Structure–property relation in two-photon absorption for symmetric molecules involving diacetylene π-conjugated bridge

The effect of introducing charges on the two-photon absorption (TPA) is examined using the models involving the dicationic styrylpyridine units linked with a diphenyl diacetylene bridge. It turns out that the introduction of charges causes the red shift and drastic enhancement of TPA cross-section as compared to that in the neutral molecule. This is primarily ascribed to be the enhancement of transition moment between the first and second excited states, the feature of which is associated with the decrease of orbital interaction among the LUMOs of both-end dicationic styrylpyridines and the HOMO and LUMO of the central diphenyl diacetylene bridge.