Photoisomerization of a phosphorus-based biradicaloid: ultrafast dynamics through a conical intersection

As previously reported, photoisomerization of the open-shell singlet biradicaloid [TerNP]₂CNDmp (2) yields its closed-shell housane-type isomer (3). In the present study, pump-probe spectroscopy was applied to investigate the excited-state dynamics of the photoisomerization, indicating ultrafast de-excitation of the S₁ state through a conical intersection, in agreement with computational predictions. The structural and electronic changes during the isomerization process are discussed to gain an understanding of the reaction pathway and the transformation of the biradicaloid to a closed-shell species.