Substitution Effects on the Photoinduced Charge-Transfer Properties of Novel Perylene-3,4,9,10-tetracarboxylic Acid Derivatives

Article abstract of DOI:10.1021/acs.jpca.7b03806

We report here the synthesis and photophysical study of a series of electron donor-acceptor molecules, in which electron-donating 4-methoxyphenoxy groups are attached to the 1,7-bay positions of four different perylene tetracarboxylic acid derivatives, na

Full text of DOI:10.1021/acs.jpca.7b03806

Article
Substitution Effects on the Photoinduced Charge Transfer Properties
of Novel Perylene-3,4,9,10-tetracarboxylic Acid Derivatives
Damla Inan, Rajeev K. Dubey, Nick Westerveld, Jorrit Bleeker, Wolter F Jager, and Ferdinand C. Grozema
J. Phys. Chem. A, Just Accepted Manuscript • Publication Date (Web): 30 May 2017
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The Journal of Physical Chemistry
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Substitution Effects on the Photoinduced Charge
Transfer Properties of Novel Perylene-3,4,9,10-
tetracarboxylic Acid Derivatives
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Damla Inan,// Rajeev K. Dubey, //† Nick Westerveld, † Jorrit Bleeker,// Wolter F. Jager,†* and
Ferdinand C. Grozema // *
//Laboratory of Optoelectronic Materials and†Laboratory of Organic Materials & Interfaces
Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629
HZ Delft, The Netherlands.
* W.F.Jager@tudelft.nl
*F.C.Grozema@tudelft.nl
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ABSTRACT
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We report here the synthesis and photophysical study of a series of electron donor-acceptor
molecules, in which electron donating 4-methoxyphenoxy groups are attached to the 1,7-bay
positions of four different perylene tetracarboxylic acid derivatives; perylene tetraesters (PTEs) 1,
perylene monoimide diesters (PMIDEs) 2, perylene bisimides (PBIs) 3, and perylene
monobenzimidazole monoimids (PMImMIs) 4. These perylene derivatives are used because of their
increasing order of electron accepting capability upon moving from 1 to 4. Two additional donor-
acceptor molecules are synthesized by linking electron donating 4-methoxyphenyl groups to the
imide position of perylene monoimide diester 2 and perylene bisimide 3. The motivation for this
study is to achieve a good control over the photoinduced charge transfer process in perylene based
systems by altering the position of electron-donor and tuning the electron deficiency of perylene
core. A comprehensive study of the photophysical properties of these molecules has shown a highly
systematic trend in the magnitude of charge transfer as a function of increased electron deficiency of
the perylene core and solvent polarity. Importantly, just by changing the attachment of electron
donating group from “bay” to “imide” position, we are able to block the charge transfer process.
This implies that the positioning of the electron donor at the perylene core strongly influences the
kinetics of the photoinduced charge transfer process. In these compounds, the charge transfer process
is characterized by the quenching of fluorescence and singlet excited-state lifetimes as compared to
model compounds bearing non-electron donating 4-tert-butylphenoxy groups. Transient absorption
spectroscopy did not reveal spectra of charge transfer states. This most likely implies that the CT
state is not accumulated, because of the faster charge recombination.
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INTRODUCTION
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A good control over photoinduced charge and energy transfer between donor and acceptor moieties
is essential for the development of artificial photosynthesis.1,2,3,4 Important variables, which dictate
the yields and kinetics of these interactions, are excited state and redox properties of the donor and
acceptor components, their relative distance, mutual orientation, and electronic coupling.5,6,7,8,9,10
During the past three decades, molecular assemblies consisting of light harvesting chromophores,
charge-separators, and catalysts have been designed and studied to gain a better understanding of the
photochemistry and photophysics involved in these systems.11,12,13 Such assemblies are of prime
importance because of their ability to mimic the natural photosynthetic process and to convert
sunlight into fuel.
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Several chromophores have been tested as integrative building blocks for light-harvesting
and charge-separation. Perylene tetracarboxylic acid derivatives, of which perylene bisimides (PBIs)
are the best known representatives, are particularly attractive chromophores due to their exceptional
photo-chemical stability, high electron deficiency, strong absorption in the visible region of the solar
spectrum, and possibility to further tune their photophysical properties by structural
modifications.14,15 Taking advantage of high photochemical robustness and strong absorption,
various light-harvesting antenna systems have been prepared using perylene tetracarboxylic acid
derivatives as the active chromophore.16,17,18,10 However, due to the high electron deficiency of the
perylene core, charge-separation has been commonly observed when these compounds are
covalently coupled even with moderately electron-rich donors.18,19
Perylene tetracarboxylic acid derivatives (mostly PBIs) are also attractive components of
charge separators, and for this application, their high electron deficiency is highly beneficial. In the
past, many separate studies on perylene based donor-acceptor systems have been carried out.19,20,21,
22,23
These studies have revealed that the efficiency and kinetics of charge transfer are highly
sensitive to even small structural variations. In a recent study on PBI based isoelectronic donor-
bridge-acceptor compounds, we have shown that small changes in the molecular bridge have a large
impact on the dynamics of charge separation.24 In another recent study, Shoer et al. have observed
that the charge separation can be an order of magnitude faster for systems in which donors are
connected to the ortho (or headland) positions of the perylene core as compared to the imide
position.25
Another recent study by Pagoaga et al. reported strong fluorescence quenching ascribed to
charge separation, for PBIs bearing 4-methoxybenzene substituents as electron donors at various bay
positions.26 Preceding work by Flamigni et al. on non-bay substituted PBIs, bearing mono-, di- and
trimethoxy-benzene at the imide-position, has revealed that charge transfer rates strongly correlate
with the redox properties of the methoxybenzene and the positioning of the methoxy group.27
A
comparison between efficiency of charge transfer and the positioning of the electron donors cannot
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be made from these studies, because 1,7-bay substitution decreases the reduction potential of the
perylene acceptor, i.e. makes the perylene core less electron deficient.14 Therefore, there is still a
need for a comprehensive study to understand the kinetics of charge transfer towards perylenes as a
function of the position at which the electron donating substituents are attached. So that perylene
containing devices can be designed in which the perylene derivatives serve a well-defined role of
energy acceptor or donor in a light harvesting antenna and that of electron acceptor in a charge
separating unit.
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In this work, we report on the design, the synthesis, and the photo physical properties of a
series of perylene-3,4,9,10-tetracarboxylic acid derivatives bearing either 4-methoxyphenoxy or 4-
methoxyphenyl groups as electron donors. The choice of these groups as electron donors is based on
reports in which facile charge transfer was observed upon photoexcitation of perylene bisimides
bearing methoxyphenyl groups as electron donors.26,27 In this study, the electrochemical and optical
properties of the perylene core were also systematically tuned by the modifications at the peri-
positions. For the photophysical characterization of our compounds, steady-state and time-resolved
spectroscopic studies were carried out in solvents of different polarity. In these compounds, the
strong fluorescence of the perylene moiety has been quenched to different extent by electron
donating groups attached to the perylene core at different positions. The aim of this work is to
establish a relation between molecular structure and the extent of fluorescence quenching observed
for these molecules in solvents of different polarity. We ascribe this fluorescence quenching to
photoinduced charge transfer, and assume that the positions from which quenching is efficient are
the appropriate positions to attach electron donors and achieve efficient charge separation. Finally,
the obtained experimental results are rationalized by computational calculations based on time
dependent density functional theory.
RESULTS AND DISCUSSION
Synthesis and Characterization: As described in Scheme 1, the reported 1,7-diphenoxy-
substituted compounds (1a–b, 2a–c, 3a–c, and 4a–b) were synthesized from their corresponding
1,7-dibromoperylene-3,4,9,10-tetracarboxylic acid derivatives, 1,7-dibromoperylene tetrabutylester
1, N-(2,6-diisopropylphenyl)-1,7-dibromoperylene monoimide dibutylester 2, N,N′-bis(2,6-
diisopropylphenyl)-1,7-dibromoperylene bisimide 3, and the N-(2,6-diisopropylphenyl)-1,7-
dibromoperylene monoimide monobenzimidazoles (4 and4′).
The syntheses of these regioisomerically pure 1,7-dibromo-precursors (1–4) was carried out
from commercially available perylene-3,4,9,10-tetracarboxylic bisanhydride (PBA) using a
previously reported procedure.28 The subsequent substitution of bromine atoms with 4-tert-
butylphenoxy and 4-methoxyphenoxy groups was achieved in high yields (80-90%) as shown in
Scheme 1. The phenoxy substitution on 1,7-dibromoperylene tetrabutylester 1 was performed in
o
anhydrous DMF at elevated temperature (115 C) owing to the low reactivity of the 1,7-
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dibromoperylene tetrabutylester towards nucleophilic substitution reactions.28 For all other
derivatives (2, 3, and 4), the reaction was carried out under milder reaction conditions in toluene at
temperatures around 90 oC.10,29
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Scheme 1. Synthesis of 1,7-di(4-tert-butylphenoxy) and 1,7-di(4-methoxyphenoxy)perylene-3,4,9,10-
tetracarboxylic acid derivatives.
An isomeric mixture of 1,7-dibromoperylene monoimide monobenzimidazole compounds (4 + 4′)
was obtained by the reaction between 1,7-dibromoperylene monoimide monoanhydride 7 and 1,2-
diaminobenzene in refluxing propionic acid (Scheme 2).30 The TLC analysis of this mixture
revealed two slightly separated spots corresponding to 4 and 4′. Efforts to separate the two region-
isomers by column chromatography, however, were not successful. The presence of two isomers
was also evident from the 1H NMR spectrum, in which two sets of signals in the aromatic region are
clearly visible (Figure 1). These signals, corresponding to the perylene core protons H8, H8ʹ and
H11, H11ʹ, were very well resolved. Based on the relative intensities of these signals, surprisingly, the
two regioisomers (4 and 4′) were found in a ratio ca. 2:1. The obtained ratio is rather surprising
because we cannot deduct differences in electron density of both anhydride carbonyl in compound 7,
based on resonance structures. Thus the reactivity of both anhydride carbonyl moieties are expected
to be identical. For the synthesis of tetrachlorobisimidazoles, both 1:131 and 2:132 isomeric mixtures
have been reported. The assignment of the signals (H8, H8ʹ and H11, H11ʹ) to the individual
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regioisomers was done based on H–1H COSY, and by the direct comparison of H NMR spectrum
of (4+4′) with the spectrum of 1,7-dibromoperylene bisimide 3 (Figure 1). The ring current effect of
the additional aromatic benzimidazole moiety was a decisive argument for explaining changes in the
chemical shifts.
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When comparing the 1H NMR spectra of compounds 3 and 4+4′, the chemical shifts for the
perylene core protons H2 and H5, in the “left” imide part of these compounds, are expected to be
very similar. Indeed, protons H2 and H5 have identical chemical shifts in compounds 3 and 4+4′.
Placement of the imidazole moiety on the “right” part of the molecule should effect the chemical
shifts of protons H8 and H11, upon going from 3 to 4 or 4′, but to a different extend. A larger shift is
expected for the proton H11 in compound 4, whereas the imidazole placement in compound 4′ should
have a larger effect on the chemical shift of proton H8ʹ. The predicted shifts are clearly visible in the
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1H NMR spectrum depicted in Figure 1, in which the proton assignment is shown.
Scheme 2. Synthesis of 4-methoxyphenyl functionalized derivatives 2c and 3c.
The two compounds 2c and 3c, containing 4-methoxyphenyl moiety at the imide position,
were synthesized to investigate photoinduced charge transfer from substituents attached to the imide
position of perylene tetracarboxylic acid derivatibes 2 and 3. The synthesis was carried out in two
steps from their corresponding monoanhydride precursors 5 and 7, respectively. In the first step,
imidization was carried out with 4-methoxyaniline in refluxing propionic acid to afford
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corresponding imides 6 and 8.29 Thereafter, nucleophilic substitution of bromine atoms with 4-tert-
butylphenol yielded the desired products 2c and 3c in good yields.
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Figure 1. Comparison between 1H NMR spectra of compound 4+4′ and 1,7-dibromoperylene bisimide 3.
Electrochemical Studies: The redox properties of compounds 1-4 were investigated by
cyclic voltammetry in dichloromethane. The obtained redox potentials (V vs Fc/Fc+) for these
molecules are summarized in Table 1.
As shown in Table 1, the redox properties of the molecules change significantly if the
substitution at the peri-positions is altered. When the groups attached to peri positions become more
electron withdrawing (for example, from tetraester to monoimide), the redox potentials of the
compounds become more positive.32,33 This clearly shows that molecules have higher electron
affinities going from compound 1 to 2 to 3, which makes them better electron acceptors. From the
data in Table 1, it is clearly seen that the perylene tetracarboxylic derivatives 3 and 4 are rather
similar as far as their electronic properties are concerned. This implies that the imide and
benzimidazole groups are electrochemically equivalent.32 Finally, it is apparent that attaching
different phenoxy groups at the bay positions does not result in notably different redox potentials.
This indicates the absence of significant interaction between these groups in the ground state.
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Table 1. First redox potentials of perylene derivatives (V vs. Fc/Fc+) obtained by cyclic voltammetry in CH2Cl2.
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Compound
E1/2 ox
−
E1/2 red
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1
−1.55
a
1a
1b
2a
2b
2c
3a
3b
3c
4a
4b
+0.84
+0.82
+0.95
+0.94
+0.97
+1.05
+1.04
+1.06
+1.01
+1.02
−
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−
−1.38b
−1.38
−1.33
−1.11
−1.10
−1.09
−1.06
c
−
aNo reduction potential was observed. bIrreversible. c Not detectable.
Steady State Absorption Studies: The absorption spectra of compounds 1-4, in chloroform,
are shown in Figure 2 and the relevant data, in toluene, chloroform, and acetonitrile (or
benzonitrile), are given in Table 2. All compounds are readily soluble in toluene and chloroform.
However, the solubility in polar and weakly polarizable acetonitrile was much lower. Especially, the
compounds 4a and 4b were insoluble in this solvent. At low solubility, perylene derivatives tend to
aggregate.34 This aggregation alters the optical properties and optoelectronic performances. In
general, spectral broadening and shifts in absorption and emission spectra, along with fluorescence
quenching, are the common signatures of this aggregation.35,36 Therefore, in order to preclude
spectral changes caused by aggregation, benzonitrile was used as a polar solvent for compounds 3
and 4.
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Figure 2. The normalized UV/Vis absorption (Left) and emission spectra (Right) of the compounds 1−4b in chloroform.
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The absorption spectra of all donor-substituted compounds (1b-4b) are characterized by a
strong absorption band at longer wavelengths (425−625 nm), and a weaker absorption band at
shorter wavelengths (Figure 2). As shown previously in literature, bay substitution leads to a
disappearance of the pronounced vibronic structure observed for perylenes without bay substitution.
This is accompanied by a bathochromic shift of the absorption bands.29,37 Upon increasing the size
of the π-system, i.e. going from compounds 1 to 2 to 3 and 4, the molar extinction coefficient
increases gradually and the absorption maxima shift to longer wavelengths. On changing the bay
substituent attached to the perylene core from tert-butylphenoxy to 4-methyoxyphenoxy small 5 nm
red shifts are observed. The influence of solvent polarity on the absorption maxima is rather modest.
Positive solvatochromism, a red shift in absorption upon increasing the solvent polarity, has been
observed, in particular for compounds with more electron deficient perylene cores, but these spectral
shifts do not exceed 15 nm.
Steady State and Time Resolved Emission Studies: The emission spectra of compounds 1-
4 roughly resemble the mirror images of the corresponding absorption spectra (Figure 2). The
positions of the emission wavelengths exhibit the same trend as those of the absorption maxima
(Table 2). While the effects of changing the bay-substituents and solvent polarity on the emission
wavelengths of these perylene compounds are modest, the emission intensities, quantified by their
fluorescence quantum yields (ΦF), are extremely sensitive to these parameters. Fluorescence
quantum yields close to unity with fluorescence lifetimes (τF) in the 4−5 ns range are observed for
compounds bearing the non-electron donating tert-butylphenoxy substituents at the bay positions
(compounds 1a−4a, Table 2).29 These fluorescent properties are similar to those of non-bay
substituted perylenes, i.e. no significant fluorescence quenching occurs from the 4-tert-butylphenoxy
substituents. It should be noted that the high fluorescence of compound 4a in toluene is remarkable,
because fluorescence quantum yields of perylene benzimidazoles are, in general, substantially lower
as compared to perylene bisimides.32
For the compounds bearing the electron donating 4-methoxyphenoxy substituents at the bay
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positions (compounds 1b−4b), fluorescence quantum yields gradually decreased with the increase in
solvent polarity and electron deficiency of the perylene core. The effect of solvent polarity is clearly
illustrated by compound 2b that has strong fluorescence in toluene (ΦF= 0.75), but shows negligible
fluorescence in acetonitrile (ΦF= 0.03). The effect of the increased electron deficiency of the
perylene core is clearly illustrated by the weak fluorescence found for compound 3b in all solvents.
These observations suggest that quenching of perylene fluorescence in these compounds is induced
by photoinduced charge transfer, although other quenching mechanisms cannot be excluded.38
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Table 2. Optical properties of compounds in toluene, chloroform, acetonitrile/benzonitrile.
[a]
τF (ns)[b]
Compound
Solvent
λabs(nm)
λem(nm)
Ɛ (M–1cm–1)
ΦF
1a
toluene
chloroform
acetonitrile
475
475
471
515
515
512
31500
25600
24800
0.91
0.84
0.90
4.26
4.40
4.73
toluene
chloroform
acetonitrile
479
478
479
515
517
517
24000
29300
33200
0.88
0.81
0.02
4.25
4.38
1b
2a
2b
2c
~0.21[c]
0.85
0.87
0.90
toluene
chloroform
acetonitrile
515
517
512
552
557
563
38900
36700
31700
4.52
4.82
5.23
0.85
0.32
0.03
toluene
chloroform
acetonitrile
520
522
517
555
561
566
34300
36000
34100
4.34
3.21
~0.08[c]
0.93
0.87
0.92
toluene
chloroform
acetonitrile
513
519
511
549
563
558
35900
36900
34700
4.36
4.73
4.69
0.94
0.91
0.86
toluene
chloroform
benzonitrile
543
547
552
572
578
586
57800
54200
54600
4.44
4.64
4.47
3a
3b
3c
~0.71[c]
~0.43[c]
~0.12[c]
0.19
0.04
0.01
toluene
chloroform
benzonitrile
549
551
561
575
580
583
53300
53100
51400
1.00
0.87
0.63
toluene
chloroform
benzonitrile
542
548
555
572
577
582
52500
51000
50900
3.80
3.89
3.30
0.71
0.66
toluene
578
607
63600
4.42
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4a
4b
chloroform
benzonitrile
581
584
614
619
63700
61350
0.70
4.31
4.22
1
2
3
4
5
6
7
0.75
0.23
0.04
toluene
chloroform
benzonitrile
582
584
591
609
616
621
63300
67600
69500
4.22
2.45
~0.43[c]
[a]Fluorescence quantum yield. [b]Fluorescence life-time. [c]Non mono-exponential decay.
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In order to establish whether the quenching depends on the position at which the electron
donating substituent is attached to the perylene core, the optical properties of the bay-substituted
compounds 2b and 3b are compared to the corresponding imide-substituted compounds 2c and 3c.
The fluorescence of the bay-substituted compounds 2b and 3b is much weaker compared to the
compounds 2c and 3c. This is clearly seen by comparing the fluorescence of compound 2b with that
of compound 2c. While the fluorescence of 2b strongly decreases upon increasing the solvent
polarity, compound 2c remains strongly fluorescent in all solvents. A similar observation is made by
comparing the fluorescence of compounds 3b and 3c. It should be noted that ascribing the
differences in photo physical properties between 2b and 2c, and 3b and 3c solely to the positioning
of the electron donor is not entirely valid. It is mainly due to the fact that the number of electron
donating substituents is different in both cases and the oxidation potential of the 4-methoxyphenoxy
bay substituent is ca. 0.30 V lower than that of the methoxyphenyl imide substituent.39 However,
since it has been previously shown that 4-methoxyphenyl substituents at all bay-positions strongly
quench the fluorescence of PBIs,26 it can still be concluded that fluorescence quenching from bay-
position is substantially faster than from imide-position. This conclusion is further supported by a
previous report,40 in which we have observed that the fluorescence quenching of perylene tetraester
by an aniline electron donor is substantially faster from the bay-position as compared to the peri-
position.
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Time-resolved fluorescence spectroscopy reveals that the fluorescence of the strongly
emitting compounds, (ΦF > 0.2), decays mono exponentially. Additionally, the emission of these
compounds is not significantly influenced by the presence of oxygen. Using the fluorescence
quantum yields and the fluorescence lifetimes, the rates of fluorescence and of non-radiative decay
(quenching by charge transfer) were calculated and summarized in Table S1 (supporting
information). From this table it is evident that upon increasing the solvent polarity, lifetimes and
rates of fluorescence decrease for all compounds. Rates of fluorescence between 2.5 and 1x108 s-1
have been determined for all compounds and these rates do not appear to be influenced by the bay
substituents. Quenching rates are in the order of 107 s-1 for the non-quenched compounds. For the
strongly quenched compounds, rates of quenching (and fluorescence) cannot be determined
accurately because fluorescence decay is no longer mono-exponential. Nevertheless, charge transfer
rates are estimated to be in the order of 109 to 1010 s-1.
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Transient Absorption Spectroscopy: To investigate the time resolved photophysics in more
detail, we have selected two series of compounds (2a-c and 3a-c) for which femtosecond pump-
probe transient absorption spectroscopy measurements were performed. In these series, the
molecules have different substitution patterns, near identical absorption spectra and markedly
different rates of fluorescence quenching in polar solvents. The transient absorption spectra were
measured in either acetonitrile (2a-2c) or benzonitrile (3a-3c) using pump wavelengths between 510
and 550 nm. The transient absorption spectra, for compounds 2a and 2b, and 3a and 3b,
immediately after excitation are shown in the inset in Figures 3 and 4, respectively. These transient
spectra are very similar to previously reported spectra with pronounced excited state absorption
features.10,19,24,41 For the monoimide compounds (2a,b,c) ground state bleaching below 520 nm,
stimulated emission between 520 and 620 nm, and a broad excited state-absorption with two maxima
near 685 nm and 800 nm are observed. For the bisimide compounds (3a,b,c) similar induced
emission and absorption features are observed but now the excited state absorptions are shifted to
longer wavelengths (710 nm and >900 nm). The spectra of 2c and 3c are depicted in Figure S5 in the
supporting information. It is interesting that the spectra for compounds 2a and 2b and those of 3a
and 3b are indistinguishable, even though very large differences in the radiative lifetime and
fluorescence quantum yields were observed.
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The identical photoinduced absorption spectra immediately after excitation (at 1 ps) indicate
that the nature of the excited states is the same in both cases. However, the lifetimes of the excited
states are much shorter for 2b and 3b than they are for 2a and 3a, respectively. In order to determine
the lifetime of the singlet-excited state of 2a-2c and 3a-3c we performed a global analysis. When we
compared the lifetime of the singlet excited state with the fluorescence lifetime for all compounds in
polar solvent, we see that these lifetimes are very close to the fluorescence lifetimes for all the
compounds (Table 3).
Figure 3. The kinetic traces at photo-induced absorption (685 nm) of molecules 2a [a] and 2b [b] in acetonitrile. The
transient absorption spectrum immediately after excitation is shown in the inset.
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Figure 4. The kinetic traces at photo-induced absorption (775 nm) of molecules 3a [a] and 3b [b] in benzonitrile. The
transient absorption spectrum immediately after excitation is shown in the inset.
Table 3. Comparison of the lifetimes of S1 state obtained from the global analysis of transient spectrum (τTA) and
fluorescence lifetimes (τF) obtained from time-resolved emission measurements in acetonitrile or benzonitrile.
Compound
τTA (ns)
τF (ns)
2a
2b
2c
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3c
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The data presented so far are in accordance to the expected photo physical behavior of 2a−2c and
3a−3c. For 2a and 2c, a very slow decay of the singlet-excited state is observed on a nanosecond
time scale. Similar lifetimes have been observed by transient absorption and emission spectroscopy.
However, for compound 2b, a 100-fold increased decay rate of the S1 state is observed. Similarly,
for 3b, a significantly increased decay rate of the S1 state is observed, which is indicative of the
occurrence of a substantially faster decay process. An explanation that is often invoked for such
observations is the formation of a charge-separated state that is stabilized in polar solvents. The
proposed scheme for such a photo physical behavior is depicted in Figure 5.
D−A*−D
KCS
.
.
D+ −A− −D
kF
hυ
kCR
D−A−D
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Figure 5. Schematic representation of photoinduced processes after photo illumination.
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Although the initial excited state disappears, it is remarkable that we do not observe the
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characteristic absorption spectrum of the perylene radical anion of the CS state D+ −A− −D. For
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related compounds, CS states have been observed upon excitation,27 but on some occasions
spectroscopic evidence of charge separation is illusive.18,40 The absence of a CS absorption can be
explained in a straightforward manner by assuming that charge recombination is faster than charge
separation, which prevents accumulation of the CS state. For compounds 2b and 3b this implies that
charge recombination rates are at least 109 to 1010 s-1, respectively (Table S1)
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Molecular Simulations: In order to gain more insight of the nature of the initial excited state
in the studied compounds, we have performed density functional theory calculations. The excitations
of compounds 2a and 2b were calculated by TD-DFT using a DZP basis set consisting of Slater-type
function and a M06-2X exchange-correlation function. All calculations were performed using the
Amsterdam Density Functional theory package. The calculated absorption spectra of compounds 2a
and 2b show a strong absorption feature with an oscillator strength close to 0.8 at 480 nm (Figure
6). In both cases, these absorptions mainly consist of the transition from HOMOperylene to
LUMOperylene. The computational transition energies are somewhat higher than those observed
experimentally. This is attributed to the absence of solvent effects in the calculations that generally
shift the absorption bands to lower energy.
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Figure 6. Optical excitation of 2a (top) and 2b (bottom) calculated using TD-DFT with DZP/M06-2X.
In the calculated spectrum of 2a, there is an additional absorption near 345 nm, which has transition
from the HOMO of bay-substituents to the LUMO of perylene core. For 2b, multiple higher-lying
bands are observed between 300−420 nm. All of these bands contain substantial contributions from
the CT transitions from occupied orbitals of the substituents to the LUMO of the perylene core.
These calculations show that for both compounds there is no clear low-energy charge transfer state
present in vacuum. However, it should be noted that the nature of the excited states is not necessarily
the same in solution. First of all, the excited states with (partial) charge transfer character will be
stabilized considerably in highly polar solvents such as acetonitrile and benzonitrile and, therefore,
arise much closer to the local excited state localized on the perylene core. From the calculations
presented here, it can be seen that for 2b the excited charge separated states are lower in energy than
for 2a, which can be understood in terms of the stronger electron donating character of the
substituents in 2b. Secondly, the presence of a polar solvent can also change the nature of the excited
state considerably after excitation. This can result in the formation of a CT state that is not present in
vacuum.
The results from the molecular simulations are in line with the experimental data obtained by TA
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and fluorescence spectroscopy. These experimental data reveal the formation of identical “locally
excited states” for all compounds of the same class, irrespective of the electron donating substituent
attached. Subsequently, fluorescence takes place for compounds bearing weak donors in all solvents,
while strong fluorescence quenching takes place for compounds bearing strong donors in polar
solvents. The fluorescence quenching takes place by electron transfer from the electron donor to the
perylene core. This process is thermodynamically favoured and, from bay-attached electron donors,
kinetically allowed. This charge separation process occurs after the primary excitation process and is
therefore not described by the molecular simulations based on density functional theory calculations.
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Conclusions
We have synthesized a series of perylene tetracarboxylic acid derivatives, bearing electron donating
4-methoxyphenoxy groups at 1,7-bay positions and, in two cases, also a 4-methoxypenyl group at
the imide position. Subsequent photophysical characterization of these compounds revealed the
various variables that dictate the charge transfer process in perylene based systems; electronic nature
of the perylene core, the position of electron donor, and the solvent polarity. For the perylene
tetraester based compound, which has the least electron deficient perylene core, charge transfer was
observed only in polar acetonitrile. Upon moving to perylene monoimide diester, which has an
increased electron deficiency due to presence of a more electron withdrawing imide group,
significant charge transfer is observed already in chloroform. An efficient charge transfer occurred
in both polar and non-polar solvents for the most electron deficient perylene bisimide based
compounds. From transient absorption spectroscopy and density functional theory calculations, it
has been concluded that charge separation takes place after local excitation of the perylene core.
The kinetics of charge transfer is strongly influenced by the positioning of the electron-donor on the
perylene scaffold. Changing position from “bay” to “imide” exerted a significantly negative impact
on the charge transfer rates. In this way, this study has revealed that the photoinduced charge
transfer process can be precisely tuned in perylene based systems by altering the electronic nature of
the perylene core, the positioning of the electron donor, and the solvent polarity.
EXPERIMENTAL SECTION
Materials. All the reagents utilized in the synthesis were purchased from commercial
suppliers, unless otherwise stated. The DMF used in the synthesis was of anhydrous grade. Toluene
was dried over sodium under an argon atmosphere prior to use. All other solvents used in the
syntheses were of reagent grade and were used as received from suppliers. The purification of the
products were performed by column chromatography (silica gel 60, mesh size 0.063−0.200 mm).
For all the spectroscopic measurements, spectroscopy grade solvents were purchased from
commercial suppliers and were used as received.
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Instrumentation and Characterization. The NMR spectra were recorded with 400 MHz
pulsed Fourier transform NMR spectrometer in CDCl3 at room temperature. The chemical shifts are
quoted relative to TMS. δ values are given in ppm and J values in Hz. Electrochemical behavior of
the compounds was studied by cyclic voltammetry in a three-electrode single-compartment cell
consisting of a platinum sheet as the working electrode, Ag wire as the reference electrode, and a Pt
wire as the counter electrode (Scan-rate = 0.5 V/s). Pre-dried CH2Cl2 containing 0.1 M
tetrabutylammonium hexafluorophosphate was used as solvent. The measurements were done under
continuous flow of nitrogen. The concentration of the prepared samples was ca. 0.5 mM. Under
these conditions, the ferrocene oxidation was observed at 0.52 V.
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Absorption measurements were carried outin Perkin Elmer Lambda 40 UV-Vis
spectrophotometer. Photoluminescence studies were done in SPEX Fluorimeter. Fluorescence
lifetimes were performed with LifeSpec-ps Fluorescence spectrometer with fixed excitation
wavelength of 400 nm. For quantum yield measurements, the formula for optically dilute solutions
was used.42 Fluorescence quantum yields of compounds 1−2 were determined by using perylene-
3,4,9,10-tetracarboxylic tetrabutylester (φF = 0.98 in CH2Cl2) as a reference. Whereas, for
compounds 3−4, N,N′-bis(1-hexylheptyl)-perylene bisimide (φF = 0.99 in CH2Cl2) was used.43
Pump-probe transient-absorption measurements were performed by using tunable Yb:KGW
laser system consisting of a YB:KGW laser (1028 nm) which operates at 5 kHz with a pulse duration
of <180 fs (PHAROS-SP-06-200 Light Conversion) and an optical parametric amplifier
(ORPHEUS-PO15F5HNP1, Light Conversion). A white light continuum probe pulse was generated
by focusing part of the fundamental 1028 nm from Pharos into a sapphire crystal. Transient
absorption data were collected using a commercial pump-probe spectrometer, HELIOS (Ultrafast
Systems) in the wavelength range 490-910 nm. The maximum time-delay between the pump and the
probe pulse was 3.3 ns. The compounds were dissolved in spectroscopic grade toluene, chloroform
and acetonitrile/benzonitrile and placed in quartz cuvettes with a 2 mm path length. In order to
prevent aggregation and photo-bleaching, the samples were stirred with a magnetic stirrer.
The geometrical and optical properties of the chromophores were investigated by density
functional theory calculations using the Amsterdam Density Functional (ADF) software package.
The geometry of the molecules was optimized using the PBE functional together with a double-zeta
plus polarization (DZP) type basis set consisting of Slater functions. The optical absorption spectra
were calculated by time dependent density functional (TD-DFT) theory calculations using the M06-
2X meta-GGA functional with a DZP basis set.
Synthesis of 1,7-di(4-tert-butylphenoxy)perylene-3,4,9,10-tetracarboxy tetrabutylester
(1a): In a 25 mL round-bottomed flask, weighed amounts of 1,7-dibromoperylene tetrabutylester 1
(200 mg, 0.25 mmol), 4-tert-butylphenol (148 mg, 0.99 mmol), and Cs2CO3 (485 mg, 1.49 mmol)
were taken. Subsequently, anhydrous DMF (8 mL) was added. The reaction mixture was stirred at
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o
115 C for 3 hours under argon atmosphere. After being cooled to room temperature, CH2Cl2 (50
mL) was added to the reaction mixture and the resultant solution was washed with water several
times. The organic layer was collected and evaporated. The crude product was chromatographed
with DCM to afford the desired product 1a (199 mg, 85%). Later on, it was recrystalized from
refulxing EtOH. 1H NMR (400 MHz, CDCl3): δ = 9.08 (d, J = 8.0 Hz, 2H), 7.98 (d, J = 8.0 Hz, 2H),
7.73 (s, 2H), 7.39 (d, J = 8.0 Hz, 4H), 7.01 (d, J = 8.0 Hz, 4H), 4.29 (t, J = 6.8 Hz, 4H), 4.23 (t, J =
6.8 Hz, 4H), 1.78–1.70 (m, 4H), 1.69–1.62 (m, 4H), 1.50–1.33 (m, 4H), 1.41–1.30 (m, 4H), 1.33 (s,
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18H), 0.96 (t, J = 6.8 Hz, 6H), 0.89 ppm (t, J = 6.8 Hz, 6H). C NMR (100 MHz, CDCl3): δ =
168.5, 167.8, 153.3, 152.2, 147.0, 132.0, 131.2, 129.4, 129.1, 127.1, 127.0, 124.7, 124.3, 122.5,
118.3, 65.3, 65.2, 34.4, 31.4, 30.6, 30.4, 19.2, 19.1, 13.8, 13.7 ppm.
Synthesis of 1,7-di(4-methoxyphenoxy)perylene-3,4,9,10-tetracarboxy tetrabutylester
(1b): Prepared from 1,7-dibromoperylene tetrabutylester 1 (100 mg, 0.12 mmol), 4-methoxyphenol
(61 mg, 0.49 mmol), and Cs2CO3 (240 mg, 0.74 mmol) according to the procedure described for
compound 1a. The crude product was purified using silica-60/CHCl3 and, subsequently,
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recrystallized from refluxing ethanol (97 mg, 88%). H NMR (400 MHz, CDCl3): δ = 9.10 (d, J =
8.0 Hz, 2H), 7.99 (d, J = 8.0 Hz, 2H), 7.68 (s, 2H), 7.04 (d, J = 8.8 Hz, 4H), 6.92 (d, J = 8.8 Hz, 4H),
4.29 (t, J = 6.8 Hz, 4H), 4.23 (t, J = 6.8 Hz, 4H), 3.82 (s, 6H), 1.78–1.71 (m, 4H), 1.71–1.63 (m,
4H), 1.52−1.41 (m, 4H), 1.40−1.30 (m, 4H), 0.97 (t, J = 7.2 Hz, 6H), 0.90 ppm (t, J = 7.2 Hz, 6H).
13C NMR (100 MHz, CDCl3): δ = 168.5, 167.8, 156.4, 152.9, 149.0, 131.2, 131.1, 129.2, 129.0,
127.1, 124.4, 123.4, 121.8, 120.5, 115.2, 65.3, 65.2, 55.7, 30.6, 30.4, 19.2, 19.1, 13.8, 13.7 ppm.
Synthesis of N-(2,6-diisopropylphenyl)-1,7-di(4-tert-butylphenoxy)perylene-3,4,9,10-
tetracarboxy monoimide dibutylester (2a): A mixture of 4-tert-butylphenol (54 mg, 0.36 mmol),
K2CO3 (100 mg, 0.72 mmol), and 18-Crown-6 (190 mg; 0.72 mmol) was stirred in anhydrous
toluene (20 mL) for 20 minutes at room temperature under argon atmosphere. Subsequently, 1,7-
dibromoperylene monoimide dibutylester 2 (100 mg, 0.12 mmol) was added and the reaction
mixture was stirred for 3h at 95oC. After being cooled to room temperature, more toluene (30 mL)
was added and the organic solution was extracted with water twice. The solvent was evaporated and
the crude product was purified by silica gel column chromatography in DCM to afford compound
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2a (105 mg; 90%). H NMR (400 MHz, CDCl3): δ = 9.30 (t, J = 8.4 Hz, 2H), 8.61 (d, J = 8.4 Hz,
1H), 8.39 (s, 1H), 8.03 (d, J = 8.4 Hz, 1H), 7.78 (s, 1H), 7.46–7.38 (m, 5H), 7.29 (d, J = 8.0 Hz, 2H),
7.09–7.02 (m, 4H), 4.31 (t, J = 6.8 Hz, 2H), 4.24 (t, J = 6.8 Hz, 2H), 2.75–2.65 (m, 2H), 1.80–1.61
(m, 4H), 1.49–1.33 (m, 4H), 1.34 (s, 9H), 1.33 (s, 9H), 1.16–1.10 (m, 12H), 0.98 (t, J = 7.2 Hz, 3H),
0.91 ppm (t, J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3): δ = 168.4, 167.6, 163.7, 163.1, 153.9,
153.8, 153.1, 152.8, 147.6, 147.4, 145.6, 134.3, 132.6, 132.1, 130.8, 130.8, 130.70, 130.66, 129.4,
129.1, 128.4, 127.8, 127.2, 127.1, 125.8, 125.7, 125.2, 124.8, 123.9, 123.8, 122.8, 121.3, 121.1,
118.7, 118.3, 65.5, 65.4, 34.5, 34.4, 31.4, 30.6, 30.4, 29.1, 24.0, 23.9, 19.2, 19.1, 13.8, 13.7 ppm.
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Synthesis of N-(2,6-diisopropylphenyl)-1,7-di(4-methoxyphenoxy)perylene-3,4,9,10-
tetracarboxy monoimide dibutylester (2b): Prepared from 4-methoxyphenol (40 mg, 0.32 mmol),
K2CO3 (89 mg, 0.64 mmol) and 18-Crown-6 (170 mg, 0.64 mmol), and 1,7-dibromoperylene
monoimide dibutylester 2 (90 mg, 0.11 mmol) as per the procedure described for the compound 2a.
The crude product was purified by column chromatography (silica-60/ CHCl3) and, subsequently,
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recrystallized from refluxing EtOH to afford the product 2b (84 mg, 85%). H NMR (400 MHz,
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CDCl3): δ = 9.41 (t, J = 8.0 Hz, 2H), 8.64 (d, J = 8.0 Hz, 1H), 8.33 (s, 1H), 8.05 (d, J = 8.0 Hz, 1H),
7.73 (s, 1H), 7.45 (t, J = 7.6 Hz, 1H), 7.30 (d, J = 8.0 Hz, 2H), 7.09 (t, J = 8.8 Hz, 4H), 6.97 (d, J =
9.2 Hz, 2H), 6.94 (d, J = 9.2 Hz, 2H), 4.32 (t, J = 6.8 Hz, 2H), 4.25 (t, J = 6.8 Hz, 2H), 3.85 (s, 3H),
3.82 (s, 3H), 2.73–2.65 (m, 2H), 1.78–1.71 (m, 2H), 1.70–1.62 (m, 2H), 1.49–1.43 (m, 2H), 1.36–
1.31 (m, 3H), 1.15−1.12 (m, 12H), 0.98 (t, J = 7.2 Hz, 3H), 0.91 ppm (t, J = 7.2 Hz, 3H). 13C NMR
(100 MHz, CDCl3): δ = 167.9, 167.1, 163.1, 162.6, 156.3, 156.1, 154.1, 154.0, 148.3, 147.9, 145.1,
133.8, 132.0, 131.6, 130.3, 130.2, 130.13, 130.08, 128.91, 128.88, 128.5, 127.9, 127.3, 125.1, 124.6,
124.0, 123.8, 123.4, 122.3, 122.2, 120.5, 120.3, 119.9, 114.9, 114.9, 65.0, 64.9, 55.2, 30.1, 29.9,
28.6, 23.4, 18.7, 18.6, 13.3, 13.2 ppm.
Synthesis
of
N,N’-bis(2,6-diisopropylphenyl)-1,7-di(4-tert-butylphenoxy)perylene-
3,4,9,10-tetracarboxy bisimide (3a): Prepared from 4-tert-butylphenol (53 mg, 0.35 mmol), K2CO3
(96 mg, 0.70 mmol), 18-Crown-6 (185 mg, 0.70 mmol), and 1,7-dibromoperylene bisimide 3 (100
mg, 0.12 mmol) in dry toluene (30 ml) at 90 oC according to the procedure described for compound
2a. The crude product was refluxed in MeOH (20 mL) and filtered to remove unreacted phenol.
Thereafter, the dried precipitate was chromatographed using silica-60/DCM to afford compound 3a
(91 mg, 79%). 1H NMR (400 MHz, CDCl3): δ = 9.67 (d, J = 8.0 Hz, 2H), 8.69 (d, J = 8.0 Hz, 2H),
8.45 (s, 2H), 7.46 (m, 6H), 7.32 (d, J = 7.2 Hz, 4H), 7.11 (d, J = 7.2 Hz, 4H), 2.72 (m, 4H), 1.36 (s,
18H), 1.20–1.12 ppm (m, 24H). 13C NMR (100 MHz, CDCl3): δ = 163.5, 162.9, 155.3, 152.6, 148.0,
145.6, 133.8, 130.7, 130.5, 129.7, 129.6, 129.0, 127.4, 125.8, 124.7, 124.5, 124.0, 122.3, 118.7,
31.4, 29.2, 24.0, 23.9 ppm.
Synthesis
of
N,N’-bis(2,6-diisopropylphenyl)-1,7-di(4-methoxyphenoxy)perylene-
3,4,9,10-tetracarboxy bisimide (3b): Prepared from 4-methoxyphenol (86 mg, 0.69 mmol), K2CO3
(191 mg, 1.38 mmol), 18-Crown-6 (365 mg, 1.38 mmol) and 1,7-dibromoperylene bisimide 3 (200
mg, 0.23 mmol) in dry toluene (50 ml) according to the procedure described for compound 2a. The
crude product was refluxed in MeOH (25 mL) and filtered (after cooling) to remove unreacted
phenol. Thereafter, the dried precipitate was chromatographed (silica-60/DCM:toluene 1:1) to afford
compound 3b (180 mg, 82%). 1H NMR (400 MHz, CDCl3): δ = 9.71 (d, J = 8.0 Hz, 2H), 8.73 (d, J
= 8.0 Hz, 2H), 8.41 (s, 2H), 7.48 (t, J = 7.6 Hz, 2H), 7.33 (d, J = 7.6 Hz, 4H), 7.16 (d, J = 7.6 Hz,
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4H), 7.01 (d, J = 7.6 Hz, 4H), 3.85 (s, 6H), 2.74 (m, 4H), 1.17 ppm (s, 24H). C NMR (100 MHz,
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CDCl3): δ = 163.5, 162.9, 157.0, 156.0, 148.3, 145.6, 133.8, 130.6, 130.5, 129.6, 129.0, 125.6,
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124.0, 123.9, 123.8, 122.2, 120.8, 115.6, 55.7, 29.2, 24.0 ppm.
Synthesis
of
N-(2,6-diisopropylphenyl)-1,7-dibromoperylene-3,4,9,10-tetracarboxy
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monoimide monobenzimidazole (4+4’): 1,7-dibromo perylene monoimide monoanhydride 7 (50
mg, 0.07 mmol) and 1,2-diaminobenzene (10 mg, 0.09 mmol) were taken in propionic acid (10 ml).
The mixture was refluxed for 3 h. After cooling down to room temperature, it was poured into water
to precipitate the crude product. The precipitate was filtered off and washed with several portions of
water to remove all the propionic acid. The precipitate was dried and chromatographed on silica-60
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eluting with DCM to afford the pure product (48 mg, 87%) as the mixture of two regioisomers 4 and
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in a ratio ca. 2:1. H NMR (400 MHz, CDCl3): δ = 9.60–9.50 (m, 2H), 9.22 (s, 0.35H), 9.11 (s,
0.65H), 8.99 (s, 1H), 8.94 (d, J = 8.0 Hz, 0.65H), 8.90 (d, J = 8.0 Hz, 0.35H), 8.78 (d, J = 8.0 Hz,
1H), 8.56–8.51 (m, 1H), 7.95–7.90 (m, 1H), 7.56–7.47 (m, 3H), 7.35 (d, J = 8.0 Hz, 2H), 2.79–2.70
(m, J = 6.8 Hz, 2H), 1.22–1.16 ppm (m, 12H). 13C NMR spectra could not be measured because of
its low solubility.
Synthesis of N-(2,6-diisopropylphenyl)-1,7-di(4-tert-butylphenoxy)perylene-3,4,9,10-
tetracarboxy monoimide monobenzimidazole (4a): Synthesized from 4-tert-butylphenol (59 mg,
0.39 mmol), K2CO3 (108 mg, 0.78 mmol), 18-Crown-6 (206 mg, 0.78 mmol) and 1,7-
dibromoperylene monoimide monobenzimidazole 4 (100 mg, 0.13 mmol) in dry toluene (25 ml)
according to the procedure described for compound 2a. The crude product was chromatographed
1
using silica-60/CHCl3 to afford compound 4a (95 mg; 80%) as the mixture of two regioisomers. H
NMR (400 MHz, CDCl3): δ = 9.68–9.52 (m, 2), 8.80–8.74 (m, 1H), 8.64–8.58 (m, 1.45 H), 8.52 (s,
0.55H), 8.49–8.45 (m, 0.60H), 8.42–8.36 (m, 1.50H), 7.83–7.75 (m, 1H), 7.51–7.38 (m, 7H), 7.30
(d, J = 7.6 Hz, 2H), 7.17–7.09 (m, 4H), 2.77–2.73 (m, 2H), 1.39–1.34 (m, 18H), 1.17–1.14 ppm (m,
12H). 13C NMR spectrum could not be measured because of its low solubility.
Synthesis of N-(2,6-diisopropylphenyl)-1,7-di(4-methoxyphenoxy)perylene-3,4,9,10-
tetracarboxy monoimide monobenzimidazole (4b): Synthesized from 4-methoxyphenol (48 mg,
0.39 mmol), K2CO3 (108 mg, 0.78 mmol), 18-Crown-6 (206 mg, 0.78 mmol) and 1,7-
dibromoperylene monoimide monobenzimidazole 4 (100 mg, 0.13 mmol) in dry toluene (30 ml)
according to the procedure described for compound 2a. The crude product was chromatographed
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using silica-60/CHCl3 to afford compound 4b (96 mg, 86%) as the mixture of two regioisomers. H
NMR (400 MHz, CDCl3): δ = 9.68–9.52 (m, 2H), 8.72 (d, J = 8.4 Hz, 1H), 8.65–8.55 (m, 1H), 8.50
(s, 0.55H), 8.41 (s, 0.45H), 8.40–8.29 (m, 2H), 7.77–7.71 (m, 1H), 7.46 (t, J = 8.0 Hz, 1H), 7.41–
7.35 (m, 2H), 7.31 (d, J = 8.0 Hz, 2H), 7.22–7.13 (m, 4H), 7.08–6.94 (m, 4H), 3.89–3.83 (m, 6H),
2.77–2.73 (m, 2H), 1.19–1.13 ppm (m, 12H). 13C NMR spectrum could not be measured because of
its low solubility.
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Synthesis
of
N-(4-methoxyphenyl)-1,7-dibromoperylene-3,4,9,10-tetracarboxy
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monoimide dibutylester (6): A 25 mL round-bottomed flask was charged with 1,7-
dibromoperylene monoanhydride dibutylester 5 (150 mg, 0.22 mmol), 4-methoxyaniline (35 mg,
0.29 mmol), and propionic acid (6 mL). The reaction mixture was refluxed for 24 h. After cooling
down to room temperature, the reaction mixture was poured into the water to precipitate the crude
product. The precipitate was filtered off and washed with several portions of water to remove all the
propionic acid. The precipitate was dried and chromatographed on silica, eluting with CH2Cl2, to
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afford the desired product 6 (140 mg, 81%). H NMR (400 MHz, CDCl3): δ = 9.24 (d, J = 8.0 Hz,
1H), 9.21 (d, J = 8.0 Hz, 1H), 8.89 (s, 1H), 8.68 (d, J = 8.0 Hz, 1H), 8.34 (s, 1H), 8.13 (d, J = 8.0
Hz, 1H), 7.24 (d, J = 8.0 Hz, 2H), 7.08 (d, J = 8.0 Hz, 2H), 4.35 (t, J = 6.8 Hz, 4H), 3.88 (s, 3H),
1.84–1.75 (m, 4H), 1.53–1.46 (m, 4H), 1.00 ppm (t, J = 7.2 Hz, 6H). 13C NMR (100 MHz, CDCl3): δ
= 167.7, 166.9, 166.8, 163.5, 162.95, 162.91, 159.7, 138.0, 136.8, 134.2, 133.7, 132.0, 131.9, 131.6,
130.8, 130.5, 130.4, 130.3, 129.6, 129.5, 129.1, 129.0, 128.2, 128.13, 128.11, 127.3, 127.0, 126.9,
122.2, 122.1, 120.3, 119.4, 114.8, 66.0, 65.8, 55.5, 30.6, 30.5, 19.3, 19.2, 19.1, 13.8, 13.7 ppm.
Synthesis
of
N-(4-methoxyphenyl)-1,7-di(4-tert-butylphenoxy)perylene-3,4,9,10-
tetracarboxy monoimide dibutylester (2c): Synthesized from 4-tert-butylphenol (50 mg, 0.33
mmol), K2CO3 (69 mg, 0.50 mmol), 18-Crown-6 (131 mg, 0.50 mmol) and 1,7-dibromoperylene
monoimide dibutylester 6 (65 mg, 0.08 mmol) in dry toluene (12 ml) according to the procedure
described for compound 2a. The crude product was chromatographed using silica-60/DCM to afford
compound 2c (56 mg, 73%). 1H NMR (400 MHz, CDCl3): δ = 9.39 (d, J = 8.4 Hz, 2H), 8.58 (d, J =
8.4 Hz, 1H), 8.34 (s, 1H), 8.04 (d, J = 8.4 Hz, 1H), 7.77 (s, 1H), 7.45–7.38 (m, 4H), 7.20 (d, J = 8.8
Hz, 2H), 7.09–7.01 (m, 6H), 4.31 (t, J = 6.8 Hz, 2H), 4.24 (t, J = 6.8 Hz, 2H), 3.85 (s, 3H), 1.78–
1.63 (m, 4H), 1.52–1.34 (m, 4H), 1.34 (s, 9H), 1.32 (s, 9H), 0.97 (t, J = 7.6 Hz, 3H), 0.90 ppm (t, J =
7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3): δ = 168.3, 167.6, 163.9, 163.6, 159.5, 153.9, 153.0,
152.7, 147.7, 147.6, 134.3, 132.7, 132.0, 130.8, 130.7, 130.5, 129.5, 129.2, 129.0, 128.4, 127.7,
127.6, 127.2, 127.1, 125.3, 124.73, 124.70, 123.6, 122.7, 121.13, 121.10, 118.8, 118.7, 114.7, 77.3,
77.0, 76.7, 65.5, 65.4, 55.5, 34.5, 34.4, 31.4, 30.6, 30.4, 19.2, 19.1, 13.8, 13.7 ppm.
Synthesis of N-(2,6-diisopropylphenyl)-N’-(4-methoxyphenyl)-1,7-dibromoperylene-
3,4,9,10-tetracarboxy bisimide (8): Synthesized as per the procedure described for compound 6
from 1,7-dibromoperylene monoimide monoanhydride 7 (150 mg, 0.21 mmol), 4-methoxyaniline
(78 mg, 0.63 mmol), and propionic acid (8 mL). The reaction mixture was refluxed for 24 h. After
cooling down to room temperature, the reaction mixture was poured into the water to precipitate the
crude product. The precipitate was filtered off and washed with several portions of water to remove
all the propionic acid. The precipitate was dried and chromatographed on silica, eluting with CH2Cl2,
to afford the desired product 8 (133 mg, 77%). 1H NMR (400 MHz, CDCl3): δ = 9.56 (d, J = 8.0 Hz,
1H), 9.54 (d, J = 8.0 Hz, 1H), 9.00 (s, 1H), 8.98 (s, 1H), 8.79 (d, J = 8.0 Hz, 1H), 8.77 (d, J = 8.0
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Hz, 1H), 7.51 (t, J = 7.6 Hz, 1H), 7.35 (d, J = 7.6 Hz, 2H), 7.24 (d, J = 8.8 Hz, 2H), 7.09 (d, J = 8.8
Hz, 2H), 3.89 (s, 3H), 2.78–2.66 (m, 2H), 1.19 (s, 6H), 1.17 ppm (s, 6H). 13C NMR (100 MHz,
CDCl3): δ = 162.7, 162.5, 159.8, 145.6, 138.4, 138.3, 133.2, 133.1, 131.0, 130.6, 130.4, 130.1,
129.9, 129.6, 129.5, 129.4, 129.0, 128.7, 127.6, 127.4, 127.1, 124.2, 123.4, 123.0, 122.8, 120.9,
114.9, 55.5, 29.3, 23.99, 23.97 ppm.
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Synthesis
of
N-(2,6-diisopropylphenyl)-N’-(4-methoxyphenyl)-1,7-di(4-tert-
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butylphenoxy)perylene-3,4,9,10-tetracarboxy bisimide (3c): Synthesized as per the procedure
described for compound 2a from 4-tert-butylphenol (50 mg, 0.33 mmol), K2CO3 (69 mg, 0.50
mmol), 18-Crown-6 (131 mg, 0.50 mmol) and 1,7-dibromoperylene bisimide 8 (65 mg, 0.08 mmol)
in dry toluene (12 ml) according to the procedure described for compound 2a. The crude product
1
was chromatographed using silica-60/DCM to afford compound 2c (65 mg, 85%). H NMR (400
MHz, CDCl3): δ = 9.67 (d, J = 8.0 Hz, 1H), 9.62 (d, J = 8.0 Hz, 1H), 8.70 (d, J = 8.0 Hz, 1H), 8.62
(d, J = 8.0 Hz, 1H), 8.43 (s, 1H), 8.35 (s, 1H), 7.50–7.42 (m, 5H), 7.31 (d, J = 8.0 Hz, 2H), 7.22 (d, J
= 8.8 Hz, 2H), 7.15–7.01 (m, 6H), 3.86 (s, 3H), 2.77–2.67 (m, 2H), 1.35 (s, 9H), 1.34 (s, 9H), 1.25–
1.11 ppm (m, 12H). 13C NMR (100 MHz, CDCl3): δ = 163.5, 163.3, 159.6, 155.5, 155.4, 152.5,
152.4, 148.2, 148.1, 145.6, 133.8, 133.7, 130.7, 130.5, 130.4, 129.6, 129.5, 129.4, 129.0, 128.9,
127.4, 127.3, 125.7, 125.3, 124.4, 124.24, 124.20, 124.0, 123.8, 122.3, 122.2, 119.0, 118.9, 114.7,
55.5, 36.8, 34.6, 34.5, 31.4, 29.2, 24.0, 23.9 ppm.
Supporting Information. Calculated rate of fluorescence and fluorescence quenching (Table
S1); Absorption and emission spectra of compounds 1−4a in chloroform (Figure S1); Absorption
and emission spectra of compounds 2c and 3c in chloroform (Figure S2); Fluorescence decay curves
of compounds 1a−b and 2a−c (Figure S3); Fluorescence decay curves of compounds 3a−c and 4a−b
(Figure S4); Transient absorption spectra of compounds 2a−c and 3a−c (Figures S5−S8); 1H and 13C
NMR spectra of all synthesized compounds (Figures S9−S19).
Acknowledgment. Financial support from the Foundation for Fundamental Research on
Matter (FOM), which is part of the Netherlands Organization for Scientific Research (NWO), is
gratefully acknowledged. This research has also received funding from the European Research
Council Horizon 2020 ERC Grant Agreement no. 648433.
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