Naphthalene- and perylenediimides with hydroquinones, catechols, boronic esters and imines in the core

Article abstract of DOI:10.1039/c1ob05702b

The green-fluorescent protein of the jellyfish operates with the most powerful phenolate donors in the push-pull fluorophore. To nevertheless achieve red fluorescence with the same architecture, sea anemone and corals apply oxidative imination, a process that accounts for the chemistry of vision as well. The objective of this study was to apply these lessons from nature to one of the most compact family of panchromatic fluorophores, i.e. core-substituted naphthalenediimides (cNDIs). We report straightforward synthetic access to hydroxylated cNDI and cPDI cores by palladium-catalyzed cleavage of allyloxy substituents. With hydroxylated cNDIs but not cPDIs in water-containing media, excited-state intramolecular proton transfer yields a second bathochromic emission. Deprotonation of hydroquinone, catechol and boronic ester cores provides access to an impressive panchromism up to the NIR frontier at 640 nm. With cNDIs, oxidative imination gives red shifts up to 638 nm, whereas the expanded cPDIs already absorb at 754 nm upon deprotonation of hydroquinone cores. The practical usefulness of hydroquinone cNDIs is exemplified by ratiometric sensing of the purity of DMF with the "naked eye" at a sensitivity far beyond the "naked nose". We conclude that the panchromatic hypersensitivity toward the environment of the new cNDIs is ideal for pattern generation in differential sensing arrays. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1ob05702b

Organic &
Biomolecular
Chemistry
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Volume 9 | Number 24 | 21 December 2011 | Pages 8205–8512
ISSN 1477-0520
FULL PAPER
Stefan Matile et al.
Naphthalene- and perylenediimides with hydroquinones,
catechols, boronic esters and imines in the core

Organic &
Biomolecular
Chemistry
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PAPER
Naphthalene- and perylenediimides with hydroquinones, catechols, boronic
esters and imines in the core†‡
Andrea Fin,§ Irina Petkova,§ David Alonso Doval, Naomi Sakai, Eric Vauthey and Stefan Matile*
Received 3rd May 2011, Accepted 11th July 2011
DOI: 10.1039/c1ob05702b
The green-fluorescent protein of the jellyfish operates with the most powerful phenolate donors in the
push–pull fluorophore. To nevertheless achieve red fluorescence with the same architecture, sea
anemone and corals apply oxidative imination, a process that accounts for the chemistry of vision as
well. The objective of this study was to apply these lessons from nature to one of the most compact
family of panchromatic fluorophores, i.e. core-substituted naphthalenediimides (cNDIs). We report
straightforward synthetic access to hydroxylated cNDI and cPDI cores by palladium-catalyzed cleavage
of allyloxy substituents. With hydroxylated cNDIs but not cPDIs in water-containing media,
excited-state intramolecular proton transfer yields a second bathochromic emission. Deprotonation of
hydroquinone, catechol and boronic ester cores provides access to an impressive panchromism up to the
NIR frontier at 640 nm. With cNDIs, oxidative imination gives red shifts up to 638 nm, whereas the
expanded cPDIs already absorb at 754 nm upon deprotonation of hydroquinone cores. The practical
usefulness of hydroquinone cNDIs is exemplified by ratiometric sensing of the purity of DMF with the
“naked eye” at a sensitivity far beyond the “naked nose”. We conclude that the panchromatic
hypersensitivity toward the environment of the new cNDIs is ideal for pattern generation in differential
sensing arrays.
transporters.8–12 The most p-acidic cNDI 6 has an inverted
Introduction
quadrupole moment of an unprecedented +39 Buckinghams.11
Core-substituted naphthalenediimides (cNDIs) are 1,4,5,8-
The synthesis of tetracyano cNDIs failed despite significant
efforts.11 To increase the p-acidity, we recently applied redox
napththalenediimides (NDIs, 1) with one or more substituents
in position 2, 3, 6 or 7 (Fig. 1).1–12 With electron donors in
the core, cNDIs become panchromatic push–pull fluorophores,
electron acceptors yield the strongest p-acids known today.1
chemistry.12 The “super-p-acid” 7 was readily synthesized by
oxidation of the four sulfides in the core of cNDI 8. Successful
at one extreme of the cNDI series, we speculated that either
cNDIs are wonderful fluorophores, covering all primary colors
acid–base or redox chemistry could be used to break records at
by exchange of single atoms only.1–8 Formal substitution of one
the other extreme as well, that is with electron-rich cNDIs. In
oxygen atom in the core of the yellow fluorophore 2 by a
many panchromatic systems, including green to red fluorescent
proteins,13 phenolate anions serve as the ultimate p-donors.
nitrogen yields red fluorophore 3. Substitution of the other oxygen
with another nitrogen is sufficient to cover the primary colors.2,3
Deprotonation of cNDIs such as 9 with a hydroquinone core
Formal addition of two more alkylamino groups converts the blue
should thus easily provide access to absorption maxima beyond
cNDI 4 into the green chlorophyll mimic 5.4 Decreasing LUMO
the 642 nm of tetraamino cNDI 5. (With core expanded cNDI,
energies with increasing bandgap identifies cNDIs as ideal for the
bathochromic shifts up to 692 nm have been reported, for cNDI
polymers with conjugated cores, the NIR frontier is at 985 nm.)8
In the following, we report that this expectation turned out to
be incorrect, also for the similarly panchromatic, pH-responsive
cNDIs 10 with catechols in the core, and for their boronic esters.
However, the expanded core-substituted perylenediimide (cPDI)14
11 shifted to 760 nm upon deprotonation with base, 74 nm
(1419 cm-1) beyond the previously reported diamino cPDI. As an
alternative approach to the NIR frontier with the most compact
cNDI fluorophores, lessons from sea anemone and corals on how
to make the green-fluorescent protein from the jellyfish fluoresce
in red13 were applied, that is oxidative imination, the same strategy
that accounts for the chemistry of vision.15
construction of multicomponent photosystems with operational
redox gradients that do not suffer from low-energy traps.5
cNDIs with electron acceptors in the core are attractive
because their exceptional p-acidity provides access to one of the
few air-stable n-semiconductors as well as to powerful anion
School of Chemistry and Biochemistry, University of Geneva, Geneva,
Switzerland. E-mail: stefan.matile@unige.ch; Fax: +41 22 379 5123;
Tel: +41 22 379 6523; Web: www.unige.ch/sciences/chiorg/matile
† In memory of Philippe Perrottet.
‡ Electronic supplementary information (ESI) available: Detailed experi-
mental procedures. See DOI: 10.1039/c1ob05702b
§ These two authors contributed equally to this work.
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Scheme 1 Synthesis of cNDI 9 with a hydroquinone core. a) Naph-
thalene dianhydride, several reported steps.16 b) Allyl alcohol, NaH,
˚
dichloromethane, 4 A MS, 4 h, rt, 86%. c) Pd(PPh3)4, phenylsilane,
1
˚
dichloromethane, 4 A MS, 10 h, rt, 80% (R = mesityl).
The absorption spectrum of cNDI 9 in a 4 : 1 mixture of
DMSO and water at pH 3 showed a maximum at 470 nm (Fig. 2
and 3, Table 1). With increasing pH, this maximum exhibited a
spectacular, biphasic bathochromic shift. The first shift occurred at
an apparent pK = 6.3 (Fig. 4 , Table 1). The strong acidity of the
᭹
a
first hydroxy group originated presumably from the stabilization of
the conjugate base 14 by resonance with the withdrawing imides.
The second shift occurred at pK = 11.1 (Fig. 4 , Table 1). The
᭹
a
weak acidity of the second hydroxy group appeared reasonable
considering intramolecular charge repulsion18 in dianion 15. The
absorption maximum of the conjugate base 15 was found at
615 nm. This places the maximum of cNDI 15 27 nm (684 cm-1)
below that of the tetramino cNDI 5 at 642 nm (Fig. 1–3, Table 1).
Fig. 1 (a) Previously reported cNDIs with HOMO/LUMO levels and
absorption maxima in nm, with super-p-acid 8 obtained with redox
chemistry from 7. (b) Panchromatic cNDIs reported in this study to
maximize bathochromism with acid–base chemistry, boronic esterification
and oxidative imination (R1 = mesityl, R2 = cyclohexyl).
Results and discussion
The synthesis of cNDI 9 with a hydroquinone core was very
straightforward (Scheme 1). Dibromo cNDI 12 was prepared
from naphthalene dianhydride following recent procedures from
the literature.16 Nucleophilic substitution in the core with allyl
alcohol gave the yellow cNDI 13 in excellent yield. Pd-catalyzed
deallylation afforded the hydroquinone in the core of 9 selectively
and under mild conditions. The cNDI 10 with catechols in the core
and the expanded cPDI 11 were prepared analogously. Detailed
procedures and analytical data for all new compounds are given
in the ESI.‡17
Fig. 2 Changes in the absorption spectra of 9 with increasing pH from
pH 3 (yellow) to pH 12 (blue) in DMSO/water 4 : 1, 25 ◦C.
Table 1 Spectroscopic properties of cNDIs and cPDIs
labs (nm)a
e (M-1 cm-1)b
lem (nm)c
t (ns)d
Ufl (%)e
pKa
f
Entry
cNDIs
1
2
3
4
5
6
7
8
9
9
470
565h
615
490
513i
570i
640i
570
708h
760
12 000
10 200h
15 200
4200
500, 630g
<0.1, 1.1g
1
6.3 (7.2)
11.1 (11.5)
14
15
10
17
18
19
11
20
21
661
12.7
64
6
520, 610g
0.8, 1.9g
3.7
9.3
12.8
4000i
3900i
6900i
6600
600
820
1.1
0.9
6
2
7.3 (8.0)
10.4 (10.6)
11 500h
20 400
10
a Absorption maximum at longest wavelength, in nanometres, measured in DMSO/water 4 : 1, 25 ◦C, at appropriate pH. pH values were measured in
DMSO/water 4 : 1 and used without correction. A 10 mM triethanolamine buffer was present if appropriate. The absorption maxima can be highly
sensitive to changes in environment, the reported values are thus subject to minor variations, particularly with intermediate conjugate bases. b Extinction
coefficient. c Emission maxima, if applicable. Spectra with unresolved excitation maxima are not reported. d Fluorescence lifetime. e Fluorescence quantum
yield in percent. f pKa in DMSO/water 4 : 1, 25 ◦C, from Hill analysis of pH profiles. Values in parenthesis are from HypSpec analysis. g Two emission
maxima, see Fig. 3, 5, and text. h Computed approximations from HypSpec analysis. i Apparent value without further analysis.
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core-expanded NDIs.7b More detailed studies on the ultrafast
photophysics of this ESIPT emission are ongoing and will be
reported in due course.
Unambiguous assignment of the absorption and emission max-
ima of the singly deprotonated intermediate 14 was problematic
because of overlapping and shifting signals (Fig. 2). Deconvolu-
tion of the overlapping spectra of the individual chromophores by
HypSpec analysis20 located the absorption maximum at 565 nm
(Fig. S3, ESI,‡ Table 1, entry 2). The same analysis gave a pKa =
7.2. This result suggested that the effective acidity of hydroquinone
9 is poorer than expected from the apparent pKa = 6.3 obtained
from the pH profile (Fig. 4, Table 1). The emission maximum is
not reported because it was not possible to identify a single species
in the excitation spectra.
Dianion 15 emitted at 661 nm (Fig. 3, Table 1). The fluorescence
quantum yield increased significantly from Ufl = 1% for protonated
cNDI to Ufl = 64% for deprotonated dianion 15 (Table 1). This
increase was correctly reflected by a decelerated fluorescence decay
from t < 100 ps for protonated 9 to t = 12.7 ns for deprotonated 15
(Table 1). These consistent trends suggested that ESIPT accounts
for the poor fluorescence of cNDIs with hydrogen bond donors in
the core.
Fig. 3 Absorption (solid) and emission spectra (dotted) of 9 (pH 3,
yellow) and 15 (pH 13, blue) in DMSO/water 4 : 1, 25 ◦C, normalized
to 1 at their maxima.
In neutral form at pH ~ 2, cNDI 10 with catechols in the core
absorbed at 490 nm, that is 20 nm (869 cm-1) red shifted from
cNDI 9 with only two p-donors in the core (Fig. 5). This is unlike
the tetraalkoxy-NDI, which exhibited 50 nm (2544 cm-1) blue
shift compared to di-alkoxy-NDI.4 The emission at 520 nm was
complemented by a second maximum at 610 nm. The increased
intensity of this bathochromic emission with four hydrogen-bond
donors in the core of cNDI 10 compared to two donors in 9 was
consistent with ESIPT.
Fig. 4 Absorption maxima of 9 ( ), 10 ( ) and 11 (¥) as a function of
᭹
᭺
pH.
Similar to the alkoxy cNDIs 2,1 hydroquinone cNDI 9 showed
green fluorescence (Fig. 3, Table 1). However, the fluorescence
quantum yield was with Ufl = 1% very poor, much poorer than the
Ufl = 22% reported for dialkoxy cNDIs. The very short lifetime
t < 100 ps of the excited state was in agreement with the poor
quantum yield of the high energy emission.
A second, equally strong emission maxima was observed at
630 nm (Fig. 3, Table 1). This bathochromic emission maximum
appeared only in water-containing solvent mixtures. The excited
state accounting for the low-energy emission was populated from
the one accounting for the high-energy emission at 500 nm and de-
cayed with a clearly longer t = 1.1 ns (Table 1). These observations
supported the occurrence of excited-state intramolecular proton
transfer (ESIPT)19 and red-shifted emission from the excited-state
tautomer 16. Consistent with this interpretation, ESIPT emission
was even stronger with the cNDI 10 with four hydrogen-bond
donors in the core but absent with cPDI 11 without hydrogen-bond
acceptor in the core (see below and Table 1). Similar observations
have been reported previously with a different explanation for
Fig. 5 Absorption (solid) and emission spectra (dotted) of 10 (pH 2,
yellow) and absorption spectra of 18 (pH 9, red) and 19 (pH 14, blue) in
DMSO/water 4 : 1, 25 ◦C. High-energy regions for 18 and 19 were removed
because they were contaminated by oxidative degradation products.
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With cNDI 10, the interpretation of the spectroscopic changes
in response to increasing pH became even more complex than with
cNDI 9 (Fig. S1). A small gradual shift at low pH suggested that
Removal of the first proton occurred at pKa = 7.3 (Fig. 4¥
and S2, ESI‡). This comparably poor acidity suggested that the
stabilization of the conjugate base 20 by resonance with the
withdrawing imides is less powerful than with cNDIs, perhaps
due to the deplanarization of the PDI core. HypSpec analysis of
all overlapping bands further reduced the acidity to pKa = 8.0 and
placed the absorption of the cPDI monoanion 20 at 708 nm (Fig.
S4, ESI,‡and Table 1). This calculated to a red shift of 138 nm
(3420 cm-1) for the first deprotonation for cPDI 11 compared to
95 nm (3578 cm-1) for the homologous cNDI 9.
removal of the first proton occurs already at pKa = 3.7 (Fig. 4 ).
᭺
The apparent maximum of the monoanion 17, could however not
be clearly identified. The high acidity of catechol 10 was reasonable
considering stabilization of the conjugated base 17 by hydrogen
bonding and resonance, and because of probability effects related
to multivalency.18 Moreover, the next clear shift to 570 nm occurred
at pKa = 9.3, an acidity that appeared too weak to originate from
catechol 10 (Fig. 4 ).
The deprotonation of monoanionic cPDI 20 occurred at pKa =
10.4 (Fig. 4¥). The resulting cPDI dianion 21 absorbed at 760 nm
and emitted at 820 nm. Contrary to the situation with cNDI
15, the removal of hydrogen-bond donors in the core did not
improve the poor fluorescence quantum yield Ufl = 2% of the
emission of cPDI 21 at 820 nm. Insensitivity was not surprising
because intramolecular hydrogen bonding including ESIPT does
not account for the poor fluorescence of hydroquinone cPDI 11.
The red shift of 52 nm (966 cm-1) for the second cPDI
deprotonation was in the range of the corresponding cNDIs.
Whereas dianionic cNDIs 15 and 18 failed to exceed the absorption
of diamino cNDIs 4, dianionic cPDIs 21 absorbed 74 nm
(1419 cm-1) beyond diamino cPDIs. Barely visible with the “naked
eye”, their NIR absorption is unprecedented in the cPDI series.14
The absorption maxima of cNDIs and cPDIs 9–11 did not show
a linear dependence on the polarity of the solvent (Fig. 7a). This
was meaningful because their pull–push–pull architecture results
in a globally symmetric molecule, where solvent stabilization by
dipole–dipole interactions is not possible. However, the absorption
maxima of cNDIs and cPDIs 9–11 showed a roughly linear
dependence on the Lewis basicity22 of the solvent (Fig. 7b). Minor
deviations are readily explicable with the quality and age of the
solvent (Fig. 8).
᭺
Intramolecular hydrogen bonding probably also accounts for
the reduced bathochromic shift to 570 nm of the conjugate base
18, that is 45 nm (1284 cm-1) less than the corresponding dianion
15 (Table 1). Further deprotonation of the putative dianion 18
was just detectable at pKa = 12.8. The absorption maximum of
the putative trianion 19 was at 640 nm, that is at the current
NIR frontier marked by tetraamino cNDIs 5 (Fig. 5 and 1, Table
1). Further deprotonation was not observable, also, with NaH in
aprotic solvents, competing oxidative degradation made processes
under basic conditions difficult to follow. Emission spectra of
deprotonated catechol cNDIs 17–19 could not be attributed to
single compounds and are thus not reported.
Charge-free at pH ~ 2, the disubstituted cPDI 11 with a
hydroquinone core absorbed at 570 nm (Fig. 6). This is 100 nm
(3733 cm-1) bathochromic from the disubstituted cNDI 9 at 470 nm
(Table 1). This red-shift originated from the expanded aromatic
system in the perylene core, PDIs without substituents in the
core already absorb at 526 nm.14 cPDI 11 emitted at 600 nm
without second emission maximum at low energy (Fig. 6). The
disappearance of the second emission maximum with increasing
distance between hydrogen-bond donors in the core and imide
acceptors in cPDI 11 was in agreement with ESIPT as origin of
the bathochromic emission with cNDIs 9 and 10. ESIPT could
thus not account for the rather low Ufl = 6% and the relatively
short t = 1.1 ns of cPDI 11 (Table 1).21
Fig. 7 Absorption maxima of 9 ( ), 10 ( ) and 11 (¥) in wavenumbers
᭹
᭺
as a function of (a) the polarity function f(e) and (b) -DH0BF3 (295.15), the
Lewis basicity of the solvent.
The large shifts obtained for small differences in the Lewis
basicity of the environment were intriguing and called for practical
applications. For instance, commercial and freshly distilled DMF
could be distinguished with the naked eye after adding a drop
of cNDI 9 (Fig. 8a). Ratiometric detectability of the purity
of DMF was ideal for quantitative analysis. The ratio of the
red absorption at 538 nm and the blue absorption at 610 nm
of cNDI in DMF purchased from commercial suppliers was
Fig. 6 Absorption (solid) and emission spectra (dotted) of 11 (pH 5, red)
and 21 (pH 12, green) in DMSO/water 4 : 1, 25 ◦C (R2 = cyclohexyl).
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Fig. 8 a) Absorption spectra of cNDI 9 added to the early fractions (2 ml
each; fraction 1, ; fraction 20, ) of the distillation of commercial DMF
᭹
᭺
(ꢀ). b) Fractional absorption A538/A610 of 9 in the early fractions of DMF
distillation ( ) compared to commercial DMF (dashed).
᭹
at A538/A610 = 1.77 (Fig. 8aꢀ; 8b, dashed line). Distillation of
commercial DMF produced first fractions of A538/A610 < 1.0
(Fig. 8a , 8b ). This high basicity of the first fractions of
᭹
᭹
Fig. 10 a) Absorption (solid) and emission (dotted) spectra of 22 (pH 3,
orange), 24 (pH 7, red) and 25 (pH 11, violet) in DMSO/water 4 : 1, 25 ◦C.
distilled DMF properly reflects the enrichment with the low-
boiling dimethylamine impurities. Ultrapure DMF obtained in
the later fractions saturated A538/A610 = 5.15 (Fig. 8a , 8b ).
b) Absorption maxima of 22 ( ) and 10 ( ) as a function of pH.
᭹
᭺
᭹
᭺
other catechols under similar conditions.23–26 The insensitivity of
the absorption maximum to up to 10 M PBA was in agreement
with the inability of cPDI 11 to form boronic esters, (Fig. 9¥).
cNDI 9 showed a relatively large hypsochromic shift of 24 nm
(1145 cm-1) at KD = 21.8 2.3 mM in response to PBA (Fig.
DMF with A538/A610 ≥ 3.0 was odorless. Remarkably, cNDI 9 thus
visualizes the purity of DMF for the “naked eye” with a sensitivity
that is far beyond the sensitivity of the “naked nose”.
The conversion of catechols in the core of cNDI 10 into boronic
esters in cNDI 22 was explored with phenylboronic acid (PBA,
Fig. 9 and Fig. 10).23–26 The absorption at pH = 8.0 showed a
᭹
9
᭺
). Intramolecular reaction of the boronic acid semi-ester with
weak red shift with increasing PBA concentration. Hill analysis
of the dose response curve gave an apparent dissociation constant
KD = 3.7 0.1 mM. This value was in the range observed for
the proximal imide carbonyl group would be consistent with this
behavior.23–26 Dehydroxylation of the obtained chromophore 23 is
further conceivable (Fig. 9).
In neutral form at pH < 3, the absorption of cNDI 22 at 486 nm
was poorly distinguishable from the one at 490 nm of the free
catechol 10 (Fig. 10). However, deprotonation of the first hydrated
boronic ester occurred with a sharp, distinctive red shift at pKa =
4.7 (Fig. 10b ). This acidity of the boronic ester was as expected
᭹
from the literature.23–26 It was consistent with the lack of resonance
with the NDI core and an only weak influence from the imide
acceptors.
Deprotonation of the hydrated conjugate base 24 was with pKa =
9.4 more difficult because of intramolecular charge repulsion.18
The final absorption of the boronate ester dianion 25 at 544 nm was
26 nm (838 cm-1) less red-shifted than that of the putative catechol
dianion 18. Poor sensitivity of boronic ester 22 to increasing pH
was consistent with the lack of resonance with the cNDI core. At
pH > 12, the absorption increased rapidly due to partial hydrolysis
of the boronate esters in cNDI 25.
cNDIs 22, 24 and 25 with boronic acid esters in the core were
fluorescent (Fig. 10a). Absorptions and emissions measured for
cNDI boronate esters were often broad and had unusual shapes.
Although contributions from decreasing extinction coefficients
Fig. 9 Absorption maxima of 9 ( ), 10 ( ) and 11 (¥) in DMSO/water
4 : 1 at pH 8.0 as a function of the concentration of phenylboronic acid
(PBA).
᭹
᭺
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deserve consideration (25: e = 1.8 mM-1 cm-1), these unsatisfactory
spectra indicated the presence of several absorbing and emitting
species under all conditions. This more complex situation with
cNDIs with boronate esters in the core was not further investigated
because it deviated from the topic of the study.
in acidity to pKa = 6.8 reflects the hybrid between a poorly acidic
phenol and a highly acidic aryl iminium proton. Iminium cNDI 37
with ortho-methoxy instead of hydroxy groups naturally lost the
reduced acidity but preserved the bathochromic shift of cNDI 36.
The oxidation of hydroquinone 9 with ceric ammonium nitrate
(CAN) followed by covalent capture of the intermediate naph-
thoquinone with arylamines gave green cNDIs 26–31 with an
iminoquinone, their protonation gave the iminium cNDI 32–37
(Fig. 11). Aniline gave the green cNDI 26 with an iminoquinone
core (Fig. 11a). With aniline, the absorption maximum shifted to
638 nm, that is 4 nm (98 cm-1) below that of tetraamino cNDI
5. Protonation of the first imine of iminoquinone 26 at pKa = 5.8
caused a significant hypsochromic shift (2088 cm-1) to 563 nm
(Fig. 11). The blue-shifted, very broad absorption of iminium
cNDI 32 was consistent with the at least partial conversion of the
p-donating imine into a strong p-acceptor (Fig. 11a). Additional p-
donors in the para-position had little influence in the spectroscopic
properties of imino cNDIs 27 and 28 and their conjugate acids 33
and 34 (Fig. 11b). Poor sensitivity to substituent effects confirmed
that, for steric reasons, the aryl groups are poorly conjugated
with the iminoquinone core. Nitro acceptors in the meta-position
of imino cNDI 29 shifted the absorption to 627 nm without
changing the pKa much. This small blue-shift was consistent with
the weakening of the imine p-donor by the nitro acceptor. Hydroxy
donors in the ortho-position of 30 shifted the absorption of the
iminium cNDI 36 to 528 nm. Competing intramolecular hydrogen
bonding to the hydroxy lone pairs is likely to account for this
more important bathochromic effect. The simultaneous decrease
Conclusions
Synthesis and characterization of naphthalene- and perylenedi-
imides with hydroquinones, catechols, boronic esters and imi-
noquinones in the core are described. They enrich the current
collection of cNDI and cPDI in a colorful manner. As in green
and red fluorescent proteins from jellyfish and corals, phenoxy
and imine groups are identified as powerful p-donors to approach
the NIR frontier. The dynamic covalent chemistry realized with
catechols and boronic acids on the one hand and quinones and
amines on the other hand provides an attractive tool to modulate
optoelectronic properties in situ and to quickly build multi-
component architectures, e.g. layer-by-layer assembly on solid
surfaces.27 Particularly impressive is the ability of hydroquinone
cNDIs to cover all primary colors by simple changes in pH. This
panchromatic responsiveness to the environment is of practical use
to sense the purity of DMF with the “naked eye” at sensitivities
far beyond the “naked nose”. This example of panchromatic
hypersensitivity demonstrates that the new cNDIs will be ideal
for pattern generation in differential sensing arrays.28
Acknowledgements
We thank A. Vargas Jentzsch, J. Areephong and T. M. Fyles
(University of Victoria, Canada) for contributions to data
Fig. 11 a) Absorption spectra of 26 (pH 9, green) and 32 (pH 4, red) in DMSO/water 4 : 1, 25 ◦C. b) Change in absorption maxima of imines 26–31
upon protonation with decreasing pH to give iminium cations 32–37.
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collection and analysis, N.-T. Lin and D.-H. Tran for contributions
to synthesis, D. Jeannerat, A. Pinto and S. Grass for NMR
measurements, the Sciences Mass Spectrometry (SMS) platform
for mass spectrometry services, and the University of Geneva,
the European Research Council (ERC Advanced Investigator,
S.M.), the National Centre of Competence in Research (NCCR)
Chemical Biology (S.M.), the NCCR MUST (E.V.) and the Swiss
NSF (S.M., E.V.) for financial support.
11 R. E. Dawson, A. Hennig, D. P. Weimann, D. Emery, S. Gabutti, J.
Montenegro, V. Ravikumar, M. Mayor, J. Mareda, C. A. Schalley and
S. Matile, Nat. Chem., 2010, 2, 533–538.
12 J. Misek, A. Vargas Jentzsch, S. Sakurai, D. Emery, J. Mareda and S.
Matile, Angew. Chem., Int. Ed., 2010, 49, 7680–7683.
13 R. Y. Tsien, Angew. Chem., Int. Ed., 2009, 48, 5612–5626.
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8252 | Org. Biomol. Chem., 2011, 9, 8246–8252
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