Molecular Spin Switch and Conversions of Localized Excess Electrons
under External Electric Field: Solvated Dielectron
C20F20@K@C20F20@K@C20F20
Jia-Min Tang,[a] Yin-Feng
Wang,*[a] Qin Tian,[a]Xue-Xia Liu,[a] Zhijun
Wang,[a] Jiangen Huang,[a]Hua-Rong Zhang,*[b] Kai
Yang,[a] and Zhi-Ru Li*[c]
[a] Dr. Y.-F. Wang, Bs. Q .Tian, Dr. X.-X. Liu, Dr. Z. Wang.
Jiangxi Province Key Laboratory of Coordination Chemistry, School of
Chemistry and Chemical Engineering,
Jinggangshan University
Ji’an, Jiangxi 343009 (P.R. China)
E-mail: cyclont@yeah.net
[b] Dr. H.-R. Zhang
Key Laboratory of Organosilicon Chemistry and Material Technology,
Hangzhou Normal University,
Hangzhou, Zhejiang 311121 (P.R. China).
E-mail: zhanghuaxy99@hznu.edu.cn
[c] Prof. Z.-R. Li
Institute of Theoretical Chemistry, Laboratory of Theoretical
Computational Chemistry,
Jilin University
Changchun 130023 (P.R. China)
E-mail: lzr@jlu.edu.cn
Abstract: By doping two potassium atoms among three
C20F20 cages, peanut-shaped single
molecular solvated dielectron
C20F20@K@C20F20@K@C20F20as new type of spin molecular switches was theoretically presented. The
triplet structure with two single-excess-electrons individually inside
left and middle cages is thermodynamically more stable than the singlet
one with lone pair of excess electrons inside middle cage. It is found
that applying an oriented external electric field (OEEF) of 111 ×
10-4 au (0.5705 V/Å) or -120 × 10-4au (-0.6168 V/Å) in the x-axis direction firstly and then releasing it,
the field-free triplet
C20F20@K@C20F20@K@C20F20with two single-excess-electrons can change into singlet one with lone
pair of excess electrons through a singlet one with lone pair of excess
electrons inside the end cage. Different spin states can bring
significantly different dipole moment component values and considerable
different intensities of maxumum wavelengths in intense absorption band.
Therefore,
C20F20@K@C20F20@K@C20F20is a good candidate for spin molecular switching materials.
Introduction
Recently, theoretical design of new high-performance molecular switching
materials driven by oriented external electric field (OEEF) have
witnessed large developments in the field of molecular
electronics.1-5
As the simplest form of an extremely reactive intermediate, the
investigation of the solvated electron plays a prominent role in
physics, chemistry, and biochemistry.6-14 For example,
Adhikari et al have reported efficient capture of presolvated electrons
by DNA base.10 Also, for the charge- and
electron-transfer and the transitions, manipulation of one or several
electrons at the molecular level remains a highly challenging
task15 considering the utmost importance in the
related fields of molecular electronics,16 artificial
photosynthesis,15,17 molecular
switches,15,18 quantum-dot cellular automata
(QCA),19-21 solar cells,22 and
supramolecular assemblies.23 As solvated electron
systems (excess electron inside molecular cluster or cage) have not
enough stabilities,14 improving their stabilities is
an important task.
To improve stabilities of general solvated electrons, in our recent
series of papers,24-29 basing on the synthesized
C20F20 and potential
C24F24 and
C60F60 cage,30,31 we
have constructed a series of interesting cage-like single molecular
solvated (di)electron systems with large stabilities due to the using
covalent cages: e@C60F60,
e2@CnFn (n=20, 28, 36,
50, 60, and 80),
e@C20F18(NH)2C20F18,
and
e@C24F22(NH)2C20F18,
which shows these perfluorinated cages are efficient containers of
excess electrons. For these cages, the dipole moments of all the exo
polarized Cδ+-Fδ- bonds of each cage
are directed toward the center of the cage to form an interior
electronic attractive potential (IEAP) which can help to trap excess
electron(s) inside these cages. These single molecular solvated
(di)electron systems can provide a base of molecular electronics device.
Basing on our
e@C20F18(NH)2C20F18,
Ma et al., have successfully suggested a new type of molecular
quantum-dot cellular automata (MQCA) candidate.20,21Recently, Li et al.,32 have constructed new kind of
electride molecular salts
e@C20F19(CH2)4NH2…Na+as novel, potential high-performance NLO materials. Also, basing on
triple-cage-like electride salt
K+[e@3C8(O)]-,
Li et al., also suggested33 that multicage strategy is
effective to enhance nonlinear optical (NLO) response. For the
double-cage-like single molecular solvated single electron systems
e-@C20F18(NH)2C20F18,26-28the excess electron can be trapped inside different cages to form
interesting inter-cage electron transfer isomers.26 In
this case, besides the double-cage-like single molecular solvated
electron systems,20,21,26-28 We are interesting in the
influence of the number of cage units on the localizations and spin
states of two excess electrons. Especially, can it switch between
different spin states by external stimulus? Obviously, exploring new
molecular spin switching material is necessary for promoting its
application in the field of molecular electronics, which is the target
of our work.
Recently, Sadlej-Sosnowska has reported that, in an uniform OEEF, a
reversible switching between the two configurations of Li-benzene
complex with significant dipole moments took place.34Straka et al demonstrated for MX@C70 (M: metal, X:
nonmetal) systems that the relative orientation of enclosed MX with
respect to a set of electrodes connected to the system can be controlled
by application of OEEF(s).2 For the double-cage-like
single molecular solvated electron systems of
e@C20F18(NH)2C20F18,
and
e@C24F22(NH)2C20F18,26-27we have also used an external electric field to realize the inter-cage
excess electron transfer and isomerization among three inter-cage
electron transfer isomers. These will provide an approach for the
manipulating localization(s) and spin states of the excess electron(s)
in multi-cage-shaped solvated dielectron systems by using external
electric field.
In this paper, by doping two potassium atoms among three
C20F20 cages, our investigation aims at
obtaining the structures, excess electron localizations, and electronic
absorption spectra of the peanut-shaped single molecular solvated
dielectron systems of
C20F20@K@C20F20@K@C20F20,
revealing the influence of the number of cage units on the localizations
and spin states of two excess electrons, exhibiting excess electron
transition under the external electric field, and suggesting the
possible candidate for the new kind of molecular spin switching
metherial.
Results and Discussion
Geometrical characteristics and excess electron localizations
The optimized geometries with all real frequencies of
C20F20@K@C20F20@K@C20F20were shown in Figure 1. The selected structural parameters in both
singlet and triplet states were listed in Table 1. For both singlet (S)
and triplet structures (T), the
C20F20@K@C20F20@K@C20F20represents face-to-face stacked C20F20cages connected by two doped K atoms. From Figure 1, for the plane where
five-membered ring is located, the plane α of cage 1 and
plane β of cage 2 are staggered with very small dihedral
angle (0.55 (S) or 0.26°(T)). The similar situation happens between the
five-membered plane γ (cage 2 ) and δ (cage3 ) but some large dihedral angle between them (15.08 (S) or
15.55°(T)).
The different sizes of three cages (1 , 2 , and3 ) are closely related to excess electron localization(s) in
both states (S and T). Results in Table 1 exhibit that cage 2are the smallest one among three cages (h 2(2 ) < h 1 (1 ) ≈h 3 (3 )) in singlet structure, and both
cage 2 (h 2) and 1(h 1) are smaller in size than cage 3(h 3) in triplet one.
Results in Table 2 show that the natural popular analysis (NPA) charges
of K1 and K2 atoms in field-free
C20F20@K@C20F20@K@C20F20are larger than 0.66 |e| for both singlet and triplet
states, which indicates the valences of both K atoms are +1 for both
states. At the same time, the NPA charge of cage 2 in singlet
structure and that of cage 1 and 2 in triplet one
suggests that the valence of cage 2 in singlet structure is -2
and that of both cage 1 and 2 are -1. Therefore, the
4s electrons of both K atoms are pulled out and trapped inside the
fluorinated C20 cage(s) to form localized excess
electrons due to the IEAPs.