Selective Extraction of C70 by a Tetragonal Prismatic Porphyrin Cage

Article abstract of DOI:10.1021/jacs.8b08555

Along with the advent of supramolecular chemistry, research on fullerene receptors based on noncovalent bonding interactions has attracted a lot of attention. Here, we present the design and synthesis of a cationic molecular cage: a cyclophane composed of two tetraphenylporphyrins, bridged face-to-face by four viologen units in a rhomboid prismatic manner. The large cavity inside the cage, as well as the favorable donor-acceptor interactions between the porphyrin panels and the fullerene guests, enables the cage to be an excellent fullerene receptor. The 1:1 host-guest complexes formed between the cage and both C₆₀ and C₇₀ were characterized in solution by HRMS and NMR, UV-vis and fluorescence spectroscopies, and confirmed in the solid state by single-crystal X-ray diffraction analyses. The results from solution studies reveal that the cage has a much stronger binding for C₇₀ than for C₆₀, resulting in a selective extraction of C₇₀ from a C₆₀-enriched fullerene mixture (C₆₀/C₇₀ = 10/1), demonstrating the potential of the cage as an attractive receptor for fullerene separation.

Full text of DOI:10.1021/jacs.8b08555

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Article
Selective Extraction of C70 by a Tetragonal Prismatic Porphyrin Cage
Yi Shi, Kang Cai, Hai Xiao, Zhichang Liu, Jiawang Zhou, Dengke Shen, Yunyan Qiu, Qinghui Guo,
Charlotte Stern, Michael R. Wasielewski, François Diederich, William A. Goddard, and J. Fraser Stoddart
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b08555 • Publication Date (Web): 28 Sep 2018
Downloaded from http://pubs.acs.org on September 28, 2018
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Selective Extraction of C by a
70
Tetragonal Prismatic Porphyrin Cage
Yi Shi , Kang Cai , Hai Xiao , Zhichang Liu , Jiawang Zhou , Dengke Shen , Yunyan Qiu ,
1,#
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Qinghui Guo , Charlotte Stern, Michael R. Wasielewski , François Diederich ,
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William A. Goddard III , and J. Fraser Stoddart
*
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Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
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Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA.
Institute of Natural Sciences, Westlake Institute for Advanced Study, Westlake University, No. 18 Shilongshan
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Road, Xihu District, Hangzhou 310064, P. R. China.
Laboratory of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland.
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Institute for Molecular Design and Synthesis, Tianjin University, Tianjin 300072, P. R. China.
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School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.
*
Eꢀmail: stoddart@northwestern.edu
MAIN TEXT
*Correspondence Address
Professor J Fraser Stoddart
Department of Chemistry
Northwestern University
2145 Sheridan Road
Evanston, IL 60208ꢀ3113 (USA)
Tel: (+1)ꢀ847ꢀ491ꢀ3793
EꢀMail: stoddart@northwestern.edu
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ABSTRACT: Along with the advent of supramolecular chemistry, research on fullerene
receptors based on noncovalent bonding interactions has attracted a lot of attention. Here, we
present the design and synthesis of a cationic molecular cage – a cyclophane composed of two
tetraphenylporphyrins, bridged faceꢀtoꢀface by four viologen units in a rhomboid prismatic
manner. The large cavity inside the cage, as well as the favorable donorꢀacceptor interactions
between the porphyrin panels and the fullerene guests, enables the cage to be an excellent
fullerene receptor. The 1:1 hostꢀguest complexes formed between the cage and both C and C
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were characterized in the solution by HRMS and NMR, UVꢀVis and fluorescence spectroscopies,
and confirmed in solidꢀstate by singleꢀcrystal Xꢀray diffraction analyses. The results from
solution studies reveal that the cage has a much stronger binding for C than for C , resulting in
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a selective extraction of C from a C ꢀenriched fullerene mixture (C /C =10/1), demonstrating
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the potential of the cage as an attractive receptor for fullerene separation.
■
INTRODUCTION
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Since their discovery in 1985, fullerenes have attracted considerable attention on account of, not
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only their unique spheroidal structures, but also because of their numerous applications in
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materials science. Along with the advent of supramolecular chemistry, which marked a
departure from the preoccupation of chemists with covalent bonds towards an understanding of
the weak intermolecular interactions, research on fullerene receptors on the basis of noncovalent
bonding interactions became an active area of research in the recent decades. To date, a number
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of covalently and supramolecularly assembled receptors, including pincer / bowl types, box /
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ring types, and cage types, have been designed as hosts for fullerenes. Among them, molecular
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cages with suitable cavity sizes demonstrate stronger binding to the spherically shaped fullerene
guests as a result of the enhanced geometric match of these allꢀcarbon molecules with threeꢀ
dimensional (3D) cavities. However, hosts, which feature both high affinity and good selectivity
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towards a certain fullerene homologue, are limited because of the geometrical similarities of the
carbon spheres.
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Previously, we have described the evolution of the Ex Boxm family, the boxꢀlike
tetracationic cyclophanes consisting of two πꢀelectronꢀpoor bipyridinium units, which are
capable of binding with various aromatic guests when the size and electronic constitution are
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appropriately matched. A variety of mechanically interlocked molecules with distinctive
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topological or electronic properties, as well as molecular machines, have been developed based
on these tetracationic cyclophanes. Recently, we have extended the “twoꢀdimensional”
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macrocyclic boxes into “threeꢀdimensional” molecular cages and synthesized ExCage and
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BlueCage as powerful receptors for polycyclic aromatic hydrocarbons (PAHs). In order to
extend the cationic cyclophane family and explore the limits of this chemistry, we have now
introduced porphyrin units, which have been demonstrated as versatile functional units in areas
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such as catalysis, selfꢀassembly, and photosynthesis, as new building blocks to construct a
cationic porphyrin cage molecule. In addition, the use of porphyrin units will extend significantly
the dimensions of the newly developed cyclophanes, thus enabling the encapsulation of large
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guests such as fullerenes or polyoxometalates. Herein, we describe how we have designed and
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synthesized a novel molecular cage TPPCage , a compound composed of two
tetraphenylporphyrins bridged faceꢀtoꢀface by four viologen units in a rhomboid prismatic
manner. The enlarged cavity inside the cage, along with their electronꢀrich πꢀconjugated
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porphyrin panels, enables TPPCage to act as an excellent host for the fullerenes C and C .
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Notably, the results of solution studies reveal that TPPCage has a much stronger binding
affinity for C70 than for C , resulting in a selective extraction of C from a C ꢀenriched
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fullerene mixture (C /C =10/1), demonstrating the potential of TPPCage as an attractive
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receptor for fullerene separation.
■ RESULTS AND DISCUSSION
Synthesis and Characterization of TPPCage•8PF . Receptor TPPCage•8PF was synthesized
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(Scheme 1) using a TBAIꢀcatalyzed ringꢀclosure strategy with bzTPP and TB•4PF as starting
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materials. TB•4PF was derived from bzTPP by substitution of the bromines with bipyridine.
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The synthesis overall was accomplished through S 2 reactions in three steps from commercially
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available starting materials. Pure TPPCage•8PF was obtained from the reaction mixture
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directly by collecting the precipitate, followed by counterion exchange (NH PF /H O) and
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bypassing the use of chromatography.
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TPPCage•8PF was characterized in solution by NMR spectroscopy. Each signal in the H
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(
Figure 1a) and C NMR (Figure 1b) spectra was assigned on the basis of a series of twoꢀ
dimensional (2D) NMR spectra including COSY, NOESY, HSQC, and HMBC. The simplicity
of the spectra concurs with the high D symmetry expected for a tetragonal prismatic cage. In
4h
addition, HRMS shows the desired molecular ion peaks at m/z 1413.8092 (calcd for
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C H F N P : m/z = 1413.8095 [M – 2 PF ] ), an observation which confirms the formation
136 100 36 16
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of TPPCage•8PF6.
Solid-State Characterization of TPPCage•8PF . In order to obtain the solidꢀstate structure of
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the cage compound and its degree of preorganization for hostꢀguest chemistry, single crystals
i
were grown by slow vapor diffusion of Pr O into a solution of TPPCage•8PF in MeCN (0.6
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mM) over the course of 4 days. The solidꢀstate structure (Figure 2a) which is commensurate with
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the nanocage TPPCage crystallizing in the P2 /c space group, consists of two parallel mesoꢀ
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tetraphenylporphyrins linked by four viologen units. The distance between the two porphyrin
panels was found to be 12.2 Å. In order to minimize the torsional strain and also reduce the free
space, while enhancing the crystal packing density, the four mesoꢀmetaphenylene connectors to
the viologen pillars are not oriented perpendicular to the porphyrin planes, but rather adopt an
angle of 131°. Further evidence in support of the cage’s prismatic structure (Figure S22) comes
from a diffusionꢀordered spectroscopy / nuclear magnetic resonance (DOSY NMR) experiment.
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DOSY NMR provides a diffusion coefficient D of 2.12 × 10 cm s , corresponding to a
hydrodynamic diameter of 24.0 Å in solution, and is commensurate with the 24.5 Å diagonal
distance from the metaꢀphenylene moiety located at the topꢀleft corner to the other metaꢀ
phenylene moiety located at the bottomꢀright corner present in the solidꢀstate structure. Although
the “open window” of the cage is measured to be 8.5 Å (distance between two viologen units),
which is slightly smaller than the van der Waals diameter (10.1 Å) of a C60 molecule, we
envision that the flexibility resulting from the rotation of the corner mesoꢀmetaphenylene rings
and/or the adjustment of the torsional angles encompassing the CH linkers will allow larger
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guests to be encapsulated in the cavity.
Fullerene Encapsulation – Solution Studies. The large void volume inside the cage – in
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addition to the wellꢀknown affinity of porphyrin units for fullerenes – establishes favorable
donorꢀacceptor interactions, and ensures that the cage acts as a good fullerene receptor. The
encapsulation of fullerenes occurs upon the addition of solid C or C to a solution of
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TPPCage•8PF in DMFꢀ
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d7, followed by sonication for 2 h at room temperature. The resulting 1:1 complexes were
characterized in solution by HRMS, and by NMR, UVꢀVis and fluorescence spectroscopies.
In the case of C encapsulation, HRMS reveals the desired peak at m/z 1774.3122, which
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corresponds to the 1:1 hostꢀguest complex C ⊂TPPCage•8PF after loss of counterions (calcd.
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for C H F N P : m/z = 1774.3112 [M – 2 PF ] ). More evidence comes from the H NMR
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spectrum (~1 m
M
solution of TPPCage•8PF in DMFꢀd ), wherein (Figure 3a) two sets of
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signals are present on account of slow hostꢀguest exchange at room temperature. By comparison
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with the H and C NMR spectra (Figure 3) of C and the empty cage TPPCage•8PF , the
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spectra of the postꢀsonication mixture indicate clearly that one set of signals corresponds to the
empty cage TPPCage•8PF , while a second set of signals can be assigned to the
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C ⊂TPPCage•8PF complex. The most significant change in chemical shift occurs for the
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resonances H (Figure 3a; for labeling of the cage atoms, see Figure 1) and C (Figure 3b). As
b
b
1
indicated by the red arrows, the H NMR resonance for H shifts upfield from 8.22 ppm in the
b
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empty TPPCage•8PF to 7.42 ppm in the C ⊂TPPCage•8PF complex, while the C NMR
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resonance of C is upfield shielded from 136.1 ppm in the empty TPPCage•8PF to 132.4 ppm
b
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in the C ⊂TPPCage•8PF complex. In contrast, resonances of all other protons and carbons
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associated with the metaꢀphenylene units are not shifted to any great extent. This observation
suggests that the chemical environment inside the cage is altered as a result of the encapsulation
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of C by TPPCage . In addition, the C NMR resonance for C in the complex is also shifted
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upfield by approximately 4 ppm, from 144.0 to 139.9 ppm, an observation which confirms the
formation of the C ⊂TPPCage•8PF complex. It is noteworthy that incomplete inclusion of C
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in TPPCage was observed, even when a large excess of C was added to a solution of
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TPPCage•8PF in DMFꢀd , This observation can be ascribed to the low concentration of C in
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a saturated DMF solution, precluding the possibility of driving the equilibrium towards the
complete formation of the C ⊂TPPCage•8PF complex. This situation, however, provides us
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with an easy method to measure the binding constant of TPPCage•8PF with C directly from
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integration of the H NMR spectrum of the solution containing a mixture of empty TPPCage
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and C ⊂TPPCage complex.
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The concentration of C60 in the saturated DMF solution was readily measured by UV
‒
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absorption spectroscopy to be [C ] = 1.58 ×10 M, allowing us to obtain the concentration of
60
free C guest in the solution containing the cage compound. On account of the slowꢀexchange
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between the C ⊂TPPCage complex and free TPPCage , signals for both the complex and
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empty cage are observed, allowing us to measure directly the ratio of the two components by H
NMR integration. As a consequence, the average of three integrated ratios obtained from the
encapsulation of C using three TPPCage•8PF solutions with different absolute concentrations
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‒1
resulted (Table S2) in an association constant, K = (4.5 ± 0.4) × 10 M . This moderately weak
a
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binding is presumably attributed to the imperfect match in size between TPPCage and C60
which is a little too small to fill the cage cavity.
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After gaining insight into the nature of the encapsulation between TPPCage and C , we
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turned our attention to the larger fullerene C , which we expected to form a stronger 1:1
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+
complex with TPPCage . In contrast with C encapsulation, in which two sets of signals can
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be identified in the H NMR spectrum (in DMFꢀd at 298 K, ~1 mM for TPPCage•8PF ), only
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one set of signals in the case of both H (Figure 4a) and C (Figure 4b) NMR spectra are
observed. This observation suggests that all the cage receptors are saturated with C in slow
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exchange on the NMR timescale (Figure S15), indicating an enhanced affinity of the TPPCage
towards the fullerene. As in the case of C ⊂TPPCage•8PF , the resonances for H – shifted
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upfield from 8.22 to 7.65 ppm, and that for C – shifted upfield from 136.1 to 132.8 ppm – move
b
the most when compared with the resonances for other protons or carbons at the corner mesoꢀ
phenylene units – as indicated by red arrows – an observation which suggests the chemical
environment inside the cage is changed as a result of the encapsulation of C by TPPCage•8PF .
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The encapsulation also results (Table S1) in the upfield shift of the five C NMR signals of C
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HRMS Data gives m/z 1834.3094, which corresponds to C ⊂TPPCage•8PF with counterion
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loss (calcd for C H F N P : m/z = 1834.3112 [M – 2 PF ] ), an observation which confirms
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the formation of the C ⊂TPPCage•8PF complex.
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Preliminary results from H NMR binding studies suggest that the binding constant of
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TPPCage•8PF to C is larger than 1.6 × 10 M , based on the assumption that the ratio of
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C ⊂TPPCage•8PF to TPPCage•8PF is over 20/1 according to the error associated with the
70
6
6
NMR spectroscopic technique, while the concentration of C in a saturated DMF solution was
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‒
4
measured as 1.2 × 10 M by UVꢀVis absorption. Accurate measurements of the binding constant
were carried out (Figure 5) by UV titration of TPPCage•8PF with a C solution in DMF. The
6
70
formation of the C ⊂TPPCage•8PF complex is characterized by a substantial decrease in
7
0
6
intensity at 419 nm and the slight red shift (3 nm) of the Soret band of the porphyrin in
comparison with that of TPPCage•8PF itself. As a result, the binding constant was determined
6
5
‒1
to be (2.4 ± 0.2) × 10 M in DMF on the basis of a 1:1 binding mode.
In addition, the fluorescence quantum yields of TPPCage•8PF , C ⊂TPPCage•8PF , and
6
60
6
C ⊂TPPCage•8PF were found to be 1.20%, 0.48%, and 0.52%, respectively. The significant
70
6
quenching of emission in fullerene⊂TPPCage•8PF complexes can be ascribed to the
6
intermolecular electron transfer from the excitedꢀstate porphyrin planes to the fullerene guests,
demonstrating the encapsulation of fullerenes by TPPCage•8PF6.
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On account of the shape persistency of the cage, DOSY NMR experiments (Figure S23 and
S24) give identical hydrodynamic diameters for the hostꢀguest complexes and the free cage, i.e.,
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+
8+
24.2 Å for both the C ⊂TPPCage and C ⊂TPPCage complexes – and similar (24.0 Å from
60
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DOSY) to that for the empty cage TPPCage•8PF , indicating that the molecular entity does not
6
change its size on addition of the fullerenes.
X-Ray Superstructures of the Fullerene⊂TPPCage•8PF Complexes. In order to gain further
6
insight into the coꢀconformational differences between the hostꢀguest complexes formed with
i
C and C , single crystals were grown by slow vapor diffusion of Pr O into a mixture of the
60
70
2
fullerenes and TPPCage•8PF in DMF/PhMe (1/1). It transpires (Figure 2b and 2c) that the cage
6
is no longer oblique. In order to achieve stronger interactions with the fullerene guests, the cage
becomes twisted and the two porphyrin panels form an eclipsed sandwich, trapping the carbon
spheres. In the C complex (space group C2/c), the cage is a distorted tetragonal antiprismatic
6
0
with an angle between the two porphrin planes of 58°. In the C complex (space group P 21),
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0
3
the geometry is only weakly distorted from being tetragonal antiprismatic and the angle between
the two porphyrin planes is 44°, near the ideal 45°. These coꢀconformational changes compared
to that of the free host expose a much larger surface area of the porphyrins and the viologen
bridges to the fullerenes, establishing much larger [π•••π] interactions. Notably, the twist endows
the hostꢀguest complex with axial chirality, resulting (Figure S27) in a racemic mixture upon
molecular packing. XꢀRay diffraction analysis also reveals that the heights of the cages in the
8
+
8+
C ⊂TPPCage and C ⊂TPPCage complexes only increase slightly by 0.2 and 0.5 Å,
60
70
8
+
respectively, while the diameters of the complexes are compressed from 24.0 Å (TPPCage ) to
8+
8+
2
1.8 Å (C ⊂TPPCage ) and to 21.9 Å (C ⊂TPPCage ). These minor differences in shape
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70
agree with DOSY NMR results, demonstrating the high degree of preorganization of this threeꢀ
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dimensional cage molecule. The distances between porphyrin panels and fullerene guests were
8
+
8+
measured as 2.64 Å and 2.48 Å in the cases of C ⊂TPPCage and C ⊂TPPCage ,
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70
respectively, implying strong [π•••π] interactions between the two porphyrin platforms and the
fullerenes. These distances are shorter than the normal distance (~3.4 Å) for [π•••π] stacking
interactions. These shorter distances can be attributed to the hollow porphyrin panel. [π•••π]
Interactions are largely concentrated on the outer perimeters of the porphyrin macrocycles. In
addition, the complex is stabilized by multiple [C–H•••π] interactions between the fullerene
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guest and the protons H pointing toward the cage cavity. The shortest fullereneꢀtoꢀviologen
b
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+
8+
distances were measured as 3.30 Å in C ⊂TPPCage and 2.94 Å in C ⊂TPPCage ,
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0
70
18
revealing that [cation•••π] interactions can still be operative. These short distances are actually
quite remarkable as the electropositive viologen pillars and fullerene guests which also possess
electropositive electrostatic potential surfaces are approaching to each other, suggesting
substantial contributions from [cation•••π] interactions.
It is conceivable that the superstructures of the host−guest complexes differ in the solid state
and solution phases. Therefore, we carried out density functional theory (DFT) calculations in
order to obtain insight into the solutionꢀstate superstructures and clarification of the preference
for encapsulation of fullerenes by the cage. The DFT calculations were performed for both C60
1
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and C70 encapsulation by the cage, employing the B3LYP functional with empirical D3
2
0
21
dispersion correction (B3LYPꢀD3), and the M06ꢀ2X functional that includes dispersion
intrinsically. The solvation effect was taken into account using the conductorꢀlike continuum
2
2
polarization model (CꢀPCM) with DMF as the solvent. In the case of the calculated
8
+
superstructures (Figure S28) of the fullerene⊂TPPCage
complexes, both B3LYPꢀD3 and
DFT
M06ꢀ2X results confirm that the encapsulation of C is preferred, with the encapsulation energy
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(
Table S4) being larger than that for C by 15.1 kcal/mol (B3LYPꢀD3) and 4.2 kcal/mol (M06ꢀ
60
2
X), respectively. The results of these calculation are consistent with the solidꢀstate
superstructures, illustrated in Figure 2b and 2c, an observation which indicates that the
ellipsoidal C provides a larger area than the perfectly spherical C to form [π•••π] interactions
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+
with two porphyrin panels. In addition, the formation of the C ⊂TPPCage is more
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8
+
thermodynamically favorable than that of C ⊂TPPCage because of stronger [cation•••π] and
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0
[
C–H•••π] interactions between the cage and the better sizeꢀmatched C .
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Selective Extraction of C . Encouraged by the different binding affinities of TPPCage•8PF6
towards C and C , we decided to explore the potential of TPPCage•8PF in the separation of
6
0
70
6
C from C . We used a mixture of C and C to carry out the binding competition experiments.
70
60
60
70
As expected, selective complexation (Figure 6) of the cage with C in a C ꢀenriched fullerene
7
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60
mixture is observed. When a mixture of solid C and C (C /C /TPPCage•8PF = 10/1/1) was
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70
60 70
6
added to a DMFꢀd solution of TPPCage•8PF (~1 mM), and sonicated, the cage selectively
7
6
bound with C to afford the C ⊂TPPCage•8PF complex in the solution, while C remained
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70
6
60
1
13
behind as a solid. From the H and C NMR spectra (Figures 6a and 6b), clearly all the signals
correspond very well to those of C ⊂TPPCage•8PF , an observation which demonstrates the
70
6
selective binding of TPPCage•8PF to C facilitating the separation of C from a C ꢀenriched
6
70,
70
60
mixture.
■ CONCLUSION
We have synthesized a covalently connected threeꢀdimensional organic molecular cage
TPPCage•8PF by employing a metalꢀfree TBAIꢀcatalyzed ringꢀclosure strategy with porphyrin
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and viologen building blocks. The tetragonal prismatic cages possess large cavities which are
capable of encapsulating fullerene guests – namely, C60 and C70 – by means of [π•••π]
(porphyrin•••fullerene), [C–H•••π] (C–H•••fullerene), and [cation•••π] interactions. Hostꢀguest
binding was investigated in solution by HRMS, and by NMR, UVꢀVis and fluorescence
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spectroscopies, while the solidꢀstate characterization of the empty cage TPPCage•8PF , as well
6
as those of the host–guest complexes C ⊂TPPCage•8PF and C ⊂TPPCage•8PF were
60
6
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carried out by singleꢀcrystal Xꢀray diffraction analysis. The comparison between empty and
complexed host demonstrates a high degree of geometric preorganization for fullerene
complexation. The cage molecule exhibits favorable binding selectivity towards the larger,
ellipsoidal C over the icosahedral C , thus facilitating the selective extraction of C from a
70
60
70
C ꢀenriched fullerene mixture (C /C = 10/1). The research highlights the potential application
60
60 70
of a hostꢀguest technology for a selective isolation process of fullerene mixtures by using
precisely design host molecules.
■
ASSOCIATED CONTENT
Supporting Information
Detailed synthetic procedures and characterization data for all. This information is available free
of charge via the internet at http://pubs.acs.org.
■ AUTHOR INFORMATION
Corresponding Author
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*
stoddart@northwestern.edu
Author Contributions
Y.S. and K.C. contributed equally.
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■
ACKNOWLEDGMENTS
This research is part of the Joint Center of Excellence in Integrated NanoꢀSystems (JCIN) at
King Abdulaziz City of Science and Technology (KACST) and Northwestern University (NU).
The authors would like to thank both KACST and NU for their continued support of this research.
Computational investigations were supported by the U.S. National Science Foundation under
grant no. EFRIꢀ1332411 (W.A.G. and H.X.). This work was also supported by the U.S.
Department of Energy, Office of Science, Office of Basic Energy Sciences under Award DEꢀ
FG02ꢀ99ER14999 (M.R.W. and J.Z.).
■
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Figure Legends
Scheme 1 | Synthesis of TPPCage•8PF6.
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Figure 1 | NMR Spectroscopic characterization of TPPCage•8PF . (a) H (600 MHz, DMFꢀd ,
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2
98 K) and (b) C (125 MHz, DMFꢀd , 298 K) NMR spectra of TPPCage•8PF
7 6.
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Figure 2 | Solidꢀstate structures of (a) TPPCage•8PF (top, looking in front of the mirror plane),
6
(
b) C ⊂TPPCage•8PF , and (c) C ⊂TPPCage•8PF obtained from singleꢀcrystal Xꢀray
6
0
6
70
6
–
diffraction. PF anions and solvent molecules are omitted for the sake of clarity.
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Figure 3 | NMR Spectroscopic characterization of C ⊂TPPCage•8PF . (a) Comparison of H
6
0
6
(
600 MHz, DMFꢀd , 298 K) NMR spectra of TPPCage•8PF and the encapsulation solution
7
6
13
which contains both TPPCage•8PF and C ⊂ TPPCage•8PF (b) Comparison of C (125
6
60
6.
MHz, DMFꢀd , 298 K) NMR spectra of free C , TPPCage•8PF and the encapsulation solution
7
60
6
which contains both TPPCage•8PF and C ⊂TPPCage•8PF .
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60
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Figure 4 | NMR Spectroscopic characterization of C ⊂ TPPCage•8PF . (a) Comparison of H
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0
6
(
600 MHz, DMFꢀd , 298 K) NMR spectra of TPPCage•8PF and the encapsulation solution
7
6
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3
which contains C ⊂TPPCage•8PF . (b) Comparison of C (125 MHz, DMFꢀd , 298 K) NMR
70
6
7
spectra of free C , TPPCage•8PF6 and the encapsulation solution which contains
70
C ⊂TPPCage•8PF .
70
6
Figure
5
|
Binding constant measurements for C ⊂TPPCage•8PF . UVꢀVis
70
6
spectrophotometric titration of a solution of TPPCage•8PF (10 µM) in DMF with a solution of
6
C70 in PhMe (1 mM) in a 0.2 cm path cuvette. The formation of the C ⊂TPPCage•8PF6
70
complex is characterized by a significant decrease in intensity at 419 nm and a slight red shift (3
nm) of the Soret band of the porphyrin. Inset: plot of ꢂA422 nm vs equivalents of C added (A
7
0
= absorption). The association constant modeled with a 1:1 equilibrium is KC70⊂TPPCage= (2.4±0.2)
5
‒1
× 10 M .
Figure 6 | Selective extraction of C . (a) Selective extraction of C from a C ꢀenriched solid
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0
70
60
1
mixture upon adding a solution of TPPCage•8PF in DMFꢀd . (b) H (600 MHz, DMFꢀd , 298 K)
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and (c) C (125 MHz, DMFꢀd , 298 K) NMR spectra of the fullerene extraction solution which
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contains only C ⊂TPPCage•8PF .
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Journal of the American Chemical Society
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Journal of the American Chemical Society
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Table of Contents Graphic
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