Design of second-order nonlinear optical molecules exhibiting improved nonlinearity-transparency trade-off and large nonlinearity

The nonlinear second-order optical susceptibilities (β) of a series of multi-branched molecules with triphenylbenezene as π center have been calculated by means of a combination of intermediate neglect of differential overlap Hamiltonian with the configuration interaction (INDO/SDCI) method combined with sum-over-states expression (SOS). The results show that the β values are increased by replacing benzene rings with thiophene rings in the branches, as well as by increasing the donating and accepting strength of the three terminal substituent. The properties of the intermolecular charge transfer were studied through the calculation of charge changes between the ground and the main excited states and the frontier orbitals of these molecules. The results also indicate that these molecules investigated here possess improved transparency-nonlinearity properties.