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, NMe, and NO 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 > NMe > CN > NH > 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 and NMe 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 state is the intermediate state in the TPA transitions to both of the final excited states.