Theoretical study of cyclohexadiene/hexatriene photochemical interconversion using spin-Flip time-Dependent density functional theory

The photochemical interconversion between 1,3-cyclohexadiene (CHD) and all-cis-hexatriene (cZc-HT) is reinvestigated using spin-flip time-dependent density functional theory in combination with various hybrid functionals, BHHLYP functional showing the best performance. The critical geometries of the ground, S${}_0$, and the first two excited-state, S${}_1$ and S${}_2$, potential energy surfaces, such as, various minima, transition state, minimum-energy crossing points between S${}_2$/S${}_1$ and S${}_1$/S${}_0$ show an excellent agreement with those obtained by multireference wave function methods. Our results show how a low-cost method based on DFT can successfully describe and characterise the most important geometries on the potential energy surfaces along the ring-opening/closure reaction coordinate involved in the CHD to cZc-HT photoconversion.