H-Bonding and charging mediated aggregation and emission for fluorescence turn-on detection of hydrazine hydrate

Article abstract of DOI:10.1039/c5cc02897c

In situ morphological transition and turn-on fluorescence of self-assembled NDI derivatives driven by hydrazine hydrate are realized through H-bonding and charging of aromatic building blocks, demonstrating a stimuli-responsive supramolecular system useful for visual detection of hydrazine hydrate.

Full text of DOI:10.1039/c5cc02897c

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DOI: 10.1039/C5CC02897C
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H-Bonding and Charging Mediated Aggregation and Emission for
Fluorescence Turn-on Detection of Hydrazine Hydrate
Received 00th January 20xx,
Accepted 00th January 20xx
Deyan Zhou,† Yangyang Wang,†,‡ Jiong Jia,† Wenzhu Yu,† Baofeng Qu,† Xia Li,† Xuan Sun†*
DOI: 10.1039/x0xx00000x
www.rsc.org/
switching8. The in situ control over self-assembly and photo-
In situ morphological transition and turn-on fluorescence of self-
assembly of NDI derivative driven by hydrazine hydrate are
realized through H-bonding and charging of the aromatic building
blocks, demonstrating a stimuli-responsive supramolecular system
to be useful for visual detection of hydrazine hydrate.
function of aromatic building blocks, such as PDIs and NDIs, arise
from the ease of reversible reduction and color change between the
three redox states (neutral, radical anion, and dianion). The
production of radical anions of the NDI in aqueous solution is
feasibly achieved by chemical reduction, rendering it colorimetric
sensors for detection of F-15-17, CN-18, or amines19. However, there is
much less information available on the aggregates of NDI radical
anions, in spite of its central role in electron- and energy-transfer
One of the important goals of supramolecular chemistry is to
develop the externally controlled systems, that is, the structure or
other physical properties of the well-defined molecular aggregates
or supramolecules can be changed or switched in a predictable
manner by an external signal. The key to a successful switch is that
the external signal strongly perturbs an important binding
interaction holding together the supramolecular complex. As
exploited in nature, H-bonding (HB) with the highly directional
nature is envisioned essential to govern and modulate the structure
and morphology of the artificial supramolecular architecture by
precise defining the spatial organization of the building blocks in the
self-assembled state. Specifically, through regulation of electronic
states, HB mediated supramolecular assemblies of photophysically
rich π-conjugated chromophores provides an exciting opportunity
for fine tuning the functions of the assemblies such as luminescence
characteristics1 or transport properties, as sensing2-4 and molecular
electronics.5-7 Charging of an aromatic primary building block is also
evidenced to be an effective way for controlling the structure of the
supramolecular assemblies8. The bisimides, having an aromatic core
such as naphthalenediimides (NDIs) or perylenediimides (PDIs) are
intriguing n-type building blocks to fabricate specific aggregated
systems20-23
.
As a class of important chemicals, hydrazine is valuable in
many fields but has toxicity, the detection is therefore quite
essential.24-28 Hydrazine contains two amino groups, and it can
easily form extended arrays of HB (NH···O and NH···N), which may
be particularly interesting for modulation of molecular assembling
through HB. Detection of hydrazine hydrate by an Au nanoparticles-
based colorimetric sensing system was realized based on HB
recognition29. Meanwhile, hydrazine is strong reductant that can
potentially
reduce
the
aromatic
electron-withdrawing
chromophores to form radical ions with characteristic spectroscopic
signatures. Adding hydrazine into a supramolecular assembly
system may trigger the reduction of the aromatic building blocks
and meditate both morphology and photo-function of the assembly
by HB and charging, which may be considered as a novel strategy
for design of hydrazine probes. As an important probe technique,
fluorescence turn-on detection is advantageous because of its high
sensitivity and easy-operation.30-34 Specificly, fluoreseence turn-on
detection based on aggregation modulation was rarely reported.
Herein we report on hydrazine modulated morphological
transformation and turn-on fluorescence of self-assembled
nanoribbons. A nearly non-fluorescent host dyad NDI-AB 1 (Scheme
1) is constructed by introducing an electron-donating moiety
azobenzene (AB) to the potential fluorophore NDI. As expected, 1 is
non-planar, as the result of the sterically demanding framework,
exhibiting weak fluorescence yielding mainly from twisted
intramolecular charge transfer (TICT) effect.33,35 In water, 1 self-
assembled into well-ordered nanoribbons with further fluorescence
structures with semiconductivity9-12 or photoluminescence13,14
.
Through reversible charging of the PDI moieties, the initially
obtained long fibers from the self-organized PDIs underwent
reversible fission, accompanied by a significant change in electronic
properties, which is envisaged for adaptive photo-function
†
Key Laboratory for Colloid & Interface Chemistry, Shandong University, Education
Ministry, Jinan, 250100, P. R. China
State Key Lab of Crystal Materials, Shandong University, Jinan, 250100, P. R. China
‡
E-mail: sunxuan@sdu.edu.cn
Electronic Supplementary Information (ESI) available: [Experimental procedures,
characterization data, and additional spectra.]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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quenching by π-π interaction. Up addition of hydrazine hydrate, electron microscopy (TEM, Fig. S3a, ESI†) and confocal fluorescent
DOI: 10.1039/C5CC02897C
interactions between aromatic monomers were attenuated by HB microscopy (CFM, Fig. 2a and 2b). The UV/vis spectroscopy of the
intervention and the reduction to anionic species, which causes nanoribbons in water shows hypochromic effect with respect to
ribbons fission accompanied by a remarkably enhanced emission that of the molecular absorption of 1 in DMSO (Fig. 1a). Meanwhile,
from the aggregated radicals.
the fluorescence of the nanoribbons further attenuates relative to
that of the monomeric compound (Fig. 1b). Combined with the
broad absorption of O-H stretching vibration at 3300-3500 cm-1 in
solid state FT-IR spectra (Fig. S4a, ESI†) and the π-stacking signal in
the wide-angle XRD pattern (Fig. S5, ESI†) of the nanoribbons, it is
demonstrates that highly ordered H-aggregation is provided by
synergy between the π-π stacking and intermolecular H-bonding.
Scheme 1. Schematic illustration of the reaction of molecule 1 with
hydrazine hydrate.
Dyad 1 was readily synthesized by one-step reaction between
the respective azobenzene derivative and naphthaleneimide, and
fully characterized using 1H NMR, 13C NMR and mass spectra
(Scheme S1, ESI†). The control compounds COOH-NDI 2 and OH-AB
3 were also synthesized and characterized, respectively (Scheme S2
and S3 ESI†). 1 is well dissolved in DMSO, showing essentially a
superposition of absorptions of 2 and 3 (Fig. S1a, ESI†), dominated
by a typical strong π-π* transition of the NDI model with
vibronically split peaks (Fig. 1). Fluorescence study of 1 in DMSO
Fig. 2 CFM images of the aggregates of 1 (a, b) before and (c, d)
after adding hydrazine hydrate.
reveals broad emission with rather weak quantum yield of ΦPL
=
Firstly, we investigated the interactions between the molecule
1 and hydrazine in DMSO followed by absorption and fluorescence
spectra. All the spectra were acquired instantly after adding
hydrazine (within 5s). From the variation in the absorption spectra
(Fig. 3a) with increasing concentrations of hydrazine, a two-step
reaction is deduced that involved between 1 and hydrazine. Upon
addition of hydrazine, a relatively broad absorption band with
maximum at 500 nm arouse promptly accompanied with the
attenuation of the NDI absorption. The intensity of this new
absorption band increased along with increasig the hydrazine
concentrations, then declined with further addition of hydrazine.
Meanwhile, a new sharp absorption band with maximum at 475 nm
appeared, referring to the typical absorption of the NDI•- (Fig. S6a,
ESI†)15-18. Compared with the azobenzene 3, which demonstrated
remarkable changes in the absorption spectra upon addition of
hydrazine (Fig. S6b, ESI†), the broad absorption at 500 nm may
ascribed to the azo-hydrazone tautomerism, which is interesting
and supposed to exist in the dynamic equilibrium in an azophenol
system36,37. The presence of the –OH group is conducive to prompt
the tautomerism to the hydrazone form and quinone structure at
the presence of hydrazine (Scheme 1). Meanwhile, the electron-
deficient NDI moiety was inclined to bind with hydrazine, and was
feasibly reduced to the radical anion. In fact, these two step
reactions may happen simultaneously as deduced from the
absorption of NDI•- at 600 nm (inset in Fig. 3a). When adding less
than 5 equiv of hydrazine, absorption of NDI•- can be observed,
2.37%, which is quenched with respective to 2 (Fig. 1 and S1b, ESI†).
The electrochemical behavior of 1 (Fig. S2, ESI†) showed two well-
separated, reversible one-electron reduction waves corresponding
to the formation of the radical anion and dianion, respectively,
which are more negative owning to the electron donating effect of
the AB moiety15.
Fig. 1 (a) UV-vis absorption spectra of molecule 1 in DMSO (25 μM,
●) and the aggregates (■), and normalized fluorescence spectra of
molecule 1 in DMSO (25 μM, ○) and the aggregates (□); (b) UV-vis
absorption spectra of aggregates in water before (■) and after (●)
adding hydrazine hydrate, and normalized fluorescence spectra of
aggregates in water before (□) and after (○) adding hydrazine
hydrate, inset is the photographical images of the aggregates
before (left) and after (right) adding hydrazine hydrate.
In water, molecule
1 gradually self-assembled into 1-D
1
nanoribbons with high aspect ratio as observed by transmission
indicating a relatively facile reduction process. H NMR spectra of
2 | J. Name., 2012, 00, 1-3
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the hydrazine addition products (Fig. S7, ESI†) well evidenced the dimension, which was not sufficiently stable for VXieRwDArticslteuOdnielinse.
formation of the quinone structure and NDI•- radical by the Concerning the favor of formation of the H-bond and the strong
DOI: 10.1039/C5CC02897C
significant peaks shift corresponding to the protons on AB unit and reductive ability of the hydrazine hydrate, the morphological
the disappearance of the signals of aromatic protons on NDI, transition from nanoribbons to nanovesicles was envisaged to be
respectively. Electron paramagnetic resonance (EPR) spectra modulated by synergetic H-bonding and charging effects. The
manifested the formation of a delocalized NDI•- radical anion16 at absorption peaks of C=O on –COOH and amide in the FT-IR shifted
to lower wave numbers after adding hydrazine hydrate, which
clearly evidenced the H-bonding meditated structure transition (Fig.
S4b, ESI†). Interestingly, the nanovesicles demonstrated an
extremely strong green emission located at 500 nm (Fig.1b and 2d),
originating from both the NDI and NDI•- radicals (Fig. S9b, ESI†),
while the local emission from the NDI moieties at 400 nm as
observed in DMSO solution was suppressed completely (Fig. S12b,
ESI†). When using F- as the reductant, which was generally applied
to reduce the bisimide aromatic molecules15-17, neither the obvious
morphological changes nor the fluorescence enhancement was
observed (Fig. S11, ESI†). This diversity from the hydrazine with F-
revealed the synergetic effects of H-bonding and charging on
modulating the assembly and the photo-function. The H-bond
formation between hydrazine and the –COOH and/or –OH groups
within the assembly of 1 greatly promoted the ability of 1 to trap
hydrazine, which then facilitated the reduction of 1. Meanwhile, H-
bonding together with the higher electron density on the radicals
interrupted π-stacking between the molecules, finally leading to the
fission of the nanoribbons and formation of the nanovesicles. Also,
the aggregation transformation of 1 toward hydrazine hydrate was
much more sensitive than that of the control compound 2 (Fig. S12,
ESI†). The much higher fluorescence quantum yield (Фf = 14.98%)38
of the nanovesicles in water compared with that of single molecule
in DMSO indicates the more stabilized radical anions in the
aggregates. Moreover, such highly emissive nature brought bright
green color of the aggregates suspension (Fig. 2d), which can be
facilely observed by naked-eye and would be beneficial for sensing.
Therefore, the present system may be potentially useful for
detection of hydrazine.
the presence of hydrazine. (Fig. S8, ESI†). Accompany with this two-
step reaction, color change was generated sharply from yellow to
deep-orange, as can be observed by naked eyes (Fig. 3a). The
absorption of the dianion of NDI was not observed with further
addition of hydrazine.
Fig. 3 (a) UV-vis absorption spectra and (b) fluorescence spectra of
molecule 1 in DMSO (25 μM) with addition of hydrazine.
With addition of hydrazine hydrate, fluorescence at 405 nm
emitted from NDI was greatly enhanced as shown in Fig. 3b.
Meanwhile,
a new broad emission emerged in the longer
wavelength region (500 – 600 nm). According to the excition of 1 in
DMSO at the presence of hydrazine (Fig. S9a, ESI†), this emission
band was contributed together from the NDI unit and its radical
anion NDI•-, which has never been investigated in previous work.
The “turn-on” fluorescence may refer to the TICT mechanism,
where hydrazine induced hydrazone and quinone structures
restrain the formation of the TICT state, directly leading to emission
recovery (Scheme 1). Time-dependent density functional theory
(TDDFT) calculations were carried out to elucidate the effect of
steric hindrance on the fluorescence of 1 (Fig. S10, ESI†). This
emission was sentive to hydrazine, while in contrast, upon addition
of a variety of other related test species, such as phenyl hydrazine,
In summary, we report facilely in situ meditate self-assembly
and photo-function of an aromatic building block AB-NDI by
synergetic effect of H-bonding and charging of aromatic systems.
The emission of the radical anion and that from the radicals in the
aggregation was studied for the first time. AB-NDI has been
designed according to the TICT mechanism, which exhibited “turn-
on” fluorescence response toward hydrazine. Aggregation
reconstruction drove by hydrazine through H-bonding and charging
exhibited extremely strong turn-on fluorescence, which is expected
to be excellent sensors for hydrazine detection. We envisage that
this methodology can be useful for the creation of adaptive
multifunctional supramolecular systems.
ethylenediamine,
ammonium
hydroxide,
hydroxylamine
hydrochloride, F-, I-, S2-, and SO32-, etc., only a fluorescence
quenching at 420 nm or an insignificant change was observed,
indicating the selectivity and specificity of 1 for hydrazine. (Fig. S11,
ESI†)
We then carried out experiments to check the effect of the
hydrazine on the molecular aggregation. After adding hydrazine
hydrate into the nanoribbons suspended in water, hyperchromic
effect in the higher energy region (300 – 400 nm, Fig. 1b and Fig.
S12a, ESI†) was displayed, corresponding to electronic transition of
NDI moiety, which may indicate the nanoribbons fission. Meanwhile,
a relatively weak absorption appeared in the lower energy region,
which may relate to the absorption of NDI•-. The fission of the
nanoribbons was evidenced by TEM (Fig. S3b, ESI†) and CFM (Fig. 2c
and 2d), revealing formation of nanovesicles with inhomogenous
This work was financially supported by NSFC (21371109) and the
“Taishan Scholar” project of Shandong Province.
Notes and references
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