Synthesis, the electronic properties and efficient photoinduced electron transfer of new pyrrolidine[60]fullerene- and isoxazoline[60]fullerene-BODIPY dyads: Nitrile oxide cycloaddition under mild conditions using PIFA

Article abstract of DOI:10.1039/c7nj02057k

Two new BODIPY-C₆₀ dyads, with a pyrrolidine linker (BDP-Pyr) and an isoxazoline linker (BDP-Is) between the two electroactive units, have been synthesized and characterized. Their photophysical and electrochemical properties have been studied

Full text of DOI:10.1039/c7nj02057k

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Synthesis, Electronic Properties and Efficient Photoinduced Electron Transfer
of New Pyrrolidine[60]fullereneꢀ and Isoxazoline[60]fullereneꢀBODIPY dyads:
Nitrile oxide cycloaddition under mild conditions by PIFA
Andrea CabreraꢀEspinoza,1,2 Braulio Insuasty, 1,2 Alejandro Ortiz*1,2
1 Heterocyclic Compounds Research Group, Department of Chemistry, Universidad del Valle,
A.A. 25360, Cali, Colombia
2 Center for Research and Innovation in Bioinformatics and PhotonicsꢀCIBioFi, Calle 13 No.
100ꢀ00, Edificio 320, No. 1069, Cali, Colombia
Abstract
Two new BODIPYꢀC60 dyads, with a pyrrolidine linker (BDPꢀPyr) and an isoxazoline linker
(BDPꢀIs) between the two electroactive units, have been synthesized and characterized. Their
photophysical and electrochemical properties have been studied in solution by comparison with
the reference compound BDP and [60]fullerene. Both BODIPYꢀC60 derivatives strongly absorb
visible light and by photoexcitation at the BDP unit, these dyads undergo photoinduced electron
transfer affording the corresponding chargeꢀseparated species. Based on their redox potentials,
also the direction of the charge transference are revealed and a comparison between the dyads
with respect to C60 suggested that the new BDPꢀIs derivative showed a better electron affinity
that BDPꢀPyr and C60. In addition, the experimental studies were complemented by a theoretical
analysis based on semiempirical computations which allowed confirm of the charge transfer
mechanism from the BDP core to the C60 cages.
Keyword: BODIPY, fullerene, electron transfer, acceptor, donor
1. Introduction
Photosynthesis and its ability to harvest solar light and to transform it into useful chemical energy
have been the main inspiration source for the development of new artificial photosynthetic
systems. In this regard, a significant synthetic work has been devoted to create artificial antennas
and electron donorꢀacceptor (DꢀA) architectures that can easily promote lightꢀinduced electron
transfer from a donor to an acceptor unit.1,2
In the development of these photosynthetic models, tetrapyrroles such as porphyrin3 and
phthalocyanine4 have been commonly employed as donors due to their close resemblance to the
natural chlorophyll pigment. Recently, derivatives of BF2ꢀchelates of dipyrromethenes, also
known as BODIPY, have attracted notable attention due to their unique and extraordinary
properties, which make these chromophores very useful buildingꢀblock for photosynthetic
antennas and charge separation units.5,6
On the other hand, [60]fullerene has been often chosen as an ideal acceptor. Indeed, its ability to
reversibly accept up to six electron and its exceptionally low reorganization energy enable the
achievement of long lasting charge separation states.7,8

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Despite different BODIPY−C60 dyads have been reported,9–12 many of them feature a reduced
electron affinity, with respect to pristine fullerene, as a consequence of the saturation of a double
bond during the C60 functionalization13 In order to overcome this problem, we envisaged the
introduction of electronegative atoms linked to the C60 core as a suitable alternative for the
preparation of BODIPYꢀC60 with unaltered electron acceptor ability.14
Herein, we report the synthesis of two new simple dyads based on BODIPYꢀC60 systems with
two different linking bridges to the fullerene cage (Fig. 1). In case of dyad BDPꢀPyr, a
pyrrolidine ring was used whereas an isoxazoline ring was incorporated in BDPꢀIs. Furthermore,
the photophysical and electrochemical characterization of both dyads have been carried out in
order to shed light on the effect of isoxazoline/pyrrolidine dyads linkers on the electronic
properties. BDP derivative, synthesized following a published procedure,15 was used for
comparison.
Fig. 1. Structures of BODIPYꢀC60 dyads BDPꢀPyr and BDPꢀIs and the reference compounds BDP.

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2. Results and discussion
2.1. Synthesis and characterization of the dyads
Scheme 1. Synthesis of the dyads BDPꢀPyr and BDPꢀIs.
The synthetic route for the preparation of BDPꢀPyr and BDPꢀIs is depicted in Scheme 1 and the
details are given in the Experimental Section. The dyads were obtained from the 4,4ꢀDifluoroꢀ8ꢀ
(4’ꢀformylphenyl)ꢀ1,3,5,7ꢀtetramethylꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene derivative 1 synthesized
using the same conditions reported in the literature.16 The BDPꢀPyr dyad was prepared by simple
treatment of 1 with C60 and Nꢀoctylglycine according to the Prato procedure.17
The synthesis of the dyad BDPꢀIs started with the synthesis of the aldoxime 2 by reaction of 1
with hydroxylamine hydrochloride under mild basic conditions in EtOH/H2O. Nonetheless, any
attempts to prepare the fulleroisoxazoline BDPꢀIs from 2 under the most commonly used
conditions (Method A)18,19 failed as a consequence of bromination at the 2ꢀ and 6ꢀpositions of
the BODIPY core by NBS. To overcome this problem and to prepare the desired product BDPꢀ
Is, a new synthetic strategy was devised, starting with the monoꢀcondensation reaction of
terephthalaldehyde 4 with NH2OH·H2O to give the formyl aldoxime 5, which was further treated
with NBS and Et3N at room temperature to yield an nitrile oxide, which was reacted in situ with
C60. The resulting aldehyde 6 was then used to obtain the corresponding derivative BDPꢀIs by
treatment with 2,4ꢀdimethylpyrrole following standard BODIPY synthetic procedures (Method
B).5 However, BDPꢀIs was isolated in low yield probably due to a retrocycloaddition process as
the C60 recover seems to indicate. Thus, in order to get a higher yield, avoiding the use of
halogenating agents for the generation of the 1,3ꢀdipole, bis(trifluoroacetoxy)iodobenzene
(PIFA) was used as an oxidising agent for the oneꢀstep conversion the aldoxime into nitrile oxide
which subsequently undergoes 1,3ꢀdipolar cycloaddition with C60 (Method C).20 These mild
conditions for formation of isoxazoline ring on fullerene, which afforded the dyad BDPꢀIs in a

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relatively high yield of 42%, render this alternative strategy as a suitable method for the synthesis
of fulleroisoxazolines from fullerene and aldoximes.
1
13
The structures of the new dyads were confirmed by Hꢀ and C NMR, and MALDIꢀTOF mass
spectrometry. The MALDIꢀTOF mass spectrum of adducts clearly shows the molecular ion peaks
at m/z of 1196.3 for BDBꢀPyr and m/z of 1085.3 for BDPꢀIs, respectively (Fig. S12 and Fig. S13
1
in the Electronic Supporting Information). The H NMR spectra of the dyads exhibited all
expected signals for the organic addends with the correct integration ratios. In the case of BDBꢀ
Pyr (Fig. 2), the spectrum additionally showed the typical signals corresponding to the
pyrrolidine ring, which appear as a doublets at 4.22 ppm due to AB system for methylene group
(Hꢀi) with a JAB = 8.4 Hz and a singlet for the proton belonging to the substituted carbon (Hꢀa) at
5.19 ppm which is overlapped with one of the two diastereotopic methylene protons.
Interestingly, some of the signals corresponding to the protons of the Nꢀoctylpyrrolidine group
and some of the aromatic ones are broad and significantly unresolved, which probably can be due
to a restricted rotation of the phenyl ring on the pyrrolidine bridge, as previously reported by
Langa and coꢀworker.21
Fig. 2. 1H NMR spectrum of BDPꢀPyr in CHCl3ꢀd at 400 MHz.
For BDPꢀIs, the isoxazoline linker between the C60 sphere and the BODIPY core rendered the
spectroscopic characterization easier. As shown in Fig. 3b, the aromatic region is now wellꢀ
resolved and a comparison with the spectrum of 2 (Fig. 3a) reveals the absence of both the
aldoxime and hydroxyl protons. A chemical shift for the proton Hꢀa, at remarkably low field, due
to the influence of the inductive deꢀshielding effect of C60, suggest an effective cycloaddition of
the nitrile oxide to the fullerene.

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Fig. 3. 1H NMR spectra of A) 2 and B) BDPꢀIs in CHCl3ꢀd at 400 MHz.
2.2. Photophysical properties
Once synthetized, the UVꢀVis absorption and fluorescence spectra for the two fullerene
derivatives, as well as for the reference compounds BDP and C60 were measured in toluene (Fig.
4a), and the spectroscopic data were collected in Table 1.
Fig. 4. a) UV/Vis absorption spectra and b) fluorescence spectra of BDPꢀPyr, BDPꢀIs, BDP and C60 in
toluene (1.0x10ꢀ5 M, 25 °C, λex = 470 nm)

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Table 1. Photophysical properties of compounds BDP, BDPꢀPyr, and BDPꢀIs in toluene at 25 °C;
absorption (λabs) and fluorescence (λem) wavelengths, molar absorption coefficients of the S0 → S1
transition (ε), fluorescence quantum yields (ΦF) and optical bandꢀgap energy (Egopt).
Egopt (eV) b
2.39
a
Compound
BDP
BDPꢀPyr
BDPꢀIs
λabs (nm)
503
ε (Mꢀ1 cmꢀ1)
77633
λem (nm)
516
ΦF
0.99
505
506
71103
74994
517
518
9.3x10ꢀ4
5.7x10ꢀ4
2.37
2.35
a
Quantum yields were measured using the comparative method with rhodamine B as standard (Φ = 0.68
in ethanol).22
b The optical bandꢀgaps were obtained from the onset of the absorption spectra.
For the BDPꢀPyr and BDPꢀIs dyads, the absorption spectrum resembled that of the BDP dye in
the visible region. The BDPꢀPyr and BDPꢀIs derivatives show a strong absorption band centered
around 500 nm corresponding to the S0 → S1 (π → π*) transition, and a shoulder in the higher
energy at ~475 nm corresponding to the respective 0ꢀ1 vibronic transition.23 It is worthy to note,
that the covalent linkage to C60 induces a small redꢀshift of the S0 → S1 transition band as well as
a reduction of absorptivity of the dyads with respect to the simplest core BDP. This can be due to
small electronic interactions between the BDP and C60 entities in the dyads.24 The longest
bathochromic shift and the highest molar absorption coefficient obtained for BDPꢀIs compared
with BDPꢀPyr can be ascribed to the greater conjugation of the lone pair electrons on the oxygen
and nitrogen atoms of the isoxazoline fragment with the conjugated πꢀsystem of the BODIPY
core, resulting in a smaller bandꢀgap energy (Table 1). At the shortest wavelengths, the sharp
band at 433 nm, observed for BDPꢀPyr,25 confirms the covalent union between the BODIPY and
the C60. The BDPꢀPyr and BDPꢀIs derivatives features intense absorptions in the ultraviolet
region between 300 to 340 nm, which have been assigned to the πꢀπ* transitions of the fullerene
unit and is hypsochromically shifted along with a comparatively lower extinction coefficient with
respect to the band C60 due to the symmetry breaking of the C60 core and decrease in conjugation
of the πꢀsystem when a [6,6]ꢀdouble bond in the fullerene fragment is removed.26
The absence of any characteristic charge transfer band in the absorption spectra of the BDPꢀPyr
and BDPꢀIs derivatives indicates that the electronic interaction between the C60 and the BDP unit
is negligible in the ground state, suggesting that any charge separation occurs only after
excitation.27 In the fluorescence emission spectra, the emission of BDP was significantly
quenched in the BDPꢀPyr and BDPꢀIs dyads (Fig. 4b) as a result of the ICT process from the
BDP to the C60 unit. Interestingly, intensity of fluorescence emission as well as the quantum
yield of BDPꢀIs (Table 1) is much lower than that for BDPꢀPyr, indicating that probably the
isoxazoline bridge allows to stabilize the chargeꢀseparation to a greater degree as compared to the
pyrrolidine bridge of BDPꢀPyr.
In order to experimentally verify the presence of the chargeꢀseparated state involving electron
transfer from BDP to C60, the emission spectra of BDPꢀPyr and BDPꢀIs were recorded in a
binary solvent mixture of MeOH–toluene, in which the methanol content (fMeOH) was varied in
the range of 0–60 vol%. As shown in Fig. 5, these two fullerene derivatives are strongly
dependent on solvent polarity; the emission intensity of the dyads decreases progressively with
increasing solvent polarity, which is consistent with the stabilization of charge separation state in
the emissive state when polar solvents are used. Also, it is can observe that the fluorescence

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emission maxima of both dyads are blueꢀshifted upon the solvent polarity, indicating that the
permanent dipole moments slightly decrease from ground state S0 to excited state S1, which is
consistent with the behavior of other BODIPY derivatives reported previously.28
Fig. 5. Fluorescence spectra (λex = 470 nm) of a) BDPꢀPyr and b) BDPꢀIs in MeOH–toluene mixtures
with volume ratios of methanol.
In addition, upon trifluoroacetic acid addition, an enhanced fluorescence intensity for the BDPꢀIs
dyad was observed (Fig. 6b), while the emission in the BDPꢀPyr derivative remained unaltered
(Fig. 6a). This result suggest that the addition of acid stopped the quenching process in the
fulleroisoxazoline, demonstrating the involvement of the nonꢀbonding electrons, of the
isoxazoline bridge on the BDPꢀIs dyad in the electronic transfer process. Instead, BDPꢀPyr dyad
exhibits a small blueꢀshift due to the increasing of energy gap as a result of nitrogen protonation
of the pyrrolidine bridge of BDPꢀPyr while the quenching of the fluorescence keeps happening
since the pyrrolidinium linkers does not alter the electronꢀtransfer process.29,30
Fig. 6. Fluorescence spectra (λex = 470 nm) of a) BDPꢀPyr and b) BDPꢀIs in toluene upon addition of
increasing amounts of TFA

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2.3. Electrochemical properties
In order to understand the effect generated by the isoxazoline bridge and pyrrolidine one between
the electroactive units on the electronic energy levels, the electrochemical properties of the dyads
BDPꢀPyr and BDPꢀIs, as well as the reference compounds BDP and C60 were studied by cyclic
voltammetry (CV) and Osteryoung square wave voltammetry (OSWV) in oꢀdichlorobenzene (oꢀ
DCB) at room temperature, using tetraꢀnꢀbutylammonium hexafluorophosphate (TBAPF6) as
supporting electrolyte and the electrochemical potentials were referred to the potential of the
ferrocene/ ferrocenium (Fc/Fc+) redox couple. The CV and OSWV results are presented in Fig. 7
and the potential data for all of the compounds were collected in Table 2. For the dyads, on the
negative potential side five reduction processes can be observed whereas on the positive one only
one oxidation occur. Four out of five reductions are quasiꢀreversible oneꢀelectron processes, and
by comparison with the voltammetric studies of pristine fullerene under the same experimental
conditions, they can confidently be attributed to the C60 moiety and the other reversible
voltammetric wave, between the second and the fourth reduction waves assigned to C60 cage, can
be attributed to the formation of the πꢀradical anion of the BODIPY core.31,32
Fig. 7. a) Cyclic voltammetry and b) Osteryoung square wave voltammetry of BDPꢀPyr, BDPꢀIs, BDP
and C60 in 0.1 M TBAPF6/oꢀDCB with ferrocene as an internal standard. Scan rate = 100 mV/s..
Interestingly, the first reduction potential of the dyad BDPꢀPyr is cathodically shifted by 150 mV
as compared with that of C60, due to the partial loss of conjugation by saturation of the double
bond in fullerene cage when the adduct is formed. In contrast, in the dyad BDPꢀIs the first
reduction potential show an anodic shift by 100 mV in comparison to C60. Therefore, this new
fulleroisoxazolineꢀBODIPY present a better ability to accept electrons than unsubstituted
fullerene and this is clearly a consequence of the combined effect of the electronegativity of the
oxygen atom linked to the C60 core and, in a less extent, to the electronꢀdeficient character of Cꢀ3
of the isoxazoline ring.33
As concerns the oxidation process, both dyads are characterized by an irreversible oxidation
wave at +0.84 V and +0.92 V (for BDPꢀPyr and BDPꢀIs, respectively), corresponding to the

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oneꢀelectron oxidation of the BODIPY nucleus to the formation of the πꢀradical cation.31,32
Compared with simple BDP, it is clear that the C60 makes renders the oxidation of the BODIPY
core more difficult due to a pronounced electron withdrawing effect of the fullerene cage.
Curiously, the presence of the isoxazoline bridge made the oxidation even more difficult,
increasing the potential by 80 mV for BDPꢀIs with respect to the dyad BDPꢀPyr, which
indicating a pronounced electrostatic effect to reduces the electronic density in the πꢀsystem of
the BODIPY core and favor the electronic transfer toward the fullerene unit in a much greater
degree as compared to the dyad BDPꢀPyr.
Table 2. Potential reductions and oxidations of the analyzed compounds (vs. Fc/Fc+) in 0.1 M TBAPF6/oꢀ
DCB at 25 °C
Compound
C60
BDP
BDPꢀPyr
BDPꢀIs
E1red/V
ꢀ1.00
ꢀ
ꢀ1.15
ꢀ0.90
E2red/V
ꢀ1.40
ꢀ
ꢀ1.44
ꢀ1.25
E3red/V
ꢀ
ꢀ1.79
ꢀ1.60
ꢀ1.52
E4red/V
ꢀ1.86
ꢀ
ꢀ1.79
ꢀ1.75
E5red/V
ꢀ2.31
ꢀ
ꢀ2.18
ꢀ1.93
E1 /V
ꢀ
+0.77
+0.84
+0.92
ox
2.4. Theoretical study
To gain further insight about the electronic level structures of the dyads and illustrate the
possibility of intramolecular electron communication, were performed quantum chemical
calculations on BODIPYꢀC60 using PM3 as semiempirical method and the STOꢀ3G basis set. The
frontier molecular orbital (FMO) plots of the dyads and the reference BDP are shown in Table 3.
In agreement with the theoretical calculations reported literature data,28 for the model BDP both
HOMO and LUMO are mainly localized only in the BODIPY moiety since the conjugation is
interrupted with the mesoꢀphenyl which is orthogonal to the BODIPY plane, canceling the
delocalization of electronic distribution on the phenyl ring and it is believed that this structural
disposition could be due to the geometrical restrictions imposed by the two methyl groups at
positions 1 and 7.34 However, in the BDPꢀPyr and BDPꢀIs derivatives the HOMO is always
localized on the BODIPY core but the LUMO is distributed on the fullerene cage. Accordingly,
charge transfer from the BODIPY moiety to C60 can occur and the coplanar orientation of the
BODIPY core with respects to the mesoꢀphenyl does not influence electronic communication
between two electroactive units, which is consistent with the previously observed photophysical
and electrochemical results.

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Table 3. Electron density maps of the frontier molecular orbital HOMO and LUMO of BDP, BDPꢀPyr
and BDPꢀIs.
FMO
BDP
BDPꢀPyr
BDPꢀIs
LUMO
HOMO
On the other hand, for the dyads the same tendency are observed between the HOMO/LUMO
values determined by voltammetry and those obtained by theoretical calculations (Table 4). The
calculated LUMO level of BDPꢀIs is lower in energy (ꢀ2.99 eV) than of BDPꢀPyr (ꢀ2.86 eV),
clearly showing the stronger electron accepting nature of fullerene when an isoxazoline ring is
using as a linker between the electroactive units, which is in agreement with electrochemical
properties previously discussed. The HOMO levels calculated at ꢀ8.52 and ꢀ8.57 eV of BDPꢀ
Pyr and BDPꢀIs are higher in energy that the BDP reference (ꢀ8.49 eV), confirming the electron
transfer centered on this unit towards the C60 core, as indicated above in the electrochemical part.
Finally, the tendency of the electrochemical band gaps and theoretical ones are in good
agreement with the optical energy gaps data (Table 1), where the magnitude of Eg decrease from
largest to smallest: BDP>BDPꢀPyr>BDPꢀIs.

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Table 4. Theoretical calculations and electrochemical data of BDP, BDPꢀPyr and BDPꢀIs
Electrochemical properties
HOMO (eV)a LUMO (eV)b
Theoretical properties
HOMO (eV) LUMO (eV) Egtheo (eV)
Compound
Egel (eV)c
2.56
1.99
1.82
ꢀ5.17
ꢀ5.24
ꢀ5.32
ꢀ2.61
ꢀ3.25
ꢀ3.50
ꢀ8.49
ꢀ8.52
ꢀ8.57
ꢀ1.93
ꢀ2.86
ꢀ2.99
6.56
5.66
5.58
BDP
BDPꢀPyr
BDPꢀIs
a
b
c
3. Conclusions
In summary, a new pyrrolidine[60]fullereneꢀBODIPY was synthesized by Prato reaction and an
isoxazoline[60]fullereneꢀBODIPY derivative has been prepared by using PIFAꢀmediated 1,3ꢀ
dipolar cycloaddition. This last method offers an easy access to fulleroisoxazoline since the
formation of nitrile oxide from aldoximes using PIFA is a singleꢀstep process that can operating
at temperatures of 0 °C and also, it provide an alternative for to obtain fulleroisoxazolines from
aldoximes susceptible to halogenation under conventional condition of cicloadición 1,3ꢀdipolar
(NXS, Et3N, C60) in good yield. The systems have been electronic characterized by means of
absorption and emission spectroscopy and electrochemistry. The electrochemical and
photophysical properties of this new family of fullerene derivatives indicate that all of these
derivatives exhibit efficient intramolecular electron transfer and the presence of the oxygen atom
linked to the C60 in the isoxazoline core improves the injection of electrons to the fullerene,
making the new BDPꢀIs derivative have a better electron affinity that BDPꢀPyr and C60.
4. Acknowledgements
We gratefully acknowledge the Universidad del Valle and Center for Research and Innovation in
Bioinformatics and Photonics (CIBioFi) for financial support. We also thank J.S.R for his help in
obtaining mass spectra.
5. Experimental Section
5.1. General methods
Chemicals were used as received unless otherwise indicated. All oxygen or moisture sensitive
reactions were performed under an argon atmosphere using dried solvents prepared according to
recommended standard procedures. 1H NMR (400 MHz), and 13C NMR (100 MHz) spectra were
recorded on the Bruker Avance (III) 400 MHz, using CHCl3ꢀd and DMSOꢀd6 as solvents.
Chemical shifts are reported in parts per million (ppm) relative to the residual solvent peak
1
13
1
(CHCl3: 7.26 ppm for H and 77.36 ppm for C; DMSO: 2.50 ppm for H and 39.51 ppm for
13C). Multiplicities are given as: s (singlet), d (doublet), t (triplet), q (quartet), dd (doublet of
doublets), m (multiplet), and the coupling constants J are given in Hz. MALDIꢀTOF spectra was
recorded on a BruckerꢀREFLEX IV MALDIꢀTOF mass spectrometer. UVꢀVis absorption spectra
of all compounds were recorded on a JASCO Vꢀ730 UVꢀVIS Spectrophotometer. Fluorescence
spectra of all the compounds were recorded on a JASCO (FPꢀ8500) spectrophotometer. The
voltammograms were recorded on a potentiostate/galvanostate Autolab PGSTAT302N using

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Glassy carbon as the working electrode (3 mm), Pt wire as the counter electrode, and Ag as the
pseudoꢀreference electrode in 0.1 M TBAPF6/oꢀDCB. The ferrocene/ferrocenium (Fc/Fc+) redox
couple was used as the internal reference to measure the potentials. Both the counter and the
reference electrodes were directly immersed in the electrolyte solution. The surface of the
working electrode was carefully polished to mirror with 0.3 and 0.5 alumina slurries prior use.
Solutions were deoxygenated by bubbling argon for few minutes prior each voltammetric scan.
Unless otherwise specified the scan rate was 100 mV/s.
5.2. Synthesis and characterization
5.2.1. Synthesis of 4,4ꢀdifluoroꢀ8ꢀ(4’ꢀhydroxyiminomethylphenyl)ꢀ1,3,5,7ꢀtetramethylꢀ4ꢀ
boraꢀ3a,4aꢀdiazaꢀsꢀindacene (2)
To a solution of the aldehyde 1 (176.1 mg, 0.50 mmol, 1 eq.), in a mixture of EtOH/H2O (6 mL,
2:1), NH2OH⋅HCl (41.7 mg, 0.60 mmol, 1.2 eq.) was added, followed by Na2CO3 (31.8 mg, 0.30
mmol, 0.6 eq.). The mixture was stirred at room temperature for 10 minutes. Then the crude was
transferred to a separation funnel and the product was extracted with diethyl ether (3 x 20 mL),
dried over anhydrous MgSO4 and filtered. The solvent was evaporated at reduced pressure and
the solid was dried under vacuum to afford the pure desired product 2 as an orange solid in 88 %
yield. 1H NMR (400 MHz, CHCl3ꢀd) δ/ppm = 8.21 (s, 1H), 7.90 (s, 1H), 7.72 (d, J = 7.6 Hz, 2H),
7.33 (d, J = 7.6 Hz, 2H), 5.99 (s, 2H), 2.56 (s, 6H), 1.40 (s, 6H). 13C NMR (101 MHz, CHCl3ꢀd)
δ/ppm = 156.1, 149.9, 143.3, 141.0, 137.0, 133.2, 131.5, 129.0, 128.0, 121.7, 14.94, 14.88.
5.2.2. Synthesis of 2,6ꢀdibromoꢀ4,4ꢀdifluoroꢀ8ꢀ(4’ꢀhydroxyiminomethylphenyl)ꢀ1,3,5,7ꢀ
tetramethylꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene (3) (Product obtained by Method A)
Nꢀbromosuccinimide (85.4 mg, 0.48 mmol, 3 eq.) was added to a solution of the aldoxime 2 (58.7
mg, 0.16 mmol, 1 eq.) in 5 mL of dry DMF. The resulting mixture was stirred for 1 h at room
temperature under argon atmosphere and then added via syringe to a purple solution of C60 (230.4
mg, 0.32 mmol, 2 eq.) in 70 mL of dry toluene. Triethylamine (112 ꢁL, 0.8 mmol, 5 eq.) was
added and the reaction was stirred for 9 h at room temperature. The resulting magenta solution
was concentrated and the residue was subjected to column chromatography on silica gel using
CH2Cl2 as eluent to obtain 3 as only product in 33 % yield. 1H NMR (400 MHz, CHCl3ꢀd) δ/ppm
= 8.21 (s, 1H), 7.74 (d, J = 8.0 Hz, 2H), 7.47 (s, 1H), 7.29 (d, J = 8.0 Hz, 2H), 2.60 (s, 6H), 1.39
(s, 6H). 13C NMR (101 MHz, CHCl3ꢀd) δ/ppm = 154.6, 149.5, 141.4, 140.8, 136.1, 133.9, 130.5,
128.8, 128.2, 112.3, 14.2, 14.1.
5.2.3. 4ꢀ((hydroxyimino)methyl)benzaldehyde (5)
Hydroxylamine hydrochloride (69.5 mg, 1.0 mmol, 1 eq.) was added to the solution of
terephthalaldehyde 4 (147.5 mg, 1.1 mmol, 1.1 eq.) and sodium hydroxide (58.3 mg, 0.55 mmol,
0.55 eq.) in a mixture of EtOH/H2O (100 mL, 4:1) for 30 min at 0 °C. The solvent was
evaporated at reduced pressure, water was added to the residue, and the product were extracted
with diethyl ether (3 x 20 mL). Then, the resulting organic phase was dried over Na2SO4, filtered
and concentrated under reduced pressure. The crude product was purified by column
chromatography on silica gel using an eluent mixture of CHCl3/MeOH (9:1) to give 5 as white
1
solid in 67 % yield. H NMR (400 MHz, DMSOꢀd6) δ/ppm = 11.67 (s, 1H), 10.00 (s, 1H), 8.25

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(s, 1H), 7.92 (d, J = 8.0 Hz, 2H), 7.80 (d, J = 8.0 Hz, 2H). 13C NMR (101 MHz, DMSOꢀd6)
δ/ppm = 192.6, 147.5, 138.7, 136.3, 129.9, 126.9.
5.2.4. Synthesis of 3’ꢀ(4ꢀformylphenyl)isoxazolo[4’,5’:1,2][60]fullerene (6)
The syntheses were carried out according to the method described in the preparation of the 3. The
aldoxime 5 (71.6 mg, 0.48 mmol, 1 eq.) was dissolved into 5 mL of dry DMF and Nꢀ
Bromosuccinimide (128.1 mg, 0.72 mmol, 1.5 eq.) was added portion wise at room temperature.
After 1 h, the starting material disappeared and it was added via syringe in another solution of
pristine C60 (691.2 mg, 0.96 mmol, 2 eq.) with TEA (335 ꢁL, 2.4 mmol, 5 eq.) in dry toluene.
The reaction was left under stirring for 5 h at room temperature. The crude mixture resulting was
concentrated to dryness and purified by silica gel chromatography using CS2 as eluent to remove
the unreacted C60, followed by a mixture of CS2/CH2Cl2 (8:2) to obtain 6 as brown solid in 52 %
yield. 1H NMR (400 MHz, CHCl3ꢀd) δ/ppm = 10.11 (s, 1H), 8.40 (d, J = 8.2 Hz, 2H), 8.07 (d, J =
13
8.2 Hz, 2H). C NMR (101 MHz, CHCl3ꢀd) δ/ppm = 191.7, 153.5, 148.2, 147.7, 146.8, 146.69,
146.67, 146.42, 146.37, 146.1, 145.8, 145.72, 145.66, 145.6, 145.0, 144.8, 144.4, 144.6, 144.2,
143.4, 143.3, 143.2, 142.8, 142.64, 142.63, 142.3, 142.1, 140.8, 140.7, 137.9, 137.6, 137.1,
135.0, 130.5, 129.8.
5.2.5. Synthesis of BDPꢀPyr
A solution of C60 (403.2 mg, 0.56 mmol, 4 eq.), 1 (50.0 mg, 0.14 mmol, 1 eq.) and Nꢀ
octylglycine (209.8 mg, 1.12 mmol, 8 eq.) in 140 mL of dry toluene was refluxed for 4h under
argon atmosphere and water formed from the reaction was removed by a DeanꢀStark trap. After
cooling, the solvent was removed under reduced pressure and the crude resulting was purified by
column chromatography on silica gel, eluting with CS2 to remove the unreacted C60 and, then,
1
using CS2/CH2Cl2 (1:1) to give BDPꢀPyr as a dark maroon solid in 48 % yield. H NMR (400
MHz, CHCl3ꢀd) δ/ppm = 8.00 (s, 2H), 7.38 – 7.35 (m, 2H), 5.91 (s, 2H), 5.20 – 5.15 (m, 2H),
4.22 (d, J = 8.4 Hz, 1H), 3.29 – 3.21 (m, 1H), 2.70 – 2.66 (m, 1H), 2.51 (s, 6H), 2.03 – 1.93 (m,
2H), 1.67 – 1.57 (m, 2H), 1.54 – 1.41 (m, 4H), 1.36 (s, 6H), 1.28 – 1.20 (m, 4H), 0.94 (t, J = 6.7
Hz, 3H). 13C NMR (101 MHz, CHCl3ꢀd) δ/ppm = 147.48, 147.45, 146.5, 146.4, 146.3, 146.1,
145.9, 145.7, 145.6, 145.45, 145.41, 145.3, 145.2, 144.7, 143.4, 142.8, 142.2, 142.1, 141.73,
141.69, 140.9, 140.4, 139.3, 136.5, 135.6, 131.5, 128.8, 121.55, 121.53, 82.4, 67.0, 32.4, 30.2,
29.9, 29.8, 28.0, 23.2, 14.8, 14.6. MS (MALDIꢀTOF): m/z calcd for [C89H38BF2N3]+: 1197.31;
found 1196.3
5.2.6. Synthesis of BDPꢀIs
Method B: To 6 (87 mg, 0.1 mmol, 1 eq.) and 2,4ꢀdimethylpyrrole (22 µL, 0.21 mmol, 2.1 eq.)
in 25 mL of dry and deoxygenated CH2Cl2, one drop of TFA was added and the mixture was
stirred overnight under argon at room temperature. The dark red solution was treated with pꢀ
chloranil (125 mg, 0.1 mmol, 1 eq.), stirring was continued for 30 min followed by the addition
of Et3N (210 ꢁL, 1.5 mmol, 15 eq.). After 15 min, BF3·Et2O (10.5 mL, 85 mmol, 17 eq.) was
added at 0 ºC, and the mixture was stirred at room temperature for further 3 h. After the solvent
was removed by evaporation under vacuum and a dark residue was obtained, which was purified
by column chromatography on silica gel using CS2/CH2Cl2 (1:2) as eluent. The product BDPꢀIs
was isolated as a maroon solid in 10 % yield. Method C: A mixture of C60 (547.2 mg, 0.76
mmol, 5 eq.), 2 (70 mg, 0.19 mmol, 1 eq.), and PIFA (120.4 mg, 0.28 mmol, 1.5 eq.) were

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dissolved in 150 mL of toluene and stirred under argon atmosphere at 0 °C for 6 h. At the end of
the reaction, the solvent was evaporated in vacuo, and the residue was separated on a silica gel
chromatography eluting with a gradient from CS to CS2/CH2Cl2 (1:2) to afford BDPꢀIs in 46 %
2
yield. 1H NMR (400 MHz, CHCl3ꢀd) δ 8.18 (d, J = 8.3 Hz, 2H), 7.33 (d, J = 8.3 Hz, 2H), 6.36 (s,
2H), 2.24 (s, 6H), 1.85 (s, 6H). BDPꢀIs shows poor solubility in common organic solvents. No
satisfying 13C NMR spectra can be measured. MS (MALDIꢀTOF): m/z calcd for
[C80H18BF2N3O]+: 1085.15; found 1085.3
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Synthesis, Electronic Properties and Efficient Photoinduced Electron
Transfer of New Pyrrolidine[60]fullerene- and Isoxazoline[60]fullerene-
BODIPY dyads: Nitrile oxide cycloaddition under mild conditions by
PIFA
Andrea Cabrera-Espinoza,1,2 Braulio Insuasty, 1,2 Alejandro Ortiz*1,2
1 Heterocyclic Compounds Research Group, Department of Chemistry, Universidad del
Valle, A.A. 25360, Cali, Colombia
2 Center for Research and Innovation in Bioinformatics and Photonics-CIBioFi, Calle 13
No. 100-00, Edificio 320, No. 1069, Cali, Colombia
Table of Contents
The first synthesis of a fulleroisoxazoline-BODIPY whose electron-accepting ability of the C60 cage
is better than that its counterparty fulleropyrrolidine-BODIPY.