Wd. Cheng et al., Enhancement of third-order nonlinear response in excited state of metallophthalocyanines (PcM; M = H-2, Mg, Ni), J PHYS CH B, 105(45), 2001, pp. 11221-11226
In this paper we calculate the dynamic third-order nonlinear optical polari
zabilities of three optical processes, third-harmonic generation, electric-
field-induced second-harmonic generation, and degenerate four-wave mixing,
for both ground and first excited singlet states in metal phthalocyanines i
n terms of the sum-over states formula. The transition moment elements and
the transition energies in this formula are obtained using the INDO-SDCI me
thod. The calculated second-order hypolarizabilities show a dispersion beha
vior with the difference from ground state and an enhancement of third-orde
r nonlinear response in the first excited state. Among the PcM (M = H-2, Mg
, Ni), there is a large enhancement of the first excited singlet state when
there is a small third-order optical polarizability of the ground state. T
he calculated value of PcNi is compared with the observed one of the substi
tuted PcNi in the order of magnitude. We also gain an understanding of enha
ncement mechanism for nonlinear processes in the excited state.