Directly Attached Bisdonor-BF2 Chelated Azadipyrromethene-Fullerene Tetrads for Promoting Ground and Excited State Charge Transfer

Article abstract of DOI:10.1002/chem.201700200

The efficiency and mechanism of electron- and energy-transfer events occurring in both natural and synthetic donor–acceptor systems depend on their distance, relative orientation, and the nature of the surrounding media. Fundamental knowledge gained from model studies is key to building efficient energy harvesting and optoelectronic devices. Faster charge separation and slower charge recombination in donor–acceptor systems is often sought out. In our continued effort to build donor–acceptor systems using near-IR sensitizers, in the present study, we report ground and excited-state charge transfer in newly synthesized, directly linked tetrads featuring bisdonor (donor=phenothiazine and ferrocene), BF₂-chelated azadipyrromethane (azaBODIPY) and C₆₀ entities. The tetrads synthesized using multi-step synthetic procedure revealed strong charge-transfer interactions in the ground state involving the donor and azaBODIPY entities. The near-IR emitting azaBODIPY acted as a photosensitizing electron acceptor along with fullerene whereas the phenothiazine and ferrocene entities acted as electron donors. The triads (bisdonor–azaBODIPY) and tetrads revealed ultrafast photoinduced charge separation leading to D^.+–azaBODIPY^.?–C₆₀ and D^.+–azaBODIPY–C₆₀^.? (D=phenothiazine or ferrocene) charge separated states from the femtosecond transient absorption spectral studies in both polar and nonpolar solvent media. The charge-separated states populated the triplet excited state of azaBODIPY prior returning to the ground state.

Full text of DOI:10.1002/chem.201700200

A Journal of
Accepted Article
Title: Directly Attached Bisdonor-BF2 Chelated Azadipyrromethene-
Fullerene Tetrads for Promoting Ground and Excited State
Charge Transfer
Authors: Francis D'Souza, M. A. Collini, M. J. Thomas, V. Bandi, and
P. A. Karr
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To be cited as: Chem. Eur. J. 10.1002/chem.201700200
Link to VoR: http://dx.doi.org/10.1002/chem.201700200
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FULL PAPER
DOI: 10.1002/chem.200((……))
Directly Attached Bisdonor-BF2 Chelated Azadipyrromethene-Fullerene Tetrads for
Promoting Ground and Excited State Charge Transfer
Melissa A. Collini,[a] Michael B. Thomas,[a] Venugopal Bandi,[a] Paul A. Karr,[b] and
Francis D’Souza*[a]
Abstract: The efficiency and mechanism
of electron- and energy transfer events
occurring in both in natural and synthetic
donor-acceptor systems depend on their
distance, relative orientation, and the nature
of the surrounding media. Fundamental
knowledge gained from model studies is
key in building efficient energy harvesting
and optoelectronic devices. Faster charge
separation and slower charge recombination
in donor-acceptor systems is often sought
out. In our continued effort to build donor-
acceptor systems using near-IR sensitizers,
in the present study, we report ground and
excited state charge transfer in newly
synthesized, directly linked, tetrads
featuring bisdonor (donor = phenothiazine
leading to D•+-azaBODIPY•–-C60 and D•+-
azaBODIPY-C60 (D = phenothiazine or
ferrocene) charge separated states from the
femtosecond transient absorption spectral
studies in both polar and nonpolar solvent
•–
and
ferrocene),
BF2-chelated
azadipyrromethane (azaBODIPY) and C60
entities. The tetrads synthesized using
multi-step synthetic procedure revealed
strong charge transfer interactions in the
ground state involving the donor and
azaBODIPY entities. The near-IR emitting
azaBODIPY acted as a photosensitizing
electron acceptor along with fullerene while
the phenothiazine and ferrocene entities
media.
The charge separated states
populated the triplet excited state of
azaBODIPY prior returning to the ground
state.
Keywords: charge separation . BF2
chelated azadipyrromethene
ferrocene, phenothiazine
. C60 .
acted as electron donors.
The triads
(bisdonor-azaBODIPY) and tetrads revealed
ultrafast photoinduced charge separation
azaBODIPY allows the excitation and emission well into the near-
IR region.[13] Consequently, azaBODIPYs are one of the highly
sought out fluorophores for energy harvesting,[8] sensing,[14] and
imaging[15] applications. Interestingly, the facile reduction of
azaBODIPYs makes it a rarely encountered electron acceptor-
photosensitizer molecule.[16] They differ from other electron
acceptor-photosensitizer molecules due to their ability to emit in the
near-IR region with high fluorescence quantum yields.
Introduction
Development of functional materials capable of light capture and
conversion are key in building devices capable of efficient
conversion of solar energy either into electricity or fuel.[1] This
would offer environmentally clean energy for human needs.[2] By
mimicking the natural photosynthesis[3] using electron donor-
acceptor based molecular/supramolecular assemblies, photocatalysis
for the production of clean fuels and materials for optoelectronics
are often targeted.[4-10] In the construction of such assemblies,
development of electron donor and electron acceptor molecules
capable of wide-band capture covering the visible and near-infrared
region of the electromagnetic spectrum and well-tuned redox states
are realized to be important. Engineered molecules with matched
spectral and redox states are expected to result in fast and efficient
charge transfer events.
BF2-chelated azadipyrromethene (azaBODIPY),[11] a structural
analogue of BF2-chelated dipyrromethene (BODIPY®),[12] has
recently
gained
much
attention
for
its
novel
photophysical/photochemical properties. AzaBODIPY absorbs in
the 300-700 nm region with very high molar absorptivities, and
desirable emission in the red region (660-750 nm) with quantum
yields exceeding 40%.[11] Additional peripheral modifications of
[a]
M. A. Collini, M. B. Thomas, Dr. V. Bandi, Prof. Dr. F. D’Souza
Department of Chemistry, University of North Texas, 1155 Union Circle,
#305070, Denton, TX 76203-5017, USA, FAX: 940-565-4318
E-mail: Francis.DSouza@unt.edu
Figure 1. Structures of the newly synthesized, directly linked bisdonor-
azaBODOPY-C60 tetrads, 1 and 2, and bisdonor-azaBODOPY triads, 1d and
2d.
[b]
Prof. Dr. P. A. Karr
Department of Physical Sciences and Mathematics, Wayne State College, 111
Main Street, Wayne, Nebraska 68787, USA
Supporting information for this article, additional spectral and femtosecond spectra,
1H and 13C NMR and MALDI-mass of triads and tetrads.
Photosynthetic
model
compounds
developed
using
For
azaBODIPY have revealed several interesting features.
example, when azaBODIPY was connected to ferrocene, efficient

1
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10.1002/chem.201700200
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photoinduced electron transfer from ferrocene to singlet excited
azaBODIPY was observed.[16] Alternatively, when C60 was
covalently linked azaBODIPY, electron transfer leading to the
derivative was obtained by reacting 1d with aluminum chloride and
dihydroxybenzaldehyde to yield 1e. Finally, 1e was dissolved in
toluene and combined with fullerene and sarcosine to yield
compound 1.
•–
formation of azaBODIPY•+-C60 was observed.[17] Excitation
transfer was observed when either chlorophyll derivatives or
BODIPY was covalently linked to azaBODIPY.[18] Interestingly,
when a bisporphyrin was covalently linked to azaBODIPY, the
resulting ‘molecular clip’ supramolecularly assembled to C60 via
metal-ligand coordination. In this supramolecular assembly, control
over energy and electron transfer events was possible to
accomplish.[19a] Furthermore, by a combination of zinc porphyrin,
BODIPY and azaBODIPY, a broad-band capturing the emitting
supramolecular triad useful for energy harvesting and building
optoelectronic devices was recently reported.[19b] This strategy was
used to develop and demonstrate excited state charge separation in
bisferrocene-azaBODIPY-C60 tetrads.[20] However, this was not the
case when ferrocene entities were replaced by phenothiazine entities
due to harder oxidation of the latter.[21] Using V-configuration of
triads, through-space and through-bond electron transfer events was
For the synthesis of 2, the desired chalcone was obtained by
grinding ferrocene carboxaldehyde and acetophenone in the
presence
of
NaOH.[26d] Following
purification
and
characterization, chalcone was combined with nitromethane in
the presence KOH and then allowed to run under reflux for 24 h.
This yielded the nitro derivative which was reacted with
ammonium acetate in ethanol under reflux conditions. Chelation
of compound 2c was achieved by combining 2c with
diisopropylethylamine and boron trifluoride diethyl etherate to
obtain 2d. Following chelation, an aldehyde derivative, 2e was
obtained by combining starting material with aluminum chloride
followed by reacting it with 3,4-dihydroxybenzaldehyde.
Finally, 2e was dissolved in toluene and combined with C60 and
sarcosine to yield compound 2. All of the new compounds were
fully characterized by 1H and 13C NMR, Maldi-TOF-Mass,
also demonstrated.[22]
Competitive electron transfer in a
supramolecular triad featuring subphthalocyanine/BODIPY,
azaBODIPY and fullerene was recently reported.[23] Self-assembly
approach involving metal-ligand axial coordination was utilized for
absorption/emission, and electrochemical methods.
The
compounds were stored in dark prior doing photochemical
studies.
build
naphthalocyanine conjugates and occurrence of excited state energy
and electron transfer were reported.[24]
More recently, by
azaBODIPY-phthalocyanine
and
azaBODIPY-
performing peripheral functionalization of azaBODIPY to extend
the absorption and emission into the near-IR region, the dyads
formed by using C60 as electron acceptor were shown to undergo
charge separation upon photoexcitation.[25]
Inspired by the above findings and our continued effort to
unravel the donor and acceptor behavior of azaBODPY derived
higher supramolecular analogs, in the present study, we report
syntheses, physico-chemical characterization, and excited state
charge transfer in directly linked bisdonor-azaBODIPY-C60 tetrads
and bisdonor-azaBODIPY triads[26] whose structures are shown in
Figure 1. As a result of direct covalent connectivity between the
donor (phenothiazine or ferrocene) entities and azaBODIPY, strong
electronic coupling have been observed. Cross-communication
between the two donor entities via the azaBODIPY macrocycle both
in the triads and tetrads have been witnessed from electrochemical
studies. This was unlike the previous studies[20] where the donor
and acceptor entities were spatially well-separated thus avoiding
strong intramolecular interactions. Excited state events in these
triads and tetrads are probed by using femtosecond transient
absorption spectroscopy.
Scheme 1. Synthetic methodology developed for triads, 1d and 2d,
and tetrads, 1 and 2.
Absorption and emission studies: Significant intramolecular
interactions leading to new charge tranfer band in the longer
wavelength region was observed for the studied triads and
Results and Discussion
tetrads.
Figure 2a shows the absorption spectra of the
Synthesis of the triads and tetrads: Scheme 1 summarizes the
syntheses of triads and tetrads while details are given in the
experimental section. Briefly, compound 1 was synthesized using
intermediates 1a-1e. To synthesize the chalcone, phenothiazine was
used to obtain the needed aldehyde derivative according to Scheme
2, first, using N-alkylation to synthesize N-ethylphenothiazine.
Then, by formylation using the phosphoryl chloride method.
Chalcone, 1a was then obtained by combining N-ethylphenothiazine
aldehyde and acetophenone in the presence of KOH. The chalcone
was combined with nitromethane in the presence of diethylamine
and then allowed to run under reflux conditions for 24 hours. This
yielded the nitro derivative, 1b. Compound 1b was reacted with
ammonium acetate and reaction proceeded as described above.
Chelation of compound 1c was achieved using the boron trifluoride
diethyl etherate to obtain 1d. Following chelation, an aldehyde
investigated compounds along with the reference pristine
azaBODIPY (the peripheral phenothiazine or ferrocene entities
were replaced by phenyl entities). The absorption bands of
pristine azaBODIPY were located at 484 and and 658 nm.
Scanning the wavelength beyond 700 nm revealed no absorbance
bands. In contrast, a new broad absorbance peak at higher
wavelengths was observed for the triads and tetrads. For 1d and
1, the new broad peak was located at 709 and 690 nm,
respectively, while the visible band of azaBODIPY core was
blue-shifted compared to pristine azaBODIPY and appeared at
602 and 610 nm. The characteristic peak of fulleropyrrolidine at
432 nm was also observed for the tetrad, 1. From a solvent
polarity study, the new broad near-IR peak was assigned to
charge transfer band (red-shif with increased solvent polarity).
2
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Similar observations were also made for compounds 2d and 2.
For triad 2d, the absorption bands were located at 464, 632 and
864 nm while for tetrad, 2 these peaks were located at 462, 620,
and 882 nm. The fulleropyrrolidine peak at 432 nm was also
observed for 2. These spectral trends were similar to that
observed for 1d and 1. In summary, strong charge transfer type
interactions leading to a new absorption band in the near-IR
region in the directly connected donor-acceptor systems is
witnessed. This is in contrast to the earlier reported donor-
acceptor systems with azaBODIPY[20] where due to distal
separation, no such such charge tranfer was witnessed.
the electronic communication between the two phenothiazine
entities as shown in Figure 3b.
That is, split oxidation
corresponding to phenothiazine located at 0.77 and 0.82 V were
observed. The splitting between these two peaks was around 50 mV.
The fullerene reductions in 1 appeared at -0.52 and -0.94, that is,
after the first reduction of azaBODIPY reduction located at -0.32 V
vs. Ag/AgCl. A similar trend in the redox chemistry of 2 and 2d
where two ferrocene entities were directly attached to the
azaBODIPY core was also observed. In the case of 2d, the split
ferrocene oxidations were located at 0.56 and 0.64 V, that is, an 80
mV potential separation was witnessed. The azaBODIPY oxidation
and reductions were located at 1.34 and -0.46 V, respectively
(Figure 3c). Covalent attachment of C60 at the boron center retained
the overall behavior in 2 (Figure 3d). That is, split oxidation with
peak positions located at 0.55 and 0.66 V and a third oxidation at
1.39 V corresponding to azaBODIPY were observed. On the
reduction side, azaBODIPY reduction at -0.46 and C60 reductions at
-0.54 and -0.96 V vs. Ag/AgCl were observed. Higher splitting in
2d/2 compared to 1d/1 indicated better ferrocene-ferrocene
interaction over phenothiazine-phenothiazine interaction via the
azaBODIPY -system in the investigated multi-modular systems.
Also, harder azaBODIPY reduction in 2 over 1 were noteworthy
observations. The electrochemical data is summarized in Table 1
below.
Figure 2. (a) Normalized absorption and (b) fluorescence spectra of the
indicated compounds in benzonitrile (see Figure 1 for structures). The
samples were excited at the most intense visible peak maxima.
As shown in Figure 2b, the fluorescence spectrum of
azaBODIPY revealed a peak at 682 nm. However, for the triads
and tetrads, no detectable fluoresence was observed (>98%
quenching). Such quenching behavior was also observed in
nonpolar toluene.
Figure 3. Differential pulse voltammograms of the indicated compounds in
benzonitrile containing 0.1 M (TBA)ClO4. The potentials are referenced to
Ag/AgCl. Scan rate = 5 mV/s, pulse width = 0.25 s, pulse height = 0.025 V.
The peak shown in asterisk corresponding to ferrocene used as internal
reference.
Electrochemical, spectroelectrochemical and computational
studies: First, electrochemical studies using cyclic and differential
pulse voltammetry were performed in benzonitrile. As reported
earlier, the first reversible oxidation and reduction processes of
azaBODIPY were located at 1.26 and -0.32 V vs. Ag/AgCl. For 1d
with two phenothiazine entities directly attached onto the
azaBODIPY -system, the first oxidation involving the
phenothiazine entities revealed split peaks located at 0.75 and 0.79
V (a 40 mV separation) instead of the anticipated a single two-
electron process involving the two phenothiazine entities (Figure 3a).
Such split suggests communication between the two redox active
phenothiazine entities via azaBODIPY -system.26 Larger the
magnitude of peak separation, higher is the interaction between
them. A third oxidation at 1.27 V vs. Ag/AgCl corresponding to
azaBODIPY oxidation was also observed. The two reductions of
azaBODIPY were located at -0.34 and -1.13 V vs. Ag/AgCl.
Appending C60 at the boron center of azaBODIPY did not perturb
Table 1. Redox Potentials (V vs. Ag/AgCl) of the investigated compounds in
deaerated PhCN containing 0.1 M (TBA)ClO4 (ADP = azaBODIPY; D =
phenothiazine or ferrocene))
Compound
C60•–/C60
--
ADP•–/ADP
–0.32
D•+/D
--
ADP•+/ADP
1.26
ADP
1d
1
--
-0.34
-0.32
-0.46
-0.46
0.75, 0.79
0.77, 0.83
0.56, 0.64
0.55, 0.66
1.27
1.28
1.34
1.39
-0.52
--
2d
2
-0.54
Next, spectroelectrochemical studies were performed to
spectrally characterize the first oxidized and reduced species of
compounds 1 and 2. Figure 4a and b, respectively, show the
spectral changes during the first oxidation and reduction of 1 in
benzonitrile containing 0.1 M (TBA)ClO4. During the first
oxidation, the peaks of neutral 1 located at 612 and 688 nm revealed
3
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10.1002/chem.201700200
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diminished intensity with the appearance of new peaks at 493, 598, linked donor (phenothiazine or ferrocene) or acceptor C60 sites was
and 780 nm. The shift of the charge transfer band from 688 nm to observed. The dihydroxyphenyl spacer group between the boron
780 nm is noteworthy. During the reduction, diminished intensity of center and fulleropyrrolidine assumed a perpendicular orientation
the peaks of neutral 1 was accompanied by new peaks at 473 and with respect to the plane of the azaBODIPY ring. The two donor
850 nm, corresponding mainly to the azaBODIPY ring reduction entities were facing away due to the nature of substitution on the
was observed. An isosbestic point at 530 nm was also observed. azaBODIPY ring causing no intramolecular type interactions
For 2 with directly attached ferrocene units, the peaks of the neutral between them. As discussed earlier, intramolecular interactions
compound located at 462, 620 and 878 nm revealed diminished between the two donor entities was observed through the
intensity with the appearance of new peaks at 642 and 906 nm azaBODIPY -system. The molecular electrostatic potential map
(Figure 4c). Isosbestic points at 482, 552, and 725 nm were (MEP map) for the tetrads is shown in Figures 5c and d revealed the
observed. During the first reduction of 2, disappearance of the expected electron rich (donor location) and deficient (azaBODIPY
peaks corresponding to the neutral compound was accompanied by a and C60 locations) sites. In summary, a very good agreement
broad peak in the 420 and 800-1000 nm range (Figure 4d). An between the optical, electrochemical and computed electronic
isosbestic point at 516 nm was also observed. These spectral data structures of the tetrads were observed.
help interpretation of the transient absorption spectral data discussed
in the next section.
Energy calculations: The energy of the charge-separated states (=
free-energy of charge recombination, GCR) were calculated using
the redox, geometric and optical data, according to Rehm-Weller
approach[28] and dielectric continuum model to account for the
solvation energy (see Table 2 footnote for pertinent equations). By
comparing these energy levels of the charge-separated states with
the energy levels of the excited singlet states of azaBODIPY or C60,
the driving forces of charge separation (-GCS) were also evaluated.
The data thus generated for the triads and tetrads is given are Table
•–
2 below. The generation of PTZ•+-ADP•–-C60 and PTZ•+-ADP-C60
•–
in 1, and Fc+-ADP•–-C60 and Fc+-ADP-C60 in 2 is found to be
exergonic either from the singlet excited state of azaBODIPY
(1azaBOPDY*) or the singlet excited state of C60 (1C60*). However,
1
the processes originating from the azaBODIPY* state were found
to be energetically much more favorable than the processes
originating from 1C60*.
Table 2. Free-energy for charge recombination (GCR) and charge
1
1
separation (GCS) from azaBOPDY* and C60* in the investigated
compounds (D = PTZ or ferrocene; ADP = azaBODIPY) in
benzonitrile.
a
b
GCR
D•+–ADP•-
GCS
D•+–ADP•-
Figure 4. Spectral changes observed during first (a) oxidation of 1, (b)
reduction of 1, (c) oxidation of 2, and (d) reduction of 2 in benzonitrile, 0.1
M (TBA)ClO4.
Compound
•-
•-
D•+–C60
--
D•+–C60
--
1d
1
-1.13
-1.13
-0.72c
-0.72c
-0.62d
-0.80c
-0.80c
-0.70d
-1.33
-0.52c
-0.41d
--
-0.72c
-0.62d
2d
2
1.05
1.06
--
1.10
a
-GCR = Eox – Ered + GS
-GCS = E00-(-GCR
(i)
(ii)
b
)
where E00 corresponds to the energy of 1azaBODIPY* (= 1.85 eV) and
1C60* (1.75 eV). The term GS refers to electrostatic energy calculated
according to dielectric continuum model (see equation iii). The Eox and Ered
represent the oxidation potential of the electron donor (PTZ or ferrocene)
and the reduction potential of the electron acceptor (azaBODIPY or C60),
respectively.
e2
1
1


1



 
1




GS 


GS =
 
R
 
(iii)




4 0
2R
2R
Figure 5. APFD/6-311G** (H, B, C, N, O, F) APFD/6-311G(df) (S, Fe)
optimized geometry (a and b) and molecular electrostatic potential map (c
and d) of 1 and 2.
RCCR
The symbols 0, and R represent vacuum permittivity and dielectric constant
of the solvent used for photochemical and electrochemical studies,
respectively. R+ and R- represent radii of the cation and anion, respectively.
Geometry optimizations using the APFD method and a mixed
basis of 6-311G** for H, B, C, N, O, and F atoms and 6-311G(df) RCC is the center-to-center distance between donor and acceptor entities of
for S and Fe atoms[27] on both the tetrads were performed. As
the dyad from the computed structures in Figure 5.
cfrom 1azaBODIPY*
shown in Figure 5a and b, no steric constraints either at the directly
4
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10.1002/chem.201700200
Chemistry - A European Journal
dfrom 1C60*
the case of 2 (see Figure 6b), the 3azaBODIPY* could undergo
triplet-triplet energy transfer to populate the Fc* prior returning to
3
Energy level diagrams were established to secure a complete
picture of the possible photophysical events in the studied
compounds. Figures S1a and S1b in the supporting information (SI)
illustrate energy level diagrams for 1d and 2d, respectively.
Formation of charge separated states, PTZ•+-azaBODIPY•– in 1d and
Fc+-azaBODIPY•– in 2d is thermodynamically possible upon
selective excitation of the azaBODIPY to its singlet excited state.
The energy of the charge separated state in both cases is slightly
the ground state. Systematic studies were performed in polar
benzonitrile and nonpolar toluene to unravel the mechanistic details
of these photochemical events.
Photodynamics probed by femtosecond transient
absorption spectroscopy: The photodynamics of the triads and
tetrads were examined in polar and nonpolar solvents by
femtosecond transient spectral measurements using 400 nm
excitation wavelength where azaBODIPY to a large extent and C60
to a lesser extent were excited. The transient spectra of pristine
azaBODIPY in benzonitrile and toluene are shown in Figure S2.
3
above that of azaBODIPY*. Under these conditions, the charge
3
separated state could populate the azaBODIPY* instead of direct
charge recombination to the ground state. Additionally, in the case
of 2d, the 3azaBODIPY* could undergo further triplet-triplet energy
The instantaneously formed azaBODIPY* revealed positive peaks
1
3
transfer to the low-lying Fc*,[29] from which the molecule could
at 542 and 1260 nm due to transitions originating from
return to the ground state via nonradiative decay path.
1azaBODIPY*.
A negative peak observed at 662 nm had
contributions from both the ground state bleaching and stimulated
emission. Similar observations were also made for azaBODIPY in
toluene. The recovery of negative peaks was relatively slow (see
Figure S2 right hand panel for time profiles) consistent with the
relatively longer lifetime of 1azaBODIPY* being 1.64 ns in
benzonitrile and 1.78 ns in toluene.
First, femtosecond transient spectral studies of the triads, 1d
and 2d were performed. As shown in Figures 7a and b, immediately
1
after excitation, the instantaneously formed azaBODIPY* revealed
the following spectral features. In benzonitrile, positive peaks with
maxima at 490 (sh) and 532 nm, and a broad negative peak centered
around 680 nm were observed. In toluene, the positive peak was
located at 523 nm, in addition, a broad peak at 1180 nm was
observed (see spectrum at delay time 1 ps). In addition, broad
negative peaks with minima at 640 and 720(sh) were observed. The
near-IR peak has been assigned to singlet-singlet transition
involving 1azaBODIPY* while the negative peak was attributed
mainly to the ground state bleaching of the visible and charge
transfer bands of 1d. Decay of the positive peaks and recovery of
the negative peaks resulted into the formation of new peak centered
985 nm in benzonitrile (see spectrum at 10 ps delay time), and 910
nm in toluene (see spectrum at 25 ps delay time). Supported by the
previously discussed spectroelectrochemical results, the spectrum at
these delay times have been attributed to the PTZ•+-azaBODIPY•–
charge separated state. With higher delay times, intensity of the
near-IR band started diminishing in intensity with new peaks at 581
and 613 nm in benzonitrile (see spectrum at 30 ps delay time), and
600 and 660 nm toluene (see spectrum at 200 ps delay time). These
Figure 6. Energy level diagram showing the different photochemical events
occurring in (a) 1 and (b) 2 in benzonitrile. Energies of different states were
evaluated from spectral and electrochemical studies. Solid arrows indicate
major photo-processes, dashed arrow indicates minor photo-process. EnT –
energy transfer, CS = charge separation, CR = charge recombination, and T
= emission from triplet excited state.
3
spectra have been attributed to azaBODIPY* formed during the
process of charge recombination (see Figure S1a in SI for energy
diagram). Nanosecond transient spectra were also recorded,
however, no detectable signal was observed. This suggests that the
decay of 3azaBODIPY* is faster than the detection limit of our
nanosecond setup being about 20 ns or signal being too weak.
The transient spectra of 2d is shown in Figures 7c and d,
respectively, in benzonitrile and toluene. The instantaneously
For the tetrads 1 and 2, a slightly more complicated energy
level diagrams were arrived, as shown in Figure 6a and b.
Formation of two types of charge separated states, viz., PTZ•+-
azaBODIPY•–-C60 and PTZ•+-azaBODIPY-C60•– in the case of 1, and
1
formed azaBODIPY* revealed a positive peak at 522 and a broad
•–
Fc+-azaBODIPY•–-C60 and Fc+-azaBODIPY-C60 in the case of 2
peak at 1230 nm, and negative peak at 630 nm in benzonitrile (see
spectrum at 20 ps delay time). In toluene, these positive peaks were
located at 523 nm and 1232 nm and the negative peak at 628 nm. In
addition to these spectral features, a broad negative signal in the
800-900 nm range where the charge transfer absorption of 2d was
observed (see Figure 2a). The positive peaks to transitions
originating from the singlet excited state and negative peak to
ground state bleaching of 2d were assigned. Decay of the positive
peaks and recovery of the negative peak revealed a weak, broad
peak at 1040 nm within 20 ps that has been attributed to the Fc+-
1
from the azaBODIPY* were energetically feasible. Additionally,
1
singlet-singlet energy transfer from azaBODIPY* to C60 within the
1
tetrad is also possible as the energy level of C60* is slightly below
that of 1azaBODIPY*. However, the spectral overlap between
azaBODIPY fluorescence and C60 absorption was poor.
Energetically, both charge separated states were slightly above that
3
of 3azaBODIPY* but not that of C60* (ET = 1.50 eV). Under such
conditions, the charge separated state could populate the
3azaBODIPY* prior returning to the ground state. Additionally, in
5
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10.1002/chem.201700200
Chemistry - A European Journal
azaBODIPY•– charge separated state. At higher delay times, a broad
peak in the 585 nm range in benzonitrile (see spectrum at 400 ps
delay time) and in the 600 nm range in toluene started to emerge,
Femtosecond transient spectral features of tetrads 1 and 2 in
the investigated solvents is shown in Figure 8. For 1 in benzonitrile,
decay of the instantaneously formed 1azaBODIPY* revealed
positive peaks at 545 and 1330 nm and negative peaks at 610 and
694 nm (Figure 8a). Signature peaks representing the charge
separated state were observed as early as 2 ps in this solvent with
peaks at 515, 920 and 1000 nm. While the 920 nm peak represented
3
attributable to the formation of azaBODIPY*. In summary, both
1d and 2d revealed transient spectral features corresponding to rapid
formation of D•+-azaBODIPY•– (D = phenothiazine or ferrocene)
charge separated state that subsequently relaxed to the ground state
via populating 3azaBODIPY*, as predicted by the energy diagram in
Figure S1a and b.
that of azaBODIPY•– (see Figure 4a and b), the 1000 nm peak that
•–
was absent in 1d was due to C60
. These results unambiguously
proved the formation of PTZ•+-azaBODIPY•–
•–
-C60 and PTZ•+-azaBODIPY-C60 charge
separated states in the case of 1. This was
also the case in toluene, however, clear
formation of the charge separated state was
seen at a delay time of 3 ps. With time the
signature peaks of the charge separated state
started disappearing with the appearance of
new peak in the 600-650 nm range
3
attributable to azaBODIPY* (see spectrum
at 10 ps in Figure 8a and 40 ps in Figure 8c).
For 2, peaks corresponding to the
charge separated state, Fc+-azaBODIPY•–-
•–
C60 and Fc+-azaBODIPY-C60 were visible
as early as 1 ps in benzonitrile and 4 ps in
toluene (Figures 8b and d). Subsequent
decay of the radical peaks populated the
3azaBODIPY* at higher delay times in both
solvents as witnessed by new peak in the 600
nm range, however, peak intensity of
3azaBODIPY* was relatively less compared
to that observed in 2d. This implies that the
3azaBODIPY* could undergo triplet-triplet
energy transfer to populated 3Fc* in the
Figure 7. Femtosecond transient spectra at the indicated delay times of 1d
(a and c) and 2d (b and d) in benzonitrile (a and b) and toluene (c and d).
tetrad. The 3Fc* thus formed is expected to nonradiatively decay to
the ground state, as shown in the energy level diagram in Figure 6b.
It may also be pointed out here that the
absence of transient peak in the 700 nm
3
range corresponding to C60* suggests lack
of population of this state as predicted from
the energy diagram.
The time constants for charge
separation observed here for the triads and
tetrads (few ps) are much lower than those
reported earlier for triad and tetrad featuring
some of these entities but having large
spacer groups connecting them.[20] The
close association of the donor and acceptor
entities in these multi-modular donor-
acceptor systems promoted excited state
charge separation. However, the charge
recombination was also found to efficient
even in the case of the tetrads featuring the
charge stabilizing fullerene entity(10-20 ps),
in part due to their close association and
populating the low-lying 3azaBODIPY*
which would promote faster charge
recombination process.
Figure 8. Femtosecond transient spectra at the indicated delay times of 1 (a
and c) and 2 (b and d) in benzonitrile (a and b) and toluene (c and d).
Conclusions
In summary, the new series of multi-modular donor-acceptor
systems designed and synthesized in the present study revealed
6
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10.1002/chem.201700200
Chemistry - A European Journal
Synthesis of 1b. 1a (2.6 g, 7.28 mmol) was dissolved in ethanol and
combined with nitromethane (4.44 g, 72.8 mmol) in the presence of
diethylamine (2.66g, 36.4 mmol) and then allowed to run under reflux for 24
hours. Reaction mixture was cooled on an ice bath and then acidified to yield
the nitro derivative compound 1b. In high concentration this compound
appeared to be a deep red, but investigation using TLC chromatography
showed a characteristic yellow color. Crude product was extracted with
DCM, washed the organic layer with water and then dried. The compound
was purified using silica gel column chromatography with 100% DCM.
Product was directly moved forward into ring close reaction.
several interesting results. These include: (i) Charge transfer
interactions between the directly attached donor entities to the
electron deficient azaBODIPY resulting in the formation of new
charge transfer bands spanning the visible and near-IR spectral
regions. (ii) The electronic communication between the two donor
via the azaBODIPY -system as witnessed by electrochemical
studies where splitting of the peak corresponding to the oxidation of
donor entity in both the triads and tetrads was observed. (iii)
Computational studies revealed no steric constraints in the polyads
even though the entities were spatially close. (iv) The reversible
Synthesis of 1c. 1b (3.18g, 8.58 mmol) was dissolved in ethanol.
Ammonium acetate (22.9g, 297.5 mmol) was then added and allowed to
reflux 24 hours. After 1-2 hours a significant color change was observed,
reaction was monitored via TLC chromatography and allowed to go until
completion. Crude product was extracted with DCM, washed the organic
layer with water and dried. The compound was purified using silica gel
oxidation
and
reduction
was
further
supported
by
spectroelectrochemical studies where new peaks for the oxidized
and reduced species were witnessed. (v) The established energy
level diagrams revealed the feasibility of excited state charge
transfer from the singlet excited azaBODIPY in the triads and
tetrads. (vi) Occurrence of excited state charge transfer was proved
by studies involving femtosecond transient spectroscopy. Owing to
the close association of the donor and acceptor entities, the time
constants for charge separation were few ps thus establishing
ultrafast charge transfer process. (vii) Finally, the charge separated
state relaxed to ground state by populating the triplet excited states
of 3azaBODIPY* (and 3Fc* in the case of 2d and 2 via triplet-triplet
energy transfer). The present study brings out the importance
strongly coupled donor-acceptor systems in governing ultrafast
photophysical events applicable towards building new generation of
optoelectronic devices.
1
column chromatography at a 45:5 DCM:Hexanes ratio. H NMR; (400 MHz,
CDCl3) δ = 8.18 (2H, t), 7.85 (2H, d), 7.8 (2H, m), 7.7 (1H, d), 7.5 (5H, m),
7.4 (4H, m), 7.0 (4H, m) 6.92 (2H, m), 6.8 (2H, m), 6.75 (2H, m), 3.8 (4H, m),
1.3 (6H, m).
Synthesis of 1d. Chelation was achieved by dissolving 1c (0.500 g, 0.669
mmol) in dry dichloromethane, followed by purging with nitrogen for 10
minutes. Diisopropylethylamine (1.33 g, 10.3 mmol) and boron trifluoride
diethyl etherate (2.553 g, 17.98 mmol) were added and mixture was allowed
to react for 24 hours yielding compound 1d. A color change was observed
between compound 1c and 1d, and after purification using silica gel column
chromatography at a 45:5 DCM: Hexanes, a metallic red sheen was observed
1
(yield 60%). H NMR (400 MHz, CDCl3) δ = 7.98 (4H, m), 7.92 (2H, M),
7.85 (2H, d), 7.45 (6H, t), 7.15 (2H, m), 7.06 (2H, d), 7.0 (2H, d), 6.9 (4H, m),
6.85, (2H, m), 4.0 (4H, m), 1.35 (6H, t). UV-Vis (benzonitrile) λmax (nm):
317.6, 624.9. HR-MS (MALDI – no matrix): m/z calc’d for C48H36BF2N5S2 =
795.2473 found = 795.5, 767.7 (M - C2H4), 738.6 (M – (C2H4)2).
Experimental Section
Chemicals. Buckminsterfullerene, C60 (+99.95%) was from SES Research,
(Houston, TX). All the reagents were from Aldrich Chemicals (Milwaukee,
WI) while the bulk solvents utilized in the syntheses were from Fischer
Chemicals. The tetra-n-butylammonium perchlorate (TBA)ClO4 used in
electrochemical studies was from Fluka Chemicals.
Synthesis of 1e. Aldehyde was obtained by dissolving 1d (0.159 g, 0.2 mmol)
in dry dichloromethane, followed by purging for 10 minutes with nitrogen.
Aluminum chloride (0.134 g, 1.01 mmol) was then added to the flask, and
after observing a significant color change 3,4-dihydroxybenzaldehyde (0.138
g, 1.01 mmol) was added. Reaction was monitored using TLC
chromatography and after thirty minutes was purified directly using first an
alumina column (45:5 DCM:Ethyl acetate), followed by silica gel column
chromatography in 100% DCM (68% yield). 1H NMR; (400 MHz, CDCl3) δ
= 9.5 (1H, s), 7.96 (1H, d), 7.94 (1H, d) 7.88 (2H, d), 7.20 (3H, m), 7.15 (2H,
t), 7.04 (4H, m), 6.9 (12H, m), 6.64 (2H, s), 6.5 (1H, d), 6.02 (1H, d).
Syntheses of triads and tetrads
Synthesis of 1a. First, N-ethylphenothiazine was synthesized according to
the following method. Phenothiazine (5g, 25 mmol) was dissolved in DMF
and cooled to 0 oC. NaH (1.8g, 75 mmol) and bromoethane (8.2 g, 75 mmol)
were added and allowed to react at room temperature overnight. Reaction
was quenched with ice, extracted with DCM, and purified via silica gel
Synthesis of 1. 1e (0.31 g, 0.35 mmol), C60 (0.400 g, 0.7 mmol), and
sarcosine(0.155 g, 1.75 mmol) were combined and dissolved in toluene.
Reaction was allowed to proceed at room temperature overnight. Crude
product was evaporated via rotary evaporation and was directly purified using
silica gel column chromatography, which was first flushed with toluene, then
product came with 100% DCM (20% yield). 1H NMR δ = 7.90 (2H, m), 7.82
(2H, m), 7.62 (1H, m), 7.46 (1H, m), 6.95 (6H, m), 6.8 (6H, t), 6.6 (2H, d),
4.9 (2H, d), 4.8 (1H, d), 4.12 (2H, m), 3.9 (4H, q), 2.48 (3H, s), 1.35 (6H, m);
UV-Vis (benzonitrile) λmax (nm): 325.2, 610.7. 13C NMR (500 Mhz, CDCl3) δ
=167.678, 132.469, 130.868, 129.160, 129.054, 128.811, 128.257, 128.045,
127.719, 127.590, 127.461, 127.301, 126.952, 125.328, 124.038, 123.439,
122.938, 147.304, 146.317, 146.204, 146.158, 146.037, 145.946, 145.323,
144.565, 144.345, 143.601, 143.138, 143.062, 142.948, 142.675, 142.455,
142.212, 142.121, 141.681, 141.507, 140.118, 140.042, 139.807, 139.769,
139.594, 115.221, 115.198, 68.121, 42.366, 38.785, 32.024, 30.430, 30.331,
30.142, 30.013, 29.808, 29.557, 29.474, 29.186, 29.003, 23.828, 23.100,
23.024, 22.819, 21.514, 14.214, 14.138, 13.114, 11.035. HR-MS (MALDI –
no matrix): m/z calc’d for C117H45BFN6O2S2 = 1640.3138 (M), found 921.5
(M-C60), 893.5 (M - C60+2(CH2CH3)].
1
column chromatography at a 2:3 DCM:Hexanes ratio. H NMR; (400 MHz,
CDCl3) δ = 7.12 (4H, d), 6.85 (3H, s), 1.42 (3H, t). UV-Vis (benzonitrile)
λmax (nm): 312.8.
Next, formylation of N-ethylphenothiazine was achieved by adding POCl3
(13.8g, 90 mmol) dropwise to DMF (6.58 g, 90 mmol) at 0 C until a glassy
solid appeared. Solid dissolved in DCM, and stirred for one hour. N-
ethylphenothiazine (4.1g, 18 mmol) was then dissolved in DCM and added to
mixture which was then allowed to react overnight at 90 oC. Product was
o
1
purified via silica gel column chromatography in 100% DCM. H-NMR (400
MHz, CDCl3) δ = 9.79 (1H, s), 7.62 (1H, q), 7.55 (1H, d), 7.14 (1H, m), 7.1
(1H, m), 6.94 (1H, m), 6.9 (2H, m), 4.0 (2H, q), 1.4 (3H, t).
Finally, for the synthesis of 1a, acetophenone (1.53 g, 12.77 mmol), N-
ethylphenothiazine aldehyde (3.257g, 12.77 mmol), and KOH (1.21 g, 25.55
mmol) were dissolved in 85/15 v/v ethanol/water mixture. Mixture was
allowed to react at room temperature for 48 hours, then cooled on an ice bath
and acidified to precipitate product (1a). Crude mixture was filtered yielding
a yellow solid which was purified via silica gel column chromatography at a
45:5 DCM to Hexanes ratio (57% yield). 1H-NMR (400 MHz, CDCl3) δ = 8.0
(2H, d), 7.7 (1H, d), 7.55 (1H, m), 7.50 (2H, m), 7.45 (2H, s), 7.43 (1H, m),
7.1 (2H, m), 6.9 (1H, t), 6.85 (2H, t), 3.9 (3H, q), 1.35 (3H, t).
Synthesis
of
2a.
Acetophenone
(1.39g,
11.6
mmol)
and
ferrocenecarboxaldehyde (2.5 g, 11.6 mmol) were ground in the presence of
NaOH (0.64 g, 16.24 mmol). The mixture was initially a liquid, and began to
thicken until solidifying over the course of fifteen minutes. After solidifying
7
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10.1002/chem.201700200
Chemistry - A European Journal
grinding continued for an additional five minutes. The solid was dissolved in (MALDI – no matrix): m/z calc’d for C109H39BFe2N4O2 = 1558.1895 found
DCM and then washed with water. The organic layer was then evaporated 1558.6 (M), 839.4 (M-C60), 837.4 (M-(C60+2H).
using rotary evaporation and resultant dark red solid was purified via silica
Instruments: The UV-visible spectral measurements were carried out
gel column chromatography using 45:5 DCM:hexanes ratio (66% yield). 1H
with
a
Shimadzu Model 2550 double monochromator UV-visible
NMR (400 MHz, CDCl3) δ = 7.90 (2H, m), 7.72 (1H, d), 7.50 (1H, m), 7.44
(2H, m), 7.08 (1H, d), 4.54 (2H, m), 4.42 (2H, m), 4.11 (5H, s).
spectrophotometer. The fluorescence emission was monitored by using a
Horiba Yvon Nanolog coupled with time-correlated single photon counting
Synthesis of 2b. 2a (3.9 g, 12 mmol) was dissolved in ethanol and combined with nanoLED excitation sources. A right angle detection method was used.
with nitromethane (14g, 240 mmol) in the presence KOH (0.13g, 2.4 mmol) The NMR spectra were recorded in CDCl3 on Bruker 500 MHz instrument.
and then allowed to run under reflux for 24 hours. This yielded the nitro Tetramethylsilane [Si(CH3)4] was used as an internal standard. All samples
derivative compound 2b (56% yield). In high concentration this compound were prepared in CDCl3 and chemical shifts were referenced to CHCl3 at 7.26
appeared to be a deep red, but investigation using TLC chromatography ppm for 1H NMR and referenced to the CDCl3 at 77.0 ppm for 13C NMR.
showed a characteristic yellow color when developed in 100% DCM. Crude
Differential pulse and cyclic voltammograms were recorded on an EG&G
product was extracted with DCM and washed with water and dried, and
PARSTAT electrochemical analyzer using a three electrode system. A
purified using silica gel column chromatography, dark orange spot came off
platinum button electrode was used as the working electrode. A platinum
the column as a yellow color with 100% DCM. Purified product was directly
wire served as the counter electrode and an Ag/AgCl electrode was used as
moved forward into ring close reaction.
the reference electrode. Ferrocene/ferrocenium redox couple was used as an
Synthesis of 2c. 2b (2.5g, 6.82 mmol) was dissolved in ethanol. Ammonium internal standard. All the solutions were purged prior to electrochemical and
acetate (18.5g, 238.6 mmol) was then added and allowed to reflux for 24 spectral measurements using argon gas.
hours. After 1-2 hours a significant color change was observed, reaction was
Spectroelectrochemical studies were performed by using a cell assembly
monitored via TLC chromatography and allowed to go until completion.
(SEC-C) supplied by ALS Co., Ltd (Tokyo, Japan). This assembly comprised
Crude product was extracted with DCM, washed with water and dried,
of a Pt counter electrode, a 6 mm x 6 mm Pt gauze working electrode, and an
Ag/AgCl reference electrode in a 1.0 mm path length quartz cell. The optical
purified using silica gel column chromatography, 40:10 DCM: Hexanes ratio.
1H NMR (400 MHz, CDCl3) δ = 7.98 (4H, m), 7.89 (2H, s), 7.46 (6H, m),
transmission was limited to 6 mm X 6 mm covering the Pt gauze working
electrode.
5.18 (4H, m), 4.48 (4h, m), 4.12 (10H, s).
Synthesis of 2d. Chelation was achieved by dissolving 1c (0.500 g, .739
mmol) in dry dichloromethane, followed by purging with nitrogen for 10
The computational calculations were performed with the use of
GAUSSIAN 09 software package[27]
.
minutes. Diisopropylethylamine (1.33 g, 10.3 mmol) and boron trifluoride
diethyl etherate (2.553 g, 17.98 mmol) were added and mixture was allowed
to react for 24 hours yielding compound 1d. A color change was observed
between compound 1c and 1d, and after purification via silica gel column
chromatography, 40:10 DCM: Hexanes ratio a metallic red sheen was
Femtosecond pump-probe transient spectroscopy. Femtosecond transient
absorption spectroscopy experiments were performed using an Ultrafast
Femtosecond Laser Source (Libra) by Coherent incorporating diode-pumped,
mode locked Ti:Sapphire laser (Vitesse) and diode-pumped intra cavity
doubled Nd:YLF laser (Evolution) to generate a compressed laser output of
1.45 W. For optical detection, a Helios transient absorption spectrometer
coupled with femtosecond harmonics generator both provided by Ultrafast
Systems LLC was used. The source for the pump and probe pulses were
derived from the fundamental output of Libra (Compressed output 1.45 W,
pulse width 100 fs) at a repetition rate of 1 kHz. 95% of the fundamental
output of the laser was introduced into harmonic generator, which produces
second and third harmonics of 400 and 267 nm besides the fundamental 800
nm for excitation, while the rest of the output was used for generation of
white light continuum. In the present study, the second harmonic 400 nm
excitation pump was used in all the experiments. Kinetic traces at appropriate
wavelengths were assembled from the time-resolved spectral data. Data
analysis was performed using Surface Xplorer software supplied by Ultrafast
Systems. All measurements were conducted in degassed solutions at 298 K.
1
observed (yield 70%). H NMR (500 MHz, CDCl3) δ = 8.12 (4H, m), 7.45
(6H, m), 6.79 (2H, s), 5.24 (4H, m), 4.74 (4H, m), 4.22 (10H, s). UV-Vis
(benzonitrile) λmax nm: 308.8, 635.2, 892.8. 13C NMR (500 MHz, CDCl3) δ
=157.54, 146.727, 132.112, 130.261, 129.236, 128.455, 116.260, 77.462,
77.303, 77.052, 76.794, 73.698, 72.788, 70.397, 53.475.HR-MS (MALDI –
no matrix): m/z calc’d for C40H30BF2Fe2N3 = 713.1120 found 713.3 (M),
508.7 (M-{2(C6H5)+BF2).
Synthesis of 2e. Aldehyde was obtained by dissolving 2d (0.369 g,
0.51mmol) in dry dichloromethane, followed by purging for 10 minutes with
nitrogen. Aluminum chloride (0.337 g, 2.53 mmol) was then added to the
flask, and after observing
a
significant color change 3,4-
dihydroxybenzaldehyde (0.349 g, 2.53 mmol) was added. Reaction was
monitored using TLC chromatography and after thirty minutes was purified
directly using first a neutral alumina column (45:5 DCM:Ethyl Acetate ratio),
1
followed by silica gel column chromatography (100% DCM). H NMR (68%
yield); (500 MHz, CDCl3) δ = 9.45 (1H, s), 7.16 (4H, m), 6.89 (2H, m), 6.82
(5H, m), 6.44 (1H, d), 6.38 (2H, s), 6.02 (1H, d), 5.2 (4H, d), 4.85 (4H, s),
4.20 (10H, s).
Acknowledgments
Support by the National Science Foundation (grant no. 1401188 to FD) is
acknowledged. The computational work was performed at the Holland
Computing Centre of the University of Nebraska.
Synthesis of 2: 2e (0.31 g, 0.35 mmol), fullerene (0.400 g, 0.7 mmol), and
sarcosine (0.155 g, 1.75 mmol) were combined and then dissolved in toluene.
Reaction was allowed to proceed at room temperature overnight. Crude
product was evaporated via rotary evaporation and was directly purified using
silica gel column chromatography, which was first flushed with toluene, then
product came with 100% DCM. Yield was 90.1%. 1H-NMR δ =7.36 (1H, s),
6.425 (1H,s), 6.435 (1H,s), 5.23 (4H, t), 5.21(2H, s) 4.88 (2H, d) 4.73 (4H, t),
4.53 (1H,s), 4.23 (10H, s), 4.11 (2H, d), 2.45 (3H, s) ; 13C-NMR (500 MHz,
CDCl3) δ = 227.427, 223.535, 220.962, 216.356, 211.985, 206.795, 204.450,
200.596, 192.628, 189.122, 184.220, 179.887, 177.558, 174.925, 171.146,
166.737, 162.601, 159.513, 154.495, 150.650, 145.384, 142.789, 140.269,
137.097, 130.693, 127.612, 123.697, 118.233, 115.775, 112.626, 109.575,
106.882, 101.342, 98.276, 93.845, 90.202, 84.739, 81.430, 76.953, 71.604,
67.741, 65.366, 60.601, 56.852, 54.212, 50.971, 48.596, 42.943, 39.217,
30.354, 27.349, 24.466, 18.851, 14.669, 11.528, 5.222, 1.14. HR-MS
[1] a) Functional Materials for Sustainable Energy Applications, Eds. J. A. Kilner, S.
J. Skinner, S. J. C. Irvine, P. P. Edwards, 2012, Woodhead Publishing Ltd. b)
Materials in Energy Conversion, Harvesting, and Storage, Ed. K. Lu, Wiley, 2014.
c) Energy Harvesting Materials (Ed.: D. L. Andrews), World Scientific,
Singapore. 2005; d) S. Gunes, H. Neugebauer, N. S. Sariciftci, Chem. Rev. 2007,
107, 1324; e) H. Imahori, T. Umeyama, S. Ito, Acc. Chem. Res. 2009, 42,1809; f)
N. Armaroli, V. Balzani, Angew. Chem. 2007, 119, 52; Angew. Chem. Int. Ed.
2007, 46, 52. g) S. Fukuzumi, in Functional Organic Materials, Eds.: T. J. J.
Müller U. H. F. Bunz, Wiley-VCH. 2007, pp. 465–510.
[2] a) N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15729;
b) P. V. Kamat, J. Phys. Chem. C 2007, 111, 2834.
[3] a) J. Deisenhofer, O. Epp, K. Miki, R. Huber, H. Michel, J. Mol. Biol. 1984, 180,
385; b) The Photosynthetic Reaction Center (Eds.: J. Deisenhofer, J. R. Norris),
Academic Press, San Diego, CA. 1993; c) C. Kirmaier, D. Holton in The
Photosynthetic Reaction Center, Vol II (Eds.: J. Deisenhofer, J. R. Norris),
Academic Press, San Diego, CA, 1993, pp 49-70.
8
This article is protected by copyright. All rights reserved.

10.1002/chem.201700200
Chemistry - A European Journal
[4] a) D. Gust, T. A. Moore, A. L. Moore, Faraday Discuss. 2012, 155, 9; b) S. D.
Straight, G. Kodis, Y. Terazono, M. Hambourger, T. A. Moore, A. L. Moore, D.
Gust, Nature Nanotechnol. 2008, 3, 280. c) D. Gust, T. A. Moore, A. L. Moore,
Acc. Chem. Res. 2009, 42, 1890;
[23] a) V. Bandi, F. P. D’Souza, H. B. Gobeze, F. D’Souza, Chem. Eur. J. 2015, 21,
2669. b) V. Bandi, F. P. D’Souza, H. B. Gobeze, F. D’Souza, Chem. Commun.
2016, 52, 579.
[24] V. Bandi, M. E. El-Khouly, V. N. Nesterov, P. A. Karr, S. Fukuzumi, F.
D’Souza, J. Phys. Chem. C 2013, 117, 5638.
[5] a) M. R. Wasielewski, Acc. Chem. Res. 2009, 42, 1910; d) V. L. Gunderson, S. M.
Conron, M. R. Wasielewski, Chem. Commun. 2010, 46, 401; e) M. T. Vagnini,
A. L. Smeigh, J. D. Blakemore, S. W. Eaton, N. D. Schley, F. D’Souza, R. H.
Carbtree, G. W. Brudvig, D. T. Co, M. R. Wasielewski, Proc. Natl. Acad. Sci.
2012, 109, 15651.
[25] V. Bandi, H. B. Gobeze, F. D’Souza, Chem. Eur. J. 2015, 21, 11483.
[26] a) C. J. Ziegler, K. Chanawanno, A. Hasheminsasab, Y. Zatsikha, E. Maligaspe,
V. N. Nemykin, Inorg. Chem. 2014, 53, 4751. b) E. Maligaspe, T. J. Pundsack, L.
M. Albert, Y. V. Zatsikha, P. V. Solntsev, D. A. Blank, V. N. Nemykin, Inorg.
Chem. 2015, 54, 4167. C) N. Balsukuri, S. Mori, I. Gupta, J. Porphyrins
Phthalocyanines, 2016, 20, 719. d) N. Balsukuri, N. Y. Lone, P. C. Jha, S. Mori,
I. Gupta, Chem. Asian J. 2016, 11, 1572.
[6] a) D. M. Guldi, Chem. Commun. 2011, 47, 606; b) D. M. Guldi, A. Rahman, V.
Sgobba, C. Ehli, Chem. Soc. Rev. 2006, 35, 471; c) G. Bottari, G. de la Torre, D.
M. Guldi, T. Torres, Chem. Rev. 2010, 110, 6768; d) N. Martin, L. Sanchez, M.
A. Herranz, B. Illesca, D. M. Guldi, Acc. Chem. Res. 2007, 40, 1015; e) J. N.
Clifford, G. Accorsi, F. Cardinali, J. F. Nierengarten, N. Armaroli, C. R. Chemie.
2006, 9, 1005; f) E. M. Pérez, N. Martín, Chem. Soc. Rev. 2008, 37, 1512.
[27] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H.
Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G.
Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.
A. Montgomery, Jr, J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N.
Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J.
Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B.
Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian 09, Revision B.01,
Gaussian, Inc, Wallingford CT. 2010.
[7] a) S. Fukuzumi, Org. Biomol. Chem. 2003, 1, 609; b) S. Fukuzumi, Bull. Chem.
Soc. Jpn. 2006, 79, 177; c) S. Fukuzumi, Phys. Chem. Chem. Phys. 2008, 10,
2283; d) S. Fukuzumi, T. Kojima, J. Mater. Chem. 2008, 18, 1427; e) H. Imahori,
S. Fukuzumi, Adv. Funct. Mater. 2004, 14, 525; f) S. Fukuzumi, Pure Appl.
Chem. 2007, 79, 981; h) S. Fukuzumi, K. Ohkubo, J. Mater. Chem.
2012, 22, 4575; i) S. Fukuzumi, K. Ohkubo, F. D'Souza J. L. Sessler, Chem.
Commun. 2012, 48, 9801.
[8] M. E. El-Khouly, S. Fukuzumi, F. D’Souza, ChemPhysChem 2014, 15, 30.
[9] a) F. D’Souza, O. Ito, Chem. Commun. 2009, 4913; b) F. D'Souza, O. Ito, Chem.
Soc. Rev. 2012, 41, 86; c) F. D’Souza, O. Ito, Coord. Chem. Rev. 2005, 249,
1410; d) M. E. El-Khouly, O. Ito, P. M. Smith, F. D’Souza, J. Photochem.
Photobiol. C. 2004, 5, 79; e) R. Chitta, F. D’Souza, J. Mater. Chem. 2008, 18,
1440; f) O. Ito, F. D’Souza, Molecules. 2012, 17, 5816. g) C. B. KC, F. D’Souza,
Coord. Chem. Rev. 2016, 322, 104.
[28] D. Rehm, A. Weller, Isr. J. Chem., 1970, 8, 259-271.
[29] Y. Araki, R. Chitta, A. S. D. Sandanayaka, K. Langenwaler, S. Gadde, M. E.
Zandler, O. Ito, F. D’Souza, J. Phys. Chem. C 2008, 112, 2222.
[10] a) Introduction of Molecular Electronics Eds. M. C. Petty, M. R. Bryce, D. Bloor,
Oxford University Press, New York. 1995; b) Molecular Switches, B. L. Feringa,
Ed, Wiley-VCH GmbH, Weinheim, 2001.
[11] Y. Ge and D. F. O’Shea, Chem. Soc. Rev. 2016, 45, 3846.
Received: ((will be filled in by the editorial staff))
Revised: ((will be filled in by the editorial staff))
Published online: ((will be filled in by the editorial staff))
[12] a) A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891; b) G. Ulrich, R. Ziessel,
A. Harriman, Angew. Chem, Int. Ed. 2007, 46, 2.
[13] a) R. Gresser, M. Hummert, H. Hartmann, K. Leo, M. Riede, Chem. Eur. J. 2011,
17, 2939; b) H. Lu, S. Shimizu, J. Mack, Z. Shen, N. Kobayashi, Chem. Asian J.
2011, 6, 1026; c) X. Zhang, H. Yu, Y. Xiao, J. Org. Chem. 2012, 77, 669.
[14] a) J. Killoran, D. F. O’Shea, Chem. Commun., 2006, 1503. b) M. J. Hall, L. T.
Allen, D. F. O’Shea, Org. Biomol. Chem., 2006, 4, 776. c) H. Li, P. Zhang, L. P.
Smaga, R. A. Hoffman, J. Chan, J. Am. Chem. Soc., 2015, 137, 15628. d) A.
Dvivedi, S. Kumar, M. Ravikanth, Sens. Actuators, B, 2016, 224, 364. e) W.-J.
Shi, R. Menting, E. A. Ermilov, P.-C. Lo, B. Roeder, D. K. P. Ng, Chem.
Commun., 2013, 49, 5277.
[15] a) B. Cheng, V. Bandi, M.-Y. Wei, Y. Pei, F. D’Souza, K. T. Nguyen, Y. Hong,
B. Yuan, PLoS ONE, 2016, 11, e0165963. b) J. Kandukuri, S. Yu, B. Cheng, V.
Bandi, F. D'Souza, K.T. Nguyen, Y. Hong, B. Yuan, IJMS, 2017, in press. c) B.
Cheng, V. Bandi, S. Yu, F. D’Souza, K. T. Nguyen, Y. Hong, L. Tang, and B.
Yuan, IJMS, 2017, in press.
[16] A. N. Amin, M. E. El-Khouly, N. K. Subbaiyan, M. E. Zandler, M. Supur, S.
Fukuzumi, F. D’Souza, J. Phys. Chem. A. 2011, 115, 9810.
[17] A. N. Amin, M. E. El-Khouly, N. K. Subbaiyan, M. E. Zandler, S. Fukuzumi, F.
D’Souza, Chem. Commun. 2012, 48, 206.
[18] a) M. E. El-Khouly, A. N. Amin, N. K. Subbaiyan, M. E. Zandler, S. Fukuzumi,
F. D’Souza, Chem. Eur. J. 2012, 18, 5239; b) Y. Kotaoka, Y. Shibata, H.
Tamiaki, Chem. Lett. 2010, 39, 953. c) S. Kumer, H. B. Gobeze, T. Chatterjee, F.
D’Souza, M. Ravikanth, J. Phys. Chem. A 2015, 119, 8338.
[19] a) F. D’Souza, A. N. Amin, M. E. El-Khouly, N. K. Subbaiyan, M. E. Zandler, S.
Fukuzumi, J. Am. Chem. Soc. 2012, 134, 654. b) V. Bandi, K. Ohkubo, S.
Fukuzumi, F. D’Souza, Chem. Commun. 2013, 49, 2867.
[20] a) V. Bandi, M. E. El-Khouly, K. Ohkubo, V. N. Nesterov, M. E. Zandler, S.
Fukuzumi, F. D’Souza, J. Phys. Chem. C. 2014, 118, 2321. b) V. Bandi, M. E.
El-Khouly, K. Ohkubo, V. N. Nesterov, M. E. Zandler, S. Fukuzumi, F. D’Souza,
Chem. Eur. J. 2013, 19, 7221. D) V. Bandi, H. B. Gobeze, V. N. Nesterov, P. A.
Karr, F. D’Souza, Phys. Chem. Chem. Phys. 2014, 16, 25537.
[21] H. B. Gobeze, V. Bandi, F. D’Souza, Chem. Phys. Chem. Phys. 2014, 16, 18720.
[22] V. Bandi, H. B. Gobeze, P. A. Karr, F. D’Souza, J. Phys. Chem. C 2014, 118,
18969.
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10.1002/chem.201700200
Chemistry - A European Journal
Intramolecular Charge Transfer
Close encounters of the charge
transfer kind: Directly connected
supramolecular triads and tetrads
Directly Attached Bisdonor-BF2
Chelated Azadipyrromethene-
Fullerene Tetrads for Promoting
Ground and Excited State Charge
Transfer
featuring
bisphenothiazine
or
bisferrocene, azaBODIPY, and C60 have
been newly synthesized to demonstrate
ground and excited state intramolecular
charge transfer.
M. A. Collini, M. B. Thomas, V. Bandi, P. A.
Karr, and F. D’Souza*
10
This article is protected by copyright. All rights reserved.