Photophysical and photochemical properties of heterocyclic analogs of 1,4-cyclohexadiene: Experimental and theoretical studies

The photophysical and photochemical properties of a series of heterocyclic analogs of 1,4-cyclohexadiene were studied by theoretical calculation and experiment. With the incorporation of different heteroatoms, the analogs presented distinct photophysical and photochemical properties from 1,4-cyclohexadiene. Their ultra-violet-visible absorption spectra were measured and found to be related to the heteroatoms on the 1,4-cyclohex-adiene ring. Calculation of the geometrical and electronic structures of the ground-states revealed that incorporation of the heteroatom affected the photophysical properties of the molecule. The de-excitation pro-cesses and electron transition modes were discussed according to the calculated values of the spin-orbit coupling matrix and the electron-hole distributions of the excited states. The reactive sites and geometrical structures showed that incorporation of a heteroatom into 1,4-cyclohexadiene changed the spin density distribution and thus influenced the photochemical properties. These findings are meaningful in explaining the photo-reactivities of these molecules, and provide foundations for further experimental/theoretical investigations and pharma-cological applications based on established structure-property correlations.