AIE Materials with Narrowed Emission Band by Light-Harvesting

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AIE Materials with Narrowed Emission Band by Light-Harvesting Strategy: Fluorescence and Chemiluminescence Imaging Xin Zhu, Jian-Xin Wang, Li-Ya Niu, and Qing-Zheng Yang Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b01338 • Publication Date (Web): 22 Apr 2019 Downloaded from http://pubs.acs.org on April 22, 2019

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Chemistry of Materials

AIE Materials with Narrowed Emission Band by Light-Harvesting Strategy: Fluorescence and Chemiluminescence Imaging Xin Zhu, Jian-Xin Wang, Li-Ya Niu*, and Qing-Zheng Yang* Key Laboratory of Radiopharmaceuticals, Ministry of Education College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China.

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Abstract Aggregation-induced emission luminogens (AIEgens) have attracted increasingly attentions in recent years on account of their attribute for overcoming the aggregationcaused quenching (ACQ) phenomenon of conventional organic fluorophores. Despite their remarkable advantages and great developments, most organic AIEgens exhibit broad emission spectra with the full width at half-maxima (FWHM) over 100 nm, which are to the disadvantage of their practical applications. Herein, supramolecular polymeric AIE materials with brighter fluorescence and narrower emission band (higher color purity) than conventional AIEgens were developed by taking advantage of light-harvesting strategy. These AIE materials, including nanoparticles, microfibers and thin films, were fabricated from supramolecular polymers comprised of quadruple hydrogen-bonded monomer tetraphenylethylene (TPE) and borondipyrromethene (BODIPY) as antenna chromophores and as energy acceptors, respectively. The excitation energy collected by TPE molecules was efficiently transferred to the BODIPY, resulting in up to 6-fold enhanced fluorescence intensity and narrowed emission band with FWHM decreasing from 148 nm to 32 nm. The resulting nanoparticles showed ~5-fold higher brightness than that of commercial quantum dots. The highly fluorescent nanoparticles were successfully applied for in vitro, in vivo fluorescence and chemiluminescence imaging, showing superior imaging performance to conventional AIE nanoparticles.


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1. Introduction Organic fluorophores have attracted increasingly attentions in recent years on account of their widely applications in organic light-emitting diodes (OLEDs), bioimaging, and fluorescent probes.1-5 Most traditional fluorophores show strong fluorescence in dilute solution but weak emission in concentrated solutions or aggregated states due to the strong π-π stacking interaction, known as aggregationcaused quenching (ACQ).6, 7 On the contratry, organic fluorogens with aggregationinduced emission characteristics (AIEgens) are non-fluorescent in solutions but highly emissive in aggregated states due to the restriction of intramolecular motion that prohibits the nonradiative energy dissipation,8 which offers an opportunity to overcome the limitation of ACQ. Impressive results have been achieved for developing novel AIE fluorophores and exploring their applications in various fields.9-16 Despite their remarkable advantages and great developments, most organic AIEgens exhibit a broad emission spectrum with the full width at half-maxima (FWHM) over 100 nm, which are to the disadvantage of their practical applications. For example, in the application of OLED display using a luminophore with a broad emission band, a filter is always needed to cut off the margin region to get the pure color, which lowers quantum yield at efficient wavelength window, and largely depresses the actual external electroluminescence quantum efficiencies (ηext) values of OLEDs.17, 18 A broad band is also not desired for the bioimaging, especially for the multi-color and colocalization imaging, because of their low utilization rate of fluorescent quantum yield and serious crosstalk among the imaging channels.19, 20 The broad band emission of AIE probably 3 ACS Paragon Plus Environment


results from: i) the AIE molecules present in different aggregation states with different excitation energy due to their multiple substitutents; ii) the freely rotated substituents of the molecules in solution may generate different conformations with different excitation energy during the aggregation. These structural features of AIE molecules make it a challenge to obtain the narrow-band materials through molecular design and structural modification. For example, TPE-decorated borondipyrromethene (BODIPY) derivatives21, 22 that aiming to transform ACQ BODIPY dyes into AIE luminogens, however, were still suffered from broad emission spectra. Hence, a new universal design principle for narrow-band AIE materials remains in high demand. Inspired by the natural light-harvesting system, in which antenna chromophores absorb solar light and transfer the excitation energy to the reaction center efficiently,2327

we propose to utilize light-harvesting strategy by co-assembly of AIEgens with

appropriate energy acceptors to narrow the emission band and increase the fluorescent intensity of AIE materials. Although efficient FRET systems have been developed based on dendrimers28, conjugated polymers29, 30, dye-loaded silica nanoparticles (NPs) 31

and polymetric NPs32, 33, etc., they were barely focusing on tuning the emission

properties, especially the FWHM of AIEgens.34 To establish a light-harvesting system with high brightness and energy collection efficiency, it is essential to confine multiple antenna chromophores per acceptor. Dendrimers constructed with covalent bonds contain limited donor chromophores per acceptor because of synthetic difficulties. Dyebased NPs are particularly promising due to high donor/acceptor ratios, but the stability may be an issue.35 Conjugated polymer NPs show remarkable stability and brightness, 4 ACS Paragon Plus Environment

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but they lack biodegradability because of their polymer carbon–carbon backbones. Supramolecular polymers, which are formed from low-molecular-weight monomers by noncovalent interactions, share the merits of both dye-loaded NPs and polymers. They not only possess controllable and dynamic components superior to covalent polymers, but also facilitate the construction of different kinds of materials such as fibers and films rather than dye-loaded NPs.36-38 Therefore, we use the quadruple hydrogenbonding unit 2-uriedo-4[1H]-pyrimidinone (UPy) modified donors and acceptors as building blocks to assemble into supramolecular polymeric materials.39 AIEgens with are highly suitable for serving as energy donors due to their bright and broad emission in aggregation states where internal rotations as non-radiative pathways are prevented. TPE derivatives are one of the typical AIE fluorophores and have been under extensive investigations due to their simple structure, easy access and modification with tunable photophysical properties.9-11,

13-15

Meanwhile, BODIPY chromophores have several

attributes (e.g. narrow emission peaks and high fluorescence quantum yields) that make them good candidates as energy acceptors.40, 41 We anticipated such light-harvesting strategy offered the following advantages for AIE materials, i) narrowing emission band width, ii) enhancing fluorescence intensity, and iii) tuning emission colors by adjusting the donor/acceptor without tedious synthesis routes and molecular modifications. In this work, AIE materials with narrowed emission band and enhanced fluorescence intensity were realized from supramolecular polymers comprised of quadruple hydrogen-bonded monomer TPE and BODIPY as antenna chromophores and as energy 5 ACS Paragon Plus Environment


acceptors, respectively (Figure 1). The excitation energy collected by TPE molecules was efficiently funneled to the BODIPY, resulting in 6-fold enhanced fluorescence intensity and a narrowed emission band with a small FWHM value decreasing from 148 nm to 32 nm compared with TPE based monomer. These highly fluorescent NPs were successfully applied for in vitro, in vivo and chemiluminescence imaging, exhibiting considerable advantages over the conventional AIE NPs in bioimaging with enhanced fluorescence signals without crosstalk between the imaging channels. In addition to NPs, fluorescent fibers and films from blue to green, yellow and deep red with high color purity including pure white emission were also fabricated from the supramolecular copolymers through the delicate adjustment of the energy acceptors.

Figure 1.

Schematic illustration of the preparation of AIE materials with light

harvesting properties and chemical structures of the UPy modified donors (TPEH, TPEP and TPEDC) and acceptors (GM, YM, RM and NIR-M). 6 ACS Paragon Plus Environment

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2. Results and Discussion 2.1. Synthesis and Characterization of TPE and BODIPY derivatives TPE based monomers containing different substituents (TPEH, TPEP, TPEDC) and BODIPY derivatives with diverse substituents or aza-BODIPY (GM, YM, RM, NIR-M) were synthesized, as shown in Figure 1. All products were characterized by 1H

NMR,

13C

NMR and HR-MS. Their absorption and fluorescence spectra were

measured, which covered the entire visible light to near infrared region (Figure S1). The N-H signal in UPy moieties of all monomers showed a large downfield shifts (10.013.5 ppm) in 1H NMR spectrum at CDCl3, suggesting the formation of the dimerization of the UPy units. The formation of supramolecular polymers36, 42 of TPE derivatives monomers (TPEH, TPEP and TPEDC) was confirmed by viscometry and diffusionordered NMR spectroscopy (DOSY).43,

44

The slope of double logarithmic plots of

specific viscosity vs. concentration increased from 0.89 to 3.16 as their concentration exceeded 19 mM and the diffusion coefficients (D) decreased from 2.95 × 10-10 to 5.93 × 10-11 m2 s-1 as the concentration of TPEH increased from 5 mM to 100 mM, verifying the concentration-dependent supramolecular polymerization of TPEH (Figure S2a and S2d). The similar results were observed in the viscometry and DOSY of TPEP and TPEDC (Figure S2). Moreover, the formation of supramolecular polymer by BODIPY monomers was studied in our previous work.45



Figure 2. FL spectra of (a) TPEH (20 μM, λex = 350 nm) and (b) RM (10 μM, λex = 560 nm) in THF/water mixtures with different water fractions (fw). (c) Scanning electron microscopy (SEM) image and (d) Dynamic light scattering (DLS) measurement of TPEH NPs. (e) Spectral overlap of emission of TPEH in water with absorption of RM in CHCl3 solution. (f) Absorbance and (g) FL spectra of TPEH-RM with different molar percentages of RM, λex = 350 nm. (h) Fluorescence decay profiles of TPEH-RM (λex = 375 nm, λmonitor = 480 nm, and RIF = instrument response function). (i) Time resolved fluorescence spectra of TPEH-RM1.5 (λex = 375 nm. The time when the emission peak of TPE reached the maximum value was set to 0 ns). [TPEH] = 4×105

M.


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AIE features of TPE derivatives based monomers were verified by the fluorescence changes of monomers in THF/water mixtures (Figure 2a and S3). Monomers were almost non-emissive in its benign solvent of pure THF, and the fluorescence intensity increased quickly when the fraction of water (fw) > 60 vol%. On the contrary, BODIPY derivatives displayed typical ACQ effect. The dilute solution of RM in THF showed strong fluorescence with sharp emission band. With gradual increase of water as poor solvent, the emission of BODIPY becomed weakened and quenched (Figure 2b) due to the π-π stacking of BODIPY molecules in aggregate states. We speculated that a light harvesting system with TPE as energy donor and BODIPY as energy acceptor, might overcome the ACQ of BODIPY by separating them with AIE donors, and retain the strong and sharp fluorescence of BODIPYs as energy acceptors. 2.2. Preparation and Characterization of AIE NPs AIE NPs were prepared from supramolecular co-polymers of TPEH with different molar percentages of RM by miniemulsion method. The resulting AIE NPs were named as TPEH-RMn (n represents the percent molar content of the acceptor). Scanning electron microscopy (SEM) indicated that nanoparticles of regular spherical morphology with comparable size of the average hydrodynamic diameter of ~90 nm from dynamic light scattering (DLS) results (Figure 2c-d and Figure S4-S5). The emission band of TPEH overlapped with the absorption spectra of RM (Figure 2e), facilitating FRET process from TPEH to RM. Upon selective excitation of TPEH, the absorption of RM at 580 nm (Figure 2f) appeared, and the fluorescence quenching of 9 ACS Paragon Plus Environment


TPEH at 480 nm and emission enhancement of RM at 600 nm were observed with increasing percentages of RM (Figure 2g), indicating the efficient energy transfer from TPEH to RM. Compared with TPEH NPs (without acceptor RM), the emission band of TPEH-RM1.5 was significantly narrowed with FWHM value decreasing from 109 nm to 35 nm, and the fluorescence intensity enhanced by 6-fold with the quantum yield (ΦF) increasing by 2.3-fold. Importantly, the quantum yield of TPEP-RM1.5 at efficient wavelength rang (defined as λEm max ± 20 nm) increased by 5.7-fold. The energy transfer from the TPEH to RM was further demonstrated by timeresolved fluorescence measurements. The excited-state lifetime of TPEH-RM decreased from 3.65 ns to 1.48 ns with the increasing the percentages of RM (Figure 2h). We also measured the time-resolved fluorescence spectra of TPEH-RM1.5 upon excitation at 375 nm. Once the emission peak of TPEH reached the maximum (set as 0 ns), with the continuous excitation, it began to decay while the fluorescence intensity of RM kept increasing in the following 0.51 ns (Figure 2i), which provided a direct evidence for the energy transfer from the excited donor TPEH to the acceptor RM. The obtained spectrum at 0.51 ns was similar to that of TPEH-RM in the steady-state fluorescence measurements (Figure 2g). The radiative (kr) and nonradiative (knr) rate of TPEH were calculated to be 3.3 × 107 S-1 and 2.4 × 108 S-1 at 298 K, respectively. The energy transfer (EnT) rate (kEnT) in TPEH-RM1.5, determined to be 4.02 × 108 S-1 according to kEnT=1/τDA-1/τD,46 was faster than kr and knr of the donor, resulting in the enhancement of fluorescence of TPEH-RM1.5 at 600 nm.


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2.3. Optical Properties of other AIE NPs To test the versatility of this strategy, we further applied diverse donor-acceptor combinations to fabricate other AIE NPs with light-harvesting properties (TPEH-GM, TPEH-YM, TPEP-RM, TPEDC-NIR) through supramolecular assembly. By delicately adjusting the energy donor/acceptors and the doping percentages, we were capable of conveniently tuning the emission color from blue to green, yellow, deep red, near-infrared and the pure white (Figure 3a and 3b). Particularly, TPEH with doping percentage of 0.1% RM was perceived as pure white-light emission with color coordinates (0.33, 0.33). All of the NPs showed enhanced fluorescence intensity with narrowed emission band through efficient energy transfer (Figure S7 and S8). For instant, the most significant change in FWHM from 148 nm to 32 nm was achieved for TPEP-RM1.0. Their photophysical properties, including the emission maxima (λEm), FWHM values of emission spectra in wavelength (λFWHM), fluorescent quantum yields (ΦF), quantum yield at efficient wavelength rang (ΦEm ± 20 nm), fluorescent lifetime (τ), were summarized in Table S1. We compared the emission properties of AIE NPs fabricated by light-harvesting strategy (TPEH-RM, TPEH-GM) with those of AIEgens obtained by structural modification (TPEP, TPEDC). As shown in Figure 3c, the λEm of TPEP and TPEH-GM were almost the same (~520 nm). However, TPEHGM displayed a narrow emission peak (λFWHM = 34 nm), and the solution exhibited highly pure green color; while TPEP NPs showed yellow fluorescence due to its board emission band (λFWHM = 148 nm). Similarly, with the emission maximum at ~600 nm, TPEH-RM showed red fluorescence with narrow emission band (λFWHM = 35 nm), 11 ACS Paragon Plus Environment


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while TPEDC exhibited orange emission color with broad emission band (λFWHM = 158 nm), as shown in Figure 3d. Remarkably, TPEP-RM1.0 and TPEDC-NIR1.5 exhibited higher brightness than commercial quantum dots (QD600 and QD720). Under a total internal reflection fluorescence (TIRF) microscope,

TPEP-RM1.0 and TPEDC-

NIR1.5 immobilized on glass surface appeared as bright spots showing ~5-and 6-fold intensity than that of QD600 and QD720 under identical conditons (Figure 3e and Figure S9).47,

48

These results revealed light-harvesting was a general and effective

strategy to increase the emission intensity and color purity.

Figure 3. (a) Images of aqueous dispersion nanoparticles of TPEH, TPEH-GM1.5, TPEH-YM1.5, TPEH-RM0.1, TPEH-RM0.5 and TPEH-GM1.5 under UV excitation at 365 nm. (b) Position of the white emission spectra in the CIE color space. CIE values (0.33, 0.33). (c) FL spectra and digital photos (inset) under UV excitation (λex = 365 nm) of TPEP NPs and TPEH-GM2.0. (d) FL spectra and digital photos (inset) under UV excitation (λex = 365 nm) of TPEDC NPs and TPEH-RM2.0. (e) Three-dimensional 12 ACS Paragon Plus Environment

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representations of wide-field TIRF images of TPEP-RM1.0 (left) and QD600 (right) excited at 405 nm. 2.4. Applications of AIE NPs for in vitro and in vivo fluorescence imaging To demonstrate the advantages of the AIE NPs with narrow emission band in bioapplications, we conducted the imaging experiments in living cells. HeLa cells were incubated with AIE NPs and the fluorescence was monitored using laser scanning confocal microscopy (LSCM). As shown in Figure 4a, TPEH-RM manifested bright fluorescence only in red channel but no obvious fluorescence in blue and green channel. By contrast, TPEH NPs without acceptors showed weak fluorescence in blue, green and red channels, indicating distinct crosstalk among the three channels under the identical conditions. The emission spectra and images of NPs from 475 nm to 650 nm (with 20 nm step) were collected by LSCM (Figure S10). The spectral profiles in cells were consistent with the fluorescence spectra in aqueous dispersion (Figure S10a). We also compared the living cell imaging of TPEH-GM1.5 with TPEP NPs that showed same λEm at 520 nm. TPEH-GM1.5 displayed bright fluorescence in green channel but negligible fluorescence in red channel. By contrast, under the identical conditions, TPEP NPs displayed emission in both green and red channels (Figure S11a). The similar result was also observed in the comparation between TPEH-RM and TPEDC NPs (Figure S11b). Moreover, the photostability of our NPs was checked by irradiating with Xe lamp (500 W) for 140 min, and the resulting of AIE NPs remained high fluorescence intensity (90%) with minor fluctuation (Figure S12), indicating that the 13 ACS Paragon Plus Environment


NPs possess good photostability. These results indicated AIE NPs with light harvesting properties showed improved performance in live-cell imaging, thus hold great potentials in multicolor and colocalization imaging. After confirming the feasibility of imaging in vitro, we further employed TPEPRM1.0 for in vivo fluorescence imaging. The fluorescence signal of TPEP-RM1.0 and TPEP NPs (as non-doped control) were collected from 500~800 nm (with 20 nm step) using IVIS living imaging system. TPEP NPs showed a broad fluorescence spectrum with maximum at 560 nm, while TPEP-RM1.0 displayed sharp emission peak with enhanced fluorescence centred at around 600 nm (Figure 4b). The nanoparticles of TPEP-RM1.0 and TPEP were injected into the left and right legs of normal mouse model, respectively. The fluorescence signal was acquired at 560 and 600 nm (emission maximum of TPEP and TPEP-RM1.0, respectively). The statistical data from experiment groups (n = 6) showed that the subcutaneous injections had little effect on the results (Figure S13). The fluorescence of TPEP-RM1.0 at 600 nm (Figure 4c, position C) was ~3-fold higher than that of TPEP at 560 nm (Figure 4c, position B). It worth noting that the fluorescence ratio of TPEP-RM1.0 at 600 nm vs. TPEP at 560 nm in solution is ~4, suggesting that the auto-fluorescence made some contributions (~25%) to the fluorescence signal of TPEP at 560 nm. Similarly, the NIR fluorescence of TPEDC-NIR1.5 at emission maximum of 740 nm is 1.5 times higher than TPEDC at emission peak of 620 nm (Figure S14). The results indicated the AIE NPs with light harvesting properties enabled an efficient enhanced fluorescent imaging in living mice.


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Figure 4. (a) Confocal images of HeLa cells treated with TPEH NPs and TPEH-RM1.5 in blue, green and red channels. λex = 409 nm. Scale bar is 20 μm. (b) FL spectra of TPEP NPs and TPEP-RM1.0 captured by IVIS living imaging system (λex = 430 nm). (c) In vivo imaging of mice injected with TPEP NPs (right leg) and TPEP-RM1.0 (left leg) acquired at 560 and 600 nm by IVIS living imaging system (λex = 430 nm). (n = 6 mice per group) 2.5. Applications of AIE NPs for chemiluminescence imaging With desired results in vitro and in vivo fluorescent imaging, we anticipated our AIE NPs with light harvesting properties might also be applied as emitters for chemiluminescence imaging, which requires no excitation light and offers better 15 ACS Paragon Plus Environment


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penetration depth and higher signal-to-noise ratio than fluorescent imaging.49, 50 The most efficient reaction of nonenzymatic chemiluminescence is initiated by hydrogen peroxide

(H2O2)

with

oxalic

acid

derivatives

(e.g.,

bis(2,4,5-trichloro-6-

carbopentoxyphenyl) oxalate (CPPO)) to form an unstable dioxetanedione intermediate, which can transfer its energy to nearby fluorophores to produce emission. To develop activatable chemiluminescence nanoparticles, we encapsulated CPPO into the supramolecular polymeric nanoparticles of TPEP-RM and afforded C-TPEP-RM (Figure 5a). SEM indicated that nanoparticles of C-TPEP-RM has regular spherical morphology (Figure S15), indicating the encapsulation of CPPO had negligible impact on the formation of NPs. The aqueous dispersion of C-TPEP-RM manifested strong chemiluminescence in the presence of H2O2, and the profile was nearly identical to its fluorescence spectrum (Figure 5b). A linear correlation between the H2O2 concentration and the chemiluminescence intensity of C-TPEP-RM1.0 was observed for the tested concentration ranging from 5 nM to 10 μΜ (R2 = 0.987) (Figure 5c), indicating that the feasibility of quantification. The C-TPEP-RM1.0 could detect H2O2 at concentrations as low as 5 nM, which is lower than previously reported chemiluminesence nanoparticles.49-51 The chemiluminescence of C-TPEP-RM1.0 was long lasting for 2.5 h (Figure S16). A linear dependence of chemiluminescence intensity on H2O2 concentration from 10 nM to 5 μM was established to confirm the feasibility of our CTPEP-RM1.0 in vivo (Figure S17a). The ability of chemiluminescence imaging of CTPEP-RM1.0 exposed to H2O2 in vivo was further explored in the mouse model of inflammation induced by lipopolysaccharide (LPS). As a control, C-TPEP-RM1.0 was 16 ACS Paragon Plus Environment

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injected into right and left legs pretreated with PBS and LPS, respectively. Almost no chemiluminescence was detected at the right leg which was not given LPS (Figure S17b). While the LPS-treated site (left leg) showed a bright emission, indicating that C-TPEP-RM1.0 are capable of responding to endougenous H2O2 of inflammation. CTPEP NPs and C-TPEP-RM1.0 were injected into the inflammatory sites of the right and left leg of a mouse, respectively, and chemiluminescence images were captured with of an acquisition time of 3 min at 560 and 600 nm. The left ankle joint injected with C-TPEP-RM1.0 showed distinct chemiluminescence at 600 nm. However, negligible chemiluminescence at the right left ankle joint with treatment of C-TPEP NPs was observed at both 560 nm and 600 nm (Figure 5d). It demonstrated that CTPEP-RM had a significant advantage in chemiluminescence imaging.

Figure 5. (a) Schematic illustration of the preparation of chemiluminescent nanoparticles and principle for chemiluminescence in the presence of H2O2. (b) CL spectra of C-TPEP NPs and C-TPEP-RM1.0 (0.1 mg/mL), taken at 20 s after addition 17 ACS Paragon Plus Environment


of H2O2 (1 mM). (c) The chemiluminescence intensities of C-TPEP NPs and C-TPEPRM1.0 at 600 nm (0.1 mg/mL) to different concentrations of H2O2 captured with a 2 min acquisition time by IVIS imaging system. (d) Chemiluminescence imaging of mice injected with C-TPEP NPs (right leg, 1 mg/mL) and C-TPEP-RM1.0 (left leg, 1 mg/mL) captured with a 3 min acquisition time at 560 and 600 nm. (n = 3 mice per group) 2.6. Fabrication of microfibers and films In addition to fabrication of AIE NPs, emission-tunable materials such as microfibers and films with bright fluorescence and high color purity were also be fabricated by this strategy. The high viscosity owing to the high degree of polymerization of supramolecular polymers of TPE in CHCl3 facilitates fiber fabrication in handy.52 A rod-like highly fluorescent microfibers with regular diameter were mechanically drawn from highly viscous chloroform solution at 50 mM (Figure 6a). Homogeneous and fluorescence films were also fabricated on quartz plate by spin coating the supramolecular polymer solution in chloroform (Figure 6b). The emission colors of microfibers or films were able to be tuned from blue to red by co-polymerization of TPEH with monomers containing different energy acceptors (GM, YM and RM). In addition, the photostability of microfibers and films was evaluated by irradiating with Xe lamp (500 W) for 140 min, and the resulting of microfibers and films remained high fluorescence intensity (90%) with minor fluctuation (Figure S18 and S19), indicating


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that our microfibers and films have good photostability. Such fluorescent microfibers and films may have applications for the fabrication of optoelectronic devices.

Figure 6. (a) Fluorescent microscopy images of fibers and (b) films under UV excitation at 365 nm of TPEH, TPEH-GM1.5, TPEH-YM1.5 and TPEH-RM1.5. 3. Conclusion In summary, we have successfully developed supramolecular polymeric AIE materials including nanoparticles, microfibers and thin films with narrow-band and enhanced emission by using light-harvesting strategy. We chose the quadruple hydrogen-bonding unit UPy modified AIEgens and BODIPYs as antenna chromophores and as energy acceptors, respectively, and assembled them into supramolecular polymeric AIE materials with light-harvesting properties. Through the efficient energy transfer, narrowed emission band and enhanced fluorescence were achieved. The emission colors of our AIE materials were tuned easily from blue to green, yellow, red, near-infrared and pure white by adjusting the donor/acceptor without tedious synthesis routes and molecular modifications. Our highly fluorescent AIE nanoparticles were successfully applied for in vitro, in vivo fluroescence and 19 ACS Paragon Plus Environment


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chemiluminescence imaging. Their enhanced fluorescence signals and sharp emission bands significantly improved imaging performance compared with conventional AIE nanoparticles. We speculate that our AIE materials with light-harvesting properties may be useful for biosensing and multicolor bioimaging, and our strategy may inspire the exploration of new AIE materials for potential applications in bioimaging and OLED display.

4. Experimental Section

Materials and instruments: Unless otherwise stated, all chemicals are of commercial quality and were used without further purification. 1H-NMR spectra and

13C-NMR

spectra were recorded on a JEOL-400 and JEOL-600 spectrometers. High-resolution mass spectrometry was conducted by using of a Bruker Daltonics Apex IV spectrometer. Viscosity measurements were performed with a micro-Ubbelohde dilution viscometer at 25 °C in chloroform (CHCl3). Scanning electron microscopic (SEM) images were obtained using a Hitachi SU-8010 instrument. Dynamic light scattering (DLS) investigations were carried out with a Dynapro nanostar dynamic light scattering detector. Absorption and fluorescence spectra were determined on a Hitachi U-3900 UV-Visible spectrophotometer and on a Hitachi F-4600 spectrophotometer, respectively. Fluorescence decay profiles and time resolved fluorescence spectra were determined by single photon counting technique using a FLS980 Edinburgh Spectrofluorometer. The quantum yield was recorded by absolute PL quantum yield spectrometer C11347-11 from Hamamatsu. The photostability was conducted under the 20 ACS Paragon Plus Environment

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irradiation of Xenon lamp without filter and monitored by F-4600 spectrophotometer. Confocal fluorescence imaging was recorded on a Nikon A1R multiphoton microscopy with a 60× oil-immersion objective lens. In addition, this microscopy was equipped with 409 nm lasers for excitation and 425-475 nm, 500-550 nm, 570-620 nm band pass filters for different emission channels. Fluorescent images of patterns were obtained with a Nikon D7100 digital Slr camera under the 365 nm UV lamp. In-vivo imaging was recorded by an IVIS Spectrum imaging system (PerkinElmer, USA). Preparation of AIE NPs by the miniemulsion method: A 200 μL solution of supramolecular polymers (20 mM) in CHCl3 was quickly added into an aqueous solution of cetyltrimethyl ammonium bromide (CTAB) surfactant (10 mL, cCTAB= 0.9 mM). The resulting mixture was ultrasonicated for 25 min, centrifugated at 12000 r/min for 30 min and washed with water to afford water-dispersible nanoparticles. Similarly, AIE NPs of copolymers were prepared from different types of supramolecular polymers in certain molar ratios by the above-described miniemulsion strategy. Fluorescence microscopy: For single-particles wide-field fluorescence microscopy measurements, the NPs were immobilized on glass surfaces adsorbed by polyethylenimine (PEI) layer. The solutions of AIE NPs and quantum dots were diluted to ~ 1010 particles/mL and 100 μL of solutions were brought onto the PEI-covered glass (2 cm × 2 cm) for 20 min, followed by extensive rinsing with Milli-Q water. Singleparticle measurements were performed on a widefield set-up based on an inverted Nikon Eclipse Ti microscope (Nikon Instruments) with the Perfect Focus System, 21 ACS Paragon Plus Environment


applying an objective-type total internal reflection fluorescence (TIRF) mode with a high-numerical aperture (NA) TIRF objective (SR Apo TIRF 100×, Oil, NA 1.49). The 405 nm laser power density was set to 10 mW cm−2. The fluorescence signal was recorded with a scalable complementary metal–oxide semiconductor (sCMOS, 0.07 μ m pixel size). The exposure time was set to 400 ms per image frame. Cell culture and cell imaging: HeLa cells were cultured in culture media (DMEM/F12 supplemented with 10% FBS, 50 U/mL penicillin, and 50 μg/mL of streptomycin) at 37 °C in an atmosphere of 5% CO2 and 95% humidified atmosphere for 24 h. For fluorescence imaging, the cells were incubated with 10 μM of AIE NPs at 37 °C under 5% CO2 for 6 h and then washed with 1× phosphate buffered saline (PBS) three times. Animals: Male BALB/c nude mice (5 weeks of age) were purchased from Vital River (Beijing, China). All animal procedures were performed under the guideline approved by the animal care committee of Beijing Normal University. In vivo fluorescence imaging: The IVIS spectrum imaging system was used to image mouse. BALB/c nude mice (male, 5 weeks of age) were anesthetized, and followed by an injection of AIE NPs (0.4 mg/mL, 100 μL) into the right leg and left leg. Fluorescence signals were captured after 1 min with emission at 560, 600, 620, 740 ± 10 nm, respectively. Preparation of C-AIE NPs: TPEP (1 mg), RM in 1.0 molar ratios of TPEP was homogeneously mixed with Pluronic F-127 (20 mg), bis[3,4,6-trichloro-222 ACS Paragon Plus Environment

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(pentyloxycarbonyl)phenyl] oxalate (CPPO, 0.4 mg) in DCM (0.6 mL). After the solvent was evaporated by air flow, the dried mixture was mixed with Milli-Q water (1 mL) and then vigorously shaken to afford an aqueous dispersion of self-assembled CTPEP-RM. In vivo chemiluminescence imaging: LPS (20 μL, 2 mg/mL in PBS) was injected into the legs of BALB/c nude mice (male, 5 weeks of age). Six hours later, mice were anesthetized, and followed by an injection of C-AIE NPs (1 mg/mL, 100 μL) in the same way as mentioned above. Chemiluminescence signals were captured with a 3 min acquisition time with emission at 560, 600, 620, 740 ± 10 nm using the IVIS spectrum imaging system, respectively. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/xxxxxxx. It consists of additional methods and data figures (PDF) AUTHOR INFORMATION Corresponding Author *E-mail (Li-Ya Niu): [email protected] *E-mail (Qing-Zheng Yang): [email protected]



ACKNOWLEDGMENT This work was financially supported by National Natural Science Foundation of China (21525206, 21472202 and 21402216).

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AIE Materials with Narrowed Emission Band by Light-Harvesting

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