Figure 5. Excess electronic absorption spectra at CIS/6-31G (d)
level, a) singlet state and b) triplet state.
The electronic absorption spectra of the
C20F20@K@C20F20@K@C20F20with and without OEEFs are depicted in Figure 5. The diagram of these
selected electronic excitations and the contour plots for their
corresponding molecular orbitals (MOs) are also presented in Figure 5.
From Figure 5a, it shows an intense absorption band with two maximum
absorption (wavelengths of 534 and 460 nm) and a weaker absorption band
at 183 nm for the field-free singlet
C20F20@K@C20F20@K@C20F20with the lone pair of excess electrons inside middle
C20F20 cage (2 ). When going
from field-free
C20F20@K@C20F20@K@C20F2with lone pair of excess electrons inside middle
C20F20 cage (2 ) to the
electrified ones with that inside the left or right
C20F20 cage (1 or 3 ),
it is found that the absorption in long wavelength appears blue-shift
(from 534 to 511 nm) and that on short wavelengths appear red-shift
(from 460 to 481 or 484 nm) for the intense absorption band. The two
absorption bands of
C20F20@K@C20F20@K@C20F20under F x = -120 × 10-4 au with
lone pair of excess electrons inside the right
C20F20 cage (3 ) are almost same
to that under F x = 110 × 10-4au with that inside the left C20F20 cage
(1 ). Results in Fig. 5a also shows that the electronic
excitation of each above absorption bands corresponds to intra-cage s →
p transition for all three
C20F20@K@C20F20@K@C20F20under F x = -120 × 10-4, 0 and
120 × 10-4 au with lone pair of excess electrons
inside right, middle and left cage, respectively.
From Figure 5b, it shows an intense absorption band with three maximum
absorptions (wavelengths of 555, 474, and 467 nm) and a much weaker
absorption band at 212 nm for field-free triplet
C20F20@K@C20F20@K@C20F20with two single-excess-electrons, respectively, inside the left and
middle C20F20 cages (1 and2 ). The electronic excitation of the strongest absorption (555
nm) corresponds to intra- and inter-cage s → p transitions (HOMO-1 →
LUMO+3), while that of the second and third ones (474 and 467 nm)
corresponds to intra-cage s → p transitions (HOMO → LUMO+11 and LUMO+8).
Obviously, the intense absorption bands with absorption wavelengths of
555 and 474 nm for field-free triplet
C20F20@K@C20F20@K@C20F20with two single-excess-electrons inside two cages (1 and2 ) just corresponds to that of 534 and 460 nm for field-free
singlet
C20F20@K@C20F20@K@C20F20with the lone pair of excess electrons inside one cage (2 ),
respectively. From field-free triplet to field-free singlet
C20F20@K@C20F20@K@C20F20,
the wavelengths of both absorptions appear blue-shift and intensity of
both absorptions considerably strengthen. When going from field-free
triplet
C20F20@K@C20F20@K@C20F2with two single-excess-electrons inside left and middle
C20F20 cage (1 and 2 )
to the electrified ones with that inside the middle or right
C20F20 cage (2 and 3 ),
it is found that the absorption in long wavelengths appears both
red-shifts for the intense absorption band.
Conclusion
In this paper, we have presented a new kind of spin molecular switches
by doping two potassium atoms among three
C20F20 cages to form peanut-shaped
single molecular solvated dielectron
C20F20@K@C20F20@K@C20F20.
The triplet structure with two single-excess-electrons inside two cages
(1 and 2 ) is thermodynamically more stable than the
singlet one with lone pair of excess electrons inside one cage
(2 ) for field-free
C20F20@K@C20F20@K@C20F20.
For the localizations of excess electrons, it is found that the lone
pair of excess electrons moves from middle
C20F20 cage to right or left one by
applying an OEEF of 111 × 10-4 au (0.5705 V/Å) or -120
× 10-4 au (-0.6168 V/Å) in the x-axis direction of
singlet
C20F20@K@C20F20@K@C20F20.
Applying an OEEF of -20 × 10-4 au (-0.1018 V/Å) in the
x-axis direction of triplet
C20F20@K@C20F20@K@C20F20can result in both left-to-right transfers of the two
single-excess-electrons.
For the interconversion between spin states, it is found that applying
an OEEF of 111 × 10-4 or -120 × 10-4au in the x-axis direction of triplet
C20F20@K@C20F20@K@C20F20firstly and then releasing it can reduce two single-excess-electron
(triplet state) changing into lone pair of excess electrons (singlet
state) and triplet
C20F20@K@C20F20@K@C20F20changing into singlet one. the field-free triplet
C20F20@K@C20F20@K@C20F20with two 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 material.
Computational Details
Because of our research systems including long-range interaction and
charge transfer, the density functional, coulomb-attenuated hybrid
exchange-correlation functional (CAM-B3LYP),37 is
used. It was reported that CAM-B3LYP provides molecular geometries close
to experimentally observed structures.38 In this work,
the optimized geometric structures of the
C20F20@K@C20F20@K@C20F20with all real frequencies in both singlet and triplet states are
obtained at CAM-B3LYP/6-31G(d) level. The spin density distribution and
natural popular analysis (NPA)39 of the structures
were also obtained at CAM-B3LYP/6-31G(d) level.
Recently, Population and novel hybrid meta exchange-correlation
functional M06-2X40 were successfully used to
calculate the vertical electron detachment energy (VDE) of series of
excess electron systems.4,5, 41,42 Therefore, the VDEs
of our structures were calculated at M06-2X/6-31G(2d) level, as the
following formulas (Cage =
C20F20@K@C20F20@K@C20F20):
VDE (I) = E [Cage]+opt -E [Cage]opt (1)
VDE (II) = E [Cage]2+opt -E [Cage]+opt (2)
The spin contamination is negligible. In the calculations, the expected
values of spin eigenvalue 〈S 2〉 are 0.0 for
[Cage] (singlet) and 2.0 for M2+ (triplet), 0.75
for [Cage]+, and 0.0 for
[Cage]2+ species.
In our previous work,28 it is found that the first
transition energy of CIS method is more close to the higher SAC-CI
results than the TD-HF, TD-B3LYP, TD-CAM-B3LYP and TD-LC-BLYP results
for molecular cluster anion
(FH)2{e-}(FH) and neutral (HCN)···Li
with excess electron. Therefore, The CIS/6-31G(d) calculations were
performed to obtain the excess electronic absorption spectrum of the
C20F20@K@C20F20@K@C20F20.
The calculations were performed with the GAUSSIAN program package
(GAUSSIAN 09 A02).43
Acknowledgements
We acknowledge the financial support from the National Natural Science
Foundation of China (Nos. 21662018, and 21764007). This work was also
supported by the Science and Technology Project of Jiangxi Provincial
Department of Science &Technology (No. 20192BAB203005), and the Natural
Science Foundation of Zhejiang Province (No. LQ17E030001).
Keywords: Spin switch • solvated electron• external electric
field • electron localization • DFT
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