Ultrafast spectral dynamics of structurally modified photochromic indolo[2,1-b][1,3]benzoxazines

Excited state dynamics of structurally modified photochromic compounds of the indolo[2,1-b][1,3]benzoxazine family were studied using femtosecond transient absorption spectroscopy. Four new compounds presented in this paper are classified into two groups according to the attachment site of the phenylic substituents. The excited state evolution was analyzed using global analysis techniques. The proposed nonlinear photoevolution model involves the formation of a short-lived photoproduct in addition to the main photoreaction pathway. The final ring-opened photoproduct is formed from the molecular excited state S1 via non-radiative transition in ca. 100 ps, and the full thermal ring closure is completed in a sub-microsecond timescale.