H. G. Yaglioglu et al. · Third-order Nonlinear Optical Properties
1359
Table 4. All static γ(0;0,0,0) components and ꢀγ (0;0,0,0) value [in atomic units] for the title molecule.
γxxxx
33229713.92
γyyyy
87560160.41
γzzzz
−190.84
γxxyy
6006970.57
γxxzz
−38057.64
γyyzz
−35632.39
ꢀγ
26531248.91
greater number of allowed electronic transitions and nificantly different from the ground state dipole mo-
hence enhances NLO effects. Since the potential of or- ment. The metal can have a large diversity of its co-
ganic materials and metal complexes for NLO devices ordination mode with various organic ligands affect-
have been proven, NLO properties of many of these ing the nonlinear activity. The central metal atom in
compounds have been investigated by both experi- organometallic complexes can readily coordinate to
mental and theoretical methods [32]. In the past five conjugated ligands with π orbital overlap facilitating
years, the efforts on NLO have been largely devoted effective electronic communication and CT transitions
to preparing third-order NLO materials using theoret- leading to large dipole moment changes. The fron-
ical methods and exploring the structure-property re- tier molecular orbitals (MOs) in the Cu(II) complex
lationships. Quantum chemical calculations have been consist of π orbitals having C=N and O2py contribu-
shown to be useful in the description of the relation- tions, admixed to varying extents to metal 3d orbitals
ship between the electronic structure of the systems of appropriate symmetry. In particular, the low energy
and its NLO response [33]. The computational ap- CT feature may be characterized as principally π → π ∗
proach allows the determination of molecular NLO in character, essentially involving the metal dxy + 02py
properties as an inexpensive way to design molecules and the C=N orbitals, and is mainly responsible for
by analyzing their potential before synthesis and to the NLO response. As a result, ꢀγ values depend on a
determine high order hyperpolarizability tensors of number of factors, which include the extent of π elec-
molecules.
tron conjugation, the dimensionality of the molecules
The calculated magnitudes of the static second hy- and the nature of substituents. Introduction of transi-
perpolarizabilities for the title complex are reported tion metals with partially filled d-shell is known to af-
in Table 4. As it is seen from this Table, the second
hyperpolarizability of the title complex is non-zero
since it is expected that the introduction of a donor
(-OCH3) /acceptor (-I) pair results in a larger polariza-
tion of the system in a way that increases significantly
fect a number of CT mechanisms like MLCT, LMCT
and d-d charge transfer [27].
Acknowledgements
This work was supported partly by Scientific and Techni-
the ꢀγ nonlinear response. Organometallic complexes cal Research Council of Turkey (TUBITAK) [105T132] and
can also possess a large NLO response due to the at- the Research Funds of Ankara University (CHE 2003 00 00
tainment of low energy excited states with dipoles sig- 041), respectively.
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