Non-linear optical reactive systems have important applications which require highly localized effects. Recently, we reported for the first time that donor-acceptor Stenhouse adducts (DASAs) have important two-photon switching properties. Here, we report on the nature of the non-linear excitation event and the resulting dynamics through femtosecond-resolved measurements. From these experiments we directly show the central role of specific higher singlet states in the initial two-photon transition step. To test the generality of the involvement of such higher states, we synthesized new two-photon switchable DASAs with varying electron accepting groups. Specifically, we detected a rapid decaying emission from the initially formed higher singlets (S