3.3 Nonlinear optical (NLO) properties and absorption spectrums
The NLO properties of the studied complexes have been explored by
calculating their static first hyperpolarizabilities
(β 0), which are given in Table 2. As listed in
Table 2, it is noticed that the β 0 values of GYs
are less than 0.50 au, whereas the
OM3+@GYs– complexes
show much larger β 0 values in the range of
227–653420 au. Among the
OM3+@GYs– series,
OLi3+@GTY– has the
largest β 0 value. Note that it has a unique
structure where the OLi3 is coplanar (d = 0.000)
with GTY.
To investigate whether the first hyperpolarizabilities of these doped
systems depend upon the atomic number of M in superalkali unit and the
pore size of graphyne subunit, the relationships betweenβ 0 values and different superalkali unit as well
as different sized graphyne are illustrated in Figure 5. For the
OM3+@GY– complexes,
the β 0 varies in the order 227 (M = Li)
< 4334 (M = K) < 7952 au (M = Na). Undoubtedly, the
maximum β 0 value belongs to
ONa3+@GY–. Upon the
combination with OM3, the β 0value of GDY dramatically increases to 224425–278540 au. Different from
the case of
OM3+@GY–, theβ 0 value of
OM3+@GDY– has no
clear dependence on the atomic number of M. Remarkably,
OLi3+@GTY– has the
largest β 0 value up to 653420 au among all the
studied complexes (see Figure 5a), which is about 40 and 15 times as
large as those of
ONa3+@GTY– (16246
au) and OK3+@GTY–(43713 au), respectively. It indicates the important effect of the
atomic number of M on β 0 value of
OM3+@GTY– (M = Li,
Na, and K).
Data in Table 2 and Figure 5b display that the β 0value increases quite rapidly in the order
OLi3+@GY–<
OLi3+@GDY–<
OLi3+@GTY–,
demonstrating that the effect of pore size of graphyne on theβ 0 value of
OM3+@GYs– is
significant. Notably, the β 0 value is enhanced by
approximate 2880-fold from 227 au
(OLi3+@GY–) to
653420 au
(OLi3+@GTY–).
Therefore, the selection of GTY with large pore is an effective strategy
for enhancing the β 0 of the
OLi3-doped graphyne molecules. When ONa3and OK3 are doped into GYs, theβ 0 values of the resulting complexes vary in the
sequence of
OM3+@GY–<
OM3+@GTY–<
OM3+@GDY– (M = Na
and K). The results suggest that the medium-sized GDY should be a better
match for OM3 (M = Na and K) in forming complexes with
higher NLO response.
TABLE 2 The first hyperpolarizabilitiesβ 0 (au), transition energies ΔE (eV),
oscillator strengths f 0, and difference of dipole
moment Δμ (Debye) between ground state and crucial excited state
of the GY/GDY/GTY and OM3@(GY/GDY/GTY) (M = Li, Na, and
K)