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Journal of Materials Chemistry B
Page 2 of 6
COMMUNICATION
Journal Name
Recently, Fluorescent organic NPs are being well explored in The hydrolytic stability of TPT-(NOD) NPs was studied by
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many scientific disciplines for their simple synthesis and analysing the stability of the nanoparticle
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flexible fluorescence tunability. Generally, their formation is this, a suspension of 1 ml (10 M) TPT-(NOD) NPs were
driven by their nonpolar nature resulting in regulated self dispersed into 1 mL of pH 5.6, 7.4 and 8.0 PBS buffers
aggregation of monodisperse π-conjugated oligomers or respectively, and stored under dark conditions at 25 ± 2 °C for
6
4
days. To study the stability of TPT-(NOD) NPs in biological
chromophores in water and can show either aggregation
induced enhanced or excimer emission.22-24 With this
background, we have designed and synthesized Nitric oxide
photodonor (NOD) molecules conjugated perylene tetra
carboxylate ester (TPT) based fluorescent organic NPs i.e.
environment the same procedure was repeated with 10%
bovine culture media. After the mentioned time the TPT-
(NOD)
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donor in these 4 samples was extracted using DCM and
1
examined by H NMR. This analysis showed negligible
decomposition (Table S1 ESI), confirming the hydrolytic
stability of the TPT-(NOD)
Later on, the photophysical properties of the TPT-(NOD)
conjuagte and TPT-(NOD) NPs were analysed (Figure 3). The
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TPT(NOD) NPs. The criteria for the selection of perylene
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NPs, under dark conditions.
derivative TPT are as following (1) Perylene derived substrates
are known to form spherical NPs by easy reprecipitation
technique.25-26 (2) A single TPT molecule can provide four
covalent linkages aiding in the formation of four armed NO
4
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absorption and emission maxima of TPT-(NOD)
5
4
conjuagte (10-
M in ACN) were observed at 380 nm and 492 nm respectively
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photodonor and hence TPT(NOD) NPs synthesis is devoid of
(Figure 3a), where as the absorption and emission spectra of
NOD loading related complexities and (3) Perylene aggregates
exhibit transition from excimer to monomer emission if there
is any sort of disruption in π-π stacking. Such environment
-5
TPT-(NOD)
4
NPs (10 M in water) were red shifted and have
maxima at 385 nm and 627 nm respectively. It has been
observed that absorption spectrum of TPT-(NOD) has n-π*
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sensitive fluorescent transitions of perylene derivatives are band of NOD moiety and π-π* of TPT moiety, where as due to
utilized in developing various biosensing techniques.27-29 Here, aggregation the UV spectrum of TPT-(NOD)
NPs appears to be
in the design of TPT(NOD)
NPs, this property is exploited in a broad spectrum with indistinctive n-π* and π-π* bands.
4
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real time reporting the photoinduced release of NO.
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Similarly, the emission spectrum of TPT-(NOD) represents
monomer emission where as TPT-(NOD) nanoaggregates show
red shifted 627 nm emission which is aggregation induced
excimer emission.
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The synthesis of TPT-(NOD)4, a four NOD molecules conjugated
perylene tetra carboxylate ester was carried out in three steps
(
Scheme S1). Initially, compound
photodonor NOD was synthesized in four steps. Next,
synthesis of TPT was carried out by the slow addition of
4 azide terminated NO
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propargyl bromide in DMF to a refluxing mixture of Perylene
tetracarboxylic dianhydride, 1,8-Diazabicyclo[5,4,0]undec-7-
ene and propargyl alcohol. Finally, compounds
coupled by carrying out a click reaction in the presence of
CuSO /sodium ascorbate in a solvent mixture of CHCl , EtOH,
O at 65 C for 1 h to yield TPT-(NOD) . Thus synthesized
TPT-(NOD)4, was characterized by H and MALDI-TOF mass
spectral analysis (Figure S1-S5 ESI).
Photoresponsive TPT-(NOD) NPs which are nanoaggregates
4 and 5 were
4
3
H
2
̊
4
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Figure 3. UV-vis absorption and emission spectra of (a) TPT-(NOD)
TPT-(NOD) NPs (10-5 M, H O)
(10-5 M, ACN),
4
1
6
4
2
4
Further, the photolysis of the TPT-(NOD) NPs (5 μM) in water)
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was carried out using visible light irradiation (≥ 410 nm) and
the photolysed sample collected at 30 min irradiation time was
subjected to MALDI-TOF MS analysis. The mass spectrum
were prepared by reprecipitation technique, and their sizes
were determined by TEM and DLS studies. From TEM images it
was observed that the TPT-(NOD)
with an average diameter of 55 nm (Figure 2a), whereas
from DLS study the average size of the TPT-(NOD) NPs was
found to be 60 nm (Figure 2b). These NPs have zeta potential
58 mV representing their stability (Figure S6). Further,
polydispersity of the TPT-(NOD) NPs taken immediately after
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NPs are globular in shape,
+
obtained has [M ] molecular ion peaks corresponding to all the
∼
expected photoproducts with a mass difference of 29 amu
indicating sequential stepwise photorelease of NO via
conversion of nitro group to hydroxyl group through nitro-
nitrite rearrangement (Figure 4). From MALDI-TOF mass
spectrum it can be stated that upon photoexcitation of TPT-
4
∼
+
4
preparation was obtained to be 0.144.
4 4
(NOD) NPs, each NOD moiety of a single TPT-(NOD) molecule
gets sequentially photoactivated, generating a stepwise NO
photorelease.
Hence, a visible light induced sequential and stepwise NO
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photorelease mechanism from TPT-(NOD) NPs has been
proposed and was explained in the following Scheme 3.2
.
Figure 2. a. TEM and b. DLS images of TPT-(NOD)
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NPs indicating their uniform Upon initial excitation, TPT-(NOD) gets to its singlet state and
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globular shape with an average diameter of
∼
55 nm
then rapidly undergoes inter system crossing to triplet state
1
(T ). From the triplet state the first NOD moiety undergoes
nitro-nitrite photorearrangement which induces N-NO
2
| J. Name., 2012, 00, 1-3
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Behara, Krishna Kalyani
