The role of the natural transition orbital density in the S0 → S1 and S0 → S2 transitions of fulvene with next generation QTAIM

Abstract We present, for the first time, the S0 → S1 (S01) and S0 → S2 (S02) natural transition orbital (NTO) densities for fulvene, using the 3-D next generation QTAIM that can visualize and quantify the rearrangement of the charge density that occurs in response to the applied torsion and as a consequence of the preferred direction of electron density accumulation. A symmetrization of the position of the bond critical point (BCP) of the torsional C2-C6 BCP along the containing bond-path was determined to be characteristic of the presence of a conical intersection (CI) for the S0 → S1 (S01) transition.