Ultrafast photochemistry of dithizonatophenylmercury(II).

The initial photochromic reaction of dithizonatophenylmercury(II) in solution was investigated by femtosecond transient absorption spectroscopy. Ultrafast excitation within less than 100 fs caused a radiationless photoreaction with a time constant of 1.5 ps, which is interpreted as C=N isomerization through a conical intersection. The orthogonally twisted intermediate state was observed through its excited-state absorption. Bifurcation along pathways towards the ground states of the orange cis and blue trans configurations occurs below the funnel of the conical intersection. The photochromism of the title compound in a very polar solvent such as methanol is observed for the first time.