Synthesis and Properties of BODIPY Appended Tetraphenylethylene Scaffolds as Photoactive Arrays

Article abstract of DOI:10.1002/ejoc.202100629

Tetraphenylethylene (TPE) and its derivatives exhibit excellent aggregation-induced emission (AIE) properties. The TPE unit is easily accessible, and many functional groups can be introduced in a facile manner to yield effective luminescent materials in both solution and the solid-state. It is because of this, several TPE-based compounds have been developed and applied in many areas, such as OLEDs and chemical sensors. Boron dipyrromethenes (BODIPYs) are a class of pyrrolic fluorophore of great interest with myriad application in both material science and biomedical applications. Through the combination of Pd-catalyzed cross-coupling reactions and traditional dipyrromethene chemistry, we present the syntheses of novel tetra-BODIPY-appended TPE derivatives with different distances between the TPE and BODIPY cores. The TPE-BODIPY arrays 6 and 9 show vastly differing AIE properties in THF/H₂O systems, with 9 exhibiting dual-AIE, along with both conjugates being found to produce singlet oxygen (¹O₂). We presume the synthesized BODIPY-appended TPE scaffolds to be utilized for potential applications in the fields of light-emitting systems and theranostics.

Full text of DOI:10.1002/ejoc.202100629

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Synthesis and Properties of BODIPY Appended
Tetraphenylethylene Scaffolds as Photoactive Arrays
Harry C. Sample,[a] Ganapathi Emandi,[a] Brendan Twamley,[b] Nitika Grover,[a]
Bhavya Khurana,[a, c] Vincent Sol,[c] and Mathias O. Senge*[a, d]
Tetraphenylethylene (TPE) and its derivatives exhibit excellent
aggregation-induced emission (AIE) properties. The TPE unit is
easily accessible, and many functional groups can be intro-
duced in a facile manner to yield effective luminescent
materials in both solution and the solid-state. It is because of
this, several TPE-based compounds have been developed and
applied in many areas, such as OLEDs and chemical sensors.
Boron dipyrromethenes (BODIPYs) are a class of pyrrolic
fluorophore of great interest with myriad application in both
material science and biomedical applications. Through the
combination of Pd-catalyzed cross-coupling reactions and tradi-
tional dipyrromethene chemistry, we present the syntheses of
novel tetra-BODIPY-appended TPE derivatives with different
distances between the TPE and BODIPY cores. The TPE-BODIPY
arrays 6 and 9 show vastly differing AIE properties in THF/H2O
systems, with 9 exhibiting dual-AIE, along with both conjugates
being found to produce singlet oxygen (1O2). We presume the
synthesized BODIPY-appended TPE scaffolds to be utilized for
potential applications in the fields of light-emitting systems and
theranostics.
Introduction
‘aggregation induced emission’ (AIE). The TPE motif is of
interest given its enhancement of AIE. In the hope of inducing
AIE, the TPE motif has been grafted onto a variety of dyes,
pyrrolic or otherwise.[12–16]
Since the first synthesis of the tetraphenylethylene (TPE) motif
in 1907,[1] it has been of considerable interest given its
electrochemical and photophysical properties.[2,3] Applications
of this motif are far reaching and all encompassing; optome-
chanical switching and storage devices,[4–6] fluorescent bio- and
chemo-sensors,[7] dyes for living cell imaging,[8] components of
dye-sensitized solar cells,[9] and much besides.[10] In 2001, Tang
and coworkers,[11] reported a novel class of organic fluorophore
which were non- or weakly emissive in solution, but upon
aggregation or in the solid state these molecules displayed
strong fluorescence. This novel phenomenon was coined
Whilst the use of the TPE core has itself yielded intriguing
results in myriad of areas of materials chemistry which has been
duly catalogued previously,[11] the incorporation of a dye yields
a second response to monitor, i.e., photoluminescence intensity
(AIE from the TPE moiety) and electronic absorption (photo-
chemistry from the dye moiety). However usually these systems
consist of one TPE and one dye moiety, or one of each in the
repeating unit of a polymeric material. E.g., TPE-hemicyanine
conjugates have been utilized in the sensing of homocysteine,
cysteine, and glutathione, all molecules which play essential
roles in biological processes such as homeostasis and
detoxification.[15] TPE-triphenylamine conjugates have been
utilized as the donor part of donor-acceptor (D-A) systems in
the generation of dye-sensitized solar cells (DSSCs) and were
found to be suitably efficient.[16] Sensing is a major contributor
to the uses of TPE; TPE-carbazole co-polymers have been found
to sense 2,4,6-trinitrotoluene (TNT),[17] and TPE-pilar[5]arene
conjugates have also been found to selectively sense 4-amino
azobenzene (Oil Yellow B), a frequently used carcinogenic
organic dye.[18] TPEs and BODIPYs have been conjugated
previously, and Dhokale et al. reported that extensive π-
stacking and D-A type interactions made the resulting con-
jugates inactive with regards to AIE.[19]
[a] H. C. Sample, Dr. G. Emandi, Dr. N. Grover, B. Khurana, Prof. Dr. M. O. Senge
School of Chemistry, Trinity College Dublin, The University of Dublin,
Trinity Biomedical Sciences Institute,
152–160 Pearse Street, Dublin 2, Ireland
[b] Dr. B. Twamley
School of Chemistry, Trinity College Dublin, The University of Dublin
Dublin 2, Ireland
[c] B. Khurana, Prof. Dr. V. Sol
Université de Limoges,
Laboratoire PEIRENE, EA 7500
8700 Limoges, France
[d] Prof. Dr. M. O. Senge
Institute for Advanced Study (TUM-IAS)
Technical University of Munich
Focus Group – Molecular and Interfacial Engineering
of Organic Nanosystems
Lichtenbergstrasse 2a, 85748 München Garchig, Germany
E-mail: sengem@tcd.ie
https://chemistry.tcd.ie/staff/people/mos/Home.html
In other previous examples of BODIPY-TPE conjugates
(Figure 1), it is apparent that the most ubiquitous systems
utilize mono-substitution of the fluorophore moiety with a
singular TPE unit, either through Pd-catalyzed cross coupling
type reactions (Figure 1, E), utilizing the TPE-moiety as the
meso-aryl group through standard BODIPY syntheses (Figure 1,
D), or otherwise building the fluorophore around the TPE unit
(Figure 1, D). Whilst tetra-substituted TPEs are utilized continu-
https://www.ias.tum.de/active-fellows/senge-mathias/
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between the TPE core, and four BODIPYs. Through the
modification of the linkages between the two cores we
envisioned the possibility of differing electronic properties
between the two conjugates.
Synthesis of TPE precursors began from 4,4’-dibromobenzo-
phenone, 1, to yield 2a, 2b and 3 (for X-ray structure see SI)
following literature procedures (Scheme 1).[21] Under standard
McMurry conditions, TPE-Br4 2a was produced cleanly in 84%
yield. Subsequent Sonogashira coupling with TMS-acetylene,
followed by K2CO3-mediated TMS deprotection yielded the
tetra-alkynyl TPE, TPE-(CCH)4 2b in 63%. Subsequently, through
the generation of 2a and 2b, different routes have been taken
to yield tetra-BODIPY-TPE arrays where the linkages between
the two cores vary both in length and degree of electronic
communication.
Treatment of 2a with 4-formylphenylboronic acid under
Suzuki conditions yielded TPE-biphenyl-aldehyde 4 in 48% yield
(Scheme 2) (for X-ray structure see SI). With regards to the
synthesis of dipyrromethanes (DPMs), there are two standard
methods of catalysis; InCl3 or trifluoroacetic acid.[20a,22] Given the
milder conditions with InCl3-mediated catalysis, along with the
lesser formation of the respective tripyrranes, we opted for
these conditions, and the respective tetra-dipyrromethane 5
was obtained in 56% yield. Treatment of 5 in the fashion similar
to BF2-insertion for more typical DPMs yielded the tetra-BODIPY
6 in 32% yield. Attempts at the utilization of coupling reactions
to form 9 were both unsuccessful starting from 2a or 2b and
Figure 1. Various dyes onto which the TPE motif has been grafted. A)
phenothiazine dyes,[9] R1,R2 =various fused thiophene moieties, B) aluminum
porphyrins where R3 =p-C6H4-C60,[12] and C,D,E) various BODIPYs and aza-
BODIPYs with substitution on all possible positions.[8,13,14]
ally in the fields of metal, and covalent, organic framework
(MOF/COF) chemistries – to our knowledge nothing has been
explored in the form of a tetra-dye appended TPE.
Given the propensity for the TPE unit to lend itself of such a
wide range of applications and our interest in new BODIPY
photonics applications,[20] we present the first tetra-BODIPY-
appended TPE conjugates. Our approach entailed building the
BODIPY onto the TPE through the generation of TPE-aldehydes
through differing Pd-catalyzed cross-coupling reactions, and
subsequent BODIPY syntheses therefrom. We have evaluated
our target compounds regarding their AIE properties, their
singlet oxygen (1O2) production, and discuss their suitability as
multi-photosensitizer arrays. We propose the use of differing
arms to link the TPE and BODIPY cores will present altered
spectroscopic responses in both solution and aggregated
states.
Results and Discussion
Synthesis Our initial targets were the structures presented
below in Figure 2. In the simplest sense, differing linkages
Scheme 1. Synthesis of TPE-Br4, 2a, and TPP-(CCH)4, 2b. Inset: reduced
representation of TPE’s, with 2b used as example. Reagents and conditions:
°
a) Zn, TiCl4, THF, 65 C, 12 h, 84% for 2a, b) TMS-CCH, CuI (20 mol%),
Pd(PPh3)2Cl2 (20 mol%), Et3N, THF, 92% for 3, c) K2CO3/THF, 63% from 2a
(over two steps), 91% from 3.
Figure 2. Initial synthetic targets of this study.
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the respective BODIPY (5-(4-bromophenyl)BODIPY or 5-(4-
ethynylphenyl)BODIPY), in our hands. Thus, akin to displayed
previously the DPM was built in a stepwise fashion. Treatment
of 2b with 4-iodobenzaldehyde under Sonogashira conditions
yielded tetra-aldehyde 7 in 41%, and subsequent InCl3-medi-
ated DPM synthesis yielded tetra-DPM 8 in 39%. Finally,
analogous complexation of BF2 gave tetra-BODIPY 9 in 19%
(Scheme 3). This yield is lowered with respect to previously
synthesized p-C6H4À CCX (X=H, Si(CH3)) BODIPYs.[23] However,
given that this is a tetra-BF2 insertion, a reduced yield is
anticipated. Interestingly, novel aldehyde 7 differed significantly
from 4 in the response upon UV illumination in the solid state,
varying in both wavelength, and intensity (Figure 3).
Aggregation Induced Emission Analysis. For analysis of AIE
properties, 6 and 9 were considered. Structurally, they differ
only in the addition of an ethynyl spacer in 9. Both were
analyzed via UV-Vis spectroscopy in THF/H2O mixtures, with
THF as the solvent and H2O as the anti-solvent, with increases
of [H2O]=10% between measurements. All analyses were
performed with solutions of [6, 9]=10 μM, and spectra are
presented in Figure 4.
Scheme 2. Synthesis of TPE-p-C6H4-CHO, 4, and subsequent TPE-p-C6H4-
BODIPY 6. Reagents and conditions: a) 4-formylphenylboronic acid, Cs2CO3,
°
Pd(PPh3)4, THF, 70 C, 24 h, 48%, b) pyrrole, InCl3, CH2Cl2, r.t., 1 h, 56% c)
DDQ, Et3N, BF3 ·OEt2, CH2Cl2, r.t., 0.75 h, 32%.
Typically, BODIPYs absorb in the region of λabs =495–
515 nm, dependent upon the solvent used for measurement,
and the electronic nature of the substituents along with their
positioning around the BODIPY core. The same arguments can
be applied to their emission wavelengths which are usually of
longer wavelength, i.e. λem >530 nm.[23g] Using these factors, we
can see that compound 6 exhibits standard photophysical
properties for BODIPYs, despite the TPE core. A decrease in
absorbance is observed at 70–80% H2O; however, there is no
one particular change in the emission intensity for the same
compound in the same solvent mixtures. In contrast, compound
9 does show a stark difference. A decrease in absorbance is
observed for 9 at 60% H2O, and the emission intensity was
found to increase greatly between 60–80% H2O.
Of particular interest in Figure 4d, is the appearance of two
emission bands for 9, present from [H2O] >70%. These two
bands at ca. λem =645, 730 nm could prove to be of particular
use with regard to theranostic application of drugs, given the
deeper tissue penetration of light through biological tissue with
increasing wavelength. In the synthesis of previous TPE-BODIPY
conjugates, Hu et al. evaluated how the linkage between TPE
and BODIPY cores affected the AIE behavior of the
conjugates.[24]
Scheme 3. Synthesis of TPE-CC-p-C6H4-CHO, 7, and subsequent TPE-p-C6H4-
CC-BODIPY, 9. Reagents and conditions: a) 4-iodobenzaldehyde, Pd(PPh3)4,
PPh3, CuI, Et3N, THF, 41%; b) pyrrole, InCl3, CH2Cl2, 39%; c) DDQ, Et3N,
BF3 ·OEt2, CH2Cl2, 19%; d) 5-(4-ethynylphenyl)-BODIPY (or 5-(4-bromophenyl)-
BODIPY), Pd(PPh3)2Cl2 (20 mol%), CuI (20 mol%), PPh3, Et3N, THF:C6H5CH3,
°
65 C, 24 h, 0%.
For a mono-BODIPY appended TPE, the spectra presented
herein present the same characteristics to those observed
previously; in the case of 6 there is a decrease in the locally
excited (LE) emission of the BODIPY core, as the water fraction
increases, and whilst a new emission does appear around λem
=
700 nm, the solution is essentially non-luminescent. For 9 there
is again a decrease in the LE emission for the BODIPY core;
however, the spectra become dominated by the emissions at
ca. λem =645, 730 nm. Given the findings of Hu et al. the
emission band at λem =645 nm could be a twisted intra-
molecular charge transfer (TICT) band. However, the second
Figure 3. Structures and photographs of aldehydes 4 and 7 being
illuminated under UV-light (360 nm) in the solid state (top) and solution
state (THF, bottom).
band at λem =730 nm is at very similar intensity to that at λem
=
645 nm. Such dual aggregation-induced emission has been
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Figure 4. UV-Vis absorption (a, b), and: emission (c, d) spectra for 6 (a, c) and 9 (b, d) through solvent titrations with mixtures of THF and H2O with [H2O]=0–
90%. [6,9]=10 μM.
observed and examined previously on the diarylethene
scaffold.[25] However, the spectra presented of 9 below is
indicative of differing πÀ π stacking modes in the aggregated
state (given that any intermolecular vibration is hindered
through dense molecular packing, resulting in a dual emission.)
Given that the intermolecular packing is so dense, we propose
that it is unlikely to be as a result of an end-to-face type
interaction (i.e. BF2 directly interacting with the TPE core), but
instead; differing face-to-face interactions of the TPE units in
perpendicular, or parallel, arrangements. A simplified represen-
tation of this is provided in Figure 5. For photographs of the
solutions used for these measurements, we refer the readers to
Figure S22 and S23.
regards to their singlet oxygen generation. Singlet oxygen (1O2)
is a key species responsible for photochemical and photo-
biological applications of various photosensitizers.[20a,d] 1,3-
Diphenylisobenzofuran (DPBF) was used as a singlet oxygen
trap under generation of cis-dibenzoylbenzene.[26]
The decrease in UV absorbance of DPBF in the presence of
both 6 and 9 was measured in CH2Cl2 :CH3OH (1:1) with
[DPBF]=0.15 M. 5,10,15,20-tetraphenylporphyrin (H2TPP) dis-
solved in CH2Cl2 such that [H2TPP]=0.15 M was achieved, and
subsequently used as a standard (Figure 6). The solutions were
irradiated for 1 h and UV-vis absorption measurements were
taken at t=0 seconds and at intervals of 100 seconds after
irradiation. Singlet oxygen experiments were repeated twice
and ΦTPE-BODIPY values were observed in a standard deviation
Singlet Oxygen (1O2) Measurements Given our prior
investigations regarding the singlet oxygen generation of
BODIPYs,[20a] we have also evaluated compounds 6 and 9 with
Figure 5. Schematic representation of the differing stackings of TPE-BODIPY
conjugate 9 resulting in aggregation induced dual emission.
Figure 6. 1,3-diphenylisobenzofuran (DPBF) degradation curves for 6 (black)
and 9 (red) in CH2Cl2 :CH3OH, 1:1, v/v.
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range of �0.05 for both sets of data. The relative quantum Conclusions
yields were calculated with reference to H2TPP (ΦH2TPP =0.62 in
CH2Cl2).[27]
In summary, we have presented the synthesis of novel tetra-
The UV-Vis absorbance of DPBF was adjusted to ca. 1.0 at
BODIPY appended TPE dyes in which the TPE and BODIPY
moieties are linked either through a phenylene spacer (6) or
phenyl-acetylene spacer (9). Intermediates such as the tetra-
aldehyde 7 offer potential modular tectons for materials science
applications. The structural differences between the linkages
have been exemplified through the photophysical analyses
undertaken; exhibiting a heightened AIE response upon the
addition of an ethynyl spacer to the system, in the same mixed
solvent system (THF/H2O), with emission bands at around
645 nm and 730 nm – yielding an aggregation induced dual
emission, through differing intermolecular πÀ π stacking ar-
rangements. Both of these systems were found to generation
singlet oxygen, with ΦΔ(6)=9.7% and ΦΔ(9)=15.9%. These
compounds (particularly 9) present themselves as ideal candi-
dates for applications such as intracellular imaging, with distinct
intense emission bands, and also as photosensitizers given the
high ΦΔ values observed. This initial investigation indicates the
possibility of further uses of the TPE core in the construction of
spatially defined photosensitizer arrays for other applications
i.e. light-emitting systems and theranostics. Further investiga-
tions utilizing this concept of are underway with a variety of
photosensitizers, and these findings will be published in due
course.
417 nm in air-saturated solvent mixture of CH2Cl2 :CH3OH, then
the photosensitizers (6 or 9) were added to the cuvette. The
slope of the curves of absorbance maxima of DPBF at 410 nm
vs. irradiation time for each photosensitizer were calculated.
The singlet oxygen quantum yield (ΦTPE-BODIPY) for each of these
TPE-BODIPY conjugates with H2TPP as a reference was calcu-
lated using the following equation (1):[28]
FTPE-BODIPY ¼ FH2TPP x STPE-BODIPY=SH2TPP
(1)
where Φ represents quantum yield, S represents the slope, and
TPE-BODIPY and TPP represent TPE substituted BODIPY and
5,10,15,20-tetraphenylporphyrin, respectively. Utilizing this
method it was found that ΦΔ(6)=9.7% whereas ΦΔ(9)=15.9%
1
(Figure 6). The enhancement of O2 generation exhibited in 9
can be rationalized as a result of increased conjugation
throughout the molecule. To our knowledge, this is the first
data regarding the generation of singlet oxygen for a TPE-
BODIPY conjugate of any kind.
Given that 9 has been shown to exhibit the AIE phenomen-
on, and the ability to generate 1O2; the question arises
1
regarding the generation of O2 in the aggregated state. It is
safe to propose that the ΦΔ of the aggregated 9 would be
significantly lower than that in the non-aggregated state.
Inherently, as a result of the processes involved, it’s highly likely Experimental Section
that the molecules closer to the center of these aggregates
General Information: Reactions involving moisture and/or air-
would not become excited, due to shielding from other
molecules closer to the edge of the aggregate, and that those
closer to the edge would likely quench via interaction with
another molecule of close proximity – possibly further enhanc-
ing the AIE response. Thus, it would be only those molecules on
the edge of the aggregate have the ability to generate 1O2
effectively, if at all.
The incorporation of multiple photosensitizers (PSs) into
one system is not a novel idea in of itself,[29] however as we
have stated previously the decoration of a TPE with four PS
moieties is. In this instance, logic would suggest that the
greater the number of PS molecules, the greater the ΦΔ,
assuming each PS acts as an individual PS. A key criterion in
these systems is the retention of the properties of the singular
PS, and subsequently that their affect is merely multiplied. The
demonstration that these conjugates can generate 1O2 is a
positive finding in terms of our eventual aim of using these
conjugates as multi-photosensitizer arrays. The differing values
of ΦΔ for the conjugates presented herein indicate that; for 6
the properties of the BODIPY are retained, whilst for compound
9 there is an additive affect as a result of the TPE-BODIPY
conjugation. Given these findings we propose that these
molecules are suitable as multi-photosensitizer arrays.
sensitive reagents were carried out in pre-dried glassware and with
standard Schlenk line techniques. All commercial reagents and
anhydrous solvents were used as received from vendors (Fischer
Scientific, and Sigma Aldrich). Dichloromethane (CH2Cl2) was dried
with P2O5. Yields refer to chromatographically and spectroscopically
(1H NMR) homogeneous material unless otherwise noted. Reactions
were monitored by thin-layer chromatography (TLC) and absorp-
tion spectroscopy. TLC was carried out on silica gel plates. Silica gel
60 *Merck, 230–400 mesh, or aluminum oxide (Brockmann Grade I)
were used for flash column chromatography. Room temperature
°
refers to 20–25 C.
Instrumentation: Melting points are uncorrected and were meas-
ured with a Digital Stuart SPM 10 melting point apparatus. NMR
spectra were recorded using Bruker DPX 400 and Agilent 400 were
used to obtain 1H (400.13 MHz), 13C{1H} (100.61 MHz), 19F{1H}
(376.60 MHz), and 11B (128.40 MHz) NMR spectra, and a Bruker AV
600 was employed for 1H (600.13 MHz) and 13C{1H} (150.90 MHz)
NMR spectra. NMR spectroscopy was carried out at room temper-
ature. Chemical shifts are given in ppm and referenced to the
residual peak of the deuterated NMR solvent. The assignment of
the signals was confirmed by 2D spectra (COSY, HMBC, HSQC).
MALDI TOF spectra were acquired using a Waters Maldi Q-Tof
Premier. The instrument was operated in positive or negative mode
as required. The laser operated at 337 nm. Samples were run using
DCTB
(trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]
malononitrile) as a MALDI matrix. The instrument was calibrated
using PEG. The internal lock mass used was [Glu] Fibrinopetide B.
MassLynx 4.1 software was used to carry out the analysis. ESI mass
spectra were acquired in positive or negative modes as required,
using a Micromass time-of-flight mass spectrometer (TOF), or a
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Bruker mircoOTOFÀ Q II spectrometer interfaced to
a
Dionex
CDCl3): δ=0.30 (t, 1JB-F =28.7 Hz, 4B) ppm; 19F NMR (376.5 MHz,
1
UltiMate 3000 LC. APCI experiments were carried out on a Bruker
microOTOF-Q III spectrometer interfaced to a Dionex Ultimate
3000 C or direct insertion probe in positive or negative modes. UV/
Vis spectra were recorded in solutions using a Specord 250
spectrophotometer from Analytik Jena (1 cm path length quartz
cell).
CDCl3): δ=À 145.06 ppm (q, JF-B =28.6 Hz, 8F) ppm; HRMS (MALDI)
calcd. for C86H56B4F8N8 [M+]: 1396.4872; found 1396.4917.
1,1,2,2-Tetrakis(4-(4’-formylphenylethynyl)phenyl)ethylene (7). To
an oven and flame dried Schlenk tube was added; 2b (215 mg,
501.7 μmol), 4-iodobenzaldehyde (1.0 g, 4.310 mmol, 8.6 eq.), PPh3
(86 mg, 0.327 mmol), Pd(PPh3)4 (65 mg, 56.3 μmol), and CuI (53 mg,
278.3 μmol). The solids were dried under high vacuum (<0.1 mbar)
for 2 h. Added to this was anhydrous 1,4-dioxane (8 mL) and
anhydrous Et3N (2 mL). The mixture underwent three freeze-pump-
Singlet oxygen studies: The photo-irradiation of the samples was
performed in quartz cuvettes (2×1×1 cm) under irradiation via a
polychromatic light source (Philips, 15 V–150 W lamp), equipped
with a 400 nm cut-off filter (Schott GG 400) and a 532 nm diode-
pumped solid state green laser system (CW532-04, average
intensity of 10 mWcmÀ 2). The temperature of the sample was
°
thaw cycles before being heated at 100 C for 25 h. Upon cooling to
RT the mixture was passed through a pad of silica (EtOAc) and
excess solvent was removed at reduced pressure. The product was
adsorbed onto silica (THF) and purified via column chromatography
(silica, EtOAc/Hex, 1/2, v/v). Excess solvent was removed under
reduced pressure, and the residue was sonicated with Et2O to yield
the product as a brick orange solid (170 mg, 201.2 μmol, 40%).
°
maintained at 18 C using a Peltier element (Cary Peltier 1×1 cell
holder). Relative singlet oxygen (1O2) yields (ΦTPE-BODIPY
) were
calculated from the degradation slopes of the 1,3-diphenylisoben-
zofuran (DPBF) conversion in the presence of different photo-
sensitizers. The absorbance of DPBF molecule was adjusted to 1.0
at 417 nm in an air-saturated solvent mixture then the correspond-
ing photosensitizer was added to the solution. The solutions were
irradiated from 0.5–1 h, and absorption spectra were recorded at
t=0 s and intervals of 100 s. A subsequent decrease in the
absorbance of DPBF was observed after each irradiation. Singlet
oxygen experiments were repeated twice and ΦTPE- values were
observed in a standard deviation range of �0.05.
M.p.=158–160 C (dec.); Rf=0.24 (SiO2, EtOAc:Hex 1:2, v/v); 1H NMR
°
(CDCl3, 400 MHz): δ=10.01 (s, 4H), 7.86 (d, J=8.3 Hz, 8H), 7.64 (d,
J=8.2 Hz, 8H), 7.35 (d, J=8.3 Hz, 8H), 7.06 (d, J=8.3 Hz, 8H) ppm;
13C NMR (CDCl3, 101 MHz): δ=191.5, 143.6, 141.3, 135.6, 132.2,
131.7, 129.8, 129.6, 121.4, 93.4, 85.9 ppm; HRMS (APCI) calcd. for
C62H36O4 [M]À : 844.2630; found: 844.2619.
1,1,2,2-Tetrakis(4-((4-(di(1H-pyrrol-2-yl)methyl)phenyl)ethynyl)
phenyl)ethylene (8). To a round bottom flask was added 7
(102 mg, 120.7 μmol) and freshly distilled pyrrole (5 mL). The
solution was purged with argon and InCl3 was added (134 mg,
605.8 μmol) and the mixture was stirred under argon until TLC
indicated complete consumption of 7 (c.a. 20mins). The reaction
mixture was diluted with CH2Cl2 (50 mL) and subsequently washed
with H2O, 0.1 M NaOH and brine (1×25 mL each, in that order). The
organic extract was dried (MgSO4) and excess solvent was removed
at reduced pressure. The product was purified via column
chromatography (SiO2 EtOAc/Hex, 1/1, v/v) to yield the desired
Compounds 2a, 2b, 3, and 4 were prepared according to literature
procedures.[21]
1,1,2,2-Tetrakis(4’-(di(1H-pyrrol-2-yl)methyl)-[1,1’-biphenyl]-4-yl)
ethylene (5). A solution of 4 (100 mg, 0.133 mmol, 1.0 equiv.) in
pyrrole (3 mL) was degassed with argon for 5 min. The solution was
stirred for 15 min at room temperature under argon in the presence
of InCl3 (118 mg, 0.534 mmol, 5.0 equiv.). The reaction mixture was
diluted with CH2Cl2 (50 mL) and washed with 0.1 M NaOH solution,
water and brine (1×25 mL each, in that order). The solvent was
removed under reduced pressure to give a dark green oil crude
product which was purified via flash column chromatography (SiO2,
EtOAc:Hex, 1:1, v/v). The title compound was obtained as a grey
°
product as a grey solid (40 mg, 30.5 μmol, 25%). M.p.= >300 C
(dec.) ; Rf =0.65 (EtOAc:Hex 1:1, v/v); H NMR (CDCl3, 400 MHz): δ=
1
7.93 (br s, 8H), 7.45 (d, J=8.2 Hz, 8H) 7.30 (d, J=8.3 Hz, 8H), 7.18 (d,
J=8.2 Hz, 8H), 7.01 (d, J=8.3 Hz, 8H), 6.70–6.71 (m, 8H), 6.15–6.18
(m, 8H), 5.91 (s, 8H), 5.47 (s, 4H) ppm; 13C NMR (CDCl3, 400 MHz):
δ=143.2, 143.1, 142.5(1), 142.5(0), 132.1, 132.0, 128.6, 121.9, 117.8,
117.6, 108.7, 108.3, 107.5, 44.0 ppm; HRMS (MALDI-TOF): calcd. for
C94H68N8 [M+]: 1308.5567; found 1308.5552.
solid upon rotary evaporation (90 mg, 0.074 mmol, 56%). M.p.= >
1
°
205–207 C (dec.); Rf =0.51 (SiO2, EtOAc:Hex, 1:1, v/v); H NMR
(400 MHz, CDCl3): δ=7.87 (s, 4H), 7.48 (d, J=7.6 Hz, 8H), 7.34 (d, J=
8.0 Hz, 8H), 7.20 (t, J=8.1 Hz, 8H), 7.17–7.11 (m, 8H), 6.66 (s, 8H),
6.15 (d, J=2.7 Hz, 8H), 5.91 (s, 8H), 5.44 (s, 4H) ppm; 13C NMR
(100 MHz, CDCl3): δ=142.8, 141.1, 140.5, 139.2, 138.5, 132.3, 132.0,
128.8, 127.0, 126.2, 117.3, 108.4, 107.2, 43.6 ppm; HRMS (MALDI)
calcd. for C86H68N8 [M+]: 1212.5567; found 1212.5504.
1,1,2,2-Tetrakis(4-((4-(4,4-difluoro-4-bora-3a,4a-diaza-s–inda-
cene)phenyl)ethynyl)phenyl)ethene (9). A solution of 8 (50 mg,
0.04 mmol) in CH2Cl2 (5 mL) was degassed with argon for 5 min.
DDQ (32 mg, 0.164 mmol) was added and the reaction mixture was
stirred for 5 min. Et3N (75 μL, 0.62 mmol) was added and the
solution was stirred for a further 3 min before addition of BF3 ·OEt2
(78 μL, 0.64 mmol). The reaction mixture was stirred for 35 min at
room temperature and monitored via TLC. The reaction was
quenched with H2O and the organic phase extracted with CH2Cl2
(2×25 mL). The organic phase was washed with water (2×25 mL),
dried (MgSO4), and the solvent evaporated to yield a crude green
product which was purified via flash column chromatography
1,1,2,2-Tetrakis(4’-(4,4-difluoro-4-bora-3a,4a-diaza-s–indacene)-
[1,1’-biphenyl]-4-yl)ethylene (6).
A
solution of
5
(50 mg,
0.04 mmol) in CH2Cl2 (5 mL) was degassed with Ar for 5 min. DDQ
(37 mg, 0.164 mmol) was added and the reaction mixture was
stirred for 5 min. Et3N (80 μL, 0.618 mmol) was added and the
solution was stirred for a further 3 min, before addition of BF3 ·OEt2
(86 μL, 0.64 mmol). The reaction mixture was stirred for 35 min at
room temperature and monitored via TLC. The reaction was
quenched with water and the organic phase extracted with CH2Cl2
(3×50 mL) The organic phase was washed twice with water
(25 mL), dried (MgSO4) and solvent evaporated to yield a crude
green product. This was purified via flash column chromatography
(EtOAc:Hex, 1:2, v/v) to yield an orange solid (11 mg, 7.37 μmol,
1
°
19%). M.p.= >150 C (dec.); Rf =0.72 (SiO2, EtOAc:Hex, 1:1, v/v); H
NMR (400 MHz, CDCl3): δ=7.96 (s, 8H), 7.68 (d, J=8.3 Hz, 8H), 7.57
(d, J=8.3 Hz, 8H), 7.52 (d, J=8.2 Hz, 8H), 7.22 (d, J=8.2 Hz, 8H),
6.95 (d, J=4.1 Hz, 8H), 6.56 (m, 8H) ppm; 11B NMR (128.4 MHz,
CDCl3): δ=0.28 (t, 1JB-F =28.7 Hz, 4B) ppm.; 19F NMR (376.5 MHz,
CDCl3): δ=À 145.08 ppm (q, 1JF-B =28.6 Hz, 8F) ppm; 13C NMR
(101 MHz, CDCl3): δ=144.5, 141.6, 134.9, 133.6, 132.2, 131.8(9),
131.8(6), 131.7, 131.5, 130.8, 130.7, 129.3, 126.4, 118.9 ppm; HRMS
(MALDI) calcd. for C102H74B3F6N8NaO4 [M-BF2 +2H+2EtOAc+Na+]:
1644.5914; found 1644.5953.
(EtOAc:Hex, 1:2, v/v) to yield an orange solid (19 mg, 32%). M.p.=
n
208–210 C (dec.); Rf =0.68 (SiO2, EtOAc: Hex, 1:1, v/v); 1H NMR
°
(400 MHz, CDCl3): δ=7.94 (s, 8H), 7.75 (d, J=8.2 Hz, 8H), 7.65–7.60
(m, 8H), 7.53 (d, J=8.2 Hz, 8H), 7.29 (d, J=8.2 Hz, 8H), 6.96 (d, J=
4.0 Hz, 8H), 6.54 (d, J=2.9 Hz, 8H) ppm; 13C NMR (101 MHz, CDCl3):
δ=143.1(7), 143.1(4), 142.5(1), 142.5(0), 132.1, 132.0, 128.6, 121.9,
117.8, 117.6, 108.7, 108.3, 107.5, 44.0 ppm; 11B NMR (128.4 MHz,
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Full Papers
doi.org/10.1002/ejoc.202100629
Crystal structure determinations. Crystals were grown via slow
evaporation at room temperature from saturated solutions of
MeOH (3) and CH2Cl2/F3CCO2H (4)
prepared with the support of the Technical University of Munich –
Institute for Advanced Study through a Hans Fischer Senior
Fellowship. Open access funding enabled and organized by Projekt
DEAL.
Single crystal X-ray diffraction data for all compounds were
collected on a Bruker APEX Kappa Duo diffractometer by using
Incoatec IμS CuKα (λ=1.54178 Å) radiation. Crystals were mounted
on a MiTeGen MicroMount and collected at 100(2) K by using an
Oxford Cryosystems Cobra low temperature device. Data were
collected by using omega and phi scans and were corrected for
Lorentz and polarization effects by using the APEX software suite.[30]
Using Olex2, the structures were solved with the XT structure
solution program, using the intrinsic phasing solution method and
refined against jF2 j with XL using least-squares minimization.[30]
Hydrogen atoms were generally placed in geometrically calculated
positions and refined using a riding model. All images were
rendered using Olex2.
Conflict of Interest
The authors declare no conflict of interest.
Keywords: Aggregation induced emission
·
BODIPY
·
Photosensitizer · Singlet oxygen · Tetraphenylethylene
Crystal Data for 3: C23H26OSi2 (M=374.62 g molÀ 1): orthorhombic,
space group Pccn (no. 56), a=33.9086(9) Å, b=5.5681(2) Å, c=
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11.6573(3) Å, α=β=γ=90 , V=2200.97(11) Å , Z=4, T=100(2) K,
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°
°
ured (2.606 �2θ�69.836 ), 2057 unique (Rint =0.0423, Rsigma
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0.0251) which were used in all calculations. The final R1 was 0.0404
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8, T=100(2) K, μ(Cu Kα)=0.514 mmÀ 1, Dcalc =1.049 gcmÀ 3, 35951
reflections measured (2.873 �2θ�58.986 ), 6752 unique (Rint
20, 1858–1867.
°
°
=
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Manuscript received: May 25, 2021
Revised manuscript received: July 6, 2021
Accepted manuscript online: July 7, 2021
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© 2021 The Authors. European Journal of Organic Chemistry published
by Wiley-VCH GmbH