Cages with Tunable Emission and Amino Acid Sensing - American

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Multicomponent Platinum(II) Cages with Tunable Emission and Amino Acid Sensing Mingming Zhang,*,† Manik Lal Saha,*,† Ming Wang,‡ Zhixuan Zhou,† Bo Song,∥ Chenjie Lu,§ Xuzhou Yan,† Xiaopeng Li,∥ Feihe Huang,⊥ Shouchun Yin,*,†,§ and Peter J. Stang*,† †

Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112, United States State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, Jilin 130012, P. R. China ∥ Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States § College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036, P. R. China ⊥ State Key Laboratory of Chemical Engineering, Center for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China ‡

S Supporting Information *

ABSTRACT: The syntheses, characterization, and emission properties of three tetragonal prismatic cages, 4a−4c, constructed from eight 90° Pt(II) acceptors, four linear dipyridyl ligands, and two tetraphenylethene (TPE)-based sodium benzoate ligands, are described. These cages are emissive in dilute solutions due to the metal-coordination-induced partial restriction of intramolecular rotation of their TPE units, while the dipyridyl moieties, which act as the pillars as well as the solvents, strongly influence these emissions. Specifically, cages 4a and 4b, bearing a 4,4′-dipyridine and a 1,2-di(4-pyridyl)ethylene as their pillar parts, respectively, display good emissions in common organic solvents at 485−493 nm that are derived from the TPE units. In contrast, cage 4c, with its BODIPY-based dipyridyl unit, exhibits two emission bands at 462−473 and 540−545 nm, originating from the TPE and BODIPY fluorophores, respectively. Moreover, cage 4b has been employed as a turn-on fluorescent sensor for thiol-containing amino acids via a self-destructive reaction, while the cage can also be regenerated via the addition of Pt(II) acceptors. The studies described herein not only enrich the ongoing research on fluorescent materials but also pave the way to prepare stimuli-responsive supramolecular coordination complexes.

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INTRODUCTION Light-emitting materials with tunable fluorescence properties are of interest due to their wide-ranging applications as chemical sensors, biological labels, organic light-emitting diodes, and so on.1 The covalent preparation of such materials often requires tedious and time-consuming chemical synthesis.2 In contrast, constructions via supramolecular chemistry, in particular metal-coordination driven self-assembly,3 benefit from fewer synthetic steps and afford highly diverse supramolecular coordination complexes (SCCs)4−6 with interesting photophysical properties. The well-defined geometry of these metallo-supramolecular structures provides precise control over the numbers, locations, and relative orientations of the chromophores in these highly concentrated chromophoric ensembles. Moreover, the interplay between the metal and ligand precursors sometimes endows the final constructs with unique properties which are not possessed by the individual components. For example, we reported a series of Pt(II)← pyridine coordination-based rhomboidal metallacycles that exhibited far red-shifted (ca. 80−100 nm) emissions in the visible region compared to the corresponding ligands.5a At the same time, the emission wavelengths of these supramolecular © 2017 American Chemical Society

constructs can be tuned by modulating the electron density of their donor building blocks. Lusby et al. prepared an Ir6L4 octahedral cage with luminescent properties, though the mononuclear metal complex itself is non-emissive.7 Nitschke and co-workers observed that the incorporation of multiple fluorophores into Fe(II)-based M4L6 cages can allow the detection of anions as well as provide white-light emission.8 However, at times the emissions of SCCs were significantly quenched either by the heavy atom effect of the transition metal ions or via intramolecular charge transfer process,9 suggesting that only an appropriate selection of building blocks can allow the construction of highly emissive SCCs. Tetraarylethylene derivatives are a class of specific fluorophores that are non-emissive in dilute solution but exhibit strong fluorescence in the aggregated state due to the restriction of molecular rotation of the aryl groups.10 This effect was termed aggregation-induced emission (AIE) by Tang and co-workers.10 Previously, we observed that the immobilization of tetraphenylethene (TPE)-based pyridyl ligands in metalloReceived: December 5, 2016 Published: March 23, 2017 5067

DOI: 10.1021/jacs.6b12536 J. Am. Chem. Soc. 2017, 139, 5067−5074

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Journal of the American Chemical Society

Figure 1. (a) Synthetic routes and cartoon representations of cages 4a, 4b, and 4c. 31P{1H} (b−e) and partial 1H NMR (f−k) spectra (121.4 or 400 MHz, CD2Cl2, 295 K) of 2 (b), 4a (c and g), 4b (d and i), 4c (e and k), 3a (f), 3b (h), and 3c (j).

supramolecular structures plays a similar role in limiting their molecular rotations, thereby furnishing highly emissive SCCs.6a Herein, we further explore this phenomenon and describe the preparation of three emissive tetragonal prismatic metallacages,

4a−4c, consisting of eight 90° Pt(II) acceptors, four dipyridyl ligands, and two sodium benzoate-decorated TPE units. Notably, the emission properties of these metallacages can be finely tuned by variation of the dipyridyl ligands as well as the 5068


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Figure 2. Experimental (red) and calculated (blue) ESI-TOF-MS spectra of 4a [M − 3OTf]3+ (a), 4b [M − 3OTf]3+ (b), and 4c [M − 3OTf]3+ (c).

to 7.72 ppm) as well as ethylene proton H5 (from 7.26 to 7.44 ppm) of 4b (Figure 1, spectra h and i). In the 1H NMR spectrum of 4c, signals for the pyridyl protons H6 (from 8.62 to 8.65 ppm) and H7 (from 7.14 to 7.17 ppm) displayed the downfield shifts, as expected, whereas the aromatic protons H10 (from 7.37 to 6.84 ppm) and H11 (from 7.26 to 6.84 ppm) and the methyl protons H8 (from 1.40 to 0.82 ppm), H9 (from 2.54 to 2.14 ppm), and H12 (from 2.45 to 2.41 ppm) shifted upfield (Figure 1, spectra j and k), likely due to the cage structure. ESITOF-MS, supports the putative stoichiometry (Figure 1) of these metallacages by showing isotopically well-resolved peaks at m/z = 2145.06, 2179.65, and 2591.76 (Figure 2), corresponding to the [M − 3OTf]3+ species of 4a−4c, respectively (where M represents the intact assembly). Molecular simulations (Figure 3) were performed to get further information about the structures of the metallacages

solvents. Cages 4a and 4b, with 4,4′-dipyridine and 1,2dipyridylethene units as the pillars, respectively, show good emission at 485−494 nm in a wide range of solvents such as DMSO, acetonitrile, acetone, dichloromethane, etc. At the same time, the presence of a 4,4-difluoro-4-bora-3a,4a-diaza-sindacene (BODIPY) dipyridyl derivative (3c) as the pillars endows the cage 4c with two distinct emission bands at 462− 475 and 540−545 nm, wherein the former displays the emission characteristics of the TPE units and the latter originates from the BODIPY fluorophores. Cage 4b is non-emissive in methanol/water (1/1, v/v), while the same solution strongly emits when thiol-containing amino acids, for instance cysteine and glutathione, are added. This allows the fluorescence sensing of these amino acids. The sensing follows a self-destructive mechanism, in which the cage is decomposed to give the TPE-based precursor which exhibits strong fluorescence in the same solvent mixture due to an AIE effect.10 Additionally, the cage was regenerated via the addition of Pt(II) acceptors, representing a novel way to create stimuliresponsive SCCs.

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RESULTS AND DISCUSSION Cage Preparation and Characterization. Cages 4a−4c (Figure 1a) were prepared in greater than 90% isolated yields by adopting a literature procedure,11 as outlined in the Experimental Section. The formation of these cages was established by multinuclear NMR spectroscopy (1H NMR and 31P{1H} NMR), electrospray ionization time-of-flight mass spectroscopy (ESI-TOF-MS), UV−vis spectroscopy, and fluorescence spectroscopy. For instance, the 31P{1H} NMR spectra (Figure 1, spectra c−e) exhibit two doublets of equal intensity with concomitant 195Pt satellites at 1.04 and −4.50 ppm for 4a, 1.09 and −4.38 ppm for 4b, and 0.89 and −4.54 ppm for 4c, supporting the formation of these discrete, chargeseparated metallacages.11 In the 1H NMR spectra of 4a, significant downfield shifts were observed for H1 (from 8.72 to 8.90 ppm) and H2 (from 7.57 to 8.03 ppm) (Figure 1, spectra f and g) as compared to the free pyridine ligand 3a, due to the coordination of the pyridyl units to the Pt(II) ions.11 Similar downfield shifts from the ligand 3b were also observed for the pyridyl protons H3 (from 8.61 to 8.68 ppm) and H4 (from 7.42

Figure 3. Simulated molecular models of 4a (a), 4b (b), and 4c (c) optimized by PM6 semiempirical molecular orbital methods. The hydrogen atoms and ethyl groups of the PEt3 were omitted for clarity.

4a−4c. All three cages are tetragonal prismatic structures where the TPE units, dipyridyl moieties, and 90° Pt(II) ions construct the faces, the pillars, and the corners, respectively. Using the distance between the Pt(II) centers, the length, width, and diameter for cages 4a−4c are computed as ca. 2.00, 1.75, and 3.80 nm, respectively. However, the heights of these cages are different, as expected: cage 4c has a higher value (1.94 nm) compared to those of cages 4a (1.12 nm) and 4b (1.34 nm). Photophysical Studies. These cages are stable in a series of solvents (Figure S15), including even some coordinating solvents like acetonitrile, DMSO, etc. This allows us to probe their photophysical properties in a wide range of solvents as shown in Figure 4. In dichloromethane, cage 4a has a broad absorption band at 282 nm and two shoulders at 320 and 361 nm, with molar absorption coefficients (ε) of 1.26 × 105, 7.41 5069


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Figure 4. (a,c,e) UV/vis absorption12 and (b,d,f) fluorescence spectra of cages 4a (a,b), 4b (c,d), and 4c (e,f) in different solvents (λex = 365 nm, c = 10.0 μM).

× 104, and 2.60 × 104 M−1 cm−1, respectively (Figure 4a). Cage 4b shows a sharp absorption peak centered at 318 nm and two shoulders at 335 and 368 nm, with ε = 2.09 × 105, 1.27 × 105, and 6.51 × 104 M−1 cm−1, respectively (Figure 4c), while two broad absorption bands at 278 and 319 nm and a sharp absorption peak at 520 nm, with ε = 1.42 × 105, 1.09 × 105, and 2.51× 105 M−1 cm−1, respectively (Figure 4e), were observed for 4c in the same solvent. The UV−vis spectra of these cages in six other solvents, as shown in Figure 4, are similar to the spectrum of their dichloromethane solution, suggesting that these solvents have negligible influence on the absorbance properties.12 We suppose that the absorption bands in the range of 350−370 nm result from the TPE derivatives,10 while the strong absorption of the BODIPY chromophore in cage 4c is characterized by the peak at 520 nm.13 Since the TPE groups are partially rigidified in these cages and the rotation of their aromatic rings is limited by the metalcoordination bonds, we anticipated that these structural characteristics endow the cages with good fluorescence properties. The emission spectra of the cages in seven different solvents are shown in Figure 4. In polar aprotic solvents such as DMSO, DMF, and acetonitrile, cages 4a and 4b show strong emission at around 493 nm, due to the emission of the TPE groups.10 Cage 4c exhibits two strong emission peaks at around 472 and 544 nm, due to the emission of both the TPE10 and BODIPY13 groups, respectively. In less polar aprotic solvents including acetone, dichloromethane, and chloroform, as well as

polar protic solvent, such as methanol, these cages show only moderate emissions. The quantum yields (ΦF) of 4a−4c (Table 1) were also determined in different solvents: in polar Table 1. Emission Data of Cages 4a−4c in Different Solvents 4a

4b

4c

solvent

λem (nm)

ΦF (%)

λem (nm)

ΦF (%)

λem (nm)

ΦF (%)

DMSO DMF acetonitrile acetone methanol dichloromethane chloroform

493 494 491 488 488 491 489

25.8 24.3 24.7 11.1 1.37 0.61 0.91

492 493 493 490 491 490 485

19.1 21.4 18.7 7.10 0.93 0.16 0.63

473, 475, 472, 469, 470, 462, 472,

13.9 12.2 11.9 9.62 3.09 4.46 2.47

545 544 540 541 540 543 543

aprotic solvents, their ΦF values were 25%, 20%, and 13%, respectively, representing the highest values among all of the solvents. These data suggest that the emission wavelengths of these cages depend largely upon their dipyridyl ligands, while their quantum yields can be finely tuned by the variation of solvents. We also sought to rigidify the cages by the encapsulation of a guest as this might further enhance their emissions. Consequently, we studied the host−guest chemistry of these cages using anthracene and pyrene as the guests. However, no 5070


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Figure 5. Fluorescence spectra of cage 4b (10 μM) after 5 min upon the addition of increasing concentrations of glutathione (a) and cysteine (c) and the emission intensities at 500 nm as a function of glutathione (b) and cysteine (d) concentration. Each spectrum was collected in methanol/ water (1/1, v/v) with λex = 365 nm. Insets: photographs of 10 μM cage 4b before (left) and after (right) the addition of 160 μM thiol-containing amino acids in methanol/water (1/1, v/v) upon excitation at 365 nm using a UV lamp at 298 K.

glutamate, and histidine which show negligible emission enhancement (Figure S20). These data suggest that 4b can be considered as a turn-on sensor for thiol-containing amino acids. To understand the mechanism of the above sensing, 1H NMR titration experiments were performed (Figures 6, S22− S27) by gradually adding cysteine or glutathione to a DMSO solution of cage 4b. After the addition of 2 equiv of the amino acids respectively with regard to the initial amount of the cage, the diagnostic α and β pyridyl protons H3 and H4 of 4b split into two sets, in which the set corresponding to the cage was present as the major amount, while the minor set appeared in a region similar to that of the free ligand 3b, suggesting that these amino acids can decompose the cage and release its precursors. This minor set of peaks gradually increased in amount as the titration advanced, and became the major set in the presence of 6 equiv of the amino acids. Moreover, the 1H NMR spectrum of cage 4b along with 8 equiv of amino acid (Figure 6f) equals the sum of the individual spectra of 3b (Figure 6h) and 5 (Figure 6g), indicating that the cage is now totally destroyed. This destruction was also confirmed by the corresponding 31 1 P{ H} NMR spectrum in which the two characteristic doublet peaks of 4b disappeared (Figure S24). The complexation between Pt(PEt3)2(OTf)2 and the amino acids was also investigated by 1H NMR (Figures S28 and S29) and ESITOF-MS spectroscopies (Figures S30 and S31), suggesting a 1:1 binding stoichiometry between Pt(PEt3)2(OTf)2 and the respective amino acids. The cage was regenerated by the addition of Pt(II) acceptors (Figure S32), suggesting that the thermodynamic stability of the Pt-amino acids complexes are more than that of the cage. The addition of 2-mercaptoethanol into the solution of 4b provides further information for the formation of complexes between Pt(II) and the amino acids.

host−guest complexes either in pure acetone or in an acetone/ water mixture were observed (see Figure S16). Thiol-Containing Amino Acid Recognition. Given the strong binding affinity of thiols to Pt(II) ions,14 we explored the use of cage 4b as a turn-on sensor for thiol-containing amino acids, which are crucial functional groups in biology.15 After examining a series of solvent compositions we chose a methanol/water (1/1, v/v) mixture for the chemo-sensing because in this medium the cage is nearly non-emissive (Figure S17), which makes it an ideal candidate for “turn-on” fluorescence sensing.16 The emissions of the other two cages are not fully quenched in this medium, indicating that the pillars likely have an influence on the quenching.10 Time-dependent fluorescence spectra of 4b (10 μM) with 1 mM glutathione (Figure S18) were collected in methanol/ water (1/1, v/v): as the reaction proceeded, the emission at 500 nm increased and reached a maximum value after 5 min, indicating that the system reached its equilibrium state at this point. Next, we studied the interactions of cage 4b with thiolcontaining amino acids (glutathione and cysteine) by fluorescence titration experiments (Figure 5). Upon the gradual addition of the amino acids into a solution of 4b (10 μM), the fluorescence emission intensity at 500 nm dramatically increased in the concentration range of 2 μM to 80 μM, while only a small increase was observed when the concentration exceeds 120 μM (Figure 5). The fluorescence intensity is linearly proportional to the concentration of the amino acids in the 0−80 μM range (Figure 5b), indicating that cage 4b is suitable for quantitative detection of these amino acids. The detection limits for glutathione and cysteine are 1.89 × 10−7 and 2.78 × 10−7 M (S/N = 3), respectively. Control experiments were performed using other amino acids such as glycine, alanine, arginine, lysine, serine, leucine, isoleucine, 5071


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Figure 6. (a) Cartoon representation of the self-destructive mechanism. (b−h) Partial 1H NMR spectra (400 MHz, CD3SOCD3, 295 K) of 1.0 mM cage 4b (b) by the addition of 2.0 (c), 4.0 (d), 6.0 (e), and 8.0 mM (f) cysteine; spectrum of 5 (g); and spectrum of 3b (h).

The cage remains stable even when 100 equiv of 2mercaptoethanol was added (Figure S33), indicating that both the thiol group and the carboxylic group act as coordinative ligands with Pt(II). We also prepared compound 5 and recorded its emission spectrum in a methanol/water (1/ 1, v/v) mixture (Figure S34). These data suggest that it is emissive in this medium because of the AIE effect. Based on these data, we propose a self-destructive mechanism (Figure 6a) for the sensing. Specifically, the amino acids act as better ligands for the Pt(II) ions, leading

to the destruction of the cage as well as formation of mononuclear Pt(II)-amino acid complexes. This then releases the emissive ligand 5, which acts as the indicator in the sensing of the thiol-containing amino acids.

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CONCLUSION In summary, we have prepared and spectroscopically characterized three different tetragonal prismatic Pt(II) metallacages, 4a−4c, which contain two benzoate-TPE groups as the faces, four dipyridyl ligands as the pillars, and eight 90° Pt(II) 5072


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was redissolved in acetone (1.0 mL) and filtered, and the filtrate was poured into ethyl ether (10 mL) to give a precipitate, which was collected by centrifugation to give 4b (8.30 mg, 95%) as a pale yellow powder. The sample was dissolved in CD2Cl2 for characterization. 1H NMR (400 MHz, CD2Cl2, 295 K): 8.66−8.72 (m, 16H), 7.70−7.78 (m, 32H), 7.44 (s, 8H), 7.43 (d, J = 8.3 Hz, 16H), 7.30 (d, J = 8.3 Hz, 16H), 7.10 (d, J = 8.3 Hz, 16H), 1.70−2.05 (m, 96H), 1.15−1.36 (m, 144H). 31P{1H} NMR (CD2Cl2, 295 K, 121.4 MHz) δ (ppm): 1.09 ppm (d, 2JP−P = 21.2 Hz, 195Pt satellites, 1JPt−P = 3420 Hz), − 4.38 ppm (d, 2JP−P = 21.2 Hz, 195Pt satellites, 1JPt−P = 3420 Hz). ESI-TOFMS: m/z 1595.37 [4b − 4OTf]4+, 2179.65 [4b − 3OTf]3+. Self-Assembly of 4c. 1 (2.25 mg, 2.50 μmol), 2 (7.30 mg, 10.0 μmol), and 3c (2.47 mg, 5.00 μmol) were mixed in a 1:4:2 molar ratio and dissolved in acetone/water (1.0 mL, 4:1, v/v). The whole reaction mixture was heated at 50 °C for 12 h and then cooled to room temperature. The solvent was removed by nitrogen flow. The residue was redissolved in acetone (1.0 mL) and filtered, and the filtrate was poured into ethyl ether (10 mL) to give a precipitate, which was collected by centrifugation to give 4c (9.47 mg, 92%) as a red powder. The sample was dissolved in CD2Cl2 for characterization. 1H NMR (400 MHz, CD2Cl2, 295 K): 8.61−8.70 (m, 16H), 7.58 (d, J = 8.3 Hz, 16H), 7.24−7.35 (m, 48H), 7.17 (d, J = 5.8 Hz, 16H), 6.83−6.87 (m, 16H), 2.41 (s, 12H), 2.14 (s, 24H), 1.70−2.05 (m, 96H), 1.10−1.40 (m, 144H), 0.81 (s, 24H). 31P{1H} NMR (CD2Cl2, 295 K, 121.4 MHz) δ (ppm): 0.89 ppm (d, 2JP−P = 19.2 Hz, 195Pt satellites, 1JPt−P = 3440 Hz), − 4.54 (d, 2JP−P = 19.2 Hz, 195Pt satellites, 1JPt−P = 3440 Hz). ESI-TOF-MS: m/z 1907.91 [4c − 4OTf]4+, 2591.76 [4c − 3OTf]3+.

acceptors as the corners. Due to the metal-coordinationinduced partial restriction of intramolecular rotations of their TPE units, these cages are emissive. The emission properties could be further tuned by different dipyridyl ligands as well as by the solvents. Furthermore, a self-destructive mechanism was demonstrated for the thiol-containing amino acid sensing properties by cage 4b in methanol/water (1/1, v/v). These emissive metallacages not only provide new types of emissive materials with tunable emission properties but also give insights into the stimuli-responsive destruction of these cages, making them potential candidates for light-emitting materials, chemosensors, and smart drug delivery systems.

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EXPERIMENTAL SECTION

Materials and Methods. All reagents were commercially available and used as supplied without further purification. Deuterated solvents were purchased from Cambridge Isotope Laboratory (Andover, MA). 1,3,5,7-Tetramethyl-2,6-diiodide-8-p-methylbenzene-BODIPY,17 1,18 and 219 were prepared according to the literature procedures. NMR spectra were recorded on a Varian Unity 300 or 400 MHz spectrometer. 1H and 13C NMR chemical shifts are reported relative to residual solvent signals, and 31P{1H} NMR chemical shifts are referenced to an external unlocked sample of 85% H3PO4 (δ = 0.0). Mass spectra were recorded on a Micromass Quattro II triplequadrupole mass spectrometer using electrospray ionization with a MassLynx operating system. The UV−vis experiments were conducted on a Hitachi U-4100 absorption spectrophotometer. The fluorescent experiments were conducted on a Hitachi F-7000 fluorescence spectrophotometer. Quantum yields were determined using quinine sulfate at 365 nm (ΦF = 56%). The quantum yields were calculated from comparisons of the integrated signals of the excitation and emission signals using the FluorEssence software package (Horiba). Synthesis of 3c. To 1,3,5,7-tetramethyl-2,6-diiodide-8-p-methylbenzene-BODIPY (296 mg, 0.5 mmol) were added 4-pyridylboronic acid (184 mg, 1.5 mmol) in toluene (40 mL), aqueous K2CO3 (207 mg, 1.5 mmol) solution (10 mL), and ethanol (10 mL). Pd(PPh3)4 (69 mg, 0.06 mmol) was then added, and the reaction mixture was stirred at 80 °C for 48 h under nitrogen atmosphere. After cooling to room temperature, the product was concentrated and purified by flash column chromatography with CH2Cl2/CH3OH (70:1, v/v) as the eluent to afford compound 5c (136 mg, 55%) as red powder. 1H NMR (400 MHz, CD2Cl2, 295 K): 8.62 (d, J = 5.8 Hz, 4H), 7.37 (d, J = 7.9 Hz, 2H), 7.26 (d, J = 7.9 Hz, 2H), 7.14 (d, J = 5.8 Hz, 4H), 2.54 (s, 6H), 2.45 (s, 3H), 1.40 (s, 6H). 13C NMR (100 MHz, CD2Cl2, 295 K): 153.8, 149.8, 141.6, 140.1, 139.6, 131.6, 130.1, 127.6, 124.9, 21.1, 13.1, 12.6. HR-MS: m/z 493.2373 ([3c + H] +, calcd. for [C30H28BF2N4]+, 493.2375. Self-Assembly of 4a. 1 (2.25 mg, 2.50 μmol), 2 (7.30 mg, 10.0 μmol), and 3a (0.78 mg, 5.00 μmol) were mixed in a 1:4:2 molar ratio and dissolved in acetone/water (1.0 mL, 4:1, v/v). The whole reaction mixture was heated at 50 °C for 12 h and then cooled to room temperature. The solvent was removed by nitrogen flow. The residue was redissolved in acetone (1.0 mL) and filtered, and the filtrate was poured into ethyl ether (10 mL) to give a precipitate, which was collected by centrifugation to give 4a (8.43 mg, 98%) as a pale yellow powder. 1H NMR (400 MHz, CD2Cl2, 295 K): 8.90 (d, J = 6.6 Hz, 16H), 8.03 (d, J = 6.6 Hz, 16H), 7.79 (d, J = 8.3 Hz, 16H), 7.42 (d, J = 8.3 Hz, 16H), 7.25 (d, J = 8.3 Hz, 16H), 7.07 (d, J = 8.3 Hz, 16H), 1.65−2.05 (m 96H), 1.13−1.40 (m, 144H). 31P{1H} NMR (CD2Cl2, 295 K, 121.4 MHz) δ (ppm): 1.04 ppm (d, 2JP−P = 21.4 Hz, 195Pt satellites, 1JPt−P = 3402 Hz), − 4.50 ppm (d, 2JP−P = 21.4 Hz, 195Pt satellites, 1JPt−P = 3402 Hz). ESI-TOF-MS: m/z 1572.17 [4a − 4OTf]4+, 2145.06 [4a − 3OTf]3+. Self-Assembly of 4b. 1 (2.25 mg, 2.50 μmol), 2 (7.30 mg, 10.0 μmol), and 3b (0.91 mg, 5.00 μmol) were mixed in a 1:4:2 molar ratio and dissolved in acetone/water (1.0 mL, 4:1, v/v). The whole reaction mixture was heated at 50 °C for 12 h and then cooled to room temperature. The solvent was removed by nitrogen flow. The residue

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.6b12536. Characterization data (NMR, ESI-TOF-MS, fluorescence spectra), including Figures S1−S34 (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] *[email protected] *[email protected] ORCID

Mingming Zhang: 0000-0003-3156-7811 Manik Lal Saha: 0000-0003-2242-3007 Ming Wang: 0000-0002-5332-0804 Zhixuan Zhou: 0000-0001-8295-5860 Bo Song: 0000-0002-4337-848X Chenjie Lu: 0000-0002-3000-1835 Xiaopeng Li: 0000-0001-9655-9551 Feihe Huang: 0000-0003-3177-6744 Shouchun Yin: 0000-0003-1086-1755 Peter J. Stang: 0000-0002-2307-0576 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS P.J.S. thanks National Science Foundation (Grant 1212799) for financial support. F.H. and P.J.S. thank National Natural Science Foundation of China (21620102006) for financial support. X.L. thanks the National Science Foundation (CHE1506722) and PREM Center of Texas State University (DMR1205670) for financial support. S.Y. thanks National Natural 5073


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Science Foundation of China (21574034, 21274034) and Zhejiang Provincial Natural Science Foundation of China (LY16B040006) for financial support. Computational resources are gratefully acknowledged from the Center for High Performance Computing (CHPC) at the University of Utah.

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