Strategy toward Designing Semiconducting Polymer Nanoparticle

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A Strategy Towards Designing Semiconducting Polymer Nanoparticle –Multichomophoric Dye Assembly Susmita Das, Bikash Jana, Tanay Debnath, Arindam Ghoshal, Abhijit Kumar Das, and Amitava Patra J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b12689 • Publication Date (Web): 31 Jan 2017 Downloaded from http://pubs.acs.org on February 1, 2017

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The Journal of Physical Chemistry

A Strategy Towards Designing Semiconducting Polymer Nanoparticle –Multichomophoric Dye Assembly

Susmita Das,a Bikash Jana,a Tanay Debnath,b Arindam Ghoshal,a Abhijit Kumar Dasb and Amitava Patraa, * a

Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, WB, India b

Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, WB, India

*

Author to whom correspondence should be addressed. Electronic mail: [email protected] Telephone: (91)-33-2473-4971. Fax: (91)-33-2473-2805.

1

ACS Paragon Plus Environment


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Abstract The design of semiconducting polymer nanoparticles based hybrids is promising for light harvesting systems. Here, we design donor-acceptor system through tuning the energy level alignment of interacting counterparts for efficient light harvesting system where Poly(N-vinyl carbazole) (PVK) nanoparticles (NPs) acts as donor and the newly designed bicolor fluorophore ([R6G][HFL]) acts as acceptor. The photophysical interaction between polymer nanoparticle and bicolor fluorophore has been investigated by spectroscopic study and density functional theory (DFT) calculations. Dynamic quenching and the shortening of decay time of PVK polymer nanoparticles are revealed due to energy and electron transfer process from PVK nanoparticle to the surface attached bicolor fluorophore. Furthermore, ultrafast spectroscopic study has been undertaken to investigate the decay dynamic of [R6G][HFL] in presence and absence of PVK. Finally, white light generation with CIE co-ordinates (0.31, 0.39) is achieved at a definite donoracceptor ratio (wt. ratio of PVK:[R6G][HFL]=5.39:1). Interesting findings reveal that polymer nanoparticle- multichoromophoric dye assembly is promising for designing light harvesting systems.

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Introduction Increasing energy consumption and clean energy generation has been a major challenge over the past decades.1-2 Extensive research in this direction has led to design of several molecular devices with special emphasis on systems with sensitizing dyes and semiconducting materials in order to mimic natural photosynthesis.3-8 Macrocyclic dyes such as porphyrins, phthalocyanines, naphthalocyanines as well as transition metal complexes with polypyridine ligands demonstrate extraordinary light harvesting properties and therefore have been widely used in photoactive and electroactive assemblies.9-13 In addition, supramolecular systems with photoinduced energy or electron transfer have also been investigated.14-17 Very recently, polymer nanoparticles have been employed in versatile applications like light harvesting antenna materials,18 drug delivery,19 bio-imaging20 and temperature sensing.21 Interestingly, semiconducting organic/inorganic nanocomposites such as conjugated polymerquantum dot hybrids have strongly appealed in the field of photovoltaics and optoelectronics.3-4, 6, 22-25

The interfacial charge transfer between the excited states of the conjugated polymer and

the quantum dot directs the optoelectronic properties of the hybrid and is a subject of great interest for applications in nanocrystal based photovoltaics and optoelectronics.4,

7,

26

Interestingly, the charge transfer phenomenon may be tuned by simply tuning the energy level alignment of interacting counterparts.27 Therefore, a rationally designed multimodular donoracceptor systems with appropriate energy level alignment should serve as an interesting light harvesting antenna. Poly(N-vinyl carbazole) (PVK) is a recognized semiconducting hole transport polymer that has been widely used in opto-electronics.28-33 It exhibits a strong UV absorption and a blue emission with HOMO and LUMO energies at -5.5 and -2.0 eV respectively.30 Due to its remarkable photoconductivity, high thermal and photochemical 3



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stability and broad emission, this polymer has been intensely used in light emitting systems.30-33 However, their use in the design of light harvesting systems is relatively less focused.34 Thus, it will be interesting to design of PVK based materials for light harvesting system. In this study, new fluorophore molecule [R6G][HFL] is designed that absorbs in the visible region with absorption spectrum strongly overlapping with solar irradiation. [R6G][HFL] is derived from a metathesis reaction between cationic Rhodamine 6G (R6G+) (λmaxabs=525 nm) and anionic monoprotonated fluorescein (HFL-) (λmaxabs=475 nm and 454 nm), an approach extensively used for the synthesis of ionic liquids.35-40 The bicolor fluorophore molecules are then attached to the surface of blue emitting PVK NPs. The relative alignment of HOMO-LUMO levels of R6G and PVK suggests the possibility of charge separation in the R6G-PVK nanoassembly.30,

41

Steady state fluorescence and ultrafast spectroscopic studies are being used to

understand the photoinduced energy/charge transfer in [R6G][HFL]-PVK NP systems.26 The white light generation by tuning the donor-acceptor ratio has been done. Experimental Section Materials Poly(N-vinyl carbazole) (PVK), the fluorophores rhodamine 6G (R6G) and fluorescein disodium salt (Na2FL) were purchased from Sigma Aldrich and used as received. Monosodium phosphate monohydrate, disodium phosphate heptahydrate, sodium acetate, and glacial acetic acid (all from Merck) were used for the preparation of phosphate buffer (pH 7.4) and acetate buffer (pH 5.5), respectively. Chromatographic-grade HPLC water was used for the preparation of all solutions. The acetone, ethanol, and dichloromethane (DCM) used was sourced from Merck.

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Synthesis and Characterization Synthesis of NaHFL Na2FL is well known to demonstrate two well separated pKa values (4.5 and 6.4), a fact which was exploited for the synthesis of NaHFL. In this synthesis, 381 mg of Na2FL was converted to monoprotonated form NaHFL by stirring in a 10 mL of 500 mM acetate buffer (pH 5.5). Monoprotonation of Na2FL resulted in reduced solubility and precipitation within the aqueous medium. Unlike the starting material, NaHFL is soluble in DCM, allowing for extraction into DCM. The extracted material was washed with pH 5.5 acetate buffer, lyophilized, and stored for subsequent use (Scheme 1). Synthesis of [R6GH][HFl] [R6GH][HFl] was also obtained through ion metathesis reaction between NaHFl and R6G in1:1.1 ratio in a DCM/ buffer (pH5.5) mixture (5:1). The product was highly soluble in DCM separated through phase separation into the DCM phase. The by-product NaCl was thus removed in the aqueous phase. The DCM phase was washed with pH 5.5 buffer a couple of times to remove any excess of precursor and finally DCM was removed in a vacuum oven and the product was lyophilized and stored for further use (yield 82%). All the products were characterized using 1H NMR and FTIR (Figures S1, S2 & S3). QY of the dye pair is found to be 40.7 % ± 0.07. The formation of [R6G][HFL] is also confirmed by the recorded emission spectra (shown in Fig. S4) of [R6G][HFL] (in water) and the mixture of R6G and NaHFL (having the same concentration with [R6G][HFL]). The emission spectrum of [R6G][HFL] is different from the mixture of two individual dyes, which is similar to the emission coming from the mixture of individual dye after addition of two dyes.

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Na2 FL

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NaHFL

+ R6G

NaHFL

[R6G][HFL]

Scheme 1: Synthesis of [R6GH][HFL] Synthesis of PVK nanoparticles Pure PVK NPs were prepared by reprecipitation technique where PVK in THF was rapidly injected into polar aqueous medium under vigorous stirring condition.42-43 First, 500 µL of 0.5 mg mL-1 PVK in THF and 500 µL of THF were mixed under an inert atmosphere. The mixed solution was then ultrasonicated to get a completely homogeneous clear solution. Then, 1.0 mL of the mixed solution was rapidly injected into 10 mL of HPLC grade water under vigorous stirring condition for 5 min. Then, this solution was ultrasonicated for 30 min and finally THF was evaporated by partial vacuum evaporation at 60°C for two hours. Thus, THF was removed and leaving behind aqueous dispersed PVK NPs (having QY of 6.6 % ± 0.05) which is stable for more than three months. In this procedure, prepared NPs were negatively charged due to surface defects.44

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Synthesis of PVK-[R6G][HFL] assembly PVK-[R6G][HFL] assembly was prepared by the addition of [R6G][HFL] to the aqueous dispersion of PVK polymer nanoparticles. Briefly, 10 µM of [R6G][HFL] in water was added to an aqueous dispersion of the synthesized PVK nanoparticles and the mixture was left for an hour to form equilibrated water dispersed PVK-[R6G][HFL] assembly through electrostatic interactions. For steady state spectroscopic measurement, 1 µM and 0.83 µM of dye pair and the polymer nanoparticles have been used, respectively. White light emitting nano-assembly was synthesized using 6 µM [R6G][HFL] in water to a specific volume of water dispersed PVK NP using the above mentioned approach. Formation of assembly is further confirmed by steady state spectroscopic investigation (Figs. S5 and S6). Characterization FTIR spectra were obtained using a Perkin Elmer Spectrum 100 FTIR spectrometer. Bruker-Avance III HD (400 MHz) and Avance III (500 MHz) spectrometers were used to obtain 1

H NMR spectra. Zeta potential of the PVK nanoparticles and [R6G][HFL] modified PVK

nanoparticles were determined using a Malvern zetasizer instrument. Nanoparticles were characterized using field emission scanning electron microscopy (FE-SEM, JEOL, JSM-6700F). SEM images have been taken with the samples prepared by drop casting solid film on glass substrate. A high resolution transmission electron microscope (HRTEM); JEOL 2010, 200 kV operating voltage) was used to obtain the TEM micrographs of the nanoparticles. Image J software was then used for the accurate sizing of these nanoparticles. Optical absorption spectra were measured using a UV-vis spectrophotometer (Shimadzu UV-Vis Spectrophotometer 2450). A Fluoromax-P (Horiba Jobin-Yvon) photoluminescence spectrophotometer was used for recording the fluorescence spectra. The absorption and fluorescence spectra were collected using 7



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1 cm pathlength quartz cuvettes and the excitation/emission slits were both maintained at 2 nm for all fluorescence measurements. Fluorescence quantum yields (Φ), QY for PVK polymer nanoparticles and white light emission of the nanoparticles were calculated using the relative method with quinine sulfate in 0.1 M H2SO4 as the standard (Φ=0.577) and QY of [R6G][HFL] was measured using disodium fluorescein in 0.1 M sodium hydroxide solution (Φ=0.95) as reference. The absorbance of quinine sulfate and the nanoparticles were maintained below 0.1 in order to eliminate bias from inner-filter effects. Emission spectra were collected upon excitation at 340 nm and quantum yields were calculated using the formula.45

Φ un = Φ std

Astd Fun  ηun  Aun Fstd  η std

  

2

(1)

Where, Φun and Φstd are the quantum yields, Aun and Astd are the absorbance values, Fun and Fstdare the integrated fluorescence intensities, and ηun and ηstd are the refractive indices of the solvents for the unknown (un) and standard (std), respectively. The overlap integral between donor emission and the acceptor absorption is calculated by using following equation45 ∞

∞

0

0

J (λ ) = ∫ FD (λ )ε A (λ )λ4 dλ / ∫ FD (λ ) dλ

(2)

Where, J(λ) is the spectral overlap integral, FD(λ) is the fluorescence intensity of the donor, and εA(λ) is the absorption coefficient of acceptor at wavelength λ (in nm). For the time-correlated single-photon counting (TCSPC) measurements, samples were excited at 340 nm (nano-LED, pd=1 ns) in an IBH Fluorocube apparatus and the decays were collected at three different emission wavelengths (440, 512, and 554 nm). The repetition rate was 1 MHz. The fluorescence decays were collected with a Hamamatsu MCP photomultiplier

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(C487802) and were analyzed using IBH DAS6 software. The following equation was used to determine the experimental time-resolved fluorescence decays, P(t).45 n  t  P(t ) = b + ∑ α i exp −  i  τi 

(3)

Here, n is the number of discrete emissive species, b is a baseline correction (“dc” offset), and ai and τi are pre-exponential factors and excited-state fluorescence lifetimes associated with the ith component, respectively. The average lifetime, ⟨τ⟩, is calculated from the following equation.45

< τ >=

n

∑βτ

(4)

i i

i =1

Where β i = α i / ∑ α i and β i is contribution of the decay component. Ultrafast spectroscopic data were investigated using a Femtosecond fluorescence upconversion spectrophotometer with a Halcyone ultrafast setup (coherent). The sample excitation was performed with a 400 nm wavelength radiation, pumped using a 800 nm femtosecond (fs) (140 fs pulse width, 80 MHz repetition rate) laser pulse (4.4 W) from a Ti:sapphire oscillator (Chameleon, Coherent) coupled to a second harmonic generator (by BBO type I crystal). The emission wavelength (554 nm) and the gate pulse of the fundamental beam (800 nm) are upconverted using nonlinear crystal (BBO type II). The FWHM of the instrument response function is about 289 fs. The femtosecond time resolved decay data were fitted using Surface Xplorer 2.3 fitting software.

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Computational Details All the ab initio molecular orbital theory calculations were performed using Gaussian 0946 suite of quantum chemistry program. For electronic structure calculations we have used density functional B3LYP47-48 method with the conjunction of 6-31+G(d) basis set. The normalmode analysis has been carried out at the same level of theories for optimized geometries and characterized as minima having no imaginary frequency. The total theoretical calculations have been done in aqueous medium. We have employed self-consistent reaction field (SCRF) method by using polarizable continuum model (PCM) to incorporate the bulk aqueous medium. SCRF requests that a calculation be performed in the presence of a solvent by placing the solute in a cavity within the solvent reaction field. Through PCM model the solute cavity is created via a set of overlapping spheres. HOMO-LUMO calculations are also performed using same aforementioned level of theory. All the calculations have been done at 0K and 1 atm pressure.

Results and Discussions The synthesized PVK nanoparticles (NPs) were characterized using TEM (Fig. S7) as well as SEM and the micrographs revealed spherical nanoparticles sizing 65 ± 18 nm (Figs. 1A & B). Surface modification of the PVK NPs using the synthesized bicolor dye [R6G][HFL] led to a highly monodisperse particle distribution with size 59 ± 4 nm while the morphology approximately remained the same (Fig. 1B). SEM micrographs of surface modified PVK NPs demonstrate an improved and more defined spherical morphology in comparison to the pure PVK nanoparticles. Pure PVK nanoparticles exhibit a high negative zeta potential value (-21 mV) accounting for its highly stable dispersion in aqueous medium. [R6G][HFL] modified nanoparticles ([R6G][HFL]-PVK NPs) however showed a drastically altered net surface charge with a high positive zeta potential (+14 mV) value. Thus, both improved monodispersity and 10


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contrasting zeta potential value of the surface modified PVK NPs indicate a strong interaction of the bicolor dye with the nanoparticle surface and the interaction is primarily considered to be electrostatic. It is assumed that PVK NPs being negatively charged attracts the positively charged R6G+ unit of [R6G][HFL] towards its surface that results in a net positive surface charge of the tailored particles and thereby confirming the surface modification. B

A

0.2 µm

0.2 µ m

Figure 1: SEM micrographs of (A) pure PVK NPs and (B) PVK-[R6G][HFL] assembly. Optical properties of PVK nanoparticles Pure PVK NPs demonstrates an absorption band in the UV region with two closely spaced strong and sharp absorption peaks namely at 330 and 345 nm (Fig. 2A).18, 31, 34, 49 In case of [R6G][HFL] - PVK NP assembly, the nature of absorption spectrum of PVK remains unaltered (Fig. 2A). However, the spectrum shows an additional band in the visible region with a small hump at 454 nm, a shoulder at 492 nm and a peak at 526 nm. The hump corresponding to HFL- at 454 nm and the peak corresponding to R6G+ at 526 nm remains unaffected upon interaction with PVK nanoparticles in comparison to free [R6G][HFL] (Fig. 2A). However, the shoulder at 492 nm is observed to become more prominent due to interaction with PVK NPs (Fig. 2A). In order to explain these changes in spectral behavior, interaction of the precursors (NaHFL and R6G) with PVK NPs are separately investigated (Fig. 2B) which indicates a small 11



increase in FWHM (36 nm to 44 nm) for R6G upon attaching with PVK NPs with the peak position and absorbance value remaining the same. However, the absorption spectrum of NaHFL undergoes a significant change due to interaction with PVK NPs. Free aqueous NaHFL shows two equally dominant peaks at 451 nm and 475 nm (Fig. 2B) characteristic of the monoanionic fluorescein.50 The 475 nm peak undergoes a 16 nm red shift appearing as the dominant peak in presence of PVK NPs. This indicates a ground state interaction between the HFL- unit of NaHFL and PVK NPs. Thus, the appearance of a more prominent shoulder at 492 nm in [R6G][HFL]PVK NPs is attributed to this ground state interactions between PVK NPs and the HFL- unit which will be established through further studies in the later section. It is also worth mentioning here that the molar absorptivity at 492 nm increases by 1.5 times upon attaching to PVK NPs in

0.20

(A)

(i) (ii) (iii)

0.15

0.10

0.05

Absorbance

0.20

0.00

(B)

0.15

(i) (ii) (iii) (iv)

0.10

Absorbance

comparison to free [R6G][HFL].

Absorbance

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0.075 0.050 0.025 0.000 400

450

500

550

Wavelength (nm)

0.05

0.00 400

500

600

400

500

600

Wavelength (nm)

Wavelength (nm)

Figure 2: Absorption Spectra of (A) (i) water dispersed pure PVK NPs, (ii) free [R6G][HFL] in water and (iii) water dispersed PVK-[R6G][HFL] assembly, (B) Absorption spectra of aqueous solution of the precursors NaHFL and R6G in absence and in presence of water dispersed PVK NPs: R6G (i), NaHFL (ii), NaHFL+PVK NP (iii), R6G+PVK NP (iv), inset shows the enlarge view of free NaHFL and R6G. 12


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Examination of the emission spectrum of pure PVK NPs demonstrates a broad band in the purplish blue region centered on 400 nm (Fig. 3A). The emission spectrum of the [R6G][HFL]-PVK NPs contains three peaks, one broad peak corresponding to PVK in blue region and the other two peaks lying in the green (508 nm) and orange (554 nm) region of the electromagnetic spectrum corresponding to HFL- and R6G+, respectively. A close comparison of emission spectra of free [R6G][HFL] and pure PVK NPs to that of the [R6G][HFL]-PVK NPs indicates 5 nm red shift with increased emission intensity in the peak corresponding to HFL-, while no peak shifting is observed for R6G+ and PVK in the surface modified NPs. However, 50% and 34% quenching are observed in the emission intensities of PVK NPs and R6G+ to their modified NPs, respectively. On this consequence, only 13% quenching of PVK emission is observed in presence of R6G (Fig. S8). However, this quenching is increased to 50% in presence of HFL, indicating the presence of HFL causes the quenching more efficiently. It is interesting to note that the quenching at R6G+ peak position (554 nm) was pronounced upon excitation at PVK absorption maxima (340 nm) than direct excitation (525 nm) (Fig. 3B). This clearly points towards one or more excited state phenomena existing between the pair in the assembly.

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Figure 3: Emission spectra of (A) (i) aqueous solution of free [R6G][HFL], (ii) water dispersed pure PVK NPs, (iii) water dispersed PVK-[R6G][HFL] assembly for λex=340 nm and (B) (i) aqueous solution of free [R6G][HFL], (ii) water dispersed PVK-[R6G][HFL] assembly for λex=525 nm. It is interesting to note that the fluorescence quenching is found in both 400 nm and 554 nm peaks corresponding to PVK and R6G+. Here, the overlap integral between the donor (PVK) and acceptor (dye pair) is 1.95 x 1010 M-1cm-1 nm4 (Fig. 4). The 5 nm red shifting and the increased emission intensity of the peak consequent of HFL- in association with 16 nm red shift in the corresponding absorption indicates proton transfer interaction between HFL- and PVK NPs.50 The dianionic form of FL is reportedly more fluorescent in aqueous medium than the monoanionic form and exhibited a red shifted absorption (~490 nm) and emission maxima (~512 nm).50 Thus, both quenching in 400 nm and 554 nm remain unclear which will be discussed in the next section.

Figure 4: Spectral overlap between emission spectrum of PVK NP (a) and absorption spectrum of [R6G][HFL] (b). Fluorescence decay time measurements were performed in order to further investigate the excited state dynamics that might be responsible for the simultaneous quenching of the two 14


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peaks in [R6G][HFL] - PVK NP assembly. For pure PVK NPs, the emission was collected at 400 nm while for [R6G][HFL] - PVK NP assembly the emission was collected at three different wavelengths (400 nm, 512 nm, 554 nm) corresponding to three peaks observed in steady state emission keeping the same excitation wavelength (λex= 340 nm). Pure PVK NPs demonstrated a triple exponential decay (Table 1) with major contribution from 727 ps (78 %) component along with minor contributions of 3.6 ns (15 %) and 15 ns (7%) with an average lifetime of 1.98 ns (Table 1). The two longer components are attributed to two different types of excimers, one high energy excimer with partially overlapping polymeric units while the other low energy excimer with sandwiched polymeric units.30 The shortest component with the major contribution is attributed to the emission of the polymeric units that does not form any excimer. Average lifetime of surface modification of PVK NPs decreased to 1.05 ns. The fluorescence decay of PVK NPs (λem= 400 nm) reveals ~ 50 % quenching in the average decay time is (Table 1) (Fig. 5A). The percent quenching of the average fluorescence lifetime at 400 nm matches that of the steady state emission quenching at the same wavelength suggesting the dynamic quenching.

(B)

(A) 1000

1000

Counts (in log)

Counts (in log)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a 100

b 10

a

100

b 10

0

10

20 30 Time (ns)

40

0

15


10

20 30 Time (ns)

40

50


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Figure 5: Fluorescence decay dynamics of water dispersed (A) (a) pure PVK NPs and (b) PVK[R6G][HFL] assembly for λex=340 nm and λem=400 nm and (B) (a) PVK-[R6G][HFL] assembly, (b) free [R6G][HFL] for λex=340 nm and λem=554 nm. For a better understanding of the possible excited state dynamics within the designed assembly, DFT calculations were performed. The calculated HOMO-LUMO energy values (Scheme 2) for pure PVK in aqueous medium lie close to reported gas phase values.30 Scheme 2A shows that the LUMO of PVK (-1.18 eV) lie just above the LUMO of [R6G][HFL] (-2.92 eV) thereby suggesting a possibility of excited state electron transfer from PVK to [R6G][HFL] in the surface modified NPs. Thus, a combination of energy and charge transfer might be responsible for the fluorescence quenching at 400 nm. The calculated HOMO-LUMO levels for [R6G][HFL]-PVK NP system suggests a type II semiconductor model that will aid in long lived charged transfer state which is desired for light emitters and photovoltaics.26, 51

PVK

LUMO -1.18 eV

hνf

λex=340 nm

HOMO -5.69 eV

LUMO

[R6G][HFL]

LUMO -2.92 eV

λex=340 nm

+

+

HOMO -5.72 eV

A

HOMO

B 16


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Scheme 2: (A) Illustration of electron transfer and energy transfer processes involved in [R6G][HFL]-PVK NPs and (B) Calculated HOMO-LUMO structures for [R6G][HFL] in aqueous phase. On the other hand, the fluorescence decay of free [R6G][HFL] at λem=515 nm exhibits a monoexponential decay with a lifetime of 3.89 ns. However, upon attachment with the PVK surface, the fluorescence decay of [R6G][HFL] exhibits a tri-exponential decay with components 104 ps (63 %), 3.85 ns (36 % ) and 22.62 ns ( 1 %) (Table 1) (Fig. S9). The decay time of 3.85 ns is assigned to the HFL- unit of [R6G][HFL] as is evident from free [R6G][HFL] decay which is consistent with reported values.50 Fluorescence decay measurement with λem=554 nm corresponding to the R6G+ unit of [R6G][HFL] demonstrates a single exponential decay for free [R6G][HFL] with a lifetime of 3.82 ns. Upon attachment to PVK surface, the decay measured at 554 nm exhibits three lifetime components of 3.75 ns (59%), 23.46 ns (3%) and -151 ps (38%) (Table 1 and Fig. 5B). In heterogeneous system, multi-exponential decay arises only due to different environments by the probe molecule. Here, 151 ps rise time confirms the energy transfer from PVK to [R6G][HFL]. Therefore, shortening of decay time of PVK is related to the energy transfer as well as charge transfer from PVK to [R6G][HFL] according to energy level alignment (Scheme 2). But, due to lack of our facility we are unable to explore more about the charge transfer process and further investigation is needed for better understanding.

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Table 1: Decay parameters of pure PVK NPs, free [R6G][HFL] and [R6G][HFL]-PVK NPs (λex=340 nm) System(λem)

a1c

τ1b (ns)

a2c

τ2b (ns)

a3c

τ3b (ns)

τav (ns)

PVK NP (400 nm)

0.16

3.59

0.05

15.34

0.79

0.72

1.98 ± 0.11

[R6G][HFL]-PVK NP (400 nm)

0.14

2

0.04

11.75

0.82

0.36

1.05 ± 0.06

[R6G][HFL] (515 nm)

1

3.89

_

_

_

_

3.89 ± 0.42


0.63

0.104

0.36

3.85

0.01

22.62

1.68 ± 0.15

[R6G][HFL] (554 nm)

1

3.82

_

_

_

_

3.82 ± 0.42


0.59

3.75

0.03

23.46

0.38

-0.151

b

± 10 %, c ±5 %

As the calculated energy levels (Scheme 2) of the designed donor-acceptor system support the possibility of charge transfer from PVK to[R6G][HFL] in a type II semiconductor system. Due to lack of facility, we have excited the samples at 400 nm instead of 340 nm which is the excitation of PVK. Thus, we excite the free and surface conjugated [R6G][HFL] at 400 nm and the decay kinetic is monitored at λem=554 nm (Fig. 6). Pure dye exhibits a single exponential decay of 526 ps whereas biexponential decay is obtained in presence of having a combination of 579 ps (92 %) and 4.6 ps (8 %). Longer lifetime component of 579 ps (92 %) is obtained from the fluorescence transient of the surface modified NP which is close to the free fluorophore and it is believed to be a characteristic of free dye molecule. However, a short lifetime component of 4.6 ps with 8 % contribution is considered to be arising from a fast charge transfer process from [R6G][HFL] to PVK NPs. This contribution of the shorter component exactly matches the steady 18


Page 19 of 31

state fluorescence quenching observed for direct excitation of [R6G][HFL] in [R6G][HFL]-PVK NPs (Figure 3B). Thus, the quenching at 554 nm encountered in [R6G][HFL]-PVK NPs is purely dynamic and is attributed to an ultrafast hole transfer process.

(a) 0.9

Normalized Counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.6 0.3 0.0

(b)

0.9 0.6 0.3 0.0

0

20

40

60

80

100

Time (ps) Figure 6: Femtosecond fluorescence upconversion decays of (a) aqueous solution of free [R6G][HFL] and (b) [R6G][HFL] in presence of water dispersed PVK NP surface in PVK[R6G][HFL] assembly.

Kinetic model To determine the equilibrium constant and the distribution of dye molecules around PVK polymer NPs, a stochastic kinetic model has been employed.52 In this model we analyze the decay curves of donor PVK and the aqueous assembly of dye-PVK polymer nanoparticles. We assume that the non-radiative process of excited PVK occurs in competition with unimolecular decay process:

PVK

* n

k0

→

PVK

n

(5)

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

nk

PVK

* n

Page 20 of 31

q

→

PVK

n

(6)

where PVK n* represents the excited state PVK with n dye molecules attached, while PVKn stands for ground state PVK with n dye molecule attached. k0 is the decay constant due to unimolecular process of excited state PVK in absence of dye molecule and kq is the rate constant for non-radiative process per one dye molecule. Now, when n number of dye molecules attached with one PVK is excited, the rate constant for decay process is k0 +nkq and the rate constant for the non radiative process is nkq. In this model we assumed that the distribution of the dye molecules around PVK follows a Poisson distribution:53

Φ 0 = (m n / n!) exp( −m)

(7)

Here, m is the mean number of dye molecules attached to one PVK. Therefore, the ensemble averaged decay curve of the excited PVK attached with m number of dye molecules is given by: I (t , m) = I 0 ∑ = I0 ∑

∞ n=0

∞

Φ (n) exp[−(k 0 + nk q )t ] n=0

(m n / n!) exp(− m) exp[−(k 0 + nk q )t ]

= I 0 exp( − k 0 t − m)∑

(8)

∞

{[ m exp(− k q t )]n / n!} n=0

= I 0 exp( −k 0 t − m) exp[m exp(− k q t )] = I 0 exp{− k 0 t − m[1 − exp( − k q t )]} Along with dye molecules, there is excimeric decay of PVK. To account the distribution of unidentified traps on the surface of PVK with average number (mt), the decay curves of the excited state of PVK in absence and presence of dye are given by: I (t ,0) = I 0 exp{− k0t − mt [1 − exp( −kqt t )]}

(9)

20


Page 21 of 31

I (t , m) = I 0 exp{−k0t − mt [1 − exp( −kqt t )] − m[1 − exp(− kqt )]}

(10)

Where, the quenching rate constant (kqt) stands for the rate constant of excimeric emission decay. We can easily determine the value of parameters mt, kqt, k0, m and kq by fitting these above two equations (Equation 9 and 10) to the decay curves of PVK in absence and presence of [R6G][HFL] dye respectively (Fig 7). 8

6

ln(Counts)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a

4

b 2

0 0

20

40

60

80

Time (ns)

Figure 7: Decay curves of PVK in absence (a) and presence (b) of [R6G][HFL] dye molecules (Red lines are fitted curve using the equation 9 and 10). The average number of dye, m attached to one PVK is related to the total concentration of dye, [R6G][HFL] mixed with PVK and the concentration of PVK. Therefore, we can say

[ Dye] = m[ PVK ] + [ DyeSOLV ] m = K [ DyeSOLV ]

(11)

K = k+ / k −

m = K [ Dye] /(1 + K [ PVK ]) where [DyeSOLV] is the concentration of dye in solvent phase. K is the equilibrium constant and related to k+ (attachment rate constant) and k- (detachment rate constant). From the value of m and concentration of PVK and [R6G][HFL], we determine the equilibrium constant, K. To determine K, concentration of PVK and [R6G][HFL] are 5 µM and 6 µM, respectively. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 31

Table 2: Parameters and equilibrium constant from the fitting of decay curves. Sample

k0 (ns-1)

Pure PVK [R6G][HFL]

mt

kqt (ns-1)

m

kq (ns-1)

K (µM-1)

0.065

0.697

1.078

0.277

2.218 0.039

2.385

+ PVK

Therefore, average number dye attached to one PVK is 0.7 and the equilibrium constant is 0.277 µM-1.

White light emission from [R6G][HFL]-PVK NPs assembly [R6G][HFL]-PVK NPs assembly, composed of a blue and a green-orange emitting bicolor fluorophore is potential for white light emission. Although, the blue and orange bands are relatively stronger in the emission spectrum of [R6G][HFL]-PVK NPs in contrast to the green band, the spectrum nearly covers the entire visible region and the CIE coordinates (0.31, 0.39) corresponding to the emission

at a specific compositional ratio (wt. ratio of

PVK:[R6G][HFL]=5.39:1)(details in experimental section) lies very close to that of pure white light (0.33, 0.33) (Fig. 8). The quantum yield for white light emission was measured to be 7.41 %. A control mixture comprising of 65 ± 18 nm PVK NPs stock and the precursors NaHFL and R6G with same molar concentration (6 µM each) as in white light emitting [R6G][HFL]-PVK NPs exhibits CIE coordinates of (0.30, 0.45) which is further from pure white light coordinates. Analysis suggests that white light generation is possible by surface modification of a blue emitting polymeric nanoparticle with bicolor fluorophore molecule.

22


Page 23 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8: (A) Emission spectrum and white light emission (inset) from PVK-[R6G][HFL] assembly for λex=340 nm, (B) CIE coordinates of the PVK-[R6G][HFL] assembly and the control mixture of PVK NPs with the precursors (NaHFL and R6G).

Conclusion We have designed a new small molecule-semiconducting polymer nanoparticles assembly by surface modification of PVK NP. The design is derived from the concept of developing a donor-acceptor system with appreciable spectral overlap and appropriate energy level alignment. In this study, nearly 50 % fluorescence quenching have been observed for both PVK and R6G+ upon excitation at 340 nm while only 8 % fluorescence quenching is observed for direct excitation of R6G+ (525 nm) in PVK-[R6G][HFL] assembly. Fluorescence upconversion measurement with exclusive excitation of [R6G][HFL] (at 400 nm) and collection of emission at R6G+ emission maxima (554 nm) suggest an ultrafast process with a decay time of 4.6 ps which is attributed to charge transfer from the HOMO of surface attached [R6G][HFL] to PVK NPs. The fact is also supported from our theoretically calculated HOMO-LUMO values 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 31

for the system (Scheme 2). Furthermore, FRET is occurred in [R6G][HFL]-PVK NPs by the appearance of a rise time (151 ps). Thus, the enhanced quenching at 554 nm observed upon excitation at 320 nm is ascribed to a combined effect of direct excitation of R6G+ and excitation through energy transfer from PVK NPs to the surface conjugated [R6G][HFL] leading to charge transfer. Thus, the shortening of average lifetime of PVK in the assembly is assumed to be a combination of energy transfer and charge transfer from PVK to [R6G][HFL] dye and is well supported by the energy level alignment obtained from our DFT calculation results. The white light emission characteristics at a suitable compositional ratio establish an additional characteristic of this nanoparticle. Therefore, this study presents a novel nanomaterial system with appropriate optical and charge transfer characteristics for application in light harvesting systems.

Supporting Information 1

H NMR and FTIR spectra of the intermediates and the final product, TEM micrograph

of PVK NPs, lifetime decay plot for λem=515 nm, femtosecond fluorescence upconversion decay. This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgement S.D. acknowledges support from CSIR through a Senior Research Associate ship under the scientist pool scheme. BJ thanks CSIR for awarding fellowship.

24


Page 25 of 31

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References: (1)

Kundu, S.; Patra, A. Nanoscale Strategies for Light Harvesting. Chem. Rev. 2017, 117, 712-757.

(2)

Barnham, K. W. J.; Mazzer, M.; Clive, B. Resolving the Energy Crisis: Nuclear or Photovoltaics?

Nat. Mater. 2006, 5, 161-164. (3)

Wang, L.; Puodziukynaite, E.; Vary, R. P.; Grumstrup, E. M.; Walczak, R. M.; Zolotarskaya, O.

Y.; Schanze, K. S.; Reynolds, J. R.; Papanikolas, J. M. Competition between Ultrafast Energy Flow and Electron Transfer in a Ru(II)-Loaded Polyfluorene Light-Harvesting Polymer. J. Phys. Chem. Lett. 2012, 3, 2453-2457. (4)

Kim, J.-S.; Lu, L.; Sreearunothai, P.; Seeley, A.; Yim, K.-H.; Petrozza, A.; Murphy, C. E.;

Beljonne, D.; Cornil, J.; Friend, R. H. Optoelectronic and Charge Transport Properties at Organic-Organic Semiconductor Interfaces: Comparison between Polyfluorene-Based Polymer Blend and Copolymer. J. Am. Chem. Soc. 2008, 130, 13120-13131. (5)

Sautter, A.; Kaletas, B. K.; Schmid, D. G.; Dobrawa, R.; Zimine, M.; Jung, G.; Van Stokkum, I.

H. M.; De Cola, L.; Williams, R. M.; Wuerthner, F. Ultrafast Energy-Electron Transfer Cascade in a Multichromophoric Light-Harvesting Molecular Square. J. Am. Chem. Soc. 2005, 127, 6719-6729. (6)

Yeo, H.; Tanaka, K.; Chujo, Y. Effective Light-Harvesting Antennae Based on BODIPY-

Tethered Cardo Polyfluorenes via Rapid Energy Transferring and Low Concentration Quenching. Macromolecules 2013, 46, 2599-2605. (7)

Choi, H.; Santra, P. K.; Kamat, P. V. Synchronized Energy and Electron Transfer Processes in

Covalently Linked CdSe-Squaraine Dye-TiO2 Light Harvesting Assembly. ACS Nano 2012, 6, 57185726. (8)

Xu, Z.; Hine, C. R.; Maye, M. M.; Meng, Q.; Cotlet, M. Shell Thickness Dependent

Photoinduced Hole Transfer in Hybrid Conjugated Polymer/Quantum Dot Nanocomposites: From Ensemble to Single Hybrid Level. ACS Nano 2012, 6, 4984-4992.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(9)

Page 26 of 31

El-Khouly, M. E.; Kim, J.-H.; Kim, J.-H.; Kay, K.-Y.; Fukuzumi, S. Subphthalocyanines as

Light-Harvesting Electron Donor and Electron Acceptor in Artificial Photosynthetic Systems. J. Phys. Chem. C 2012, 116, 19709-19717. (10)

El-Khouly, M. E.; Kim, J. H.; Kay, K.-Y.; Choi, C. S.; Ito, O.; Fukuzumi, S. Synthesis and

Photoinduced Intramolecular Processes of Light-Harvesting Silicon Phthalocyanine-NaphthalenediimideFullerene Connected Systems. Chem. Eur. J. 2009, 15, 5301-5310. (11)

Liu, J.-Y.; El-Khouly, M. E.; Fukuzumi, S.; Ng, D. K. P. Mimicking Photosynthetic Antenna-

Reaction-Center Complexes with a (Boron Dipyrromethene)3-Porphyrin-C60 Pentad. Chem. Eur. J. 2011, 17, 1605-1613. (12)

D'Souza, F.; Maligaspe, E.; Ohkubo, K.; Zandler, M. E.; Subbaiyan, N. K.; Fukuzumi, S.

Photosynthetic Reaction Center Mimicry: Low Reorganization Energy Driven Charge Stabilization in Self-Assembled Cofacial Zinc Phthalocyanine Dimer-Fullerene Conjugate. J. Am. Chem. Soc. 2009, 131, 8787-8797. (13)

Bhattacharyya, S.; Jana, B.; Sain, S.; Barman, M. K.; Pradhan, S. K.; Patra, A. Photoswitching

and Thermoresponsive Properties of Conjugated Multi-chromophore Nanostructured Materials. Small 2015, 11, 6317-6324. (14)

Bandi, V.; El-Khouly, M. E.; Ohkubo, K.; Nesterov, V. N.; Zandler, M. E.; Fukuzumi, S.;

D'Souza, F. Bisdonor-azaBODIPY-Fullerene Supramolecules: Syntheses, Characterization, and LightInduced Electron-Transfer Studies. J. Phys. Chem. C 2014, 118, 2321-2332. (15)

Gust, D.; Moore, T. A.; Moore, A. L. Solar Fuels via Artificial Photosynthesis. Acc. Chem. Res.

2009, 42, 1890-1898. (16)

Bottari, G.; de la Torre, G.; Guldi, D. M.; Torres, T. Covalent and Noncovalent Phthalocyanine-

Carbon Nanostructure Systems: Synthesis, Photoinduced Electron Transfer, and Application to Molecular Photovoltaics. Chem. Rev. 2010, 110, 6768-6816.

26


Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(17)

Fukuzumi, S.; Ohkubo, K.; D'Souza, F.; Sessler, J. L. Supramolecular Electron Transfer by Anion

Binding. Chem. Commun. 2012, 48, 9801-9815. (18)

Jana, B.; Bhattacharyya, S.; Patra, A. Functionalized Dye Encapsulated Polymer Nanoparticles

Attached with a BSA Scaffold as Efficient Antenna Materials for Artificial Light Harvesting. Nanoscale 2016, 8, 16034-16043. (19)

Zhao, L.; Xiao, C.; wang, L.; Gai, G.; Ding, J. Glucose-Sensitive Polymer Nanoparticles for Self-

Regulated Drug Delivery. Chem. Commun. 2016, 52, 7633-7652. (20)

Peters, M.; Zaquen, N.; D’Olieslaeger, L.; Bové, H.; Vanderzande, D.; Hellings, N.; Junkers, T.;

Ethirajan, A. PPV-Based Conjugated Polymer Nanoparticles as a Versatile Bioimaging Probe: A Closer Look at the Inherent Optical Properties and Nanoparticle–Cell Interactions. Biomacromolecules 2016, 17, 2562-2571. (21)

Wu, Y.; Liu, J.; Ma, J.; Liu, Y.; Wang, Y.; Wu, D. Ratiometric Nanothermometer Based on

Rhodamine Dye-Incorporated F127-Melamine-Formaldehyde Polymer Nanoparticle: Preparation, Characterization, Wide-Range Temperature Sensing, and Precise Intracellular Thermometry. ACS Appl. Mater. Interfaces 2016, 8, 14396-14405. (22)

Jana, B.; Bhattacharyya, S.; Patra, A. Conjugated Polymer P3HT-Au Hybrid Nanostructures for

Enhancing Photocatalytic Activity. Phys. Chem. Chem. Phys. 2015, 17, 15392-15399. (23)

Morgenstern, F. S. F.; Rao, A.; Bohm, M. L.; Kist, R. J. P.; Vaynzof, Y.; Greenham, N. C.

Ultrafast Charge- and Energy-Transfer Dynamics in Conjugated Polymer: Cadmium Selenide Nanocrystal Blends. ACS Nano 2014, 8, 1647-1654. (24)

Lee, H. J.; Yum, J.-H.; Leventis, H. C.; Zakeeruddin, S. M.; Haque, S. A.; Chen, P.; Seok, S. I.;

Gratzel, M.; Nazeeruddin, M. K. CdSe Quantum Dot-Sensitized Solar Cells Exceeding Efficiency 1% at Full-Sun Intensity. J. Phys. Chem. C 2008, 112, 11600-11608.

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(25)

Page 28 of 31

Nozik, A. J.; Beard, M. C.; Luther, J. M.; Law, M.; Ellingson, R. J.; Johnson, J. C.

Semiconductor Quantum Dots and Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells. Chem. Rev. 2010, 110, 6873-6890. (26)

Chuang, C.-H.; Doane, T. L.; Lo, S. S.; Scholes, G. D.; Burda, C. Measuring Electron and Hole

Transfer in Core/Shell Nanoheterostructures. ACS Nano 2011, 5, 6016-6024. (27)

Lasser, L.; Ronca, E.; Pastore, M.; De Angelis, F.; Cornil, J.; Lazzaroni, R.; Beljonne, D. Energy

Level Alignment at Titanium Oxide-Dye Interfaces: Implications for Electron Injection and Light Harvesting. J. Phys. Chem. C 2015, 119, 9899-9909. (28)

Dai, Q.; Duty, C. E.; Hu, M. Z. Semiconductor-Nanocrystals-Based White Light-Emitting

Diodes. Small 2010, 6, 1577-1588. (29)

Rogach, A. L.; Gaponik, N.; Lupton, J. M.; Bertoni, C.; Gallardo, D. E.; Dunn, S.; Li Pira, N.;

Paderi, M.; Repetto, P.; Romanov, S. G., et al. Light-Emitting Diodes with Semiconductor Nanocrystals. Angew. Chem. Int. Ed. 2008, 47, 6538-6549. (30)

Lo, S.-S.; Yang, L.; Chiu, C.-P. ZnO/Poly(N-vinylcarbazole) Coaxial Nanocables for White-

Light Emissions. J. Mater. Chem. C 2015, 3, 686-692. (31)

Martin, C.; Bhattacharyya, S.; Patra, A.; Douhal, A. Single and Multistep Energy Transfer

Processes within Doped Polymer Nanoparticles. Photochem. Photobiol. Sci. 2014, 13, 1241-1252. (32)

Wang, S.; Yang, S.; Yang, C.; Li, Z.; Wang, J.; Ge, W. Poly(N-Vinylcarbazole)

Photoconductivity Enhancement Induced by Doping with CdS Nanocrystals through Chemical Hybridization. J. Phys. Chem. B 2000, 104, 11853-11858. (33)

Hellerich, E. S.; Intemann, J. J.; Cai, M.; Liu, R.; Ewan, M. D.; Tlach, B. C.; El Jeffries, M.;

Shinar, R.; Shinar, J. Fluorescent Polymer Guest:Small Molecule Host Solution-Processed OLEDs. J. Mater. Chem. C 2013, 1, 5191-5199. (34)

Bhattacharyya, S.; Sen, T.; Patra, A. Host−Guest Energy Transfer: Semiconducting Polymer

Nanoparticles and Au Nanoparticles. J. Phys. Chem. C 2010, 114, 11787-11795. 28


Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35)

Tang, S.; Baker, G. A.; Zhao, H. Ether-and Alcohol-Functionalized Task-Specific Ionic Liquids:

Attractive Properties and Applications. Chem. Soc. Rev. 2012, 41, 4030-4066. (36)

Burrell, A. K.; Del Sesto, R. E.; Baker, S. N.; McCleskey, T. M.; Baker, G. A. The Large Scale

Synthesis of Pure Imidazolium and Pyrrolidinium Ionic Liquids. Green Chem. 2007, 9, 449-454. (37)

Tesfai, A.; El-Zahab, B.; Kelley, A. T.; Li, M.; Garno, J. C.; Baker, G. A.; Warner, I. M.

Magnetic and Nonmagnetic Nanoparticles from a Group of Uniform Materials Based on Organic Salts. ACS Nano 2009, 3, 3244-3250. (38)

Bwambok, D. K.; El-Zahab, B.; Challa, S. K.; Li, M.; Chandler, L.; Baker, G. A.; Warner, I. M.

Near-Infrared Fluorescent NanoGUMBOS for Biomedical Imaging. ACS Nano 2009, 3, 3854-3860. (39)

Das, S.; Bwambok, D.; El-Zahab, B.; Monk, J.; de Rooy, S. L.; Challa, S.; Li, M.; Hung, F. R.;

Baker, G. A.; Warner, I. M. Nontemplated Approach to Tuning the Spectral Properties of Cyanine-Based Fluorescent NanoGUMBOS. Langmuir 2010, 26, 12867-12876. (40)

Das, S.; Magut, P. K. S.; de Rooy, S. L.; Hasan, F.; Warner, I. M. Ionic Liquid-Based Fluorescein

Colorimetric pH Nanosensors. RSC Adv. 2013, 3, 21054-21061. (41)

Das, S.; Debnath, T.; Basu, A.; Ghosh, D.; Das, A. K.; Baker, G. A.; Patra, A. Efficient White-

Light Generation from Ionically Self-Assembled Triply-Fluorescent Organic Nanoparticles. Chem. Eur. J. 2016, 22, 8855-8863. (42)

Tian, Z.; Yu, J.; Wu, C.; Szymanski, C.; McNeill, J. Amplified Energy Transfer in Conjugated

Polymer Nanoparticle Tags and Sensors. Nanoscale 2010, 2, 1999-2011. (43)

Bhattacharyya, S.; Jana, B.; Patra, A. Multichromophoric Organic Molecules Encapsulated in

Polymer Nanoparticles for Artificial Light Harvesting. ChemPhysChem 2015, 16, 796-804. (44)

Clafton, S. N.; Beattie, D. A.; Mierczynska-Vasilev, A.; Acres, R. G.; Morgan, A. C.; Kee, T. W.

Chemical Defects in the Highly Fluorescent Conjugated Polymer Dots. Langmuir 2010, 26, 17785-17789. (45)

Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.; Springer, 2006.

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(46)

Page 30 of 31

Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;

Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision C.01; Gaussian, Inc.: Wallingford, CT, USA, 2009. (47)

Becke, A. D. Density-Functional Thermochemistry. III. The role of Exact Exchange. J. Chem.

Phys. 1993, 98, 5648-52. (48)

Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula

into a Functional of the Electron Density. PRB 1988, 37, 785-9. (49)

Bhattacharyya, S.; Paramanik, B.; Patra, A. Energy Transfer and Confined Motion of Dyes

Trapped in Semiconducting Conjugated Polymer Nanoparticles. J. Phys. Chem. C 2011, 115, 2083220839. (50)

Sjoeback, R.; Nygren, J.; Kubista, M. Absorption and Fluorescence Properties of Fluorescein.

Spectrochim. Acta A 1995, 51, L7-L21. (51)

Lo, S. S.; Mirkovic, T.; Chuang, C.-H.; Burda, C.; Scholes, G. D. Emergent Properties Resulting

from Type-II Band Alignment in Semiconductor Nanoheterostructures. Adv. Mater. 2011, 23, 180-197. (52)

Sadhu, S.; Tachiya, M.; Patra, A. A Stochastic Model for Energy Transfer from CdS Quantum

Dots/Rods (Donors) to Nile Red Dye (Acceptors). J. Phys. Chem. C 2009, 113, 19488-19492. (53)

Tachiya, M. Application of a generating function to reaction kinetics in micelles. Kinetics of

quenching of luminescent probes in micelles. Chem. Phys. Lett. 1975, 33, 289-292.

30


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TOC Graphic

e e

h h [R6G][HFL]

PVK NP

31


Strategy toward Designing Semiconducting Polymer Nanoparticle

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