Photoswitchable J-aggregated processable organogel by integrating a photochromic acceptor

Article abstract of DOI:10.1021/acs.joc.9b01555

A novel αchromophoric 1,4-bis(anthracenylethynyl)benzene (BAB)-based highly emissive J-aggregated organogel has been synthesized and characterized. Single-crystal structure determination of asymmetric π-chromophoric bola-amphiphilic BAB1 (dodecyl and triethyleneglycolmonomethylether containing side chains of bis(anthracenylethynyl)benzene) supports J-aggregation. Further, a photochromic acceptor chromophore, 4,4′-(perfluorocyclopent-1-ene-1,2-diyl)bis(5-methylthiophene-2-carbaldehyde), is noncovalently encapsulated in the gel and photoswitching studies have been performed based on photochromic F?rster resonance energy transfer. The modulated emission of the processable soft material is further exploited for rewritable display. However, BAB2 (dodecyl side chain on both sides) does not show gelation property due to its low solubility.

Full text of DOI:10.1021/acs.joc.9b01555

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Article
Photoswitchable J-aggregated Processable
Organogel by Integrating a Photochromic Acceptor
Debabrata Samanta, Ashish Singh, Parul Verma, Sohini
Bhattacharyya, Syamantak Roy, and Tapas Kumar Maji
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01555 • Publication Date (Web): 12 Aug 2019
Downloaded from pubs.acs.org on August 12, 2019
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Photoswitchable J-aggregated Processable Organogel by
Integrating a Photochromic Acceptor
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Debabrata Samanta, Ashish Singh, Parul Verma, Sohini Bhattacharyya, Syamantak Roy and
Tapas Kumar Maji*
Molecular Materials Laboratory, Chemistry and Physics of Materials Unit (CPMU), School of Advanced
Materials (SAMat), Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur, Bangalore-
560064, India.
*Email id: tmaji@jncasr.ac.in
Table of Content
Rewritable Display
Energy Transfer
OFF
Energy Transfer
ON
UV
Visible
Non-
radiative
decay
UV Vis
Masked UV
irradiation
Abstract: A novel π-chromophoric 1,4-bis(anthracenylethynyl)benzene (BAB) based highly
emissive J-aggregated organogel has been synthesized and characterized. Single crystal
structure determination of asymmetric π chromophoric bola-amphiphilic BAB1 (dodecyl and
triethyleneglycolmonomethylether
(TEG)
containing
side
chains
of
bis(anthracenylethynyl)benzene) supports J-aggregation. Further, a photochromic acceptor
chromophore 4,4'-(Perfluorocyclopent-1-ene-1,2-diyl)bis(5-methylthiophene-2-carbaldehyde)
(PBMC) is non-covalently encapsulated in the gel and photoswitching studies have been
performed based on pcFRET. The modulated emission of the processable soft material is
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further exploited for rewritable display. However, BAB2 (dodecyl side chain on both sides)
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does not show gelation property due to its low solubility.
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Introduction
Reversible modulation of emission intensity of a fluorescent system has attracted
significant attention because of its potential application in several areas such as optical data
storage,1 sensing,2 and fluorescence microscopy3. Such intriguing class of compounds can be
prepared by covalent/non-covalent integration of organic fluorophores with a suitable
photochromic molecule.4 The fluorescence modulation relies on the photochromic Förster
resonance energy transfer (pcFRET)4,5 process and photoinduced charge/electron transfer
(PET)6 where fluorescence of the donor is quenched by the wavelength selective
photoirradiation of an acceptor photochrome. Among the different photochromic molecules,
di(thiophenyl)ethene (DTE) are widely used because of their reversible photo-conversion
between a colorless open to a colored closed form, ease of functionalization, high
chemical/thermal stability and fatigue resistance.7 DTE has been hybridized in several
chromophoric system for pcFRET such as BODIPY, anthracene, oligothiophene, perylene,
porphyrin, rhodamine, metal complexes and semiconductor quantum dots.8
Scheme 1. Schematic Showing Photo-switching Gel Material Based on pcFRET.
Energy Transfer OFF
Energy Transfer ON
UV
Visible
Non-
radiative
decay
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With the aim of developing a new pcFRET system, we have utilized a J-aggregated
fluorophoric material as an efficient FRET donor. The J-aggregated fluorescent systems
render several advantages, which accounts for their wide applicability, including narrow red-
shifted emission, high quantum efficiency/brightness in aggregated state, extreme stability
and long-lived excited state lifetime.9 However, design and synthesis of J-aggregated
fluorophore is a highly challenging assignment as most fluorophores undergo H-aggregation
resulting in aggregation induced emission quenching.10 Furthermore, the gel state will provide
additional advantages of easy processability as well as proper alignment of acceptor
fluorophores for efficient FRET process.11,12
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Herein, we report the design and synthesis of a novel π-chromophoric asymmetric
bola-amphiphilic 1,4-bis(anthracenylethynyl)benzene (BAB1) based J-aggregated emissive
gel BAB1-G (Scheme 1). The central phenyl ring of BAB1 was strategically decorated with
mixed polar side chain functionality i.e.
a
n-dodecyl (non-polar) and
triethyleneglycolmonomethylether (TEG, polar) to induce gelation as well as solubility. The
side chain functionalities directed to a parallel offset packing (θ1 = 46.1° & θ2 = 50.0°) of the
π chromophores resulting in the J-aggregation. Further, a photochromic acceptor molecule
DTE has been noncovalently encapsulated to study photoswitching property based on
pcFRET. The ensemble demonstrated photoinduced ON-OFF energy transfer and utilized for
rewritable display. In contrast, synthesized BAB2 (Scheme 2a), which contains dodecyl
chains on both sides did not show any gelation property due to its low solubility in common
organic solvents indicating the necessity of mixed polar side chain functionality to induce
solubility and corresponding gelation (Table S1).
Results and Discussion
The designed BAB derivatives, BAB1&2 were synthesized by Pd(0) catalyzed Sonogashira-
Hagihara cross-coupling reaction between 9-ethynylanthracene and functionalized 1,4-
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diiodobenzene in 2:1 stoichiometry (Scheme S1&2, SI).13 The DTE derivative, 4,4'-
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(Perfluorocyclopent-1-ene-1,2-diyl)bis(5-methylthiophene-2-carbaldehyde)
(PBMC-open)
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was synthesized by following a reported procedure (Scheme S3, SI).14 The UV-Vis spectrum
of a methanolic solution (10-6 M) of BAB1 shows two vibronic absorption bands at 440 and
460 nm (molar extinction coefficient = 2.1×105 M-1 cm-1), and the solution exhibits cyan
emission with two overlapping bands at 479 and 505 nm when excited at 460 nm (Figure
1a,b). The Stokes shift is around 19 nm. BAB2 also displayed UV-Vis (molar extinction
coefficient = 2.2×105 M-1 cm-1) and PL spectra (Figure S1) similar to BAB1 due to structural
similarities. Strikingly, in solid state, both BAB1&2 exhibited a new red-shifted absorption
band at 509 and 501 nm, respectively (Figure 1a/S1a). The corresponding excitation resulted
in bright-red emission with maximum at 617 nm and 591 nm for BAB1 and BAB2,
respectively (Figure1b/S1b). The mirror-image relationship of UV-Vis and PL spectra in
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Scheme 2. (a) Structures of BAB1&2 With Their Photograph in Solid State and Methanolic
Solution Under UV Light. (b) Open and Closed Form of PBMC Along With Photographs in
Methanolic Solution.
(a)
BAB1
BAB1 BAB2
BAB2
(b)
solution, appearance of a distinct red-shifted absorption band and bright-red emission
(Scheme 2a) in the solid state intrigued us to investigate the aggregation behavior. For this,
UV-Vis and PL measurements were carried out with methanolic solutions by successive
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addition of water as “poor solvent” which triggers intermolecular aggregation (Figure
1c,d/S2).15 Notably, the water addition with BAB1 solution resulted in a new absorption band
at 505 nm. This band can be attributed to J-aggregation due to it’s red-shifted appearance.9
The aggregation also resulted in an additional red-shifted emission band at 570 nm (λexc = 505
nm). Dynamic light scattering (DLS) revealed that the aggregated particles have
hydrodynamic radius centered at 817 nm (Figure S3). Field emission scanning electron
microscopy (FESEM) and transmission electron microscopy (TEM) also showed the presence
of aggregated particles (Figure S4, S5). However, the aggregation-based emission band
predominates in the solid at 617 nm (Figure 1b). The emission quantum yield of BAB1 in
methanol is 36%. The emission property remains similar in solid state as the observed
quantum yield is 27%. The fluorescence lifetime was found to be 2.28 and 2.51 ns in solid
and methanolic solution, respectively. All these observations clearly supported the J-
aggregation behavior of BAB1. BAB2 also revealed the appearance of J band upon successive
addition of water in methanolic solution (Figure S2).
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(a)
(b)
(c)
(d)
J band
*
* = J emission
(g)
(e)
(f)
60 C
2 μm
RT
Figure 1. (a) UV-Vis and (b) PL spectra of BAB1 in methanol (10-6 M, λexc = 460 nm),
methanol/water (1:1, λexc = 505 nm), xerogel (λexc = 509 nm) and solid (λexc = 509 nm).
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Volume corrected UV-Vis (c) and emission spectra (d) of a methanolic solution of BAB1 (10-
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M) with varied amount of water. Volume correction to the absorbance was performed by
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multiplying absorbance with {(V+x)/V}, where V = initial volume and x = volume of added
water. (e) Thermo reversibility test of BAB1-G (14.6 mM). (f) Digital photograph of BAB1-
G (14.6 mM) under UV light and (g) TEM image of BAB1 xerogel.
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BAB1 forms a gel BAB1-G in a mixture of 5:1 methanol:dichloromethane,
instantaneously (Figure 1e,f).16 The formation of gel was confirmed by inversion test. Sol-gel
thermo reversibility of the gel was also observed. The preformed gel was converted to a sol
phase upon heating at 60 °C and the produced sol was transformed again into a gel phase by
cooling to room temperature. Moreover, the gel also formed sol phase upon sonication and
again returned to a gel phase upon standing. This indicated thixotropic nature of the gel. The
critical gelation concentration of BAB1 was found to be 12.1 mM. FESEM and TEM
microscopy demonstrated a cross-linked fibrous network of BAB1 xerogel (Figure 1g/S6/S7).
BAB1 also exhibited high emission in the gel phase with 34% fluorescence quantum yield
(Figure 1f). The UV-Vis spectrum of BAB1 xerogel showed two vibronic absorption bands at
470 and 446 nm, and a J-band at 509 nm (Figure 1a). Excitations at these wavelengths
resulted in a broad emission in the range of 530-700 nm with a maximum at 608 nm (Figure
1b).
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q2
q1
3.036
2.756
q1 = 46.1
q2 = 50.0
2.856
Figure 2. Parallel offset arrangement of BAB1. Distances are given in angstrom unit (Å).
Further to support and understand the molecular packing leading to J-aggregation,
BAB1 was successfully crystallized by slow evaporation technique from a solution of toluene
at room temperature. Red colored rhombus shaped single crystals of BAB1 were obtained and
̅
single crystal X-ray diffraction (SXRD) revealed that BAB1 crystallized in the triclinic P1
space group wherein each molecule consists of a rigid core formed by two terminal
anthracenyl moieties and one central phenyl ring, connected by two ethynyl modules (Figure
2, S8-12, Table S2). All these aromatic moieties are coplanar. The individual molecules of
BAB1 are packed in parallel offset fashion via multiple C−H···π interactions between
hydrogens of dodecyloxy chain and π cloud of the anthracenyl group from adjacent molecule.
The C−H···π distances are in the rage of 2.756 – 3.036 Å. Time-dependent density functional
theory (TD-DFT) computation on a model system of BAB1 revealed that the direction of
transition electric dipole moment (TEDM) of the longest wavelength electronic transition
(HOMO→LUMO, λ = 534 nm, f = 1.19) is parallel to the long axis of molecule i.e. parallel to
the conjugated backbone (see SI). Along this direction, the offset in crystal packing (θ1 =
46.1° & θ2 = 50.0°, Figure 2) remains in the range of J-aggregation (J-aggregate: 0°<θ<54.7°;
H-aggregate: 54.7°<θ<90°).17 The simulated PXRD pattern displayed a peak at 2θ = 24.2°
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(222) which passes in between two molecules and parallel to the π conjugated backbones
(Figure S12). The peak is retained in solid, methanol/water (1:1) aggregates and xerogel of
BAB1, indicating similar π arrangement between the chromophoric backbone of
BAB1(Figure S13). Notably, BAB2, in solid state, also displayed the peak at 2θ = 24.2°, thus
showing presence of similar π arrangement as of BAB1 and combination of UV-Vis studies
(vide supra) supported J aggregation in BAB2(Figure S14).
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Since, the central phenyl ring of BAB1 contains both hydrophilic (TEG) and
hydrophobic (n-dodecyl) side chains, we measured water contact angle on a gel coated glass
surface to understand exterior decoration. The measured contact angle was 44°, indicating
exterior decorated TEG chains and, consequently, n-dodecyl chains pointed inward direction
of the film (Figure S15). Since the gelation was performed in methanol medium (major), TEG
groups got exposed on the outer surface of the film in order to reduce surface energy.
PBMC was chosen to incorporate in the gel to study ON-OFF energy transfer process
via pcFRET as it can be switched between open (PBMC-open) and closed form (PBMC-
closed) by UV (365 nm) and visible light (590 nm) irradiation, respectively (Scheme 2b).
Moreover, PBMC-closed exhibited an absorption band in the range 490-730 nm with a
maximum at 622 nm (purple color) which has partial overlap with the emission band of
BAB1-G (500-700 nm) (Figure 3a). This overlap is desirable for excitation energy transfer
from BAB1 to PBMC. The open form showed no absorption in the emission range of BAB1-
G, indicating that PBMC-open cannot act as an acceptor of the emitted energy from BAB1-
G. The formyl substitutions in PBMC results in red-shifted absorption spectrum and
facilitates faster kinetics of interconversion between open and closed form allowing to study
ON-OFF energy transfer process.18 Moreover, PBMC can be embedded easily into the gel
matrix by multiple supramolecular interactions such as C−H···π, C−F···H, π-stacking etc.
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Therefore, PBMC incorporated gel would be suitable to study photo modulated emission via
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ON-OFF energy transfer process.
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(a)
(b)
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(c)
(e)
(d)
UV
Vis
(f)
501 nm
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
PBMC@BAB1-G
PBMC@BAB1-G after
25 min UV irr
Vis
UV
400
500
600
700
Wavelength (nm)
Figure 3. (a) UV-Vis spectra of PBMC-open and PBMC-closed, and emission spectrum of
BAB1-G (λexc = 470 nm). (b) ON-OFF energy transfer study of PBMC@BAB1-G (14.6 mM)
by emission spectroscopy (λexc = 470 nm) in gel phase. (c) Digital photograph of gel coated
glass slide (under UV light) before and after masked UV irradiation (JNC), (d) ON-OFF
energy transfer cycles, (e) UV-Vis spectra with digital photographs and (f) fluorescence
lifetime of PBMC@BAB1-G before and after 25 min UV light irradiation (365 nm).
Incorporation of PBMC-open (30 mol%) in BAB1-G was performed in situ during
gel formation to obtain PBMC-open@BAB1-G. Upon PBMC-open incorporation, the J
band in UV-Vis spectrum was blue shifted by 8 nm (509 nm→501 nm) and the emission band
was red-shifted by 6 nm (578 nm→584 nm). Elemental mapping by Energy-Dispersive X-
Ray Spectroscopy (EDS) revealed homogeneous distribution of PBMC into the gel phase
(Figure S16). The PXRD of PBMC@BAB1-G showed moderate crystallinity with shift in
several peak positions when compared with BAB1-G, indicating change in packing upon
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PBMC encapsulation (Figure S17). Importantly, the PXRD pattern showed retention of the
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peak at 2θ = 24.2° ((222) plane) after encapsulation of PBMC-open, indicating retention π
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arrangement and J aggregation. Notably, the emission intensity of BAB1-G was retained upon
PBMC-open incorporation as the quantum yield was measured to be 30%. The ON-OFF
energy transfer process was studied by PL spectroscopy, excited state fluorescence lifetime
and quantum yield measurement (Figure 3). For this study, PBMC-open@BAB1-G was
irradiated with 365 nm light (intensity: 308 W/m2) for 25 min. The irradiation resulted in
greenish-orange color of the gel (Figure 3e, inset) and the UV-Vis spectrum showed
appearance of 622 nm band, indicating the formation of PBMC-closed@BAB1-G (Figure
3e). Interestingly, the emission intensity (λexc = 584 nm) was quenched by ~80% and the
fluorescence lifetime was decreased to 360 ps from 2.36 ns (Figure 3b,d,f). The quantum
yield was drastically reduced to 2.5% upon UV irradiation. In the next step, visible light
irradiation (λ = 590 nm, intensity = 796 W/m2) on PBMC-closed@BAB1-G for 2 h,
converted PBMC-closed to PBMC-open as evident from the disappearance of 622 nm band
in UV-Vis spectrum and, consequently, the emission intensity regenerated completely. These
observations are strongly supportive of the occurrence of energy transfer from BAB1 to
PBMC in its closed state and absence of such process in the open form. Notably,
incorporation of 35 mol% PBMC into BAB1-G resulted in complete energy transfer process
as observed by the complete emission quench upon UV irradiation (Figure S18). However,
the result demonstrated an on-demand energy transfer process in a highly processable
material. The material was coated on a glass slide and rewritable capability was demonstrated
by masked UV irradiation (Figure 3c). The ON-OFF energy transfer assisted reversible
emission quench and regain was verified up to three cycles (Figure 3d). The rate constants for
fluorescence decay and enhancement, due to light induced ring opening and closing reactions
of PBMC in gel phase, were calculated by fitting the relative change in emission intensity at
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584 nm with mono-exponential function (Figure S19). The fluorescence decay and
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enhancement profile revealed a rate constant of 2.08×10−3 s−1 and 2.05×10−4 s−1, respectively.
Free energy calculations based on DFT, at B3LYP/6-31G* level, indicated that the electron
transfer processes from the photoexcited BAB1 (BAB1*), PBMC-open (PBMC-open*) and
PBMC-closed (PBMC-closed*) to the counter component in ground state are
thermodynamically unfavorable (see SI). Therefore, an alternative PET mechanism is not
considered.
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Conclusions
The forgoing results demonstrate development of a highly processable soft material
with tunable optical property via ON-OFF energy transfer process. BAB1 displayed high
quantum yield 28-36% ranging from gel to solid phase due to J-aggregation. The adopted
functionalization strategy allowed parallel offset packing leading to J-aggregation via multiple
C−H···π interactions between dodecyl side chain and anthracene moiety as evident from the
crystal structure. The mixed-polar side chain functionality in BAB1resulted in gelation
allowing facile encapsulation of PBMC into the gel matrix for successful ON-OFF energy
transfer via pcFRET. This finding could potentially broaden the landscape of J-aggregated
emission as a donor for photo-switchable optoelectronic applications.
Experimental Section.
General. All commercially available solvents and reagents were purchased and used without
further
purification.
Pd(PPh3)4,
hydroquinone,
1-bromododecane,
2-(2-(2-
methoxyethoxy)ethoxy)ethanol, iodine monochloride, 18-crown-6, p-toluene sulfonyl
chloride, 9-bromoanthracene, and trimethylsilyl acetylene were purchased from Sigma-
Aldrich chemical Co. All solvents were purchased from Spectrochem, India. 9-
Ethynylanthracene,19
1-(dodecyloxy)-2,5-diiodo-4-(2-(2-(2-
methoxyethoxy)ethoxy)ethoxy)benzene,12a 1,4-bis(dodecyloxy)-2,5-diiodobenzene20 and 4,4'-
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were synthesized using reported procedure.
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Physical Measurements. Elemental analysis was performed using a Thermo Fischer Flash
2000 Elemental Analyzer. FT-IR spectroscopy were performed on a Bruker IFS 66v/S
spectrophotometer using KBr pellets in the region 4000–400 cm-1. Powder X-ray diffraction
(PXRD) patterns were measured utilizing a Bruker D8 Discover instrument using Cu−Kα
radiation. The field emission scanning electron microscopic (FESEM) images and elemental
mapping were recorded on a Nova Nanosem 600 FEI. The BAB1 xerogels were dispersed in
hexane and then drop casted onto a small piece of silicon wafer for FESEM measurements. In
case of methanol/water (1:1) aggregate of BAB1, a 10-6 M methanolic solution was treated
with equal volume of water, and the resulted solution was drop casted onto a silicon wafer.
For PBMC-open@BAB1, xerogel was dispersed in water and drop casted on a silicon wafer
for elemental mapping via Energy-Dispersive X-Ray Spectroscopy (EDS). We chose water
for dispersion as no component is soluble in water. Transmission electron microscope was
measure on a JEOL JEM3010 instrument with 200 kV incident beam. The TEM samples were
prepared in a similar procedure as mentioned above, but drop casted onto a carbon-coated
TEM grid. BAB1 xerogel was dispersed in hexane and spin coated on a glass slide which was
utilized for water contact angle measurement. The solid, gel and solution phase fluorescence
quantum yield was determined by using integrating sphere, an absolute quantum yield
measurement and calculated by Horiba Jobin Yvon. The synthesized gel in a cuvette was
directly used for this measurement. Dynamic Light Scattering (DLS) was measured utilizing a
NanoZS (Malvern UK) employing a 505 nm laser at a back-scattering angle of 173°. HR-MS
was measured using Agilent Technologies 6538 UHD Accurate-Mass Q-TOFLC/MS. Perkin
Elmer Lambda 900 UV-VIS-NIR Spectrometer was used for UV-Vis measurement. Perkin-
Elmer model LS 55 luminescence spectrometer was utilized for PL measurement. A time-
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correlated single photon counting spectrometer of Horiba-Jobin Yvon with 350-450 nm
picosecond Ti-saphhire laser was used for Fluorescence decay measurements. All1H spectra
were recorded at frequency of 400 MHz using a Bruker AVANCE 400 MHz spectrometer.
Whereas, 13C-spectrum for BAB1 was recorded at 150 MHz frequency using Varian Inova
600 MHz spectrometer.
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Synthesis procedure of 9,9'-((2-(dodecyloxy)-5-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-
1,4-phenylene)bis(ethyne-2,1-diyl))dianthracene (BAB1). A Schlenk tube was charged
with 1-(dodecyloxy)-2,5-diiodo-4-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzene (500 mg,
739 μmol),12a 9-ethynylanthracene (374 mg, 1.85 mmol), tetrahydrofuran (20 mL) and
triethylamine (2 mL). The resulting solution was degassed thoroughly with argon by freeze-
pump-thaw method and then Pd(PPh3)4 (171 mg, 148 μmol) was added to the solution. The
reaction vessel was further degassed by the above-mentioned procedure. The thus degassed
reaction mixture was refluxed for 36 h at 70 °C in oil-bath to complete coupling process.
Upon cooling the reaction mixture to room temperature, red colored precipitate of BAB1 was
formed. The precipitate was filtered by Whatman 40 filter paper, washed with methanol and
dried under vacuum to obtain BAB1 (482mg, 79%) as pure compound. FT-IR (KBr pellet,
4000−400 cm−1): 3083 (w), 3051 (m), 2917 (s), 2848 (s), 2191 (w), 1502 (s), 1468 (s), 1427
1
(s), 1388 (m), 1347 (m), 1282 (m), 1219 (s), 1202 (s), 1120 (s), 730 (s). H NMR (400 MHz,
CDCl3): δ = 0.87 (t, J = 6.9 Hz, 3H), 1.21-1.27 (m, 14H), 1.43 (quint, J = 7.8 Hz, 2H), 1.64
(quint, J = 7.6 Hz, 2H), 2.10 (quint, J = 7.6 Hz, 2H), 3.29 (s, 3H), 3.43 (t, J = 5.2 Hz, 2H),
3.55 (t, J = 5.2 Hz, 2H), 3.61 (t, J = 4.8 Hz, 2H), 3.81 (t, J = 5.6 Hz, 2H), 4.11 (t, J = 5.1 Hz,
2H), 4.25 (t, J = 6.6 Hz, 2H), 4.44 (t, J = 5.2 Hz, 2H), 7.30 (s, 1H), 7.35 (s, 1H), 7.52-7.67 (m,
8H), 8.04 (d, J = 8.4 Hz, 4H), 8.46 (s, 2H), 8.82 (t, J = 7.9 Hz, 4H) ppm. 13C{1H} NMR (150
MHz, CDCl3): δ =14.1, 22.7, 26.1, 29.3, 29.6 (3C), 29.6, 29.6, 29.7, 31.9, 58.9, 68.9, 69.5,
69.8, 70.4, 70.6, 70.9, 71.8, 92.4, 92.5, 97.6, 97.6, 114.2, 114.4, 115.7, 115.7, 116.4, 116.4,
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117.6, 117.6, 125.7, 126.5, 126.6, 127.1, 127.7, 127.8 (2C), 127.8, 128.6, 128.7, 131.2, 132.6,
153.4, 154.2 ppm. HRMS-EI (m/z) for C57H60O5 [M+] Calcd. 824.4441, found 824.4451.
Anal. Calcd. for C57H60O5: C, 82.97; H, 7.33. Found: C, 82.90; H, 7.38.
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The BAB1 was further crystallized from toluene by slow evaporation technique to
obtain rhombus-shaped single crystals. X-ray diffraction of the single crystal allowed
structure elucidation.
Synthesis
procedure
of
9,9'-((2,5-bis(dodecyloxy)-1,4-phenylene)bis(ethyne-2,1-
diyl))dianthracene (BAB2). A sealed-tube was loaded with 1,4-bis(dodecyloxy)-2,5-
diiodobenzene (516 mg, 739 μmol),20 9-ethynylanthracene (374 mg, 1.85 mmol),
tetrahydrofuran (20 mL) and triethylamine (2 mL). The resulting solution was degassed with
argon thoroughly by freeze-pump-thaw method and then Pd(PPh3)4 (171 mg, 148 μmol) was
added. The reaction vessel was again degassed by the same procedure and refluxed for 36 h at
70 °C in oil-bath. Upon cooling to room temperature, red colored precipitate was obtained
which was filtered by Whatman 40 filter paper, washed with methanol and dried under
vacuum to get BAB2 (532 mg, 85%) as pure compound. FT-IR (KBr pellet, 4000−400 cm−1):
3081 (w), 3054 (m), 2918 (s), 2846 (s), 2189 (w), 1509 (s), 1467 (m), 1483 (s), 1393 (m),
1
1348 (m), 1278 (m), 1226 (s), 1207 (s), 1120 (s), 737 (s). H NMR (400 MHz, CDCl3): δ =
0.87 (t, J = 6.9 Hz, 6H), 1.22-1.28 (m, 28H), 1.43 (quint, J = 7.8 Hz, 4H), 1.62 (quint, J = 7.6
Hz, 4H), 2.12 (quint, J = 7.6 Hz, 4H), 4.26 (t, J = 6.6 Hz, 4H), 7.31 (s, 2H), 7.54 (t, J = 7.6,
4H), 7.62 (t, J = 8.4 Hz, 4H), 8.04 (d, J = 8.4 Hz, 4H), 8.46 (s, 2H), 8.83 (d, J = 8.4, 4H) ppm.
HRMS-EI (m/z) for C62H70O2 [M+] Calcd. 846.5376, found 846.5381. Anal. Calcd. for
C62H70O2: C, 87.90; H, 8.33. Found: C, 87.94; H, 8.18. 13C NMR measurement was not
possible due to insufficient solubility.
Synthesis procedure of 4,4'-(Perfluorocyclopent-1-ene-1,2-diyl)bis(5-methylthiophene-2-
carbaldehyde) (PBMC-open). Synthesis of 4-bromo-5-methylthiophene-2-carbaldehyde, 3-
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bromo-5-(diethoxymethyl)-2-methylthiophene and PBMC-open was performed by following
literature report (Scheme S3).21 Herein, a modified synthesis procedure for the last step
yielding PBMC-open is stated bellow. To a solution of 3-bromo-5-(diethoxymethyl)-2-
methylthiophene (8.0 g, 28.7 mmol) in THF (80 mL) in a three-necked round-bottomed flask
(250 mL), n-butyl lithium (2.5 M in hexane, 14.9 mL, 37.3 mmol) was added dropwise at -78
oC regulated through thermostat julabo temperature controller and stirred for 1 h at the same
temperature under argon atmosphere. Octafluorocyclopentene (1.8 mL, 13.5 mmol) was then
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o
added dropwise maintaining the temperature at −78 C. The resulting mixture was stirred for
4 h and then warmed it up to room temperature. It was stirred at room temperature for 8 h to
complete the reaction. The resulting solution was quenched with water (100 mL) and
extracted with diethyl ether (3 × 200 mL). The combined organic layer was washed with
water (2 × 200 mL), brine (200 mL), dried over anhydrous MgSO4 and concentrated under
reduced pressure to obtain the crude product. The crude material was dissolved in THF (150
mL) and then trifluoroacetic acid (6.7 mL, 87.5 mmol) was added dropwise. After 2 h, the
reaction mixture was concentrated by rotary evaporator and the solid residue was purified by
column chromatography (silica gel, ethylacetate/hexane = 4:1) to afford PBMC-open (4.5g,
37%) as light yellow solid. The spectroscopic data matches well with the literature report.191H
NMR (400 MHz, CDCl3): δ = 1.92 (s, 6H), 7.51 (s, 2H), 9.86 (s, 2H) ppm. Anal. Calcd. for
C17H10F6O2S2: C, 48.11; H, 2.38; S, 15.11. Found: C, 48.25; H, 2.30; S, 14.88. HRMS-EI
(m/z) for C17H10F6O2S2 [M+] Calcd. 424.0026, found 424.0043.
Supporting Information Available: The Supporting Information is available free of charge
on the ACS Publications website.
X-ray crystallography data, CIF file, computational data, FESEM and TEM
microscopy, UV−vis, PL, IR, PXRD, and NMR spectra (PDF).
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Accession Code. CCDC 1871732 contains the supplementary crystallographic data of BAB1.
This data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing da-ta_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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Acknowledgement. TKM is grateful to the Department of Science and Technology (DST,
Project No. MR-2015/001019). TKM and DS also ac-knowledge TRC (Project No. TRC-
DST/C.14.10/16-2724, JNCASR) for financial support. AS thanks SERB-DST, India for
providing National Post-Doc Fellowship (NPDF, Project No: PDF/2016/002324).
Notes and References
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