Fine Tuning of Emission Behavior, Self-Assembly, Anion Sensing, and

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Fine Tuning of Emission Behavior, Self-Assembly, Anion Sensing, and Mitochondria Targeting of PyridiniumFunctionalized Tetraphenylethene by Alkyl Chain Engineering Nan Li, Yan Yan Liu, Yan Li, Jia Bao Zhuang, Rong Rong Cui, Qian Gong, Na Zhao, and Ben Zhong Tang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b04113 • Publication Date (Web): 25 Jun 2018 Downloaded from http://pubs.acs.org on June 26, 2018

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ACS Applied Materials & Interfaces

Fine Tuning of Emission Behavior, Self-Assembly, Anion Sensing, and Mitochondria Targeting of Pyridinium-Functionalized Tetraphenylethene by Alkyl Chain Engineering Nan Li,a,‡ Yan Yan Liu,a,‡ Yan Li,a Jia Bao Zhuang,a Rong Rong Cui,a Qian Gong,a Na Zhaoa,* and Ben Zhong Tang b,*

a.

Key Laboratory of Macromolecular Science of Shaanxi Province, Key Laboratory of Applied

Surface and Colloid Chemistry of Ministry of Education, Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, and School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xi’an, 710119, China.

b.

Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water

Bay, Kowloon, Hong Kong 999077, China.

‡These authors contributed equally to this work.

KEYWORDS: aggregation-induced emission, color tunable, alkyl chain engineering, selfassembly, mitochondria targeting

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ABSTRACT: Compared to the many studies that focus on the development of novel molecular frameworks pertaining to functionalized fluorescent materials, there is lesser emphasis on side chains even though they have a significant impact on the properties and applications of fluorescent materials. In this study, a series of pyridinium-functionalized tetraphenylethene salts (TPEPy-1 to TPEPy-4) possessing different alkyl chains are synthesized and the influence of chain length on their optical performance and applications are thoroughly investigated. By changing the alkyl chain, the fluorogens exhibit opposite emission behavior in aqueous media because of their distinct hydrophobic nature, and their solid-state emission can be fine-tuned from green to red owing to their distinct molecular configuration. In addition, by increasing the chain length, the microstructure of the self-assembled fluorogens converts from microplates to microrods with various emission colors. Moreover, TPEPy-1 exhibits dual-mode fluorescence “turn-on” responses towards NO3– and ClO4– in aqueous media, because the anions induce the self-assembly of fluorogens. Furthermore, the fluorogens display cellular uptake selectivity while the proper alkyl chain impels the fluorogens to penetrate the cell membrane and accumulate in the mitochondria with high specificity.

1. INTRODUCTION Organic fluorescent materials with intense emission offer a myriad of applications in chemistry, biology, and materials sciences, e.g., organic light-emitting diodes (OLEDs), optical devices, fluorescent probes, biological imaging, and diagnostics.1-7 Their widespread utility has


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driven extensive efforts to develop novel organic molecular systems, and significant progress has been achieved. However, compared to their strong emission in dilute solution, most of the traditional organic fluorogens present weak or even none emission in high concentration or solid state. This reduction in luminescence efficiency might be ascribed to the strong intermolecular π–π interaction8-9 or hydrogen bonding10. Recently, Tang and co-workers discovered a novel type of fluorogen exhibiting the unique aggregation-induced emission (AIE) effect. These AIE fluorogens (AIEgens) produce faint emission in the solution state, but exhibit intense emission in their condensed state.11 This abnormal phenomenon was attributed to the restriction of intramolecular rotations (RIR), which can block the nonradiative pathway and open up the radiative channel.12-13 Subsequent studies indicated that the highly twisted configuration of AIE molecules can further prevent the fluorogens from unfavorable π–π stacking in the solid state. This specific feature enabled the AIEgens to exhibit remarkable optical properties and enjoy latent applications in diverse fields.14-27 Among the pervasive AIE molecular systems, a class of cationic AIEgens bearing Nheterocyclic salts including pyridinium, indolium, and quinolinium, has received considerable attention. A quaternized unit is an outstanding electron acceptor, and generally endows fluorogens with the typical twisted intramolecular charge transfer (TICT) character; thus, the corresponding AIEgens possess long emission wavelengths and high environment sensitivity.28,29 Meanwhile, the cationic feature enables those AIEgens to possess special sensing properties30-35 and excellent capability in subcellular organelle targeting36-40. Nevertheless, the barriers that


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limit the performance of the cationic AIEgens are not only their molecular core, but also the side chain on the quaternized N atom. Compared to many studies that focused on the construction of various molecular backbones, the influence of the side chain on the optical properties and applications of cationic AIEgens has been rarely investigated. To suitably manipulate the optical properties of cationic AIEgens, we explored the strategy of introducing different lengths of the alkyl chain on the N atom of the pyridinium unit, because simple linear alkyl chains are critical in intermolecular interactions as well as molecular packing.41-48 Herein, we design and synthesize four pyridinium-functionalized tetraphenylethene salts (TPEPy-1 to TPEPy-4) with various linear aliphatic chains (n-C3H7, n-C6H13, n-C9H19, and n-C12H25). We systematically investigate the relationship between the extended alkyl chains and the luminescence propensity of the corresponding fluorogens. We substantiate that the sequential elongation of the alkyl chains results in remarkable emission behavior in the condensed state, a self-assembled morphology, anion sensing, and subcellular organelle targeting. 2. RESULTS AND DISCUSSION 2.1. Synthesis and characterization. The synthetic routes of TPEPy-1 to TPEPy-4 are illustrated in scheme 1. Precursor (E)-4-(4-(1,2,2-triphenylvinyl)styryl) pyridine (TPEPy) was easily synthesized based on previous literature.49 The installation of different alkyl chains was best achieved by a simple salt formation reaction between the corresponding bromoalkane and TPEPy under the refluxed condition in acetonitrile. All fluorogens were prepared with


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reasonable yield and characterized by 1H, 13C NMR and high-resolution mass spectroscopy, from which satisfactory results to their molecular structures were obtained.

Scheme 1. Synthetic route of fluorogens.

2.2. Optical properties and AIE effect. At the initial step, we studied the optical properties of four fluorogens in the solution state. As shown in Figure S1, all fluorogens exhibited similar absorption profiles in DMSO. The short absorption band appearing at approximately 316 nm could be attributed to the π–π* transition, and the longest absorption band at approximately 396 nm could be assigned to the TICT transition from the electron-donating TPE group to the electron-accepting pyridinium unit.26,50 This indistinctive absorption spectrum for all fluorogens suggested that the length of the alkyl chain has negligible influence on the optical properties in the dispersed state owing to their similar electronic structure. Consistent with the identical absorption spectra, the four fluorogens displayed a similar emission peak at ~580 nm with close quantum yield (Φf ~14%) in DMSO upon photoexcitation. When water was introduced into the DMSO solution, the emission of the fluorogens was weakened gradually owing to the TICT effect, which intensified with increasing polarity of the mixed solvents. It is noteworthy that when the water fraction (fw) exceeded 70% (or 80%), two


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different types of emission changes were observed. For both TPEPy-1 and TPEPy-2, the emission decreased and reached a minimum at fw 99% with Φf of ~2% (Figure 1A-1B and S2). Meanwhile, the solution was observed to be faint in color under 365 nm irradiation. However, for the analogues of TPEPy-3 and TPEPy-4 bearing longer alkyl chains, the fluorescence was significantly enhanced with an increase in fw (Figure 1C-1D and S3). The emission intensity was enhanced nearly 20-fold at fw 99%, compared to the pure DMSO solution (Φf ~22.5% for TPEPy-3 and Φf ~34.3% for TPEPy-4). Considering their similar electronic structures, this completely opposite emission behavior could be associated with the length of the different alkyl chains.

Figure 1. PL spectra of (A) TPEPy-1 (20 µM) and (C) TPEPy-3 (20 µM) in DMSO/water mixtures with different water fractions (fw). (B) Plots of relative emission intensity (I/I0) at 570


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nm versus the composition of water in mixtures for TPEPy-1 and TPEPy-2. (D) Plots of relative emission intensity (I/I0) at 560 nm versus the composition of water in mixtures for TPEPy-3 and TPEPy-4. Inset: photographs of (B) TPEPy-1 and (D) TPEPy-3 in DMSO/water mixtures with fw values of 0 and 99% under 365 nm UV irradiation. Excitation wavelength: 375 nm.

To ascertain the reason for this alkyl chain-regulated emission behavior, the distribution of particle size at fw 99% was measured using dynamic light scattering (DLS). As shown in Figure 2A, the particle size decreased with an increase in the chain length, was estimated to be 294.1 nm, 270.0 nm, 196.6 nm, and 115.3 nm, respectively, in order from TPEPy-1 to TPEPy-4. This difference is attributable to the distinct hydrophobicity of the fluorogens, which in turn resulted in the different aggregation states. To further evaluate their hydrophobicity, the static water contact angle was measured using dried cast films of the fluorogens, the recorded images for which are shown in Figure 2B-2E. The static water contact angle was 19.1°, 26.3°, 56.3°, and 85.9°, respectively, in the order from TPEPy-1 to TPEPy-4, suggesting that the hydrophobicity became stronger by extending the chain length, which is consistent with the variation in the particle size. Based on the results above, both TPEPy-3 and TPEPy-4 could form tighter aggregates in aqueous media owing to their stronger hydrophobicity that restricted intramolecular rotation and led to the sharp emission enhancement. In contrast, both TPEPy-1 and TPEPy-2 formed comparatively looser aggregates because of their better hydrophilicity that could not effectively restrict the intramolecular rotation and yielded weak emission. The AIE


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properties were also measured in acetone (as a good solvent) and n-hexane (as a poor solvent) mixtures. All exhibited weak emission in acetone, but turned into strong yellow emitters when the nanoaggregates were formed at 99% n-hexane fraction (Figure S4 and S5). The aggregate formation was further confirmed by DLS measurement (Figure S6). This observation further confirmed that the weak emission of TPEPy-1 and TPEPy-2 in aqueous media could be attributed to their better hydrophilicity.

Figure 2. (A) Particle size distribution of fluorogens (20 µM) at fw 99%. Photographs of the static contact angle of a water droplet on the surface of (B) TPEPy-1, (C) TPEPy-2, (D) TPEPy-3, and (E) TPEPy-4 cast films.

2.3. Color-tunable solid-state emission. To gain an in-depth understanding of the relationship between the alkyl chain length and emission in the solid state, we grew crystals of the four fluorogens by slow evaporation from dichloromethane/n-hexane mixtures and successfully obtained them in powder form. Crystals of both TPEPy-1 and TPEPy-2 were suitable for X-ray diffraction owing to their high quantity. The crystal data are summarized in Table S1.


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Table 1. Optical properties of the fluorogens. Solutiona

Aggregationb

Solidc

Compd.

λabs [nm]

ε [cm-1 M-1]

λem [nm]

Φfd

λem [nm]

Φfd

λem [nm]

Φfd

TPEPy-1

396

29500

580

14.2

570

2.1

575

35.9

TPEPy-2

396

30930

580

13.8

570

2.0

560

34.7

TPEPy-3

396

32480

580

13.9

560

22.5

566

41.3

TPEPy-4

396

28725

580

13.8

555

34.3

531

25.3

a

DMSO solution (20 µM); b99% fw in DMSO solution (20 µM); cCrystalline powder; dAbsolute fluorescence quantum yield measured using the calibrated integrating sphere system. Further, we performed powder X-ray diffraction (PXRD) on the crystalline sample. As shown in Figure S7, the PXRD patterns of all fluorogens show intense and sharp diffraction peaks but a distinguished profile between each other, indicating the existence of different molecular arrangements in their crystalline state. Notably, lamellar crystals of TPEPy-1, TPEPy-2, and TPEPy-3 were observed, whereas TPEPy-4 presented a tiny acicular shape (Figure 3A-3D). More importantly, the crystalline samples of TPEPy-1 to TPEPy-4 presented various emission colors from red, yellow, and orange, to green under the fluorescent microscope. Additionally, the corresponding maximum emission of TPEPy-1 to TPEPy-4 was measured as 575 nm (Φf ~

35.9%), 560 nm (Φf ~ 34.7%), 566 nm (Φf ~ 41.3%), and 531 nm (Φf ~ 25.3%), respectively (Table 1 and Figure 3E). Considering the identical conjugated backbone of the four fluorogens, the significant difference in their PXRD patterns as well as the tuned emission color could be attributed to the variation in the alkyl chain length, which affected the molecular arrangement in


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the crystalline state. This strategy of altering the side chain length also provides an ideal and facile method to fabricate color-tunable solid-state fluorescent materials.

Figure 3. Fluorescent image of (A) TPEPy-1, (B) TPEPy-2, (C) TPEPy-3, and (D) TPEPy-4 in their crystalline state under the fluorescent microscope. (E) PL spectra of corresponding crystalline sample. Scale bar: 100 µm. Excitation wavelength: 362 nm.

To further obtain the underlying reasons for this alkyl chain-dependent emission, the molecular structures and packing mode of TPEPy-1 and TPEPy-2 were investigated. As displayed in Figure 4, owing to the propeller-shaped TPE unit, both TPEPy-1 and TPEPy-2 adopted highly twisted conformation that prevented the molecules from forming π–π stacking in both crystals. It is noteworthy that two individual configurations existed in the crystals of TPEPy-1 and TPEPy-2 (Figure 4B-4C, 4G-4H), which were induced by the cis/trans isomerization of the vinyl linker between the TPE group and pyridinium moiety. We termed them as Z-type and E-type, respectively. The image along the b-axis shows that adjacent molecules of TPEPy-1 were stacked to form a polymeric column in the slipped head-to-head and tail-to-tail manner (head:


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TPEPy segment; tail: alkyl chain segment, Figure 4D-4E). A similar molecular packing mode and polymeric column were also found in the crystal of TPEPy-2 (Figure 4I-4J). Meticulous evaluation of the crystal configuration further revealed that the torsion angles between the bridged phenyl ring and vinyl core of TPE in TPEPy-1 were 44.75° and 62.14° for the Z-type and E-type of the molecules, respectively, while the corresponding values varied to 51.03° and 62.75°, respectively, in the TPEPy-2 crystal. Apparently, TPEPy-1 exhibited better molecular conjugation than TPEPy-2, which may result in the bathochromic emission of TPEPy-1. In addition, multiple C–H···Br hydrogen bonds between the cationic unit and bromide ion were observed in the crystals of TPEPy-1 and TPEPy-2, which could help rigidify the molecular conformation and enhance the emission efficiency of the crystals (Figure S8).


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Figure 4. Single crystal structures and view of the molecular packing of (A-E) TPEPy-1 and (FJ) TPEPy-2. Counter-ion and solvent were omitted for clarify.

2.4. Self-assembly. The unique performance of crystalline powders drove us to investigate the effect of alkyl chain length on the self-assembly behaviors. By rapidly injecting a specific amount of fluorogens in a MeCN solution into an ultrasonic aqueous solution containing sodium dodecyl sulfate (SDS) and aging the mixture overnight, floc aggregates were generated.51 The aggregates were characterized by scanning electron microscopy (SEM). The SEM images in Figure 5 revealed that TPEPy-1 assembled into microplates with irregular sizes. For TPEPy-2, in addition to the existence of microplates, some microrods were also formed. Increasing the alkyl chain length resulted in more microrods in TPEPy-3; meanwhile, microrods became dominant in TPEPy-4. This phenomenon of morphology transformation from microplates to microrods demonstrated that increasing the alkyl chain length successfully regulated the self-assembly behavior.


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Figure 5. SEM image of self-assembled (A) TPEPy-1, (B) TPEPy-2, (C) TPEPy-3, and (D) TPEPy-4. Inset: photographs of corresponding solution under 365 nm UV irradiation.

This morphology change had likely originated from the different hydrophobicities of the alkyl chain and could be elucidated by the packing parameter (p) that was used to explain the formation of different nanostructures based on amphiphilic compounds.52-54 p is defined as ν/(aolc), where ν is the volume of the hydrophobic unit, lc is the length of the hydrophobic part, and ao is the optimum area of the head group. Generally, when 1/3 < p < 1/2, cylindrical or rodshaped structures are favored; by increasing the p value to 1/2 < p < 1, planar bilayer structures would be dominant. Increasing the alkyl chain length from TPEPy-1 to TPEPy-4 increased lc. However, the growth rate of the volume (ν) occupied with various hydrophobic alkyl chains was smaller than that of lc, thus causing the value of ν/lc as well as p to be gradually decreased, and resulting in the self-assembly morphology to transform from planar to rod. Apart from the alkyl chain-dependent microstructure, it is interesting that the self-assembled aggregates produced various emission colors. As displayed in Figure 5 and Figure S9, a remarkable green emission of TPEPy-1 with the emission maximum at 510 nm was observed. In comparison, the other three fluorogens exhibited coincident yellow emission with the emission peak at 538 nm. The difference in emission color was likely due to the varied molecular packing arising from the length of the alkyl chain. TPEPy-1 favored the formation of the most crowded


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packing owing to its shortest alkyl chain. To adapt to the crowded space, the molecules of TPEPy-1 had to adopt more twisted configurations, which led to a blue-shifted emission. 2.5. Anion-induced emission. As mentioned earlier, TPEPy-1 and TPEPy-2 emitted weakly in aqueous media (fw 99%). Unexpectedly, upon the addition of specific anions into their solution, the emission became significantly brighter. As described in Figure 6A, progressively adding NO3– into the solution of TPEPy-1 resulted in the gradual reduction of the absorbance at 390 nm with a slight blue shift. Meanwhile, a new emission peak at 540 nm appeared (Figure 6B). The colorless solution turned into bright yellow when the concentration of NO3– reached 3.0 mM under 365 nm UV irradiation (Figure 6C). Moreover, the intensity at 540 nm displayed a good linear relationship (R2 = 0.9962) for the NO3– concentration ranging from 0.8 mM to 1.3 mM (Figure S10A), while the detection limit for NO3– was calculated to be 4.3 × 10-7 M based on the 3σ/k method. Unlike NO3–, the introduction of ClO4– yielded a distinct change in both the UV-Vis and emission spectra for TPEPy-1. The absorbance peak at 390 nm deceased with a remarkable red shift of approximately 10 nm in the presence of ClO4–, (Figure 6D). Meanwhile, a new emission peak at 570 nm was observed because of the bathochromic shift of ~30 nm compared to NO3– (Figure 6E). When 1.2 mM ClO4– was employed, the system exhibited a bright orange emission under 365 nm UV irradiation (Figure 6F). The intensity at 570 nm also showed a good linear relationship (R2 = 0.9851) when the ClO4– concentration was varied from 0 to 0.3 mM (Figure


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S10B), and the detection limit for ClO4– was calculated to be 3.8 × 10-7 M based on the 3σ/k method.

Figure 6. UV-Vis and PL spectra change of TPEPy-1 (20 µM) in the presence of (A-B) NO3– and (D-E) ClO4–. Plot of relative emission intensity (I/I0) at (C) 540 nm versus the concentration of NO3– and (F) 570 nm versus the concentration of ClO4–. Inset: photographs of TPEPy-1 without and with (C) NO3– or (F) ClO4– under 365-nm UV irradiation. Excitation wavelength: 375 nm. Compared to NO3– and ClO4–, other anions including F–, Cl–, Br–, I–, CO32–, H2PO4–, HCO3–, HPO42–, PO43–, S2–, and SO42– (3.0 mM) caused negligible fluorescence changes (Figure S11), suggesting that TPEPy-1 had superior selectivity towards NO3– and ClO4–. Similar UV-Vis and fluorescence responses were obtained for TPEPy-2. We observed that upon the addition of NO3–


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or ClO4–, the absorbance peak at 390 nm decreased with an identical red shift, and the same enhancement in the maximum emission at 570 nm was observed (Figure S12-S13). The results indicate that TPEPy-1 gave a specific dual-mode fluorescence “turn-on” response towards NO3– and ClO4–, which is rare in AIE systems. To study the mechanism of this unusual anion sensing, the microstructure of TPEPy-1 incubated with NO3– and ClO4– was examined using SEM. As shown in Figure 7, TPEPy-1 formed amorphous particles. However, the addition of NO3– resulted in regular microcubics while microplates were formed after the incubation with ClO4–. Similarly, obvious self-assembly procession of TPEPy-2 in the presence of NO3– or ClO4– was also observed (Figure S14). The suitable weak interactions between the cationic unit and NO3– (or ClO4–) as well as the Van der Waals interactions through the alkyl chains were responsible for facilitating the ordered organization of TPEPy-1 (or TPEPy-2), which effectively enhanced the luminescence.55,56 Compared to the single fluorescence response of TPEPy-2, the dual-mode fluorescence response of TPEPy-1 for NO3– and ClO4– could be ascribed to the shortest alkyl chain in TPEPy-1, and resulted in its molecular configuration being more susceptible to the molecular packing.

Figure 7. SEM image of (A) TPEPy-1 (20 µM) without and with (B) NO3– or (C) ClO4–.


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2.6. Mitochondria targeting. Considering the excellent photoluminescence property and cationic feature of our fluorogens, we proceeded to investigate the relationship between the alkyl chain length and cell image. HeLa and HEK-293T cells were selected as tumor and normal cells, respectively. Two cell lines were cultured in the presence of different fluorogens for 12 h to evaluate their toxicity using an MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide) assay. As shown from Figure S15, negligible toxicities were observed for the HeLa cells when the concentration of fluorogens reached 10 µM and the similar viability trends within HEK-293T cells were obtained, indicating the good biocompatibility of all fluorogens. Subsequently, the retention of fluorogens (2 µM) in different cell lines was investigated by confocal fluorescence microscopy. As depicted in Figure 8, TPEPy-1 and TPEPy-2 accumulated extensively in the HeLa cells and emitted distinct fluorescence in the yellow channel, whereas significantly lower fluorescence retention was detected for TPEPy-3 and a nearly negligible fluorescence signal was observed for TPEPy-4. Switching to the HEK-293T cells produced similar imaging results that punctate the fluorescence that only appeared within the cells when labeled with TPEPy-1 and TPEPy-2. This observation indicates that fluorogens with suitable hydrophobicity can penetrate the cell membrane and illuminate the cells. However, because of the strong hydrophobicity, TPEPy-4 was unable to enter both the tumor and normal cells.


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Figure 8. CLSM images of HeLa and HEK-293T cells after treatment with four fluorogens (2 µM). Scale bar: 20 µm. Based on cell imaging experiments and previous reports,36,37,50 the strong fluorescent signals observed were primarily distributed throughout the mitochondria. To further verify the exact distribution of the fluorogens in the cells, we performed co-staining experiments using MitoTracker Deep Red – a well-established commercial mitochondria-targeted dye. As shown in Figure 9, Figure S16, and S17, when both the fluorogens and Mito-Tracker Deep Red were present in the culture medium, the yellow fluorescence signal from our fluorogen and the red


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fluorescence signal from Mito-Tracker Deep Red were overlapped with different degrees in the cells. Furthermore, the Pearson correlation coefficient, which can quantify the overlap between fluorogens and MitoTracker Deep Red, was calculated to be 0.74, 0.84, and 0.52 for TPEPy-1, TPEPy-2, and TPEPy-3, respectively, in the HeLa cells. Similar results were obtained in HEK293T cells and the Pearson correlation coefficient was calculated to be 0.65, 0.73, and 0.48, respectively, in the order from TPEPy-1 to TPEPy-3. The results show that TPEPy-2 possesses excellent specificity to mitochondria, implying that this specificity in mitochondria staining is primarily dependent on the length of the alkyl chain. A lysosome staining dye (Lyso-Tracker Red) was also used for the co-staining experiments and almost no co-localization was observed (Figure S18), which supported the capability of mitochondria-targeting for those fluorogens.

Figure 9. CLSM images of HeLa and HEK-293T cells after treatment with TPEPy-2 (2 µM) and co-stained with Mito-Tracker Deep Red (100 nM). Scale bar: 20 µm.


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3. CONCLUSION In conclusion, we designed and synthesized a series of pyridinium-functionalized tetraphenylethene salts (TPEPy-1 to TPEPy-4) with various alkyl chains and thoroughly investigated the influence of the alkyl chain length on the performance and applications of the cationic fluorogens. Owing to the stronger hydrophobicity of TPEPy-3 and TPEPy-4 bearing longer alkyl chains, tighter aggregates were formed in the aqueous media and resulted in the significant enhancement in fluorescence. Unlike the emission behavior in aqueous media, all fluorogens emitted intense fluorescence in the solid state and the emission color could be tuned from green to red by simply controlling the length of the alkyl chain. In addition, by extending the alkyl chain length, the morphology of the self-assembled fluorogens could also be regulated from microplates to microrods, while TPEPy-1 produced a blue-shifted emission compared to other fluorogens. Moreover, TPEPy-1 displayed a unique dual-mode fluorescence “turn-on” response towards NO3– and ClO4– because the anions induced the self-assembly of the fluorogens. Furthermore, the alkyl chain length distinctly influenced the cellular uptake while the fluorogens with the proper chains enabled the high specific mitochondria targeting. This strategy of side chain engineering provides an ideal method to fine-tune the optical performance and applications of AIEgens as well as a straightforward approach to investigate the structure– property relationship. ASSOCIATED CONTENT


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Supporting Information. Synthesis and characterization, optical spectra, crystal data and NMR spectra.

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected], [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

This work was supported by National Natural Science Foundation of China (21672135, 21402115 and 51403122), Fundamental Research Funds for the Central Universities (GK201703024 and GK201702002), Young Talent fund of University Association for Science and Technology in Shaanxi (2017030021) and Natural Science Foundation of Shaanxi Province (2016JQ2020).

REFERENCES (1) Gather, M. C.; Köhnen, A.; Meerholz, K. White Organic Light-Emitting Diodes. Adv. Mater., 2011, 23, 233-248.


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(2) Im, Y.; Byun, S. Y.; Kim, J. H.; Lee, D. R.; Oh, C. S.; Yook, K. S.; Lee, J. Y. Recent Progress in High-Efficiency Blue-Light-Emitting Materials for Organic Light-Emitting Diodes. Adv. Funct. Mater., 2017, 27, 1603007.

(3) Padalkar, V. S.; Seki, S. Excited-State Intramolecular Proton-Transfer (ESIPT)-Inspired Solid State Emitters. Chem. Soc. Rev., 2016, 45, 169-202.

(4) Chan, J.; Dodani, S. C.; Chang, C. J. Reaction-Based Small-Molecule Fluorescent Probes for Chemoselective Bioimaging. Nat. Chem., 2012, 4, 973-984.

(5) Zielonka, J.; Joseph, J.; Sikora, A.; Hardy, M.; Ouari, O.; Vasquez-Vivar, J.; Cheng, G.; Lopez,

M.;

Kalyanaraman,

B.

Mitochondria-Targeted

Triphenylphosphonium-Based

Compounds: Syntheses, Mechanisms of Action, and Therapeutic and Diagnostic Applications. Chem. Rev., 2017, 117, 10043-10120.

(6) Liu, J. N.; Bu, W.; Shi, J. Chemical Design and Synthesis of Functionalized Probes for Imaging and Treating Tumor Hypoxia. Chem. Rev., 2017, 117, 6160-6224.

(7) Kumar, R.; Shin, W. S.; Sunwoo, K.; Kim, W. Y.; Koo, S.; Bhuniya, S.; Kim, J. S. Small Conjugate-Based Theranostic Agents: an Encouraging Approach for Cancer Therapy. Chem. Soc. Rev., 2015, 44, 6670-6683.

(8) Dreuw, A.; Plötner, J.; Lorenz, L.; Wachtveitl, J.; Djanhan, J. E.; Brüning, J.; Metz, T.; Bolte, M.; Schmidt, M. U. Molecular Mechanism of the Solid-State Fluorescence Behavior of


22

Page 23 of 32 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


the Organic Pigment Yellow 101 and Its Derivatives. Angew. Chem. Int. Ed., 2005, 44, 77837786.

(9) Mizukami, S.; Houjou, H.; Sugaya, K.; Koyama, E.; Tokuhisa, H.; Sasaki T.; Kanesato, M. Fluorescence Color Modulation by Intramolecular and Intermolecular π−π Interactions in a Helical Zinc(II) Complex. Chem. Mater., 2005, 17, 50-56.

(10) Yoshida, K.; Uwada, K.; Kumaoka, H.; Bu, L.; Watanabe, S. Fluorescence Sensing Behavior of Crystals of an Imidazole-Type Clathrate Host upon Contact with Gaseous Carboxylic Acids. Chem. Lett., 2001, 8, 808-809.

(11) Luo, J.; Xie, Z.; Lam, J. W. Y.; Cheng, L.; Chen, H.; Qiu, C.; Kwok, H. S.; Zhan, X.; Liu, Y.; Zhu, D.; Tang, B. Z. Aggregation-Induced Emission of 1-Methyl-1,2,3,4,5-pentaphenylsilole. Chem. Commun., 2001, 0, 1740-1741.

(12) Mei, J.; Leung, N. L. C.; Kwok, R. T. K.; Lam; J. W. Y.; Tang, B. Z. AggregationInduced Emission: Together We Shine, United We Soar! Chem. Rev., 2015, 115, 11718-11940.

(13) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission. Chem. Soc. Rev., 2011, 40, 5361-5388.

(14) Chen, S.; Wang, H.; Hong, Y.; Tang, B. Z. Fabrication of Fluorescent Nanoparticles Based on AIE Luminogens (AIE dots) and Their Applications in Bioimaging. Mater. Horiz., 2016, 3, 283-293.


23


Page 24 of 32

(15) Zhao, Z.; He, B.; Tang, B. Z. Aggregation-Induced Emission of Siloles. Chem. Sci., 2012, 6, 5347-5365.

(16) Chen, L.; Jiang, Y.; Nie, H.; Lu, P.; Sung, H. H. Y.; Williams, I. D.; Kwok, H. S.; Huang, F.; Qin, A.; Zhao, Z.; Tang, B. Z. Multichannel Conductance of Folded Single-Molecule Wires Aided by Through-Space Conjugation. Adv. Funct. Mater., 2014, 24, 3621-3630.

(17) Tsujimoto, H.; Ha, D. G.; Markopoulos, G.; Chae, H. S.; Baldo, M. A.; Swager, T. M. Thermally Activated Delayed Fluorescence and Aggregation Induced Emission with ThroughSpace Charge Transfer. J. Am. Chem. Soc., 2017, 139, 4894-4900.

(18) Yoshii, R.; Hirose, A.; Tanaka, K.; Chujo, Y. Functionalization of Boron Diiminates with Unique Optical Properties: Multicolor Tuning of Crystallization-Induced Emission and Introduction into the Main Chain of Conjugated Polymers. J. Am. Chem. Soc., 2014, 136, 1813118139.

(19) Shustova, N. B.; Cozzolino, A. F.; Reineke, S.; Baldo M.; Dincă, M. Selective Turn-On Ammonia Sensing Enabled by High-Temperature Fluorescence in Metal–Organic Frameworks with Open Metal Sites. J. Am. Chem. Soc., 2013, 135, 13326-13329.

(20) Li, D.; Yu, J. AIEgens-Functionalized Inorganic-Organic Hybrid Materials: Fabrications and Applications. Small, 2016, 12, 6478-6494.


24

Page 25 of 32 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


(21) Yang, J.; Gao, X.; Xie, Z.; Gong, Y.; Fang, M.; Peng, Q.; Chi, Z.; Li, Z. Elucidating the Excited State of Mechanoluminescence in Organic Luminogens with Room-Temperature Phosphorescence. Angew. Chem. Int. Ed., 2017, 56, 15299-15303.

(22) Li, J.; Liu, K.; Han, Y.; Tang, B. Z.; Huang, J. B.; Yan Y. Fabrication of Propeller-Shaped Supra-amphiphile for Construction of Enzyme-Responsive Fluorescent Vesicles. ACS Appl. Mater. Interfaces, 2016, 8, 27987-27995.

(23) Ravotto, L.; Ceroni, P. Aggregation Induced Phosphorescence of Metal Complexes: From Principles to Applications. Coord. Chem. Rev., 2017, 346, 62-76.

(24) Butler, T.; Morris, W. A.; Samonina-Kosicka, J; Fraser, C. L. Mechanochromic Luminescence and Aggregation Induced Emission of Dinaphthoylmethane β-Diketones and Their Boronated Counterparts. ACS Appl. Mater. Interfaces, 2016, 8, 1242-1251.

(25) Wang, E.; Lam, J. W. Y.; Hu, R.; Zhang, C.; Zhao, Y. S.; Tang B. Z. Twisted Tntramolecular Charge Transfer, Aggregation-Induced Emission, Supramolecular Self-Assembly and the Optical Waveguide of Barbituric Acid-Functionalized Tetraphenylethene. J. Mater. Chem. C, 2014, 2, 1801-1807.

(26) Sasaki, S.; Drummen, G. P. C.; Konishiac, G. Recent Advances in Twisted Intramolecular Charge Transfer (TICT) Fluorescence and Related Phenomena in Materials Chemistry. J. Mater. Chem. C, 2016, 4, 2731-2743.


25


Page 26 of 32

(27) Zhang, J. N.; Kang, H.; Li, N.; Zhou, S. M.; Sun, H. M.; Yin, S. W.; Zhao, N.; Tang, B. Z. Organic Solid Fluorophores Regulated by Subtle Structure Modification: Color-Tunable and Aggregation-Induced Emission. Chem. Sci., 2017, 8, 577-582.

(28) Zhao, N.; Yang, Z.; Lam, J. W. Y.; Sung, H. H. Y.; Xie, N.; Chen, S.; Su, H.; Gao, M.; Williams, I. D.; Wong, K. S.; Tang, B. Z. Benzothiazolium-Functionalized Tetraphenylethene: an AIE Luminogen with Tunable Solid-State Emission. Chem. Commun., 2012, 48, 8637-8639.

(29) Cheng, Y.; Wang, J.; Qiu, Z.; Zheng, X.; Leung, N. L. C.; Lam, J. W. Y.; Tang, B. Z. Multiscale Humidity Visualization by Environmentally Sensitive Fluorescent Molecular Rotors. Adv. Mater., 2017, 46, 1703900.

(30) Zhang, R. X.; Li, P. F.; Zhang, W. J.; Li, N.; Zhao, N. A Highly Sensitive Fluorescent Sensor with Aggregation-Induced Emission Characteristics for the Detection of Iodide and Mercury Ions in Aqueous Solution. J. Mater. Chem. C, 2016, 4, 10479-10485.

(31) Zhang, W. J.; Yang, H. X.; Li, N.; Zhao, N. A Sensitive Fluorescent Probe for Alkaline Phosphatase and an Activity Assay Based on the Aggregation-induced Emission Effect. RSC Adv., 2018, 8, 14995-15000.

(32) Gao, X.; Feng, G.; Manghnani, P. N.; Hu, F.; Jiang, N.; Liu, J.; Liu, B.; Sun, J. Z.; Tang, B. Z. A Two-Channel Responsive Fluorescent Probe with AIE Characteristics and Its


26

Page 27 of 32 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


Application for Selective Imaging of Superoxide Anions in Living Cells. Chem. Commun., 2017, 53, 1653-1656.

(33) Zhuang, Y.; Huang, F.; Xu, Q.; Zhang, M.; Lou, X.; Xia, F. Facile, Fast-Responsive, and Photostable Imaging of Telomerase Activity in Living Cells with a Fluorescence Turn-On Manner. Anal. Chem., 2016, 88, 3289-3294.

(34) Shen, W.; Yu, J.; Ge, J.; Zhang, R.; Cheng, F.; Li, X.; Fan, Y.; Yu, S.; Liu, B.; Zhu, Q. Light-Up Probes Based on Fluorogens with Aggregation-Induced Emission Characteristics for Monoamine Oxidase-A Activity Study in Solution and in Living Cells. ACS Appl. Mater. Interfaces, 2016, 8, 927-935.

(35) Lin, P.; Chen, D.; Wang, Y.; Tang, X.; Li, H.; Shi, J.; Tong, B.; Dong, Y. A Highly Sensitive "Turn-On" Fluorescent Probe with an Aggregation-Induced Emission Characteristic for Quantitative Detection of γ-Globulin. Biosens. Bioelectron., 2017, 92, 536-541.

(36) Zhao, N.; Chen, S. Hong, Y.; Tang B. Z. A Red Emitting Mitochondria-Targeted AIE Probe as an Indicator for Membrane Potential and Mouse Sperm Activity. Chem. Commun., 2015, 51, 13599-13602.

(37) Gui, C.; Zhao, E.; Kwok, R. T. K.; Leung, A. C. S.; Lam, J. W. Y.; Jiang, M.; Deng, H.; Cai, Y.; Zhang, W.; Su, H.; Tang, B. Z. AIE-Active Theranostic System: Selective Staining and Killing of Cancer Cells. Chem. Sci., 2017, 8, 1822-1830.


27


Page 28 of 32

(38) Huang, Y.; Zhang, G.; Hu, F.; Jin, Y.; Zhao, R. Zhang, D. Emissive Nanoparticles from Pyridinium-Substituted Tetraphenylethylene Salts: Imaging and Selective Cytotoxicity towards Cancer Cells in Vitro and In Vivo by Varying Counter Anions. Chem. Sci., 2016, 7, 7013-7019.

(39) Jayaram, D. T.; Ramos-Romero, S.; Shankar, B. H.; Garrido, C.; Rubio, N.; Sanchez-Cid, L.; Gómez, S. B.; Blanco, J.; Ramaiah, D. In Vitro and in Vivo Demonstration of Photodynamic Activity and Cytoplasm Imaging through TPE Nanoparticles. ACS Chem. Biol., 2016, 11, 104112.

(40) Gu, X.; Zhao, E.; Zhao, T.; Kang, M.; Gui, C.; Lam, J. W. Y.; Du, S.; Loy, M. M. T.; Tang, B. Z. A Mitochondrion-Specific Photoactivatable Fluorescence Turn-On AIE-Based Bioprobe for Localization Super-Resolution Microscope. Adv. Mater., 2016, 28, 5064-5071.

(41) Xue, S.; Qiu, X.; Sun, Q.; Yang, W. Alkyl Length Effects on Solid-State Fluorescence and Mechanochromic Behavior of Small Organic Luminophores. J. Mater. Chem. C, 2016, 4, 15681578;

(42) Dong, J.; Solntsev, K. M.; Tolbert, L. M. Activation and Tuning of Green Fluorescent Protein Chromophore Emission by Alkyl Substituent-Mediated Crystal Packing. J. Am. Chem. Soc., 2009, 131, 662-670.

(43) Carayon, C.; Ghodbane, A.; Gibot, L.; Dumur, R.; Wang, J.; Saffon, N.; Rols, M. P.; Solntsev, K. M.; Fery-Forgues, S. Conjugates of Benzoxazole and GFP Chromophore with


28

Page 29 of 32 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


Aggregation-Induced Enhanced Emission: Influence of the Chain Length on the Formation of Particles and on the Dye Uptake by Living Cells. Small, 2016, 12, 6602-6612.

(44) Gu, X.; Yao, J.; Zhang, G.; Yan, Y.; Zhang, C.; Peng, Q.; Liao, Q.; Wu, Y.; Xu, Z.; Zhao, Y.;

Fu,

H.;

Zhang,

D.

Polymorphism-Dependent

Emission

for

Di(p-

methoxylphenyl)dibenzofulvene and Analogues: Optical Waveguide/Amplified Spontaneous Emission Behaviors. Adv. Funct. Mater., 2012, 22, 4862-4872.

(45) Samanta, S. K.; Bhattacharya, S. Aggregation Induced Emission Switching and Electrical Properties of Chain Length Dependent pi-Gels Derived from Phenylenedivinylene BisPyridinium Salts in Alcohol-Water Mixtures. J. Mater. Chem., 2012, 22, 25277-25287.

(46) Soni, M.; Das, S. K.; Sahu, P. K.; Kar, U. P.; Rahaman, A.; Sarkar, M. Synthesis, Photophysics, Live Cell Imaging, and Aggregation Behavior of Some Structurally Similar Alkyl Chain Containing Bromonaphthalimide Systems: Influence of Alkyl Chain Length on the Aggregation Behavior. J. Phy. Chem. C, 2013, 117, 14338-14347.

(47) Lei, T.; Wang, J. Y.; Pei, J. Roles of Flexible Chains in Organic Semiconducting Materials. Chem. Mater., 2014, 26, 594-603.

(48) Zhan, X.; Zhang, J.; Gong, Y.; Tang, S.; Tu, J.; Xie, Y.; Peng, Q.; Yu G.; Li, Z. Alkyl Chain Engineering of Pyrene-Fused Perylene Diimides: Impact on Transport Ability and Microfiber Self-Assembly. Mater. Chem. Front., 2017, 1, 2341-2348.


29


Page 30 of 32

(49) Chen, X.; Shen, X. Y.; Guan, E.; Liu, Y.; Qin, A.; Sun, J. Z.; Tang, B. Z. A PyridinylFunctionalized Tetraphenylethylene Fluorogen for Specific Sensing of Trivalent Cations. Chem. Commun., 2013, 49, 1503-1505.

(50) Zhao, N.; Li, M.; Yan, Y.; Lam, J. W. Y.; Zhang, Y. L.; Zhao, Y. S.; Wong, K. S.; Tang, B. Z. A Tetraphenylethene-Substituted Pyridinium Salt with Multiple Functionalities: Synthesis, Stimuli-Responsive Emission, Optical Waveguide and Specific Mitochondrion Imaging. J. Mater. Chem. C, 2013, 1, 4640-4646.

(51) Chen, P. Z.; Zhang, H.; Niu, L. Y. ; Zhang, Y.; Chen, Y. Z.; Fu, H. B.; Yang, Q. Z. A Solid-State Fluorescent Material Based on Carbazole-Containing Difluoroboron β-Diketonate: Multiple Chromisms, the Self-Assembly Behavior, and Optical Waveguides. Adv. Funct. Mater., 2017, 27, 1700332.

(52) Po, C.; Tam, A. Y. Y.; Yam, V. W. W. Tuning of Spectroscopic Properties via Variation of the Alkyl Chain Length: a Systematic Study of Molecular Structural Changes on SelfAssembly of Amphiphilic Sulfonate-Pendant Platinum(ii) Bzimpy Complexes in Aqueous Medium. Chem. Sci., 2014, 5, 2688-2695.

(53) Israelachvili, J. N.; Mitchell, D. J.; Ninham, B. W. Theory of Self-Assembly of Hydrocarbon Amphiphiles into Micelles and Bilayers. J. Chem. Soc., Faraday Trans. 2, 1976, 72, 1525-1568.


30

Page 31 of 32 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


(54) Nagarajan, R. Molecular Packing Parameter and Surfactant Self-Assembly: The Neglected Role of the Surfactant Tail. Langmuir, 2002, 18, 31-38.

(55) Yang, Y.; Chen, S.; Ni, X. L. Anion Recognition Triggered Nanoribbon-Like SelfAssembly: A Fluorescent Chemosensor for Nitrate in Acidic Aqueous Solution and Living Cells. Anal. Chem., 2015, 87, 7461-7466.

(56) Varghese, R.; George, S. J.; Ajayaghosh, A. Anion Induced Modulation of Self-Assembly and Optical Properties in Urea End-Capped Oligo(p-phenylenevinylene)s. Chem. Commun., 2005, 593-595.


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Fine Tuning of Emission Behavior, Self-Assembly, Anion Sensing, and

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