Design of new tetrazine-triphenylamine bichromophores - Fluorescent switching by chemical oxidation

Article abstract of DOI:10.1002/ejoc.201101584

Original new fluorescent and electroactive compounds have been prepared, which feature two different fluorescent groups linked through an oxygen atom spacer. We describe here the synthesis, photophysical and electrochemical properties and their interplay, and our theoretical calculations. These molecules are composed of two fluorophores, an electron-rich triphenylamine unit and an electron-poor tetrazine unit. Although the bichromophores are not fluorescent in the neutral state due to a photoinduced electron transfer from the triphenylamine unit to the tetrazine unit, one can restore the fluorescence by oxydation of the triphenylamine moiety. Thus, a redox-fluorescent switch has been realized. Tetrazine-triphenylamine bichromophores linked by an oxygen atom were designed and synthesized. Their photophysical and electrochemical properties were investigated. These dyads are nonfluorescent compounds in their neutral state because of phoinduced electron transfer. However, tetrazine fluorescence was restored by chemical oxidation (cation radical formation). Copyright

Full text of DOI:10.1002/ejoc.201101584

FULL PAPER
DOI: 10.1002/ejoc.201101584
Design of New Tetrazine–Triphenylamine Bichromophores – Fluorescent
Switching by Chemical Oxidation
Cassandre Quinton,[a] Valérie Alain-Rizzo,*[a] Cécile Dumas-Verdes,*[a] Gilles Clavier,[a]
Fabien Miomandre,[a] and Pierre Audebert*[a]
Keywords: Donor–acceptor systems / Synthesis design / Redox chemistry / Fluorescence / Molecular modeling
Original new fluorescent and electroactive compounds have
been prepared, which feature two different fluorescent
groups linked through an oxygen atom spacer. We describe
here the synthesis, photophysical and electrochemical prop-
erties and their interplay, and our theoretical calculations.
These molecules are composed of two fluorophores, an elec-
tron-rich triphenylamine unit and an electron-poor tetrazine
unit. Although the bichromophores are not fluorescent in the
neutral state due to a photoinduced electron transfer from
the triphenylamine unit to the tetrazine unit, one can restore
the fluorescence by oxydation of the triphenylamine moiety.
Thus, a redox-fluorescent switch has been realized.
dizing potentials. Hence, tetrazine–triphenylamine dyads
could behave as a two-state redox-mediated off–on fluores-
cent switches (Figure 1).
Introduction
We are interested in the study of fluorescent electroactive
chromophores based on tetrazines[1] and boron–dipyrro-
methene (BODIPY).[2] These molecules present different
photophysical properties according to the redox state of the
molecule (neutral, oxidized or reduced). For example, inter-
play between fluorescence and redox characteristics in the
case of 3-chloro-6-methoxytetrazine could lead to a revers-
ible switching of fluorescence (also called electrofluorochro-
mism).[3] Although there is interest in and possible applica-
tions for the reversible fluorescent electrochemical switch of
a molecule (or oligomer) composed of a single unit that is
both electroactive and fluorescent,[3] multiple fluorophore
systems present their own advantages.[2,4] Indeed, instead of
an on–off two-state system, it should be possible to prepare
dyads that display off-to-on fluorescent switching upon re-
dox activation. Such dyads should present complementary
properties to 3-chloro-6-methoxytetrazine. Hence, dyads
composed of an electroactive donating group and a fluoro-
phore accepting group should be good candidates for re-
dox-fluorescent switchable devices.[5]
Figure 1. Two redox-state system with different fluorescent proper-
ties.
We have prepared several dyads, which should meet the
above requirements and feature one or two triphenylamine
moieties that bear different groups on their para positions,
Tetrazines are particularly well adapted fluorophores for
the accepting unit.[1] Triphenylamine compounds are well-
known electron-rich derivatives, which are used in many ap-
plications, such as organic optoelectronics[6] and electro-
chromism,[7] and could be a good choice as a partner
fluorophore as these molecules mostly display extremely
stable cation radicals, which can be formed at moderate oxi-
[a] PPSM, CNRS UMR8531, ENS Cachan, UniverSud
61 Avenue du Président Wilson, 94235 Cachan, France
Fax: +33-1-47402454
E-mail: audebert@ppsm.ens-cachan.fr
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101584.
Figure 2. Design of dyads.
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Design of New Tetrazine–Triphenylamine Bichromophores
linked by an oxygen atom to a chloro- or alkoxytetrazine,
which represents the electron-poor fluorescent moiety (Fig-
ure 2).
We have investigated the photophysical and electrochemi-
cal properties and carried out theoretical quantum calcula-
tions of the newly synthesized chromophores 7–9. We have
also investigated the photophysical behaviour (absorption
and emission) of the cation radical of these dyads.
Results and Discussion
Synthesis
The designs of the triphenylamine precursors were ra-
tionalized in order to realize nucleophilic aromatic mono-
or disubstitution of chloro-s-tetrazines. Knowing that 3,6-
dichlorotetrazine 3 can undergo mono- or disubstitution
with phenol compounds, we decided to synthesize (di-
arylamino)phenols. Triphenylamines are known to form
stable cation radicals and to polymerize through the para
position. For future applications, it was thus necessary to
prepare triphenylamine compounds that bear blocking
groups, such as bromo or methyl groups, in the para posi-
tions. Compounds 1a, 1b and 1c were targeted (Figure 3).
Scheme 1. Synthetic route to 6a–6c.
The bichromophoric derivatives were synthesized by an
SNAr reaction with tetrazines 3 or 4. Benefiting from the
work of Hiskey and Chavez,[10] multigram syntheses of 3,6-
dichlorotetrazine (3) and 1-chloro-6-methoxytetrazine (4)
have been optimized by our group.[1a] The nucleophilic aro-
matic monosubstitution of 3 or 4 has been studied in the
presence of 1 equiv. of collidine with a variety of nucleo-
philes, in particular, with alcohols[1d,11] and phenols:[1d,2,12]
mono- and disubstitution of 3 can occur. Disubstitution is
usually more difficult than monosubstitution, and it was
necessary to strengthen the conditions by heating or by
using a sealed tube. The introduction of 1 equiv. of 1a, 1b
and 1c to 3 was realized at room temperature to afford 7a,
7b and 7c, respectively, in good yields (59–100%,
Scheme 2).
Figure 3. Design of (diarylamino)phenols.
Precursors 6a, 6b and 6c were successfully prepared by
The disubstitution of 3 or the monosubstitution of 4 ap-
Hartwig–Buchwald coupling[8] on anisidine with an excess peared to be more difficult; as predicted, heating at 160 °C
of the corresponding bromo derivatives 2a, 2b or 2c in a sealed tube for 1 week gave 9a, 9b, 8a, 8b and 8c with
(Scheme 1). It should be noted that in the case of 6a, the varying yields (16–64%, Scheme 3). In the case of 9a, after
triphenylamine core was synthesized in good yield in one 1 week, 4 and 1b were still present in the mixture as judged
step, whereas with the bromo and hydrogen substituents, by TLC. Purification was first carried out by chromatog-
the preparation of the intermediate diphenylamines 5b and raphy, which gave fractions of a mixture of 4 and 9a. These
5c were required followed by a second coupling step to ob- were purified by the sublimation of 4 under reduced pres-
tain 6b and 6c, respectively, in reasonable yields. The tar- sure, which left pure 9a in a yield of 16%. For 9b, the con-
geted nucleophiles 1a, 1b and 1c were obtained in excellent version of 1b was very poor; degradation of the mixture led
yield by using the standard deprotection of methoxyphenyl us to stop the reaction before total conversion of 1b had
[9]
group with BBr3 (Scheme 2).
been reached, which explains the yield of 31%.
Scheme 2. Synthetic route to 7a–c.
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Scheme 3. Synthetic routes to 8 and 9.
Hence, the syntheses of new bichromophoric compounds Table 1. Electrochemical data for 7–9. Potentials [V] are referenced
to Ag+/Ag. The reference electrode was checked vs. ferrocene. All
measurements in dichloromethane + Bu4NPF6 on C.
based on tetrazine and triphenylamine moieties were suc-
cessfully realized in few steps by using the key SNAr step
with 3 and 4.
[a]
[b]
E°Tz
E°TPA
7a
8a
9a
7b
8b
9b
7c
8c
–0.83
–1.12
–1.08
–0.77
–0.94
–1.01
–0.98
–1.05
0.48
0.48
0.51
0.72
0.75
0.70
Electrochemistry
The redox properties of 7–9 were investigated by cyclic
voltammetry (CV), and the electrochemical data are sum-
marized in Table 1. Two well-defined redox systems were
identified, which correspond to the oxidation of the tri-
phenylamine moiety into its cation radical and to the re-
duction of the tetrazine moiety into its anion radical. These
[c]
[c]
0.67
0.55
[a] Tz = tetrazine. [b] TPA = triphenylamine. [c] Estimated value
for the first cycle.
peaks are fully reversible although the peak-to-peak separa- potential than triphenylamine that bears a methyl group by
tion is larger than 60 mV due to electron-transfer kinetics, approximately 0.2 V. This is close to the difference between
which have been previously discussed for tetrazine.[11] One tris(4-bromophenyl)amine and tris(4-tolyl)amine.[14]
exception is the case of H-substituted 7c and 8c where poly-
merization occurred upon oxidation, which was expected that it is directly linked to. A chlorine atom as the electron-
because the para positions of triphenylamine were free.[13]
withdrawing group (7a and 7b) stabilizes the anion radical
The standard potential of tetrazine depends on the atom
The data reported in Table 1 show that the standard po- better than an oxygen linker (8a, 8b, 9a and 9b), which
tential of the triphenylamine moiety seems to be insensitive makes the reduction easier as in the parent chloro(meth-
to the other substituent of tetrazine but depends on the oxy)- and dimethoxytetrazine derivatives.[1d] The tetrazine
nature of substituent in the para position. The electron- potential is insensitive to the number of triphenylamine
withdrawing bromine atom (7b, 8b and 9b) increases the moieties linked to the tetrazine. This means that there is no
potential of the oxidation, because it destabilizes the cation real conjugation between triphenylamine and tetrazine in
radical in comparison to the methyl group (7a, 8a and 9a). the different bichromophoric compounds. In the case of 9a
Therefore, the formation of the cation radicals of 7b, 8b and and 8b, the results are in agreement with the expected 1:1
9b is more difficult and requires the application of a higher and 2:1 exchange ratios, respectively (Figure 4).
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Design of New Tetrazine–Triphenylamine Bichromophores
Figure 4. CVs of 8b and 9a in dichloromethane + 0.1 m Bu4NPF6
Figure 5. Molar absorption coefficients of 8a, 9a and 9b in dichlo-
romethane. Inset: molar absorption coefficients of 8a, 9a and 9b in
the 400–700 nm region.
on C. Potentials referenced to Ag+/Ag. Scan rate: 100 mVs–1.
In conclusion, the two redox moieties are electroactive
and behave independently in the dyads.
Table 2. Photophysical properties for 6–9 in dichloromethane: ab-
sorption wavelength [λmax, nm], molar absorption coefficient [ε,
Lmol–1 cm–1], emission wavelength [λem, nm], fluorescence quan-
tum yield [φF].
Photophysical Properties
λmax
ε
λmax
ε
λmax
ε
λem
φF
6a
6b
7a
8a
9a
7b
8b
9b
301 25000
304 26000
299 28000
301 52000 476 686 536 690
301 28000
309 32000
–
–
–
–
–
–
–
–
–
–
382
389
0.04[a]
The absorption spectra of some of these newly synthe-
sized compounds are displayed in Figure 5, and the absorp-
tion data are collected in Table 2. The absorption properties
of the dyads are similar to the sum of the disconnected
parts. These bichromophores display two or three bands de-
pending on the substitution of the tetrazine moiety. For all
of the compounds, there is an intense band in the UV re-
gion in agreement with π–π* transitions located on the
tetrazine and triphenylamine units. The corresponding mo-
lar absorption coefficient is ca. 30000 Lmol–1 cm–1 for com-
pounds with one triphenylamine unit, 25000 Lmol–1 cm–1
for 6a and ca. 5000 Lmol–1 cm–1 for the tetrazine deriva-
tives.[1e] For 8a and 8b, the molar absorption coefficient is
nearly twice that of 7a and 7b, respectively, because of the
presence of two triphenylamine units. The second band is
located at ca. 530 nm and displays a weak molar absorption
coefficient (ca. 600 Lmol–1 cm–1) because of a forbidden n–
π* transition centred on the tetrazine unit. This transition
is also very weakly sensitive to the substituent effects on the
triphenylamine moiety.[1a,1d] The third band appears only
for the homodisubstituted tetrazines (8a and 8b) and is lo-
cated at ca. 460 nm. Its molar absorption coefficient is also
very low (ca. 600 Lmol–1 cm–1), because there is a very
weak orbital overlap in this transition (see theoretical calcu-
lations section).
0.001[a]
523 580
550 0.0006[b]
–
–
–
–
–
–
533 650
524 540
551 0.0003[b]
559
–
0.001[b]
–
309 67000 455 450 536 600
308 27000
–
–
532 630 n.d.[c]
n.d.[c]
[a] Fluorescence quantum yield measured with coumarin 153 in
ethanol as a standard (φF = 0.53).[15] [b] Fluorescence quantum
yield measured with quinine sulfate in H2SO4 (0.5 n) as a standard
(φF = 0.546).[16] [c] Not determined.
Even if the triphenylamine and tetrazine units are fluo-
rescent when they are disconnected, our bichromophoric
compounds are not fluorescent in their neutral state as ex-
pected. In fact, fluorescence quenching occurs because of
the proximity of the two moieties through a photoinduced
electron transfer from the triphenylamine unit to the tetra-
zine unit, as it was reported for a solution of disconnected
parts.[1d] For all of the bichromophoric compounds, the
fluorescence quantum yields are lower than 10–3. An esti-
mation for 7a, 9a and 7b is provided in Table 2. For exam-
ple, the fluorescence quantum yield of 7a is 0.0006 even if
it is 0.04 for 6a, and 0.38[1a] for 4.
By comparing the substitution with a bromine atom or
a methyl group, one can observe that there is no influence
on the n–π* transition, but there is a weak bathochromic
Fluorescent Switching
In their neutral state, there is no fluorescence of the
shift (ca. 8 nm) for the π–π* transitions in the UV region, bichromophoric compounds. The fluorescence of both tri-
and a hypsochromic shift can be observed for the third phenylamine[17] and tetrazine[1] are cancelled out by an elec-
band. An explanation for this shift is given in the theoreti- tron transfer from triphenylamine to tetrazine. When tri-
cal calculations section.
phenylamine is oxidized, the electron transfer should not
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Figure 6. (a) Absorption spectra recorded upon oxidation of 7a by Cu(ClO4)2 in CH3CN as a function of R = [CuII]/[7a]. Bichromophore
concentration: 7ϫ10–5 molL–1. (b) Correlation of the absorbance at 675 nm with the amount of Cu(ClO4)2.
occur, and thus the fluorescence of tetrazine should be re- and at least 2.5 equiv. for 7b for a concentration of ca.
stored (Figure 1). To confirm this assumption, tri- 7ϫ10–5 molL–1 (Figures S2b, S3b and S4b). This is in line
phenylamine was chemically oxidized to its cation radical.
with the one-electron reduction of Cu(ClO4)2 and the
The generation of the triphenylaminium cation can be number of triphenylamine units to oxidize (the two units
achieved either by electrochemical or chemical oxidation. are oxidized at the same potential in the homodisubstituted
Although electrochemical anodic oxidation provides clean chromophores). By comparing the number of equivalents
oxidation, it is difficult to complete and to study the tran- for 7a and 7b, one can see that the ratio is close to two,
sient species. Therefore, a one-electron chemical oxidation because it is more difficult to oxidize 7b than 7a, which is
was chosen, and Cu(ClO4)2 was used as a mild and clean in agreement with a potential difference of around zero for
oxidant, which has been recently reported to effectively gen- 7b and 0.22 V for 7a.
erate arylaminium cation radicals.[18] Another advantage of
The fluorescence spectra were recorded upon oxidation
using Cu(ClO4)2 is that it gives no absorption or emission in in the same [CuII]/[dyad] ratios as those used for the spec-
the UV/Vis region at low concentrations, and its reduction trophotometric titrations but lower concentrations (ca.
potential in acetonitrile is 0.7 V vs. Fc/Fc+, which matches 7ϫ10–6 molL–1) in order to avoid reabsorption artefacts.
the arylamines well.[18] It was therefore possible to oxidize
Figure 7 displays the spectral evolution upon oxidation
the bichromophoric compounds. The cation radicals of the by excitation at the isosbestic point (329 nm) for 7a. One
bichromophoric compounds and 6a were thus generated by can observe a linear enhancement of fluorescence upon oxi-
using Cu(ClO4)2 in acetonitrile and characterized by ab- dation by Cu(ClO4)2, which is in accord with the formation
sorption and emission spectroscopy.
Upon titration with Cu(ClO4)2, one can observe the ap-
pearance of isosbestic points in the UV/Vis absorption
measurements: one at ca. 260 nm and another at 329, 328,
326 and 333 nm, respectively, for 7a, 8a, 9a and 7b, which
is in agreement with an equilibrium between the dyad and
the oxidized triphenylamine chromophore. Two bands grad-
ually appear at ca. 350 and 680 nm and a new shoulder
emerges at 575 nm, whereas the absorption band centred at
300 nm (π–π* transition located on triphenylamine) de-
creases (Figure 6a; see Figures S2a, S3a and S4a, Support-
ing Information). When oxidation is complete, one can see
the π–π* transition located on tetrazine at the same wave-
length. The new absorption bands are attributed to the for-
mation of the cation radical centred on the triphenylamine
core by comparison with the absorption spectrum of the
radical cation of 6a (Figure S5a).
The correlation of the absorbance for the lower energy
band with the amount of Cu(ClO4)2 revealed that all of the
Figure 7. Emission spectra recorded upon oxidation of 7a by
Cu(ClO4)2 in CH3CN as a function of R = [CuII]/[7a]. Bichromo-
compound is oxidized when 1.25 equiv. of Cu(ClO4)2 was
added for 7a (Figure 6b), 2 equiv. for 8a, 1.7 equiv. for 9a phore concentration: 7.4ϫ10–6 molL–1. λexc = 329 nm.
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Design of New Tetrazine–Triphenylamine Bichromophores
of the cation radical. In order to prove the origin of this of the tetrazine is found at lower energy. Conversely, the
band, the cation radical of 6a was studied by emission spec- lowest unoccupied molecular orbital (LUMO) is a π* or-
troscopy. No fluorescence in this region was observed for bital centred on the tetrazine ring.
this cation radical (Figure S5b). The appearance of an emis-
All compounds show one absorption band at ca. 300 nm
sion band at ca. 560 nm is typical of the tetrazine moiety.[1a] (for H- or CH3-substituted triphenylamine) or 310 nm (for
By oxidation of the triphenylamine unit, the photoin- Br-substituted triphenylamine). This absorption band is
duced electron transfer from triphenylamine to tetrazine due to two types of transition: one from the HOMO to the
was cancelled out, and fluorescence of the tetrazine was re- π* orbital (L+1) centred on the tetrazine and the phenyl
stored as expected. The fluorescence is multiplied by 17, 7 ring and the second from the HOMO to the π* orbital
and 4 for 7a, 9a and 7b, respectively, but the fluorescence (L+3) centred on the diphenylamine (Figure 9). The impor-
quantum yields of the cation radical remain low (Table 3). tant overlap between the orbitals of the latter transition ex-
These values are unfortunately still far from the value for 4 plains the intense absorption. A weak transition is found
(0.38).[1a] This can be explained by a possible energy trans- at ca. 524 nm [for alkoxy(chloro)tetrazines] or 535 nm (for
fer in the cation radical because of an overlap of its ab- tetrazines linked to two oxygen atoms), which is localized
sorbance and its emission (Figures 6 and 7).
on the tetrazine ring (n–π*) and the difference of symmetry
of the H-4 orbitals and the LUMO explains the weak oscil-
lator strength found experimentally (Table 4). Calculations
show also a weak bathochromic shift when a chlorine atom
replaces the oxygen atom. Indeed, chlorine stabilizes full n
orbitals better than empty π* orbitals. Finally, for these
bands, calculations fit well with experimental data both for
wavelengths and molar absorbance coefficients (Table 4).
Table 3. Fluorescence quantum yields for 7a, 9a and 7b with R =
[CuII]/[dyad].[a]
R = 0.5
R = 1
R = 1.5
R = excess
7a
9a
7b
0.0018
–
–
0.0045
–
–
0.0076
–
–
0.01
0.0065
0.0013
[a] Measurements in acetonitrile. Fluorescence quantum yield mea-
sured with coumarin 153 in ethanol as a standard (ΦF = 0.53).[15]
Thus, new bichromophoric compounds based on tri-
phenylamine and tetrazine were designed and synthesized
that have two states: a neutral state, in which the bichromo-
phore is not fluorescent, whereas the cation radical is fluo-
rescent. A fluorescent switch by oxidation was obtained.
Theoretical Calculations
Figure 9. Representation of the main molecular orbitals involved
in the electronic transitions of 9a.
Quantum chemical calculations were carried out on 7a,
8a, 9a and 7b. Geometry optimizations were first performed
at the B3LYP level of theory and with the 3-21g basis set.
Time-dependant (TD)DFT calculations at the PBE0 level
of theory with the 6-31+g(d) basis set were subsequently
performed.
In each case, the two aromatic cycles (tetrazine and
phenyl rings) bound by the oxygen atom are in the same
plane, whereas the two other phenyl rings of triphenylamine
make a small angle with this plane (Figure 8).
Table 4. Experimental and calculated absorption wavelengths [λ,
nm] and molar absorption coefficients [ε, Lmol–1 cm–1] for 7a, 8a,
9a and 7b in vacuo [TD-DFT, PBE0, 6-31+ g(d)].
λ1exp λ1calc
ε1exp
ε1calc
λ2exp λ2calc ε2exp ε2calc
7a
7b
8a
9a
299
309
301
301
307 28000 31000 523
314 32000 30000 524
350 52000 65000 536
336 28000 38000 533
533
533
540
538
580
540
690
650
400
400
500
300
Symmetrical 8a and 8b also exhibit a weak band at 455
and 475 nm, respectively, which does not exist for the un-
symmetrical compounds. This absorption band is not seen
by calculations performed in vacuo for 8a. Therefore, calcu-
lations in dichloromethane have been performed by using
the integral-equation formalism polarizable continuum
model. Thus, 8a displays a band at 422 nm due to a transi-
tion from a π orbital centred on the triphenylamine
(H-2, see Figure S8) to the LUMO (π* orbital centred on
the tetrazine). This is an intramolecular charge-transfer
Figure 8. Calculated geometries of 7a, 8a, 9a and 7b.
The molecular orbitals are localized on each chromo- band.
phore. The highest occupied molecular orbital (HOMO) is
Experimentally, the cation radical of 9a shows two im-
always a π orbital centred on the triphenylamine, which re- portant bands at 362 and 683 nm, a shoulder at 580 nm and
flects its electron-donating ability. The nonbonding orbital a weak band at 292 nm. Calculations have been performed
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on the cation radical of 9a, and Figure 10 shows the charge thochromic shift of the cation radical absorption is in pro-
localization on this cation radical. One can observe that the gress.
unpaired electron is localized on the triphenylamine core as
A fluorescent switch by oxidation was designed, which
expected. The band at 730 nm is due to a transition from features a neutral state without fluorescence and a stable
the π orbital centred on the tetrazine (S-2) to the SOMO cation radical state with restored fluorescence. We are cur-
(Figure 11). The shoulder has been modelled by two transi- rently trying to achieve a third state with these dyads with
tions: one from a π orbital centred on the diphenylamine restored fluorescence of the triphenylamine moiety by re-
part (S-3) to the SOMO at 620 nm and the second from a ducing the tetrazine ring. Fluorescence modulation by elec-
π orbital centred on the phenyl (S-6) to SOMO at 571 nm. trochemistry[1a,3d,19] could be also performed by coupling
The n–π* transition on the tetrazine ring is found at to epifluorescence microscopy, which is currently under de-
538 nm. The band at 362 nm is also due to two transitions: velopment in our laboratory.
one from the SOMO to a π* orbital centred on the diphen-
ylamine unit (S+4) at 340 nm and the second from the
HOMO to a π* orbital centred on the phenyl ring (S+2) at
338 nm.
Experimental Section
Spectroscopic Measurements: UV/Vis absorption spectra were re-
corded with a Uvikon 942 spectrophotometer in 1 cm optical
length quartz cuvettes. Corrected emission spectra were obtained
with a Jobin–Yvon Horiba Spex FluoroMax-3 spectrofluorometer.
Dichloromethane and acetonitrile (Aldrich, spectrometric grade or
SDS, spectrometric grade) were employed as solvents for absorp-
tion and fluorescence measurements. The fluorescence quantum
yields were determined by using coumarin 153 in ethanol as a stan-
dard (ΦF = 0.53)[13] or quinine sulfate in H2SO4 (0.5 n) as a stan-
dard (ΦF = 0.546).[14] The estimated experimental error is less than
10%. For the emission measurements, a right-angle configuration
was used, the absorbance at the excitation wavelength was kept
below 0.1 and the concentration below 8ϫ10–6 molL–1 for the un-
symmetrical compounds in order to avoid reabsorption artefacts.
Figure 10. Spin density on the cation radical of 9a.
Electrochemistry: Solvents (SDS, HPLC grade) and electrolyte salts
(Bu4NPF6 from Fluka, puriss.) were used without further purifica-
tion. CV was performed in a three-electrode cell with a potentiostat
(CH Instruments 600) driven by a PC. A carbon electrode (1 mm
diameter) was used as the working electrode, and platinum wire
and Ag+ (0.01 m in acetonitrile)/Ag were used as the counter and
reference electrodes, respectively. All the investigated solutions were
deaerated by bubbling with argon for at least 2 min before per-
forming the electrochemical measurements.
Figure 11. Representation of the main molecular orbitals involved
in the electronic transitions of the cation radical of 9a.
Quantum Chemical Calculations: Calculations were performed with
the Gaussian 03 software[20] at the MESO calculation centre of the
ENS Cachan (Nec TX7 with 32 processors of type Itanium 2).
Conclusions
Dyads based on tetrazine–triphenylamine units have
been synthesized, and their photophysical and electrochem-
ical properties have been investigated. The generation of tri-
phenylaminium cations was achieved by chemical oxidation
and their photophysical properties have also been investi-
gated. It appears that for unsymmetrical dyads (7 and 9),
the absorption properties are similar to the disconnected
parts, and for symmetrical dyads (8), another transition be-
tween a π orbital centred on triphenylamine and a π* or-
bital centred on tetrazine was observed, which is supported
by theoretical calculations. As expected, the bichromo-
phores exhibit very low fluorescence quantum yields in
their neutral state because of a photoinduced electron
transfer from the triphenylamine part to the tetrazine part.
By the formation of cation radicals, the emission of tetra-
zine was restored, although fluorescence quantum yields re-
main low because of a possible energy transfer. In order to
avoid this transfer and to enhance the fluorescence quan-
Synthesis: Reagents were commercially available from Aldrich and
used without further purification. Column chromatography was
performed with SDS 0.040–0.063 mm silica gel. All compounds
were characterized by the usual analytical methods: 1H and 13C
NMR spectra were recorded with a JEOL ECS (400 MHz) spec-
trometer. All chemical shifts are referenced to the solvent peak.
Melting points were measured with a Kofler melting point appara-
tus. IR spectra were recorded with a Nicolet Avatar 330 FTIR spec-
trometer. Mass spectra were recorded with a Bruker MicrOTOF –
QII instrument in direct introduction ASAP in APCI mode.
N,N-Ditolyl-4-anisidine (6a): To a solution of tris(dibenzylidene-
acetone)dipalladium(0) [Pd2(dba)3, 120 mg, 0.131 mmol) and 1,1Ј-
bis(diphenylphosphanyl)ferrocene (DPPF, 140 mg, 0.258 mmol) in
dry toluene (35 mL) under argon was added 4-bromotoluene
(4 mL, 32.5 mmol) at room temperature. The resulting mixture was
stirred for 10 min. Sodium tert-butoxide (2.070 g, 21.54 mmol) and
4-anisidine (0.99 g, 8.04 mmol) were added. The resulting mixture
was stirred at 110 °C for 19 h, cooled to room temperature and
concentrated under reduced pressure. The crude product was puri-
tum yield, the design of new bichromophores with a ba- fied by silica gel column chromatography [petroleum ether/CH2Cl2
1400 Eur. J. Org. Chem. 2012, 1394–1403
www.eurjoc.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Design of New Tetrazine–Triphenylamine Bichromophores
(8:2) to petroleum ether/CH2Cl2 (5:5)] to give 6a (2.048 g, 93%) as
a grey solid. M.p. 70 °C. H NMR (400 MHz, CDCl3): δ = 7.08–
16.56 mmol) at room temperature. The resulting mixture was
stirred for 10 min. Sodium tert-butoxide (1.379 g, 14.35 mmol) and
5c (1.100 g, 5.52 mmol) were added, and the mixture was stirred at
90 °C for 20 h. After this time, the starting materials had disap-
peared as judged by TLC. The reaction mixture was cooled to room
temperature, and water was added. It was extracted with CH2Cl2,
dried with anhydrous sodium sulfate, filtered and concentrated un-
der vacuum. The crude product was purified by silica gel column
chromatography [petroleum ether to petroleum ether/CH2Cl2 (1:1)]
1
7.05 (m, 4 H), 6.97 (d, J = 8.2 Hz, 2 H), 6.84 (d, J = 8.7 Hz, 2 H),
3.82 (s, 3 H), 2.33 (s, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 155.7, 146.0, 141.4, 131.3, 129.8, 126.5, 123.2, 114.7, 55.5,
20.8 ppm. IR: ν = 3024–2830, 1606, 1499, 1273, 812 cm–1.
˜
N-(4-Bromophenyl)-4-anisidine (5b): To a solution of Pd2(dba)3
(242 mg, 0.264 mmol) and DPPF (289 mg, 0.529 mmol) in dry tol-
uene (70 mL) under argon was added 1,4-dibromobenzene (15.31 g,
64.90 mmol) at room temperature. The resulting mixture was
stirred for 10 min. Sodium tert-butoxide (4.22 g, 43.90 mmol) and
4-anisidine (2.03 g, 16.5 mmol) were added, and the mixture was
stirred at 110 °C for 17 h. The reaction mixture was cooled to room
temperature, and water (100 mL) was added. The aqueous layer
was extracted with CH2Cl2 (3ϫ30 mL). The organic layer was
dried with anhydrous sodium sulfate, filtered and concentrated un-
der reduced pressure. The crude product was purified by silica gel
column chromatography [petroleum ether/CH2Cl2 (8:2) to CH2Cl2]
to give 5b (3.681 g, 81%) as a grey solid. M.p. 84 °C. 1H NMR
(400 MHz, CDCl3): δ = 7.29 (d, J = 8.7 Hz, 2 H), 7.06 (d, J =
1
to give 6c (1.069 g, 79%) as a white solid. M.p. 102 °C. H NMR
(400 MHz, CDCl3): δ = 7.19 (dd, J = 8.2, 7.3 Hz, 4 H), 7.08 (m, 6
H), 6.97 (t, J = 7.3 Hz, 2 H), 6.87 (d, J = 9.2 Hz, 2 H), 3.83 (s, 3
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 156.2, 148.3, 140.9,
129.1, 127.4, 123.0, 121.9, 114.9, 55.6 ppm. IR: ν = 3003–2835,
˜
1595, 1584, 1488, 1237, 728, 692 cm–1.
Procedure for the Deprotection of the Phenols: In a three-necked
round-bottomed flask was placed the protected phenol compound
(2.23 mmol) in anhydrous CH2Cl2 (30 mL). A solution of 1 m
boron tribromide (3 mL, 3.00 mmol) was added dropwise at
–78 °C, and the mixture was stirred at room temperature for 3 h.
8.7 Hz, 2 H), 6.89 (d, J = 8.7 Hz, 2 H), 6.76 (d, J = 8.7 Hz, 2 H), The mixture was poured onto ice and extracted with CH2Cl2
5.52 (s, 1 H), 3.82 (s, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ
(3ϫ30 mL). The organic layers were dried with anhydrous sodium
sulfate, filtered and concentrated under reduced pressure. The
crude product was purified by silica gel column chromatography.
= 155.7, 144.5, 135.1, 132.1, 122.8, 117.0, 114.8, 111.0, 55.6 ppm.
IR: ν = 3419, 3050–2850, 1594, 1508, 1491, 1243, 1030, 813 cm–1.
˜
N-Phenyl-4-anisidine (5c): To a solution of Pd2(dba)3 (137 mg,
0.150 mmol) and DPPF (130 mg, 0.238 mmol) in dry toluene
(40 mL) under argon was added 4-bromobenzene (2.5 mL,
23.74 mmol) at room temperature. The resulting mixture was
stirred for 10 min. Sodium tert-butoxide (2.564 g, 26.70 mmol) and
4-anisidine (1.233 g, 10.01 mmol) were added, and the mixture was
stirred at 90 °C for 22 h. After this time, the starting materials had
disappeared as judged by TLC. The reaction mixture was cooled
to room temperature, and water was added. It was extracted with
diethyl ether, dried with anhydrous sodium sulfate, filtered and con-
centrated under reduced pressure. The crude product was purified
by silica gel column chromatography [petroleum ether/CH2Cl2 (1:1)
to CH2Cl2] to give 5c (1.169 g, 42%) as a grey solid. M.p. 102 °C.
1H NMR (400 MHz, CDCl3): δ = 7.25–7.20 (m, 2 H), 7.10–7.06
(m, 2 H), 6.93–6.82 (m, 5 H), 5.55 (s, 1 H), 3.81 (s, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 155.2, 145.2, 135.8, 129.3, 122.1,
4-(Ditolylamino)phenol (1a): The crude product was purified by sil-
ica gel column chromatography [petroleum ether/ethyl acetate (4:1)]
to give 1a as a white solid (quantitative yield). M.p. 68 °C. 1H
NMR (400 MHz, CD3OD): δ = 7.00 (d, J = 7.8 Hz, 4 H), 6.88 (d,
J = 8.7 Hz, 2 H), 6.84 (d, J = 8.2 Hz, 4 H), 6.73 (d, J = 8.7 Hz, 2
H), 2.27 (s, 6 H) ppm. 13C NMR (100 MHz, CD3OD): δ = 154.7,
147.5, 141.5, 132.1, 130.5, 128.0, 123.8, 117.0, 20.7 ppm. IR: ν =
˜
3250, 3027, 1605, 1502, 1276, 1216, 813 cm–1. UV/Vis (CH2Cl2):
λmax (ε, Lcm–1 mol–1) = 300 (21400); ΦF = 0.013 in CH2Cl2.
4-[Bis(4-bromophenyl)amino]phenol (1b): The crude product was
purified by silica gel column chromatography [petroleum ether/
ethyl acetate (4:1)] to give 1b (714 mg, 87%) as a white solid. 1H
NMR (400 MHz, CDCl3): δ = 7.29 (d, J = 8.7 Hz, 4 H), 6.98 (d,
J = 8.7 Hz, 2 H), 6.90 (d, J = 8.7 Hz, 4 H), 6.84 (d, J = 8.7 Hz, 2
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 153.4, 146.8, 139.3,
132.1, 127.7, 124.2, 116.6, 114.4 ppm.
119.6, 115.7, 114.7, 55.6 ppm. IR: ν = 3386, 3008–2836, 1595, 1500,
˜
1489, 1249, 1032, 749, 694 cm–1.
4-(Diphenylamino)phenol (1c): The crude product was purified by
silica gel column chromatography [petroleum ether/CH2Cl2 (1:1) to
CH2Cl2/ethanol (85:15)] to give 1c (777 mg, 85%) as a grey solid.
M.p. 121 °C. 1H NMR (400 MHz, CDCl3): δ = 7.26–7.18 (m, 4 H),
7.11–6.89 (m, 8 H), 6.85–6.7 (m, 2 H), 5.07 (S, 1 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 152.0, 148.2, 141.0, 129.2, 127.6,
N,N-Bis(4-bromophenyl)-4-anisidine (6b): To
a
solution of
Pd2(dba)3 (282 mg, 0.308 mmol) and DPPF (230 mg, 0.421 mmol)
in dry toluene (10 mL) under argon was added 1,4-dibromobenzene
(5.17 mg, 21.92 mmol) at room temperature. The resulting mixture
was stirred for 10 min. Sodium tert-butoxide (1.53 g, 15.92 mmol)
and 5b (1.12 g, 5.25 mmol) were added, and the mixture was stirred
at 110 °C for 15 h. After this time, the starting materials had disap-
peared as judged by TLC. The reaction mixture was cooled to room
temperature and concentrated under reduced pressure. The crude
product was purified by silica gel column chromatography [petro-
leum ether/CH2Cl2 (8:2) to petroleum ether/CH2Cl2 (1:3)] to give
6b (1.740 g, quantitative yield) as a white solid. M.p. 75 °C. 1H
NMR (400 MHz, CDCl3): δ = 7.32 (d, J = 9.2 Hz, 4 H), 7.07 (d,
J = 9.2 Hz, 2 H), 6.93 (d, J = 8.7 Hz, 4 H), 6.88 (d, J = 8.7 Hz, 2
H), 3.82 (s, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 156.7,
123.0, 122.0, 116.4 ppm. IR: ν = 3300, 3050–2830, 1584, 1506,
˜
1488, 1281, 1229, 752, 694 cm–1.
Procedure for the SNAr Reaction with 3,6-Dichlorotetrazine: To a
solution of the phenol compound (1.14 mmol) in anhydrous
CH2Cl2 (25 mL) were added 3,6-dichlorotetrazine (1.14 mmol) and
2,4,6-collidine (1.14 mmol). The mixture was stirred at room tem-
perature for 1 h and concentrated under reduced pressure. The
crude product was purified by silica gel column chromatography.
3-Chloro-6-[4-(ditolylamino)phenoxy]-1,2,4,5-tetrazine (7a): The
crude product was purified by silica gel column chromatography
[petroleum ether/CH2Cl2 (1:1)] to give 7a (270 mg, 59%) as a pur-
ple solid. M.p. 170 °C. 1H NMR (400 MHz, CDCl3): δ = 7.10–7.07
(m, 8 H), 7.02 (d, J = 8.7 Hz, 4 H), 2.32 (s, 6 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 167.9, 165.2, 147.2, 145.6, 145.1, 133.2,
146.8, 139.7, 132.2, 127.4, 124.3, 115.1, 114.6, 55.5 ppm. IR: ν =
˜
3050–2830, 1578, 1504, 1482, 1237, 813 cm–1.
N,N-Diphenyl-4-anisidine (6c): To a solution of Pd2(dba)3 (253 mg,
0.276 mmol) and DPPF (202 mg, 0.370 mmol) in dry toluene
(40 mL) under argon was added 4-bromobenzene (1.7 mL,
130.2, 125.0, 123.1, 121.3, 21.0 ppm. IR: ν = 3050–2850, 1604,
˜
Eur. J. Org. Chem. 2012, 1394–1403
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1401

V. Alain-Rizzo, C. Dumas-Verdes, P. Audebert, et al.
FULL PAPER
1497, 1432, 1354, 1274, 1154, 819 cm–1. HRMS: calcd. for
1355, 1273, 1155, 819 cm–1. HRMS: calcd. for C42H36N6O2 [M]+
656.28942; found 656.2892.
C22H18N5O35Cl [M]+ 403.11944; found 403.1194.
3-{4-[Bis(4-bromophenyl)amino]phenoxy}-6-chloro-1,2,4,5-tetrazine 3,6-Bis{4-[bis(4-bromophenyl)amino]phenoxy}-1,2,4,5-tetrazine (8b):
(7b): The crude product was purified by silica gel column
The crude product was purified by silica gel column chromatog-
chromatography [petroleum ether/CH2Cl2 (7:3) to petroleum ether/
raphy [petroleum ether/CH2Cl2 (7:3) to CH2Cl2] to give 8b as a
1
CH2Cl2 (4:6)] to give 7b as a red solid (quantitative yield). M.p. pink solid (36%). M.p. 148 °C. H NMR (400 MHz, CDCl3): δ =
154 °C. 1H NMR (400 MHz, CDCl3): δ = 7.38 (d, J = 8.7 Hz, 4
H), 7.15–7.14 (m, 4 H), 6.97 (d, J = 8.7 Hz, 4 H) ppm. 13C NMR
7.37 (d, J = 8.7 Hz, 8 H), 7.17–7.10 (m, 8 H), 6.96 (d, J = 8.7 Hz,
8 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 167.5, 148.0, 146.3,
(100 MHz, CDCl3): δ = 167.7, 165.4, 147.1, 146.2, 145.8, 132.7, 145.4, 132.7, 125.8, 125.4, 122.1, 116.2 ppm. IR: ν = 2988, 1579,
˜
125.9, 125.2, 121.9, 116.3 ppm. IR: ν = 1578, 1502, 1484, 1358,
1501, 1483, 1398, 1267, 825 cm–1. HRMS: calcd. for
˜
1270, 823 cm–1. HRMS: calcd. for C20H12N5O35Cl79Br2 [M]+ C38H24N6O279Br4 [M]+ 911.86887; found 911.8684.
530.90916; found 530.9091.
3,6-Bis[4-(diphenylamino)phenoxy]-1,2,4,5-tetrazine (8c): The crude
3-Chloro-6-[4-(diphenylamino)phenoxy]-1,2,4,5-tetrazine (7c): The
crude product was purified by silica gel column chromatography
[petroleum ether to petroleum ether/CH2Cl2 (2:8)] to give 7c
(113 mg, 87%) as a red solid. M.p. 102 °C. 1H NMR (400 MHz,
CDCl3): δ = 7.28 (dd, J = 8.2, 7.3 Hz, 4 H), 7.16–7.11 (m, 8 H),
product was purified by silica gel column chromatography [petro-
leum ether/CH2Cl2 (1:1) to CH2Cl2/ethanol (95:5)] to give 8c
(174 mg, 26%) as a red powder. M.p. 236 °C. 1H NMR (400 MHz,
CDCl3): δ = 7.27 (dd, J = 8.7, 7.3 Hz, 8 H), 7.14–7.09 (m, 16 H),
7.03 (t, J = 7.3 Hz, 4 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
7.08–7.03 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 167.9, 167.5, 147.7, 147.3, 146.3, 129.5, 124.9, 124.5, 123.3, 121.7 ppm.
165.3, 147.6, 146.8, 146.4, 129.6, 124.7, 124.5, 123.5, 121.5 ppm.
IR: ν = 3050–2830, 1587, 1502, 1488, 1385, 1276, 1198, 755,
˜
IR: ν = 3050–2830, 1591, 1502, 1492, 1358, 1278, 1200, 843,
699 cm–1.
˜
813 cm–1.
Supporting Information (see footnote on the first page of this arti-
Procedure for the SNAr Reaction with 3-Chloro-6-methoxy-1,2,4,5-
tetrazine: To a solution of the phenol compound (1.17 mmol) in
anhydrous CH2Cl2 (25 mL) were added 3-chloro-6-methoxytetra-
zine (1.17 mmol) and 2,4,6-collidine (1.17 mmol). The mixture was
stirred at 150 °C in a sealed tube for 1 week and concentrated under
reduced pressure. The crude product was purified by silica gel col-
umn chromatography.
cle): CV data, photophysical data and theoretical data.
Acknowledgments
We thank the CNRS and the Ministry of French Research for
funding the project. We also thank Dr C. Allain for fruitfull dis-
cussions.
3-[4-(Ditolylamino)phenoxy]-3-methoxy-1,2,4,5-tetrazine (9a): The
crude product was purified by silica gel column chromatography
[petroleum ether/CH2Cl2 (3:7)] to give 9a (74 mg, 16%) as a red
solid. M.p. 190 °C. 1H NMR (400 MHz, CDCl3): δ = 7.10–7.05 (m,
8 H), 7.00 (d, J = 8.2 Hz, 4 H), 4.26 (s, 3 H), 2.31 (s, 6 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 167.3, 166.7, 146.8, 146.5, 145.2,
[1] a) G. Clavier, P. Audebert, Chem. Rev. 2010, 110, 3299–3314; b)
P. Audebert, S. Sadki, F. Miomandre, G. Clavier, Electrochem.
Commun. 2004, 6, 144–147; c) P. Audebert, S. Sadki, F. Miom-
andre, G. Clavier, M. C. Vernieres, M. Saoud, P. Hapiot, New
J. Chem. 2004, 28, 387–392; d) P. Audebert, F. Miomandre, G.
Clavier, M. C. Vernières, S. Badré, R. Méallet-Renault, Chem.
Eur. J. 2005, 11, 5667–5673; e) Y.-H. Gong, F. Miomandre, R.
Méallet-Renault, S. Badré, L. Galmiche, J. Tang, P. Audebert,
G. Clavier, Eur. J. Org. Chem. 2009, 35, 6121–6128.
132.8, 130.1, 124.7, 123.6, 121.5, 57.0, 20.9 ppm. IR: ν = 3050–
˜
2850, 1605, 1497, 1441, 1370, 1274, 1197, 818 cm–1. HRMS: calcd.
for C23H21N5O2 [M]+ 399.16898; found 399.1683.
3-{4-[Bis(4-bromophenyl)amino]phenoxy}-3-methoxy-1,2,4,5-tetra-
zine (9b): The crude product was purified by silica gel column
chromatography [petroleum ether/CH2Cl2 (7:3) to petroleum ether/
CH2Cl2 (1:1)] to give 9b as a red solid (31%). M.p. 140 °C. 1H
NMR (400 MHz, CDCl3): δ = 7.35 (d, J = 8.7 Hz, 4 H), 7.17–7.11
(m, 4 H), 6.97 (d, J = 9.2 Hz, 4 H), 4.27 (s, 3 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 167.1, 166.8, 148.2, 146.3, 145.1, 132.6,
[2] C. Dumas-Verdes, F. Miomandre, E. Lépicier, O. Galangau,
T. T. Vu, G. Clavier, R. Méallet-Renault, P. Audebert, Eur. J.
Org. Chem. 2010, 13, 2525–2535.
[3] a) Y. Kim, E. Kim, G. Clavier, P. Audebert, Chem. Commun.
2006, 34, 3612–3614; b) Y. Kim, J. Do, E. Kim, G. Clavier, L.
Galmiche, P. Audebert, J. Electroanal. Chem. 2009, 632, 201–
205; c) F. Miomandre, R. Méallet-Renault, J. J. Vachon, R.
Pansu, P. Audebert, Chem. Commun. 2008, 16, 1913–1915; d)
F. Miomandre, E. Lépicier, S. Munteanu, O. Galangau, J. F.
Audibert, R. Méallet-Renault, P. Audebert, R. B. Pansu, ACS
Appl. Mater. Interfaces 2011, 3, 690–696.
125.7, 125.5, 122.0, 116.0, 57.1 ppm. IR: ν = 3050–2850, 1576,
˜
1500, 1484, 1379, 1270, 1206, 823 cm–1. HRMS: calcd. for
C21H15N5O279Br2 [M]+ 526.9587; found 526.9588.
[4] a) A. C. Benniston, G. Copley, K. J. Elliott, R. W. Harrington,
W. Clegg, Eur. J. Org. Chem. 2008, 16, 2705–2713; b) R. Zhang,
Z. Wang, Y. Wu, H. Fu, J. Yao, Org. Lett. 2008, 10, 3065–3068.
[5] a) U. Resch-Genger, G. Hennrich in Topics in Fluorescence
Spectroscopy (Eds.: C. D. Geddes, J. R. Lakowicz), Springer
US, 2005, vol. 9, pp. 189–218; b) T. Komura, G. Y. Niu, T.
Yamaguchi, M. Asano, Electrochim. Acta 2003, 48, 631–639;
c) R. Bergonzi, L. Fabbrizzi, M. Licchelli, C. Mangano, Coord.
Chem. Rev. 1998, 170, 31–46; d) R. W. Wagner, J. S. Lindsey, J.
Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc. 1996,
118, 3996–3997; e) J. Otsuki, M. Tsujino, T. Iizaki, K. Araki,
M. Seno, K. Takatera, T. Watanabe, J. Am. Chem. Soc. 1997,
119, 7895–7896; f) G. Hennrich, H. Sonnenschein, U. Resch-
Genger, J. Am. Chem. Soc. 1999, 121, 5073–5074; g) R. Zhang,
Z. Wang, Y. Wu, H. Fu, J. Yao, Org. Lett. 2008, 10, 3065–3068;
h) L. Liu, G. Zhang, W. Tan, D. Zhang, D. Zhu, Chem. Phys.
Procedure for the SNAr Disubstitution Reaction with 3,6-Dichloro-
tetrazine: To a solution of the phenol compound (1.50 mmol) in
anhydrous CH2Cl2 (8 mL) were added 3,6-dichlorotetrazine
(0.75 mmol) and 2,4,6-collidine (1.50 mmol). The mixture was
stirred at 160 °C in a sealed tube for 1 week and concentrated under
reduced pressure. The crude product was purified by silica gel col-
umn chromatography.
3,6-Bis[4-(ditolylamino)phenoxy]-1,2,4,5-tetrazine (8a): The crude
product was purified by silica gel column chromatography [petro-
leum ether/CH2Cl2 (5:5)] to give 8a (303 mg, 64%) as a purple so-
1
lid. M.p. 170 °C. H NMR (400 MHz, CDCl3): δ = 7.15–7.05 (m,
16 H), 7.04 (d, J = 8.2 Hz, 8 H), 2.34 (s, 12 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 167.5, 146.6, 146.5, 145.2, 132.9, 130.1,
124.8, 123.6, 121.5, 20.9 ppm. IR: ν = 3000–2850, 1604, 1497, 1432,
˜
1402
www.eurjoc.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 1394–1403

Design of New Tetrazine–Triphenylamine Bichromophores
Lett. 2008, 465, 230–233; i) T. Suzuki, A. Migita, H. Higuchi,
H. Kawai, K. Fujiwara, T. Tsuji, Tetrahedron Lett. 2003, 44,
6837–6840.
[15]
M. Grabolle, M. Spieles, V. Lesnyak, N. Gaponik, A.
Eychmüller, U. Resch-Genger, Anal. Chem. 2009, 81, 6285–
6294.
[6] a) Y. Shirota, H. Kageyama, Chem. Rev. 2007, 107, 953; b)
C. C. Chi, C. L. Chiang, S. W. Liu, H. Yueh, C. T. Chen, C. T.
Chen, J. Mater. Chem. 2009, 19, 5561–5571; c) X. Liu, D. Xu,
R. Lu, B. Li, C. Qian, P. Xue, X. Zhang, H. Zhou, Chem. Eur.
J. 2011, 17, 1660–1669; d) Q. Li, L. Lu, C. Zhong, J. Huang,
Q. Huang, J. Shi, X. Jin, T. Peng, J. Qin, Z. Li, Chem. Eur. J.
2009, 15, 9664–9668; e) B. Wang, Y. Wang, J. Hua, Y. Jiang, J.
Huang, S. Qian, H. Tian, Chem. Eur. J. 2011, 17, 2647–2655.
[7] B. Lim, Y. C. Nah, J. T. Hwang, J. Ghim, D. Vak, J. M. Yun,
D. Y. Kim, J. Mater. Chem. 2009, 19, 2380–2385.
[8] S. Thayumanavan, S. Barlow, S. R. Marder, Chem. Mater.
1997, 9, 3231–3235.
[9] J. G. Linkletter, G. A. Pearson, R. I. Walter, J. Am. Chem. Soc.
1977, 99, 5269–5272.
[10] a) D. E. Chavez, M. A. Hiskey, J. Heterocycl. Chem. 1998, 35,
1329; b) D. E. Chavez, M. A. Hiskey, J. Energ. Mater. 1999,
17, 357; c) M. D. Coburn, G. A. Buntain, B. W. Harris, M. A.
Hiskey, K. Y. Lee, D. G. Ott, J. Heterocycl. Chem. 1991, 28,
2049.
[11] a) Y.-H. Gong, P. Audebert, J. Tang, F. Miomandre, G. Clavier,
S. Badré, R. Méallet-Renault, J. Marrot, J. Electroanal. Chem.
2006, 592, 147–152; b) Y.-H. Gong, P. Audebert, G. Clavier, F.
Miomandre, J. Tang, S. Badré, R. Méallet-Renault, E. Naidus,
New J. Chem. 2008, 32, 1235–1242.
[12] Q. Zhou, P. Audebert, G. Clavier, R. Méallet-Renault, F. Mi-
omandre, Z. Shaukat, T. T. Vu and J. Tang, J. Phys. Chem. C
2011, 115, 21899–21906.
[13] a) C. Lambert, G. Nöll, Synth. Met. 2003, 139, 57–62; b) A.
Petr, C. Kvarnström, L. Dunsch, A. Ivaska, Synth. Met. 2000,
108, 245–247; c) A.-D. Bendrea, L. Vacareanu, M. Grigoras,
Polym. Int. 2009, 59, 624–629; d) H.-Y. Lin, G.-S. Liou, J. Po-
lym. Sci. Polym. Chem. Ed. 2009, 47, 285–294; e) C. Zhan, Z.
Cheng, J. Zheng, W. Zhang, Y. Xi, J. Qin, J. Appl. Polym. Sci.
2002, 85, 2718–2724.
[16]
[17]
J. N. Demas, G. A. Crosby, J. Phys. Chem. 1971, 75, 991.
a) E. Ishow, A. Brosseau, G. Clavier, K. Nakatani, P. Tauc,
C. l. Fiorini-Debuisschert, S. Neveu, O. Sandre, A. Léaustic,
Chem. Mater. 2008, 20, 6597–6599; b) H. G. Zhang, X. T. Tao,
K. S. Chen, C. X. Yuan, S. N. Yan, M. H. Jiang, Chin. Chem.
Lett. 2011, 22, 647–650; c) L. Yang, F. Gao, J. Liu, X. Zhong,
H. Li, S. Zhang, J. Fluores. 2010, 21, 545–554; d) B. Li, Q. Li,
B. Liu, Y. Yue, M. Yu, Dyes Pigm. 2011, 88, 301–306.
[18] C.-C. Chang, H. Yueh, C.-T. Chen, Org. Lett. 2011, 13, 2702–
2705.
[19] a) M. Voicescu, D. Rother, F. Bardischewsky, C. G. Friedrich,
P. Hellwig, Biochemistry 2011, 50, 17–24; b) J. Daub, M. Beck,
A. Knorr, H. Spreitzer, Pure Appl. Chem. 1996, 68, 1399–1404.
[20] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T.
Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pom-
elli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D.
Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J.
Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Revision C.02,
Gaussian, Inc., Wallingford, CT, 2004.
Received: October 21, 2011
Published Online: January 9, 2012
[14] K. Idzik, J. Soloducho, M. Lapkowski, S. Golba, Electrochim.
Acta 2008, 53, 5665–5669.
Eur. J. Org. Chem. 2012, 1394–1403
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