In
this work, seven complexes based on graphitic carbon nitride
(g-C3N4) were systematically investigated. Density
functional theory calculations demonstrated that the energy gap between
the highest occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) of the complexes conspicuously narrowed by
doping Li atom. The value of HOMO–LUMO energy gap is decreased
from 3.89 eV for C18N27H8 to 0.78
eV for C18N27H8Li, similar regularity
is also found in other nondoped and doped Li atom g-C3N4 complexes. It has been shown that the Li doping can remarkably
enhance the first hyperpolarizability (β0) of g-C3N4. The Li-doped g-C3N4 complex
C18N27H8Li exhibits its large β0 up to 1.66 × 104 au, which is much larger
than that of the nondoped complex C18N27H8 (1.03 × 102 au). In this study, the calculated
nonlinear optical (NLO) properties show that the β0 values of nondoped and doped Li atom g-C3N4 complexes are in the range of (0–2.36) × 103 au and 1.66 × 104 au to 1.25 × 106 au, respectively. This theoretical study implies that Li-doped g-C3N4 is a novel candidate for high-performance NLO
materials. The theoretical evidence for the possibility of using g-C3N4 to construct materials with excellent NLO properties
has been provided.
As a novel kind of organosilicon complex, dipyridyldisilane and 1‐phenyl‐2‐pyridyl‐disilane with a donor‐ acceptor link by the σ‐π interaction and intramolecular charge transfer, has been investigated by the density functional theory. It is found that the phenyl replaced by the pyridy in diphenyldisilane can significantly narrow the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gap, and enhance the electronic polarization, thus make the electronic distribution more diffuse. As a result, the static first hyperpolarizability (β0) of dipyridyldisilane is enhanced to the range of 10.365×10−30 esu ∼ 26.385×10−30esu. And in order to know the effect of the number of pyridyl ring and the position of pyridyl ring on NLO responses, we calculated the β0 values for 1‐phenyl‐2‐pyridyl‐disilane, they are in the range of 6.475×10−30 esu ∼ 1482.613×10−30esu. The smaller HOMO‐LUMO gap and the smaller transition energy make the larger value of β0. This kind of organosilicon complex is one of the potentially versatile and fascinating nonlinear optical materials.
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