Structures and properties of excited states of some para-disubstituted benzenes

What is it about?

Structural optimization of low-lying singlet and triplet excited states in para-disubstituted benzenes: p-difluorobenzene, p-quinol, p-fluoroaniline,and p-nitroaniline. were carried out quantum chemically We studied the extent of both in-plane and out-of-plane distortions exerted by the substituents on the low-lying triplet and singlet states The effect of para substitution on the quinoidal character of the excited states were investigated. Adiabatic excitation energies, equilibrium geometries, dipole moments, and aromaticity are presented and discussed.

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Why is it important?

Geometry optimization of the excited states revealed that the 3Al state is most affected leading to a quinoidal form of the ring and to out-of-plane distortions of the substituent atoms. These states can be best described as 1,4 diradicals. Aromaticity is decreased in all excited states, mostly in the triplet. The large dipole moment of 12 D of the 1A1 state of p-nitroanilineis due to charge transfer from the NH2 to the NO2 site.

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