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electrons. This is known as “resonance” is least. That is why ꢀmax are
ment to p-position for all substituents makes ꢀmax longer, because
the Cl or Br join to the conjugation. The electron-donating ability of
substituents is Br ≈ Cl > CH3, and the sequence of ꢀmax Br ≈ Cl > CH3,
as explained in Section 3.2.
Table 7 lists the energies of the frontier orbitals of stud-
ied molecules at PCM-TD-PBE1PBE/6-311G(2d,2p)//PBE1PBE/6-
311G(2d,2p) level. The sequence of excitation energy for the
substituents is Br ≈ Cl < CH3 which is consistent with the sequence
of ꢀmax. The calculation represented the excitation corresponding
HOMO–LUMO transition with the strongest oscillator strength. It
is seen that the main transition corresponds to → * excitation
for studied formazans. It is depicted the HOMO and the LUMO of
TPF in Fig. 4. It can be seen from the figure that the HOMO of TPF is
distributed at the main molecular skeleton, and the LUMO is local-
ized in the Ph–N N–C N–N–Ph skeleton. The frontier orbitals of
considered substituted formazans are similar to that of TPF.
ied compounds indicate that they are supported each other. It was
observed that the energy difference between HOMO and LUMO was
decreased by the electron-donating substituents, and ꢀmax of sub-
stituted compounds were longer wavelengths relative to that of
unsubstituted formazans. From the view of excitation spectra, TD-
DFT method will be helpful for the further study on the electronic
spectra of formazans.
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1-Substituted (CH3, Br, Cl) phenyl-3,5-diphenylformazans were
synthesized and their UV–vis spectra were studied experimentally
and theoretically. Structural stabilities of the studied formazans
were effected by steric effect. When the o-position of 1-phenyl
group has a substituent, the substituted phenyl group was out of
the main skeleton plane. It was found that the deviation of 1-phenyl
group of o-bromo formazan was greater than that of o-Cl and o-CH3
substituted formazans. The main skeletons of all studied formazans
that form the pseudo six-membered ring are nearly planar. But the
phenyl group attached to C3-atom on the skeleton of formazan is
out of this plane.
˙
TD-PBE1PBE-PCM method was applied to the UV–vis spectra of
formazans. 6-311G(2d,2p) basis set provided the best results. The
comparisons of calculated and experimental ꢀmax values of stud-
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