Photoinduced Charge Transfer in Push/Pull Systems of Two-Photon Absorption

A series of stilbene derivatives have been constructed by modifying the stilbene systems with different H, CN, NH 2 , NMe 2 , and NO 2 groups. In a vacuum, it was found that a redshift in the ultraviolet-visible spectrum occurred because of the enhancement of the donor/acceptor capabilities of this group, with the order of redshift being NO 2 > NMe 2 > CN > NH 2 > H. For stilbene molecular systems, the peak of two-photon absorption (TPA) observed in the simulated spectra should be attributed to two transitions that are contributed by two excited states with similar energy. In the case of derivatives, such a transition is separated by energy, and two TPA peaks can be clearly observed (derivatives containing NO 2 and NMe 2 groups have two TPA peaks), where the magnitude of the separation is directly related to the intensity of the peripheral group. In addition, the S 1 state is the intermediate state in the TPA transitions to both of the final excited states.