A peptide based two component white light emitting system

Article abstract of DOI:10.1039/c3cc43371d

A peptide based two component white light emitting system has been designed and developed on the basis of a co-assembly of a PDI containing peptide system as an acceptor and a stilbene containing peptide system as a donor in organic solvents.

Full text of DOI:10.1039/c3cc43371d

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A peptide based two component white light emitting
system†
Cite this: Chem. Commun., 2013,
49, 6909
Dibakar Kumar Maiti and Arindam Banerjee*
Received 7th May 2013,
Accepted 12th June 2013
DOI: 10.1039/c3cc43371d
www.rsc.org/chemcomm
A peptide based two component white light emitting system has peptide based donor and acceptor molecules for the white light
been designed and developed on the basis of a co-assembly of a PDI emission. So, there is a real need for the design and construction
containing peptide system as an acceptor and a stilbene containing of a peptide based system, in which the donor and acceptor parts
peptide system as a donor in organic solvents.
are suitably crafted within the same or different molecules to
trigger the fluorescence resonance energy transfer from the donor
Nowadays, light emitting devices account for almost 20% of the to the acceptor to ultimately develop a white light emitting
total global energy consumption. The worldwide demand for substance under suitable conditions.
light emitting devices is increasing by leaps and bounds and
Herein, we report a peptide based new donor–acceptor system
the white light emitting material can be used as a light emitting to generate a white light emitting substance in solution. To the
source for future generation and this may replace the present best of our knowledge, this is the first example of a peptide based
incandescent light bulbs and fluorescent tubes. White-light-emitting white light emitting substance by the proper choice of donor and
materials are particularly important due to their potential acceptor moieties in fluorescence resonance energy transfer.
application in light emitting devices and displays.1 The white Peptide 1 (Fig. 1a) contains a stilbene moiety, which acts as a
light contains either a combination of three primary colors (red, donor, whereas peptide 2 (Fig. 1a) contains a perylenediimide
green and blue) or at least two complementary colors. There are (PDI), which acts as an acceptor, and the equimolar mixture of 1
several reports on the generation of white light emission by using and 2 in o-dichlorobenzene (ODCB) produces a white light. The
organic light emitting materials,2 organic–inorganic hybrids,3 synthetic method for making a stilbene moiety containing a
polymers,4,5 metal complexes,6,7 micro and nanomaterials,8 peptide was reported by us earlier.12 Perylenediimide containing
9
¨
and others. In most of these cases, Forster resonance energy
transfer10 between the donor and the acceptor components has
been used to generate white light.5,7 Organic white light emitting
materials are particularly interesting because of their good
solubility in organic solvents and these materials can be either
soaked on a solid material or to coat over a solid surface. There
are several examples of organic compound based white light
emitting substances.11 Recently, Li and coworkers have demon-
strated a solution processable white light emitting hybrid semi-
conducting material with a high quantum efficiency.11 Wu and
coworkers have prepared another solution processed white
organic light emitting diode.11 Recently, Nakanishi and coworkers
have discovered a three component solvent free white luminiscent
organic liquid.11 However, none of these above examples include
Department of Biological Chemistry, Indian Association for the Cultivation of Science,
Jadavpur, Kolkata 700032, India. E-mail: bcab@iacs.res.in,
arindamkol1966@gmail.com; Fax: +91-33-2473-2805
† Electronic supplementary information (ESI) available: Synthetic procedures for
making peptides 1, 2 and other compounds are given in detail. Spectroscopic data
and copies of 1H and 13C NMR of compounds 1 and 2. See DOI: 10.1039/
c3cc43371d
Fig. 1 (a) Chemical structures of Boc-Leu-Val-Phe-ST-OMe (1) and MeO-Phe-Val-
Leu-PDI-Leu-Val-Phe-OMe (2); the UV absorption spectrum of 1 (b), 2 (c) and the
white light emitting solution in ODCB (d).
c
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peptide based orange emitting molecule 2 was synthesized by
coupling of perylene tetracarboxylic bisanhydride and NH2-Leu-Val-
Phe-COOMe (14). These compounds were well characterized using
1H NMR spectroscopy and high resolution mass spectroscopy
(HRMS) and these pure compounds were used for all studies.
The UV-Vis spectroscopic study of the white light emitting
solution was carried out to probe its absorption pattern. At first,
UV-Vis spectroscopic studies of individual components (stilbene
containing peptide 1 and perylenediimide (PDI) containing
peptide 2) were carried out by using o-dichlorobenzene (ODCB)
as a solvent. It is clearly observed from Fig. 1b that the stilbene
containing peptide 1 has a UV absorption band at 342 nm
corresponding to the stilbene moiety.12 This gives rise to a blue
fluorescent material, when the solution is exposed to a 365 nm
UV-lamp (Fig. 1b). However, the PDI containing peptide 2 has
several absorption bands ranging from 450 nm to 550 nm
corresponding to S0 to S1 transitions of the perylenediimide
moiety. There are three peaks in the UV absorption spectrum,
out of which the 498 nm and 536 nm peaks are sharp and of
high intensity, whereas the 468 nm peak appears as a broad
peak with a lower intensity of absorption (Fig. 1c). Upon
exposure to the 365 nm UV-lamp this solution gives rise to an
orange fluorescence emission (Fig. 1c).
Fig. 2 Fluorescence excitation and emission spectra of 1 (a), 2 (b); (c) fluores-
cence emission spectra of the mixture of donor and acceptor peptides 1 and 2
respectively, in different proportions, showing the white light emission at the
equimolar mixture (1 : 1) in ODCB solvent. This also shows FRET from the donor to
the acceptor under different conditions. (d) CIE (1931) chromaticity diagram for
the white light emitting solution, (e) the white light emitting solution coated on
UV LED, (f) UV exposure of the writing using the white light emitting solution
upon a silica coated surface.
Interestingly, the equimolar mixture of 1 and 2 in ODCB
solution shows a white light emission upon exposure to a UV of component 2 to 1 results in a steady decrease in the fluores-
lamp (365 nm). An UV-Vis spectroscopic study of the equimolar cence emission intensity at 425 nm, whereas intensities of new
mixture of 1 and 2 clearly indicates the presence of a white light peaks at 547 nm, 590 nm and 643 nm are steadily increased.
emitting solution with a broad absorption range from 330 nm So, the emission intensity for the stilbene containing peptide at
to 600 nm. This consists of several peaks corresponding to its 425 nm decreases with the increase in the emission intensity of the
individual components. These peaks are at 342 nm, 468 nm, PDI containing peptide at 547 nm, 590 nm and 643 nm (Fig. 2c).
498 nm and 536 nm (Fig. 1d).
A fluorescence spectroscopic study of this white light emitting donor and the PDI containing peptide 2 acts as the acceptor.
mixture is useful to identify the donor and the acceptor compo- The calculation of CIE (Commission Internationale d’Eclairage,
This suggests that the stilbene containing peptide 1 acts as the
nents and to elucidate the process of the energy transfer from the 1931) coordinates was performed using the fluorescence emission
donor to the acceptor. All these fluorescence spectroscopic studies data for the white light emitting solution. The CIE chromaticity
were carried out in ODCB solvent. The stilbene containing peptide diagram exhibited the coordinates for the white light emission
1 has the fluorescence excitation at 343 nm and fluorescence (0.34, 0.34: Fig. 2d), and this is quite close to those of pure white
emission at 425 nm and this establishes that it is a blue emitter light emission (0.33, 0.33). It is also evident from the CIE diagram
(Fig. 2a). The quantum yield is 1.18% for the donor peptide 1.
that the emission color is also tunable from the blue to orange
The PDI containing peptide 2 shows several peaks in its range as per requirements.
respective fluorescence excitation and fluorescence emission
The white light emitting solution can be applied upon the
spectra (Fig. 2b). In the excitation spectra, it has three peaks silica surface. For this purpose, the silica surface was made by
centered at 469 nm, 499 nm and 537 nm, out of which the peak making a thin film of silica gel on the glass plate, and then the
at 537 nm is the major fluorescence excitation peak. It also has white light emitting solution was soaked into it. The resulting
a weak and broad excitation within the range of 300 nm to layer emits a white light on exposure to the UV-lamp (365 nm)
400 nm. Fluorescence excitation at 537 nm gives rise to two (Fig. 2f). The white light emitting solution is very useful as it
major emission peaks at 547 nm and 590 nm with a hump at can be used for coating over the required surface. Moreover, the
643 nm, and the 547 nm peak appears as the major peak. The coating of this white light emitting solution on the UV-LED
quantum yield of this component is 15.66%.
emits a marvelous white light (Fig. 2e).
Investigation of the fluorescence spectra of the white light
The time correlated single photon counting (TCSPC) study
emitting solution gives an interesting result. The gradual addition shows the relative fluorescence decay and respective life times
of the PDI containing peptide 2 to the ODCB solution of stilbene for different components (1 and 2) and the white light emitting
containing peptide 1 was done to understand the mechanism of solution (see ESI,† Fig. S7). Fluorescence lifetimes were
white light emission. During the gradual addition of MeO-FVL- measured in ODCB solvent. The average fluorescence lifetime
PDI-LVF-OMe (2) to Boc-LVF-ST-OMe (1), the solution was always of the stilbene containing peptide 1 is 0.21 ns (at its emis-
excited at 343 nm (fluorescence excitation of component 1) with a sion wavelength of 425 nm) at an excitation of 340 nm.
constant slit width (2.5 nm) of the fluorometer. Gradual addition The average fluorescence lifetime of the peptide 2 is 1.56 ns
c
6910 Chem. Commun., 2013, 49, 6909--6911
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(at its major emission wavelength of 547 nm) at an excitation of
D.K.M. would like to acknowledge CSIR, New Delhi, India,
440 nm, whereas the white light emitting solution shows the for financial assistance.
average fluorescence lifetime of 5.38 ns at an emission wavelength
Notes and references
of 547 nm (excited at 340 nm). The average fluorescence lifetime
of donor 1 is decreased to 0.12 ns at its emission wavelength of
425 nm in the presence of acceptor 2. So, in the white light
emitting solution, the average lifetime of acceptor 2 is increased
and consequently the average lifetime of donor 1 is decreased.
The energy transfer efficiency has been calculated from the
TCSPC life time study by using the following equation.13
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`
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microscopic images of the stilbene containing peptide 1 show
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ESI†). These fibers are several micrometers in length and the
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SEM study of the compound 2 also shows the formation
of nanofibers in ODCB solution (Fig. S9b, ESI†) and widths
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solution are within the range of 70 nm to 80 nm width and
they are different from both of their individual components
(Fig. S9c, ESI†).
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A new white light emitting substance has been discovered.
It consists of two different fluorophores containing peptides
Boc-LVF-ST-OMe (1) and MeO-FVL-PDI-LVF-OMe (2), out of
which the stilbene containing peptide 1 acts as a donor and
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the PDI containing peptide 2 acts as an acceptor in Forster
´
´
resonance energy transfer (FRET). Moreover, the emission light
can be tuned from blue to white to orange as shown by CIE
(1931) coordinates. This white light emitting solution can be
used to make white light emitting thin layers made of silica.
Such a white light emitting solution holds future promises for
the potential application as an advanced material that may be
used in solution-processed organic electronic devices.
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c
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Chem. Commun., 2013, 49, 6909--6911 6911