A Double plug-socket system capable of molecular keypad locks through controllable photooxidation

Article abstract of DOI:10.1002/chem.200901206

Two robust divalent complexes have been successfully constructed by using complementary rigid spacers (anthracene vs. 1,4,5,8-naphthalenediimide (NDI)) and two pairs of [24]crown-8 ethers and secondary dialkylammonium functionalities as binding motifs. It

Full text of DOI:10.1002/chem.200901206

DOI: 10.1002/chem.200901206
A Double Plug–Socket System Capable of Molecular Keypad Locks through
Controllable Photooxidation
Wei Jiang,[a, b] Min Han,[a] Heng-Yi Zhang,[a] Zhi-Jun Zhang,[a] and Yu Liu*[a]
Abstract: Two robust divalent com-
plexes have been successfully con-
structed by using complementary rigid
spacers (anthracene vs. 1,4,5,8-naphtha-
lenediimide (NDI)) and two pairs of
[24]crown-8 ethers and secondary dia-
lkylammonium functionalities as bind-
ing motifs. It was demonstrated that
properly selected, rigid spacers are
more efficient than flexible ones for
achieving strong multivalent associa-
tion. This is presumably due to the pre-
organization of the rigid spacers, the
cooperation between charge-transfer
interactions of rigid spacers, and the
complexation of the binding motifs.
Furthermore, the intermolecular photo-
induced electron transfer (PET) be-
tween rigid spacers in these robust
complexes could be switched on and
off by modulating their complexation
through acid–base reactions, which is
reminiscent of a plug–socket system ca-
pable of electron transfer. In addition,
the self-sensitized photooxidation of
the divalent host with anthracene as a
spacer can be completely inhibited
after complexation with the divalent
guests that contain NDI as spacers.
This process could also be understood
by invoking intermolecular PET and
could be turned on and off through
acid–base reactions. The photophysical
and photochemical properties of these
robust complexes have been interpret-
ed as molecular keypad locks with
alarm systems. Thus, a double plug–
socket system and molecular keypad
locks were successfully integrated
inside robust multivalent systems and
then the normal molecular devices
were endowed with logic functions.
Keywords: logic gate · multivalen-
cy · photooxidation · self-assembly ·
supramolecular chemistry
Introduction
that keep the components together.[2] The plug–socket sys-
tems have been demonstrated to carry out switching of elec-
tron- or energy-transfer processes[3] and could be useful for
information processing at the molecular level. In the macro-
scopic world, logic devices are built into normal machines
and devices to endow them with logic functions. Analogous-
ly, molecular plug–socket systems may also cooperate with
molecular logic devices to perform more complex functions,
which may even allow such a system to make a decision by
itself.[4]
The bottom-up construction of molecular machines and de-
vices[1] has attracted extensive attention in the last two de-
cades due to the potential applications of these machines
and devices as smart materials. A molecular plug–socket
system is a sort of supramolecular species, which can be dis-
assembled and reassembled by modulating the interactions
The development of molecular logic gates,[5] as an emerg-
ing research field, has inspired many scientists to try and
solve the miniaturization problems faced by Si-based elec-
tronics. Since the first explicit correlation of Boolean logic
with molecules synthesized by de Silva et al.,[6] numerous
molecules capable of basic logic functions, including
AND,[6,7] OR,[8] NAND,[9] INHIBIT,[10] NOR,[11] XOR,[12]
and XNOR,[13] have been presented in the literature. Molec-
ular combinatorial logic circuits, such as a digital adder,[14,15]
subtractor,[15,16] comparator,[15e,17] and multiplexer,[18] have
also been realized. More recently, a molecular keypad
lock,[19] one of the most important achievements in this
field, was successfully demonstrated and involves a system
[a] W. Jiang,+ M. Han,+ Prof. Dr. H.-Y. Zhang, Z.-J. Zhang,
Prof. Dr. Y. Liu
Department of Chemistry
State Key Laboratory of Elemento-Organic Chemistry
Nankai University, Tianjin, 300071 (P.R. China)
Fax : (+86)22-2350-3625
E-mail: yuliu@nankai.edu.cn
[b] W. Jiang+
Present Address: Institut fꢀr Chemie und Biochemie
Freie Universitꢁt Berlin, Takustrasse 3
14195 Berlin (Germany)
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200901206.
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in which the output signal is dependent on both the combi-
nation of inputs and their inputting sequence. It is worth
emphasizing that it is the first nonlinear logic circuit to be
described with single molecules. Besides the functional com-
plexity, diverse logic functions can also be integrated inside
single molecules through superposition[12a] or reconfigura-
tion.[20] Although highly complex logic functions can be ach-
ieved with single molecules, a molecular computer is a more
complicated device. Interconnection[5c,21] between different
logic devices is required to create more complex logic cir-
cuits, which still remains as a challenge in this field. As
learned from natural systems, self-assembly[22] and self-sort-
ing[23] may work as a glue to interconnect different molecu-
lar logic gates and thus achieve higher-level logic functions.
From this point of view, logic gates based on molecular as-
semblies[24] are even desirable for the construction of a mo-
lecular computer. In addition, the advantage of the molecu-
lar logic gate relies on the size of a single molecule. There-
fore, the integrity of self-assembled logic devices has to be
ensured for the execution of logic functions at the single-
molecule/assembly level. This problem may be resolved by
harnessing multivalent effects.
keypad locks with alarm systems are superposed with the
double plug–socket system according to the controllable
supramolecular photochemical and photophysical properties
of [1·2-H2]ACHTUNTRGNEUNG[PF6]2.
Multivalency[25] is an important concept in supramolecular
chemistry. It not only governs numerous biological interac-
tions in nature,[25a] but also provides a self-assembly ap-
proach for the construction of robust nanostructures and
molecular machines.[26] In artificial systems, the multivalent
effect is often improved by using flexible spacers and more
valencies (binding motifs), however, this seems to lack effi-
ciency. A strong multivalent effect could also be effectively
achieved by using a highly complementary multivalent host–
guest system; rigid spacers can be used to achieve the de-
sired arrangement of the host and guest.[27] Design of such a
complementary host–guest system, however, requires very
careful selection of complementary spacers and binding
motifs, even to nano- or picometer accuracy,[25b] otherwise it
may lead to even weaker binding affinities than the corre-
sponding multivalent systems with flexible spacers.
Results and Discussion
Synthesis: The anthracene-bridged divalent host 1 was syn-
thesized in a convergent manner from two intermediate
compounds
(Scheme 1a). The divalent guests [2a-H2]
[PF6]2 (Scheme 1b) with NDI as the rigid spacer and [3-H2]-
[PF6]2 (Scheme 1c) with triethylene glycol as a flexible
5
and
6
in
a
reasonable yield (20%)
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
Herein, we report the first molecular keypad locks based
on robust self-assembled systems; [24]crown-8 ethers and
secondary dialkylammonium groups are selected as the
binding motifs and anthracene (in divalent host 1) and
1,4,5,8-naphthalenediimide (NDI) (in divalent guest [2-H2]-
ACHTUNGTRENNUNG
spacer were achieved from amidation and Schiff base reac-
tions, respectively, followed by protonation and counterion
exchange.
A
Multivalent interactions: Multivalent association between
multivalent systems. The resulting binding affinity in these
systems was proven to be much stronger than that between
the divalent host 1 and the divalent guest [3-H2]ACHTUNGTRENNUNG[PF6]2,
which has a flexible spacer, was established by NMR spec-
troscopy and electrospray ionization mass spectrometry
(ESIMS) experiments. As shown in Figure 1, the downfield
shifts of Ht and Hu indicate the pseudorotaxane structure
complexation between the [24]crown-8 ether and the secon-
dary dialkylammonium group. The striking upfield shifts of
Hr (d=À0.61 ppm) and Hs (d=À0.35 ppm) are likely to be
due to shielding by the aromatic ring current of anthracene
1 and divalent guest [3-H2]
sumably derived from improved multivalent effect and co-
operation. Furthermore, the divalent complex [1·2-H2][PF6]2
ACHTUGNTERN[NUNG PF6]2 with a flexible spacer, pre-
AHCTUNGTRENNUNG
was demonstrated to be a double plug–socket system capa-
ble of intermolecular photoinduced electron transfer (PET)
by the control of their disassembly/reassembly through an
acid–base reaction. This complex was, therefore, found to
work as a switchable “molecular shield” to protect the an-
thracene moiety in 1 from self-sensitized photooxidation
through intermolecular PET from an excited anthracene of
in 1, which strongly suggests that a 1:1 adduct [1·3-H2]ACHTUNGTRENNUNG[PF6]2
with Hr and Hs on top of anthracene is formed in solution.
Interestingly, Hq is shifted downfield, presumably resulting
from the p–p stacking and hydrogen-bonding interactions
1 to NDI of [2-H2]ACHTUNGTRENNUNG[PF6]2. As one step further, two molecular
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9939

Y. Liu et al.
the host and the NDI of the
guest. These observations sug-
gest that the 1:1 complex [1·2b-
H2]ACHTNUGTRNEG[UN PF6]2 in which anthracene
and NDI are located directly
over each other dominates in
the equimolar mixture of 1 and
[2b-H2]ACHTUNRGTNEUNG[PF6]2, which is also sup-
ported by the Jobꢃs plot (Fig-
ure S12 in the Supporting Infor-
mation). The strong binding af-
finity and 1:1 stoichiometry was
further confirmed by an ESI
mass spectrum in which only
one intense peak at m/z 783 at-
tributed to [1·2b-H2]2+ was ob-
served (Figure 3). Analogously,
the exclusive formation of
Scheme 1. Synthetic procedures to divalent host 1 (a), and divalent guests [2-H2]ACTHUNTGRNENUG[PF6]2 (b) and [3-H2]AHCTUNGTREN[NGUN PF6]2 (c).
i) Cs2CO3, dry MeCN, reflux, 5 d; ii) 1) Et3N, iPrOH, reflux, 3 d; 2) concentrated HCl, MeOH; 3. NH4PF6, ace-
tone; iii) 1) CH3OH, reflux, 24 h; 2) NaBH4, reflux, 24 h; 3) concd HCl, MeOH; 4. NH4PF6, acetone.
[1·2a-H2]
ACHTUGNTRENUN[NG PF6]2 from 1 and [2a-
H2][PF6]2 has also been con-
AHCTUNGTRENNUNG
Figure 1. Partial 1H NMR spectra (400 MHz, CDCl3/CD3CN=1:1, 5 mm,
298 K) of [3-H2]ACHTUNGTRENNUNG[PF6]2 (a), 1:1 adduct [1·3-H2]AHCTUNGTRNEN[UGN PF6]2 (b), and 1 (c). *=re-
sidual solvent.
Figure 2. Partial 1H NMR spectra (400 MHz, CDCl3/CD3CN=1:1, 5 mm,
298 K) of [2b-H2]ACHTUNGTRNEN[GU PF6]2 (a), 1:1 adduct [1·2b-H2]CAHTUNTGERN[NUGN PF6]2 (b), and 1 (c). *=
residual solvent.
between 1 and [3-H2]
ethylene glycol spacer to the deshielding field of anthracene.
The 1:1 binding stoichiometry between 1 and [3-H2][PF6]2
was further confirmed by ESIMS experiments (Figures S10
and S11 in the Supporting Information).
ACHTUGNRTNE[NUNG PF6]2, which directs the flexible tri-
1
1
firmed from the H NMR and H–1H COSY spectra and the
ESIMS experiments (Figures S14–S16 in the Supporting In-
formation).
AHCTUNGTRENNUNG
To obtain the information on the superiority of a rigid
As noted above, the design of well-complementary multi-
valent systems with rigid spacers requires nano- or picome-
ter accuracy.[25b] To test the complementarity between the
anthracene of the host and the NDI of the guest, NMR
spectroscopy and ESIMS experiments were performed on
an equimolar mixture of the two substrates. The strong mul-
spacer over
1H NMR spectroscopy experiments on 1:1:1 mixture of 1, [2-
H2][PF6]2, and [3-H2][PF6]2 were performed (Figure S17 in
the Supporting Information). According to the integral
values of Hj(uc), Hj(c), and Hr(c) in 1, [2-H2][PF6]2, and [3-
H2]
[PF6]2, we estimated that the association constant[28] be-
tween 1 and [2-H2][PF6]2 is two orders of magnitude higher
than that between 1 and [3-H2][PF6]2. That is to say, com-
pound 1 binds more strongly to [2-H2][PF6]2 than to [3-H2]-
[PF6]2 and the carefully selected rigid spacer (NDI vs. an-
a flexible one in multivalent association,
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
tivalent interactions between 1 and [2b-H2]
N
ACHTUNGTRENNUNG
indicated by the obvious and complete downfield shifts of
Hm (d=0.26 ppm) and Hw (d=0.65 ppm) relative to free
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
[2b-H2]
N
ACHTUNGTRENNUNG
of Hj (d=À0.35 ppm) and Hg (d=À0.59 ppm) should result
thracene) is more suitable for forming a multivalent com-
plex. In the present case, the rigid spacers in 1 and [2-H2]-
from the mutual shielding effects between the anthracene of
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Controllable Photooxidation
FULL PAPER
the multivalent association between the two binding motifs
and, in return, the strong multivalent binding gathers an-
thracene and NDI close enough for CT interactions to form,
which further contributes to the enhanced binding affinity
between 1 and [2b-H2]ACHTNUTRGNEUNG[PF6]2. In other words, the CT inter-
actions between the rigid spacers and the multivalent associ-
ation between the binding motifs cooperate to contribute to
the enhanced binding affinity between 1 and [2-H2]
ACHTUNGTRENNUNG
In addition, the disassembly/reassembly of [1·2-H2]
ACHTUNGTRENNUNG
could be achieved by well-established acid/base chemistry
(Figures S20 and S21 in the Supporting Information).[26f]
This is reminiscent of a double plug–socket system, especial-
ly when considering the intermolecular PET process from
electron-rich anthracene[29] to electron-poor NDI[30] during
excitation of [1·2-H2]ACHTNUTRGNEUNG[PF6]2 (see below). The schematic rep-
resentation of the double plug–socket species is illustrated
in Scheme 2.
Figure 3. ESIMS (low resolution) spectrum of the equimolar mixture of 1
and [2b-H2]
ACHTUNGTRENNUNG[PF6]2 (0.1 mmol) in CDCl3/CD3CN (1:1). The major peak at
m/z 783 is assigned to the dication [1·2b-H2]2+
.
ACHTUNGTRENNUNG[PF6]2 preorganize the binding motif, which leads to the two
pairs of [24]crown-8 ether and the secondary ammonium
groups being in the perfect position for multivalent associa-
tion. This thus improves the efficiency of multivalency to
achieve a strong association between the host and the guest
by use of a minimum binding motif.
To further understand the roles of rigid spacers in the en-
hancement of the binding affinity, we performed absorption
Scheme 2. The schematic representation of the double plug–socket spe-
cies.
experiments on 1, [2b-H2]
absorption band centered at 620 nm is observed in the spec-
trum of [1·2b-H2][PF6]2 relative to the free host and guest
(Figure 4), which indicates the presence of charge transfer
(CT) upon complexation of 1 with [2b-H2][PF6]2. This is also
in agreement with the color change from light yellow of
both 1 and [2-H2][PF6]2 to dark green of [1·2-H2][PF6]2 at
high concentration (5 mm). No obvious interaction was ob-
served between 1 and neutral 2, or between 1 and 4 (Fig-
ure S19 in the Supporting Information). It is likely that the
ACHUTNTGRNE[NUG PF6]2, and [1·2b-H2]ACHTUGNTREN[NUGN PF6]2. A new
G
Controllable photooxidation: As is well known, there are
two types[31] of photosensitized oxidation. Both reactions in-
volve the absorption of light by a sensitizer to produce an
excited sensitizer. Type I is a reaction in which the radical or
radical ions evolved from an excited sensitizer react with
the ground-state oxygen (3O2) to give photooxygenated
compounds. For type II, the excited oxygen (1O2) is first pro-
duced by the triplet state of an excited sensitizer and then
adds to substrates to produce oxygenated products. In the
absence of other sensitizers, unsubstituted anthracene is rel-
atively more stable to visible light in solution than the larger
acenes, which may undergo self-sensitized photooxidation.[32]
Surprisingly, without any other sensitizer, compound 1 can
also be photooxidized in solution to produce an endoperox-
ide (1·O2; Scheme 3) in which O2 is added at the 9,10-posi-
tions of anthracene, which is clearly validated by the disap-
pearance or the shift in resonance of the aromatic-ring-cur-
rent-shielded protons Hc’, Hd’, Hf, and Hg of 1 after irradia-
tion by visible light (Figure 5a, b). This observation is also
AHCTUNGTRENNUNG
E
ACHTUNGTRENNUNG
complementary rigid spacers in 1 and [2b-H2]ACTHNUTRGNE[UGN PF6]2 enhance
1
supported by time-dependent H NMR and UV-visible spec-
troscopies, and ESI mass spectrometry (Figures S18–S22 in
the Supporting Information). Presumably, the four electron-
donating ether substituents in 1 enhance the reactivity of an-
1
[33]
thracene towards O2 and the propyl groups in the 9,10-
positions of anthracene cause steric hindrance for photodi-
merization and favor photooxidation.[34] Consequently, the
Figure 4. Absorption spectra of 1 (a), [2b-H2]
[PF6]2 (c) (CDCl3/CD3CN=1:1, 1.5 mm).
ACHTNUGTRENN[UGN PF6]2 (b), and [1·2b-H2]-
ACHTUNGTRENNUNG
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Y. Liu et al.
divalent complex with [2-H2]
that a concerted process, which involves the simultaneous
formation of 1·O2 and the disassembly of [2-H2][PF6]2, exists
because of the high binding affinity and the slow kinetics be-
tween 1 and [2-H2][PF6]2.
As seen in Figure 6, the fluorescence of [1·2b-H2]ACHTUNGTRENNUNG[PF6]2
ACHTUNGTREN[NNUG PF6]2. It can also be ruled out
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
shows no obvious change after irradiation by visible light
(Figure 6, line b). Upon the addition of an excess of base to
Scheme 3. Chemical structure of photooxygenated 1 (1·O2).
Figure 6. Emission spectra (CDCl3/CD3CN=1:1, 0.01 mm, excited at l=
375 nm) of 1 (a), [1·2b-H2]
light (b), [1·2b-H2][PF6]2 after the addition of 5 equiv of (Bu)3N (c) or
(Bu)3N and CF3COOH (d), and [1·2b-H2][PF6]2 after the addition of
5 equiv of (Bu)3N and irradiation by visible light (e). [1·2b-H2][PF6]2 can
work as a NAND logic gate with the addition of a base and then irradia-
tion with visible light as sequential inputs.
ACHTUGNTRNEN[UNG PF6]2 with and without irradiation of visible
Figure 5. Partial 1H NMR spectra (400 MHz, CDCl3/CD3CN=1:1, 5 mm,
298 K) of 1 before (a) and after (b) irradiation by visible light, and [1·2b-
H2]ACHTUNGTRENNUNG[PF6]2 before (c) and after (d) irradiation by visible light. *=residual
solvent.
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
photooxidation of 1 is probably due to a self-sensitized pro-
cess.
a solution of [1·2-H2]
ACHTUGNTERN[NUNG PF6]2, compound 1 is released from
Surprisingly, after formation of the divalent complex [1·2-
the shield of [2-H2][PF6]2 and can then be photooxidized.
ACHTUNGTRENNUNG
H2]
1H NMR spectrum of [1·2b-H2]
changes, even after four months of solar irradiation (Fig-
ure 5c, d). That is, compound [2-H2][PF6]2 can work as a mo-
lecular shield to protect 1 from photooxidation. The phe-
nomenon could be understood by invoking an intermolecu-
lar PET process from excited anthracene to NDI and by the
G
The PET process is partly switched off by the addition of
acid and the emission intensity was found to increase
(Figure 6, line c), although it is still lower than that of 1
probably due to the existence of long-range PET and ab-
sorption competition by neutral 2b (Figure S27 in the Sup-
porting Information). With the presence of excess base, neu-
tral 2b cannot protect 1. Uncomplexed 1 was therefore pho-
tooxidized to the nonfluorescent state (1·O2; Figure 6, line
e). When the nonfluorescent solution was heated, the O2
from 1·O2 was released and the florescence was recovered.
Without irradiation, the assembly and disassembly of [1·2-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
high binding affinity between 1 and [2-H2]ACHTNUGTRNEUNG[PF6]2. During the
solar irradiation, some parts of the excited anthracenes are
relaxed through the PET process and not much energy can
3
1
1
be used for the conversion of O2 to O2. Thus, O2 for pho-
tooxidation is not available. In addition, considering the
H2]ACHTNUTRGNE[UGN PF6]2 can be reversibly controlled and the emission in-
high binding affinities between 1 and [2-H2]
[PF6]2, the con-
tensity recovered to the original state (Figure 6, line d) by
the addition of base and then acid for at least five repeating
cycles,.
centration of the free host and guest are very low in solution
1
and cannot be seen in the H NMR spectrum (Figure 5 and
Figure S14 in the Supporting Information). As a result, the
divalent complexes [1·2-H2]
[PF6]2 are the only predominant
Molecular keypad lock: With base and visible light as inputs
and the fluorescent intensity at 415 nm as an output, a
NAND logic gate can be constructed from the solution of
species in this solution. The photooxidation, however, has to
1
occur between free 1 and O2, but both of them are rare in
this solution.[35] Moreover, the photooxidation of 1 will obvi-
ously change its conformation from a relatively “planar”
structure to a “dihedral” structure, and thus decreases the
distance between the two crown ether motifs of 1. The pho-
tooxygenated complex of 1 (1·O2)[36] is unsuitable to form a
[1·2b-H2]ACHTUGNTERNNU[G PF6]2. The NAND logic function is highly reliant
on the sequence of the two inputs. With no input (Figure 6,
line b), inputting either one of the two inputs (Figure 6,
lines b and c), or first inputting visible light and then base
(line c), the output signal is on (1). Only the sequential
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Controllable Photooxidation
FULL PAPER
input of first base and then visible light (Figure 6, line e)
can switch off the fluorescence of [1·2b-H2]ACTHNUTRGNE[NUG PF6]2 (0).
This input-sequence-specific NAND logic gate can be fur-
ther interpreted as a two-digit molecular keypad lock with
base (B) and visible light (L) as inputs (Figure 7a, b). Only
the two-digit sequential input BL can switch off the fluores-
binding motifs and a pair of electronically complementary
spacers. The intermolecular PET process from one rigid
spacer (anthracene) to the other (NDI) during the excitation
of the complexes could be switched on and off by control-
ling the disassembly and reassembly with an acid–base reac-
tion, which is reminiscent of a double plug–socket system.
Furthermore, the self-sensitized
photooxidation of an uncom-
plexed host with anthracene as
a spacer could be shut down
upon complexation with diva-
lent guests with NDI as
a
spacer. Therefore, the photo-
physical and photochemical
properties of the complexes
could be finely modulated. By
using these features, with moni-
toring fluorescence change as
output, the robust multivalent
complexes have been interpret-
ed as molecular keypad locks
with additional alarm systems,
which are only dependent on
Figure 7. The truth table (a) of a two-digit molecular keypad lock with alarm system (b), and an improved mo-
lecular keypad lock with four possible inputs and two three-digit passwords (c).
cence of [1·2b-H2]
[PF6]2 and this is used as the password. In-
the equilibrium states and not on the kinetic behavior of
this system.[4] Finally, the double plug–socket system and
molecular keypad locks are integrated inside the robust mul-
tivalent complexes. Thus, normal molecular devices are
made more intelligent by the cooperation with molecular
logic gates.
terestingly, the inputting of the reverse sequence (LB) will
increase the emission intensity at 415 nm by 50%, which
makes it a perfect alarm system to warn or scare away the
“thief” who puts in the wrong sequence, but it also makes
the brave thief closer to the password.
Considering the oxidation process, O2 is indispensable and
can be removed by normal degassing processes. Therefore,
O2 (O) can also be considered as another input. With acid
(A) as an interfering input, the combination amongst the
four inputs (A, B, L, and O) is complex enough to avoid de-
ciphering the password. Two three-digit combinations (OBL
and BOL) are the passwords for the improved molecular
keypad lock (Figure 7c), which may allow two independent
people to have their own keys. The different sequential or-
ganization of the same inputs, BLO, LBO, LOB, and OLB,
will trigger the alarm system and make the keypad lock
even safer. As discussed above, the recycling of this keypad
lock system could be achieved by heating and the addition
of acid. Noticeably, the two molecular keypad locks present-
ed above rely solely on the equilibrium states, not on the ki-
netic behavior of this system, which may make them unre-
stricted by a long operation time.
Experimental Section
General: All reagents, unless otherwise indicated, were obtained from
commercial sources. Compound 4,[37] 5,[38] and 7[39] were synthesized ac-
cording to literature procedures. Analytical-grade MeCN was dried over
P2O5 at room temperature for 2 d and then distilled to give the anhy-
drous solvent for reaction. Commercially available chromatography-
grade MeCN was used for UV and fluorescence measurements. Anhy-
drous CHCl3 was obtained by distillation from CaH2. Melting points
were determined on a XT-4 melting-point apparatus. 1H and 13C NMR
spectra were recorded on a Varian Mercury VS400 NMR spectrometer.
All chemical shifts are reported in ppm with residual solvents as the in-
ternal standards; the coupling constants (J) are in Hertz. The following
abbreviations were used for signal multiplicities: s, singlet; d, doublet; t,
triplet; m, multiplet. Low-resolution ESIMS and high-resolution ESIMS
were obtained on a Thermofinnigan LCQ Advantage ESI mass spec-
trometer and a Ionspec ESIHRMS (7.0 T) mass spectrometer, respective-
ly. The electrospray ionization Fourier-transform ion cyclotron resonance
(ESI-FT-ICR) mass spectrometric experiments were performed with a
Varian/IonSpec QFT-7 FTICR mass spectrometer (7.0 T). Absorption
spectra were recorded with a Shinadazu UV-2401PC instrument. Fluores-
cence spectra were measured in a conventional quartz cell (10ꢄ10ꢄ
45 mm) at 258C on a JASCO FP-750 spectrometer with excitation and
emission slits 5 nm in width.
Conclusion
We have successfully demonstrated a double plug–socket
system capable of electron transfer based on robust multiva-
lent complexes with complementary rigid spacers, which
were proven to be superior to a flexible spacer. The en-
hanced binding affinity results, not only from the improved
multivalent effects through the preorganization of rigid
spacers, but also from the cooperation between two pairs of
Anthracene bis-crown ether 1: A suspension of Cs2CO3 (6.60 g, 20 mmol)
in anhydrous MeCN (150 mL) under an N2 atmosphere was stirred vigo-
rously and heated to reflux. A solution of 5 (2.70 g, 4 mmol) and 6
(0.65 g, 2 mmol) in anhydrous MeCN (200 mL) was added dropwise to
the suspension over 48 h. The reaction mixture was stirred under reflux
for an additional 3 d. After cooling to room temperature, the reaction
mixture was removed by filtration and the residue was washed with
Chem. Eur. J. 2009, 15, 9938 – 9945
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9943

Y. Liu et al.
CH2Cl2 (150 mL). The filtrate was concentrated under reduced pressure
to give a dark tar, which was partitioned between CH2Cl2 (150 mL) and
H2O (150 mL). The aqueous layer was washed with CH2Cl2 (2ꢄ50 mL).
The organic layer was combined, dried (anhydrous Na2SO4), and concen-
trated under reduced pressure to afford the crude product, which was
subjected to column chromatography (silica gel; eluent: 100:1 CH2Cl2/
CH3OH). The obtained solid was recrystallized from CHCl3/isopropyl al-
cohol (2:1) and then washed with methanol to give 1 as a yellowish solid
[MÀ2PF6ÀÀH+]+; 687 [MÀPF6À]+; 1519 [2MÀPF6À]+. HRMS
ACHTUNGTRENUN(NG ESI): m/z:
calcd for C34H42N2O4: 541.3061; found: 541.3061.
Acknowledgements
This work was supported by the 973 Program (2006CB932900), TNSF
(07QTPTJC29700), NNSFC (Nos. 20721062 and 20772063), and the Pro-
gram for New Century Excellent Talents in University (NCET-05–0222).
We thank Prof. Dr. Christoph A. Schalley for help with the ESIFTICR
experiments.
1
(400 mg, 20%). M.p. 182–1848C; H NMR (400 MHz, CDCl3): d=1.10 (t,
J=7.2 Hz, 6H), 1.74–1.83 (m, 4H), 3.33 (t, J=7.2 Hz, 4H), 3.84–3.95 (m,
24H), 4.03–4.05 (m, 8H), 4.14–4.16 (m, 8H), 4.30–4.32 (m, 8H), 6.85–
6.86 (m, 8H), 7.36 ppm (s, 4H); 13C NMR (100 MHz, CDCl3): d=15.1,
23.9, 30.9, 69.3, 69.6, 70.0, 70.2, 71.5, 71.6, 104.7, 114.2, 121.6, 125.8, 129.6,
148.5, 149.1 ppm; HRMS (ESI): m/z: calcd for C55H74O16Na: 1025.4869;
found: 1025.4862.
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added. The reaction mixture was stirred overnight at room temperature
and evaporated under reduced pressure. The residue was suspended in
water (100 mL) and stirred at room temperature for 5 h. The mixture was
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ACHTUNGTRENNUNG[2a-H2]ACHTUNGTRENNUNG[PF6]2: Yield: 230 mg, 14%; M.p.>2108C (decomposition);
1H NMR (400 MHz, CD3CN): d=3.50 (4H), 4.31 (s, 4H), 4.51 (4H),
7.42–7.53 (m, 10H), 8.80 ppm (s, 4H); 13C NMR (100 MHz, CD3CN): d=
37.3, 46.8, 52.1, 126.9, 127.0, 129.4, 130.2, 130.5, 131.3, 142.5, 164.0 ppm;
HRMS (ESI): m/z: calcd for C32H30F6N4O6P: 679.19034; found:
679.19035.
ACHTUNGTRENNUNG[2b-H2]ACHTUNGTRENNUNG[PF6]2: Yield: 800 mg, 47%; M.p.> 2368C (decomposition);
1H NMR (400 MHz, CDCl3): d=2.10–2.20 (m, 4H), 3.13 (t, J=6.4 Hz,
4H), 4.20 (s, 4H), 4.22 (t, J=6.4 Hz, 4H), 7.44–7.54 (m, 10H), 8.73 ppm
(s, 4H); 13C NMR (100 MHz, CD3CN): d=25.2, 38.0, 46.2, 52.7, 127.6,
127.7, 130.1, 130.8, 131.0, 131.4, 131.8, 164.7 ppm; HRMS (ESI): m/z:
calcd for C34H34F6N4O6P: 707.2216; found: 707.2210.
Divalent guest [3-H2]ACHTUNGTRENNUNG[PF6]2: A solution of 8 (3.58 g, 10 mmol) and ben-
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zylamine (2.2 mL, 20 mmol) in MeOH (40 mL) was heated under reflux
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mixture was heated under reflux for a further 24 h. The solvent was
evaporated under reduced pressure and the residue was partitioned be-
tween CH2Cl2 (100 mL) and water (100 mL). The aqueous layer was
washed with CH2Cl2 (2ꢄ50 mL). The organic phases were combined and
dried over Na2SO4. Filtration, followed by evaporation of the solvent re-
sulted in a yellow oil. The yellow oil was dissolved in MeOH (20 mL)
and concentrated HCl was added to adjust to pH 2. The reaction mixture
was stirred at room temperature for a further 4 h and the solvent was
evaporated. After the residue was washed with CH2Cl2, a white solid was
obtained. The white solid was dissolved in acetone (30 mL) and a saturat-
ed solution of NH4PF6 was added until the solution become clear. The re-
action mixture was stirred for another 3 h and the solvent was evaporated
under reduced pressure. The residue was suspended in water (50 mL)
and stirred at room temperature for 5 h. The mixture was filtered, the
residue washed with water and dried in air to afford the product [3-H2]-
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[PF6]2 as a white solid (3.70 g, 44%). M.p. 90–928C; 1H NMR (400 MHz,
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9944
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Chem. Eur. J. 2009, 15, 9938 – 9945

Controllable Photooxidation
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[21] For some examples on interconnection between logic gates, see:
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Dunphy, M. Tomasulo, F. M. Raymo, A. Credi, Chem. Eur. J. 2009,
Received: May 7, 2009
Published online: August 5, 2009
Chem. Eur. J. 2009, 15, 9938 – 9945
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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9945