Visible-Light-Triggered Generation of Ultrastable Radical Anion from Nitro-substituted Perylenediimides

Article abstract of DOI:10.1021/acs.joc.8b02023

An efficient method for visible-light-triggered generation of radicals from mono- and dinitro-substituted perylenediimide derivatives is developed. UV-vis-NIR and electron paramagnetic resonance measurements were carried out to confirm the formation of ra

Full text of DOI:10.1021/acs.joc.8b02023

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Note
Visible Light-triggered Generation of Ultra-stable
Radical Anion from Nitro-substituted Perylenediimides
Vikas Sharma, Unnikrishnan Puthumana, Pirudhan Karak, and Apurba Lal Koner
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b02023 • Publication Date (Web): 15 Aug 2018
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The Journal of Organic Chemistry
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Visible Light-triggered Generation of Ultra-stable Radical Ani-
on from Nitro-substituted Perylenediimides
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Vikas Sharma, Unnikrishnan Puthumana, Pirudhan Karak and Apurba Lal Koner*
Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal Bypass Road, Bhauri, Bhopalꢀ
462066, Madhya Pradesh, INDIA
Supporting Information Placeholder
ABSTRACT: An efficient method for visible lightꢀtriggered generation of radical from mono and dinitroꢀsubstituted Peryleneꢀ
diimide (PDI) derivatives is developed. UVꢀVis.ꢀNIR and EPR measurements were carried out to confirm the formation of radical.
Most importantly, these radical anions were remarkably stable for several months. Subsequently, the reversible nature of anions
was validated by both chemical and spectroelectrochemical methods for the application in electrochromic materials.
Over the past few years, there has been a steadily growing
interest in making stable organic radicals.1ꢀ5 Redoxꢀactive radꢀ
icals have found applications in photovoltaics,6 organic elecꢀ
tronics,7ꢀ13 and catalysis.3, 14ꢀ15 Modulation of electronic propꢀ
erties by changing the substitutions, we can fineꢀtune the radiꢀ
cal properties and efficiency of organic radical generation.
Photoꢀtriggered generation of metalꢀfree organic radicals is a
keyꢀadvancement towards developing efficient photoꢀcatalysts
and solar cells.3 The radical generation efficiency, kinetics,
and its stability in ambient conditions are equally important.
However, only limited number of purely organic compounds
are known to possess such qualities.5 Particularly, peryleneꢀ
diimide (PDI) dyes, an important class of rylene dyes, known
for their high brightness and exceptional stability are promisꢀ
ing candidates for generating organic radicals.16ꢀ18 Mostly, the
stability of the radicals generated from PDI is attributed to the
presence of electron withdrawing imide groups. Hence, incorꢀ
poration of additional electronꢀwithdrawing groups can lower
the reduction potential and enhance their radical stability.
radical anions by reducing a pentafluoroꢀphenoxylꢀsubstituted
PDI was also reported.25 Recently, a supramolecular strategy is
explored for stabilizing PDI radical anions and for their appliꢀ
cation in photoꢀthermal therapy.26ꢀ28 Moreover, the ease of
conversion and stability of the radical anions from bayꢀ
halogenated PDI derivatives are shown to be much better than
that of nonꢀhalogenated. Similarly, the chlorinated PDI
showed a stronger effect compared to brominated PDI. With
this realization, we explored the potential of highly electron
withdrawing nature of nitro group for stabilizing the radical
anion originated from mono (1) and diꢀnitro (2) substituted
PDI. Although a class of nitroꢀsubstituted PDI had been reꢀ
ported,29 to our best knowledge, generation of radical anions
on these nitroꢀsubstituted PDIs and quantification of the role
of visible light in this process is still unexplored.
Herein, we have demonstrated a facile generation of visibleꢀ
light triggered ultraꢀstable organic radical anions from two
nitroꢀsubstituted PDI derivatives (see Scheme 1). Various
spectroscopic and electrochemical techniques such as UVꢀ
Vis.ꢀNIR, EPR spectroscopy, and spectroelectrochemistry
were employed to characterize the radical anions. The photoꢀ
generated radical anions were stable for several months under
ambient conditions. Further, the chemical and electrochemical
reversibility was verified using various reducing and oxidizing
agents and by spectroꢀelectrochemistry.
In this direction, Wasielewski and coꢀworkers reported a series
of electron deficient PDI with cyano and trifluoromethyl
groups in the bay region to stabilize radical anions.19ꢀ20
Rybtchinski group synthesized a waterꢀsoluble PDI derivative
with polyethylene glycol chains at the imide positions and
generated its dianions using Na2S2O4 as a reducing agent.21
Furthermore, Würthner group has developed ambient stable
PDI dianionꢀdisodium salt and zwitterionic PDIꢀcentered radiꢀ
cal anion.22ꢀ24 Interestingly, the generation of ambientꢀstable
1
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Page 2 of 6
Scheme 1. Chemical structures of mononitroꢀsubstituted
The UVꢀVis. spectrum of 1 shows characteristic peaks around
1
2
3
PDI (1) and dinitroꢀsubstituted PDI (2) and schematic repꢀ
resentation of the reversibility of visible light triggered
radical generation
520 and 485 nm (see Figure 1a) however, upon exposing to
visible light the characteristic peaks of 1•
̄
(at 680, 500 and
425 nm) appeared.30 The characteristic peaks of 1•
̄
conferred
the singleꢀelectron transfer process from N,Nꢀdimethyl amine
present in DMF to excited 1 and the conversion was complete
within 10 min. The reduction of 2 also followed a very similar
kinetic and spectral feature (Figure 1b and 1d). As shown in
Figure 1b, peak at 520 nm disappears and a set of peaks at
4
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680, 525 and 420 nm appear as is 2•
̄ formed. Moreover, the
occurrence of isosbestic points in multiple wavelengths also
suggests the coꢀexistence of only dye and photogenerated radꢀ
ical anion species in solution.
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Subsequently, to confirm the generation of radical anions, we
have performed electron paramagnetic resonance (EPR) specꢀ
troscopy and it provided the unequivocal evidence of 1• /2•
̄ ̄.
In DMF, radical anion formed from 1 gave a peak at 3350 G
(Figure 2a) with a gꢀfactor of 2.01. While the radical anion
formed from 2 also gave a similar peak at around 3355 G
(Figure 2b) with a gꢀfactor of 2.01. Further to assess the stabilꢀ
ity of the radical anion in ambient conditions, in the UVꢀVis.ꢀ
After synthesis and characterization of 1 and 2 using modified
protocol (see experimental section and Figure S1ꢀ5), the reꢀ
duction of both dyes, 1 and 2 in DMF at the different time
with visible light exposure were monitored using UVꢀVis.ꢀ
NIR spectroscopy (Figure 1). The reduction was found to proꢀ
ceed in dimethyl formamide (DMF) even without the addition
of any additional reductant. The solution of 1, initially red in
color, turned into lightꢀgreen (Figure 1c, Scheme S2) as it was
exposed to visible daylight, due to the presence of electron
rich N,Nꢀdimethyl amine in DMF because of its decomposiꢀ
tion. The prerequisite of light and the presence of amine have
been verified using freshly distilled DMF and addition of sacꢀ
rificial amine such as N,Nꢀdiethylamine (DEA, see Figure S6ꢀ
NIR spectra of 1• /2•
̄ ̄ solutions were monitored for several
months (see Figure 2c and 2d). The absorbance intensities at
680 nm were plotted against time in days. Interestingly, no
change in the peak intensity was observed even after monitorꢀ
ing for 40 days. The occurrence of multiple isosbestic points
further confirms that ultraꢀstability of the photogenerated radiꢀ
cal anions. The extraꢀstability is thought to be due to the
presence of the highly electronꢀwithdrawing nitro group in the
bay position, stabilizes the formation of radical anions.
9). The calculated excitedꢀstate oxidation potential of 1•
and 2•
/2 is 1.74 V and 2.01 V respectively (see experimental
̄ /1
̄
section). Higher excitedꢀstate oxidation potential of compound
2 in comparison to 1 is reflecting that its oxidation of is diffiꢀ
cult compared to 1 in the excitedꢀstate. Similarly, solution of 2
in DMF also changed from red to oliveꢀgreen (Figure 1d) only
upon exposure to visible daylight.
Figure 2. (Top) Confirmation of radical by EPR spectroscopy;
EPR spectra of radicals formed from 1 mM of (a) 1 and (b) 2 in
DMF. Peaks centered around 3350 G is indicating the unmistakaꢀ
ble presence of the paramagnetic radical anion species. (Bottom)
Superꢀstable radicals; Absorption spectra of (c) 1 and (d) 2 in
DMF in the course of 40 days. Inset shows the plot of absorption
at 680 nm with time. The intensity has not decreased significantly
even after 40 days verifying the superꢀstability of the radical aniꢀ
ons in the solutions
Figure 1. Monitoring radicalꢀformation using UVꢀVis.ꢀNIR abꢀ
sorption spectroscopy: (Top) The electronic absorption spectra of
radicalꢀformation from 50 µM of (a) 1 and (b) 2 in DMF. (Botꢀ
tom) Formation kinetics and visible color change; plot of absorbꢀ
ance at 680 nm against exposure time for (c) 1 and (d) 2 to visible
daylight. Inset shows a visible color change of the solution due to
radical formation.
The reduction of 1 was further explored in other solvents by
addition of various wellꢀexplored reductants.30 An efficient
and photoꢀtriggered radical generation using 1 equivalent of
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tetrabutylammonium fluoride (TBAF) in various solvents such
0.7 V indicating a possibility of further second reduction. This
would suggest that a dianionic state could be formed by furꢀ
ther reduction of the radical anion. Thus, we tried to chemicalꢀ
ly generate the dianionic state from 1 using tetrabutylammoniꢀ
um hydroxide (TBAOH). Surprisingly, the dianionic state was
formed by addition of just two equivalent of TBAOH in THF
whereas no others have reported the formation of dianions
using such low concentrations of reductants (see SI, Figure
S19), which is also corroborating its high electron affinity.
The formation of this dianionic state from a radical state is
associated with a visible color change in solution from green
to blue (see Figure S20). Further, we tried to generate dianions
in various solvents such as DMF, chloroform and toluene
(Figure S19). The formation of blue color dianionic state from
green color radical anionic state has been associated with a
hypsochromic shift in absorption peak from 680 nm to 600
nm. The peak at around 600 nm thus could be attributed as the
dianionic state.22
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as toluene, THF, and chloroform is shown in Figure S10ꢀ12.
To verify, the role of TBAF in the reduction process, we have
performed 1H NMR experiment and obtained unidentified
peaks (Figure S13) hinted a complicated reduction mechanism
as indicated recently.31ꢀ33 It shows that the emerging peak
intensity at 680 nm which gets saturated within 15 min in
DMF, chloroform, and THF (Figure 1 and S10aꢀb) while it
took ca. 30 minutes to get the saturation in toluene (Figure
S7c). This could be due to nonꢀpolar nature of toluene, which
would be unfavorable to the forming radical.22
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Also, by addition of higher equivalent of reductant in toluene
showed no considerable increase in the peak intensity, indicatꢀ
ing that the conversion was completed by the use of just one
equivalent of TBAF (Figure S11). The relative percentile of
radical formation of 1 in different solvents is assessed (Figure
S12). As it can be seen from Figure S12, in toluene, the perꢀ
centage conversion is significantly low. However, in other
solvents such as THF, DMF and chloroform, addition of highꢀ
er equivalents of strong TBA bases resulted in a dianionic
state. Further, this was confirmed by spectroelectrochemistry
measurements (vide infra.). To assess the reduction process by
various other reductants were also examined (Figure S14ꢀ15).
Interestingly, the reduction was also found to be happening
even with a weak base TBACN (Figure S15). Likewise, the
reduction of 2 was also carried out in both DMF and chloroꢀ
form in addition of other reductants (see SI).
However, the dianionic state was found to have not formed in
toluene which could be again due to the unfavorable thermoꢀ
dynamics of formation in a highly nonꢀpolar toluene as shown
earlier.30 The cyclic voltammogram of 2•
̄ however, did not
show any such distinguishable oxidation peaks (Figure S15b).
As a result, dianion of 2 was not found to have formed even
upon treating 2 with greater equivalents of reductants. To get a
better insight, spectroelectrochemistry was performed on both
1 and 2 to study the changes in absorption spectra upon applyꢀ
ing potentials (Figure 3). Upon applying the negative potential
(ꢀ0.64 V) to 1, the peak 520 nm disappeared and a new specꢀ
trum emerged with a characteristic peak at 680 nm (Figure 3a
and S21a). This was accompanied by a change in the color of
solution from red to green, similar to what we have already
observed in chemical reduction. This confirms that the elecꢀ
trochemical reduction of 1 results in the same radical comꢀ
pound as the chemical reduction. Also, upon applying a posiꢀ
tive potential of +0.35 V, the solution changed its color from
green to red. Also, a shift in peak was observed from 680 nm
to 520 nm, indicating regeneration of 1 by oxidation of radical.
Further, to validate the reversibility in the switching, we have
performed two rounds of reduction/oxidation cycles on 1 using
spectroelectrochemistry (Figure 3a). Such reversibility of PDI
dyes might be crucial in various applications such as switches.
Similarly, upon electrochemically reducing 2, peak at 520 nm
disappeared and peaks characteristic to radical anion appeared
at 680, 525 and 420 nm upon applying a potential of ꢀ0.34 V
(Figure 3a and S21b). Color of the solution changed from iniꢀ
tial red to olive green. Further, when a potential of +510 mV
was applied, the peaks at 680, 525 and 420 nm started to diꢀ
minish and a peak at 520 nm appeared with dominating intenꢀ
sity. A visible color change from olive green colored solution
to red was also observed. The peak at 520 nm is characteristic
to 2 and its reꢀappearance confirms the oxidative regeneration
of 2 from its radical anion. Since, both 1 and 2 could be easily
switched between radical and neutral state by using electroꢀ
chemical techniques, the PDIꢀreductant interaction can be
thought as purely electrochemical in nature. Therefore, we
have fabricated a prototype of an electrochromic device (ECD,
Figure S22). The electrochemical reversibility also opens up
the possible chemical reversibility, we tried chemically reversꢀ
ing the reduction of both 1 and 2 using a strong oxidant nitroꢀ
sonium tetrafluoroborate (NOBF4). As shown in Figure 3bꢀc,
we were able to generate back the characteristic peak of both 1
and 2 by just using 1 equivalent of NOBF4. Notably, this corꢀ
Figure 3. (Top) Switchability between 1 and 1• ̄. UVꢀVis.ꢀNIR
absorption spectra of MNPDI in DMF upon applying different
potentials. Corresponding color changes in solution taken in
cuvettes are also shown in different time intervals. (Bottom)
Chemical oxidation: Absorption spectra of radicals generated
from (b) 1 and (c) 2 before and after addition of NOBF4 in chloroꢀ
form.
To understand the electrochemical properties of 1 and 2 and
their radical anion, we have performed cyclic voltammetry
(Figure S16ꢀ18). Cyclic voltammogram of radical generated
from 1 (Figure S17) shows a reversible reduction peak at ca. –
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relation between reversible spectroꢀelectrochemical and chemꢀ used was 0.1 M of tetrabutylammonium hexafluorophosphate
Page 4 of 6
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ical reduction suggests that the said reduction is a oneꢀelectron
transfer process involving no covalent bond formation.
(TBAPF6).
Mass Spectrometry. All mass spectrometric data were recꢀ
orded using atmospheric pressure chemical ionization (APCI)
on MicroTOFꢀQꢀII mass spectrometer using chloroform as a
solvent.
In conclusion, two nitroꢀsubstituted PDI derivatives were sucꢀ
cessfully synthesized for the generation of visibleꢀlight trigꢀ
gered ultraꢀstable organic radical anions. The generated radical
anions were found to be stable in solutions for months. The
paramagnetic nature of radical anions was confirmed through
EPR spectroscopy and spectroelectrochemical investigations.
The radical anions were efficiently generated via simple reꢀ
ductants or electronꢀrich solvent such as DMF. This study on
reversible charging of simple nitroꢀsubstituted PDI dyes with
ultraꢀstability will surely be an important addition to radical
chemistry; visibleꢀlight mediated organic photocatalysis and
an omnipotent extension to the field of organic electronics.
2,9-dicyclohexyl-5-nitroanthra[2,1,9-def:6,5,10-
d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone 1: Under open
air, PDI (100 mg, 0.18 mmol), Sodium nitrite (15 mg, 0.22
mmol), nitric acid (520 µl,12.45 mmol), was added in 30 ml
9
dichloromethane and stirred at room temperature for 4 h. After
that the reaction mixture was neutralized with 15% KOH soluꢀ
tion and extracted with chloroform.The crude product was
purified by silica gel column chromatography using eluent as
dichloromethane afforded the pure compound 1 as an amorꢀ
phous solid (90 mg, 83.25 %). 1H NMR (500 MHz, CDCl3): δ
= 8.74 (d, J = 8.0 Hz, 1H), 8.71 – 8.62 (m, 4H), 8.55 (d, J =
8.1 Hz, 1H), 8.17 (d, J = 8.1 Hz, 1H), 5.02 (t, J = 12.1 Hz,
2H), 2.54 (q, J = 12.4 Hz, 4H), 1.92 (d, J = 11.3 Hz, 4H), 1.77
(d, J = 11.3 Hz, 6H), 1.52 – 1.29 (m, 6H). 13C NMR (126
MHz, CDCl3) : δ = 163.6, 163.3, 163.2, 162.3, 147.7, 135.4,
132.9, 132.9, 131.4, 131.2, 129.4, 129.4, 129.0, 128.0, 127.6,
126.6, 126.5, 126.4, 125.5, 124.8, 124.6, 124.1, 123.7, 54.6,
54.4, 29.3, 29.2, 26.7, 26.6, 25.5, 25.5. HRMS (APCI) m/z:
[M+H]+ Calcd for C36H30N3O6 600.2056 Da; Found
600.2135 Da.
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EXPERIMENTAL SECTION
Steadyꢀstate absorption spectroscopy. Steadyꢀstate absorpꢀ
tion measurements, if not otherwise mentioned were perꢀ
formed using Cary 5000 Spectrophotometer from Agilent
Technologies using 1 cm path length quartz cuvette. Samples
were taken at a concentration of 50 ꢁM if not mentioned othꢀ
erwise. Scan rate used was 400 nm/min. and sample interval,
0.667. Absorption measurements required for spectroelectroꢀ
chemistry were measured using an HR 4000 spectrophotomeꢀ
ter from Ocean Optics along with a 1 cm cuvette holder and
DTꢀMINIꢀ2ꢀGS UVꢀVis.ꢀNIR lightsource. All the experiꢀ
ments were carried out at ambient temperature (298 K) if not
otherwise stated. The intensity was measured by LXꢀ101 lux
meter by Lutron. As there was no change in spectrum upon
keeping the solution inside the spectrophotometer, it was exꢀ
posed to light for short timeꢀperiods between the measureꢀ
ments. These time periods are termed as the ‘exposureꢀtime’.
2,9-dicyclohexyl-5,12-dinitroanthra[2,1,9-def:6,5,10-
d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone 2: Under niꢀ
trogen atmosphere, compound 1 (400 mg, 0.67 mmol), cerium
(IV) ammonium nitrate (800 mg, 1.46 mmol), nitric acid (5
ml, 79.36 mmol), was added in 100 ml dichloromethane and
stirred at room temperature for 48 h. After that the reaction
mixture was neutralized with 15% KOH solution and extracted
with chloroform. The crude product was purified by silica gel
column chromatography using eluent as dichloromethaneafꢀ
forded a mixture of 1,7ꢀ and 1,6ꢀdinitroperylene bisimides and
after analysis of 1H NMR (500 MHz, CDCl3) it was found in
the ratio of 3:1. By repetitive crystallisation pure 1,7ꢀ
dinitroperylene bisimide was obtained as an amorphous solid 2
Electron paramagnetic resonance spectroscopy. The samꢀ
ples required for EPR spectroscopy were prepared in DMF at
1 mM concentration and measurements were done at 140 K
temperature. Modulation amplitude was set to 1 and time conꢀ
stant 24.
Cyclic voltammetry. Cyclic voltammetric measurements
were taken using an electrochemical analyzer of CH Instruꢀ
ments. Working electrode used was Pt along with an
Ag/AgNO3 reference electrode and Pt counter electrode. For
the measurement, 1 mM of both 1 and 2 were dissolved in
DMF. Supporting electrolyte used was tetrabutylammonium
hexafluorophosphate (TBAPF6).
1
(150 mg, 35 %). H NMR (500 MHz, CDCl3): δ = 8.80 (s,
2H), 8.64 (d, J = 8.0 Hz, 2H), 8.31 (d, J = 8.0 Hz, 2H), 5.01
(m, 2H), 2.57 – 2.45 (m, 4H), 1.92 (s, 4H), 1.75 (d, J = 11.5
Hz, 6H), 1.34 (d, J = 12.5 Hz, 4H). HRMS (APCI) m/z:
[M+H]+ Calcd for C36H28N4O8 645.1907 Da; Found
645.1959 Da
Fabrication of a prototype ECD device. Since the spectroeꢀ
lectrochemistry proves that 1 and 2 can be electrochemically
switched between radical and neutral states, this reveals a posꢀ
sible application of these PDI dyes in fabricating certain elecꢀ
trochromic materials. Here, we mix coat a mixture of 1 and
polymethyl methacrylate (PMMA) on an Indium tin oxide
(ITO) and examine if this film exhibits a change in color upon
application of potential. For the fabrication of this device, 1
mM mononitro PDI was dissolved in a 33:53:14 w/w mixture
of PMMA, propylene carbonate (PC) and TBAPF6 in THF.35ꢀ36
Mixture was tightly closed and stirred for 24 hours. Then, this
mixture was dropꢀcasted onto an ITO film to create a colored
conducting layer. This ITO was then dipped in an electrolyte
solution and potential was applied to it. Upon application of
potential, instantaneously the red colored film coated on ITO
turned dark, with greenish trace inside it (Figure S19). This
greenish trace could be attributed to the formation of radical
Calculation of the excitedꢀstate oxidation potential of 1 and
2. The excitedꢀstate oxidation potential of 1 and 2 is calculated
according to the RehmꢀWeller equation34 using a reduction
potential value of ꢀ0.64 V vs SCE (1•ꢀ/1) and ꢀ0.37 V vs SCE
(2•ꢀ/2) in DMF. The E0–0 transition energy of ca. 2.38 eV is
calculated at 520 nm (from the absorption maxima as comꢀ
pound 1 and 2 both are nonꢀfluorescent). Taking these two
values in account, the excitedꢀstate oxidation potential in the e
is expected to be +1.74 V for 1 and +2.01 V for 2 vs SCE.
Spectroelectrochemistry. Absorption spectra were taken usꢀ
ing an HR 4000 spectrophotometer developed by Ocean Opꢀ
tics along with a 1 cm cuvette holder and DTꢀMINIꢀ2ꢀGS UVꢀ
VisꢀNIR lightsource. A CH electrochemical analyzer was used
to hold the samples at desired potentials. A Pt working elecꢀ
trode, Ag/AgNO3 reference electrode and a Pt counter elecꢀ
trode were also used for this purpose. Supporting electrolyte
4
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13.
Sharma, V.; Sahoo, D.; Chandra, F.; Koner, A. L., Highly
anions and the remaining dark red traces to the remaining,
unconverted neutral 1.
Fluorescent Periꢀfunctionalized Perylenemonoimide Derivatives with
Tunable Optical Properties for Selective Sensing of Electronꢀrich
Aromatic Amines. ChemistrySelect 2017, 2, 11747ꢀ11754.
1
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ASSOCIATED CONTENT
Supporting Information
14.
Ghosh, I.; Ghosh, T.; Bardagi, J. I.; König, B., Reduction
of aryl halides by consecutive visible lightꢀinduced electron transfer
processes. Science 2014, 346, 725ꢀ728.
15.
Visible Light Mediated Photoredox Catalytic Arylation Reactions.
Acc. Chem. Res. 2016, 49, 1566ꢀ1577.
16.
The Rylene Colorant Family—Tailored Nanoemitters for Photonics
Research and Applications. Angew. Chem. Int. Ed. 2010, 49, 9068ꢀ
9093.
The Supporting Information is available free of charge on the
ACS Publications website. The synthetic scheme, other spectroꢀ
scopic, elcctrochemical characterization, and prototype electroꢀ
chromic device are given via a link at the end of the document.
(file type, i.e., PDF)
Ghosh, I.; Marzo, L.; Das, A.; Shaikh, R.; König, B.,
Weil, T.; Vosch, T.; Hofkens, J.; Peneva, K.; Müllen, K.,
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AUTHOR INFORMATION
Corresponding Author
17.
Zeng, W.; Qi, Q.; Wu, J., Toward Long Rylene Ribbons
and Quinoidal Rylene Diradicaloids. Eur. J. Org. Chem. 2018, 2018,
Eꢀmail: akoner@iiserb.ac.in
ORCID: 0000ꢀ0002ꢀ8891ꢀ416XX
7ꢀ17.
18.
Sharma, V.; Chandra, F.; Sahoo, D.; Koner, A. L., An
Efficient Microwaveꢀassisted Synthesis of Sonogashiraꢀcoupled PMI
Derivatives: Impact of Electron Donating Groups on Optoelectronic
Properties. Eur. J. Org. Chem. 2017, 2017, 6901ꢀ6905.
ACKNOWLEDGMENT
This work is supported by Council of Scientific & Industrial Reꢀ
search (CSIR), (Grant no: 02(0134)/17/EMRꢀII), India.
19.
Roznyatovskiy, V. V.; Gardner, D. M.; Eaton, S. W.;
Wasielewski, M. R., Radical Anions of Trifluoromethylated Perylene
and Naphthalene Imide and Diimide Electron Acceptors. Org. Lett.
2014, 16, 696ꢀ699.
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