Supramolecular Nano-Aggregates Based on Bis (Pyrene) Derivatives

Article pubs.acs.org/JPCC

Supramolecular Nano-Aggregates Based on Bis(Pyrene) Derivatives for Lysosome-Targeted Cell Imaging Lei Wang,† Wei Li,†,‡ Jing Lu,‡ Ying-Xi Zhao,† Gang Fan,† Jing-Ping Zhang,‡,* and Hao Wang†,* †

CAS Key Laboratory for Biological Effects of Nanomaterials and Nanosafety, National Center for Nanoscience and Technology (NCNST), Beijing, 100190, P. R. China ‡ Faculty of Chemistry, Northeast Normal University, Changchun, 130024, P. R. China S Supporting Information *

ABSTRACT: The supramolecular packing mode of organic π-conjugated molecules in the solid state plays a crucial role in determination of the resulting material properties and functionalities. Control and understanding of supramolecular packing of individual building blocks constitute an important step toward optoelectronic and biomedicine. In this work, we have designed and synthesized a series of bis(pyrene) derivatives, i.e., BP1−BP4 with 1,3-dicarbonyl, pyridine-2,6dicarbonyl, oxaloyl and benzene-1,4-dicarbonyl as linkers, respectively. In solution, all compounds showed low fluorescence quantum yields (Φ < 1.7%) in variable organic solvents due to the twisted intramolecular charge transfer (TICT). In a sharp contrast, BP1 and BP2 in the solid state were selfassembled to form J-type aggregates with almost 30-fold fluorescence enhancement (Φ was up to 32.6%) compared to that in solution. Nevertheless, H-type aggregates of BP3 and BP4 were observed with poor emissive efficiencies (Φ < 3.1%). The proposed molecular aggregates types were confirmed by powder X-ray patterns and single crystal structures. The slipping angles of adjacent molecules of J-type aggregates were 41.07−44.58°, which were smaller than that (64.58−68.45°) in H-type aggregates. Subsequently, B3LYP/6-31G quantum chemistry calculation was performed and the results indicated that the excimeric emission of BP1−BP4 aggregates was closely related to their molecular packing orientation and parameters. Furthermore, the morphologies of supramolecular aggregates based on BP1−BP4 were observed by transmission electron microscope (TEM) and the results showed that BP1 and BP2 were dot-shape nanoaggregates with 2−6 nm in diameters, while BP3 and BP4 showed sheet-like morphologies with 5−10 nm in width and 20−100 nm in length. The nanoaggregates of BP1 and BP2 coated with F108 surfactants showed good pH and photostability in physiological condition. Finally, the nanoaggregates of BP1 and BP2 were successfully employed as fluorescence nanoprobes for lysosome-targeted imaging in living cells with negligible cytotoxicity.

■

experimental results.20 They clarified that face-to-face π−π interactions of π-conjugated molecules could form an almostforbidden lowest energy transition, resulting low fluorescence quantum yield. However, the nature of large organic πconjugated molecules made them tend to stack in columns by face-to-face interactions with poor optical properties (H-type aggregates). To obtain highly emissive materials in the solid state, the following basic strategy have been utilized, e.g., (i) avoid the π−π interactions by introducing bulky group;21−23 (ii) utilize aggregation-induced emission (AIE)24,25 and aggregation-induced enhanced emission (AIEE)26−28 mechanisms to obtain high fluorescence in aggregation state; (iii) control J-type aggregates of fluorophores.29−40 The J-type aggregates could be formed via noncovalent van-der-Waals interactions of molecules, which have highly ordered structure

INTRODUCTION Organic π-conjugated molecules have attracted extensive attention in recent years due to their extraordinary electronic and optical properties for optoelectronic and biomedicine, such as organic field effect transistor,1,2 organic light-emitting diode,3,4 organic photovoltaic,5−7 biosensors,8,9 and bioimaging agents.10−13 These intensive experimental studies have demonstrated that in the solid state (not in solution state), which are generally utilized for practical applications, intermolecular interactions and supramolecular packing modes of π-conjugated molecules can dramatically affect the performance of materials. It is still a challenge to find out the relationship between the supramolecular packing mode and the properties and to get excellent materials of organic πconjugated molecules through rational molecular design.14−19 Jean-Luc Bredas and co-workers demonstrated the insight of the relationship between intermolecular interactions in organic π-conjugated materials and the electronic structure and optical properties based on the theoretical calculations and related © 2013 American Chemical Society

Received: September 25, 2013 Revised: November 25, 2013 Published: November 26, 2013 26811

dx.doi.org/10.1021/jp409557g | J. Phys. Chem. C 2013, 117, 26811−26820

The Journal of Physical Chemistry C

Article

The 96-well coning culture plates were purchased from Corning Company. Instruments and Measurements. 1H NMR spectra were recorded on an Advance Bruker 400 M spectrometer in deuterated chloroform. Chemical shifts are quoted in parts per million (ppm) and referenced to tetramethylsilane. The 13C NMR spectra were recorded at 100 MHz on the same spectrometer in deuterated chloroform. Chemical shifts were defined relative to the 13C resonance shift of chloroform (77.0 ppm). The UV absorption was determined with a Shimadzu 2600 UV/vis spectrometer. Fluorescence spectrum was recorded on F-280 spectrometer from Tianjin Gangdong Sci&Tech. Development. Co., Ltd. High-resolution mass spectrometry was taken on a GCT Premier instrument from Waters Co. Time-resolved fluorescence spectra were measured with Edinburgh Analytical Instruments F900 (Edinburgh Instruments). The UV source used for photobleaching resistance experiment is from ML-3500S Maxima/ FA ultrahigh intensity UV-A lamp (365 nm, Spectronics Corporation). The dynamic light scattering (DLS) was determined by Zetasizer Nano ZS (Malvern Instruments Ltd.) and the morphology was observed by transmission electron microscope (TEM, Tecnai G2 F20 U-TWIN). The powder X-ray diffraction (XRD) was measured on D/ MAX-TTRIII (CBO). Single crystal X-ray diffraction was carried out on Gemini single crystal X-ray diffraction systems from Agilent Technologies. Preparation of Nanoaggregates. The nanoaggregates were prepared by the rapid injection method. The BP1−BP4 DMSO solution (50 μL) with high concentration was injected into 950 μL of water, and the mixture was sonicated for 40 min. The nanoaggregates could be used for DLS measurement directly. The nanoaggregates for TEM was stained by uranium acetate for 30 s and washed by distilled water twice. The nanoaggregates for time courses, photo- and pHstability was prepared by using a similar method. Cell Culture. KB cells were cultured in regular growth medium consisting of RPMI 1640 medium supplemented with 10% fetal bovine serum (FBS). All cultures were kept in an atmosphere of 5% CO2 and 95% air at 37 °C. Subcellular Localization of Nanoaggregates. KB cells were seeded on glass-bottomed dishes with 5 × 104 cells per well and allowed to grow until 60% confluent. Cells were washed twice with PBS, and then incubated with 1 mL of freshly prepared nanoaggregates suspension (25 μM) in a serum free RPMI 1640 medium. After incubation at 37 °C for 3 h, cells were washed twice with ice-cold PBS and stained with 10 μM LysoTracker red following the manufacturer’s instructions. The intracellular localization was visualized under a confocal laser scanning microscope (CLSM) Zeiss LSM710. Cytotoxicity of Nanoaggregates. The cytotoxicity of nanoaggregates to KB cells was investigated. Briefly, cells at logarithmic growth phase were added to 96-well culture plates at 5 × 104 cells mL−1, 100 μL per well, and incubated overnight. The culture medium was then replaced with 200 μL of nanoaggregates suspension of different concentrations (from 6.25 to 100 μM). The cells were incubated at 37 °C and 5% CO2 atmosphere for 24 h. The cell viability was determined by CCK-8 assay.

in a slipped arrangement. Because of a strong coupling between transition dipole moments of the constituent molecules, excitonic states created by optical excitation result in bathochromically shifted absorption band and high fluorescence quantum yield. The supramolecular engineering provides an important method to control J-type aggregation formation over H-type aggregation. Researchers have tried to control the π−π interactions to J-type aggregates mode by using H-bond,29−32 electrostatic,33,34 host−guest interactions35,36 and substitutions for steric hindrance effect.37−40 We were also interested in Jtype aggregates with optical activities and developed a series of J-type aggregates based on hydrogen-bonded perylene dyes. The perylene dyes showed high fluorescence quantum yield, which usually display weak emission because of the H-type aggregation.29 Pyrene is a prototypical molecule, which has high fluorescence quantum yield in dilute solution.41 More importantly, the pyrene shows characteristic excimer emission in concentrated solution or solid state.41−46 However, the excimer emission in aggregation state was either falls down47−49 or rises50,51 due to the variable supramolecular packing modes. How to control the intermolecular arrangement and obtain the supramolecular aggregates with desired properties becomes one of the important but less investigated topics. To answer this question, we attempted to design and synthesize a series of bis(pyrene) derivatives with different aggregation type and the optical properties, and find out how the aggregation type affect their optical properties. Herein, we synthesized four bis(pyrene) derivatives, i.e., BP1−BP4, where the two pyrenes are covalently connected with (aromatic) dicarbonyl as linkers and steric hindrance groups. The BP1 and BP2 with benzene-1,3-dicarbonyl and pyridine-2,6-dicarbonyl as linkers showed J-type aggregates with almost 30-fold fluorescence enhancement (Φ = 32.6%) compared with that of individual molecular state in solution. In sharp contrast, the BP3 and BP4 with benzene-1,4-dicarbonyl and oxaloyl as linkers formed H-type aggregates with poor excimer emission. The different aggregation types were confirmed by powder X-ray patterns and single crystal structures. BP1 and BP2 are dot-shape nanoaggregates with 2−6 nm in diameters, while BP3 and BP4 showed sheet morphologies with 5−10 nm in width and 20−100 nm in length. The J-type nanoaggregates of BP1 and BP2 exhibited strong excimer emission between 520 and 540 nm with high pH- and photostability in physiological condition. Finally, the photostable nanoaggregates of BP1 and BP2 were successfully employed as fluorescence nanoprobes for lysosome-targeted imaging in living cells with negligible cytotoxicity. Our results indicate that the rational design of molecular building blocks and control of the molecular packing in aggregates provide a valid strategy for preparing functional supramolecular assemblies.52,53

■

■

RESULTS AND DISCUSSION Syntheses of Bis(pyrene) Derivatives. The four targeted molecules BP1−BP4 were synthesized from pyrene and alkyl (aryl) dichloride in one step according to the route depicted in Scheme 1. The Friedel−Crafts acylation reaction between pyrene and alkyl (aryl) dichloride in the present of AlCl3 afforded the bis(pyrene) derivatives in 45−61% yields. The BP1−BP4 were purified by column chromatography and characterized by 1H NMR, 13C NMR, MALDI−TOF and HRMS. (For further details, see the Supporting Information, Figures S1−S11.) The BP1 and BP2 could be dissolved in common organic solvent, such as chloroform, diethyl ether, DMSO and THF. The BP3 and BP4 showed lower solubility, which were only dissolved in DMSO and chloroform.

EXPERIMENTAL SECTION

Materials. All reagents and solvents for organic syntheses were purchased from commercially available sources and used without further purification. RPMI 1640 medium, phosphate-buffered saline (PBS), and fetal bovine serum (FBS) were obtained from HyClone/ Thermo fisher (Beijing, China). KB cell line was purchased from Cell Culture Center of Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences (Beijing, China). Lyso-tracker red was purchased from Invitrogen. Cell counting kit assay (CCK-8) was obtained from Beyotime Institute of Biotechnology (Shanghai, China). 26812



Article

(Figure 1), where the molecules were separated two orthogonal units, preventing the fluorescence emission.27,58,59 The

Scheme 1. Synthetic Route of Targeted Compounds BP1, BP2, BP3, and BP4

Spectroscopic Characterizations in Solution. The absorption spectra of BP1, BP2, and BP4 in diluted DMSO (Table 1) show four major absorption band peaks between 300 Table 1. Optical Properties of Bis(pyrene) Derivatives BP1− BP4 in DMSO compound

λmax [nm]

ε [M−1 cm−1]

λem [nm]a

BP1 BP2 BP3 BP4

342 378 417 340

39 050 25 350 31 650 10 450

506 394 391 398

Φem (%) 1.1 1.1 0.5 0.8

± ± ± ±

0.2 0.2 0.1 0.1

a

Fluorescence quantum yields were determined in DMSO solution (c = 2 × 10−5 M) by using quinine sulfate as a reference compound.54 Values are the averages of more than three independent measurements.

Figure 1. Contour plots of LUMOs and HOMOs in the first excited states for BP1 (a), BP2 (b), BP3 (c), and BP4 (d) in DMSO in detail (L denotes LUMO; H denotes HOMO).

and 400 nm (Figure S12). The absorption bands located at higher energies (lower than 300 nm) are likely due to π−π* and n-π* transitions localized on the aryl fragments.41 The BP3 showed two typical absorption bands at 383 and 419 nm. The bathochromical shift of BP3 compared to BP1, BP2, and BP4 indicates that oxaloyl is a more effective electron withdrawing group in BP3. The fluorescence emission of BP1 and BP2 in solution state were tested in different solvents. Interestingly, the fluorescence quantum yields BP1 and BP2 are very low in all tested solvents with some differences in emission wavelength (Table S1). In DMSO, the emission at about 400 nm of BP1 is from pyrene units. However, the peaks at 505 nm, which was obviously red shift compare to pyrene monomer emission, is originated from intramolecular charge transfer on the electronic structures. Similarly, the peaks at 400 and 570 nm of BP2 could be attributed to pyrene units and intramolecular charge transfer species.55−57 These assignments could be further supported by quantum chemistry calculation and the time-resolved fluorescence measurements (see below). Because of the poor solubility, the fluorescence spectra of BP3 and BP4 were only measured in DMSO solvent (Figure S12). Again, the emission peaks (located at around 400−500 nm) could be assigned to pyrene units and intramolecular charge transfer species. Similar to BP1 and BP2, the fluorescence quantum yields of BP3 and BP4 were low in DMSO solution. These phenomena could be explained from the molecular structure, which involves four single C−C bonds between aromatic and carbonyl groups (for BP3, three single C−C bonds). On the one hand, the intramolecular rotational relaxation of C−C bonds of bis(pyrene)s in solution can consume the hv energy for twisting over fluorescence emission, which is in accordance with AIE molecules in solution27,58,59 On the other hand, the free rotation of C−C bonds give the possibility to form TICT states

quantum chemistry calculation by using Gaussian 09 (DFT/ TDDFT in B3LYP/6-31G(d) level)60−62 in DMSO further support the experimental results and explanations. First, the calculated emission wavelengths (481, 414, 393, and 410 nm for BP1, BP2, BP3 and BP4, respectively) are well consistent with the experimental results. Furthermore, the calculated HOMOs and LUMOs are localized in different moieties suggesting the intramolecular charge transfer, and the low overlap between the HOMOs and LUMOs (Figure 1) indicates that electron transition from LUMO (S1) to HOMO (S0) is prohibited.58,59 This is further confirmed by the small oscillator strength (f values in the range from 0.0005 to 0.0149, Table S2), corresponding to the low intensity of emission. Spectroscopic Characterizations in Aggregation State. Followed the optical investigation of monomeric molecules in solution, the aggregation study was carried out in DMSO and water mixture solvent system. First, the UV absorption spectra were recorded when the water was added to the DMSO solution of BP1 as shown in Figure 2a. The absorption peak of BP1 monomer at around 300−400 nm decreased and the new bathochromical absorption peak emerged at 418 nm and increased with the increasing content of water. Similarly, the UV absorption of BP2 was also bathochromical-shifted with increasing water ratio in mixed solvent (Figure 2b). These are typical J-band corresponding to J-type aggregates, which could be slipped face-to-face packing between the monomers. 29−40,63 On the contrary, the absorption peaks of BP3 hypsochromically shifted from 418 to 370 nm. This is typical H-band corresponding to H-type aggregates, which could be face-to-face packing between the monomers (Figure 2c).29−40,63 During the aggregation of BP4, the absorption peaks of BP4 in UV spectrum did not change significantly (Figure 2d). It is hard to propose the aggregation type by J and H theory based on UV−vis spectra. 26813



Article

Figure 2. UV−vis spectra of BP1 (a), BP2 (b), BP3 (c), and BP4 (d) (c = 2.0 × 10−5 M) in DMSO/H2O mixture with different volume fractions of H2O.

Figure 3. Fluorescence spectra of BP1 (a), BP2 (b), BP3 (c), and BP4 (d) (c = 2.0 × 10−5 M) in DMSO/H2O mixture with different volume fractions of H2O. Excitation wavelength: 340 nm.

The fluorescence emission spectra were recorded with the same procedure as UV absorption measurement (Figure 3). The emission at 520−570 nm of compounds BP1−BP4 emerged and increased with the formation of aggregates upon addition of water, which were typical intermolecular excimer emission of pyrenes. The aggregation-induced enhanced emission could be due to high rigidity of aggregates, which inhibited the rotation to the most stable conformation of TICT state.64 However, the BP1 and BP2, which were proposed as Jtype aggregates by UV absorption spectra showed strong fluorescence emission. The fluorescence quantum yields of BP1 and BP2 in the aggregation state were 32.6% and 10.5%,

respectively, corresponding to 29.6 and 9.1 times enhancements compared with that in solution (Figure S13). The results are consistent with the photophysical properties of reported Jtype aggregates.29,37,63 On the contrary, the speculated H-type aggregates of BP3 show poor fluorescence emission (Φ = 1.6% when water content is 80%), which could be attributed to the dipole-forbidden nature of the emitting state of BP3 H-type aggregates. The BP4 displayed similar fluorescence properties with BP3, which were weak excimer emission (Φ = 3.1% when water content is 80%) in aggregation state compare to solution state. Therefore, we took it for granted that BP4 formed H-type aggregates. It can be concluded that although limitation of 26814



Article

Table 2. Time-Resolved Fluorescence Data of BP1−BP4 in Solution and in Aggregation Statesa BP1 BP2 BP3 BP4

τ1 [ns]

τ2 [ns]

χ2

av [ns]

0.85 (99.75) 0.75 (99.79) N.D.b N.D.

21.88 (0.25) 19.49 (0.21) N.D. N.D.

1.234 1.242

0.90 ± 0.02 0.79 ± 0.01

τ′1 [ns] 6.05 3.12 1.05 1.54

τ′2 [ns]

(80.45) (85.09) (88.20) (93.40)

19.92 12.55 4.61 6.60

(19.55) (14.91) (11.80) (6.6)

χ2 1.375 1.431 1.571 1.386

av [ns] 8.76 4.53 1.85 1.87

± ± ± ±

0.08 0.03 0.03 0.02

a

Excitation was at 375 nm, and the emission was detected at 540-470 nm. BP1 and BP2 in DMSO are detected at 540 and 570 nm, respectively; BP1-4 in aggregation states are detected at 540, 550, 570, and 540 nm, respectively. bN.D. = not detected. Values are the averages of more than three independent measurements.

Figure 4. ORTEP drawing of BP1 (a) and BP2 (d) at the 50% probability level. BP1 (b, c) and BP2 (e, f) molecular packing determined by single crystal X-ray diffractions.

intramolecular rotation relaxation could increase the fluorescence quantum yield in aggregation state,24−28 the supramolecular packing mode (e.g., J- or H-type aggregates) is a leading factor to affect their resulting fluorescence properties. Time-Resolved Fluorescence Measurements. Timeresolved fluorescence spectra of BP1−BP4 in solution and aggregation state were measured to investigate decay dynamics (Figure S14−S19), which were summarized in Table 2. The decay curve of BP1 and BP2 in solution could be analyzed as a biexponential decay consisting two components. The minor component (less than 1%) could be assigned to normal intermolecular excimer (E2) of pyrene, which was usually observed in concentrated solution with long-lifetime (τ2 = 21.88 and 19.49 ns for BP1 and BP2, respectively).41,65,66 The dominant lifetimes (major component) of BP1 and BP2 in solution are only 850 and 750 ps, respectively, which are rather short compared to normal intermolecular excimer. The fluorescence decay dynamics support the view that the emission from the BP1 and BP2 excitons with a strong charge-transfer character, which is constitute with the assignment of fluorescence emission band. The fluorescence lifetimes of BP3 and BP4 in solution are not available due to the low quantum yield. In the aggregation states, BP1−BP4 showed two long and short lifetime decays, which are two species of pyrene excimers usually found in the highly ordered structure,

such as crystals, aggregation state or in some organized media.41,65,66 The long-lived component (τ′2 is from 4.61 to 19.92 ns) can be assigned to E2, similarly to the solution. The short-lived component (τ′1 = 1.05 to 6.05 ns) is typical of intermolecular excimer (E1) of pyrene, which is only observed in ordered structure (Table 2). Supramolecular Packing Structure Determined by Xray Diffractions. In order to identify the proposed supramolecular packing mode (J- or H-type aggregates) and build the relationship between the supramolecular packing mode and the optical properties, the single crystals of BP1−BP4 were prepared and their structures were analyzed by using SHELX 9767 structure solution program (Table S3−S6). The two pyrene units in a BP1 molecule are coplanar and twisted from the phenyl ring (Figure 4a). Packing of the BP1 molecules generates parallel pyrene units interacting with adjacent ones in a slipped face-to-face fashion through intermolecular π−π interactions, where the two repeat units are shown in Figure 4b. The shortest carbon−carbon distance between the adjacent molecules is 3.361 Å. The smallest angle of centroids of two neighboring pyrene planes is 44.58°. Finally, the pyrene units form one-dimensional chains through π−π interactions (Figure 4c). This is in agreement with J-type aggregates as proposed. Unlike in the BP1 molecule, the two pyrene units in a BP2 molecule connected to the central pyridyl groups in different 26815



Article

Figure 5. ORTEP drawing of BP3 (a) and BP4 (c) at the 50% probability level. BP3 (b) and BP4 (d) molecular packing determined by single crystal X-ray diffractions.

Figure 6. X-ray diffraction pattern of BP1 (a), BP2 (b), BP3 (c) and BP4 (d) as simulated from single X-ray diffraction and measured based on aggregates.

torsion angles (Figure 4d). BP2 molecules stack in a herringbone mode, which is a typical J-type aggregates.63,68 The two pyrene units packed in a slipped face-to-face style through intermolecular π−π interactions (Figure 4e), which form two distinct supramolecular chains (Figure 4f). Consequently, the shortest carbon−carbon distances between the adjacent pyrene units in the two types of supramolecular chains are 3.263 and 3.421 Å, respectively; the smallest angles of centroids of two adjacent pyrene units are 41.07° and 44.17°, respectively. It is also in agreement with the parameters for Jtype aggregates. The single crystal X-ray data show that the BP3 form dimeric H-type aggregates in which one pyrene unit is involved in face-to-face π−π interactions (the shortest distance is 3.408 Å, the smallest angle 68.45°) and the other pyrene unit does not participate in π−π interactions (Figure 5a and b). Structural analysis indicates that the two pyrene units in one BP4 molecule are coplanar and twisted from the central phenyl group (Figure 5c). The two pyrene units between two adjacent BP4 molecules form H-type aggregates in ABAB mode with almost face-to-face π−π interactions (Figure 5d). For A··· B pyrene units form H-type aggregates, the distance is 3.343 Å with the angle of 64.58°. The B···A pyrene units are separated

with 3.472 Å (shortest carbon−carbon distance) and the angle 55.61° (the smallest angle). From the theory of J and H-type aggregation, the angle is just the boundary angle of J-type aggregates and H-type aggregates. This actually could be displayed in the UV−vis spectra (not obvious bathochromical or hypsochromical shift, Figure 2d). To ensure that single crystal structures are comparable to the aggregates obtained by rapid injection method, we measured and compared the XRD patterns of aggregates with the powder XRD patterns simulated from single crystal X-ray data (Figure 6). The highly consistent patterns indicate the similar molecular packing modes in both cases. To provide further proof in theory, excimer emission of aggregates with different aggregation types of BP1−BP4 were simulated by quantum chemistry calculation, the J-type aggregates of BP1 and BP2 have large f values (0.0209 for BP1 and 0.0159 for BP2) and transition dipole moment (0.3392 for BP1 and 0.2943 for BP2).69−71 The relative larger f values are ascribed to higher probability of emission of radiation in transitions between energy levels of a molecule, suggesting the higher fluorescence emission efficiency and quantum yield of BP1 and BP2 aggregates. On the contrary, the electronic 26816



Article

Table 3. Fluorescence Emission Wavelength (λem), Corresponding Transition Contribution, and Oscillator Strength (f) of BP1−BP4 in Aggregation State λem [nm]

oscillator strength [f ]

transition electric dipole moments [Au]

major transition

contrib [%]

expt [nm]

BP1

494

0.0209

0.3392

564

0.0159

0.2943

BP3

588

0.0034

0.0666

BP4

508

0.0000

0.0000

73 19 70 25 69 22 98

512

BP2

LUMO → HOMO LUMO → H-1 L + 1 → HOMO L + 2 → HOMO LUMO → HOMO LUMO → H-4 LUMO → H-2

541 576 528

transition from the excited state to the ground of the H-type aggregates is almost prohibited with very small f values (0.0034 for BP3 and 0.0000 for BP4) and transition dipole moment (0.0666 for BP3 and 0.0000 for BP4), reflecting the weak fluorescence of BP3 and BP4 aggregates observed in the experiments (Table 3 and Figure S20−S23). Why do BP1−BP4 molecules with different linkers pack in J and H types, respectively? First, small-sized oxaloyl linker (BP3) can not provide effective steric hindrance to suppress bis(pyrene) to form H-type aggregates, which is the nature of large π-conjugated molecules with strong π−π interactions. Second, aromatic (benzene and pyridine) dicarbonyl could be large enough for steric hindrance in size. However, the substitution positions further contribute to the aggregation type. BP4 with 1,4-substituted dicarbonyl (as linear linker, Scheme 2) could pack more closely compare to BP1 and BP2 Scheme 2. Illustration of Bis(pyrene)s with Different Linkers in Aggregation Statesa

Figure 7. TEM images of as-prepared BP1 (a), BP2 (b), BP3 (c), and BP4 (d) nanoaggregates in mixed solvent with the ratio of DMSO:H2O = 5:95%, v/v.

the F108 was utilized as a passivator to stabilize the nanoaggregates of BP1 and BP2 in cell culture medium for 48 h. Furthermore, the long-term imaging capacity of the resultant nanoaggregates was evaluated by monitoring fluorescence variation in 2 weeks. As shown in Figure 8a, the fluorescence intensities of BP1- and BP2-based nanoaggregates remained more than 95% of its initial value after 14 days. For the purpose of comparison, FITC as a commonly used fluorophore for biolabeling, was chosen as reference molecule. The fluorescence intensity of FITC decayed to half at the same condition. Moreover, the photostability is one of the most important parameters to assess the quality of imaging probes. We irradiated the BP1, BP2 and FITC solutions for 180 min with excitation wavelength at 365 nm (100 mW cm−2). The results indicated that the photostability of nanoaggregates (BP1 and BP2) was comparable with that of FITC (Figure 8b). The pH stability of nanoaggregates was also studied in buffer solutions with pH values from 5.0 to 10.0. No detected precipitation and fluorescence change were observed in a wide range of pH (Figure S24). Cell Imaging with BP1 and BP2 Nanoaggregates. The endocytosis pathway was known to lead to the formation of primary endosomes, which consequently formed late endosomes and lysosomes. After incubation of KB cells (human oral epidermoid carcinoma) with BP1 and BP2 nanoaggregates for

a

H or J-type aggregates were constructed in solid state owing to the different substitution positions.

with 1,3-substituted dicarbonyl (as V-shaped linker, Scheme 2), which resulted in different aggregation types. The deduction are supported by packing efficiency evaluated by the ratio of the calculated density (ρcalc from single crystal X-ray data) to molecular weight (Mw) (Table S7). Preparation and Characterizations of Bis(pyrene)Based Nanoaggregates. The supramolecular aggregates of BP1−BP4 were prepared by rapid injection method (details see Experimental Section). BP3 and BP4 aggregates showed sheet morphologies with 5−10 nm in width and 20−100 nm in length, which was confirmed by TEM (Figure 7, parts c and d). Nevertheless, the sizes of aggregates formed by BP1 and BP2 were 4.5 ± 1.5 nm and 3.0 ± 1.0 nm, respectively (Figure 7a and b). The narrow size distribution in aqueous solution was further confirmed by DLS (Table S8). The nanosized aggregates with ideal fluorescence features based on BP1 and BP2 were further investigated for biological applications. The nanoaggregates of BP1 and BP2 were not stable in DMSO and H2O mixture (5:95%, v/v) and prone to self-assemble into clusters with the size of 48.8 ± 5.4 nm after 6 h (Table S8) at the room temperature. To prevent this unfavorable instability, 26817



Article

Figure 8. Stability of BP1 and BP2 nanoaggregates. (a) Time courses of fluorescence intensity change and (b) photobleaching resistance to the continuous irradiation by a laser beam at 365 nm. FITC is shown for comparison.

3 h, the fluorescent images of KB cells conducted by CLSM showed that the fluorescence from BP1 and BP2 nanoaggregates mainly localized in lysosomes labeled with LysoTracker red (Figure 9). It can be concluded that the

nanoaggregates with 2−6 nm in diameters, while BP3 and BP4 showed sheet morphologies with 5−10 nm in width and 20− 100 nm in length. The nanoaggregates of BP1 and BP2 displayed high pH-stability and photostability. The nanoaggregates could be used as stable fluorescent probe for lysosome staining in living cells. This article presented that the supramolecular control in molecular level can regulate the properties of resulting aggregates in solid state, which plays a crucial role in bio and/or electronic applications.

■

ASSOCIATED CONTENT

S Supporting Information *

Experimental procedures and characterization data. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (H.W.). * E-mail: [email protected] (J.P.Z.).

Figure 9. Colocalization of LysoTracker red and nanoaggregates. KB cells were double labeled with LysoTracker red (a, d) and nanoaggregates (b for BP1 and e for BP2). The overlay of images is presented in parts c (merger of parts a and b) and f (merger of parts d and e). Excitation wavelength: 577 nm (for LysoTracker red) and 350 nm (for BP1 and BP2).

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

■

BP1 and BP2 nanoaggregates can be used as a lysosome targeted nanoprobe. Finally, the cell viability was carried out by CCK-8 assay and no obvious cytotoxicity was observed at the experimental condition (Figure S25).

ACKNOWLEDGMENTS This work was supported by National Basic Research Program of China (973 Program, No. 2013CB932701), the 100-Talent program of the Chinese Academy of Sciences, National Natural Science Foundation (Nos. 51102014, 21374026, 21304023 and 51303036) and Beijing Natural Science Foundation (No. 2132053).

■

CONCLUSION In summary, we designed and synthesized four bis(pyrene) derivatives, BP1−BP4. The photophysical properties of them in solution and in aggregation state were studied and analyzed by UV−vis spectroscopy, fluorescence spectroscopy, single Xray structure analyses and quantum chemistry calculations. In solution, all compounds showed low fluorescence quantum yields due to the twisted intramolecular charge transfer (TICT). In aggregation state, the results indicated that different linkers lead to different packing efficiencies and packing modes, which determine the fluorescence quantum yields. The supramolecular J-type aggregates based on BP1 and BP2, where two pyrenes linked by meta aromatic dicarbonyl, show ideal fluorescence properties. However, BP3 (oxaloyl) and BP4 (para aromatic dicarbonyl linker) form H-type aggregates, resulted in poor fluorescence emission. Two types aggregates showed different morphologies. BP1 and BP2 are dot-shape

■

REFERENCES

(1) Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. Functionalized Pentacene: Improved Electronic Properties from Control of Solid-State Order. J. Am. Chem. Soc. 2001, 123, 9482−9483. (2) Garnier, F.; Yassar, A.; Hajlaoui, R.; Horowitz, G.; Deloffre, F.; Servet, B.; Ries, S.; Alnot, P. Molecular Engineering of Organic Semiconductors: Design of Self-Assembly Properties in Conjugated Thiophene Oligomers. J. Am. Chem. Soc. 1993, 115, 8716−8721. (3) Brunner, K.; Dijken, A.; Borner, H.; Bastiaansen, J.; Kiggen, N. M. M.; Langeveld, B. M. W. Carbazole Compounds as Host Materials for Triplet Emitters in Organic Light-Emitting Diodes: Tuning the HOMO Level without Influencing the Triplet Energy in Small Molecules. J. Am. Chem. Soc. 2004, 126, 6035−6042.

26818



Article

Behaviour of Novel Light-Emitting Liquid Crystals. Liq. Cryst. 2005, 32, 1251−1264. (24) Li, K.; Qin, W.; Ding, D.; Tomczak, N.; Geng, J.; Liu, R.; Liu, J.; Zhang, X.; Liu, H.; Liu, B.; Tang, B. Z. Photostable Fluorescent Organic Dots with Aggregation-Induced Emission (AIE Dots) for Noninvasive Long-Term Cell Tracing. Sci. Rep. 2013, 3, 1150. (25) Qin, W.; Ding, D.; Liu, J.; Yuan, W. Z.; Hu, Y.; Liu, B.; Tang, B. Z. Biocompatible Nanoparticles with Aggregation-Induced Emission Characteristics as Far-Red/Near-Infrared Fluorescent Bioprobes for In Vitro and In Vivo Imaging Applications. Adv. Funct. Mater. 2012, 22, 771−779. (26) An, B.-K.; Gierschner, J.; Park, S. Y. pi-Conjugated Cyanostilbene Derivatives: A Unique Self-Assembly Motif for Molecular Nanostructures with Enhanced Emission and Transport. Acc. Chem. Res. 2012, 45, 544−554. (27) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission. Chem. Soc. Rev. 2011, 40, 5361−5388. (28) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Aggregation-Induced Emission: Phenomenon, Mechanism and Applications. Chem. Commun. 2009, 4332−4353. (29) Kaiser, T. E.; Wang, H.; Stepanenko, V.; Würthner, F. Supramolecular Construction of Fluorescent J-Aggregates Based on Hydrogen-Bonded Perylene Dyes. Angew. Chem., Int. Ed. 2007, 46, 5541−5544. (30) Schmidt, R.; Stolte, M.; Gruene, M.; Würthner, F. HydrogenBond-Directed Formation of Supramolecular Polymers Incorporating Head-to-Tail Oriented Dipolar Merocyanine Dyes. Macromolecules 2011, 44, 3766−3776. (31) Yagai, S.; Nakano, Y.; Seki, S.; Asano, A.; Okubo, T.; Isoshima, T.; Karatsu, T.; Kitamura, A.; Kikkawa, Y. Supramolecularly Engineered Aggregation of a Dipolar Dye: Vesicular and Ribbonlike Architectures. Angew. Chem., Int. Ed. 2010, 49, 9990−9994. (32) Yoon, S.-J.; Chung, J. W.; Gierschner, J.; Kim, K. S.; Choi, M.G.; Kim, D.; Park, S. Y. Multistimuli Two-Color Luminescence Switching via Different Slip-Stacking of Highly Fluorescent Molecular Sheets. J. Am. Chem. Soc. 2010, 132, 13675−13683. (33) Egawa, Y.; Hayashida, R.; Anzai, J. PH-Induced Interconversion between J -Aggregates and H-Aggregates of 5,10,15,20-Tetrakis(4sulfonatophenyl)porphyrin in Polyelectrolyte Multilayer Films. Langmuir 2007, 23, 13146−13150. (34) De Luca, G.; Romeo, A.; Villari, V.; Micali, N.; Foltran, I.; Foresti, E.; Lesci, I. G.; Roveri, N.; Zuccheri, T.; Scolaro, L. M. SelfOrganizing Functional Materials via Ionic Self Assembly: Porphyrins H- and J-Aggregates on Synthetic Chrysotile Nanotubes. J. Am. Chem. Soc. 2009, 131, 6920−6921. (35) Gadde, S.; Batchelor, E. K.; Weiss, J. P.; Ling, Y.; Kaifer, A. E. Control of H- and J-Aggregate Formation via Host-Guest Complexation using Cucurbituril Hosts. J. Am. Chem. Soc. 2008, 130, 17114− 17119. (36) Jiao, D.; Biedermann, F.; Tian, F.; Scherman, O. A. A Systems Approach to Controlling Supramolecular Architecture and Emergent Solution Properties via Host-Guest Complexation in Water. J. Am. Chem. Soc. 2010, 132, 15734−15743. (37) Dautel, O. J.; Wantz, G.; Almairac, R.; Flot, D.; Hirsch, L.; LerePorte, J. P.; Parneix, J. P.; Serein-Spirau, F.; Vignau, L.; Moreau, J. J. E. Nanostructuration of Phenylenevinylenediimide-Bridged Silsesquioxane: From Electroluminescent Molecular J-Aggregates to Photoresponsive Polymeric H-Aggregates. J. Am. Chem. Soc. 2006, 128, 4892−4901. (38) Davis, R.; Kumar, N. S. S.; Abraham, S.; Suresh, C. H.; Rath, N. P.; Tamaoki, N.; Das, S. Molecular Packing and Solid-State Fluorescence of Alkoxy-Cyano Substituted Diphenylbutadienes: Structure of the Luminescent Aggregates. J. Phys. Chem. C 2008, 112, 2137−2146. (39) Thomas, R.; Varghese, S.; Kulkarni, G. U. The Influence of Crystal Packing on the Solid State Fluorescence Behavior of Alkyloxy Substituted Phenyleneethynylenes. J. Mater. Chem. 2009, 19, 4401− 4406.

(4) Müller, C. D.; Falcou, A.; Reckefuss, N.; Rojahn, M.; Wiederhirn, V.; Rudati, P.; Frohne, H.; Nuyken, O.; Becker, H.; Meerholz, K. Multi-Colour Organic Light-Emitting Displays by Solution Processing. Nature 2003, 421, 829−833. (5) Peumans, P.; Uchida, S.; Forrest, S. R. Efficient Bulk Heterojunction Photovoltaic Cells Using Small-Molecular-Weight Organic Thin Films. Nature 2003, 425, 158−162. (6) Choi, M. S.; Yamazaki, T.; Yamazaki, I.; Aida, T. Bioinspired Molecular Design of Light-Harvesting Multiporphyrin Arrays. Angew. Chem., Int. Ed. 2004, 43, 150−158. (7) Ajayaghosh, A.; Praveen, V. K.; Vijayakumar, C. Organogels as Scaffolds for Excitation Energy Transfer and Light Harvesting. Chem. Soc. Rev. 2008, 37, 109−122. (8) Wang, B.; Yu, C. Fluorescence Turn-On Detection of a Protein through the Reduced Aggregation of a Perylene Probe. Angew. Chem., Int. Ed. 2010, 49, 1485−1488. (9) Wang, L.; Li, L.-L.; Ma, H. L.; Wang, H. Recent Advances in Biocompatible Supramolecular Assemblies for Biomolecular Detection and Delivery. Chin. Chem. Lett. 2013, 5, 1−8. (10) Petkau-Milroy, K.; Sonntag, M. H.; Onzen, A. H. A. M.; Brunsveld, L. Supramolecular Polymers as Dynamic Multicomponent Cellular Uptake Carriers. J. Am. Chem. Soc. 2012, 134, 8086−8089. (11) Mizusawa, K.; Takaoka, Y.; Hamachi, I. Specific Cell Surface Protein Imaging by Extended Self-Assembling Fluorescent Turn-On Nanoprobes. J. Am. Chem. Soc. 2012, 134, 13386−13395. (12) Wang, L.; Li, L.-L.; Fan, Y.-S.; Wang, H. Host−Guest Supramolecular Nanosystems for Cancer Diagnostics and Therapeutics. Adv. Mater. 2013, 25, 3888−3898. (13) Xu, J.-H.; Gao, F.-P.; Liu, X.-F.; Zeng, Q.; Guo, S.-S.; Tang, Z.Y.; Zhao, X.-Z.; Wang, H. Supramolecular Gelatin Nanoparticles as Matrix Metalloproteinase Responsive Cancer Cell Imaging Probes. Chem. Commun. 2013, 49, 4462−4464. (14) Ke, D.; Zhan, C.; Xu, S.; Ding, X.; Peng, A.; Sun, J.; He, S.; Li, A. D. Q.; Yao, J. Self-Assembled Hollow Nanospheres Strongly Enhance Photoluminescence. J. Am. Chem. Soc. 2011, 133, 11022−11025. (15) George, S. J.; Ajayaghosh, A. Self-Assembled Nanotapes of Oligo(p-phenylene vinylene)s: Sol−Gel-Controlled Optical Properties in Fluorescent π-Electronic Gels. Chem.Eur. J. 2005, 11, 3217− 3227. (16) Pisula, W.; Kastler, M.; Wasserfallen, D.; Mondeshki, M.; Piris, J.; Schnell, I.; Müllen, K. Relation between Supramolecular Order and Charge Carrier Mobility of Branched Alkyl Hexa-peri-hexabenzocoronenes. Chem. Mater. 2006, 18, 3634−3640. (17) Mativetsky, J. M.; Kastler, M.; Savage, R. C.; Gentilini, D.; Palma, M.; Pisula, W.; Müllen, K.; Samori, P. Self-Assembly of a Donor-Acceptor Dyad Across Multiple Length Scales: Functional Architectures for Organic Electronics. Adv. Funct. Mater. 2009, 19, 2486−2494. (18) De Feyter, S.; De Schryver, F. C. Two-Dimensional Supramolecular Self-Assembly Probed by Scanning Tunneling Microscopy. Chem. Soc. Rev. 2003, 32, 139−150. (19) Yan, X.; Wang, F.; Zheng, B.; Huang, F. Stimuli-Responsive Supramolecular Polymeric Materials. Chem. Soc. Rev. 2012, 41, 6042− 6065. (20) Cornil, J.; Beljonne, D.; Calbert, J. P.; Bredas, J. L. Interchain Interactions in Organic π-Conjugated Materials: Impact on Electronic Structure, Optical Response, and Charge Transport. Adv. Mater. 2001, 13, 1053−1067. (21) Wu, J. S.; Fechtenkotter, A.; Gauss, J.; Watson, M. D.; Kastler, M.; Fechtenkotter, C.; Wagner, M.; Müllen, K. Controlled SelfAssembly of Hexa-peri-hexabenzocoronenes in Solution. J. Am. Chem. Soc. 2004, 126, 11311−11321. (22) Lai, W.-Y.; Xia, R.; He, Q.-Y.; Levermore, P. A.; Huang, W.; Bradley, D. D. C. Enhanced Solid-State Luminescence and LowThreshold Lasing from Starburst Macromolecular Materials. Adv. Mater. 2009, 21, 355−360. (23) Aldred, M. P.; Eastwood, A. J.; Kitney, S. P.; Richards, G. J.; Vlachos, P.; Kelly, S. M.; O’Neill, M. Synthesis and Mesomorphic 26819



Article

(40) Okada, S.; Segawa, H. Substituent-Control Exciton in JAggregates of Protonated. Water-Insoluble Porphyrins. J. Am. Chem. Soc. 2003, 125, 2792−2796. (41) Winnik, F. M. Photophysics of Pre-Associated Pyrene in Aqueous Polymer Solutions and in Other Organized Media. Chem. Rev. 1993, 93, 587−614. (42) Sagara, Y.; Kato, T. Stimuli-Responsive Luminescent Liquid Crystals: Change of Photoluminescent Colors Triggered by a ShearInduced Phase Transition. Angew. Chem., Int. Ed. 2008, 47, 5175− 5178. (43) Jiao, D.; Geng, J.; Loh, X. J.; Das, D.; Lee, T.-C.; Scherman, O. A. Supramolecular Peptide Amphiphile Vesicles through Host-Guest Complexation. Angew. Chem., Int. Ed. 2012, 51, 9633−9637. (44) Tovar, J. D.; Claussen, R. C.; Stupp, S. I. Probing the Interior of Peptide Amphiphile Supramolecular. Aggregates. J. Am. Chem. Soc. 2005, 127, 7337−7345. (45) De Halleux, V.; Calbert, J. P.; Brocorens, P.; Cornil, J.; Declercq, J. P.; Bredas, J. L.; Geerts, Y. 1,3,6,8-Tetraphenylpyrene Derivatives: Towards Fluorescent Liquid-Crystalline Columns? Adv. Funct. Mater. 2004, 14, 649−659. (46) Diring, S.; Camerel, F.; Donnio, B.; Dintzer, T.; Toffanin, S.; Capelli, R.; Muccini, M.; Ziessel, R. Luminescent Ethynyl-Pyrene Liquid Crystals and Gels for Optoelectronic Devices. J. Am. Chem. Soc. 2009, 131, 18177−18185. (47) Muccini, M. A Bright Future for Organic Field-Effect Transistors. Nat. Mater. 2006, 5, 605−613. (48) Banerjee, M.; Vyas, V. S.; Lindeman, S. V.; Rathore, R. Isolation and X-Ray Structural Characterization of Tetraisopropylpyrene Cation Radical. Chem. Commun. 2008, 1889−1891. (49) Crawford, A. G.; Dwyer, A. D.; Liu, Z.; Steffen, A.; Beeby, A.; Palsson, L.-O.; Tozer, D. J.; Marder, T. B. Experimental and Theoretical Studies of the Photophysical Properties of 2-and 2,7Functionalized Pyrene Derivatives. J. Am. Chem. Soc. 2011, 133, 13349−13362. (50) Kashida, H.; Sekiguchi, K.; Liang, X.; Asanuma, H. Accumulation of Fluorophores into DNA Duplexes To Mimic the Properties of Quantum Dots. J. Am. Chem. Soc. 2010, 132, 6223−6230. (51) Nakamura, M.; Murakami, Y.; Sasa, K.; Hayashi, H.; Yamana, K. Pyrene-Zipper Array Assembled via RNA Duplex Formation. J. Am. Chem. Soc. 2008, 130, 6904−6905. (52) Schenning, A.; Jonkheijm, P.; Peeters, E.; Meijer, E. W. Hierarchical Order in Supramolecular Assemblies of HydrogenBonded Oligo(p-phenylene vinylene)s. J. Am. Chem. Soc. 2001, 123, 409−416. (53) Percec, V.; Glodde, M.; Bera, T. K.; Miura, Y.; Shiyanovskaya, I.; Singer, K. D.; Balagurusamy, V. S. K.; Heiney, P. A.; Schnell, I.; Rapp, A.; et al. Self-Organization of Supramolecular Helical Dendrimers into Complex Electronic Materials. Nature 2002, 419, 384−387. (54) Melhuish, W. H. Quantum Efficiencies of Fluorescence of Organic Substances:Effect of Solvent and Concentration of the Fluorescent Solute 1. J. Phys. Chem. 1961, 65, 229−235. (55) Suzuki, Y.; Morozumi, T.; Nakamura, H.; Shimomura, M.; Hayashita, T.; Bartsh, R. A. New Fluorimetric Alkali and Alkaline Earth Metal Cation Sensors Based on Noncyclic. Crown Ethers by Means of Intramolecular Excimer Formation of Pyrene. J. Phys. Chem. B 1998, 102, 7910−7917. (56) Schazmann, B.; Alhashimy, N.; Diamond, D. Chloride Selective Calix[4]arene Optical Sensor Combining Urea Functionality with Pyrene Excimer Transduction. J. Am. Chem. Soc. 2006, 128, 8607− 8614. (57) Nishizawa, S.; Kato, Y.; Teramae, N. Fluorescence Sensing of Anions via Intramolecular Excimer Formation in a PyrophosphateInduced Self-Assembly of a Pyrene-Functionalized Guanidinium Receptor. J. Am. Chem. Soc. 1999, 121, 9463−9464. (58) Rettig, W. Intramolecular Rotational Relaxation of Compounds Which Form ″Twisted Intramolecular Charge Transfer″ (TICT) Excited States. J. Phys. Chem. 1982, 86, 1970−1976. (59) Lakowicz, J. R. Principles of Fluorescence Spectroscopy; Springer: New York, 1999.

(60) Hehre, W. J.; Ditchfield, R.; Pople, J. A. Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules. J. Chem. Phys. 1972, 56, 2257−2261. (61) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785−789. (62) O’Boyle, N. M.; Tenderholt, A. L.; Langner, K. M. cclib: A Library for Package-Independent Computational Chemistry Algorithms. J. Comput. Chem. 2008, 29, 839−845. (63) Würthner, F.; Kaiser, T. E.; Saha-Möller, C. R. J-Aggregates: From Serendipitous Discovery to Supramolecular Engineering of Functional Dye Materials. Angew. Chem., Int. Ed. 2011, 50, 3376− 3410. (64) Kuzmanich, G.; Simoncelli, S.; Gard, M. N.; Spänig, F.; Henderson, B. L.; Guldi, D. M.; Garcia-Garibay, M. A. Excited State Kinetics in Crystalline Solids: Self-Quenching in Nanocrystals of 4,4′Disubstituted Benzophenone Triplets Occurs by a Reductive Quenching Mechanism. J. Am. Chem. Soc. 2011, 133, 17296−17306. (65) Tsujii, Y.; Itoh, T.; Fukuda, T.; Miyamoto, T.; Ito, S.; Yamamoto, M. Multilayer Films of Chromophoric Cellulose Octadecanoates. Studied by Fluorescence Spectroscopy. Langmuir 1992, 8, 936−941. (66) Winnik, F. M.; Tamai, N.; Yonezawa, J.; Nishimura, Y.; Yamazaki, I. Temperature-Induced Phase Transition of PyreneLabeled(hydroxypropyl) Cellulose in Water: Picosecond Fluorescence Studies. J. Phys. Chem. 1992, 96, 1967−1972. (67) Sheldrick, G. A Short History of SHELX. Acta Crystallogr., Sect. A 2008, 64, 112−122. (68) Nüesch, F.; Moser, J. E.; Shklover, V.; Grätzel, M. Merocyanine Aggregation in Mesoporous Networks. J. Am. Chem. Soc. 1996, 118, 5420−5431. (69) Hu, B.; Gahungu, G.; Zhang, J. Optical Properties of the Phosphorescent Trinuclear Copper(I) Complexes of Pyrazolates: Insights from Theory. J. Phys. Chem. A 2007, 111, 4965−4973. (70) Hu, B.; Zhang, J. Theoretical Investigation on the White-Light Emission from a Single-Polymer System with Simultaneous Blue and Orange Emission. Polymer 2009, 50, 6172−6185. (71) Hu, B.; Zhang, J.; Chen, Y. Theoretical Investigation on the White-Light Emission from a Single-Polymer System with Simultaneous Blue and Orange Emission (Part II). Eur. Polym. J. 2011, 47, 208−224.

26820


Supramolecular Nano-Aggregates Based on Bis (Pyrene) Derivatives

Recommend Documents