Electrochromic and electrofluorochromic properties of a new boron dipyrromethene-ferrocene conjugate

Article abstract of DOI:10.1016/j.electacta.2012.09.048

A new boron dipyrromethene-ferrocene (BODIPY-Fc) conjugate with pentafluorophenyl as the meso substituent and two Fc termini was synthesized and its spectroscopic and electrochemical features were analyzed. An intramolecular charge transfer from the donor Fc to the acceptor BODIPY has been predicted by theory and confirmed experimentally, leading to efficient fluorescence quenching when the dyad is in the neutral state. Fluorescence can be triggered by oxidizing both ferrocenyl units either chemically or electrochemically. Eventually, a fully reversible fluorescence switch is evidenced by coupling TIRF microscopy with electrolysis in an electrochemical cell.

Full text of DOI:10.1016/j.electacta.2012.09.048

Electrochimica Acta 87 (2013) 809–815
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrochromic and electrofluorochromic properties of a new boron
dipyrromethene–ferrocene conjugate
O. Galangaua, I. Fabre-Franckea, S. Munteanua, C. Dumas-Verdesa, G. Claviera, R. Méallet-Renaulta,
R.B. Pansua, F. Hartlb, F. Miomandrea,∗
a P.P.S.M., CNRS UMR 8531, Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan Cedex, France
b Department of Chemistry, University of Reading, Reading RG6 6AD, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
A new boron dipyrromethene–ferrocene (BODIPY–Fc) conjugate with pentafluorophenyl as the meso
substituent and two Fc termini was synthesized and its spectroscopic and electrochemical features were
analyzed. An intramolecular charge transfer from the donor Fc to the acceptor BODIPY has been predicted
by theory and confirmed experimentally, leading to efficient fluorescence quenching when the dyad is
in the neutral state. Fluorescence can be triggered by oxidizing both ferrocenyl units either chemically
or electrochemically. Eventually, a fully reversible fluorescence switch is evidenced by coupling TIRF
microscopy with electrolysis in an electrochemical cell.
Received 25 July 2012
Received in revised form
12 September 2012
Accepted 15 September 2012
Available online xxx
Keywords:
Boron dipyrromethene
Ferrocene
© 2012 Elsevier Ltd. All rights reserved.
Electrochromic
Fluorescence
Redox switch
1. Introduction
which has been demonstrated by chemical oxidation of other
BODIPY–Fc conjugates [14,15]. In this communication, a new
The design of redox active fluorophores represents a very
promising research field that has attracted much interest for a
couple of years [1–6]. Practical applications in sensors of redox
active compounds or in electrically driven light emitting devices
can be envisaged. Among the various examples of such compounds
described in the literature, ferrocene (Fc) derivatives constitute the
most popular family of redox-active moieties associated to fluo-
rophores due to their redox stability and versatility of chemical
functionalization [7–9]. Besides, boron dipyrromethene (BOD-
IPY) is also one of the most encountered organic fluorophores
because of its very convenient spectroscopic properties, namely
strong UV–visible absorption, quite narrow fluorescence bands
and corresponding high fluorescence quantum yields (˚f > 0.7)
[10–13]. Nevertheless, only a few examples of BODIPY–ferrocene
dyads have been reported so far [14–17], despite their poten-
tially interesting properties. Indeed, they are likely to display
a low-lying intramolecular charge transfer (ICT) in the neutral
form, as well as photoinduced electron transfer (PET) resulting
in quenching of BODIPY-based fluorescence. These phenomena
are likely to be canceled upon changing the redox state of Fc,
BODIPY–Fc compound with enhanced charge transfer between a
donor mesityl styryl branch and an acceptor pentafluorophenyl
meso substituent was synthesized and its electrochemical and
spectroscopic properties were analyzed in comparison with a
model compound having the ferrocenyl termini replaced by mesityl
groups (see Chart 1). Compared to previously published similar
compounds, the difference arises from the meso substituent that
is likely to enhance the attracting power of the BODIPY core in
the final donor–acceptor–donor dyad. We will demonstrate that
this compound represents an electrochemically controlled switch
of fluorescence monitored by coupling TIRF microscopy and elec-
trochemistry; this combination is known to be an efficient tool to
highlight electrofluorochromism phenomena [18].
2. Experimental
2.1. Materials and synthesis
All reagents were purchased from Sigma–Aldrich and used as
received. CH2Cl2 and petroleum ether were purchased from SDS
and used as received. Toluene was distilled under N2 prior to use
from sodium/benzophenone.
∗
Column chromatography was carried out under positive pres-
sure, using 40–63 ␮m silica gel (SDS) and the indicated solvents.
Corresponding author. Tel.: +33 1 47 40 53 39; fax: +33 1 47 40 24 54.
E-mail address: mioman@ppsm.ens-cachan.fr (F. Miomandre).
0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.electacta.2012.09.048

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O. Galangau et al. / Electrochimica Acta 87 (2013) 809–815
Chart 1. The BODIPY–ferrocenyl (Fc) conjugate (2) and the reference compound BODIPY–mesityl (1).
Solvent evaporation was conducted under reduced pressure at
temperatures lower than 45 ◦C. Further drying of the residue was
accomplished under high vacuum.
were used as working electrodes, while a platinum wire and
Ag+ (10−2 M in acetonitrile)/Ag were used as counter and refer-
ence electrodes, respectively. All the investigated solutions were
deaerated by argon bubbling for at least 5 min before performing
electrochemical measurements.
Electronic absorption spectra were recorded on a Cary 500
(Varian) spectrophotometer in 1 cm quartz cuvettes. Fluorescence
spectra were recorded on a Fluorolog3 (Horiba) spectrofluorimeter,
in a quartz cell at the right angle beam geometry. The solutions had
OD below 0.1 at the excitation wavelength.
UV–Vis spectroelectrochemistry at variable temperature was
performed in an optically transparent thin layer electrochemical
(OTTLE) cell [21] equipped with Pt minigrid working and auxiliary
electrodes and a silver wire as a pseudoreference electrode. The
BODIPY–Fc (1) solutions in dichloromethane freshly distilled from
CaH2 contained pre-dried 3 × 10−1 M Bu4NPF6 (Aldrich) as the sup-
porting electrolyte. The electrode potential during electrolyses was
controlled by a PA4 potentiostat (Laboratory Devices, Polná, Czech
Republic). The UV–Vis spectra were recorded on a SCINCO S-3100
photodiode array spectrophotometer.
NMR spectra were recorded on a JEOL ECS 400 MHz spec-
trometer. FTIR analyses were carried out on a Nicolet Avatar 330
FTIR. Melting point was obtained without correction with a STU-
ART SMP 10 apparatus. Liquid secondary ion high-resolution mass
spectrometry data (HRMS) were obtained from the CRMPO mass
spectrometry laboratory at the University of Rennes (France).
The synthesis of BODIPY–mesityl (1) has already been pub-
lished by our group [19]. BODIPY–Fc (2) was synthesized according
to the following procedure. Piperidine (50 ␮L) was added to
a solution of 8-pentafluorophenyl 1,7-dimethyl-2,6-diethyl-4,4-
difluoro-4-bora-3a,4a-diaza-s-indacene (209 mg, 0.44 mmol) in
toluene (30 mL), under an argon atmosphere, followed by fer-
rocenecarboxaldehyde (213 mg, 0.99 mmol) in toluene (10 mL). The
resulting mixture was refluxed for 30 h. The solvent was removed
under vacuum and the residue was purified by silica gel col-
umn chromatography, using CH2Cl2:petroleum ether 2:8 (v/v) as
the eluent. The blue fraction was collected to afford a dark blue
solid (199 mg, yield 52%). M.p.: 160–165 ◦C. IR: 1606 (ꢀC C), 1497
(ꢀC N) cm−1 1H NMR (CDCl3, 400 MHz) ı 1.18 (t, J = 7.6 Hz, 6H), 1.53
.
2.4. TIRF microscopy coupled to electrochemistry measurements
(s, 6H), 2.60 (q, J = 7.4 Hz, 4H), 4.24 (s, 10H), 4.46 (s, 4H), 4.66 (s, 4H),
7.20 (d, J = 16.6 Hz, 2H), 7.31 (d, J = 16.5 Hz, 2H). 13C NMR (CDCl3,
100 MHz) ı 151.3, 137.8, 135.9, 134.7, 117.3, 83.2, 70.7, 69.9, 68.2,
18.4, 14.3, 10.8. 11B NMR (CDCl3, 133 MHz) ı 0.26 (t, J = 34.5 Hz, 1B).
19F NMR (CDCl3, 376 MHz) ı 159.9 (m, 2F), 151.2 (m, 1F), 138.7 (m,
4F). HRMS (electrospray): calculated for C45H38N2F7BFe2 862.1709,
found 862.1726.
The experimental setup used for these measurements has been
described in more detail in a recent paper [18]. Briefly, it is based on
the coupling of a three-electrode electrochemical cell with an epi-
fluorescence microscope under excitation with either 515-nm laser
pulses or white light and wavelength selection through filters. The
working electrode is a very thin (ca. 25 nm) Pt layer coated on a glass
microscope slide (170 ␮m thin) on which the cell is stuck. Counter
and pseudoreference electrodes are Pt and Ag wires, respectively.
The setup allows simultaneous recording of the faradaic current
and fluorescence intensity when applying a potential signal to the
working electrode. The fluorescence intensity is recorded through
a side port of the microscope and collected by a single photon pho-
tomultiplier or dispatched on a grating spectrometer for recording
emission spectra under electrochemical control.
2.2. DFT calculations
Quantum chemical calculations were performed with the
Gaussian 03 (Rev C.02) software [20]. Geometry optimizations
were done at the B3LYP/Lanl2dz level of theory without symmetry
constraint. In order to confirm the optimized structure is a true min-
imum, vibrational frequencies were calculated at the same level of
theory when the geometry optimization was successful.
3. Results and discussion
2.3. Electrochemistry and spectroscopy
3.1. Synthesis
Solvents (SDS, HPLC grade) and electrolyte salts (Fluka, puriss.)
were used without further purification. Cyclic voltammetry was
recorded in a three electrode cell with a potentiostat (CH Instru-
ments 600) driven by a PC. Platinum or gold disks (1 mm diameter)
BODIPY–Fc (2) was synthesized according to the same
procedure as reference BODIPY–mesityl (1), viz. through
a
Knoevenagel-type condensation of ferrocenecarboxaldehyde

O. Galangau et al. / Electrochimica Acta 87 (2013) 809–815
811
Fig. 1. Electronic absorption spectra of (1) (blue full line) and (2) (red full line) and emission spectrum of (1) (blue dashed line, excitation: 640 nm) in dichloromethane. (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
Table 1
Spectroscopic data for compounds (1) and (2) in dichloromethane.
em
max
Compound
ꢁambasx 1/nm
ꢁambasx 2/nm
ꢁambasx 3/nm
ꢁ
/nm
ε
␭1
(×103) M−1 cm−1
BODIPY–mesityl (1)
BODIPY–Fc (2)
–
739
643
590
364
342
688
–
54
30
with
8-pentafluorophenyl-2,6-diethyl-1,3,5,7-tetramethyl-
As can be seen in Table 2, the reduction of BODIPY is nearly unaf-
fected by the presence of Fc moieties, because the added electron
in both radical anions remains located on the BODIPY core (see the
discussion on the LUMO below). As expected, the reduction poten-
tial is slightly less negative than reported for a similar compound
lacking the pentafluorophenyl meso substituent [17]. Conversely,
the oxidation of BODIPY occurs at a much more positive potential
for (2) than for (1), due to the coulombic repulsion between the
positive charge on the BODIPY core and those created when oxi-
dizing Fc into ferrocenium (Fc+). It seems also that the chemical
stability of the fully oxidized BODIPY–Fc3+ species is lower than
the one of oxidized BODIPY in (1) as shown by the smaller ratio
of the backward vs. forward currents in the CV (this is confirmed
by the spectroelectrochemical data, see below). Interestingly, the
anodic wave corresponding to Fc oxidation in (2) is split into two
components, as further evidenced by the differential pulse voltam-
metry (DPV) curve in Fig. 2c. This feature corresponds to a mixed
valence state in singly oxidized (2) that makes the second oxida-
tion occur at a higher potential; this is the signature of a significant
electronic interaction between the two Fc moieties in (2). While the
first oxidation occurs nearly at the potential of free ferrocene (see
Table 2), the oxidation of the second Fc moiety is positively shifted
by 80 mV (non-interacting redox centers normally display a dif-
ference of 35 mV between their redox potentials [23]). The redox
potential values for the Fc termini are found very close to those pub-
lished for the parent compounds without the pentafluorophenyl
meso substituent [17].
4,4-difluoro-4-bora-3a,4a-diaza-s-indacene in the presence
of piperidine [19]. The ␲-extended BODIPY–Fc product was
obtained in 52% yield and characterized by multinuclear NMR, IR
spectroscopy and mass spectrometry.
3.2. Spectroscopy and electrochemistry
Fig. 1 displays the electronic absorption spectra of BODIPY–Fc
(2) and the BODIPY–mesityl (1) model compound as well as the
luminescence spectrum of (1). The main absorption band of (1)
in the visible region corresponding to the BODIPY chromophore
is split into two bands in BODIPY–Fc (2); the additional absorp-
tion band in the red part of the visible spectrum (739 nm) can be
ascribed to an ICT between the donor Fc and the acceptor BODIPY
subunits, while the other one (590 nm) is mainly due to the BOD-
IPY centered S0 → S1 transition, significantly blue shifted (53 nm)
compared to (1). The bands in the UV region are ascribed to ␲–␲*
S0 → S2 transitions located on the BODIPY backbone with addi-
tional contributions from ␲–␲* (350 nm) and metal centered d–d
transitions (430 nm) located on the Fc subunits in (2) [22].
BODIPY–mesityl (1) emits light at ꢁmax = 688 nm having the
characteristic features of BODIPY fluorescence (i.e., high quantum
yield, small Stokes shift) [19], while BODIPY–Fc (2) does not exhibit
any emission. This behavior is ascribed to an efficient PET between
ferrocene (acting as a donor) and the excited state of BODIPY (acting
as an acceptor).
Table 1 summarizes the spectroscopic features of both dyes.
Fig. 2 displays the electrochemical behavior of BODIPY–Fc (2)
compared to the model BODIPY–mesityl (1). Three pairs of redox
peaks can be identified in the cyclic voltammogram (CV) of (2) and
unambiguously ascribed to monoelectronic reduction of BODIPY,
poorly resolved bielectronic oxidation of Fc and monoelectronic
oxidation of BODIPY going from the cathodic to the anodic elec-
trode potentials. The anodic peak current ratios are in agreement
with the respective number of exchanged electrons in each case.
Table 2
Redox formal potentials for compounds (1) and (2) measured vs.
ferrocene/ferrocenium.
Compound
E◦1/V
E◦2/V
E◦3/V
BODIPY–mesityl (1)
BODIPY–Fc (2)
−1.33
−1.32
–
0.47
0.75
0.05; 0.13

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O. Galangau et al. / Electrochimica Acta 87 (2013) 809–815
Table 3
•+
BODIPY
BODIPY
I /µA
Calculated and experimentally deduced frontier orbital energies (eV).
A
Compound DFTa
UV–Vis
Electrochemistryc
1
0
spectroscopyb
LUMO
HOMO
HOMO–LUMO gap
LUMO
HOMO
(1)
(2)
−3.17
−5.19
–
–
−3.77
−5.57
1.80
−3.78
−5.15
1.37
2.02 1.92
−3.16
–
–
−5.11
HOMO–LUMO gap
1.95 1.67
a
Level of theory: B3LYP/Lanl2dz.
•-
BODIPY
BODIPY
b
c
Calculated using data from Table 1 and EHOMO–LUMO (eV) = 1240/ꢁmax (nm).
Calculated using data from Table 2 and E(Fc) = −5.1 eV [23].
-1.5 -1.2 -0.9 -0.6 -0.3
0.0
0.3
0.6
0.9
1.2
E /V
The orbital modeling of the ‘trans’ configuration of (2) is shown
in Fig. 3B. The LUMO is, as expected, mainly centered at the BOD-
IPY core, although with a small contribution from the ferrocenyl
termini. The conjugation is clearly predicted by the calculations
when looking at the HOMO, since the electron density is spread
over the whole molecule backbone and not confined only on the
ferrocenyl moieties. Table 3 compares the energy levels obtained by
the calculations with the ones derived from spectroscopic and elec-
trochemical data. The calculated HOMO–LUMO gap for BODIPY–Fc
(2) is close to that determined experimentally. However, it was dif-
ficult to find a satisfactory geometry for BODIPY (1) and its LUMO
energy and thus HOMO–LUMO gap are therefore clearly overes-
timated. The dication of BODIPY–Fc (2) was also calculated. The
single electrons are clearly distributed over both ferrocenyl units
as expected from electrochemistry (see Fig. 3C).
1
0
B
•+
BODIPY
BODIPY
Fc
I /µA
Fc+
•-
BODIPY
BODIPY
-1.6
-1.1
-0.6
-0.1
0.4
0.9
1.4
E /V
3.4. UV–Vis spectroelectrochemistry
The spectroelectrochemical behavior of BODIPY–Fc (2) was
investigated in an optically transparent thin layer cell allowing
rapid exhaustive electrolysis and outstanding resolution of close
lying redox steps (Fig. 4). First, when a negative potential (E◦1) is
applied to generate the anion radical of (2) (Fig. 4a), one can clearly
observe a dramatic drop of the intensity associated with the ICT
band in the red part of the spectrum. Several isosbestic points as
well as full recovery upon reoxidation give evidence that the elec-
trochemical reduction leads to a single stable species under the
C
0.2
I/µA
BODIPY
Fc
Fc+
0.1
experimental conditions. When applying a positive potential (E◦
)
BODIPY
Fc+
2
Fc+
0
corresponding to the first oxidation (Fig. 4b), the ICT band inten-
sity starts to fall down while a new band in the 600 nm range rises.
There is also a small but significant band of the monocation rising at
ca. 870 nm, which probably corresponds to the Fe(II)–Fe(III) inter-
valence electron transfer (IVCT), for it again disappears when the
dication is formed.
0
-0.4
-0.2
0.2
0.4
E /V
Fig. 2. CV of (A) BODIPY–mesityl (1) and (B) BODIPY–Fc (2) 1 mM in
dichloromethane (+ TBAPF6) on Pt microdisc (scan rate: 50 mV/s). Potentials are vs.
Ag+/Ag reference. (C): DPV of BODIPY–Fc (2) (pulse width: 50 ms; pulse amplitude:
10 mV; scan rate: 5 mV/s).
Sweeping the anodic potential to the second oxidation (E◦
)
3
makes the original ICT band totally vanish while a second new
band just below 700 nm clearly appears. The latter has also a charge
transfer character but now the BODIPY core acts as the donor and
the ferrocenium moieties as the acceptors. This is confirmed by
the disappearance of this band when the BODIPY is oxidized in its
turn, but this final oxidation is not fully reversible, as expected from
the CV (Fig. 2b). The results are consistent with those from similar
compounds [16] but in the present case the signature of the three
successive oxidized steps has been identified.
The anodic spectroelectrochemistry of (2) in dichloromethane
was repeated at 243 K (see Supplementary data). It resulted in a
slightly different intensity pattern of the dication in the visible
region and increased stability of the fully oxidized tricationic prod-
uct.
3.3. Molecular and orbital modeling
The geometry of (2) was calculated using the DFT B3LYP
optimization method (see Fig. 3A). The pentafluorophenyl meso
substituent is found almost perpendicular to the BODIPY core due to
the steric hindrance of the methyl side groups. The vinyl bridges are
almost in the same plane as the BODIPY (dihedral angle: 13◦) and
the cyclopentadienyl groups (dihedral angle: 8◦). These facts sug-
gest that the conjugation between both ferrocenyl centers through
the BODIPY core is facilitated by the geometry. Besides, both ‘cis’
and ‘trans’ configurations for the relative positions of the ferrocenyl
groups are allowed, since the energy difference is small (0.08 eV).

O. Galangau et al. / Electrochimica Acta 87 (2013) 809–815
813
Fig. 3. (A) Optimized geometries (left: ‘cis’ form; right: ‘trans’ form) of BODIPY–Fc (2). (B) Frontier molecular orbitals of (2). (C) Spin density difference (spin(˛)–spin(ˇ)) for
the dication of BODIPY–Fc (2) (blue lobes correspond to excess ␣ spin density). (For interpretation of the references to color in this figure legend, the reader is referred to the
web version of the article.)
3.5. Electrochemical monitoring of the fluorescence
electrochemically instead of chemically. Having coupled TIRF
microscopy with the electrochemical cell set-up, we were able
to record the luminescence intensity modulation as a function of
applied potential. Fig. 6 shows that the luminescence of (2) can
reversibly be switched between the emitting bielectronic oxidized
state and the non-emitting neutral state. Increasing the positive
potential limit makes the modulation faster and the amplitude
greater. Note that the potentials are different from the ones deter-
mined by CV due to uncompensated ohmic drop in the TIRFM
electrochemical setup (the working electrode area in the latter is
larger). The two potential values applied at the end of the step
correspond to oxidation of the Fc moieties while the BODIPY core
remains neutral. It confirms that canceling the donor character of
It has already been demonstrated that in this kind of dyad the
fluorescence can be switched on upon ferrocene oxidation [16].
First we checked this possibility by chemical oxidation using FeCl3
as the oxidizing agent. Fig. 5 shows the evolution of the emission
spectra recorded in a cuvette upon successive additions of FeCl3
when exciting at 590 nm (at this wavelength the absorption does
not change upon oxidation, see Fig. 4). A new emission band starts
to appear at 610 nm, in agreement with previously observed behav-
ior [15]. This fluorescence is associated with the absorption peak
at 610 nm that rises in Fig. 4d with a very small Stokes shift. To
confirm this result, we tried to monitor the luminescence switch

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O. Galangau et al. / Electrochimica Acta 87 (2013) 809–815
0,5
0,4
0,3
0,2
0,1
0,0
0,5
A
A
0,4
0,3
0,2
0,1
A
C
0,0
300
400
500
600
700
800
900
1000
300
400
500
600
700
800
900
1000
Wavelength /nm
Wavelength /nm
Wavelength, nm
0,5
0,4
0,3
0,2
0,1
0,0
0,5
0,4
0,3
0,2
0,1
0,0
A
A
B
D
300
400
500
600
700
800
900
1000
300
400
500
600
700
800
900
1000
Wavelength /nm
Wavelength /nm
Fig. 4. UV–Vis spectroelectrochemistry of BODIPY–Fc (2) 10−3 M in dichloromethane (+0.3 M TBAPF6) at 283 K (OTTLE cell). (A) One electron reduction into the radical anion;
(B) one-electron oxidation into the corresponding cation; (C) one-electron oxidation of the cation into the corresponding dication; (D) irreversible one-electron oxidation of
BODIPY–Fc2+
.
20000
15000
10000
5000
0
0.01000
0.00500
0.00000
-0.00500
-0.01000
-0.01500
a
b
Intensity / a.u.
4 105
0
50
100
150
200
250
Time,sec
Time /s
3 105
2 105
1 105
0
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
0.01500
0.01000
0.00500
0.00000
-0.00500
-0.01000
-0.01500
0
50
100
150
200
Time,sec
Time /s
600
620
640
660
680
700
Wavelength /nm
Fig. 6. Simultaneous variations of fluorescence intensity (upper curve, left scale in
a.u.) and current (lower curve, right scale in A) recorded under microscope upon
potential steps between −0.4 V and resp. 1.2 V (a) or 0.9 V (b) for 30 s, for BODIPY–Fc
(2) 1 mM in dichloromethane. Excitation: laser pulse (515 nm).
Fig. 5. Emission spectral changes (ꢁexc = 590 nm) of BODIPY–Fc (2) 5.4 ␮M in
dichloromethane upon addition of FeCl3. The FeCl3 concentration was varied from
0 to 70 ␮M by 10 ␮M steps.

O. Galangau et al. / Electrochimica Acta 87 (2013) 809–815
815
References
[1] A.C. Benniston, G. Copley, K.J. Elliott, R.W. Harrington, W. Clegg, Redox-
controlled fluorescence modulation in BODIPY-quinone dyad, European
Journal of Organic Chemistry (2008) 2705.
a
[2] R.A. Illos, E. Harlev, S. Bittner, A novel all-organic chemical and electrochemical
fluorescent switch, Tetrahedron Letters 46 (2005) 8427.
[3] H. Röhr, C. Trieflinger, K. Rurack, J. Daub, Proton- and redox-controlled
switching of photo- and electrochemiluminescence in thiophenyl-substituted
boron–dipyrromethene dyes, Chemistry – A European Journal 12 (2006) 689.
[4] X.W. Xiao, W. Xu, D.Q. Zhang, H. Xu, L. Liu, D.B. Zhu, Novel redox-fluorescence
switch based on a triad containing tetrathiafulvalene and pyrene units with
tunable monomer and excimer emissions, New Journal of Chemistry 29 (2005)
1291.
[5] G.X. Zhang, D.Q. Zhang, X.F. Guo, D.B. Zhu, A new redox-fluorescence switch
based on a triad with tetrathiafulvalene and anthracene units, Organic Letters
6 (2004) 1209.
[6] C. Dumas-Verdes, F. Miomandre, E. Lepicier, O. Galangau, T.T. Vu, G. Clavier,
R. Meallet-Renault, P. Audebert, BODIPY-tetrazine multichromophoric deriva-
tives, European Journal of Organic Chemistry (2010) 2525.
[7] R.L. Zhang, Z.L. Wang, Y.S. Wu, H.B. Fu, J.N. Yao, A novel redox-fluorescence
switch based on a triad containing ferrocene and perylene diimide units,
Organic Letters 10 (2008) 3065.
[8] A. Togni, T. Hayashi, Ferrocenes: Homogeneous catalysis; organic synthesis;
materials science, Wiley-VCH, Weinheim, 1995.
[9] M.J. Carney, J.S. Lesniak, M.D. Likar, J.R. Pladziewicz, Ferrocene derivatives as
metalloprotein redox probes - electron-transfer reactions of ferrocene and fer-
ricenium ion derivatives with cytochrome-C, Journal of the American Chemical
Society 106 (1984) 2565.
Fig. 7. Emission spectroelectrochemistry of BODIPY–Fc (2): 0.2 mM in acetonitrile,
recorded under fluorescence microscope, using TIRF illumination, at various elec-
trolysis times (reversal time: 30 s). Electrode potential: 1 V vs. Ag pseudoreference
electrode. Excitation: white mercury lamp with FITC filter (460–500 nm).
[10] A. Loudet, K. Burgess, Bodipy dyes and their derivatives, Chemical Reviews 107
(2007) 4891.
[11] R. Ziessel, G. Ulrich, A. Harriman, The chemistry of Bodipy: a new El Dorado for
fluorescence tools, New Journal of Chemistry 31 (2007) 496.
[12] G. Ulrich, R. Ziessel, A. Harriman, The chemistry of fluorescent bodipy dyes:
versatility unsurpassed, Angewandte Chemie International Edition 47 (2008)
1184.
[13] A.C. Benniston, G. Copley, Lighting the way ahead with boron dipyrromethene
(Bodipy) dyes, Physical Chemistry Chemical Physics 11 (2009) 4124.
[14] T.K. Khan, R.R.S. Pissurlenkar, M.S. Shaikh, M. Ravikanth, Synthesis and studies
of covalently linked meso-furyl boron-dipyrromethene-ferrocene conjugates,
Journal of Organometallic Chemistry 697 (2012) 65.
[15] M.R. Rao, K.V.P. Kumar, M. Ravikanth, Synthesis of boron-dipyrromethene-
ferrocene conjugates, Journal of Organometallic Chemistry 695 (2010) 863.
[16] X.D. Yin, Y.J. Li, Y.L. Li, Y.L. Zhu, X.L. Tang, H.Y. Zheng, D.B. Zhu, Electrochromism
based on the charge transfer process in a ferrocene-BODIPY molecule, Tetra-
hedron 65 (2009) 8373.
the Fc moiety upon oxidation can actually restore the BODIPY fluo-
rescence and that this process can be controlled reversibly. Finally
the recording of emission spectra upon application of electrode
potential shows an emerging band with a maximum near 610 nm
that disappears when the potential is stepped back to 0 V (Fig. 7).
This confirms that the electrogenerated emitting species is the
same as in the chemical oxidation experiments. The reversibility
proves that the luminescence does not come from residual BOD-
IPY or BODIPY liberation upon oxidation of BODIPY–Fc (2). Thus it
is demonstrated that (2) actually exhibits an electrofluorochromic
behavior between the neutral and bielectronic oxidized states.
[17] R. Ziessel, P. Retailleau, K.J. Elliott, A. Harriman, Boron dipyrrin dyes exhibit-
ing “Push-Pull-Pull” electronic signatures, Chemistry – A European Journal 15
(2009) 10369.
4. Conclusion
[18] F. Miomandre, E. Lepicier, S. Munteanu, O. Galangau, J.F. Audibert, R.
Meallet-Renault, P. Audebert, R.B. Pansu, Electrochemical monitoring of the flu-
orescence emission of tetrazine and bodipy dyes using total internal reflection
fluorescence microscopy coupled to electrochemistry, ACS Applied Materials
and Interfaces 3 (2011) 690.
[19] O. Galangau, C. Dumas-Verdes, R. Meallet-Renault, G. Clavier, Rational design of
visible and NIR distyryl-BODIPY dyes from a novel fluorinated platform, Organic
Biomolecular Chemistry 8 (2010) 4546.
[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. Pomelli, 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. Fores-
man, 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, R.C. Gaussian 03, Gaussian, Inc.,
Wallingford, CT, 2004.
A new dyad involving an organic fluorophore (BODIPY) con-
nected to two redox-active moieties (ferrocenyl termini) has been
synthesized and its electrochemical and spectroscopic features
analyzed with a support from theoretical modeling. In the dyad
the two ferrocene units are conjugated with the BODIPY core,
the fluorescence of which being totally quenched by a photoin-
duced electron transfer. It has been demonstrated that bielectronic
oxidation of the termini to ferrocenium (either chemical or elec-
trochemical) triggers the fluorescence of the BODIPY chromophore
at 610 nm. The process is fully reversible. Applications in the field
of electrofluorochromic displays or highly sensitive sensors can be
envisaged using this approach.
Acknowledgment
J.F. Audibert is warmly acknowledged for the TIRF microscopy
measurements.
[21] F. Hartl, H. Luyten, H.A. Nieuwenhuis, G. Schoemaker, Versatile cryostated
optically transparent thin-layer electrochemical (OTTLE) cell for variable-
temperature UV–Vis IR spectroelectrochemical studies, Applied Spectroscopy
48 (1994) 1522.
Appendix A. Supplementary data
[22] U.M. Rabie, Intra- and intermolecular charge transfer: twin themes and simul-
taneous competing transitions involving ferrocenes, Spectrochimica Acta. Part
A, Molecular and Biomolecular Spectroscopy 74 (2009) 746.
[23] A.J. Bard, L.R. Faulkner, Electrochemical Methods: Fundamentals and Applica-
tions, New York, Wiley, 2001.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.
electacta.2012.09.048.