, Stokes shifts (in cm−1) and
lifetime (in ns) for 1, [1(ZnCl2)2], 5 and [5(ZnCl2)2] in CH3CN solutions
Fig. 5 (a) Electronic absorption and emission spectra for 2 in CH3CN
solution. (b) Calculated HOMO and LUMO energies (B3LYP/6-311G**) of
2 relative to unsubstituted fluorene.
Compound
Φ
Stokes shift/cm−1
Lifetime/ns
1
0.22
0.36
0.15
0.08
3060
898
8750
3170
4.6(2)
1.8(4)
7.6(6)
1.3(5)
shape and energies of the HOMO and LUMO orbitals of phe-
nazine and fluorene. The isodensity surfaces for these orbitals
are visualized in Fig. 4c and 5b. It can be seen that the guani-
dino groups contribute to the HOMO, especially in the case of
1. As expected, they cause a significant increase of the HOMO
energies and a less strong increase of the LUMO energy. Con-
sequently, the HOMO–LUMO gap shrinks from 3.66 eV in phe-
nazine to 3.24 eV in 1 and from 4.99 eV in fluorene to 4.13 eV
in 2. The decrease of the HOMO–LUMO gap is in line with the
observed colour changes and the difference in the lowest-ener-
getic transitions detected in the absorption spectra (484 nm
for 1 and 371 nm for 2 in CH3CN solution). It will be shown
below that this band can indeed be assigned to the HOMO–
LUMO excitation.
[1(ZnCl2)2]
5
[5(ZnCl2)]
433 nm in Et2O and 435 nm in THF) is blue-shifted with
respect to 1, but still red-shifted with respect to unsubstituted
phenazine (363 nm in CH3CN). This fits with the expectations
of a significantly higher HOMO energy in 1 compared with 5.
The wavenumber of the emission maximum (568 nm in Et2O,
599 nm in CH3CN and 588 nm in THF) is much larger for 5.
This leads to large Stokes shifts of 5490 cm−1 in Et2O,
8751 cm−1 in CH3CN and 5982 cm−1 in THF. Compound 1 has
an average fluorescence lifetime of 4.6(2) ns in CH3CN, com-
pared to 7.6(6) ns of compound 5 (see Table 2 and Fig. S4†).
Interestingly, the average lifetimes are nearly independent of
the excitation wavelength in CH3CN.
Finally, we studied the absorption and emission spectra of
compound 2. As example, Fig. 5 shows the spectra recorded
for a CH3CN solution. The lowest-energetic electronic tran-
sition occurred at 371 nm. The fluorescence signal was only
weak (quantum yield below 0.01), with the maximum of emis-
sion at 428 nm and a long tail towards higher energies.
Coordination chemistry
Next we analysed the effect of metal coordination (especially
d10 metal ions) on the optical properties of the new phenazine
derivatives. We started our work by comparing the lumines-
cence of a solution of 1 upon addition of various metal salts,
and observed quenching of the luminescence signal upon
addition of CuI salts, but a blue-shift of the signal in the pres-
ence of AgI or ZnII salts. To find out more about the coordi-
nation of these metals, we carried out more directed
experiments. The reaction between compound 1 and 2 eq. of
CuI yielded the complex [1(CuI)2] in a moderate yield of
Quantum chemical calculations were carried out to analyse
in more detail the influence of the guanidino groups on the
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Fig. 6 Molecular structures of (a) [1(ZnCl2)2] and (b) [5(ZnCl2)]. Vibrational ellipsoids drawn at the 50% probability level. Hydrogen atoms omitted for
sake of clarity. Selected structural parameters (bond distances in Å, bond angles in °): For [1(ZnCl2)2]: Zn–Cl1 2.2238(9), Zn–Cl2 2.2582(8), Zn–N1
2.035(2), Zn–N4 2.039(2), N1–C1 1.408(3), N1–C7 1.342(3), N2–C7 1.338(4), N3–C7 1.356(4), N4–C2 1.409(3), N4–C12 1.334(3), N5–C12 1.344(3),
N6–C12 1.359(3), N7–C4 1.351(3), N7’–C5 1.349(3), C1–C2 1.448(4), C1–C6 1.377(4), C2–C3 1.372(4), C3–C4 1.422(4), C4–C5 1.432(4), C5–C6
1.422(4). For [5(ZnCl2)]: Zn–Cl1 2.2306(8), Zn–Cl2 2.2473(7), Zn–N1 2.031(2), Zn–N4 2.034(2), N1–C1 1.397(3), N1–C13 1.345(3), N2–C13 1.355(3),
N3–C13 1.338(3), N4–C12 1.398(3), N4–C18 1.351(3), N5–C18 1.352(3), N6–C18 1.337(3), Cl1–Zn–Cl2 113.49(3), N1–Zn–N4 81.74(8). (c) Absorption
and emission spectra measured for [5(ZnCl2)] in THF solutions. (d) Photos showing the color arising from light absorption and that arising from light
emission for [5(ZnCl2)] solutions in THF. For comparison, each photo also shows the uncoordinated ligand 5. It could be seen that coordination only
slightly influences the absorption of light, while the emission is strongly changed.
ca. 50%. The lowest energy band in the absorption spectrum coordination of CuI. We strictly avoided air contact, so that oxi-
(see Fig. S5 of the ESI†) occurred at 493 nm in CH3CN. This dation of CuI to CuII could be excluded. In this case, we could
band has a shoulder at 465 nm, which we assign to excitation not exclude the participation of a triplet state.
into an excited vibronic level (due to the difference of
Reaction of 1 with two equivalents of ZnCl2 gave a product
1222 cm−1 and the similar intensity ratios in all experiments). which could be identified as the dinuclear complex [1(ZnCl2)2].
In CH2Cl2, the band maximum shifts only slightly to 501 nm. Fig. 6a displays its structure from single-crystal X-ray diffrac-
An extremely weak luminescence signal (too weak to determine tion experiments. Again, the absorption spectrum of this
its quantum yield) was observed at 533 nm in CH3CN and complex showed little difference to that of free 1, with the
519 nm in CH2Cl2. Hence the coordination of two CuI units lowest-energetic band measured at 484 nm in CH3CN and
caused a sharp decrease of the luminescence signal of com- 486 nm in CH2Cl2. However, in sharp contrast to the copper
pound 1 to almost vanishing point. This is surprising since complex, the fluorescence signal remained strong. A quantum
CuI is a d10 metal ion (like ZnII and AgI), which normally does yield for fluorescence of 0.36 was measured in CH3CN solu-
not lead to luminescence quenching. Often luminescence tion. The quantum yield of free 1 in CH3CN solution amounts
quenching by CuI is explained by disproportionation of CuI in to only 0.22 (see Table 2). The increase of the quantum yield
solution into CuII and Cu. However, our results clearly show upon zinc coordination might point to the presence of a PET
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mechanism in free 1, which is removed upon coordination 498 nm in THF and 514 nm in CH3CN solutions (see Fig. 6c).
(see the discussion in the Introduction). The emission The large Stokes shift observed for free 5 (8750 cm−1 in
maximum of [1(ZnCl2)2] was reached at 506 nm in CH3CN and CH3CN) is greatly reduced upon zinc coordination (3169 cm−1
512 nm in CH2Cl2, being significantly blue-shifted with for CH3CN) (see also the data in Table 1). To highlight this
respect to free 1 (568 nm). The Stokes shift decreases upon difference, Fig. 6d compares the absorption and emission
coordination in CH3CN from 3060 cm−1 (free 1) to 898 cm−1
.
colours. The average fluorescence lifetime of [5(ZnCl2)2] in
At the same time, the average fluorescence lifetime of CH3CN (1.3(5) ns) is also significantly reduced with respect to
[1(ZnCl2)2] in acetonitrile (1.8(4) ns) is drastically shorter than free 5 (7.6(6) ns).
for 1 (4.6(2) ns) underlining the strong influence of coordi-
When further ZnCl2 was added to a solution of [1(ZnCl2)2]
nation on the optical properties (see Table 2).
in CH2Cl2, the colour of the solution gradually changed from
The corresponding mononuclear complex [5(ZnCl2)] was yellow to purple. In Fig. 7a, the UV/Vis spectra recorded for an
also synthesized (see Fig. 6b). As for [1(ZnCl2)2], coordination experiment in which a concentrated solution of ZnCl2 in CH3CN
leads to an increase of the imino CvN bond lengths (1.321(4)/ was step-wise added to a CH2Cl2 solution of [1(ZnCl2)2] (c =
1.312(4) Å in 5 and 1.345(3)/1.351(3) Å in [5(ZnCl2)]). The metal 1.28 × 10−5 mol l−1) is displayed, and the colour changes upon
atom is in plane with the phenazine core. Also in this case, the ZnCl2 addition are shown underneath (Fig. 7b). The yellow-
absorption spectrum is similar to that of the free ligand 5, and colored solution turned to intense purple upon addition of 2
the lowest-energy band showed at 442 nm in CH3CN and eq. of ZnCl2. In the UV/Vis spectra, the band at 486 nm with a
445 nm (with a shoulder at 425 nm) in THF solutions. On the shoulder at 459 nm decreased and gave way for an intense
other hand, the emission spectrum clearly differs from that of absorption at 581 nm and another one at 543 nm. The relative
the free ligand. Hence the maximum of emission is reached at intensities of the two new absorptions varied and therefore
Fig. 7 (a) Absorption spectra for addition of a ZnCl2 solution in CH3CN (1 µL = 0.2 eq.) to a 1.2811 × 10−5 mol l−1 solution (3 mL) of [1(ZnCl2)2] in CH2Cl2.
(b) Photos showing the color changes upon ZnCl2 addition.
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Scheme 5 Formation and aggregation of the [1(ZnCl2)2] units via ZnCl2.
they should belong to (at least) two different species in solu- gation might lead to a chain oligomer or polymer of the com-
tion. In the case of solutions with low concentrations of position [1(ZnCl2)3]n. Indeed, we observed the formation of a
[1(ZnCl2)2] (c = 0.64 × 10−5 mol l−1, see Fig. S6 in the ESI†), solid material for addition of a large excess of ZnCl2 (the pre-
more equivalents of ZnCl2 were necessary to decrease the cipitation started upon addition of four equivalents for a
486/459 nm band, pointing to an aggregation equilibrium. The CH2Cl2 solution of [1(ZnCl2)2] with c = 1.28 × 10−5 mol l−1, and
obvious inference is that the excess ZnCl2 binds to the N atoms of ten equivalents for the lower concentration (c = 0.64 × 10−5
of the phenazine core and connects the [1(ZnCl2)2] complex mol l−1). In preliminary experiments, we recorded a diffuse
units to oligomeric chains or rings (see Scheme 5). Aggregation- reflectance measurement of this solid embedded in a BaSO4
induced changes in the optical properties of metal complexes matrix. This spectrum (see Fig. S7 in the ESI†) displays elec-
were also observed in other cases.35 Indeed we were able to syn- tronic absorptions around 305, 455 and 545 nm (the latter as a
thesize the complex [(1)2(ZnCl2)5] by reaction of 1 with 2.5 eq. of shoulder and with a tail towards larger wavenumbers). The
ZnCl2. Purple-colored crystals of this compound were grown position of the 545 nm band fits quite well with the absorption
from a CH2Cl2–Et2O solvent mixture. Fig. 8 shows the molecular at 543 nm measured in the solution spectra. In summary we
structure of [(1)2(ZnCl2)5] as derived from single-crystal X-ray explain the spectra shown in Fig. 7a as follows: the 486 nm
diffraction. As expected, two [1(ZnCl2)2] complex units are band clearly belongs to [1(ZnCl2)2], the 581 nm should belong
linked via a ZnCl2 unit. The Zn–N bond distances within the to [(1)2(ZnCl2)5] and the 543 nm band is tentatively assigned to
[1(ZnCl2)2] units (in average 2.034 Å long) are shorter than the higher aggregates [1(ZnCl2)3]n.
Zn–N bonds which link the [1(ZnCl2)2] units together (2.099 Å
in average). This result indicates that the latter bonds are ZnCl2, we observed a similar reaction pattern. On the other
weaker, in line with the observed equilibrium (see Scheme 5). hand, with ZnMe2 the reaction stopped at the stage of the
When the experiment was repeated with ZnBr2 in place for
Quantum chemical calculations (B3LYP/def2-SV(P)) were dinuclear complex; aggregation was not observed. The Lewis
carried out to obtain some preliminary information about the acidity of ZnMe2 is obviously not high enough for additional
Gibbs free energy changes associated with the coordination of coordination at the phenazine N atoms. We also carried out
ZnCl2 to compound 1. For the first step, reaction of 1 with two some quantum chemical calculations (again B3LYP/def2-SV
equivalents ZnCl2 to give the dinuclear complex [1(ZnCl2)2], a (P)), which are fully consistent with the experimental results.
ΔG value (at 298 K, 1 bar) of −365 kJ mol−1 was calculated. For Hence reaction between 1 and two eq. of ZnMe2 to give [1
the second step, reaction of two [1(ZnCl2)2] complex units with (ZnMe2)2] is still mildly exergonic by −28 kJ mol−1, but further
ZnCl2 to give the pentanuclear complex [(1)2(ZnCl2)5], we calcu- reaction of two eq. of [1(ZnMe2)2] with ZnMe2 is endergonic by
lated a gas-phase Gibbs free energy change of −162 kJ mol−1
.
+41 kJ mol−1 (at 298 K, 1 bar). Hence only strong Lewis acidic
The calculated ΔG values neglect solvent effects, which are metals are capable to form the aggregates.
likely to be significant, especially in the case of ZnCl2. On the
In Fig. 9a, the absorption spectra of free 1, [1(ZnCl2)2] and
other hand, the difference in the Gibbs free energy changes of a mixture of [1(ZnCl2)2] together with 2 eq. of ZnCl2, all dis-
between the first and the second step is in full agreement with solved in CH2Cl2, are compared. In Fig. 9b and 9c the TD-DFT
the experimental results. According to Scheme 5, further aggre- spectra calculated with B3LYP/def2-SV(P) and BP/def2-SV(P),
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Fig. 8 Molecular structure of [(1)2(ZnCl2)5]. Vibrational ellipsoids drawn
at the 50% probability level. Hydrogen atoms omitted for sake of clarity.
Selected structural parameters (bond distances in Å, bond angles in °):
Zn1–N1 2.036(4), Zn1–N4 2.037(3), Zn1–Cl1 2.2079(15), Zn1–Cl2 2.2466
(13), Zn2–N10 2.025(5), Zn2–N7 2.037(4), Zn2–Cl3 2.2268(16), Zn2–Cl4
2.2411(17), Zn5–N63 2.093(4), Zn5–N13 2.104(4), Zn5–Cl10 2.2375(13),
Zn5–Cl9 2.2462(14), N1–C13 1.340(6), N4–C18 1.343(6), N7–C23 1.343
(7), N10–C128 1.134(17), N1–Zn1–N4 82.74(14), N1–Zn1–Cl1 116.34(12),
N4–Zn1–Cl1 107.03(10), N1–Zn1–Cl2 111.30(11), N4–Zn1–Cl2 116.89
(11), Cl1–Zn1–Cl2 117.63(6), N10–Zn2–Cl4 126.36(15), N7–Zn2–Cl4
105.17(13), Cl3–Zn2–Cl4 113.89(6), N10–Zn2–N7 82.64(18), N10–Zn2–
Cl3 103.87(17), N7–Zn2–Cl3 122.87(11), N63–Zn5–N13 107.68(15), N63–
Zn5–Cl10 118.86(11), N13–Zn5–Cl10 97.03(11), N63–Zn5–Cl9 98.59(11),
N13–Zn5–Cl9 120.09(10), Cl10–Zn5–Cl9 115.69(6).
Fig. 9 (a) Comparison between the experimentally obtained absorption
spectra of 1, [1(ZnCl2)2] and a mixture of [1(ZnCl2)2] with a large excess
of ZnCl2. (b) and (c) Simulations of the absortion spectra of 1, [1(ZnCl2)2]
and [(1)2(ZnCl2)5] on the basis of TD-DFT calculations with (b) B3LYP/
def2-SV(P) and (c) BP/def2-SV(P).
respectively, for the three species 1, [1(ZnCl2)2] and
[(1)2(ZnCl2)5] are shown. The calculations (see Tables S1 and
S2 and Fig. S8–S10 in the ESI† for details) show that the
lowest-energetic transition of 1 (observed at 487 nm in CH2Cl2
and calculated at 441 nm (B3LYP)/503 nm (BP)) and of
[1(ZnCl2)2] (observed at 486 nm and calculated at 462 nm correctly a red-shift of the lowest-energetic electronic transition
(B3LYP)/540 nm (BP)) can be assigned to more or less pure upon formation of [(1)2(ZnCl2)5]. In the case of [(1)2(ZnCl2)5], a
HOMO–LUMO excitations. The calculated spectra also predict number of orbitals contribute to the lower energy electronic
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different colors can be found in differences in the degree of
aggregation. Hence THF could compete successfully with
[1(ZnCl2)2] in coordinating to ZnCl2, and consequently the solu-
tion mainly consist of [1(ZnCl2)2]. We observed that an initially
pink-colored solution in THF in minutes changed colour to
yellow, showing that THF not only prohibits aggregation, but
also could break up the aggregates. On the other hand, CHCl3
solutions mainly consist of aggregates; the band due to
[1(ZnCl2)2] at 486/459 nm is relatively small. Additional exper-
iments were carried out in which the concentrations were
varied for all three solvents (see Fig. S11 in the ESI†). These
experiments show that the percentage of aggregates increases
with increasing concentration (as already discussed for
CH2Cl2), in line with the presence of an equilibrium. The
effect of temperature on the relative band intensities turned
out to be much weaker, and only slight variations were observed
in the temperature region −60–(+20) °C in CH2Cl2 solution.
Finally, we inspected the fluorescence properties of aggre-
gate mixtures. Fig. 11 displays the fluorescence signals
measured for a solution of [(1)2(ZnCl2)5] in CH2Cl2. Two fluo-
rescence signals were detected, one at 506 nm, which belongs
to the dinuclear complex [1(ZnCl2)2], and another one at
599 nm. Measurements with different excitation wavelengths
(see Fig. 11) clearly showed that the 581 nm absorption is the
corresponding band of this species in the UV/Vis spectrum,
and therefore the fluorescence signal at 599 nm could be
assigned to the complex [(1)2(ZnCl2)5] (Stokes shift of
517 cm−1). We could qualitatively state that coordination at the
phenazine N atoms greatly reduces the fluorescence quantum
yield, although the absolute quantum yield for [(1)2(ZnCl2)5]
cannot be determined due to the equilibrium. The oligomeric
or polymeric [1(ZnCl2)3]n is fluorescence silent, and therefore
the 543 nm band in the absorption spectra has no equivalent
in the emission spectra. Our results show that the electronic
and optical properties of the new fluorescent dye 1 could be
Fig. 10 (a) Photo showing the color of solutions of [(1)2(ZnCl2)5] in
CH3CN, THF, CH2Cl2 and CHCl3. (b) Comparison between the UV/Vis
spectra of [(1)2(ZnCl2)5] (a 2 : 1 mixture of [1(ZnCl2)2] and ZnCl2) in three
different solvents (THF, CH2Cl2 and CHCl3), showing the equilibrium
between [1(ZnCl2)2] and the aggregates.
transitions (see Table S1, Fig. S8 and S9 in the ESI†). The greatly influenced by coordination.
experimentally observed red-shift of 95 nm from [1(ZnCl2)2] to
[(1)2(ZnCl2)5] compares with a calculated one of ca. 40 nm
(B3LYP)/48 nm (BP). In summary, the calculations fully
support our assignment.
Conclusions
A number of additional measurements were made to obtain Guanidino groups could be effectively used to tune the optical
further information about the aggregation equilibrium. Due to properties of aromatic compounds. They are a valuable alterna-
the distinct color changes upon aggregation, we predominantly tive to the traditionally employed amino groups, which they
relied on UV/Vis spectroscopy as analytical technique. outperform in several aspects. The guanidino groups decrease
However, it should be noted that aggregation is also visible the HOMO–LUMO gap, increase the fluorescence quantum
with other techniques. For example, in the aromatic region in yield, and offer sites for metal coordination. In this work we
the 1H NMR spectrum of CD2Cl2 solutions, a signal at δ (ppm) show that substitution of phenazines with guanidino groups
= 6.89 can be assigned to [1(ZnCl2)2] and two signals at leads to highly fluorescent dyes. The absorption and emission
δ (ppm) = 7.04 and 6.71 to [(1)2(ZnCl2)5]. Higher aggregates are spectra were studied in detail in several solvents. The Stokes
responsible for signals at δ (ppm) = 8.65 and 6.11. 2D HSQC shifts vary with the solvent and shifts of 2130–8750 cm−1 were
experiments (HSQC = Heteronuclear Single Quantum Coher- measured. Especially remarkable are the Stokes shifts of
ence) proved all these signals to arise from C–H protons, but a 5040 cm−1 for 1 in H2O and of 8750 cm−1 for 5 in CH3CN. The
more detailed assignment was not possible.
quantum yield for fluorescence reaches a record value of 0.39
The complex [(1)2(ZnCl2)5]) was dissolved in different sol- for 1 dissolved in Et2O. In contrast to the highly-fluorescent
vents. The colour of the solution varied between yellow (in guanidino-functionalized phenazines, the guanidino-substi-
THF) and pinc (in CHCl3) (see Fig. 10b). The reason for the tuted fluorene 2, which was also synthesized in this work,
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nation of ZnCl2. The measured lifetimes are independent of
the excitation wavelength which makes these compounds
highly interesting for further spectroscopic studies. For the
strong Lewis basic compound 1, an excess of ZnCl2 initiates
aggregation in the course of which the dinuclear [1(ZnCl2)2]
complex units are connected by ZnCl2. The degree of aggrega-
tion is strongly solvent dependent. Aggregation is
accompanied by a color change from yellow to purple, and the
UV/Vis spectra displays lower-energetic bands. We were able to
structurally characterize the compound [(1)2(ZnCl2)5], in which
two [1(ZnCl2)2] units are connected via a ZnCl2 bridge. In
ongoing work we are extending our studies to other guanidino-
substituted fluorescent dyes.
Experimental details
If not stated otherwise, the reactions were carried out under Ar
atmosphere using Schlenk techniques. Solvents were dried
prior to use by standard methods, and preserved over 4 Å
molecular sieves. NMR spectra were measured with Bruker
Avance II 400 or Bruker Avance DPX AC200 NMR machine.
Elemental analyses were carried out at the Microanalytical Lab-
oratory of the University of Heidelberg. IR spectra were
recorded with a Biorad Excalibur FTS 3000 spectrometer. UV/
Vis measurements were recorded with a Varian Cary 5000 UV/
Vis/NIR spectrophotometer. Fluorescence measurements were
recorded with a Varian Cary Eclipse machine. Fluorescence
quantum yields were obtained by using flouresceine in 0.1 M
NaOH as standard (Φ = 0.82).36 Fluorescence lifetimes were
determined with a PicoQuant FluoTime 100 Compact Fluo-
rescence Lifetime spectrometer. Fluorescence excitation was
performed with a 280 nm pulsed LED at 10 MHz repetition
rate. Electrochemical studies were carried out at r.t. using an
EG&G model 273A potentiostat/galvanostat. The auxiliary elec-
trode was a platinum wire and the working electrode was a
glassy carbon disk. The reference electrode was an aqueous
Ag/AgCl in 3 M KCl electrode. A Bruker ApexQe FT-ICR (ESI)
machine was used for mass spectrometry.
Fig. 11 Fluorescence spectra for [(1)2(ZnCl2)5] in CH2Cl2 solution,
excited with light of different wavelengths.
shows little fluorescence. The bisguanidino-phenazine 5 also is
a strongly fluorescent dye, but the fluorescence quantum yield
is lower than for 1. We note that the extremely large Stokes
shifts measured for 5 (up to 8750 cm−1) together with the rela-
tively low wavenumber of the lowest-energetic transition in the
UV/Vis spectrum might qualify the compound for applications
in electroluminescent devices (see the discussion in ref. 34).
The influence of coordination at the guanidino groups of
the phenazine systems on the optical properties was sub-
sequently analyzed. CuI coordination leads to luminescence
quenching. By contrast, coordination with ZnCl2 leads to
intensively fluorescent metal complexes. Both the dinuclear
complex [1(ZnCl2)2] and the mononuclear complex [5(ZnCl2)]
were structurally characterized. While little changes were
observed in the absorption spectra upon coordination, the
Stokes shifts decrease significantly. Also, the fluorescence life-
times of 1 and 5 in CH3CN are dramatically reduced by coordi-
2,3,7,8-Tetrakis(tetramethylguanidino)phenazine, 1 (in three
steps)
1. Step (2,3,6,7-tetraamino-phenazine): this compound was
prepared as described in the literature.29 Briefly, 1,2,4,5-tetra-
amino-benzene-tetrahydrochloride (1.338 g, 4.712 mmol) were
dissolved in 30 mL destilled water. Then 3.091 g sodium
acetate (37.69 mmol) were added. The reaction mixture was
heated to reflux, while passing compressed air though the
solution. After 5h, the reaction mixture was cooled to room-
temperature, during which time a deep purple colored solid
precipitated. The solid was separated by filtration, washed
with water and dried under vacuum. Yield: 0.733
g
(2.097 mmol, 89%). Elemental analysis for 2·(2,3,6,7-tetra-
amino-phenazine)·3HCl, C24H27Cl3N12 (349.65): calcd C 48.86,
H 4.61, N 28.49; found C 48.27, H 4.63, N 27.71. 1H NMR
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(200 MHz, d6-DMSO): δ (ppm) = 5.47 (s, 8 H, NH2), 6.78 (s, 2.65 to 28.5°. Reflections measd. 8641, indep. 4477, Rint
=
4 H, Har). MS (ESI+): m/z = 241.4 u ([M + H]+, 100%).
0.0445. Final R indices [I > 2σ(I)]: R1 = 0.059, wR2 = 0.153.
2. Step (2-chloro-1,1,3,3-tetramethylformamidinium chlor-
ide, [ClC(NMe2)2]Cl): oxalylchloride (0.965 ml, 11.25 mmol,
1.428 g) was added drop-wise to a solution of 0.270 mL
2,3,6,7-Tetrakis(tetramethylguanidino)fluorene, 2 (in five
steps)
(2.250 mmol, 0.261 g) 1,1,3,3-tetramethyl-urea in 10 mL 1. Step (2,7-diamino-fluorene): 2.000 g (7.806 mmol) of 2,7-
CHCl3. The pale yellow reaction mixture was heated to reflux dinitrofluorene were added to a suspension of 14.11 g
for a period of 16h, and then allowed to cool to room tempera- (74.40 mmol) SnCl2 in 48 mL Et2O. After addition of 30 mL
ture. Subsequently the solvent was removed under vacuum concentrated HCl solution the suspension was heated under
and the solid residue washed three times with 19 mL portions stirring for a period of 4 h to reflux. 2,7-diamino-fluorene·2HCl
of Et2O. Finally the activated urea was dried under precipitated in the form of a pale-yellow colored solid, which
vacuum and directly used for the subsequent guanidinylation was separated from the solution by filtration and subsequently
reaction.
washed three times with 10 mL portions of concentrated HCl
3. Step (2,3,7,8-tetrakis(tetramethylguanidino)phenazine, solution. 1H NMR (200 MHz, d6-DMSO): δ (ppm) = 7.92 (d,
1): 0.745 ml (5.400 mmol) NEt3 were added to a solution of 2 H, 1J = 8.2 Hz, H4/5ar), 7.47 (s, 2 H, H1/8ar), 7.28 (d, 2 H, 1J = 8.2
0.133 g (0.45 mmol) 2,3,7,8-tetramino-phenazine·1.5HCl in Hz, H3/6ar), 4.00 (s, 2 H, CH2). 13C NMR (150 MHz, d6-DMSO):
5 mL CH3CN. To this suspension, a solution of 0.385 g δ (ppm) = 121.95 (C4/5ar), 121.08 (C1/8ar), 120.02 (C3/6ar), 36.36
(2.250 mmol) 2-chloro-1,1,3,3-tetramethylformamidinium (CH2). MS (FAB+): m/z = 196.5 u ([M]+, 100%). MS (ESI+): m/z =
chloride in 10 mL CH3CN was added. Subsequently the reac- 197.2 u ([M + H]+, 100%). The 2,7-diamino-fluorene·2HCl was
tion mixture was stirred for a period of 5 h at a temperature of dissolved in H2O and a saturated NaHCO3 solution was added
60 °C, leading to the precipitation of a brown-colored solid. until a pH value of 8 was reached. The yellow precipitate of
After removal of the solvent under vacuum, the pale-brown 2,7-diamino-fluorene was separated by filtration, dried under
solid was dissolved in destilled water. Upon addition of 25% vacuum and used in the next step without further purification.
1
NaOH solution, an orange-brown solid precipitated, which was 1H NMR (200 MHz, d6-DMSO): δ (ppm) = 7.25 (d, 2 H, J = 8.0
extracted with CHCl3. The CHCl3 solution was dried over Hz, H4/5ar), 6.68 (s, 2 H, H1/8ar), 6.49 (d, 2 H, 1J = 8.0 Hz,
K2CO3 before the solvent was removed under vacuum. Yield of
H
3/6ar), 4.87 (br s, 4 H, NH2), 3.57 ppm (s, 2 H, CH2).
crude product: 0.199–0.227 g (0.314–0.359 mmol, 70–80%).
2. Step (2,7-diacetamidofluorene): 1.532 g (7.806 mmol) of
Recrystallization from toluene at −18 °C afforded the orange- 2,7-diaminofluorene were suspended in 135 mL glacial acetic
colored solid product in a yield of up to 74%. Deep-orange acid. Then 45 mL acetic anhydride were added. Under an Ar
colored crystals were obtained from Et2O solutions at room atmosphere the solution was heated to reflux for a period of
temperature. Solutions of the compound are yellow-orange 30 min, then cooled back to room temperature and poured
colored. Elemental analysis for C32H52N14 (632.85): calcd C onto ice. The milky white precipitate of 2,7-diacetamidofluo-
60.73, H 8.28, N 30.99; found C 60.12, H 7.63, N 30.33. 1H rene was separated by filtration and dried under vacuum.
NMR (600.13 MHz, CD3CN): δ (ppm) = 6.78 (s, 4 H, Har), 2.72 A yield of 75% referring to 2,7-dinitrofluorene was obtained.
(s, 48 H, Me). 13C NMR (150.92 MHz, CD3CN): δ (ppm) = 1H NMR (200 MHz, d6-DMSO): δ (ppm) = 9.94 (s, 2 H, NH),
1
160.34 (Cguanidin), 150.25 (Car), 141.34 (Car), 114.05 (Car-H), 7.86 (s, 2 H, H1/8ar), 7.68 (d, 2 H, J = 8.2 Hz, H3/6ar), 7.48 (d,
39.97 (Me). MS (ESI+): m/z = 633.3 u ([1 + H]+, 100.0%), 317.3 u 2 H, 1J = 8.2 Hz, H4/5ar), 3.85 (s, 2 H, CH2), 2.06 (s, 6 H, CH3).
([1 + 2H]2+, 99.24%), 272.4 u ([1 − 2NMe2]2+, 14.77%). MS
3.
Step
(3,6-dinitro-2,7-diaminofluorene):
1.703
g
(FAB+): m/z = 633.5 u ([1 + H]+. UV/Vis (CH3CN, c = 1.58 × 10−5 (6.073 mmol) 2,7-diacetamidofluorene were suspended in
mol l−1, d = 0.5 cm): λmax (ε, in L mol−1cm−1) = 222 (3.6228 × 40 mL CH2Cl2. After addition of 35 mL glacial acetic acid the
104), 309 (5.6556 × 104), 480 (3.5612 × 104) nm. UV/Vis (H2O, c mixture was cooled to −10 °C, and a −10 °C cold solution of
= 1.1503 × 10−5 mol l−1, d = 1 cm): λmax (ε, in L mol−1 cm−1) = 17.5 mL fuming nitric acid in 50 mL CH2Cl2 drop-wise slowly
229 (5.7353 × 104), 300 (5.6211 × 104), 432 (2.0927 × 104), 484 added, keeping the temperature below −5 °C. The color of the
(1.6961 × 104) nm. Fluorescence (CH3CN, λex = 480 nm): λmax, reaction mixture changes first from white to deep-green. After
= 568 nm. Fluorescence (H2O, λex = 484 nm): λmax,em
=
complete addition of the HNO3–CH2Cl2 solution it slowly
em
640 nm. Quantum yield: Φ (H2O) = 0.02, Φ (CH3CN) = 0.22 and bleached and an orange-colored precipitate formed. After stir-
Φ (Et2O) = 0.39. IR (CsI): ˜ν = 3042w, 3001w, 2991w, 2930m, ring for an additional 10 min the solution was poured on ice.
2884m, 2794w, 1571s, 1508m, 1478m, 1433s, 1422s, 1379s, The yellow-colored precipitate was separated by filtration and
1358m, 1333m, 1314w, 1266m, 1234m, 1189s, 1142s, 1106w, washed with some H2O, yielding 67% of 3,6-dinitro-2,7-diacet-
1060m, 1019s, 932w, 923w, 907m, 867m, 855m, 794w, 777m, amidofluorene. 1H NMR (200 MHz, d6-DMSO): δ (ppm) =
741m, 718m, 676w, 669w, 654w, 597m, 583m, 530w, 457w 10.30 (s, 2 H, NH), 8.73 (s, 2 H, H4/5ar), 7.89 (s, 2 H, H1/8ar),
cm−1. Crystal data for 1, C32H52N14: Mr = 632.88, 0.40 × 0.25 × 4.21 (s, 2 H, CH2), 2.11 (s, 6 H, CH3). MS (EI+): m/z = 370.1 u
0.20 mm3, monoclinic, space group P2(1)/c, a = 774.7(2), b = ([M]+, 52%), 279.1 u ([2,7-diacetamido-fluorene – H]+, 100%).
15.440(3), c = 15.074(3) Å, α = 90.00°, β = 96.68(3)°, γ = 90.00°, Then 0.500 g (1.351 mmol) of 3,6-dinitro-2,7-diacetamidofluo-
V = 1790.80 Å3, Z = 2, dcalc = 1.174 Mg m−3, Mo Kα radiation rene were suspended in 150 mL acetone. After addition of
(graphite monochromated, λ = 0.71073 Å), T = 100 K, θrange 30 mL concentrated HCl solution, the mixture was heated for
3480 | Dalton Trans., 2015, 44, 3467–3485
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Dalton Transactions
Paper
7 h to a temperature of 75 °C, leading to a color change from monochromated, λ = 0.71073 Å), T = 100 K, θrange 2.25 to
orange to deep-red. The reaction mixture was allowed to cool 27.71°. Reflections measd. 31 289, indep. 8875, Rint = 0.0820.
back to room temperature and then poured on ice. The deep- Final R indices [I > 2σ(I)]: R1 = 0.0673, wR2 = 0.1721.
red colored precipitate was separated by filtration and dried
2,3-Bis(tetramethylguanidino)phenazine, 5
ene. 1H NMR (200 MHz, d6-DMSO): δ (ppm) = 8.41 (s, 2 H, 722 mg (7.14 mmol) of NEt3 was added to a suspension of
under vacuum, yielding 78% of 3,6-dinitro-2,7-diaminofluor-
Har), 7.54 (br s, 4 H, NH2), 7.09 (s, 2 H, Har), 3.96s, 2 H, CH2).
4. Step (2,3,6,7-tetraminofluorene): 4.5 mL concentrated Then a solution of 1.22 g (7.14 mmol) of 2-chloro-1,1,3,3-tetra-
HCl solution was added to suspension of 0.148 methylformamidinium chloride in 8 mL CH3CN was slowly
300 mg of 2,3-diaminophenazine (1.43 mmol) in 4 mL CH3CN.
a
g
(0.516 mmol) of 3,6-dinitro-2,7-diaminofluorene in 15 mL drop-wise added over a period of 10 min. The reaction
EtOH. The pale-yellow colored precipitate of 2,3,6,7-tetramino- mixture, which turns deep-brown, was stirred for a period of
fluorene·4HCl was separated by filtration, washed three times 3 h at a temperature of 50 °C. After the mixture has cooled
with 4 mL portions of concentrated HCl solution and dried back to room-temperature, the solvent was removed in vacuum
under vacuum to obtain 2,3,6,7-tetramino-fluorene·4HCl in a and the remaining deep-brown colored solid re-dissolved in
yield of 58%. 1H NMR (200 MHz, d3-CD3CN): δ (ppm) = 7.90 (s, water. The product was then precipitated by addition of 25%
2 H, H4/5ar), 7.62 (s, 2 H, H3/6ar), 4.08 (s, 2 H, CH2). MS NaOH solution, and subsequently extracted 5 times with
(HR-ESI): m/z = 226.12128 u ([M]+, 100%).
15 mL portions of CHCl3. The organic phase was dried over
5. Step (2,3,6,7-Tetrakis(N,N,N′,N′-tetramethylguanidino)- K2CO3, and then the solvent removed to yield 337 mg (58%)
fluorene, 2): 0.546 g (5.400 mmol) NEt3 were added to a solu- crude product as brown-colored solid. The crude product was
tion of 0.102 g (0.450 mmol) 2,3,6,7-tetraminofluorene-tetrahy- re-dissolved in CH3CN and the yellow-colored insoluble side
drochloride in 5 mL CH3CN. This suspension was cooled at product of the reaction was removed by filtration, before the
0 °C. To this suspension, a solution of 0.385 g (2.250 mmol) of solvent was removed from the filtrate under vacuum. In this
2-chloro-1,1,3,3-tetramethylformamidinium chloride in 8 mL way one obtains 121 mg (0.30 mmol, total yield 21%) orange-
CH3CN was added. The reaction mixture was stirred for a colored clean product. Elemental analysis for
C22H30N8
period of 2 h at a temperature of 0 °C, leading to the precipi- (406.53): calcd C 65.00, H 7.44, N 27.56; found C 64.72, H 7.15,
1
tation of a brown-colored solid. After removal of the solvent N 27.49. H NMR (400 MHz, CD3CN): δ (ppm) = 2.75 (s, 25 H,
under vacuum, the light-brown solid was dissolved in 10% HCl CH3), 6.84 (s, 2 H, CH5ar), 7.60 (q, J = 3.39 Hz, 2 H, Har), 7.96
solution. Upon the addition of 25% NaOH solution, the (q, J = 3.39 Hz, 2 H, Har). 13C NMR (400 MHz, CD3CN): δ (ppm)
aqueous solution was extracted with Et2O (4 × 15 mL), and the = 40.15 (CH3), 113.05 (CH5ar), 128.13 (CHar), 129.48 (CHar).
organic phases were dried over KCO3. The solvent was removed Four quaternary C atoms were not detected. IR (CsI): ˜ν = 2927
under vacuum, and the crude product as yellow-brown solid w (ν(C–H)), 1577 vs. (ν(CC)), 1510m (C–H def), 1437 vs. (C–H
was dried under vacuum. The purification was carried out by def), 1383m (C–H def), 1233 w, 1133m, 1019m, 891 w, 757 w
sublimation at 210–220 °C and the white solid was obtained. (Car–H def), 595 w, 505 w cm−1. MS (DART): m/z = 407.26683
Yield: 0.162 g (0.261 mmol, 58%). Elemental analysis for ([M + H]+, 100.0%). [C22H31N8]+, calcd 407.26662, [M + H]+
C33H54N12 (618.86): calcd C 64.05, H 8.79, N 27.16; found C (100.0%), found 407.26683, diff. −0.2 mmu. UV/Vis (CH3CN,
1
63.57, H 8.89, N 26.25. H NMR (600 MHz, CD3CN): δ (ppm) = c = 1.28 × 10−5 mol l−1, d = 1 cm): λmax (ε, in L mol−1 cm−1) =
6.63 (s, 2 H, H4ar), 6.51 (s, 2 H, H1ar), 3.55 (s, 2 H, CH2), 2.64 (s, 233 (3.63 × 105), 276 (5.32 × 105), 393 (1.58 × 105) nm. UV/Vis
58 H, CH3). 13C NMR (150 MHz, CD3CN): δ (ppm) = 159.01 (s, (Et2O, c = 1.18 × 10−5 mol l−1, d = 1 cm): λmax (ε, in L mol−1
C
guanidin), 143.88 (s, C2/3ar), 143.13 (s, C2/3ar), 136.47 (s, C5/6ar), cm−1) = 277 (3.91 × 105), 433 (1.77 × 105) nm. Fluorescence
136.30 ppm (s, C5/6ar), 118.57 ppm (s, C1ar), 111.98 ppm (s, (CH3CN, λex = 233 nm): λmax,em = 599 nm; Fluorescence (THF,
4ar), 36.32 ppm (s, CH2), 39.76 ppm (s, CH3). MS (HR-ESI): λex = 447 nm): λmax,em = 588 nm. Quantum yield: Φ (THF) =
C
m/z = 1237.92446 u ([2M + H]+, 4.90%), 619.46635 u ([M + H]+, 0.17, Φ (CH3CN) = 0.15, Φ (Et2O) = 0.11. Crystal data for
100%), 310.23695 u ([M+2H]2+, 32.0%). UV/Vis (CH3CN, c = 5·2H2O, C22H34N8O2: Mr = 442.57, 0.50 × 0.50 × 0.45 mm3,
1.0341 × 10−5 mol l−1, d = 1 cm): λmax (ε, in L mol−1 cm−1) = monoclinic, space group P2/c, a = 15.900(3), b = 9.2100(18), c =
371 (2.431 × 104), 319 (1.529 × 104), 269 (2.546 × 104, shoulder), 16.379(3) Å, β = 94.82(3)°, V = 2390.0(8) Å3, Z = 4, dcalc = 1.230
226 (3.990 × 104) nm. Fluorescence (CH3CN, λex = 342 nm): Mg m−3, Mo Kα radiation (graphite monochromated, λ =
λmax,em = 428 nm. IR (CsI): ˜ν = 2999w, 2924m, 2886m, 2803w, 0.71073 Å), T = 100 K, θrange 2.21 to 30.04°. Reflections measd.
1612s, 1601s, 1587s, 1549m (shoulder), 1497m, 1476w, 1460m, 13 359, indep. 6949, Rint = 0.0323. Final R indices [I > 2σ(I)]:
1437w, 1423m, 1406w, 1371s, 1333w, 1325w, 1277m, 1261m, R1 = 0.0910, wR2 = 0.2642.
1233m, 1215m, 1190w, 1173w, 1165m, 1138s, 1107w, 1092w,
[1(CuI)2]: Compound 1 (0.0669 g, 0.1058 mmol) were dis-
1063m, 1018s, 1001s, 955w, 939w, 920m, 858m, 833w, 800m, solved in 8 mL CH2Cl2. Then 2 equivalents of CuI (0.0403 g,
789m, 735w, 671w, 637m, 579w, 505w cm−1. Crystal data for 0.2116 mmol) were added. The dark red reaction mixture was
2·CH3CN, C35H57N13: Mr = 659.94, 0.35 × 0.20 × 0.15 mm3, tri- stirred for a period of 1 h at room temperature. Subsequently
ˉ
clinic, space group P1, a = 7.8850(16), b = 13.540(3), c = 18.573 the solvent was removed under vacuum. The dark red precipi-
(4) Å, α = 103.13(3)°, β = 90.59(3)°, γ = 92.60(3)°, V = 1928.6(7) tate was washed with Et2O (3 × 5 mL), and dried under
Å3, Z = 2, dcalc = 1.136 Mg m−3, Mo Kα radiation (graphite vacuum. The solid was re-dissolved in CH2Cl2 and upon
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Dalton Transactions
addition of Et2O precipitated as a clean product. The product (ZnCl2)2]·2CH2Cl2, C36H60Cl12N14Zn2: Mr = 1245.12, 0.30 × 0.30
was filtrated and dried under vacuum. Yield: 0.055
× 0.20 mm3, monoclinic, space group P2(1)/c, a = 13.162(3), b =
g
(0.0539 mmol, 51%). Elemental analysis for C32H52Cu2I2N14 13.499(3), c = 16.472(3) Å, β = 108.30(3)°, V = 2778.63 Å3, Z = 2,
(1013.75): calcd C 37.91, H 5.17, N 19.34; found C 37.65, H dcalc = 1.488 Mg m−3, Mo Kα radiation (graphite monochro-
5.06, N 19.18. MS (HR-ESI+): m/z = 823.29278 u ([1 + CuI + H+]+, mated, λ = 0.71073 Å), T = 100 K, θrange 4.4 to 60.1°. Reflections
20.5%), 950.129723 u ([1 + CuI + I− + H+]+, 14.7%). MS (FAB+): measd. 16 059, indep. 8111, Rint = 0.0482. Final R indices [I >
m/z = 588.4 ([1 − NMe2]+, 21.2%), 633.5 u ([1 + H+]+, 9.6%), 2σ(I)]: R1 = 0.045, wR2 = 0.128.
696.1 u ([1 + Cu+]+, 17.3%), 824.0 u ([1 + CuI+2H+]+, 13.5%),
[5(ZnCl2)]. 0.010 g (1 eq., 0.0738 mmol) of ZnCl2 was added
1012.7 u ([M+]+, 9.6%). UV/Vis (CH3CN, c = 0.9081 × 10−5 mol to a solution of 0.030 g (0.0738 mmol) of 5 in 5 mL CH3CN.
l−1, d = 1 cm): λmax (ε, in L mol−1 cm−1) = 226 (6.2067 × 104), The reaction mixture was stirred for a period of 4 h at room
243 (5.7190 × 104), 317 (7.4615 × 104), ca. 465 (3.4082 × 104, temperature. The solvent was partially removed under vacuum
shoulder), 493 nm (5.9110 × 104) nm. UV/Vis (CH2Cl2, c = before the solution was stored at +4 °C for several days. The
1.3024 × 10−5 mol l−1, d = 1 cm): λmax (ε, in L mol−1 cm−1) = needle shaped crystals which were formed in the solution were
321 (8.8200 × 104), ca. 474 (4.2945 × 104, shoulder), 501 (7.2754 filtered off and washed three times with Et2O and n-hexane.
× 104) nm. Fluorescence signals almost extinguished by CuI The remaining yellow solid was dried under vacuum. Upon
coordination. Fluorescence (CH2Cl2, λex = 460 nm): λmax,em
ca. 519 nm. Fluorescence (CH3CN, λex = 465 nm): λmax,em
=
=
recrystallization from CH3CN crystals of [5(ZnCl2)] were
obtained. Elemental analysis for C22H30Cl2N8Zn, (542.81):
ca. 533 nm. IR (CsI): ˜ν = 3047w, 3005w, 2936m, 2890m, 2793w, calcd C 48.68, H 5.57, N 20.64; found C 48.36, H 5.50, N 21.16.
1574s, 1515s, 1451s, 1417s, 1401s, 1325m, 1263m, 1232w, 1H NMR (400 MHz, CD3CN): δ (ppm) = 2.88 (br. s., 12 H), 3.06
1199m, 1157m, 1142m, 1108w, 1064w, 1026m, 958w, 917w, (br. s., 12 H), 6.99 (s, 2 H), 7.70 (q, J = 3.39 Hz, 2 H), 8.04 (q, J =
905w, 855w, 810w, 796w, 785w, 740w, 733w, 714w, 696w, 668w, 3.64 Hz, 2 H). 13C NMR (400 MHz, CD3CN): δ (ppm) = 112.57
610m, 502w cm−1
.
(CH5ar), 129.42 (CHar), 129.77 (CHar), 143.02 (Cq), 143.65 (Cq),
[1(ZnCl2)2]: 0.0256 g (2 eq., 0.1878 mmol) of ZnCl2 was dis- 147.78 (Cq). IR (CsI): ˜ν = 2932 w (ν(C–H)), 1571m (CvC val),
solved in 2 mL CH3CN and added dropwise to a solution of 1530m (C–H def), 1453s (C–H def), 1405s (C–H def), 1340m,
0.0594 g (0.0939 mmol) of 1 in 2 mL CH3CN. The reaction 1232m, 1163m, 1036m, 897w, 816w, 762w (Car–H def), 603w,
mixture was stirred for a period of 2 h at room temperature. 503w cm−1. MS (HR-FAB): m/z = 540.1262 ([M]+, 80.0%).
The solvent was removed to obtain an orange solid that was re- [C22H30N8ZnCl2]+ calcd 540.1262, [M]+ (80.0%); found
dissolved in 1.5 mL CH2Cl2 and filtered to remove the insolu- 540.1262, Diff.: 0.0 mmu. UV/Vis (CH3CN, c = 1.18 × 10−5 mol
ble rest. Upon addition of Et2O the product precipitates as a l−1, d = 1 cm): λmax (ε, in L mol−1 cm−1) = 231 (3.34 × 105), 283
crystalline orange solid. The product was filtered, washed (3.79 × 105), 302 (3.40 × 105), 424 (2.02 × 105), 442 (2.31 × 105)
three times with 1 mL portions of Et2O and dried under nm. Fluorescence (THF, λex = 445 nm): λmax,em = 498 nm. Fluo-
vacuum. Upon recrystallization from CH2Cl2 crystals of rescence (CH3CN, λex = 302 nm): λmax,em = 514 nm. Quantum
[1(ZnCl2)2] were obtained. Yield 0.0450 mg (0.0498 mmol, 53%) yield: Φ(CH3CN) = 0.08. Crystal data for [5(ZnCl2)]·CH3CN,
product. Elemental analysis for C32H52Cl4N14Zn2 (905.42): C24H33Cl2N9Zn: Mr = 583.86, 0.50 × 0.50 × 0.50 mm3, mono-
calcd C 42.45, H 5.79, N 21.66; found C 42.16, H 5.66, N 21.26. clinic, space group P2(1), a = 10.558(2), b = 23.182(5), c =
1H NMR (600 MHz, CD3CN): δ (ppm) = 6.89 (s, 4 H, Har), 3.03 22.678(5) Å, β = 90.44(3)°, V = 5550.40(8) Å3, Z = 8, dcalc = 1.397
(s, 24 H, Me), 2.84 (s, 24 H, Me). 13C NMR (150 MHz, CD3CN): Mg m−3, Mo Kα radiation (graphite monochromated, λ =
δ (ppm) = 166.23 (s, Cguan), 145.49 (s, Cq,ar), 141.51 (s, Cq,ar), 0.71073 Å), T = 100 K, θrange 1.8 to 60.2°. Reflections measd.
113.02 (s, Car–H), 41.21 (s, Me), 40.52 (s, Me). 1H NMR 32 157, indep. 32 131, Final R indices [I > 2σ(I)]: R1 = 0.039,
(600 MHz, CD2Cl2): δ (ppm) = 6.88 (s, 4 H, Har), 3.06 (s, 24 H, wR2 = 0.101.
Me), 2.90 (s, 24 H, Me). 13C NMR (150 MHz, CD2Cl2): δ (ppm)
[(1)2(ZnCl2)5]: To 0.0362 g (2.5 eq., 0.2656 mmol) of ZnCl2
= 165.74 (s, Cguan), 144.61 (s, Cq,ar), 141.09 (s, Cq,ar), 112.55 (s, in CH2Cl2 was added a solution of 0.0672 g (0.1062 mmol) of 1
Car–H), 41.17 (s, Me), 40.38 (s, Me). UV/Vis (CH3CN, c = 1.1486 in 8 mL CH2Cl2. The reaction mixture was stirred for a period
× 10−5 mol l−1, d = 1 cm): λmax (ε, in L mol−1 cm−1) = 228 of 2 h at a temperature of 45 °C until it became dark red. After
(5.8829 × 104), 316 (7.6583 × 104), 458 (3.7518 × 104), 484 the mixture had cooled back to room temperature, the solvent
(5.7725 × 104) nm. UV/Vis (CH2Cl2, c = 1.4137 × 10−5 mol l−1
,
was partially removed. To this concentrated solution was
d = 0.5 cm): λmax (ε, in L mol−1 cm−1) = 228 (5.3921 × 104), 319 added 8 mL Et2O. The mixture was stored at 0 °C to get a crys-
(6.9684 × 104), 459 (3.5629 × 104), 486 (5.4647 × 104) nm. Fluo- talline red precipitate. The solid was filtrated, washed with
rescence (CH3CN, λex = 484 nm): λmax,em = 506 nm. Fluo- Et2O and n-hexane and dried under vacuum. Purple crystals
rescence (CH2Cl2, λex = 486 nm): λmax,em = 512 nm. Quantum were obtained from a CH2Cl2–Et2O mixture. Yield: 0.0289 g
˜
yield: Φ(CH3CN) = 0.36. IR (CsI): ν = 3049w, 3009w, 2935m, (0.0149 mmol, 28%). Elemental analysis for C64H104Cl10N28Zn5
2895w, 2799w, ca. 1615m shoulder, 1565s, 1522s, 1452s, (1947.13): calcd C 39.48, H 5.38, N 20.14; found C 38.72, H
1420s, 1408s, 1400s, 1329m, 1261m, 1234w, 1193m, 1162m, 5.91,
N
20.30. Crystal data for [(1)2(ZnCl2)5]·4.7CH2Cl2,
2346.25, 0.35 0.30
1144w, 1110w, 1065w, 1035m, 1027m, 957w, 919w, 907w, 68.70H113.40Cl19.40N28Zn5: Mr
C
=
×
×
3
ˉ
861w, 810w, 789w, 740w, 735w, 715w, 707w, 611w, 575w, 561w, 0.30 mm , triclinic, space group P1, a = 17.629(4), b = 18.298
506w, 503w, 492w, 473w cm−1
.
Crystal data for [1 (4), c = 18.587(4) Å, α = 90.87(3)°, β = 104.98(3)°, γ = 108.66(3)°,
3482 | Dalton Trans., 2015, 44, 3467–3485
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Paper
V = 5455.9(19) Å3, Z = 2, dcalc = 1.428 Mg m−3, Mo Kα radiation
(graphite monochromated, λ = 0.71073 Å), T = 100 K, θrange
References
2.48 to 27.52°. Reflections measd. 45 548, indep. 24 658, Rint
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Suitable crystals were taken directly out of the mother liquor,
immersed in perfluorinated polyether oil and fixed on top of a
cryo loop. Measurements were made with a Nonius-Kappa
CCD diffractometer with low-temperature unit using graphite-
monochromated Mo Kα radiation. The temperature was set to
100 K. The data collected were processed using the standard
Nonius software.37 All calculations were performed using the
SHELXT-PLUS software package. Structures were solved by
direct methods with the SHELXS-97 program and refined with
the SHELXL-97 program.38,39 Graphical handing of the struc-
tural data during solution and refinement was performed with
XPMA.40 Atomic coordinates and anisotropic thermal para-
meters of non-hydrogen atoms were refined by full-matrix
least-squares calculations. CCDC-1016464 (1), 1016465 (2),
1034621 ([1(ZnCl2)2]), 1016466 ([5(ZnCl2)]), 1016467 (5·2H2O),
1016468 ([1H2](BF4)2), and 1016832 ([(1)2(ZnCl2)5]) contain the
supplementary crystallographic data for this paper..
Details of the quantum chemical calculations
The density functional calculations on the uncoordinated com-
pounds and protonated 1 were carried out with the B3LYP
functional41 and the 6-311G** basis set.42 The GAUSSIAN43
program package was used. To speed up the investigation for
the different complexes, the calculations, including the
TD-DFT calculations, were performed with the smaller def2-SV
(P) basis set44 in combination with the BP8641a,45 and B3LYP
functionals. The structures were optimized with the BP86 func-
tional, using the resolution of the identity (RI) approximation
and the appropriate auxiliary SV(P) basis set.46 Then final ener-
gies were obtained with the B3LYP functional using thermo-
dynamic contributions from the BP86 results. These
calculations used the TURBOMOLE47 program package.
A comparison of the structures (Table S2 in the ESI†) and
the HOMO–LUMO gap of compound 1 shows that in the case
of the structure the usage of a different basis set and func-
tional and in the case of the HOMO–LUMO gap the usage of a
different basis set has only a minor impact on the calculated
quantities. Within the B3LYP/6-311G** calculations the
HOMO–LUMO gap amounts to 3.24 eV, whereas within the
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Acknowledgements
The authors thank the Deutsche Forschungsgemeinschaft
(DFG) for continuous financial support.
This journal is © The Royal Society of Chemistry 2015
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