From blue to green: Fine-tuning of photoluminescence and electrochemiluminescence in bifunctional organic dyes

Article abstract of DOI:10.1021/jacs.6b12247

We describe the synthesis, computational analysis, photophysics, electrochemistry and electrochemiluminescence (ECL) of a series of compounds formed of two triphenylamines linked by a fluorene or spirobifluorene bridge. The phenylamine moieties were modif

Full text of DOI:10.1021/jacs.6b12247

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Article
From Blue to Green: Fine Tuning of Photoluminescence and
Electrochemiluminescence in Bifunctional Organic Dyes
Fabio Rizzo, Federico Polo, Gregorio Bottaro, Simona Fantacci,
Sabrina Antonello, Lidia Armelao, Silvio Quici, and Flavio Maran
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b12247 • Publication Date (Web): 15 Jan 2017
Downloaded from http://pubs.acs.org on January 15, 2017
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Journal of the American Chemical Society
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From Blue to Green: Fine Tuning of Photoluminescence and
Electrochemiluminescence in Bifunctional Organic Dyes
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Fabio Rizzo,a,b,* Federico Polo,c,§,* Gregorio Bottaro,d Simona Fantacci,e Sabrina Antonello,c
Lidia Armelao,c,d Silvio Quici,b Flavio Maranc,*
a Institute of Molecular Science and Technologies (ISTM), National Research Council (CNR), PST-CNR, via Fantoli
16/15, 20138 Milano, Italy
b Institute of Molecular Science and Technologies (ISTM), National Research Council (CNR), and INSTM, c/o
Department of Chemistry, University of Milano, via Golgi 19, 20133 Milano, Italy
c Department of Chemistry, University of Padova, via Marzolo 1, 35131 Padova, Italy
d Institute of Condensed Matter Chemistry and Technologies for Energy (ICMATE), National Research Council
(CNR), c/o Department of Chemistry, University of Padova, via Marzolo 1, 35131 Padova, Italy
e Institute of Molecular Science and Technologies (ISTM), National Research Council (CNR), c/o Department of
Chemistry, University of Perugia, via Elce di Sotto 8, 06123 Perugia, Italy
§ Author current address: National Cancer Institute - Centro di Riferimento Oncologico, via Franco Gallini 2, 33081
Aviano, Italy
E-mails: fabio.rizzo@istm.cnr.it; federico.polo@cro.it; flavio.maran@unipd.it
KEYWORDS. Electrochemiluminescence, spirobifluorene, fluorene, triphenylamines, emission tunability
ABSTRACT:
We
describe the
synthesis,
computational analysis,
photophysics,
electrochemistry
and
electrochemiluminescence (ECL) of a series of compounds formed of two triphenylamines linked by a fluorene or
spirobifluorene bridge. The phenylamine moieties were modified at the para-position of the two external rings by
electron-withdrawing or electron-donating substituents. These modifications allowed for fine tuning of the
photoluminescence (PL) and ECL emission from blue to green, with an overall wavelength span of 73 (PL) and 67 (ECL)
nm, respectively. For all compounds, we observed a very high PL quantum yield (79 - 89%) and formation of stable radical
ions. The ECL properties were investigated by direct annihilation of the electrogenerated radical anion and radical cation.
The radical-ion annihilation process is very efficient and causes an intense greenish-blue ECL emission, easily observable
even by naked eye, with quantum yield higher than the standard 9,10-diphenylanthracene. The ECL spectra show one
single band that almost matches the PL band. Because the energy of the annihilation reaction is higher than that required
to form the singlet excited state, the S-route is considered the favored pathway followed by the ECL process in these
molecules. All these features point to this type of molecular system as promising for ECL applications.
1A* → A + h
ν
(4)
In electrochemically generated chemiluminescence or
electrochemiluminescence
(ECL),
electrochemical
Reaction 3 is favored over an ET reaction that directly
forms the neutral species in their ground-state; this is
because the latter falls in the Marcus inverted region in
which the ET rate decreases as the reaction becomes very
exergonic.2 The mechanism shown in eqs 1-4 is defined as
the “S-route” because a singlet state 1A* is directly
generated. Systems with insufficient energy follow the “T-
route”, in which a triplet state is produced first (eq 5) and
then a triplet-triplet annihilation step generates the
singlet excited state 1A* (eq 6) that emits light (eq 4).
activation of suitable molecules or ions generates species
that undergo sufficiently exergonic electron-transfer (ET)
reactions to form excited state species (emitters) capable
of causing luminescence.1 The ECL reaction mechanism
may involve formation of an excited singlet state via a
direct annihilation of the radical ions generated from a
species
A by stepping the electrode potential at
appropriate positive and negative values (eqs 1-4). The
two ECL-active radical ions may be electrogenerated also
by using two different molecules.
A● + + A● – → 3A* + A
3A* + 3A* → 1A* + A
(5)
(6)
A – e → A●+
A + e → A●–
A●+ + A●– → 1A* + A
(1)
(2)
(3)
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Alternatively to the S-route and the T-route, ion- ECL behavior is made possible by chemically assembling
1
2
annihilation reactions may lead to formation of excimers
(eq 7) or exciplexes (eq 8):
luminophore systems that display bifunctional redox
features, i.e., systems in which the electroreducible and
3
4
5
A●+ + A● – → A2*
A●+ + B● – → (AB)*
(7)
(8)
electrooxidizable moieties are, to
decoupled.
a
large extent,
6
7
8
9
where B represents a second electroactive molecule. A
further ECL pathway relies on the use of a coreactant
liable to produce a strong reducing or oxidizing species.3
For example, dibenzoyl peroxide undergoes concerted
reductive cleavage of the O-O bond4,5 to form a
carboxylate RO– but also the strong oxidant RO●.4
EXPERIMENTAL
Full experimental details for the preparation and
characterization of compounds 1-6 are provided in the
Supporting Information.
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Spectroscopic Characterization. The UV-vis absorption
spectroscopy measurements were carried out in
anhydrous, freshly distilled DMF solutions by using a
double-beam CARY5E spectrophotometer with a spectral
bandwidth of 1 nm. The emission spectra were obtained
Since its early development, ECL found particular use
as an analytical tool because the light intensity is
proportional to the concentration of the emitting
species.6,7 For example, ECL provides a convenient
detection approach in immunoassays.8 Other applications
regard light-emitting devices based on liquid emitting
materials, such as liquid organic light-emitting diodes
(liquid-OLED),9,10 ECL cells,11 and light-emitting
electrochemical cells (LECs),12 which can provide self-
emission under appropriate voltage conditions.
Ruthenium polypyridyl complexes, especially ruthenium
(II) tris(bipyridine), are the most widely used ECL
emitters, especially in bio-related applications. However,
there is an increasing demand for the synthesis,
characterization and application of new ECL materials,
such as organic dyes,13-15 metal complexes (mainly
iridium16-18 and platinum19), and nanoparticles,20,21,22 that
could emit at wavelengths other than those typical of
ruthenium complexes. Devising systems that could allow
for fine tuning of the emission wavelength holds a
tremendous potential for future applications of multicolor
ECL.18-20,23,24 In this context, it has been shown that the
emission color can be modified using a combination of
ruthenium(II) and iridium(III) complexes.24 Arguably,
however, organic compounds could offer a more general
answer to this challenge particularly because of their
chemical versatility and, therefore, the possibility of
modulating electronic and photophysical properties
precisely. Organic molecules have been designed and
synthesized for ECL purposes,25-27,28 but few systematic
studies focused on substituent effects on the ECL
emission energy and efficiency.29-32 Recently, we described
the photophysical and ECL properties of compounds
obtained by linking two triphenylamine moieties to
fluorene or spirobifluorene.33 These compounds showed
intense blue photoluminescence (PL) and ECL emission
with high quantum efficiency.
with
spectrofluorimeter
monochromator in both the excitation and emission
sides, and coupled to R928P Hamamatsu
a
Fluorolog-3
(Horiba
Jobin
double-grating
Yvon)
equipped
with
a
photomultiplier; a 450 W Xe arc lamp was used as the
excitation source. The emission spectra were corrected for
detection and optical spectral response of the
spectrofluorimeter through a calibration curve supplied
by the manufacturer. Absolute photoluminescence
quantum yields (QYPL) were calculated by corrected
emission spectra obtained with an apparatus consisting of
a Spectralon® coated integrating sphere accessory (4", F-
3018, Horiba Jobin Yvon), fitted in the fluorimeter sample
chamber. For each compound, three independent
measurements were carried out, with an estimated error
of ± 20%. Quantum-yield values were independent of the
excitation wavelength in the investigated range.
Photoluminescence lifetimes in the ns range were
measured with a time-correlated single-photon counting
device (Fluorohub-b, Horiba Jobin-Yvon) coupled with
Fluorolog-3, using pulsed NanoLED excitation sources at
295 nm (pulse width ≤ 1 ns). Analysis of the luminescence
decay profiles vs time was accomplished with the DAS6
Decay Analysis Software provided by the manufacturer.
Experimental uncertainties in the lifetime determinations
are estimated to be 10%.
Here we describe the synthesis, photophysics,
electrochemistry, and computational study of two series
of compounds containing triphenylamines and fluorene
or spirobifluorene moieties. The triphenylamine groups
were substituted at the para positions of the external
rings with electron-withdrawing or electron-donating
groups (Chart 1). ECL was triggered by direct annihilation
of the radical ions electrogenerated by pulsing the
electrode potential between positive and negative values.
This study shows that effective fine tuning of the PL and
Chart 1. Structures of the investigated compounds.
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Electrochemistry. DMF (Sigma-Aldrich, 99.8 %) was
equipped with a PMT (Hamamatsu, H10723-20). The
pulsing potential was set to 100 mV past the peak
potentials of the oxidation wave and the first or second
reduction wave. The pulse width was 25 ms, unless
otherwise stated. The photocurrent detected by the PMT
1
2
3
4
5
6
7
8
treated with anhydrous Na2CO3 and then doubly distilled
at reduced pressure under a nitrogen atmosphere. Tetra-
n-butylammonium perchlorate (TBAP, Fluka, 99%) was
recrystallized from a 2:1 ethanol–water solution and dried
at 60 °C under vacuum. The working electrode was a
homemade glassy-carbon disk electrode (3 mm diameter,
Tokai GC-20) connected to a copper wire with silver
epoxy and sealed in a PEEK body. The electrode was
polished as already described.34 Before experiments, the
electrode was further polished with a 0.25 μm diamond
paste (Struer) and electrochemically activated in the
background solution by means of several voltammetric
cycles at 0.5 Vs-1 between the anodic and the cathodic
solvent/electrolyte discharges, until the expected quality
features were attained.35 A platinum wire served as the
counter electrode and a silver wire, separated from the
main electrolytic compartment by a Vycor® frit, was used
as a quasi-reference electrode. At the end of each
experiment, its potential was calibrated against the
ferricenium/ferrocene couple, used as an internal redox
standard. In DMF/0.1 M TBAP, ferricenium/ferrocene has
a formal potential of 0.464 V against the KCl saturated
calomel electrode (SCE);34 all potentials will be given
against SCE. The cyclic voltammetry (CV) experiments
were carried out in DMF/0.1 M TBAP, using a 1 mM
concentration for the electroactive compound. The
diffusion coefficient values were determined with
reference to that of ferrocene, which in this
solvent/electrolyte system is 1.13 x 10-5 cm2 s-1.35 The CV
and ECL experiments were conducted at 25 °C under an
Ar atmosphere using a cell consisting of a purposely
modified quartz cuvette. A CHI 760D Electrochemical
Workstation (CH Instruments) was used. For the CV
experiments, we employed the feedback correction to
minimize the ohmic drop between the working and the
reference electrodes.
was converted to
a
voltage signal through the
photosensor module and acquired by the external input
channel of the analog-to-digital converter (ADC) of the
CHI 1040B workstation. The transients and the faradic
currents were managed by using the software provided
with the CHI workstation. The ECL spectra were acquired
using a calibrated electron multiplying charge couple
device (EM-CCD) camera (Andor technology, Newton
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EM-CCD) coupled with
a
spectrograph (Andor
Technology, Shamrock 163). ECL emission was also
recorded with an 8 MP camera of iPhone 4s (Apple).
RESULTS AND DISCUSSION
Synthesis. The syntheses were carried out according to
strategies that share the step consisting in the preparation
of the core (9,9-dimethyl-9H-fluorene and 9,9’-
spirobifluorene) bearing two bromine atoms in position 2
and 7 (compounds 740 and 841).
The
synthesis
of
2,7-bis-(4-(N,N-bis-(4-
fluorophenyl)amino)phen-1-yl)-9,9-dimethyl-9H-fluorene
(1) and 2,7-bis-(4-(N,N-bis-(4-fluorophenyl)amino)phen-
1-yl)-9,9’-spirobifluorene (2) (Scheme 1) was achieved
through Suzuki coupling between the core (compounds 7
or 8) and the boronic ester of the fluorinated
triphenylamine (12). Introduction of fluorine on the para-
position of triphenylamine under Ullmann condition was
already described, but the product was recovered in low
yield.42 We obtained a similar low yield (ca. 30%) under
Hartwig-Buchwald condition, by reacting aniline with 2
equiv of 1-bromo-4-fluorobenzene. When the reaction
was carried out with an excess of dihaloarene, however,
we found that the secondary amine N-(4-fluorophen-1-
yl)benzeneamine (9) occurred as the main product in very
good yield (93%). Subsequently, by reacting 9 with an
excess of 1-bromo-4-fluorobenzene under the same
condition of cross-coupling reaction, N,N-bis(4-
fluorophen-1-yl)benzeneamine (10) could be obtained in
very good yield (93%, 86% over 2 steps). The selective
bromination with N-bromosuccinimide (11) followed by
Computational Details. Density functional theory (DFT)
methods, including time-dependent DFT (TDDFT), were
used to model the spirobifluorene systems' properties.
Calculations were performed by using the software
Gaussian09 (G09).36 The molecular structure of 2, 4, 6 and
18 (in which the triphenylamines are unsubstituted on the
external rings) were optimized without any symmetry
constraints by using M06 as exchange correlation
functional37 and 6-31g** as basis set.38 For all species, we
optimized the ground state (S0) geometry and the lowest
singlet (S1) excited state geometry. The geometry
optimizations were performed in vacuo and with a
polarizable continuum model of the solvent (DMF, ε =
37), as implemented in G09.39
reaction
with
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane gave the boronic ester derivative 12. The
final products 1 and 2 were prepared by Suzuki cross-
coupling reaction between 12 and the corresponding
fluorene or spirobifluorene core (7 or 8, respectively),
with 67% and 78% yield, respectively.
2,7-bis-(4-(N,N-bis-(4-methylphenyl)amino)phen-1-yl)-
9,9-dimethyl-9H-fluorene (3), 2,7-bis-(4-(N,N-bis-(4-
methylphenyl)amino)phen-1-yl)-9,9’-spirobifluorene (4),
2,7-bis-(4-(N,N-bis-(4-methoxyphenyl)amino)phen-1-yl)-
9,9-dimethyl-9H-fluorene (5) and 2,7-bis-(4-(N,N-bis-(4-
methoxyphenyl)amino)phen-1-yl)-9,9’-spirobifluorene (6)
were prepared by starting from the commercially
ECL. The ECL experiments were conducted using the
same electrochemical cell configuration as described
above. The glassy-carbon electrode was polished and
activated and then positioned a few millimeters from the
photomultiplier tube (PMT). The reference and the
counter electrodes were the same. ECL transients were
recorded using a CHI 1040B electrochemical workstation
(CH Instruments) coupled with a photosensor module
available
bis-(4-methylphenyl)amine
and
bis-(4-
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methoxyphenyl)amine (Scheme 2). The first step was a
Suzuki reaction between the core and 4-
of multi-brominate compounds. The sought compounds
1
2
3
4
5
6
3–6 were obtained through C-N bond formation between
15 or 16 with the appropriate secondary amine (a, (bis-(4-
methylphenyl)amine; b, bis-(4-methoxyphenyl)amine)
under Hartwig-Buchwald cross-coupling conditions.43
After column purification, the products were recovered in
good yield (3, 63%; 4, 78%; 5, 82%; 6, 79%).
(trimethylsilyl)phenylboronic acid to give 13 and 14. The
presence of the trimethylsilyl protecting groups allowed
introducing the halogen atoms selectively at the para-
position of the two phenyl rings in two steps with good
yield (compounds 15 and 16), thereby avoiding formation
7
8
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Scheme 1. Synthetic route for the synthesis of 1 and 2.
HO
OH
B
Na2CO3 2M
Pd(PPh3)4
R
R
R
R
Si
Si
+
Br
Br
THF dry
reflux
Si
R = CH3 (7)
R = CH3 (13) 67%
R = Ph Ph (8)
R = Ph Ph (14) 78%
THF dry
0 o
Br2
X
X
C
RT
NaOAc
N
H
X
X
X = CH3 (a), OCH3 (b)
NaOtBu
R
R
Pd(OAc)2 PtBu3
R
R
Br
Br
N
N
Toluene dry
reflux
X
X
R = CH3, X = CH3 (3) 63%, OCH3 (5) 82%
R = Ph Ph X = CH3 (4) 78%, OCH3 (6) 79%
R = CH3 (15) 94%
R = Ph Ph (16) 92%
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Scheme 2. Synthetic route for the synthesis of 3-6.
1
2
Photophysical Characterization. Figure 1a shows the
absorption spectra of 1-6. The presence of different para-
substituents on the triphenylamine groups does not
substantially affect the absorption and thus the energetics
of the systems. The spectra display a similar pattern
characterized by a single absorption band centered in the
UVA region (Table 1) and attributed to π- π* transitions of
the conjugate system.33 Compared to the spectra of
fluorene 17 and spirobifluorene 18, in which the
triphenylamines are unsubstituted on the external rings,33
the presence of the electron-withdrawing fluorine in 1 and
2 induces a hypsochromic effect in the absorption band,
whereas the presence of electron-donor substituents (Me
in 3 and 4, and OMe in 5 and 6) induces a bathochromic
effect, which is particularly evident for the methoxy group
(Table 1). The PL spectra (Figure 1b) display a more
pronounced dependence on the triphenylamine para-
substituents. In the fluorene series, as one goes from 1 to 5
the band maximum shifts from 445 to 500 nm, with a
Stokes shift increasing from 77 (1) to 118 (5) nm. A similar
although more pronounced trend is observed for the
spirobifluorene series, as the emission maximum shifts
from 458 for 2 to 518 nm for 6, and the corresponding
Stokes shift increases from 86 to 134 nm. Noteworthy,
both absorption and emission maxima are appreciably
red-shifted relative to those of comparable para-
3
4
5
6
7
8
9
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substitued
triphenylamine32a
and
fluorene
and
spirobifluorene44-47 derivatives. In 1-6, fine tuning of the
PL emission from blue to green is attributed to the
increasing donor strength of the substituents in the para-
position of the external triphenylamine rings. The
observed shifts are also associated with a variation in the
polarity of the excited states, as supported by
measurements performed in a less polar solvent, such as
dichloromethane (see Figure S1 and Table S1 in the
Supporting Information).
Figure 1. (a) Absorption spectra of 10-6 M 1-6 in DMF. (b)
Emission spectra of 10-6 M 1-6 in DMF, excited at 370 nm.
The peaks were normalized for the peak intensity.
As one goes from DMF to dichloromethane, the
decrease in solvent polarity affects the absorption
maximum of the ground state only marginally, with a
difference of only 5, 2 and 3 nm for molecules 2, 4 and 6,
respectively. On the other hand, the PL spectra show a
more pronounced bathochromic shift in DMF that
increases with the increase in donor strength of the para-
substituent. The excited state of these molecules has thus
a higher charge-separation character than the ground
state. In DMF, this stabilization results in a larger red
shift in the emission spectra and in a larger Stokes shift
compared to a less polar solvent. 48
Table 1. Photophysical Data.
Abs λmax
ε
× 104
PL λmax
Absolute
τ
Comp
(nm)
(M-1 cm-1)
(nm)
QYPL (%) (ns)
1
368
372
6.611
445
458
86
89
1.3
1.6
2
7.063
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17 a
18a
3
371
374
378
380
382
384
6.537
7.302
6.531
7.135
6.108
7.218
451
456
458
472
500
518
81
87
86
87
81
1.2
1.3
1.7
2.1
3.2
3.2
significant conformational changes and specific ion-pair
interactions.53
1
2
3
4
5
6
7
8
4
5
6
79
a From reference 33.
9
Regarding the difference between each pair of the
fluorene/spirobifluorene systems, the spirobifluorene
compounds are always red-shifted in both absorption and
PL emission spectra. This points to the existence of some
conjugation between the two fluorenyl moieties, which
our results show to be strong enough to cause a decrease
of the HOMO-LUMO energy gap. We attribute this
interaction to spiroconjugation.49 It is also worth noting
that, independently of the specific substituent and pair
system, a very high absolute PL quantum yield (QYPL) was
consistently observed (80-90%). Finally, Table 1 shows
that all luminescence lifetimes are in the ns range, which
points to fluorescence as the emission mechanism.
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Electrochemistry. The CV experiments were carried out
in DMF/0.1 M TBAP at 25 °C. The formal potential (E°)
values (or, for evidently multielectron waves, apparent E°
values) were obtained as the average between the
cathodic and anodic peak potentials. Table 2 shows the
results obtained for 1-6; for comparison, the data
pertaining to 17 and 1833 are also included. The 9,9'-
dimethylfluorene and spirobifluorene series display
similar electrochemical behaviors, as exemplified in
Figure 2 for the spirobifluorene series. Whereas the
maximum substituent effect on the reduction peaks is
modest (at the most, 0.07 V), it is much more pronounced
for the electrooxidation: 0.25 and 0.24 V for the 9,9'-
dimethylfluorene and spirobifluorene series, respectively.
This is easily understood because oxidation directly
involves the triphenylamine moieties, where the
substituents are varied, in agreement with the trend
expected on the basis of the
values.50
σp-Hammett constant
For both series, two CV peaks are detected on the
negative-going scan (Figure S2). The first peak (R1) shows
a peak-to-peak separation (∆Ep,R1) compatible with the
reversible formation of the fluorene radical anion. The
second reduction peak (R2) is partially reversible at low
scan rates, and this is attributed to the basicity of the
dianion. This peak becomes fully reversible at moderate
scan rates, and this allows its E°R2 to be determined
precisely.
Figure 2. Background-subtracted CVs in DMF/0.1 M TBAP
for the oxidation (a) and reduction (b) of
1 mM
spirobifluorene derivatives 2 (F, black), 4 (Me, blue), 6 (OMe,
red). Scan rate 0.2 V s-1. (c) Correlation between ∆E0O1/R1 and
The oxidation peak (O) is fully reversible. For all
compounds, however, ∆Ep is distinctly larger (Table 2)
than the typical one-electron value of 59 mV at 25 °C.51 It
is also significantly larger than the ca. 29 mV separation
expected for a fully developed two-electron process, i.e.,
when the second heterogeneous ET is thermodynamically
easier than the first one by at least 0.1 V,52 an eventuality
made possible when the second ET process entails
the Hammett σp for fluorene (black dots) and spirobifluorene
(red diamonds) series respectively.
The observed ∆Ep values are constant in a relatively
large scan-rate range and this implies that they truly
reflect a thermodynamic effect rather than intrinsically
slow heterogeneous ETs or ohmic-drop effects. Finally, for
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Journal of the American Chemical Society
units: see text. c Difference between the two triphenylamine
E°O values.
all compounds the ratio between the peak currents of the
oxidation and first reduction peaks, ip,O/ip,R1 is
d
Absolute ratio at 0.2 V s-1, where ip,R1
1
,
2
3
4
5
6
7
8
9
corresponds to a one-electron process.
significantly larger than one. As both reduction processes
are clearly one-electron process, ip,O/ip,R1 shows that the
oxidation peak is the result of a simultaneous oxidation of
two amine units.
Comparison (Figure 3) of the CV of 4 with the CVs of
spirobifluorene and tris(4-methylphenyl)amine, which
provide models for the two electroactive moieties, shows
that in 4 the spirobifluorene group is more easily reduced,
whereas amine oxidation becomes slightly more difficult.
It is also worth noting that the peak currents are
substantially different, despite the electrode used and the
concentrations were kept constant. Because the diffusion
coefficients (D) of 4, spirobifluorene, and tris(4-
methylphenyl)amine are 5.68·10-6, 7.28·10-6, and 1.46·10-5
cm2 s-1, respectively, the oxidation peaks confirm that 4
undergoes a two-electron process. Moreover, the ratio of
the reduction peak currents of 4 and spirobifluorene,
0.62, is in full agreement with the value calculated for the
ratio between the square root of the two diffusion
coefficients (ip is proportional to D1/2).51
The occurrence of a two-electron process can be
explained by considering that in these type of compounds
the two external phenyl moieties are not significantly
conjugated to the fluorene core. Generally speaking, when
an electron is removed from (or added to) the first of two
identical groups on the same molecule, the free energy for
the second ET step is function of the extent by which
such two moieties interact. If the two relevant orbitals (in
the present case, the otherwise degenerate HOMOs)
interact through bonds via the bridging group, an energy
gap between such orbitals is established. The larger the
gap, the larger the through-bond contribution to the
overlap between the two frontier orbitals. If there is no
interaction, entropic reasons make the second process
less favored by a factor (2RT/F) ln 2 = 35.6 mV (at 25 °C).54
Digital simulation of the experimental CVs provided the
∆E°O values gathered in Table 2 and could also reproduce
the experimental ip,O/ip,R1 ratios (for example, see Figure S3
for 6). The values are indeed only slightly larger than 35.6
mV and this indicates that the two triphenylamine
moieties are largely electronically independent. Figure 2c
shows that the potential difference between the first
oxidation and first reduction steps changes with the
Hammett σp corresponding to the triphenylamine
substituents. The difference between the corresponding
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∆E0
values for the fluorene and the spirobifluorene
O1/R1
series is approximately constant, 64 ± 7 mV. The main
conclusion of this part of the electrochemical analysis is
thus that the two triphenylamine moieties are oxidized at
very similar potentials, and the minor interaction
between the two redox centers point to two poorly
interacting HOMOs.
Figure 3. CVs of 1 mM 4 (black), spirobifluorene core (blue),
and tris(4-methylphenyl)amine (red) in DMF/0.1 TBAP. Scan
rate 0.2 V s-1.
Table 2. Electrochemical data in DMF/0.1 M TBAP.
Finally, whereas the difference between the two
oxidation potentials is limited, that between the
reduction peaks is substantial. Spirobifluorene undergoes
reversible reduction at -2.51 V and irreversible reduction
(not shown) at -2.77 V, whereas in 4 the first and second
reduction steps are easier by 340 and 320 mV,
respectively; for reference, the reduction of the simple
fluorene systems occurs at -2.69 V. This simple
comparison shows that addition of triphenylamines to
one of the two fluorene moieties makes reduction of the
molecule significantly easier. It also indicates that the
LUMO of compounds such as 4 is largely localized onto
this specific fluorenyl unit of the spirobifluorene system,
rather than on both fluorenyl units; on the contrary, the
first two LUMOs of unsubstituted spirobifluorene are
degenerate and localized onto either fluorenyl unit.55
Finally, the modest substituent effect exerted by the
specific substitution pattern on the outer triphenylamine
rings (Table 2) suggests that the LUMO spreads mostly
b
c
E°O
∆Ep,O ∆E°O
E°R1
∆Ep,R1 ip,O
/
E°R2
d
(V)
(mV) (mV)
(V)
(mV) ip,R1
(V)
1
0.980
84
76
82
78
75
78
74
77
52
48
51
-2.185
-2.136
-2.221
-2.154
-2.213
-2.133
-2.259
-2.184
72
63
69
67
65
62
60
66
1.79
-2.417
2
0.971
1.77 -2.386
17 a 0.954
18a 0.959
1.76
1.74
-2.441
-2.393
49
48
50
46
48
3
4
5
6
0.880
0.892
0.731
1.74 -2.452
1.82 -2.400
1.86 -2.489
1.79 -2.434
0.740
a
Compounds 17 and 18 were investigated in DMF
containing 0.1 M Bu4NPF6.33 b This is an apparent E°O because
the peak is caused by oxidation on both triphenylamine
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only on the adjacent phenyl groups of the two
Page 8 of 13
1
triphenylamine moieties.
2
3
4
5
6
7
8
9
Theoretical Calculations. We studied the geometrical,
electronic, and optical properties of species 2, 4, 6, and 18
by using DFT and TDDFT based methods. Computational
modeling provides quantitative information on the
molecular structures of the investigated species at the S0
and S1 states, the energy and electronic charge
distribution of the frontier molecular orbitals, and the
UV-vis absorption spectra. This allows assessing the
charge flow associated with the S0-S1 electronic transition
responsible for the absorption band.
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The ground-state geometries of the investigated
spirobifluorene compounds in vacuo and in DMF are very
similar. The optimized geometries show mainly
a
variation in the planarity of the triphenylamine moiety
with respect to the fluorene plane, as measured by the
dihedral angle α between the latter and the fluorene-
linked phenyl of the triphenylamine (Figure S4 and Table
S2 in Supporting Information). In the ground state and
for all compounds, the average α is 146°-147°, whereas for
the S1 state α markedly increases to 165° (18), 166° (2), 162°
(4) and 161° (6). This shows that more planar systems are
attained upon S0-S1 excitation; this effect is less
pronounced for the compounds carrying electron-
donating substituents.
Figure 4. (Top) Frontier orbitals energies (eV) of
spirobifluorenes 18, 2, 4 and 6 in DMF. (Middle) Electronic
isodensity plots (contour value = 0.25) of HOMO/HOMO-1
and LUMO/LUMO+1 of spirobifluorene 4. (Bottom) Density
difference upon the first and second oxidation of 4; a red
(blue) color indicates a decrease (increase) of the electron
density upon oxidation.
The energy and electronic distribution of the frontier
orbitals are quite similar, with slight differences in the
occupied orbitals (Figure 4 and Figure S5). For all
compounds, the HOMO is delocalized on the
triphenylamines and the fluorene unit connecting them
(but not on the second spirobifluorene half), showing in 2
and 6 contributions due to the p orbitals of F and O
atoms, respectively. The tilting of the triphenylamines
with respect to the fluorene core lowers the electronic
communication between these groups.
The LUMO shows bonding character between the
fluorene core and the phenyl ring connecting the
triphenylamines (Figure 4), in line with the molecules
planarization calculated in the excited states. Substitution
of hydrogen by fluorine (18 to 2) only marginally affects
the energy of the frontier molecular orbitals, whereas
substitution with the electron-donating Me and OMe (4
and 6, respectively) causes a progressive destabilization of
the HOMO (and HOMO-1) by ca. 0.25 eV compared to 18.
Instead, the energy of both LUMO and LUMO+1 are
virtually unaffected. The HOMO destabilization leads to a
slight decrease of the HOMO-LUMO gap (see Figure 4),
which ultimately determines the tuning of the optical
properties. The simulated absorption spectra in DMF thus
evidence a red-shift when moving from H to OMe (Figure
S6) in agreement with the experimental observation. This
bathochromic shift is related to a larger increase of the
dipole moment on going from the ground state to the
excited state (Table S3). The computed S1 excited state is
indeed more polar than the ground state, with an increase
in polarity difference that follows the order 2 < 18 < 4 < 6.
The main absorption band is originated by a single
excitation S0→S1, which is essentially a HOMO→LUMO
transition (ca. 90%). To visualize the S0→S1 excitation we
computed the isodensity plots of the electron density
difference between S1 excited state and the ground state
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for all the investigated compounds (Figure S6). A charge
transfer from the peripheral triphenylamines to the inner
fluorene core moiety is observed, suggesting a similar
localization of holes/electrons upon oxidation/reduction.
1
2
3
4
5
6
7
8
9
To evaluate electronic charge rearrangement occurring
upon oxidation beyond a simple orbital picture, we
explicitly calculated the radical cation considered in the
electrochemistry analysis, 4●+ and the doubly oxidized
species 42+; similar conclusions hold for all the
investigated compounds. These calculations effectively
account for the electronic relaxation effects due to
oxidation in a more rigorous way than the single orbitals.
Notably, for both the first and second oxidation the larger
electron-density difference (Figure 4 Bottom) is observed
mainly on the nitrogen atoms, and no communication
with the rest of the system is evident. These results are,
therefore, fully consistent with the outcome of the
electrochemical analysis that evidenced the almost
independent electrooxidation behavior of the two
triphenylamine moieties.
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ECL. Figure 5 compares the ECL spectra for 1-6. The
ECL spectra were obtained by pulsing the electrode
potential between 100 mV past the oxidation peak and 100
mV past the second reduction peak, each step consisting
of 25 ms. Radical cations and radical anions annihilated to
form an excited state whose subsequent emission signal
was integrated for 1 s using a 1 nm slit width. The short
exposition time employed to collect the ECL emission
spectra indicates that the annihilation process in these
molecules is highly efficient. Figure 5 shows that for both
series of compounds the ECL spectra display one
maximum that nearly matches that of the PL pattern
(Figure 1b). Similarly to the PL data, the effect of the para
substituents on the triphenylamine rings is particularly
significant, as both types of spectra undergo a red shift
when one goes from fluorine to methoxy with a
remarkable ∆λ of 67 (ECL) and 73 (PL) nm, respectively.
The effect exerted by the substituents is summarized in
Figure 6 where the emission wavelength maxima are
plotted against the σp-Hammett. For comparison, the
data for 17 and 18 are also shown. The emission
wavelength maxima are collected in Table 3.
Figure 5. ECL spectra of 1 mM solutions (DMF/0.1 M TBAP)
of (graph a) 1 (black), 3 (blue), and 5 (red), or (graph b) 2
(purple), 4 (green), and 6 (orange).
To check the importance of having both the
triphenylamines and the fluorene/spirobifluorene centers
in the same molecule, we carried out also experiments
using
spirobifluorene
(1
mM)
and
tris(4-
methylphenyl)amine (2 mM), under the same
experimental conditions used for 1 mM 4. We found that
when a 25 ms pulse is employed, ECL emission occurs,
but the intensity of the light emitted is ~300 times lower
than that obtained with 4 (Figure S9). Furthermore, when
the pulse time is made slightly longer than 25 ms no ECL
occurs for the bimolecular system, whereas compounds 1-
6 display light emission even for longer pulse times (>200
ms). For simplicity, we now denote triphenylamine (as a
single molecule or as triphenylamine units) and
spirobifluorene (again, as a single molecule or as a bridge)
as TPA and SBF, respectively. During the negative step,
just before the potential is stepped positively, the surface
concentration of SBF●– is at its maximum value. Upon
positive electrode polarization, TPA●+ is generated and,
concomitantly, the surface concentration of SBF●– drops
to zero because of its concurrent quantitative reoxidation
to SBF.
The ECL quantum yields (QYECL) were calculated, via a
comparative method, as the photons emitted per redox
event relative to 9,10-diphenylanthracene (DPA) under
the same experimental conditions: for DPA in DMF,
QYECL was determined to be 0.0025.56 For all compounds
we found values higher than DPA (Table 3). To the best of
our knowledge, these are among the highest values so far
achieved with polyaromatic hydrocarbon compounds
emitting in the blue-green region. In terms of QYECL, no
evident effect is brought about by the substituents on the
external rings or the passage from the fluorene to the
spirobifluorene systems. The emission intensity tends to
decrease as the number of pulses increases (Figure S7).
However, even after several pulses the light emitted was
still so intense to be seen by naked eye and recorded with
a smartphone camera (Figure S8 and video in Supporting
Information).
Table 3. ECL data in DMF/0.1 M TBAP
c
Es (eV)a -∆Hann (eV)b
QYECL
ECL λmax
3.5
1
455
2.79
3.04 (3.32)
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Page 10 of 13
same molecule, and sufficiently separated relevant
orbitals.
To understand which pathway is followed by ECL in the
fluorene and spirobifluorene systems, we calculated the
energy of the excited state from the fluorescence
3.7
3.0
1.7
2
17 c
18c
3
465
453, 484
450, 493
468
2.71
2.75
2.72
2.71
2.98 (3.28)
3.05 (3.32)
2.99 (3.28)
2.97 (3.26)
2.90 (3.22)
2.87 (3.14)
2.80 (3.10)
1
2
3
4
5
6
7
8
3.0
2.7
4.2
3.2
spectrum using equation Es (eV) = 1239.81/λ, where λ (in
nm) is the wavelength at the maximum emission peak.1
Table 3 shows the estimated values for the energy of the
first singlet excited state. The annihilation enthalpy ∆Hann
(in eV) can be calculated as ∆Hann = –(E0 – E0 – 0.1),
4
478
2.63
2.48
2.39
5
505
9
O1
R1
6
517
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where the -0.1 eV term is a commonly adopted entropy
correction.1 Table 3 shows that for all compounds the
energy associated with -∆Hann is larger than Es and,
therefore, all these systems are energy sufficient. This
points to luminescence as arising from a species in a
singlet excited state, and thus that the process follows the
S-route.1 This is in keeping with the similarity between
the ECL and PL results and the PL luminescence lifetimes.
a
b
Es estimated from fluorescence emission maximum.
–
∆Hann = E0 – E0 – 0.1; the corresponding values for E0
O1
R1
O2
/E0 are in parenthesis. Relative to DPA, taking QYECL of
c
R2
DPA = 1. c From reference 33.
At this stage, the difference between the two separate
species and 4 is that in the latter two TPA●+ radical
cations form simultaneously: due to the slightly favored
comproportionation
reaction
(for
4,
the
It is finally worth noting that for all compounds the
ECL intensity decreases by pulsing to potentials of the
first reduction peak (Figure 7). This behavior appears to
be associated with the stoichiometry of the radical ions
present in solution.57,58 Whereas at the potentials of the
positive step a dication forms (each amine moiety
undergoes a nearly independent one-electron oxidation),
in the negative step the radical anion or the dianion is
produced selectively; the latter undergoes a favored ET
with a neutral molecule (for the whole series, Kc is
between 5.2 x 103 and 3.3 x 104) to form two radical
anions. By pulsing between the oxidation and the first
reduction peaks, excess diradical dications and radical
cations (because of the comproportionation reaction)
form in the reaction layer. When the spectrum is
recorded by including the second reduction peak, the
stoichiometry of radical ions is balanced and the
annihilation reaction of the dication-dianion pair
produces a higher intensity ECL emission.
comproportionation equilibrium constant is Kc = 7.0; for
the whole series, Kc is in the range from 6.5 to 7.6), some
dication reacts with a neutral molecule to form two
separate radical cations. For both molecular systems, the
diffusion layer is still rich of SBF●– that can exchange one
electron with the TPA●+ (or with one of the TPA●+
moieties in 4) diffusing toward the bulk. For the two
separated ions, annihilation generates the excited state
TPA*. For the complex systems, on the other hand, the
HOMO and the LUMO are located in substantially
different parts of the molecule and, therefore,
annihilation can be seen as generating a radical-ion pair
consisting of a TPA oxidized moiety and a SBF (or
fluorene) reduced moiety. Consequently, the same
excited-state species obtained upon direct light
absorption in the PL experiments forms.
Figure 6. ECL emission wavelength maxima (nm) of fluorene
(black dots) and spirobifluorene (red diamonds) derivatives
versus σp-Hammett.
Figure 7. ECL spectra of 1 collected by pulsing between the
oxidation and the first (black) or second (red) reduction
peak.
The process can be described as an intramolecular
charge-transfer emission. The different ECL efficiency in
the two types of system is thus related to the presence of
the fluorene-type bridge, two triphenylamine units in the
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CONCLUSIONS
Journal of the American Chemical Society
(6) Richter, M. M. Chem. Rev., 2004, 104, 3003-3036 and
references therein.
1
We have described the synthesis, photophysics,
computational analysis, and electrochemical behavior of
efficient ECL emitting bifunctional dyes consisting of a
fluorene or spirobifluorene core linked to para-
substituted triphenylamines. The compounds were
prepared in good yield, through two different approaches,
by using Suzuki or Hartwig-Buchwald cross-coupling
reaction. All compounds show blue-green emission, with
high quantum yields. ECL spectra almost match those
obtained by photoluminescence, and ECL efficiency is
higher than for the standard ECL emitter 9,10-
diphenylanthracene. The effect of the substituent groups
on the amine moieties allows fine tuning of the emission
properties with a remarkable ꢀλ of 73 (PL) and 67 (ECL)
nm, respectively. Analysis of the results indicates that all
systems are energy-sufficient and ECL emission is caused
by the singlet-excited state obtained by the S-route. This
class of ECL systems have the merits of showing (i)
reversible and stable electrochemical behavior, (ii) very
high PL quantum yields, and (iii) high ECL efficiency
without formation of excimers. The investigated
molecules demonstrate the effective possibility to design
highly emitting systems for ECL applications with tunable
emission wavelength. Concerning possible developments,
we note that although both the fluorene and the
spirobifluorene systems show very nice PL and ECL
behaviors, the spirobifluorene system offers the chance of
introducing suitable electron-withdrawing substituents in
second fluorene moiety. By this strategy, an even more
effective separation of HOMO and LUMO should be
attained, resulting in a further fine-tuned red shift.
(7) Miao, W. Chem. Rev. 2008, 108, 2506-2538 and references
therein.
(8) Sardesai, N. P.; Barron, J. C.; Rusling, J. F. Anal. Chem. 2011,
83, 6698–6703.
2
3
4
5
6
7
8
9
(9) Xu, D.; Adachi, C. Appl. Phys. Lett. 2009, 95, 053304.
(10) Hirata, S.; Kubota, K.; Jung, H. H.; Hirata, O.; Goushi, K.;
Yahiro, M.; Adachi, C. Adv. Mater. 2011, 23, 889-893.
(11) Kasahara, T.; Matsunami, S.; Edura, T.; Ishimatsu, R.;
Oshima, J.; Tsuwaki, M.; Imato, T.; Shoji, S.; Adachi, C.; Mizuno,
J. Sens. Actuat. A 2014, 214, 225-229.
(12) (a) Barbante, G. J. ; Hogan, C. F.; Mechler, A.; Hughes, A.
B. J. Mater. Chem. 2010, 20, 891-899. (b) Filiatrault, H. L.;
Porteous, G. C.; Carmichael, R. S.; Davidson, G J. E.; Carmichael,
T. B. Adv. Funct. Mater. 2012, 24, 2673-2678.
(13) Nepomnyashchii, A. B.; Bard, A. J. Acc. Chem. Res. 2012,
45, 1844-1853.
(14) Qi, H.; Teesdale, J. J.; Pupillo, R. C.; Rosenthal J.; Bard, A.
J. J. Am. Chem. Soc. 2013, 135, 13558-13566.
(15) Ishimatsu, R.; Matsunami, S.; Kasahara, T.; Mizuno, J.;
Edura, T.; Adachi, C.; Nakano, K.; Imato, T. Angew. Chem. Int.
Ed. 2014, 53, 6993-6996.
(16) Fernández-Hernández, J.; Longhi, E.; Cysewski, R.; Polo,
F; Josel, H.-P.; De Cola, L. Anal. Chem. 2016, 88, 4174-4178.
(17) Zanarini, S.; Felici, M.; Valenti, G.; Marcaccio, M.; Prodi,
L.; Bonacchi, S.; Contreras-Carballada, P.; Williams, R. M.;
Feiters, M. C.; Nolte, R. J. M.; De Cola, L.; Paolucci, F. Chem. Eur.
J. 2011, 17, 4640-4647.
(18) Schmittel, M.; Shu, Q.; Cinar, M. E. Dalton Trans. 2012, 41,
6064-6068.
(19) Reid, E. F.; Cook, V. C.; Wilson, D. J. D.; Hogan, C. F.
Chem. Eur. J. 2013, 19, 15907-15917.
(20) Valenti, G.; Rampazzo, E.; Bonacchi, S.; Khajvand, T.;
Juris, R.; Montalti, M.; Marcaccio, M.; Paolucci, F.; Prodi L.
Chem. Commun. 2012, 48, 4187-4189.
(21) Lingling, L.; Hongying, L.; Yuanyuan, S.; Jianrong, Z.; Jun-
Jie, Z. Anal. Chem. 2011, 83, 661-665.
(22) Li, H.; Daniel, J.; Verlhac, J.-B.; Blanchard-Desce, M.;
Sojic, N. Chem. Eur. J. 2016, 22, 12702-12714.
(23) Valenti, G.; Bruno, C.; Rapino, S.; Fiorani, A.; Jackson, E.
A.; Scott, L. T.; Paolucci, F.; Marcaccio, M. J. Phys. Chem. C 2010,
114, 19467-19472.
(24) Kerr, E.; Doeven, E. H.; Barbante, G. J.; Hogan, C. F.;
Bower, D. J.; Donnelly, P. S.; Connell, T. U.; Francis, P. S. Chem.
Sci., 2015, 6, 472-479.
(25) (a) Omer, K. M.; Ku, S.-Y.; Wong, K.-T.; Bard, A. J. J. Am.
Chem. Soc. 2009, 131, 10733-10741; (b) Omer, K. M.; Ku, S.-Y.;
Wong, K.-T.; Bard, A. J. Angew. Chem., Int. Ed. 2009, 48, 9300-
9303; c) Omer, K. M.; Ku, S.-Y.; Cheng, J.-Z.; Chou, S.-H.; Wong,
K.-T.; Bard, A. J. J. Am. Chem. Soc. 2011, 133, 5492-5499.
(26) Swanick, K. N.; Price, J. T.; Jones, N. D.; Ding, Z. J. Org.
Chem. 2012, 77, 5646-5655.
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Corresponding Authors.
E-mail: fabio.rizzo@istm.cnr.it
E-mail: federico.polo@cro.it
E-mail: flavio.maran@unipd.it
Acknowledgment. This work was financially supported by
AIRC (FM, Project 12214: Innovative Tools for cancer risk
assessment and early diagnosis – 5 per mille) and FIRB-MIUR
(Project RBAP114AMK: RINAME – Integrated Network for
Nano-Medicine) for financial support.
Supporting Information. Full experimental details on
methods and syntheses, and further photophysical and
electrochemical characterization results. This material is
available free of charge via the Internet at
http://pubs.acs.org.
(27) Natarajan, P.; Schmittel, M. J. Org. Chem. 2013, 78, 10383-
10394.
(28) Adam, C.; Wallabregue, A.; Li, H.; Gouin, J.; Vanel, R.;
Grass, S.; Bosson, J.; Bouffier, L.; Lacour, J.; Sojic, N. Chem. Eur. J.
2015, 21, 19243-19249.
REFERENCES
(1) Electrogenerated Chemiluminescence; Bard, A. J., Ed.;
Marcel Dekker, New York, 2004.
(2) Marcus, R. A.; Sutin, N. Biochim. Biophys. Acta 1985, 811,
265−322.
(3) Ludvík, J. J. Solid State Electrochem. 2011, 15, 2065–2081.
(4) Antonello, S.; Maran, F. J. Am. Chem. Soc. 1999, 121, 9668-
9676.
(29) Ketter, J. B.; Wightman, R. M. J. Am. Chem. Soc. 2004,
126, 10183-10189.
(30) (a) Fungo, F.; Wong, K.-T.; Ku, S.-Y.; Hung, Y.-Y.; Bard, A.
J. J. Phys. Chem. B, 2005, 109, 3984-3989. (b) Qi, H.; Chen, Y.-H.;
Cheng, C.-H.; Bard, A. J. J. Am. Chem. Soc. 2013, 135, 9041-9049.
(31) (a) Elangovan, A.; Yang, S.-W.; Lin, J.-H.; Kao, K.-M.; Ho,
T.-I. Org. Biomol. Chem. 2004, 2, 1597-1602; (b) Elangovan, A.;
Lin, J.-H.; Yang, S.-W.; Hsu, H.-Y.; Ho, T.-I. J. Org. Chem. 2004,
(5) Antonello, S.; Hesari, M.; Polo, F.; Maran, F. Nanoscale
2012, 4, 5333-5342.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 13
69, 8086-8092; (c) Ho, T.-I.; Elangovan, A.; Hsu, H.-Y.; Yang, S.-
W. J. Phys. Chem. B 2005, 109, 8626-8633.
(40) Saroja, G.; Pingzhu, Z.; Ernsting, N. P.; Liebscher, J. J.
Org. Chem. 2004, 69, 987-990.
1
2
3
4
5
6
7
8
(32) (a) Quinton, C.; Alain-Rizzo, V.; Dumas-Verdes, C.;
Miomandre, F.; Clavier, G.; Audebert, P. RSC Adv. 2014, 4, 34332–
34342. (b) Quinton, C.; Alain-Rizzo, V.; Dumas-Verdes, C.;
Miomandre, F.; Clavier, G.; Audebert, P. Chem. Eur. J. 2015, 21,
2230–2240.
(33) Polo, F.; Rizzo, F; Veiga-Gutierrez, M.; De Cola, L.; Quici,
S. J. Am. Chem. Soc. 2012, 134, 15402-15409.
(34) Antonello, S.; Musumeci, M.; Wayner, D. D. M.; Maran, F.
J. Am. Chem. Soc. 1997, 119, 9541-9549.
(41) Yu, W.-L.; Pei, J.; Huang, W.; Heeger, A. J. Adv. Mater.
2000, 12, 828-831.
(42) He, Z.; Wong, W.-Y.; Yu, X.; Kwok, H.-S.; Lin, Z. Inorg.
Chem. 2006, 45, 10922-10937.
(43) Hartwig, J. F.; Kawatsura, M.; Haula, S. I.; Shaughnessey,
K. H.; Alcazar-Roman, L. M. J. Org. Chem. 1999, 64, 5575-5580.
(44) Wong, K.-T.; Chien, Y.-Y.; Chen, R.-T.; Wang, C.-F.; Lin,
Y.-T.; Chiang, H.-H.; Hsieh, P.-Y.; Wu, C.-C.; Chou, C. H.; Su, Y.
O.; Lee, G.-H.; Peng, S.-M. J. Am. Chem. Soc. 2002, 124, 11576-
11577.
9
(35) Meneses, A. B.; Antonello, S.; Arévalo, M.-C; Maran, F.
Electroanalysis. 2006, 18, 363-370.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(45) Kotaka, H.; Konishi, G.-i; Mizuno, K. Tetrahedron Lett.
2010, 51, 181-184.
(36) Gaussian 09, Revision E.01, Frisch, M. J.; Trucks, G. W.;
Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.;
Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A.
F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.;
Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A.,
Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers,
E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi,
J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross,
J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli,
C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V.
G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.;
Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford CT, 2009.
(37) Y. Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120,
215-41.
(46) Yi, C.; Sun, Y.; Song, B.; Tian, W.; Qi, Q.; Zheng, Y.; Dai,
Y.; Jiang, W. Nanotechnology 2013, 24, 435704.
(47) Tao, S.; Peng, Z.; Zhang, Z.; Wang, P.; Lee, C.-S.; Lee, S.-T.
Adv. Funct. Mater. 2005, 15, 1716-1721.
(48) Principles of Fluorescence Spectroscopy, 3rd edition,
Lakowicz, J.R.; Springer-Verlag, 2006.
(49) Boo, B. H.; Choi, Y. S.; Kim, T.-S.; Kang, S. K.; Kang, Y. H.;
Lee, S. Y. J. Mol. Struct. 1996, 377, 129-136.
(50) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165-
195.
(51) Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 706-723.
(52) Polcyn, D. S.; Shain, I. Anal. Chem. 1966, 38, 370-375.
(53) Evans, D. H. Chem. Rev. 2008, 108, 2113–2144.
(54) Ammar, F.; Saveant, J.-M. Electroanal. Chem. 1973, 47,
215-221.
(55) Thiery, S.; Tondelier, D.; Declairieux, C.; Seo, G.; Geffroy,
B.; Jeannin, O.; Rault-Berthelot, J.; Métivier, R.; Poriel, C. J.
Mater. Chem. C 2014, 2, 4156-4166.
(56) Bezman, R.; Faulkner, L. R. J. Am. Chem. Soc. 1972, 94,
6317-6323
(57) Shen, M.; Rodríguez-López, J.; Huang, J.; Liu, Q.; Zhu, X.-
H.; Bard, A. J. J. Am. Chem. Soc., 2010, 132, 13453-13461.
(58) Shen, M.; Rodríguez-López, J.; Lee, Y.-T.; Chen, C.-T.;
Fan, F.-R. F.; Bard, A. J. J. Phys. Chem. C, 2010, 114, 9772-9780.
(38) Petersson, G. A.; Bennett, A.; Tensfeldt, T. G.; Al-Laham,
M. A.; Shirley, W. A.; Mantzaris, J. J. Chem. Phys. 1988, 89, 2193-
218.
(39) a) Miertus, S.; Scrocco, E.; Tomasi, J. Chem. Phys. 1981,
55, 117-129; b) Cossi, M.; Barone, V.; Cammi, R.; Tomasi, J. Chem.
Phys. Lett. 1996, 255, 327-335.
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